DIY switching power supply for umzch. Switching power supply for amplifiers

01.07.2023

This article is devoted to the 2161 Second Edition (SE) series of switching power supplies based on the IR2161 controller.

Short circuit and overload protection;
Auto reset short circuit protection;
Frequency modulation "dither" (to reduce EMI);
Microcurrent startup (for initial startup of the controller, a current of no more than 300 μA is sufficient);
Possibility of dimming (but we are not interested in this);
Output voltage compensation (a kind of voltage stabilization);
Soft start;
Adaptive dead time ADT;
Compact body;
Produced using lead-free technology (Leed-Free).

I will give some important ones for us specifications:

Maximum inflow/outflow current: +/-500mA
A sufficiently large current allows you to control powerful switches and build quite powerful switching power supplies based on this controller without the use of additional drivers;

Maximum current consumed by the controller: 10mA
Based on this value, the power circuits of the microcircuit are designed;

Minimum operating voltage of the controller: 10.5V
At a lower supply voltage, the controller switches to UVLO mode and the oscillation stops;

Minimum stabilization voltage of the zener diode built into the controller: 14.5V
The external zener diode must have a stabilization voltage no higher than this value to avoid damage to the microcircuit due to shunting excess current to the COM pin;

Voltage at the CS pin to trigger overload protection: 0.5V
The minimum voltage at the CS pin at which the overload protection is triggered;

Voltage at the CS pin for short circuit protection: 1V
The minimum voltage at the CS pin at which short circuit protection is triggered;

Operating frequency range: 34 - 70 kHz
The operating frequency is not directly set and depends only on the power consumed by the load;

Default dead time: 1µS
Used when it is impossible to work in adaptive dead time (ADT) mode, as well as when there is no load;

Operating frequency in soft start mode: 130 kHz
The frequency at which the controller operates in soft start mode;

The main attention should now be paid to what operating modes of the microcircuit exist and in what sequence they are located relative to each other. I will focus on describing the operating principle of each of the circuit blocks, and I will describe the sequence of their operation and the conditions for transition from one mode to another more briefly. I'll start with a description of each of the blocks of the diagram:

Under-voltage Lock-Out Mode (UVLO)- the mode in which the controller is when its supply voltage is below the minimum threshold value (approximately 10.5V).

Soft Start Mode- operating mode in which the controller oscillator operates at an increased frequency for a short time. When the oscillator is turned on, its operating frequency is initially very high (about 130 kHz). This causes the converter output voltage to be lower because the power supply transformer has a fixed inductance which will have a higher impedance at higher frequency and thus reduces the voltage on the primary winding. Reduced voltage will naturally result in reduced current in the load. As the CSD capacitor charges from 0 to 5V, the oscillation frequency will gradually decrease from 130 kHz to the operating frequency. The duration of the soft start sweep will depend on the capacitance of the CSD capacitor. However, since the CSD capacitor also sets the shutdown delay time and participates in the operation of the voltage compensation unit, its capacitance must be strictly 100nF.

Soft start problem. I would like to be completely honest and mention the fact that if there are high-capacity filter capacitors at the output of the power supply, soft start most often does not work and the SMPS starts immediately at the operating frequency, bypassing the soft start mode. This happens due to the fact that at the moment of start, the discharged capacitors in the secondary circuit have a very low intrinsic resistance and a very high current is required to charge them. This current causes a short-circuit protection to operate briefly, after which the controller immediately restarts and goes into RUN mode, bypassing the soft start mode. You can combat this by increasing the inductance of the chokes in the secondary circuit, located immediately after the rectifier. Chokes with high inductance extend the charging process of the output filter capacitors; in other words, the capacitors are charged with a smaller current, but longer in time. A lower charging current does not trigger the protection at start and allows the soft start to perform its functions normally. Just in case, regarding this issue, I contacted the manufacturer’s technical support, to which I received the following answer:

"A typical halogen converter has an AC output without rectifiers or output capacitors. Soft starting works by reducing the frequency. To achieve soft starting, the transformer needs to have significant leakage. However, this should be possible in your case. Try placing the inductor on the secondary side of the bridges diodes to the capacitor.

Best wishes.
Infineon Technologies
Steve Rhyme, Support Engineer"

My assumptions about the reason for the unstable operation of soft start turned out to be correct and, moreover, they even offered me the same method of dealing with this problem. And again, to be completely honest, it should be added that the use of coils with increased inductance, relative to those usually used at the output of the SMPS, improves the situation, but does not completely eliminate the problem. However, this problem can be tolerated given that there is a thermistor at the SMPS input that limits the inrush current.

Run Mode, operating mode. When the soft start is completed, the system enters voltage compensated operating mode. This function provides some stabilization of the converter output voltage. Voltage compensation occurs by changing the operating frequency of the converter (increasing the frequency reduces the output voltage), although the accuracy of this type of “stabilization” is not high, it is nonlinear and depends on many parameters and, therefore, is not easy to predict. IR2161 monitors the load current through a current resistor (RCS). The peak current is detected and amplified in the controller and then applied to the CSD pin. The voltage on the CSD capacitor, in operating mode (voltage compensation mode), will vary from 0 (at minimum load) to 5V (at maximum load). In this case, the generator frequency will vary from 34 kHz (Vcsd = 5V) to 70 kHz (Vcsd = 0V).

It is also possible to attach feedback to the IR2161, which will allow you to organize almost complete stabilization of the output voltage and will allow you to much more accurately monitor and maintain the required voltage at the output:

We will not consider this scheme in detail within the framework of this article.

Shut Down Mode, shutdown mode. The IR2161 contains a two-position automatic shutdown system that detects both short circuit and overload conditions of the inverter. The voltage at the CS pin is used to determine these conditions. If the output of the converter is shorted, a very large current will flow through the switches and the system must shut down within a few periods of time on the grid, otherwise the transistors will be quickly destroyed due to thermal runaway of the junction. The CS pin has a turn-off delay to prevent nuisance tripping, either due to inrush current at turn-on or due to transient currents. Lower threshold (when Vcs > 0.5< 1 В), имеет намного большую задержку до отключения ИИП. Задержка для отключения по перегрузке приблизительно равна 0,5 сек. Оба режима отключения (по перегрузке и по короткому замыканию), имеют автоматический сброс, что позволяет контроллеру возобновить работу примерно через 1 сек после устранения перегрузки или короткого замыкания. Это значит, что если неисправность будет устранена, преобразователь может продолжить нормально работать. Осциллятор работает на минимальной рабочей частоте (34 кГц), когда конденсатор CSD переключается к цепи отключения. В режиме плавного пуска или рабочем режиме, если превышен порог перегрузки (Vcs >0.5V), IR2161 quickly charges CSD up to 5V. When the voltage at the CS pin is greater than 0.5V and when the short circuit threshold of 1V is exceeded, the CSD will charge from 5V to the controller supply voltage (10-15V) in 50ms. When the overload threshold voltage Vcs is more than 0.5V but less than 1V, the CSD is charged from 5V to the supply voltage in approximately 0.5 sec. It should be remembered and taken into account the fact that high-frequency pulses with a 50% duty cycle and a sinusoidal envelope appear at the CS pin - this means that only at the peak of the network voltage the CSD capacitor will be charged in stages, in each half-cycle. When the voltage on the CSD capacitor reaches the supply voltage, the CSD is discharged to 2.4V and the converter starts again. If the fault is still present, the CSD starts charging again. If the fault disappears, the CSD will discharge to 2.4V, and then the system will automatically return to the voltage compensation operating mode.

STANDBY mode, standby mode- the mode in which the controller is in the case of insufficient supply voltage, while it consumes no more than 300 μA. In this case, the oscillator is naturally turned off and the SMPS does not work; there is no voltage at its output.

Blocks Fault Timing Mode, Delay and Fault Mode, although shown in the block diagram, are not essentially operating modes of the controller; rather, they can be attributed to transition stages (Delay and Fault Mode) or conditions for transition from one mode to another (Fault Timing Mode).

Now I’ll describe how does it all work together:
When power is applied, the controller starts in UVLO mode. As soon as the controller supply voltage exceeds the minimum voltage value required for stable operation, the controller switches to soft start mode, the oscillator starts at a frequency of 130 kHz. The CSD capacitor charges smoothly up to 5V. As the external capacitors charge, the operating frequency of the oscillator decreases to the operating frequency. Thus, the controller switches to RUN mode. As soon as the controller enters RUN mode, the CSD capacitor is instantly discharged to ground potential and is connected by an internal switch to the voltage compensation circuit. If the SMPS is started not at idle, but under load, there will be a potential at the CS pin proportional to the load value, which, through the internal circuits of the controller, will affect the voltage compensation unit and will not allow the CSD capacitor, after the completion of the soft start, to completely discharge. Thanks to this, the start will not occur at the maximum frequency of the operating range, but at a frequency corresponding to the load value at the output of the SMPS. After switching to RUN mode, the controller works according to the situation: either it remains working in this mode until you get tired and unplug the power supply from the outlet, or... In case of overheating, the controller goes into FAULT mode, the oscillator stops working . After the chip cools down, a restart occurs. In the event of an overload or short circuit, the controller goes into Fault Timing mode, and the external capacitor CSD is instantly disconnected from the voltage compensation unit and connected to the shutdown unit (the CSD capacitor in this case sets the controller shutdown delay time). The operating frequency is instantly reduced to the minimum. In case of overload (when the voltage at the CS pin > 0.5< 1 В), контроллер переходит в режим SHUTDOWN и выключается, но происходит это не мгновенно, а только в том случае, если перегрузка продолжается дольше половины секунды. Если перегрузки носят импульсный характер с продолжительностью импульса не более 0,5 сек, то контроллер будет просто работать на минимально возможно частоте, постоянно переключаясь между режимами RUN, Fault Timing, Delay, RUN (при этом будут отчетливо слышны щелчки). Когда напряжение на выводе CS превышает 1В, срабатывает защита от короткого замыкания. При устранении перегрузки или короткого замыкания, контроллер переходит в режим STANDBY и при наличии благоприятных условий для перезапуска, минуя режим софт-старта, переходит в режим RUN.

Now that you understand how the IR2161 works (I hope so), I will tell you about the switching power supplies themselves based on it. I want to immediately warn you that if you decide to assemble a switching power supply based on this controller, then you should assemble the SMPS guided by the latest, most advanced circuit on the corresponding printed circuit board. Therefore, the list of radio elements at the bottom of the article will be given only for the latest version of the power supply. All intermediate editions of the IIP are shown only to demonstrate the process of improving the device.

And the first IIP that will be discussed is conventionally named by me 2161 SE 2.

The main and key difference of the 2161 SE 2 is the presence of a controller self-supply circuit, which made it possible to get rid of boiling quenching resistors and, accordingly, increase the efficiency by several percent. Other equally significant improvements were also made: optimization of the printed circuit board layout, more output terminals were added for connecting the load, and a varistor was added.

The SMPS diagram is shown in the image below:

The self-powering circuit is built on VD1, VD2, VD3 and C8. Due to the fact that the self-supply circuit is connected not to a low-frequency 220V network (with a frequency of 50Hz), but to the primary winding of a high-frequency transformer, the capacity of the self-supply quenching capacitor (C8) is only 330pF. If self-supply was organized from a low-frequency 50Hz network, then the capacity of the quenching capacitor would have to be increased 1000 times, and of course such a capacitor would take up much more space on the printed circuit board. The described method of self-powering is no less effective than self-powering from a separate winding of a transformer, but it is much simpler. Zener diode VD1 is necessary to facilitate the operation of the built-in zener diode of the controller, which is not capable of dissipating significant power and without installing an external zener diode can simply be broken, which will lead to a complete loss of functionality of the microcircuit. The stabilization voltage VD1 should be in the range of 12 - 14V and should not exceed the stabilization voltage of the controller's built-in zener diode, which is approximately 14.5V. As VD1, you can use a zener diode with a stabilization voltage of 13V (for example, 1N4743 or BZX55-C13), or use several zener diodes connected in series, which is what I did. I connected two zener diodes in series: one of them was 8.2V, the other was 5.1V, which ultimately gave a resulting voltage of 13.3V. With this approach to powering the IR2161, the controller’s supply voltage does not sags and is practically independent of the load size connected to the SMPS output. In this scheme, R1 is only needed to start the controller, so to speak, for the initial kick. R1 gets a little warm, but not nearly as much as it was in the first version of this power supply. The use of high-resistance resistor R1 provides another interesting feature: the voltage at the output of the SMPS does not appear immediately after being connected to the network, but after 1-2 seconds, when C3 is charged to the minimum voltage of 2161 (approximately 10.5V).

Starting with this SMPS and all subsequent ones, a varistor is used at the SMPS input; it is designed to protect the SMPS from exceeding the input voltage above the permissible value (in this case - 275V), and also very effectively suppresses high-voltage interference by preventing them from entering the SMPS input from network and without releasing interference from the SMPS back into the network.

In the rectifier of the secondary power supply of the power supply, I used SF54 diodes (200V, 5A) two in parallel. The diodes are located on two floors, the leads of the diodes should be as long as possible - this is necessary for better heat dissipation (the leads are a kind of radiator for the diode) and better air circulation around the diodes.

The transformer in my case is made on a core from a computer power supply - ER35/21/11. The primary winding has 46 turns in three 0.5mm wires, two secondary windings have 12 turns in three 0.5mm wires. The input and output chokes are also taken from the computer power supply.

The described power supply is capable of delivering 250W to the load for a long time (without operating time limitation), and 350W for a short time (no more than a minute). When using this SMPS in dynamic load mode (for example, to power an audio frequency power amplifier of class B or AB), it is possible to power an UMZCH with a total output power of 300W (2x150W in stereo mode) from this switching power supply.

Oscillogram on the primary winding of the transformer (without snubber, R5 = 0.15 Ohm, 190W output):

As can be seen from the oscillogram, with an output power of 190 W, the operating frequency of the SMPS is reduced to 38 kHz; at idle, the SMPS operates at a frequency of 78 kHz:

From the oscillograms, in addition, it is clearly visible that there are no outliers on the graph, and this undoubtedly characterizes this SMPS positively.

At the output of the power supply, in one of the arms you can see the following picture:

The ripple has a frequency of 100Hz and a ripple voltage of approximately 0.7V, which is comparable to the ripple at the output of a classic, linear, non-stabilized power supply. For comparison, here is an oscillogram taken when operating at the same output power for a classic power supply (capacitor capacity 15000 μF in the arm):

As can be seen from the oscillograms, the supply voltage ripple at the output of a switching power supply is lower than that of a classic power supply of the same power (0.7V for an SMPS, versus 1V for a classic unit). But unlike a classic power supply, a small high-frequency noise is noticeable at the output of the SMPS. However, there is no significant high-frequency interference or emissions. The ripple frequency of the supply voltage at the output is 100Hz and is caused by the voltage ripple in the primary circuit of the SMPS along the +310V bus. To further reduce ripple at the SMPS output, it is necessary to increase the capacitance of capacitor C9 in the primary circuit of the power supply or the capacitance of the capacitors in the secondary circuit of the power supply (the former is more effective), and to reduce high-frequency interference, use chokes with higher inductance at the SMPS output.

The PCB looks like this:

The following SMPS diagram that will be discussed is 2161 SE 3:

The finished power supply assembled according to this diagram looks like this:

There are no fundamental differences in the circuit from SE 2; the differences mainly concern the printed circuit board. The circuit added only snubbers in the secondary windings of the transformer - R7, C22 and R8, C23. The values of the gate resistors have been increased from 22 Ohm to 51 Ohm. The value of capacitor C4 has been reduced from 220 µF to 47 µF. Resistor R1 is assembled from four 0.5W resistors, which made it possible to reduce the heating of this resistor and make the design slightly cheaper because In my area, four half-watt resistors are cheaper than one two-watt one. But the opportunity to install one two-watt resistor remains. In addition, the value of the self-feeding capacitor was increased to 470pF, there was no particular point in this, but it was done as an experiment, the flight was normal. MUR1560 diodes in a TO-220 package are used as rectifier diodes in the secondary circuit. Optimized and reduced printed circuit board. The dimensions of the SE 2 printed circuit board are 153x88, while the SE 3 printed circuit board has dimensions of 134x88. The PCB looks like this:

The transformer is made on a core from a computer power supply - ER35/21/11. The primary winding has 45 turns in three 0.5mm wires, two secondary windings have 12 turns in four 0.5mm wires. The input and output chokes are also taken from the computer power supply.

The very first inclusion of this SMPS in the network showed that the snubbers in the secondary circuit of the power supply were clearly superfluous; they were immediately soldered off and were not used further. Later the snubber of the primary winding was also soldered off, as it turned out it did much more harm than good.

It was possible to extract 300-350W of power from this power supply for a long time; for a short time (no more than a minute) this SMPS can supply up to 500W; after a minute of operation in this mode, the overall radiator heats up to 60 degrees.

Look at the oscillograms:

Everything is still beautiful, the rectangle is almost perfectly rectangular, there are no outliers. With snubbers, oddly enough, everything was not so beautiful.

The following diagram is the final and most advanced 2161 SE 4:

When assembled, the device according to this diagram looks like this:

Like last time, there were no major changes in the scheme. Perhaps the most noticeable difference is that the snubbers have disappeared, both in the primary circuit and in the secondary ones. Because, as my experiments have shown, due to the peculiarities of the IR2161 controller, snubbers only interfere with its operation and are simply contraindicated. Other changes were also made. The values of the gate resistors (R3 and R4) have been reduced from 51 to 33 Ohms. In series with the self-feeding capacitor C7, a resistor R2 is added to protect against overcurrents when charging capacitors C3 and C4. Resistor R1 still consists of four half-watt resistors, and resistor R6 is now hidden under the board and consists of three SMD resistors of the 2512 format. Three resistors provide the required resistance, but it is not necessary to use exactly three resistors; depending on the required power, you can use one, two or three resistors are acceptable. Thermistor RT1 has been moved from the SMPS to the +310V target. The remaining measurements concern only the layout of the printed circuit board and it looks like this:

A safety gap has been added to the printed circuit board between the primary and secondary circuits, and a through cut has been made in the board at the narrowest point.

The transformer is exactly the same as in the previous power supply: it is made on a core from a computer power supply - ER35/21/11. The primary winding has 45 turns in three 0.5mm wires, two secondary windings have 12 turns in four 0.5mm wires. The input and output chokes are also taken from the computer power supply.

The output power of the power supply remained the same - 300-350W in long-term mode and 500W in short-term mode (no more than a minute). From this SMPS you can power a UMZCH with a total output power of up to 400W (2x200W in stereo mode).

Now let's look at the oscillograms on the primary winding of the transformer of this switching power supply:

Everything is still beautiful: the rectangle is rectangular, there are no outliers.

At the output of one of the arms of the power supply, at idle, you can observe the following picture:

As you can see, the output contains negligible high-frequency noise with a voltage of no more than 8 mV (0.008 V).

Under load, at the output, you can observe the already well-known ripples with a frequency of 100 Hz:

With an output power of 250W, the ripple voltage at the output of the SMPS is 1.2V, which, considering the lower capacitance of the capacitors in the secondary circuit (2000uF in the shoulder, versus 3200uF for SE2) and the high output power at which the measurements were made, looks very good. The high-frequency component at a given output power (250W) is also insignificant, has a more ordered character and does not exceed 0.2V, which is a good result.

Setting the protection threshold. The threshold at which the protection will operate is set by resistor RCS (R5 - in SE 2, R6 - in SE 3 and SE 4).

This resistor can be either output or SMD format 2512. RCS can be composed of several resistors connected in parallel.
The RCS denomination is calculated using the formula: Rcs = 32 / Pnom. Where, Pnom is the output power of the SMPS, above which the overload protection will operate.
Example: let's say that we need the overload protection to be triggered when the output power exceeds 275W. We calculate the resistor value: Rcs=32/275=0.116 Ohm. You can use either one 0.1 Ohm resistor, or two 0.22 Ohm resistors connected in parallel (which will result in 0.11 Ohm), or three 0.33 Ohm resistors, also connected in parallel (which will result in 0.11 Ohm) .

Now it’s time to touch on the topic that interests people the most - calculation of a transformer for a switching power supply. Due to your numerous requests, I will finally tell you in detail how to do this.

First of all, we need a core with a frame, or just a core if it is a ring-shaped core (shape R).

Cores and frames can be of completely different configurations and can be used in any way. I used an ER35 frame core from a computer power supply. The most important thing is that the core does not have a gap; cores with a gap cannot be used.

By default, immediately after starting the program, you will see similar numbers.
Starting the calculation, the first thing we will do is select the shape and dimensions of the core in the upper right corner of the program window. In my case, the shape is ER, and the sizes are 35/21/11.

The dimensions of the core can be measured independently; how to do this can be easily understood from the following illustration:

Next, select the core material. It’s good if you know what material your core is made of, if not, then it’s okay, just choose the default option - N87 Epcos. In our conditions, the choice of material will not have a significant impact on the final result.

The next step is to select the converter circuit; ours is half-bridge:

In the next part of the program - “supply voltage”, select “variable” and indicate 230V in all three windows.

In the “converter characteristics” part, we indicate the bipolar output voltage we need (voltage of one arm) and the required output power of the SMPS, as well as the diameter of the wire with which you want to wind the secondary and primary windings. In addition, the type of rectifier used is selected - “bipolar with a midpoint”. There we also check the box “use the desired diameters” and under “output stabilization” select “no”. Select the type of cooling: active with a fan or passive without it. You should end up with something like this:

The actual values of the output voltages will be greater than what you indicate in the program when calculating. In this case, with a voltage of 2x45V specified in the program, the output of a real SMPS will be approximately 2x52V, so when calculating, I recommend specifying a voltage that is 3-5V less than required. Or indicate the required output voltage, but wind one turn less than indicated in the program calculation results. The output power should not exceed 350W (for 2161 SE 4). The diameter of the wire for winding, you can use any one you have, you need to measure and indicate its diameter. You should not wind the windings with a wire with a diameter of more than 0.8 mm; it is better to wind the windings using several (two, three or more) thin wires than one thick wire.

After all this, click on the “calculate” button and get the result, in my case it turned out like this:

We focus our attention on the points highlighted in red. The primary winding in my case will consist of 41 turns, wound in two wires with a diameter of 0.5 mm each. The secondary winding consists of two halves of 14 turns, wound in three wires with a diameter of 0.5 mm each.

After receiving all the necessary calculation data, we proceed directly to winding the transformer.
It seems to me that there is nothing complicated here. I'll tell you how I do it. First, the entire primary winding is wound. One of the ends of the wire(s) is stripped and soldered to the corresponding terminal of the transformer frame. After which the winding begins. The first layer is wound and then a thin layer of insulation is applied. After which the second layer is wound and a thin layer of insulation is applied again and thus the entire required number of turns of the primary winding is wound. It is best to wind the windings turn to turn, but you can also do it askew or just “anyhow”, this will not play a noticeable role. After the required number of turns have been wound, the end of the wire(s) is cut off, the end of the wire is stripped and soldered to another corresponding terminal of the transformer. After winding the primary winding, a thick layer of insulation is applied to it. It is best to use a special Mylar tape as insulation:

The same tape is used to insulate the windings of pulse transformers of computer power supplies. This tape conducts heat well and has high heat resistance. From available materials, it is recommended to use: FUM tape, masking tape, paper plaster or a baking sleeve cut into long strips. It is strictly forbidden to use PVC and fabric insulating tape, stationery tape, or fabric plaster to insulate windings.

After the primary winding is wound and insulated, we proceed to winding the secondary winding. Some people wind two halves of the winding at once and then separate them, but I wind the halves of the secondary winding one by one. The secondary winding is wound in the same way as the primary. First, we strip and solder one end of the wire(s) to the corresponding terminal of the transformer frame, wind the required number of turns, applying insulation after each layer. Having wound the required number of turns of one half of the secondary winding, we strip and solder the end of the wire to the corresponding terminal of the frame and apply a thin layer of insulation. We solder the beginning of the wire of the next half of the winding to the same terminal as the end of the previous half of the winding. We wind in the same direction, the same number of turns as the previous half of the winding, applying insulation after each layer. Having wound the required number of turns, solder the end of the wire to the corresponding terminal of the frame and apply a thin layer of insulation. There is no need to apply a thick layer of insulation after winding the secondary winding. At this point, the winding can be considered complete.

After winding is completed, it is necessary to insert the core into the frame and glue the core halves together. For gluing, I use one-second super glue. The adhesive layer should be minimal so as not to create a gap between the parts of the core. If you have a ring core (shape R), then naturally you won’t have to glue anything, but the winding process will be less convenient and will take more effort and nerves. In addition, the ring core is less convenient due to the fact that you will have to create and mold the transformer leads yourself, as well as think about attaching the finished transformer to the printed circuit board.

Upon completion of winding and assembly of the transformer, you should get something like this:

For convenience of narration, I will also add here the SMPS 2161 SE 4 diagram for a brief description talk about the element base and possible replacements.

Let's go in order - from entrance to exit. At the input, the mains voltage meets fuse F1; the fuse can have a rating from 3.15A to 5A. Varistor RV1 must be designed for 275V, such a varistor will be marked 07K431, but it is also possible to use variators 10K431 or 14K431. It is also possible to use a varistor with a higher threshold voltage, but the effectiveness of protection and noise suppression will be noticeably lower. Capacitors C1 and C2 can be either regular film capacitors (such as CL-21 or CBB-21) or noise-suppressing type (for example X2) for a voltage of 275V. We unsolder the dual inductor L1 from a computer power supply or other faulty equipment. The inductor can be made independently by winding 20-30 turns on a small ring core, with a wire with a diameter of 0.5 - 0.8 mm. The VDS1 diode bridge can be any for a current from 6 to 8A, for example, indicated in the diagram - KBU08 (8A) or RS607 (6A). Any slow or fast diode with a current from 0.1 to 1A and a reverse voltage of at least 400V is suitable as VD4. R1 can consist of either four half-watt resistors of 82 kOhm, or be one two-watt resistor with the same resistance. Zener diode VD1 must have a stabilization voltage in the range of 13 - 14V; it is allowed to use either one zener diode or a series connection of two zener diodes with a lower voltage. C3 and C5 can be either film or ceramic. C4 should have a capacitance of no more than 47 µF, voltage 16-25V. Diodes VD2, VD3, VD5 must be very fast, for example - HER108 or SF18. C6 can be either film or ceramic. Capacitor C7 must be designed for a voltage of at least 1000V. C9 can be either film or ceramic. The R6 rating must be calculated for the required output power, as described above. As R6, you can use either SMD resistors of the 2512 format or output one- or two-watt resistors; in any case, the resistor(s) are installed under the board. Capacitor C8 must be film (type CL-21 or CBB-21) and have an allowable operating voltage of at least 400V. C10 is an electrolytic capacitor with a voltage of at least 400V; the magnitude of low-frequency ripples at the output of the SMPS depends on its capacitance. RT1 is a thermistor, you can buy it, or you can unsolder it from a computer power supply, its resistance should be from 10 to 20 Ohms and the permissible current should be at least 3A. Both the IRF740 indicated in the diagram and other transistors with similar parameters, for example, IRF840, 2SK3568, STP10NK60, STP8NK80, 8N60, 10N60, can be used as transistors VT1 and VT2. Capacitors C11 and C13 must be film (type CL-21 or CBB-21) with a permissible voltage of at least 400V, their capacitance must not exceed the 0.47 μF indicated in the diagram. C12 and C14 are ceramic, high-voltage capacitors for a voltage of at least 1000V. The VDS2 diode bridge consists of four diodes connected by a bridge. As VDS2 diodes, it is necessary to use very fast and powerful diodes, for example, such as - MUR1520 (15A, 200V), MUR1560 (15A, 600V), MUR820 (8A, 200V), MUR860 (8A, 600V), BYW29 (8A, 200V) , 8ETH06 (8A, 600V), 15ETH06 (15A, 600V). Chokes L2 and L3 are soldered from the computer power supply or made independently. They can be wound either on individual ferrite rods or on a common ring core. Each of the chokes should contain from 5 to 30 turns (more is better), with a wire with a diameter of 1 - 1.5 mm. Capacitors C15, C17, C18, C20 must be film (type CL-21 or CBB-21) with a permissible voltage of 63V or more, the capacitance can be any, the larger their capacitance, the better, the stronger the suppression of high-frequency interference. Each of the capacitors designated in the diagram as C16 and C19 consists of two 1000uF 50V electrolytic capacitors. In your case you may need to use higher voltage capacitors.

And as a final touch, I’ll show you a photo that shows the evolution of the switching power supplies I created. Each subsequent SMPS is smaller, more powerful and better quality than the previous one:

That's all! Thank you for your attention!

List of radioelements

Designation	Type	Denomination	Quantity	Note	My notepad
	Switching Power Supply 2161 SE 4

R1	Resistor	82 kOhm	4	0.5W	To notepad
R2	Resistor	4.7 Ohm	1	0.25W	To notepad
R3, R4	Resistor	33 Ohm	2	0.25W	To notepad
R5	Resistor

There are many IPS schemes, especially on the Internet, but there are few workers, just a few. How many expensive field-effect transistors and microcircuits were collected and burned! Some blocks could be made to work, some not. The circuit given below begins to work immediately, is not critical to the choice of parts, practically does not cause interference, and can be assembled even by novice radio amateurs.

At first glance, the circuit seems complicated, but when examined block by block, everything becomes clear and simple. All parts are inexpensive, readily available, have many replacements, and most parts are found in computer power supplies. Four blocks were assembled, of different configurations, on different printed circuit boards, all started working immediately and are still working. The last block is designed for the well-known amplifier "". The circuit is taken as a basis, supplemented with a soft start device, and transferred to a modern element base. Some elements have been redesigned to produce more power and reduce rectified voltage ripple.

Specifications:
Rated power: 500W
Conversion frequency: 100 kHz
Output voltage: +/- 65V
Efficiency 0.75

The power of the unit when using the same parts can easily reach 800W; only recalculation of the TP2 transformer is required.

Brief job description

The master oscillator is assembled using DD1 elements; the frequency is changed by a trimming resistor within the range of 100-200 kHz. The trigger on element DD2 reduces the frequency by half and generates pulses with steeper edges. Through a complementary emitter follower on transistors VT3 - VT4, pulses pass to transformer TP1 and control powerful transistors VT5, VT6. The master oscillator is powered by a separate stabilizer assembled on elements C5, C6, C7, C8, diodes D7-D10 and transistor VT2. The soft start device is made on thyristor VD1. When the unit is connected to the network, filter capacitor C10 is charged through resistor R5. Capacitor C4 is charged through resistors R3 R4. When the voltage on this capacitor reaches approximately 1V, the thyristor opens and shunts R5.
The surge protector and rectifier have no special features. The rectifier is followed by a transistor filter on transistor VT1, which reduces the ripple of the rectified voltage by 125 times in order to eliminate modulation of the rectangular signal by a voltage with a frequency of 100 Hz.

The voltage received from transformer TP2 (windings 2 and 3) is rectified by the diode bridge D13-D16 and through inductor L2 is supplied to the output filter C16, C17, L3, L4, C18, C19, C20, C21. Choke L2 is necessary mainly to limit the charging current through the bridge diodes, because The output filter uses high-capacity capacitors. More details about the operation of the circuit can be found in.

Schematic diagram:

Construction and details

Structurally, the unit is made on three printed circuit boards: on one - the power part of the unit with a soft start device and a transistor filter, on the other - a master oscillator with its own power supply, on the third - transformer TP2 and an output filter. The output filter can be assembled directly on the amplifier board, then TP2 is attached to the chassis. The layout may vary. Drawings of printed circuit boards 1 and 2 are attached. Due to its extreme simplicity, the output filter board was not developed. When using different parts (diodes, capacitors), the board design will be individual in each specific case. Capacitors C14, C15 and resistors R4, R5, R7, R11, R12 are installed on the board standing up. Capacitors C14, C15 and resistors R11, R12 at the upper point are connected and form the connection point for the lower transformer TP2 according to the output diagram of winding 1. Thyristor VD1 and transistor VT1 are installed on the same radiator through insulating gaskets. When using a thyristor in another housing, you can install it on a separate radiator.
When assembling, you should try to make all connections as short as possible.

About details

Microcircuits 511 series should not be replaced by others. You can use an imported analogue: for K511LA1 the analogue is N102, for K511TV1 the analogue is N110.

Transistors. In place of transistors VT3, VT4, you can use almost any high-frequency transistors: VS639 and VS640, VS635 and VS636, VS337 and VS638, KT 315 and KT361, KT502 and KT503, etc. it is only advisable to select them with the highest gain.

It is better to choose transistors VT5, VT6 in a large package. When using transistors in a TO-220 package, it is necessary to adjust the printed circuit board. You can also make them portable. Transistors of the 2SC series - 3996 - 3998, 5144, 2204, 3552, 3042, 3306, 5570, 2625, etc. with a voltage of at least 400V and a collector current of at least 10A are suitable for replacement. It is advisable to select them with a similar gain. When installing these transistors on a common radiator, you must use mica spacers lubricated with KTP-8 paste. The radiator area for each transistor must be at least 65 cm2. Transistor VT1 can be replaced with KT898A or A1. These are Darlington transistors, found in switches of transistor ignition systems. You can install the 2SC series transistors mentioned above, but you will have to install them on a separate radiator with an area of at least 150 cm2. In addition, you will have to recalculate the secondary winding of transformer TP2, because There will be a voltage loss of about 20V across the transistor. It’s better to make a composite transistor yourself by adding another one, for example MJE13005,13007,13009, etc. A section of the diagram is given. Instead of the KT815G transistor, you can use the KT817G or BD135, BD137, BD139.

Fragment:

Diodes. The BR1010 diode bridge can be replaced with another one, at least 10A - 400V, or separate diodes with the same characteristics. The bridge is equipped with a small radiator.
Diodes D11, D12 - any fast ones for a voltage of at least 400V. FR104 - 107, FR154 - FR157, SF16 are suitable; from domestic ones you can supply KD104A. D5 – FR157, SF16. 1N4007 diodes can be replaced with KD105G or others with a current of more than 0.5A and a voltage of 400V or more. Diodes KD2997A,B can be replaced with KD2999A,B or imported fast diodes with a voltage of at least 200V and a current of 15 - 20A. As a last resort, you can put KD213, but two pieces per shoulder in parallel. Among the imported ones, 15ETH06, 30ETH06, 30EPH06, BYW29-500, etc. are suitable. Schottky diodes can be used if the output voltage does not exceed 60V. See datasheets.

Any 15V zener diode D17, for example KS515 or imported. It can be made up of two, for example KS175A, D814A.

Thyristor VT151 can be replaced by another with a maximum current of at least 10A and a voltage of 400V, for example KU202N1.

Capacitors C2, C3C5, C9, C13-C19 film, C1, C12 – ceramics. Capacitors C14, C15 can be supplied with a smaller capacity, but not less than 1 µF. They must be identical and must be film, with a voltage of at least 250V. Capacity C2, C3, C9 is not critical and can be changed. Better on the big side. Capacitor C10 is made up of two capacitances of 220 and 330 uF 400V. If the unit will have a different power, these capacitors should be installed at the rate of 1 μF per 1 W of power. Although a transistor filter is used, the capacitance of these capacitors should not be greatly reduced in order to maintain the rigidity of the load characteristics of the unit. Capacitor C8 can have a capacity of 100 - 200 μF. Capacitors C16, C17 can be composed of several smaller capacitances, which is even better. The larger the total capacity, the better, within reasonable limits. To facilitate high-frequency operation of capacitors C20, C21, it is advisable to solder ceramic capacitors with a capacity of 0.033 - 0.1 µF directly to their terminals on the back side of the board.

Resistors- power indicated on the diagram. R1 – preferably multi-turn. R6 is used to discharge capacitors, nominal 390 - 910 kOhm. Resistors R11, R12 must be the same and can be rated from 47 to 200 kOhm. The total resistance of resistors R3 and R4 should be 43 - 46 kOhm.

Chokes and transformers. Inductor L1 is wound on a ferrite ring of grade M2000 with an outer diameter of 20 mm. Winding is carried out in one layer with two wires with a diameter of 0.8-1.2 mm at once until it is filled. You can also use an W-shaped core, for example from a TV power supply. Not critical. Choke L2 is wound with a wire with a diameter of 1.2 mm on a cup core made of M2000 ferrite with a diameter of 35 mm or more. Winding is carried out in two wires until the frame is filled. Since the inductor operates on direct current, it is necessary to place a dielectric spacer approximately 0.3 mm thick in the gap. You can try winding it around the ring core from the group stabilization choke of the computer power supply. Chokes L3 L4 are ready from a computer power supply, those that are wound with a thick wire. Must be the same. You can make them yourself by winding 10-20 turns of wire with a diameter of 1.2 mm onto pieces of round ferrite from a radio antenna 25 mm long.

Transformer TR1 made on a ring of ferrite grade M2000, size 16*8*6 and contains 90 turns of PELSHO 0.12 wire wound with three wires at once. The size, brand of wire and number of turns are not critical. To facilitate operation, this transformer can be wound on a cup magnetic core with a diameter of approximately 20 mm, also in three wires. If there is nothing suitable, you can wind it on a small W-shaped ferrite magnetic core.

The most important part of the work is winding transformer TP2. It is wound on a core consisting of two rings of standard size 40*25*11. The rings need to be glued together, the edges rounded off with coarse sandpaper. Then the magnetic circuit is wrapped with two layers of varnished cloth or fluoroplastic tape. The primary winding is wound in two wires (in parallel) with a diameter of 0.8 mm and contains 26 turns, evenly distributed around the ring. On top of the primary winding there are again two layers of varnished fabric. The secondary winding (2,3) is wound in three wires with a diameter of 0.8 mm and contains 2 * 13 turns. The operating procedure is as follows: take a wire of the required length, fold it into 6 layers, twist it slightly for convenience, and wind 13 turns evenly over the primary winding. Then we divide it into two parts by ringing and connect the beginning of one part to the end of the other. This way we get two windings with three wires and a connection point. We wrap everything again with varnished cloth. The finished transformer can be impregnated with paraffin, nitro varnish or epoxy resin. But in the latter case it will turn out to be non-separable. To select the voltage more accurately, immediately after winding the primary winding, wind 10 turns of any wire, connect it to the diode bridge and measure the voltage. Then calculate the required number of turns. It turns out to be approximately 5V per turn.

When winding all chokes and transformers, it is extremely important to respect the beginnings and ends of the windings. The beginnings of the windings are marked with dots in the diagram.

If other output voltages are needed, you need to recalculate the number of turns of the secondary winding. There may be several windings. If you need to calculate the TP2 transformer for a different power or for a different magnetic circuit, you must use.

Out of many programs, this one was chosen as it is simple and gives real, reliable results.

Setting up We start with the pulse generator. To do this, we connect only a small printed circuit board to the network, separately from the large one. Using an oscilloscope, we observe antiphase rectangular pulses on windings 2 and 3 of transformer TP1. Then, using resistor R1, we set the frequency of these pulses to 100 kHz. Many people don’t have an oscilloscope, what to do? We take a board with a soldered network cable and go to the nearest TV studio. Surely they will not be denied one dimension. After this, you can connect the power part of the power supply. It is better to do this by plugging in an incandescent lamp with a power of 75-100 W into the break in the network wire. The lamp should light up briefly and go out. If it lights up constantly, check that the assembly is correct. If everything is normal, remove the lamp. The unit cannot be turned on without a load, so during the test we will load it with two-watt resistors of 500-600 Ohms. We measure the output voltages. If the voltages differ from the calculated ones, measure the network voltage - it may be very different from 220V. We check the operation of the soft start device. To do this, connect the avometer in parallel with resistor R5. When the unit is turned on, the device should show a constant voltage of about 30V. After one or two seconds, the tension should almost completely disappear. In parallel with capacitor C2, you can turn on a varistor, for example JVR-7N391K, or another, for a voltage of about 400V. There are holes in the printed circuit board. The unit is protected by an 8A fuse.

Literature:
"RADIO" No. 1 1987 pp.35-37

List of radioelements

Designation	Type	Denomination	Quantity	My notepad
DD1	Chip	K511LA1	1	To notepad
DD2	Chip	K511TV1	1	To notepad
D1-D4	Diode bridge	BR1010	4	To notepad
VT1	Bipolar transistor	BU931P	1	To notepad
VT2	Bipolar transistor	KT815G	1	To notepad
VT3	Bipolar transistor	2N5551	1	To notepad
VT4	Bipolar transistor	2N5401	1	To notepad
VT5, VT6	Bipolar transistor	MJE13009	2	To notepad
D5, D11, D12	Rectifier diode	HER108	3	To notepad
D7-D10	Rectifier diode	1N4007	4	To notepad
D13-D16	Diode	KD2997A	4	To notepad
D17	Zener diode	KS515A	1	To notepad
VD1	Thyristor	BT151-800	1	To notepad
C1	Capacitor	1500 pF	1	To notepad
C2, C3		0.22uF 400V	2	To notepad
C4	Electrolytic capacitor	2200uF 10V	1	To notepad
C5, C9	Electrolytic capacitor	1uF 400V	2	To notepad
C6	Electrolytic capacitor	470uF 100V	1	To notepad
C7	Electrolytic capacitor	10uF 10V	1	To notepad
C8	Electrolytic capacitor	150uF 400V	1	To notepad
C10	Electrolytic capacitor	550uF 400V	1	To notepad
C11	Electrolytic capacitor	100uF 25V	1	To notepad
C12	Capacitor	0.033 µF	1	To notepad
C13	Capacitor	0.1 µF	1	To notepad
C14, C15	Electrolytic capacitor	4.7uF 250V	2	To notepad
C16, C17	Electrolytic capacitor	4.7uF 160V	2	To notepad
C18, C19	Capacitor	0.22 µF	2	To notepad
C20, C21	Electrolytic capacitor	10000uF 83V	2	To notepad
R1	Variable resistor	22 kOhm	1	To notepad
R2	Resistor

A switching power supply, providing bipolar voltage +/-50V with a power of up to 300 W, is intended for use, or high-power laboratory power supplies (). This relatively simple switching power supply circuit is assembled mainly from radio elements taken from old AT/ATX power supplies.

Schematic diagram of the converter 220/2x50V

Scheme of a homemade pulse power supply for UMZCH

The inverter transformer was wound on an ETD39 ferrite core. The winding data is practically the same, only the output windings are slightly wound to accommodate the increase in voltage. The key transistors are powerful IRFP450. The driver is the popular TL494 chip. Power is supplied through a special stabilizer. In it, the starting resistor with the rectified mains voltage charges the power capacitor, on which, when the voltage reaches the threshold, the stabilizer turns on, starting the driver. It will be powered only when energy is accumulated on the capacitor, and after the converter starts, the additional winding of the transformer will take over the driver power.

The operating principle of this launch option has been known for a long time and is used in the popular m/s UC384x.

Printed circuit board

Power cascade

Another feature of the power supply circuit design is the control of field-effect transistors. Here the lower IRFP450 circuit is controlled directly from the driver output, and the upper one is controlled using a small transformer. In addition, the system was equipped with current protection, monitoring the current of the lower field worker using its resistance.

Rdson

PSU test results

Finished power supply - board with parts

In practice, it was possible to obtain about 100-150 output power from 4 ohm speakers. The voltage +/-50V is set by resistor P1 10k. Of course, it can take any value, depending on the ULF circuit used. The system currently operates as a .
We bring to the attention of readers a switching power supply (SMPS) that provides a bipolar output voltage and is designed to power the UMZCH. This device differs from a similar SMPS (Moskatov E. “Switching power supply for UMZCH.” - Radio, 2007, No. 10, pp. 36-39) by almost twice the maximum output power, the presence of an output voltage stabilization system and a significantly smaller number elements used. Main technical characteristics AC supply voltage, V.....230 ±15% Supply voltage frequency, Hz........50 Conversion frequency, kHz .....132 Stabilized output voltage, V.........2x50 Maximum load power, W, no more........290 Output voltage ripple amplitude, V......0, 15Maximum efficiency, % ...........84The schematic diagram of the device is shown in the figure. The mains voltage is supplied through fuse link FU1 and power switch SA1 to filter C1L1C3, which suppresses interference entering the network from the SMPS. Varistor RU1 protects the SMPS elements from an emergency increase in the supply voltage. After the filter, the mains voltage rectifies the diode bridge VD4, and capacitor C5 smoothes out the ripples of the rectified voltage. Thermistor RK1 with negative TCR limits the charging current of this capacitor when the device is turned on. Protective diode VD2 limits voltage surges on winding I of transformer T1 and thereby protects microcircuit DA1 from failure. Diodes VD6 and VD7 together with capacitors C6, C7 form a bipolar rectifier, and LED HL1 together with current-limiting resistor R6 - a circuit indicating the presence of an output SMPS voltage. A half-wave rectifier based on the VD5 diode with a smoothing capacitor C8 is designed to power the M1 fan with a constant voltage of 12 V. This fan is necessary for blowing the heat sink and, in addition, together with the indication circuit, it performs the function of a constant SMPS load. An additional low-power rectifier is assembled on the VD3 diode , capacitor C4 smoothes out the ripples of the rectified voltage. Stabilization of the output voltage of the SMPS is carried out using optocoupler U1 and zener diode VD8. As the output voltage increases, the current through the emitting diode of the optocoupler increases, the resistance of the phototransistor of this optocoupler decreases and the voltage at input C of the DA1 microcircuit increases - the duty cycle of the pulses through winding I increases, therefore, the output voltages of the SMPS decrease. A low-pass filter is assembled on elements C9, C10, L2, which reduces the amplitude of output voltage ripples. The device uses fixed resistors MLT, OMLT, S2-22, S2-23, the power of resistor R3 (2 W) was chosen not because of the power dissipation, but only taking into account the maximum permissible voltage. Trimmer resistor - 3329N-1 or SPZ-19a, varistor RU1 - JVR-7N391K, JVR-10N391K, JVR-10N431K, JVR-14N391K, JVR-14N431K. Thermistor RK1 with negative TKS - any of the NTC series, having a resistance in the normal state of 10...33 Ohms, allowing the flow of a current of at least 3 AO. Oxide capacitors - imported from Elzet or SarHop, they must be designed to operate on a pulsating voltage with a frequency pulsations of at least 132 kHz. They can be replaced with domestic capacitors K50-35 and similar, provided that they are shunted with ceramic (KM-5, KM-6, K10-17) or film (K73-16, K73-17) capacitors for an operating voltage of at least 50 V and a capacity of 0.047...0.47 µF. Capacitors C1, SZ - FKP1 or MKR10 series from Wima. The KBU8M diode bridge can be replaced with a BR1010, KBU606, KBU8K, KBU10K or RS807 bridge, the ZY6.2 zener diode can be replaced with 1N4735A, ZY6.8, BZX85B-6V2, BZX85C-6V2, 1 N5341B or 1N5342B, and the 1.5KE350CA diode - on SMBJ200CA or P6KE300CA. Diodes 15ETH03 are replaceable with 15ETH06, 15ETX06S, 30ЭН06, 30ЭН06, BYV29-500, BYC10-600, DSEI12-06A or FES16JT, diodes 1N4934 - with BYD33D, ES1B, ES2B, ER1B, ER1D, 103, MUR120, FYR120, MURS110,SF12, SF22, UF4002. Instead of the KIPD02G-1L LED, you can use the KIPD36Zh1-R, KIPD36I1-R, KIPM15M-1R, KIPD02V-1L, AL307GM, AL307NM, AL307PM LEDs, and instead of the RS817 optocouplers - LTV816, LTV817, LTV817A PC816. The power switch must provide switching of an alternating voltage of 250 V at a current of up to 3 A; for example, SC768 is suitable. Choke L1 is wound with PELSHO 0.8 wire on a magnetic core KP15x7x6.5 made of MP-140 material. Winding is carried out with a double folded wire until the window is filled. For exile
The pulse transformer is manufactured using a magnetic core Ш 12x15 made of 3000NMS ferrite, specially designed for operation in strong magnetic fields. The thickness of the gap in the magnetic core is 0.16 mm. Winding I contains 60 turns of PEV-2, PELSHO 0.6 wire, and winding II contains 5 turns of the same wire with a diameter of 0.12 mm. Winding III contains 15+2+2+15 turns of litzent wire, consisting of 16 strands of insulated wire, each with a diameter of 0.15 mm. The windings are insulated from one another with three layers of fluoroplastic, mylar or lacquer tape. The same Litz wire is used for the manufacture of inductor 12 - it is wound on a toroidal magnetic core KP24x13x6.5 mm made of MP-140 material, winding is also carried out with a double folded wire until it is filled. The TOP250Y microcircuit (in the TO-220-7C case) can be replaced with a TOP250R (in case TO-263-7С) or TOP250F (in case TO-262-7С). In any case, the microcircuit is mounted on a heat sink with a surface area of at least 40 cm2. It is advisable to lubricate the place of thermal contact between the microcircuit and the heat sink with heat-conducting paste, for example KPT-8. On the same heat sink, diodes VD6 and VD7 are attached through dielectric heat-conducting spacers. Fan M1 with dimensions 40x40x12 mm and a supply voltage of 12 V is manufactured by Gembird, but a similar one from computer equipment can be used. The setup comes down to accurately setting the constant output voltages using trimming resistor R5. Chapter:

Making a good power supply for a power amplifier (UPA) or other electronic device is a very responsible task. The quality and stability of the entire device depends on the power source.

In this publication I will tell you about making a simple transformer power supply for my homemade low-frequency power amplifier "Phoenix P-400".

Such a simple power supply can be used to power various low-frequency power amplifier circuits.

Preface

For the future power supply unit (PSU) for the amplifier, I already had a toroidal core with a wound primary winding of ~220V, so the task of choosing “switching PSU or based on a network transformer” was not present.

Switching power supplies have small dimensions and weight, high output power and high efficiency. A power supply based on a network transformer is heavy, easy to manufacture and set up, and you don’t have to deal with dangerous voltages when setting up the circuit, which is especially important for beginners like me.

Toroidal transformer

Toroidal transformers, in comparison with transformers with armored cores made of W-shaped plates, have several advantages:

less volume and weight;
higher efficiency;
better cooling for windings.

The primary winding already contained approximately 800 turns of 0.8 mm PELSHO wire; it was filled with paraffin and insulated with a layer of thin fluoroplastic tape.

By measuring the approximate dimensions of the transformer iron, you can calculate its overall power, so you can estimate whether the core is suitable for obtaining the required power or not.

Rice. 1. Dimensions of the iron core for the toroidal transformer.

Overall power (W) = Window area (cm 2) * Sectional area (cm 2)
Window area = 3.14 * (d/2) 2
Sectional area = h * ((D-d)/2)

For example, let's calculate a transformer with iron dimensions: D=14cm, d=5cm, h=5cm.

Window area = 3.14 * (5cm/2) * (5cm/2) = 19.625 cm2
Cross-sectional area = 5cm * ((14cm-5cm)/2) = 22.5 cm 2
Overall power = 19.625 * 22.5 = 441 W.

The overall power of the transformer I used turned out to be clearly less than I expected - about 250 watts.

Selection of voltages for secondary windings

Knowing the required voltage at the output of the rectifier after the electrolytic capacitors, you can approximately calculate the required voltage at the output of the secondary winding of the transformer.

The numerical value of the direct voltage after the diode bridge and smoothing capacitors will increase by approximately 1.3..1.4 times compared to the alternating voltage supplied to the input of such a rectifier.

In my case, to power the UMZCH you need a bipolar DC voltage - 35 Volts on each arm. Accordingly, an alternating voltage must be present on each secondary winding: 35 Volts / 1.4 = ~25 Volts.

Using the same principle, I made an approximate calculation of the voltage values for the other secondary windings of the transformer.

Calculation of the number of turns and winding

To power the remaining electronic units of the amplifier, it was decided to wind several separate secondary windings. A wooden shuttle was made to wind the coils with enameled copper wire. It can also be made from fiberglass or plastic.

Rice. 2. Shuttle for winding a toroidal transformer.

Winding was done with enameled copper wire, which was available:

for 4 power windings UMZCH - wire with a diameter of 1.5 mm;
for other windings - 0.6 mm.

I selected the number of turns for the secondary windings experimentally, since I did not know the exact number of turns of the primary winding.

The essence of the method:

We wind 20 turns of any wire;
We connect the primary winding of the transformer to the ~220V network and measure the voltage on the wound 20 turns;
We divide the required voltage by that obtained from 20 turns - we will find out how many times 20 turns are needed for winding.

For example: we need 25V, and from 20 turns we get 5V, 25V/5V=5 - we need to wind 20 turns 5 times, that is, 100 turns.

The calculation of the length of the required wire was done as follows: I wound 20 turns of wire, made a mark on it with a marker, reeled it off and measured its length. I divided the required number of turns by 20, multiplied the resulting value by the length of 20 turns of wire - I got approximately the required length of wire for winding. By adding 1-2 meters of reserve to the total length, you can wind the wire onto the shuttle and safely cut it off.

For example: you need 100 turns of wire, the length of 20 wound turns is 1.3 meters, we find out how many times 1.3 meters each need to be wound to get 100 turns - 100/20 = 5, we find out the total length of the wire (5 pieces of 1, 3m) - 1.3*5=6.5m. We add 1.5 m for reserve and get a length of 8 m.

For each subsequent winding, the measurement should be repeated, since with each new winding the wire length required by one turn will increase.

To wind each pair of 25 Volt windings, two wires were laid in parallel on the shuttle (for 2 windings). After winding, the end of the first winding is connected to the beginning of the second - we have two secondary windings for a bipolar rectifier with a connection in the middle.

After winding each pair of secondary windings to power the UMZCH circuits, they were insulated with thin fluoroplastic tape.

In this way, 6 secondary windings were wound: four for powering the UMZCH and two more for power supplies for the rest of the electronics.

Diagram of rectifiers and voltage stabilizers

Below is a schematic diagram of the power supply for my homemade power amplifier.

Rice. 2. Schematic diagram of the power supply for a homemade low-frequency power amplifier.

To power the LF power amplifier circuits, two bipolar rectifiers are used - A1.1 and A1.2. The remaining electronic units of the amplifier will be powered by voltage stabilizers A2.1 and A2.2.

Resistors R1 and R2 are needed to discharge electrolytic capacitors when the power lines are disconnected from the power amplifier circuits.

My UMZCH has 4 amplification channels, they can be turned on and off in pairs using switches that switch the power lines of the UMZCH scarf using electromagnetic relays.

Resistors R1 and R2 can be excluded from the circuit if the power supply is permanently connected to the UMZCH boards, in which case the electrolytic capacitors will be discharged through the UMZCH circuit.

KD213 diodes are designed for a maximum forward current of 10A, in my case this is enough. The D5 diode bridge is designed for a current of at least 2-3A, assembled from 4 diodes. C5 and C6 are capacitances, each of which consists of two capacitors of 10,000 μF at 63V.

Rice. 3. Schematic diagrams of DC voltage stabilizers on microcircuits L7805, L7812, LM317.

Explanation of names on the diagram:

STAB - voltage stabilizer without adjustment, current no more than 1A;
STAB+REG - voltage stabilizer with regulation, current no more than 1A;
STAB+POW - adjustable voltage stabilizer, current approximately 2-3A.

When using LM317, 7805 and 7812 microcircuits, the output voltage of the stabilizer can be calculated using a simplified formula:

Uout = Vxx * (1 + R2/R1)

Vxx for microcircuits has the following meanings:

LM317 - 1.25;
7805 - 5;
7812 - 12.

Calculation example for LM317: R1=240R, R2=1200R, Uout = 1.25*(1+1200/240) = 7.5V.

Design

This is how it was planned to use the voltage from the power supply:

+36V, -36V - power amplifiers on TDA7250
12V - electronic volume controls, stereo processors, output power indicators, thermal control circuits, fans, backlighting;
5V - temperature indicators, microcontroller, digital control panel.

The voltage stabilizer chips and transistors were mounted on small heatsinks that I removed from non-working computer power supplies. The cases were attached to the radiators through insulating gaskets.

The printed circuit board was made of two parts, each of which contains a bipolar rectifier for the UMZCH circuit and the required set of voltage stabilizers.

Rice. 4. One half of the power supply board.

Rice. 5. The other half of the power supply board.

Rice. 6. Ready-made power supply components for a homemade power amplifier.

Later, during debugging, I came to the conclusion that it would be much more convenient to make voltage stabilizers on separate boards. Nevertheless, the “all on one board” option is also not bad and is convenient in its own way.

Also, the rectifier for UMZCH (diagram in Figure 2) can be assembled by mounted mounting, and the stabilizer circuits (Figure 3) in the required quantity can be assembled on separate printed circuit boards.

The connection of the electronic components of the rectifier is shown in Figure 7.

Rice. 7. Connection diagram for assembling a bipolar rectifier -36V + 36V using wall-mounted installation.

Connections must be made using thick insulated copper conductors.

A diode bridge with 1000pF capacitors can be placed separately on the radiator. Installation of powerful KD213 diodes (tablets) on one common radiator must be done through insulating thermal pads (thermal rubber or mica), since one of the diode terminals has contact with its metal lining!

For the filtering circuit (electrolytic capacitors of 10,000 μF, resistors and ceramic capacitors of 0.1-0.33 μF), you can quickly assemble a small panel - a printed circuit board (Figure 8).

Rice. 8. An example of a panel with slots made of fiberglass for mounting smoothing rectifier filters.

To make such a panel you will need a rectangular piece of fiberglass. Using a homemade cutter (Figure 9), made from a hacksaw blade for metal, we cut the copper foil along its entire length, then cut one of the resulting parts perpendicularly in half.

Rice. 9. A homemade cutter made from a hacksaw blade, made on a sharpening machine.

After this, we mark and drill holes for the parts and fastenings, clean the copper surface with fine sandpaper and tin it using flux and solder. We solder the parts and connect them to the circuit.

Conclusion

This simple power supply was made for a future homemade audio power amplifier. All that remains is to supplement it with a soft start and standby circuit.

UPD: Yuri Glushnev sent a printed circuit board for assembling two stabilizers with voltages +22V and +12V. It contains two STAB+POW circuits (Fig. 3) on LM317, 7812 microcircuits and TIP42 transistors.