Switching power supply circuit for an amplifier. Switching power supply unit UHF Power supply circuits for transistor amplifiers

Have a good time everyone. Let me introduce a power inverter for powering a powerful audio amplifier. Unfortunately, they are especially repeatable. Therefore, it was decided to make such a power source from scratch. It took a lot of time to design, build and test this UPS. And now, having carried out the last tests (all tests were successful), we can say that the project is finished and can be presented to the respected amateur radio audience of the site. 2 Schemes.ru

The project of this inverter is perfect for, in fact, it was developed for it. The converter is not complicated and should be successfully assembled by not very advanced electronics engineers. You don't even need an oscilloscope to run it, but of course it would be useful. The basis of the power supply circuit is m/s TL494.

It is short circuit protected and should provide 250W of continuous power. The converter also has an additional output voltage of +/- 9..12 V, which will be used to power the preamplifier, fans, etc.

Switching power supply for an amplifier - circuit diagram

The converter is made in accordance with this scheme. Board dimensions 150×100 mm.

The inverter consists of several basic modules found in most similar power supplies, such as an ATX power supply. The fuse, thermistor and line filter consisting of C21, R21 and L5 go to the 220V AC power supply. Then the rectifier bridge D26-D29, inverter input capacitors C18 and C19 and power transistors Q8 and Q9 to switch the voltage at the transformer. Power transistors are controlled using an additional transformer T2 by one of the most popular PWM controllers - TL494 (KA7500). Current transformer T3 for measuring output power is connected in series with the primary winding. Transformer T1 has two separated secondary windings. One of them generates a voltage of 2×35 V, and the other 2×12 V. On each of the windings there are fast diodes D14-D17 and D22-D25, which in total form 2 rectifier bridges.

After loading the +/- 34 V line with a 14 ohm resistor, the voltage drops to +/- 31 V. This is a pretty good result for such a small ferrite core. After 5 minutes, diodes D22-D25, the main transformer and MOSFET heated up to a temperature of about 50C, which is quite safe. After connecting two channels of TDA7294, the voltage dropped to +/- 30 V. The inverter elements heated up like a resistive load. After experiments, the output circuit is equipped with 2200uF capacitors and 22uH/14A chokes. The voltage drop is slightly higher than in the case of 6.8uH, but their use clearly reduces the heating of the MOSFETs.

Output voltage under load of both outputs with 20 W bulbs:

Operating principle of a switching power supply

The 220 V voltage is rectified by a bridge with diodes D26-D29. The input capacitors C18 and C19 charge to a total voltage of 320V, and since the inverter operates in a half-bridge system, they divide them in half, resulting in 160V per capacitor. This voltage is further balanced by resistors R16 and R17. Thanks to this separation, it is possible to connect transformer T1 to one channel. The potential between the capacitors is then treated as ground, one end of the primary winding is connected to +160 V, the other to -160 V. The switching voltage of the primary winding of transformer T1 is carried out using a variable N-MOSFET transistor Q8 and Q9.

Capacitor C10 and the primary winding of current transformer T3 are located in series with the primary winding. The coupling capacitor is not needed for the operation of the circuit, but it plays a very important role - it protects against unbalanced energy consumption from the input capacitors and, therefore, before charging one of them to more than 200 V. The current transformer T3, also located in series with the primary winding, acts as short circuit protection. The current transformer provides galvanic isolation and allows you to measure the current value, reduced to the accuracy of its transmission. Its task is to inform the controller about the amount of current flowing through the primary winding T1.

In parallel with the primary winding of the main transformer there is a so-called pulse suppression circuit, which is formed by C13 and R18. It suppresses voltage surges generated when switching power transistors. They are not harmful to MOSFETs because their built-in diodes effectively protect against drain overvoltage. However, voltage surges can negatively affect the efficiency of the inverter, so it is important to eliminate them.

The power MOSFETs cannot be driven directly from the controller due to the change in the potential of the upper transistor source. The transistors are controlled using a special transformer T2. This is an ordinary pulse transformer operating in push-pull mode, opening power transistors. The control transformer T2 has at the input a set of voltage control elements on the windings, which, in addition to generating the voltage dictated by the controller, protect against the occurrence of core demagnetizing voltage. An uncontrolled demagnetization voltage would keep the transistor open. The elements directly responsible for eliminating the demagnetization voltage are diodes D7 and D9, as well as transistors Q3 and Q5. During idle time, when both MOSFETs are off, current flows through D7 and Q5 (or D9 and Q3) and maintains the demagnetization voltage around 1.4 V. This voltage is safe and cannot open the power transistor.

Voltage oscillogram at MOSFET inputs:

On the oscillogram you can clearly see the moment when the core stops being demagnetized by diodes D7 and D8 (D6 and D9) and begins to be magnetized in the opposite direction by transistors Q3 and Q4 (Q2 and Q5). During the core demagnetization phase, the voltage at the T2 gate reaches 18 V, and during the magnetization phase it drops to approximately 14 V.
Why is one of the IR type drivers not used? First of all, the control transformer is more reliable, more predictable. IR drivers are very capricious and error prone.

An alternating voltage is generated on the secondary winding of the main transformer T1, so it needs to be rectified. The role of the rectifier is played by rectifying fast diodes, generating a symmetrical voltage. The output chokes are located behind the diodes - their presence affects the efficiency of the inverter, suppressing the surges that charge the output capacitors when one of the power transistors is turned on. Next are the output capacitors with preload resistors, which prevent the voltage from rising to too high values.

Pulse IP controller

The controller is the basis of the inverter, so we will describe it in more detail. The inverter uses a TL494 controller with a set operating frequency the same as in ATX power supplies, that is, 30 kHz. The inverter does not have output voltage stabilization, so the controller operates with a maximum duty cycle of 85%. The controller is equipped with a soft start system consisting of elements C5 and R7. After starting the inverter, the circuit provides a smooth increase in the duty cycle starting from 0%, which eliminates the charging surge of the output capacitors. The TL494 can operate from 7 V, and this voltage supplying the buffer of the control transformer T2 causes the generation of a voltage at the gates of the order of 3 V. Such not fully open transistors will output tens of volts, which will lead to huge power losses and there is a high probability of exceeding the dangerous limit. To prevent this, protection is provided against too high a voltage drop. It consists of a resistor divider R4 - R5 and transistor Q1. After the voltage drops to 14.1 V, Q1 discharges the soft start capacitor, thereby reducing the charge to 0%.

Another function of the controller is to protect the inverter from short circuit. Information about the primary winding current is obtained by the controller through the current transformer T3. The current in the secondary winding T3 flows through resistor R9, across which a small voltage drops. Information about the voltage on R9 is sent via potentiometer PR1 to the error amplifier TL494 and compared with the voltage of the resistor divider R1 and R2. If the controller detects a voltage higher than 1.6 V on potentiometer PR1, it turns off the transistors before they cross the dangerous limit and is latched through D1 and R3. The power transistors remain off until the inverter is restarted. Unfortunately, this protection only works correctly on the +/- 35 V line. The +/- 12 V line is much weaker and in the event of a short circuit there may not be enough current for the protection to operate.

The controller's power supply is transformerless using capacitor resistance. The two capacitors C20 and C24 consume reactive energy from the mains and hence by causing current to flow, they charge the filter capacitor C1 through the rectifier D10-D13. Zener diode DZ1 protects against too high voltage on C1 and stabilizes them at 18 V.

Pulse transformers in power supply

The quality and performance of a pulse transformer affects the efficiency of the entire converter and the output voltage. However, the transformer not only performs the function of converting electricity, but also provides galvanic isolation from the 220 V network and thus has a great impact on safety.

Here's how to make such a transformer correctly. First of all there must be a ferrite core. It cannot have an air gap; its halves must fit perfectly together. Theoretically, a toroidal core can be used here, but making good insulation and winding will be quite difficult.

We recommend taking the main ETD34, ETD29 as a last resort, but then the maximum continuous power will be no more than 180 W. They don't cost much, so the best solution is to get a damaged ATX power supply. Burnt PC power supplies, in addition to all the necessary transformers, contain many more useful elements, including a surge protector, capacitors, diodes, and sometimes TL494 (KA7500).

Transformers must be carefully desoldered from the ATX power supply board, preferably using a hot air gun. After desoldering, do not try to disassemble the transformer because it will break. The transformer should be placed in water and boiled. After 5 minutes, you need to carefully grab the core halves through the fabric and separate them. If they don't want to separate, don't pull too hard - you'll break them! Place back and cook for another 5 minutes.

The process of winding the main transformer should begin with counting the amount of wire that will be wound. Due to the constant operating frequency and the specified maximum induction, the number of primary windings depends only on the cross-sectional area of ​​the main ferrite core column. The maximum induction is limited to 250 mT due to half-bridge operation - here the magnetization asymmetry is simple.

Formula for calculating the number of turns:

n = 53 / Qr,

• Qr is the cross-sectional area of ​​the main core rod, given in cm2.

Thus, for a core with a cross-section of 0.5 cm2, you need to wind 106 turns, and for a core with a cross-section of 1.5 cm2, you will only need 35. Remember, do not wind half a turn - always round up to one plus. Calculating the number of secondary windings is the same as for any other transformer - the ratio of the output voltage to the input voltage is exactly equal to the ratio of the number of secondary windings to the number of primary windings.

The next step is to calculate the thickness of the winding wires. The most important thing to consider when calculating the thickness of the wires is the need to fill the entire core window with wire - this determines the magnetic connection of the transformer windings, and therefore the output voltage drop. The total cross-section of all wires passing through the core window should be about 40-50% of the cross-section of the main window (the main window is where the wire passes through the core). If this is your first time winding a transformer, you should get closer to this 40%. The calculations must also take into account the currents flowing through the cross-section of the windings. Typically the current density is 5 A/mm2 and this value should not be exceeded, the use of lower current densities is desirable. In the simulation, the primary side current is 220 W / 140 V = 1.6 A, so the wire cross-section should be 0.32 mm2, which means its thickness will be 0.6 mm. On the secondary side, a current of 220W/54V would be 4.1A, resulting in a cross-section of 0.82mm and an actual wire thickness of 1mm. In both cases, the maximum voltage drop during loading was taken into account. It should also be remembered that due to the skin effect of pulse transformers, the thickness of the wire is limited by the operating frequency - in our case at 30 kHz the maximum wire thickness is 0.9 mm. Instead of a 1mm thick wire, it is better to use two thinner wires. After calculating the number of coils and wires, check whether the calculated filling of the copper window corresponds to 40-50%.

The primary winding of the transformer must be placed in two parts. The first part of the primary (of 35 turns) is wound like the first, on an empty frame. It is necessary to maintain the direction of the winding towards the frame - the second part of the winding must be wound in the same direction. After winding the first part, you need to solder the other end to an adapter, shortened pin, which is not included in the board. Then apply 4 layers of insulation tape on the winding and wind the entire secondary winding - this means the winding method. This improves the symmetry of the windings. The following +/- 12V secondary winding can be wound directly onto the +/- 35V winding in areas where a small amount of free space has been saved, and then completely insulated with 4 layers of electrical tape. Of course, it is also necessary to insulate the places where the ends of the windings are driven to the housing pins. As the last winding, wind the second part of the primary winding, always in the same direction as the previous one. After winding, you can insulate the last winding, but it is not necessary.

When the windings are ready, fold the core halves. The best and proven solution is to connect it with electrical tape and a drop of glue. We wrap the core with insulating tape several times.

The control transformer is made like any other pulse transformer. A small EE/EI obtained from ATX power supplies can be used as the core. You can also buy a TN-13 or TN-16 toroidal core. The number of windings depends, as usual, on the cross-section of the core.

In the case of toroids, the formula is:

n = 8 / Qr,

• where n is the number of windings of the primary winding,
• Qr is the cross-sectional area of ​​the core, given in cm2.

The secondary windings should be wound with the same number of turns as the primary windings, only minor deviations are allowed. Since the transformer will only drive one pair of MOSFETs, the thickness of the wire is not important, its minimum thickness is less than 0.1 mm. In this case 0.3 mm. The first half of the primary winding must be wound in series - insulating layer - first secondary winding - insulating layer - second secondary winding - insulating layer - second half of the primary winding. The direction of the winding of the windings is very important, here the MOSFETs must be turned on one by one, and not simultaneously. After winding, we connect the core in the same way as in the previous transformer.

The current transformer is similar to the above. The number of coils here is arbitrary; in principle, the number of windings of the secondary winding is sufficient:

n = 4 / Qr,

• where n is the number of windings of the secondary winding,
• Qr is the cross-sectional area of ​​the core circumference, given in cm2.

But since the currents here are very small, it is always better to use a larger number of turns. On the other hand, it is more important to maintain the appropriate ratio of the number of turns of both windings. If you decide to change this ratio, you will have to adjust the value of resistor R9.

Here is the formula for calculating R9 depending on the number of turns:

R9 = (0.9Ω * n2) / n1,

• where n2 is the number of windings of the secondary winding,
• n1 is the number of windings of the primary winding.

With the change in R9, it is also necessary to change C7 accordingly. The current transformer is easier to wind on a toroidal core, we recommend TN-13 or TN-16. However, you can make a transformer with an Sh-core. If you wind a transformer on a toroidal core, first wind the secondary winding with a large number of turns. Then insulating tape and, finally, the primary winding with 0.8 mm thick wire.

Description of circuit elements

Almost all elements can be found in an ATX power supply. Diodes D26-D29 with a breakdown voltage of 400 V, but it is better to take a little higher, at least 600 V. The finished rectifier can be found in the ATX power supply. It is also advisable to use diode bridges for powering the controller at least 600 V. But they can be cheap and popular 1N4007 or similar.

The zener diode that limits the controller supply voltage must withstand 0.7 W of power, so its power rating must be 1 W or more.

Capacitors C18 and C19 can be used with a different capacitance, but not less than 220 µF. Capacitances of more than 470 uF should also not be used due to the excessively increased current when the inverter is connected to the network and the large size - they may simply not fit on the board. Capacitors C18 and C19 are also found in each ATX power supply.

Power transistors Q8 and Q9 are very popular IRF840, available in most electronic stores for 30 rubles. In principle, you can use other 500V MOSFETs, but this will involve changing resistors R12 and R13. When set to 75 ohms, the gate open/close time is about 1 µs. Alternatively, they can be replaced with either 68 - 82 ohms.

Buffers in front of the MOSFET inputs and control transformer I, using BD135 / 136 transistors. Any other transistors with a breakdown voltage above 40 V can be used here, such as BC639 / BC640 or 2SC945 / 2SA1015. The latter can be torn out from ATX power supplies, monitors, etc. A very important element of the inverter is capacitor C10. This should be a polypropylene capacitor adapted to high pulse currents. This capacitor is found in ATX power supplies. Unfortunately, it is sometimes the cause of power supply failure, so you need to check it carefully before soldering it into the circuit.

The diodes D22-D25 that rectify +/- 35V are used UF5408 connected in parallel, but a better solution would be to use BY500/600 single diodes which have a lower drop voltage and higher current rating. If possible, these diodes should be soldered on long wires - this will improve their cooling.

Chokes L3 and L4 are wound on toroidal powder cores from ATX power supplies - they are characterized by a predominant yellow and white color. Cores with a diameter of 23 mm, 15-20 turns on each of them, are sufficient. However, tests have shown that they are not needed - the inverter works without them, reaches its power, but the transistors, diodes and capacitor C10 become hotter due to pulse currents. Reactors L3 and L4 improve inverter efficiency and reduce failure rates.

The D14-D17 +/- 12V rectifiers have a big impact on the efficiency of this line. If this line will power a preamp, additional fans, an additional headphone amplifier, and for example a level meter, diodes should be used at least 1 A. However, if the +/- 12 V line will only power the preamp, which pulls up to 80 mA , you can even use 1N4148 here. Chokes L1 and L2 are practically not needed, but their presence improves the filtering of interference from the power supply. As a last resort, you can use 4.7 Ohm resistors instead.

Voltage limiters R22 and R23 can consist of a series of power resistors connected in series or in parallel to produce a single higher power resistor and corresponding resistance.

Starting and setting up the inverter

After etching the boards, begin assembling the elements, starting from the smallest to the largest. It is necessary to solder all components except inductor L5. After completing assembly and checking the board, set the PR1 potentiometer to the leftmost position and connect the mains voltage to the 220 V INPUT connector. There should be a voltage of 18 V across the capacitor C1. If the voltage stops at approximately 14 V, this indicates a problem with the control of the transformer or power transistors, that is, a short circuit in the control circuit. Oscilloscope owners can check the voltage at the transistor gates. If the controller is working correctly, check that the MOSFET is switched correctly.

After turning on the 12 V power and the controller power supply, +/- 2 V should appear on the +/- 35 V line. This means that the transistors are controlled properly, one at a time. If the light on the 12V power supply was turned on and there was no voltage at the output, this would mean that both power transistors were opening at the same time. In this case, the control transformer must be disconnected, and the wires of one of the secondary windings of the transformer must be changed. Next, solder the transformer back and try again with a 12 V power supply and a lamp.
If the test is successful and we get +/- 2 V at the output, you can turn off the lamp power supply and solder inductor L5. From this moment on, the inverter must operate from a 220 V network through a 60 W lamp. After connecting to the network, the light should blink briefly and immediately turn off completely. +/- 35 and +/- 12 V should appear at the output (or other voltage depending on the transformer speed ratio).

Load them with a small amount of power (for example, from an electronic load) for testing and the light at the input will start to glow a little. After this test, you need to switch the inverter directly to the network, and connect a load with a resistance of about 20 Ohms to the +/- 35 V line to check the power. PR1 should be adjusted so that the inverter does not turn off after charging the heater. When the inverter starts to heat up, you can check the voltage drop on the +/- 35V line and calculate the power output. A 5-10 minute test is sufficient to check the power output of the inverter. During this time, all components of the inverter will be able to heat up to their rated temperature. It is worth measuring the temperature of the MOSFET heatsink, it should not exceed 60C at an ambient temperature of 25C. Finally, you need to load the inverter with an amplifier and set the PR1 potentiometer as far to the left as possible, but so that the inverter does not turn off.

The inverter can be adapted to any power needs of various UMZCHs. When designing the plate, we tried to make it as universal as possible for mounting various types of elements. The location of the transformer and capacitors makes it possible to mount a fairly large heatsink for MOS transistors along the entire length of the board. After proper bending of the leads of the diode bridges, they can be installed in a metal case. Increasing the heat dissipation allows the converter power to be theoretically increased to 400 W. Then you need to use a transformer on the ETD39. This change requires 470uF capacitors C18 and C19, 1.5-2.2uF capacitors C10 and the use of 8 BY500 diodes.

This section offers some options for implementing PP power supplies for amplifiers. A power supply circuit with separation of a bank of capacitors by resistors with a resistance in the range of 0.15-0.47 Ohms was proposed by L. Zuev:

Layout of the ULF power supply board by Vladimir Lepekhin in lay format

For ULF Natalie, boards were laid out for electrolytic capacitors with a landing diameter of d=30, 35 and 40 mm with snap-in terminals

Circuit with stabilized power supply for UN-a and operational amplifier on m/s M5230L

For the project, an ASR amplifier on a MOSFET with a current OOOS from Maxim_A (Andrey Konstantinovich), V. Lepekhin laid out boards for a low-power power supply unit for the amplifier and a powerful power supply unit for the output stage.

PSU board low-power top

PSU board low-power bottom

ULF top power supply board

ULF power supply board bottom

For the implementation of dual mono, power supplies will be used on the following PCBs:

BP ULF V2012EA

This power supply is used to power the VC (output stage). The board can be used to install electrolytes with Snap-in mounts with a diameter of up to 30 mm; mounting for diodes in TO220-3 and TO220-2 packages is provided, which expands the range of diodes used. PP dimensions 66 x 88 mm.

To power the UN with separate power supply, the following power supply board will be used:

BP ULF V2012EA

PP dimensions 66 x 52 mm. The diodes have a universal fit; they can also be installed in the TO220-2 housing; they fit electrolytes with a diameter of up to 25 mm.

Many people know how much I like to deal with different power supplies. This time I have a somewhat unusual power supply on my desk, at least I haven’t tested one yet. And by and large, I’ve never seen reviews of power supplies of this type before, although the thing is interesting in its own way and I’ve made similar power supplies myself before.
I decided to order it out of pure curiosity, I decided that it might be useful. However, more details in the review.

In general, it’s probably worth starting with a short lyrical introduction. Many years ago I was quite keen on audio equipment, I went through both completely homemade versions and “hybrids”, which used PAs with a power of up to 100 Watts from the Young Technician store, and half-assembled Radio equipment UKU 010, 101 and Odyssey 010, then there was Phoenix 200U 010S .
I even tried to assemble Sukhov’s UMZCH, but something didn’t work out then, I don’t even remember what exactly.

The acoustics were also different, both homemade and ready-made, for example Romantika 50ac-105, Cleaver 150ac-009.

But most of all I remember Amfiton 25AC 027, although they were slightly modified. Along with minor changes in the circuit and design, I replaced the original 50 GDN speakers with 75 GDN ones.
This and the previous photos are not mine, since my equipment was sold a long time ago, and then I switched to Sven IHOO 5.1, and then generally began to listen only to small computer speakers. Yes, this is such a regression.

But then thoughts began to wander in my head, to do something, for example, a power amplifier, perhaps just like that, perhaps to do everything differently. But in the end I decided to order a power supply. Of course, I can do it myself, moreover, in one of the reviews I not only did this, but also posted detailed instructions, but I’ll come back to this later, but for now I’ll move on to the review.

I'll start with a list of declared technical characteristics:
Supply voltage - 200-240 Volts
Output power - 500 Watt
Output voltages:
Basic - ±35 Volts
Auxiliary 1 - ± 15 Volts 1 Ampere
Auxiliary 2 - 12 Volt 0.5 Ampere, galvanically isolated from the rest.
Dimensions - 133 x 100 x 42 mm

The channels ± 15 and 12 Volts are stabilized, the main voltage ± 35 Volts is not stabilized. Here I will probably express my opinion.
I am often asked which power supply to buy for one or another amplifier. To which I usually answer - it’s easier to assemble it yourself based on the well-known IR2153 drivers and their analogues. The first question that follows after this is that they don’t have voltage stabilization.
Yes, personally, in my opinion, stabilizing the supply voltage of the UMZCH is not only unnecessary, but sometimes even harmful. The fact is that a stabilized power supply usually makes more noise at HF ​​and, in addition, there may be problems with the stabilization circuits, because the power amplifier does not consume energy evenly, but in bursts. We listen to music, not just one frequency.
A power supply without stabilization usually has a slightly higher efficiency, since the transformer always operates in optimal mode, has no feedback and is therefore more similar to a regular transformer, but with lower active resistance of the windings.

Here we actually have an example of a power supply for power amplifiers.

The packaging is soft, but wrapped in such a way that it is unlikely to be damaged during delivery, although the confrontation between the post office and sellers will probably be eternal.

Externally it looks beautiful, you can’t really complain.

The size is relatively compact, especially when compared with a conventional transformer of the same power.

More clear sizes are available on the product page in the store.

1. There is a connector installed at the input of the power supply, which turned out to be quite convenient.
2. There is a fuse and a full-fledged input filter. But they forgot about the thermistor, which protects both the network and the diode bridge with capacitors from current surges, this is bad. Also in the area of ​​the input filter there are contact pads that must be closed to transfer the power supply to a voltage of 110-115 Volts. Before turning on for the first time, it is better to check whether the sites are closed if your network is 220-230.
3. Diode bridge KBU810, everything would be fine, but it does not have a radiator, and at 500 W it is already desirable.
4. The input filter capacitors have a declared capacitance of 470 µF, but the actual capacitance is about 460 µF. Since they are connected in series, the total input filter capacitance is 230 µF, not enough for an output power of 500 watts. By the way, the board requires the installation of one capacitor. But in any case, I would not recommend raising the container without installing a thermistor. Moreover, to the right of the fuse there is even a place for a thermistor, you just need to solder it and cut the track under it.

The inverter uses IRF740 transistors, although they are far from new transistors, but I have also used them widely in similar applications before. Alternatively, IRF830.
The transistors are installed on separate radiators; this was done partly for a reason. The radiators are connected to the transistor body, not only at the mounting location of the transistor itself, but also the mounting pins of the radiator are connected on the board itself. In my opinion, this is a bad decision, since there will be excess radiation into the air at the conversion frequency; at least I would disconnect the lower transistor of the inverter (in the photo it is the farthest one) from the radiator, and the radiator from the circuit.

An unknown module controls the transistors, but judging by the presence of a power resistor, and just my experience, I think that I won’t be much mistaken if I say that there is a banal IR2153 inside. However, why to make such a module remains a mystery to me.

The inverter is assembled using a half-bridge circuit, but the middle point is not the connection point of filtering electrolytic capacitors, but two film capacitors with a capacity of 1 μF (in the photo, two parallel to the transformer), and the primary winding is connected through a third capacitor, also with a capacity of 1 μF (in the photo, perpendicular to the transformer) .
The solution is well-known and convenient in its own way, since it makes it very easy not only to increase the capacity of the input filter capacitor, but also to use one at 400 Volts, which can be useful when upgrading.

The size of the transformer is very modest for the declared power of 500 watts. Of course, I will still test it under load, but I can already say that in my opinion its real long-term power is more than 300-350 watts.

On the store page, in the list of key features, it was indicated -

3. Transformers 0.1 mm * 100 multi-strand oxygen-free enameled wire, heat is very low, efficiency is more than 90%.

They didn’t forget about the capacitor connecting the “hot” and “cold” sides of the power supply, and installed it of the correct (Y1) type.

The output rectifier of the main channels uses diode assemblies MUR1620CTR and MUR1620CT (16 Amperes 200 Volts), and the manufacturer did not collectively farm “hybrid” options, but supplied, as expected, two complementary assemblies, one with a common cathode, and the other with a common anode. Both assemblies are mounted on separate heatsinks and, just like in the case of transistors, they are not isolated from the components. But in this case, the problem can only be in terms of electrical safety, although if the case is closed, then there is nothing wrong with that.
The output filter uses a pair of 1000 µF x 50 Volt capacitors, which in my opinion is not enough.

In addition, to reduce ripple, a choke is installed between the capacitors, and the capacitors after it are additionally shunted with 100 nF ceramic.
In general, on the product page it was written -

1. All high-frequency low-impedance electrolytic capacitors specifications, low ripple.

There are no discharge resistors parallel to the capacitors, although there is space on the board for them, so “surprises” may await you, since the charge lasts quite a long time.

Additional power channels are connected to their own windings of the transformer, and the 12 Volt channel is galvanically isolated from the rest.
Each channel has independent voltage stabilization, chokes to reduce interference, and ceramic output capacitors. But you probably noticed that there are five diodes in the rectifier. The 12 Volt channel is powered by a half-wave rectifier.

At the output, as well as at the input, there are terminal blocks, and they are of very good quality and design.

On the product page there is a photo at the top where you can see everything at once. It was only later that I noticed that in all the photos in the store there were mounting stands; mine did not have them :(

The printed circuit board is double-sided, the quality is very high, fiberglass is used, and not the usual getinax. A protective slot is made in one of the bottlenecks.
A pair of resistors were also found at the bottom, I assume that this is a primitive overload protection circuit, which is sometimes added to drivers on IR2153. But to be honest, I wouldn't count on it.

Also at the bottom of the printed circuit board there are output markings and output voltage options for which these boards are manufactured. Two things intrigued me a little - two identical ± 70 Volt options and a custom option.

Before moving on to the tests, I’ll tell you a little about my version of such a power supply.
About three and a half years ago I posted an regulated power supply unit, which used a power supply assembled in approximately the same way.

When assembled it also looked pretty similar, sorry for the poor quality of the photo.

If we remove from my version everything “unnecessary”, for example, a unit for adjusting fan speed depending on temperature, as well as a more powerful transistor driver and an additional power supply circuit from the inverter output, then we will get the circuit of the reviewed power supply.
In essence, this is the same power supply, only there are more output voltages. In general, the circuit design of this power supply is quite simple, only a banal self-oscillator is simpler.

In addition, the reviewed power supply is equipped with a primitive output power limiting circuit; I suspect that it is implemented as shown in the selected section of the circuit.

But let’s see what this circuit and its implementation in the reviewed power supply are capable of.
It should be noted here that since there is no stabilization of the main voltage, it directly depends on the voltage in the network.
With an input voltage of 223 Volts, the output is 35.2 in idle mode. The consumption is 3.3 watts.

In this case, there is noticeable heating of the transistor driver power resistor. Its nominal value is 150 kOhm, which at 300 Volts gives a power dissipation of about 0.6 Watts. This resistor heats up regardless of the load on the power supply.
A slight heating of the transformer is also noticeable; the photo was taken approximately 15 minutes after switching on.

For the load test, a structure was assembled consisting of two electronic loads, an oscilloscope and a multimeter.
The multimeter measured one power channel, the second channel was controlled by a voltmeter of the electronic load, which was connected with short wires.

I won’t bore the reader with a large list of tests, so I’ll go straight to the oscillograms.
1, 2. Different output points of the power supply to the diode assemblies, and with different sweep times. The inverter operating frequency is 70 kHz.
3, 4. Ripple before and after the 12 Volt channel choke. After Krenka, everything is generally smooth, but there is a problem, the voltage at this point is only about 14.5 Volts without load on the main channels and 13.6-13.8 with load, which is not enough for a 12 Volt stabilizer.

The load tests went like this:
First, I loaded one channel by 50%, then the second by 50%, then the load of the first was raised to 100%, and then the second. The result was four load modes - 25-50-75-100%.
First, the RF output, in my opinion, is very good, the ripple is minimal, and when installing an additional choke, it can be reduced to almost zero.

But at a frequency of 100 Hz everything is quite sad, the input capacitance is too small, too small.
The total ripple swing at 500 watts of output power is about 4 volts.

Load tests. Since the voltage sagged under load, I gradually increased the load current so that the output power roughly corresponded to the range 125-250-375-500 Watts.
1. First channel - 0 Watt, 42.4 Volts, second channel - 126 Watts, 33.75 Volts
2. The first channel - 125.6 Watts, 32.21 Volts, the second channel - 130 Watts, 32.32 Volts.
3. The first channel - 247.8 Watts, 29.86 Volts, the second channel - 127 Watts, 30.64 Volts.
4. The first channel is 236 Watts, 29.44 Volts, the second channel is 240 Watts, 29.58 Volts.

You probably noticed that in the first test the voltage of the unloaded channel is more than 40 Volts. This is due to voltage surges, and since there is no load at all, the voltage gradually rose, even a small load returned the voltage to normal.

At the same time, consumption was measured, but since there is a relatively large error in measuring output power, I will also give the calculated efficiency values ​​approximately.
1. 25% load, efficiency 89.3%
2. 50% load, efficiency 91.6%
3. 75% load, efficiency 90%
4. 476 Watt, about 95% load, efficiency 88%
5, 6. Just out of curiosity, I measured the power factor at 50 and 100% power.

In general, the results are approximately similar to the stated 90%

Tests showed pretty good performance of the power supply and everything would have been great if not for the usual “fly in the ointment” in the form of heating. At the very beginning, I estimated the power of the power supply at approximately 300-350 watts.
During the usual test with gradual warming up and intervals of 20 minutes, I found out that at a power of 250 watts the power supply behaves just fine, heating the components approximately as follows:
Diode bridge - 71
Transistors - 66
Transformer (magnetic core) - 72
Output diodes - 75

But when I raised the power to 75% (375 Watt), then after 10 minutes the picture was completely different
Diode bridge - 87
Transistors - 100
Transformer (magnetic core) - 78
Output diodes - 102 (more loaded channel)

Having tried to figure out the problem, I found out that the transformer windings were severely overheating, as a result of which the magnetic circuit warmed up, its saturation induction decreased and it began to enter saturation, as a result, the heating of the transistors sharply increased (later I recorded the temperature up to 108 degrees), then I stopped test. At the same time, “cold” tests with a power of 500 watts passed normally.

Below are a couple of thermal photos, the first at 25% load power, the second at 75%, respectively, after half an hour (20+10 minutes). The temperature of the windings reached 146 degrees and there was a noticeable smell of overheated varnish.

In general, I will now summarize some results, some of which are disappointing.
The overall workmanship is very good, but there are some design nuances, such as installing transistors without insulation from the heatsinks. Pleased with the large number of output voltages, for example 35 Volts to power the power amplifier, 15 for the pre-amplifier and independent 12 Volts for all kinds of service devices.

There are circuit defects, for example, the absence of a thermistor at the input and the low capacitance of the input capacitors.
In the specifications it was stated that additional 15 Volt channels can produce a current of up to 1 Ampere, in reality I would not expect more than 0.5 Ampere without additional cooling of the stabilizers. The 12 Volt channel most likely will not produce more than 200-300 mA at all.

But all these problems are either not critical or can be easily solved. The most difficult problem is heating. The power supply can supply up to 250-300 Watts for a long time, 500 Watts only for a relatively short time, or you will have to add active cooling.

Along the way, I had a small question for the respected public. There are thoughts about making your own amplifier, according to the reviews. But which one would be more interesting, a power amplifier, a preliminary amplifier, if a PA, then at what power, etc. Personally, I don’t really need it, but I’m in the mood to dig deeper. The reviewed power supply has little to do with this :)

That's all for me, I hope that the information was useful and, as usual, I look forward to questions in the comments.

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