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SMPS 2 x 50V 350W Circuit for Audio Power Amplifiers

SMPS 2 x 50V 350W Circuit for Audio Power Amplifiers

This article will illustrate a simple procedure to devise an unregulated 50V switching SMPS symmetric power supply of 350W. This unit can be substituted with the standard audio amplifier power supply to reduce expense and also the weight. The proposed power supply works as a half-bridge with no regulation.

Written and Submitted by: Dhrubajyoti Biswas

Mosfets as Power Devices

My power supply relies on two N MOSFET and run by IR2153 integrated circuit. The IR2153 is powered by a power resistor of 27K 6W. The ripple at full load is recorded below 2V.

The use of Zener diode (15V) ensures voltage stabilization and the operating frequency is set to 50 kHz (approx.).

At the point of the input, I have placed a thermistor to force a check on the peak current when the capacitor is getting charged.

This same phenomenon can be found in AT/ATX power supply unit of a computer. Moreover, to ensure low leakage inductance and full voltage output, the first half of the primary is wounded in 20 turns followed by the secondary wound.

Also to assure safety in the system, do be sure to connect the output (center tap 0V) to the earth.

Chokes for Filtering RF

The chokes used in the design will facilitate removal of RF output ripple. The number of turns and the core which is found in PC supply is not a critical factor.

Additionally, the 6k8 resistors at the output section is used to discharge capacitors after it is switched off and this way it helps to prevent the voltage increase during no load.

The proposed Switched power supply 2x 50V 350W operates in single switch forward topology. It has an operating frequency of 80-90 kHz and has IRF2153 control circuit which is very much similar to that of US3842. However, the duty cycle is lesser and is limited to 50%.

Rewinding an ATX Trafo

The Tr1 transformer was devised by rewinding the SMPS ATX transformer and its primary inductance is 6.4 mH (approx.).

The core of the system has no air gap and the primary inductance is further broken in two parts: The first half is the wind and the second is the winding.

Moreover, it is also feasible to deploy the original primary bottom half without rewinding. This type of power supply aptly suits for power amplifier applications.

If required it may be also safeguarded against overload or short circuit and the voltage of the output could be stabilized. The Feedback of the system may be enabled through the help of optocoupler.

It is important to note that in regard to 350W power, care should be taken that in the conductive state the typical resistance should not cross more than 0.8R. MOSFET can also be used to lower the point of resistance.

Interestingly, the smaller the resistance better is with the system.

The voltage tolerance is in the range of 900-1000V. In the worst case scenario 800V can be used. Considering this, the best MOSFET I found was SPP17N80C3 or 900V IGBTs.

Circuit Diagram

Coil Winding Details:

The main transformer which can be seen integrated with the mosfets may be wound on a standard 90 by 140mm^2 ferrite bobbin core assembly.

The primary side winding consists of  40 turns of 0.6mm super enameled copper wire.

Remember to stop after 20 turns, put an insulation layer with an insulation tape and wind the secondary winding, once the secondary is wound, insulate it again and continue with the remaining 20 turns over it.

Meaning the secondary winding gets sandwiched between the primary 20 + 20 turns.

The center tap of this 20+20 may be connected with the body of the SMPS for an improved stabilization and cleaner outputs in terms of ripples or buzzing interferences.

The secondary consists of a center tapped 14 x 2nos turns made by winding 0.6mm super enameled copper wire.

The input and output filter coils may be wound on ferrite torroidal cores. The paired winding must be wound on the same individual torroidal cores using 0.6mm super enameled copper wire with 25 turns on each arm of the relevant supply terminals.


The above design 350 watt SMPS circuit was further improved by one of the dedicated members of this website Mr. Ike Mhlanga. The complete schematic of the same can be witnessed in the following figure:


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

100 thoughts on “SMPS 2 x 50V 350W Circuit for Audio Power Amplifiers”

  1. Dear Swagatam,
    I couldn’t find IRF2153, BY 400. What can use for those? can 4N25 be used instead of CNY17?

    • Dear Hemantha, you can use any similar half bridge driver IC, you can search the term in Google “half bridge driver IC” you may find many alternative.

      yes 4N25 is fine!

  2. Dear Swagatam,
    Many thanks for your article.
    How to change it for 30V-0-30V and 24V-0-24V?
    Does the secondary of transformer wind 14turns, tap and 14turns?
    Please help.

  3. Pak saya pengen blajar bagaimana merancang sirkuit elektronika,bagaimana menentukan nilai2 sebuah komponennya,selama ini hanya merakit kit separuh jadi.rasanya kurang puas kalau meniru rangkaian yg sudah jadi,kemana saya bsa belajar pak,mohon informasinya pak

    • Hi Zair, I appreciate your interest, however I have not yet created a tutorials for this, I may do it someday soon. Actually learning electronics is a dedicated long and slow process. You will have to first learn how small circuits work, like circuits using a single transistor or a few transistors, and then learn how logic ICs work, and then how special ICs like 4017, 4060, 4049, 4047 work. Once you start grasping their working then slowly you can combine them to create new customized circuits and in this way learn how to design your own circuits.

      You can comment on desired pages I’ll try to solve your specific queries.

    • Google cho “trình điều khiển IC nửa cầu với bộ dao động”, bạn sẽ có thể tìm thấy nhiều sản phẩm thay thế

  4. sir–smps modification for +-22 v dc 350 w—-primary—turns –no of wires–gauge

    secondary—turns –no of wires–gauge

    also toroid coil specs

    —-thank you

  5. Morning Sir. Really educative post. I would love you to write an article on SMPS, clearly differentiating the topologies Half bridge and Push pull, including their switching waveforms. These two have got me puzzled for a while, before I finally figured it. Also, clearly differentiate between a regular synchronous buck converter and the half bridge, in terms of their switching waveform.
    Finally, could you also explain more about the feedback for this system, since w know the chip has no provision for feedback. What is the rationale behind using the shut down pin to achieve a regulated output?
    Thanks a million for your answers, I read you blog daily, and its been most educating.

    • Thank you Mho, I had thought of presenting one such article by referring to the details from the following document


      But I felt it lengthy and stopped the work due to lack of time, but in future I may consider introducing it in my website.

      the shut down pin can be used for disabling the output as soon as an over-voltage is detected at the output, this situation will try to shut down the output which will cause an instant drop in the output voltage, which in turn will switch ON the circuit, and this cycle will keep repeating rapidly forcing the output to remain within the predetermined limits…

  6. Swagatam ! Does it require modification in circuit too, if i don’t want to use center tap in secondary? Because, I don’t need dual output as my purpose is to get high current for welding. I’ll be increasing MOSFET’s and using thicker wires (maybe parallel twisted etc).
    Second thing as i understood from the description you wrote. On primary side as there are 40T so i need to wind 20T create insulation then wind secondary turns and create insulation then finally wind back remaining 20T for priminary. Which means overall i need to keep secondary between the winding of primary.

    • Hi Edeson, You can use the same circuit which is explained in the above article, and only modify the winding with higher current wires…the winding method will be also the same, the wires could be upgraded by using bifilar system where many thinner wires are used together to make the winding capable of handling more power.
      and yes the secondary center tap can be removed and modified into a single winding

      however please note that whatever I am saying it is with an assumption, so please proceed with the necessary cautions.

  7. Hai sir , I follow your site regularly its very good . i want to design 3amps/65v output smps . Its very urgent please help me .

    • Thanks for your replay i need only +50v not -50v .what changes should i do . need to change transformer windings or anything
      .pls explain me

      • if you remove the center tap then the negative voltage side will go…..the secondary winding turns can be decreased to get a lower value at the output

  8. Dear Swagatam!

    You wrote that the center tap of the primary coil should be tied to the body. Directly or through a series capacitor? The wiring diagram is not marked. I have not seen such a solution yet in other circuits, and it is strange to me that the high-voltage coil is directly connected to the body, which, in any case, acts as a protective ground. Is not the secondary side’s gnd bound to the body? I’m confused!
    The value of the potentiometer in the second drawing is not indicated. How much is its resistance? The two mosfets can be IRF840?

    Thank You for Your help!

    • Dear Zollee, the article was written by another author, and may be the secondary ws referred to as the primary, because the primary does not have any center tap.

      the secondary is completely isolated from the primary therefore the center tap can be connected with the body to increase stability and reduce noise.

      the value of the pot can be selected with the some trial and error or by referring to other similar SMPS designs.

  9. Dear Swagatam,

    Very nice circuits. Is the circuits already been tested?
    Can i use the Ei33 core? do i need to used gapped or ungapped core.?
    And what is the size of the wire? can i use a litz wire here?
    Thanks to your blog is very helpful to our newbie..


    • Thanks odie,

      yes it is a fully tested circuit, the size of the wire is given in the article under the winding details, it is 0.6mm for both the sides, the wire should be a super enameled copper wire. yes you can use a EI33 core just make sure the winding perfectly accommodates within the bobbin….the core surfaces in contact with each other must be separated with a paper gap.

  10. DearSwagatam,

    hank you for the pearls of wisdom. I have seen another scheme which has a BC457 transistor tied to pin 3. It however is not simple. I will mess around with what you have suggested. I would however like to send you ms Eagle schematic for corrections. How do I do that??

  11. Dear Swagatam,

    Thank you for the feed back. I will try to implement using feedback via optocoupler. Its a more elegant way of implementing the control and self adjust to demand.

    I have researched the net esp on edaboard.com and it seems the IR 2153 has no pin for voltage regulation but one for shut down ie pin 3. Could you suggesta schematic for implementing voltage control Mr Swagatam?? Thanx in advance for the help.



  13. Hello Swagatam,

    My name is Prince Jose… This is a nice diagram. I want +/-90v 8A, how i can make it with you diagram, and also can i change the winding wire thickness…..

    • Thank you Prince,

      you can certainly achieve it by tweaking the secondary winding of the transformer….the current can be increased by using more number of parallel wires across both sides

  14. Hello Swagatam,

    I'm new here and I'm not sure if you have already posted the circuit that I'm looking for. I need a power supply/inverter/smps with 12VDC input (from car battery) with an output of +50VDC & -50VDC at least 10ampere current capacity or more. Much better if the circuit is configured in SMPS.
    Thank you and more power to you….

    • Hi Roberto, you can try the above explained concept with some modifications.

      Instead of the mains you can apply 12V to the left hand side circuit…and you will need to modify the primary/secondary winding of the transformer.

      For the primary side you could try around 5 turns and for the secondary 20 + 20 turns

      the turn ratio might require further analysis and modifications, since it's not calculated by me precisely

  15. Hi!
    I thought of doing so circuit (with these components):
      the first capacitors 0.470uF (400V) with 0.100uF (400V)
      1000uF capacitors (200V) with 470uF (200V)
      The 2.2uF capacitor (400V) with 0.5 uF (400V)
    Potrebe work?
    To me I need a single output of 50V 3-4A and no more than 200W.
    You can do with these changes?

  16. Hi!
    I have a question about the two capacitors of 1000uF (200V). Can I use two 470uF (200V) instead of two 1000uF (200V)?

  17. Dear Swagatam, I would like to build a regulated smps for my audio amplifier which will be capable of around 400 watts, and having a voltage of 50-0-50. If possible using the TL494 or similar device. I have quite a few ATX power supplies at hand and can salvage parts from them.
    Thanks in advance

    • Hi Nitin, a torroidal core will work, but might require an entirely different winding data which I am not sure how to calculate….you can try it and find the most optimal results with some experimentation.

  18. Hi Swagatam…
    In my Country, IR2153 IC is still rare. Because IR2153 IC is for a PWM Generator, can i change the IC to LM555 or CD4047?

    • Hi Naufan,

      LM555 or CD4047 will not work, because these are not equipped with high-side drivers…..these are just ordinary oscillators, while IR2153 is a specialized half-bridge driver IC…

  19. Thanks for this sir, though i saw it several days ago;the reason why i did't consider it much is all about the IC, i think i will a serious problem to find it in my local shop here in Tanzania, is there any other way around without involving ic?
    Thanks though sir, thanks

    • Raymonds, unfortunately there's no easy alternative to the above IC because it's a specialized half bridge driver IC…and does not depend on a center tap trafo, rather uses a two wire trafo for an efficient performance.

  20. please boss i need your help now, i want you show me how to build power inverter, if you teach i will be happy for you?

  21. Sir,
    What will be effect on system ( Panasonic amplifier 7.1) if we give 50hz instead of 60 hz. Power supply is smps based.

    2. The source of mosfet be given 110volt .but how can I get 110 volts .
    Please help me

    • Hi Style,

      frequency change will not make any difference to an SMPs, for getting 110v you can eliminate the center tap of the above circuit and acquire the required 110 V from it.

  22. Sir I have one system which is operational on 110volt 60 hz.. What can I do to make its operational,as we have 220V 50hz.. Help me sir

  23. What if I use a ferrite EDT49, whether the number of turns on the primary and secondary side as you say?
    And if the switching frequency is 90kHz, if there is a change in the circuit or component changes?

    • you can use any EE core as long as it accommodates the winding comfortably it'll be fine.
      you'll have tweak and adjust the 47k/300pf values for getting the desired frequency with some trial and error.

  24. Dear Sir
    For making PCB what specification i have to tell to shop . i want to make 1000 watt stereo
    I want good quality COPPER BOARD

  25. Dear sir
    What is the primary frequency because one place its mentioned 50khz and in another place 80- 90 kHz
    Second thing what is the primary current to the transformer
    Thanks and Regards

    • Dear style, it doesn't make much of a difference whether it's 50 khz or 80 khz, for precise answers you can calculate it yourself by referring to the IC datasheet and by inserting the 47k and 300pF in the given formula

  26. Dear sir ,
    Sir I want power supply 50-0-50. /12 amps. Wat would be the gauge of secondary coil and number of turn
    Thanks and regards

  27. Thanks a lot sir..
    You have any topic related to transformer making . I mean to say like calculation of E and I core calculations, bobbins size calculation, what size of gauge wire to be use. So that I can make a different voltage and wattage of transformers.
    Thanks and regards

    • style, presently I do not have all the info regarding ferrite transformer designing, once I collect it will surely update them in this blog…

  28. Sir,
    Above circuit can be use for audio Amplifier which u have given . in this article the difficult part is transformer. Is it possible for you give a separate topic on this with picture
    Thanks and regards

    • style, there's nothing difficult in it if you read and follow the instructions carefully, if you have problems you can always ask me for further help….

    • Dear Swagatam,
      I would like to sympathize with style for his difficulties in understanding the transformer winding details. Though the idea behind this article is very innovative and commendable, the narration is very sloppy and written in poor English with a lot of grammatical errors. I am not criticizing your post, but I suggest a more detailed proof reading of technical articles for a better presentation. For an experienced hand it is okay, but for a less initiated person or a novice, it can be very confusing. A few drawings or pictures would have made a lot of difference, as suggested by style.

      I congratulate you on the excellent articles you have written in your blog, keep it up.


    • Dear Chinmoy,

      yes the article is a rephrased version and may have a few errors since it was written by a person with only general electronic knowledge.

      the circuit actually has nothing complex in it.
      the IC is a half bridge IC which generates a push pull output for the connected mosfets, which in turn switch in a full-bridge manner due to the involved dual AC input configuration.

      this results in an efficient induction across the output winding

      if you can go through the datasheet of the IC, you'll be able to get a better picture of its functioning details

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