This 40V dual power supply circuit was designed in response to a request made by Michael from Philippines. His application is to power the 150 Watt amplifier circuit published here. I think this power supply design is adequate for the purpose. The transformer T1 steps down the mains voltage, bridge D1 performs the rectification, C1 and C2 does the job of filtering.C3 and C4 are decoupling capacitors.

Circuit diagram with Parts list.



  • The T1 must be a 230V primary, 30-0-30V secondary, 200VA transformer.
  • All capacitors must be rated at least 63V.
  • C3 and C4 are polyester capacitors.
  • If 8A bridge is not available, make one using diodes like P600A.


  1. Hi..I also have this transformer 8amp two 30v AC do I change its output voltage to 12 DCV??pls help..

  2. i want to make -30V t0 + 30V dual regulator power supply so plzz give me some circuit of it if u have…Regards

  3. is it posible to make -40V with out using negative regulator ic?

  4. Rajashree

    hi seetha raman i want to make a INPUT 16 to 60V AC/DC. OUTPUT +5V-5V, 20 mile AMP power supply of plz send me the circuit diagram to my Email address.

  5. hi seetharaman, so if I want to change this power supply to a variable one, potentiometers at the output are not enough ?

  6. For using this power supply to power two 150W amp modules slight modifications are required

    Transformer must be raised to 350 VA.
    Current rating of the bridge must be raised to 12 or 15 A.
    Fuses must be changed to 12A.

  7. u’re jst xcelent.u tak d pain 2find soln 2peopls prblems.u’re a ist clas engr and mentor. thanks and kep it up

  8. Seetharaman

    Hi Mounica you require a maximum current limitting of 30% of the rated battery capacity that is 30amps (for flat battery of less than 11volts terminal voltage)and normal charging current of 1/10 of the rating that is 10 amps at 12volt.

  9. Seetharaman

    Hi Mounica you can use 100AHbattery for operating the UPS but it is not rated to charge it, hence you have use an external charger.
    Hi Adnan When you bridge two identical amplifiers into the speaker of same impedance, then it will give 4 times the rated power. i will email you the details

  10. Hello seethraman i have APC ES-500 UPS it has 12v 7Ah battery
    can i use 12v 100Ah battery instead of 7Ah
    this 100Ah battery will spoil the ups?

  11. what changing will i have to do for increase or decrease the voltage?

  12. Seetharaman

    Hi Adnan my PC is through I will send you by wednesday positively.
    Regarding these power amplifiers they are not Class A type that is conuming constant current, but they are class B type hence as per volume their current requirement vary from few mA to few thousands of mA. hence the voltage will vary from 12 volt to almost the AC supply voltage which is likely to kill all the components hence you have to use a shunt regulator to take care for the full current capability.

  13. your PC is Ok now so kindly mail me the 60v dual supply modified circuit

  14. But Mr Seetharaman if i use 220uF capacitor instead of 120uf capacitor as you told me then according to your calculation it will have to give approximate 9A
    (0.47 X 9) / 0.02=211.5uf apprx 220uf????

  15. its mean i can use this power supply 12v @ 5A for TDA1554?

  16. what changing will i have to do for increase the voltage?

  17. Seetharaman

    Hi Adnan the max current can be 5 Amps at 12 volts. if you want to increase the output voltage the current will fall down. If you short the output the maximum current can be 5amps only.

  18. if use 220uf @ 400v instead of 12ouf what will be the output current @ 12volts?
    and if we want to increase the voltage what changing will required???

  19. Seetharaman

    Hi Adnan with 0.47uF you will get 20mA, for 5Amps you require (0.47 X 5) / 0.02 you require around 120uF 400 volt capacitor for continuous rating. check for the availability and price. this may be very expensive comparing to switched mode power supplies which are quite efficient and pretty small in size. 12 volt 5amp Halogen bulb power supplies are available for as low as INR150/- very small 2″ X 1″ X 1″ few grams in weight. efficiency >90%

  20. Seetharaman

    Hi Adnan my PC is back. I am just on the job by tuesday i will mail the revised circuit

  21. seetharaman

    Hi Adnan if by chance if the output is shorted or load takes higher current as per the capability of the trransformer then the rectifier will get destroyed. hence it is preferable to use higher rating bridge rectifier.

  22. if we have 4Amp transformer then we have to use more than 4Amp bridge like 6amp why we use high ampere rating bridge?and what will happened if we use low ampere bridge when transformer current is high??

  23. seetharaman

    Please wait my PC will be ready this sunday you will positively get it on tuesday.

  24. plz send the modifies circuit with thyristor and zener u’ve told me last week?

  25. if the transistor quantity is decreased it will better for me because i will easily afford it thankyou

  26. i asked today in the electronics market but the TIP122 & TIP127 is not available in the market

  27. seetharaman

    With 12 amp transformer your short circuit dissipation of the trasistors are 1200 watts 600 at + and 600 at -. That is you require around 20 transistors in parellel on heat sink.
    to reduce the number of transistors a thyristor to be added with suitable zener and transistor, you can make a very compact high current variable power pack. i will send the circuit by next week.

  28. if i want to use 50-0-50v @ 12amp transformer in that power supply you’ve mailed me then what changing will be made except of bridge rectifier or will the circuit remain same??????

  29. Thank you very much Mr seetha raman for the circuit you solve a big problem for me now after implementing this supply i will be able to power many of amplifier circuit and other circuit thanks again
    i understand all the working of this supply but tell me that why we use too much transistors?what happened if we decrease the quantity of transistor?n tell me if there any replacement exist to decrease the quantity of transistors?

  30. seetharaman

    Hi Adnan please bear with me for few more days my desk top is down i am using my mini for just emails no graphics possible.

  31. no no Mr seetharaman its ok i’ll wait for 3 or 4 days thankyou for all the help

  32. seetharaman

    Hi Adnan i will mail it to you in 3 to 4 days time sorry for the delay.

  33. seetharaman

    Use a 7812 3pin voltage regulator. add 1k resistance to the input of the regulator IC

  34. Hi seetharaman

    i want to reduce this 40v to 12v to connect to pre-amplifier

    how can we reduce tell me please

  35. plz send me the circuit diagram with the series pass transistor

  36. seetharaman

    Hi Adnan you can provide series pass transistors with its base being controlled by variable reference.

  37. can i make the above power supply into a variable power supply for both channel

  38. seetharaman

    Hi Adnan with higher capacity power supply(current) you can always draw lesser current. but not the other way round.

  39. i cant understand what do you mean by $1000 and $600

  40. seetharaman

    Hi Adnan you have US$1000 in your account hence you can draw easily US$600 from your account.
    You can draw 6 amps comfortably.

  41. seetharaman

    Hi Adnan why not for very low currents. for higher current add few series pass transistors.
    Any transformer you can use, out put will be root 2 times the AC input.

  42. if i connect two potentiometer in parallel at +40-0 and -40-0 will it become a variable power supply?

  43. if i use 35-0-35 @ 4amp transformer instead of 30-0-30 what will be the output?

  44. if i have a power supply of 30 volts 12 amp.Is this is possible to get 30 volts 6amperes from the 30volts 12amps power supply??

  45. p600A diodes can make a 8 amp bridge
    tell me the equivalent diodes for 6 amp bridge, 4 amp bridge and 2 amp bridge diodes name???

  46. p600 diodes can make a 8 amp bridge
    tell me the equivalent diodes for 6 amp bridge, 4 amp bridge and 2 amp bridge diodes name???

  47. seetharaman

    Hi ADnan the capacitor will get heated up and explode. For a 25 volt capacitor 20volt will be safe limit. in some capacitor they would have mentione the voltage at 85deg C. These capacitors can be used upto the rated voltage. if temp is not mentioned in a capacitor, it is to be taken as 25deg C and derate it and use it at one third the voltage indicated. since inside the equipment the ambient may raise to 75 deg C.

  48. if i give more than 25v to a 220uf 25 volts capacitor what will happen?what will the output or the capacitor will destroy??

  49. if i have a power supply of 30 volts 12 amp.Is this is possible to get 30 volts 6amperes from the 30volts 12amps power supply????

  50. if i need 220uf 50v capacitor but i have a capacitor of 220uf 400v can i use 220uf 400v capacitor instead of 220uf 50v???

  51. seetharaman

    By increasing the voltage of the capacitor will not have any effect on the output power.
    200va / 60volt is 3.333Amps.
    30-0-30volt transformer, both the 30 volt winding should be capable of giving >3amps current.

  52. 200va means how much amperes of transformer tell me?

  53. if we increase the capacitor voltage rating to 200v 4700uf what will be the effect on output voltage

  54. In order for this supply to be used for two 150W amps – left and right – would it be necessary to increase the VA of the transformer – if so – by how much? Cheers

  55. Jared Cook

    Would this be suitable for a stereo amp based on two of the 150W amplifiers or would two separate power supplies be required? Cheers

    • two seperate power supply will reduce noise, but it is very costly.
      Here a single power supply with double ratings is enough for stereo mode.