100W MOSFET power amplifier

100W MOSFET power amplifier.

A 100W MOSFET power amplifier circuit based on IRFP240 and IRFP9240 MOSFETs is shown here. The amplifier operates from a +45/-45 V DC dual supply and can deliver 100 watt rms into an 8 ohm speaker and 160 watt rms into a 4 ohm speaker. This Hi-Fi amplifier circuit is suitable for a lot applications like general purpose amplifier, guitar amplifier, keyboard amplifier. The amplifier can be also used as a sub woofer amplifier but a subwoofer filter stage has to be added before the input stage. The amplifier has a low distortion of 0.1%, a damping factor greater than 200, input sensitivity of 1.2V and the bandwidth is from 4Hz to 4 KHz.

Circuit diagram.

mosfet power amplifier

100W mosfet power amplifier circuit

About the circuit.

Capacitor C8 is the input DC decoupling capacitor which blocks DC voltage if any from the input source. IF unblocked, this DC voltage will alter the bias setting s of the succeeding stages. Resistor R20 limits the input current to Q1 C7 bypasses any high frequency noise from the input. Transistor Q1 and Q2 forms the input differential pair and the constant current source circuit built around Q9 and Q10 sources 1mA. Preset R1 is used for adjusting the voltage at the output of the amplifier. Resistors R3 and R2 sets the gain of the amplifier. The second differential stage is formed by transistors Q3 and Q6 while transistors Q4 and Q5 forms a current mirror which makes the second differential pair to drain an identical current. This is done in order to improve linearity and gain. Power amplification stage based on Q7 and Q8 which operates in the class AB mode. Preset R8 can be used for adjusting the quiescent current of the amplifier. The network comprising of capacitor C3 and resistor R19 improves high frequency stability and prevents the chance of oscillation. F1 and F2 are safety fuses.

Circuit setup.

Set R1 at midpoint before powering up and then adjust it slowly in order to get a minimum voltage (less than 50mV0 at the output. Next step is setting up the quiescent current and keep the preset R8 in minimum resistance and connect a multimeter across points marked X & Y in the circuit diagram. Now adjust R8 so that the multimeter reads 16.5mV which corresponds to 50mA quiescent current.

Notes.

  • Assemble the circuit on a good quality PCB.
  • Use a +45/-45 V DC, 3A dual supply for powering the circuit.
  • Power supply voltage must not exceed +55/-55 V DC.
  • Before connecting the speaker, check the zero signal output voltage of the amplifier and in any case it should not be higher than 50mV. If it is higher than 50mV, check the circuit for any error. Replacing Q1, Q2 with another set could also solve the problem.
  • Fit Q7 and Q8 to a 2°C/W heat sink. Both Q7 and Q8 must be isolated from the heat sink using mica sheets. Heat sink mounting kits for almost all power transistors/ MOSFETs of almost all package styles are readily available in the market.
  • All resistors other than R10, R11 and R19 are 1/4 watt metal film resistors. R10 and R11 are 5W wire wound type while R19 is a 3W wire wound type.

Power supply for the 100W MOSFET power amplifier.

+45/-45 dual supply mosfet amplifier

+45 / -45 dual supply for the 100W mosfet power amplifier

A basic dual power supply is used for the amplifier circuit. If 6A ampere bridge is not available, then make one using four 6A6 diodes.C10 and C11 are high frequency bypass capacitors. Filter capacitors C8 and C9 must be at least 10000uF, higher the value lesser the ripple. Optional 3A fuses can be added to the +45 and -45 lines. Transformer T1 can be a 230V primary, 35-0-35 V secondary, 300VA step down transformer.

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70 Responses to “100W MOSFET power amplifier”

  • s vaja says:

    In the centre of Q4 & Q5 base to collector is that jumper ?

  • Midhunmp says:

    Thank you sir, god bless you

  • Midhunmp says:

    If i connect 25v 5amp ac and 10inch 4ohm subwoofer, what power will actually get when it use as a subwoofr amp? Please help me sir

    • Seetharaman says:

      You cannot use 25 volt transformer. you have to use 25 – 0 – 25 volt 5 Amp transformer with bridge rectifier and filter capacitors to get plus and minus 35 volt power supply for the amplifier. With this power supply and 4 ohms load (speaker) you will get 100 watts RMS output power.

  • Midhunmp says:

    If i connect 25v 5amp ac and 10inch 4ohm subwoofer, what power will actually get when it use as a subwoofr amp?

  • Midhunmp says:

    Can i use it as a subwoofr amp? What power will get when i connect 10inch 4ohm subwoofr? Please help me sir

  • Abubakar says:

    Can dis circuit wrk with bc557? Pls

    • Seetharaman says:

      Hi BC556 VCeo is 80 volt but 557 is only 50volts, hence it will be oprating at the brim and may get damaged, hence it is preferable to use BC556 only.

  • Abubakar says:

    Can I use 20pf in place of c4 n c5??

  • Chiliman says:

    Can i attach the mosfets from two circuits to a 1 C/W heatsink?

    • Seetharaman says:

      If you are using 2 similar amplifiers yes with proper insulating kits you can use provided the sink is sufficiently big to take care of the generated heat. If heat sink temperature is used for thermal compensation it cannot be used. It is a better practice to use separate heat sink for each different application.

  • stroex1 says:

    Is this corect?
    „Now adjust R8 so that the multimeter reads 16.5mV which corresponds to 50mA quiescent current.”
    16.5mV/0.33ohm=50mA or (R10 or R11)
    16.5mV/(0.33+0.33)ohm=25mA …? (R10+R11)
    Finaly the quiescent current MUST BE 50mA? Pls seed!

  • Chiliman says:

    If I power up six of these with the same power supply, what value should each rectifier diode have?

    • Seetharaman says:

      Hi Chiliman the bridge rectifier should be capable 25amps. The filter capacitor should be atleast 10 X 10000uF for both positive & negative supply. Instead I would like you to use separate filters and rectifier for each amplifier, you mount bridge rectifier and filter capacitors of the value shown in each circuit board. Use a single transformer may be torroid one capable of 20amps capacity

  • Togor Mathias says:

    Is good circuit have tested it and it works well the circuit is better for very high voltage

  • Chiliman says:

    Wich tracks carries the largest currents?

  • Hello,
    Please, could I add another 3 pairs of MOSFET at the output stage thereby making it a 400 watts??

  • Clinton Downer says:

    Hello,
    Please, could I add another 3 pairs of MOSFET at the output stage thereby making it a 400watts.

  • Hiflyer says:

    Hi, I have one question. Does output of this circuit is short circuit protected?

  • Rex says:

    Seetharam, we need Very High Power Amplifeir circuit, like 200W, 300W, 400W, 500W, 1000W, 2000W – 5000W

  • Rex says:

    Seetharaman, please post the 400W mosfet Amplifeir circuit here

  • msdava says:

    süpperrrr mosfet amp

  • jijesh says:

    not avail the transistor mje340/350. bd139/140 not suitable.

  • sarath says:

    hi,can u plz send me the full pcb layout design, inc P.S

    I’ve one doubt how to ctrl the vol of the amp?
    also in the electronic shop the transformer is rated in ‘A’ not in ‘va’
    ,is 300va=6.5A?

  • viswanathan says:

    Sir,

    Can you please provide the PCP layout..

    Thanks
    viswa

  • Theofrastos says:

    Hello!
    First of all i want to tell you that its a VERY LOUD amplifier even with dual 27V transformer,i will try it with 40v when i buy the new transformers, i have only one question, what kind of pot is the ideal to adjust the volume?
    I use a 100k pot but when i turn it off i stil have sound in my speakers, a 1M ohm pot would be good or even it will be small?
    Thank you very much!

    • Seetharaman says:

      Hi Theofrastos 100K logarithmic control that should take care for volume problem at lower settings, do not use Lin controls.

  • elaigwu robert says:

    sir,can i pls get the circuit theory analysis of the 100watt mosfet amplifier.my email:treborzonelife@gmail.com

  • elaigwu robert says:

    sir,can i pls get the circuit theory analysis of the 100watt mosfet amplifier.

  • Niklas says:

    Hello, both my transistor burned out in 2 secounds (Q8 and Q7), what can cause this problem? I have also changed the value of pot R8 to 5k (i could’t find any 3k pot multiturn from my store) but i dont think it have anything to do with the burn transistors ? Thanks for the help

    • Seetharaman says:

      Hi Niklas in the place of R8 put a link. Reduce the fuse rating to 500mA. If every thing is oK it should stay alright if the fuse blows indicates something wrong in the wiring. Please check and correct and proceed as above. If it is ok replace link with say 2k2 pot and set the current through the fuse for 50 to 60 mA.

  • Prakash says:

    Hi… plz, provide me the pcb layout. My mail ID: prakash_bytari@yahoo.co.in

  • abubakar bala says:

    sir i want to construct an inverter using eight IRFT250N four in opposite side. what size of transformer will be suitable for this construction. thanks

  • ifte says:

    whenever i connect the circuit, the resistor R7 burn out…
    i could not collect the mosfet IRFP240 & IRFP9240…instead i used two IRF9240 with proper biasing. please help…

  • Baz says:

    Hi, I’m a little confused here…. looking at setting R8 for 16.5mV across 2 x 0.33 ohms looks like 25mA to me? Am I missing something or should the measurement be across just 1 x 0.33 ohm OR 33mV across points X to Y? Thanks, Baz

  • Seetharaman says:

    Hi Ifte without feeding any input to the amplifier (say volume control fully closed no sound from speakers)connect a multimeter across points marked X & Y in the circuit diagram and adjust R8 so that the multimeter reads 16.5mV which corresponds to 50mA quiescent current.

  • ifte says:

    1. what is zero signal output voltage of the amplifier? and how can i measure it?

  • harry says:

    tell me anyone using this amplifier is this working?

  • harry says:

    thanx Seetharaman, but this is a 400W mosfet amplifier layout how can i use it for 100 W mosfet amplifier.

  • seetharaman says:

    Hi Harry can be used.
    Use the following link for your PCB layout
    http://hobbyelectronicsdri.blogspot.in/2011/06/400w-mosfet-amplifier-circuit-with.html

  • Ramdas says:

    Dear Sir…
    Can I get the PCB for the same or atleast PCB Layout…pls reply..

    Ramdas

  • harish says:

    plz give me a reply………

  • harry says:

    i have a 35-0-35 5Amp. transformer is this suitable for this amplifier

  • harry says:

    hi……..
    i build this amplifier but when i switch on the power supply the IRFP9240 heats up and gets burn. so what should i do. i want ur help guyz…….
    reply

  • tino says:

    Hi to all
    someone have the PCB layout for this amplifier?
    many thanks in advance

  • TAHINA says:

    I need 200watts(rms)amplifier circuit diagram

  • Leandro says:

    This escheme was not designed for this author. This amplifier work fine, but in the scheme displayed here, have some issues. The “pots” (R8 and R1 must be mult turn), the value of R17 is not a 47K. The R17 must set a current aprox of 1mA, so, we need a 330r to 470r. R*I=U, R=?, I=0,001A U=0.650v,(equal a VBE voltage). Do the calc, and see for yourself. Be carefully for use others MOSFET. The bandwidth is 3,6Hz to 39.4KHz. Don’t exceed 55V dc for each rail. All that you need is 40+40AC 225VA trafo for each channel@160Wrms/4ohms. Good Luck.

    Brazil.

  • Leandro says:

    T7 = IRFP240, 2SK1530, 2SJ162, BUZ900DP, BUZ901DP (take care for pin layout : GDS GSD)
    T8 = IRFP9240, 2SJ201, 2SK1058, BUZ905DP, BUZ906DP (take care for pin layout : GDS GSD)

  • Leandro says:

    This escheme was not designed for this author. This amplifier work fine, but in the scheme displayed here, have some issues. The “pots” (R8 and R1 must be mult turn), the value of R17 is not a 47K. The R17 must set a current aprox of 1mA, so, we need a 330r to 470r. R*I=U, R=?, I=0,001A U=0.650v,(equal a VBE voltage). Do the calc, and see for yourself. Be carefully for use others MOSFET. The bandwidth is 3,6Hz to 39.4KHz. Don’t exceed 55V dc for each rail. All that you need is 40+40AC 225VA trafo for each channel@160Wrms/4ohms. Good Luck.

  • seetharaman says:

    Hi Joel this amplifier’s bandwidth is 4Hz to 40KHz, which is quite fine for audio use. what is written is wrong a zero is missing in the upper limit.

  • saint saim says:

    @you can u go and check the parameter of irfp240 and see if there is any similarity at http://www.alltransistors.com

  • JOEL says:

    Bandwidth is too short how can i increase it i need at least 15KHz

  • seetharaman says:

    Hi Gamerandds most economical IRFP540 / 9540 pair also can be used. It can work with 4 ohms speaker delivering around 200watts. below this impedance it is risky to operate the amplifier it may blow the FETs.

  • Gamerandds says:

    WILL THIS RUN ON 2 OHMS STABLE?

  • Gamerandds says:

    Will the Irfp250 work instead of the 240 in this circuit?

  • seetharaman says:

    Hi Mike you can try is the standing current is not raising to required level with R8, you may have to raise R8 to 4.7k pot. otherwise it should work.

  • mike says:

    gud day, s it possible to use 35v instead of 45v for the power supply of this circuit?tnx

  • Gamer andds says:

    I will make a pbc for this circuit if u want it just ask, but has anyone considered using Irfp250 for this circuit instead? I dont wanna just buy 20 if them and they don’t work. ???

  • Gamer andds says:

    Selanco add another pair of mosfets with it’s own resistors, I’m planning on adding 4 more to get around 500 watts rms. Remember that in 4 ohms one pair can Play up to 160 watts!!

  • Moragroth42 says:

    Does bass preamp will work like a filter?

  • Moragroth42 says:

    Hi!
    Will this circuit work for a bass amp/combo? I think that it will do the job, but I want to be sure. Also has anyone saw or made/could make, a pcb project for this schematic?

    Cheers from Poland

  • selango says:

    dear sir,
    i need 200watts (rms) mosfet subwoofer amplifier circuit diagram.