I need help with this mosfet amplifier

Hi,

i am simulating this circuit using M*I*C*R*O*C*A*P VII and i am not getting any results.

In my opinion it seems to work, but that's not what i am getting.

I have to build a simple power amplifier to output AC current to a capacitive load, so i decided to use mosfet as output amplifiers (operating in class B).

I believe that the OPAMP cancels the cross-over effect of the Vth (threshold voltage of the MOSFET).

The main problem is that the OPAMP (according to simulations) has a DC voltage at its output plus the AC voltage that i want to amplify and i think this effect is saturating the output waveform (similar effect to a saturated transistor when it is working as a amplifier)

Please help me to find where i go wrong. I also would appreciate any sugestions on possible circuits and books where i could lear about MOSFET.

I got this example circuit from:
https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/first11/part9/page1.html

Thanks very much.
mcoster

What sort of supply voltages are you using?

If you used BJTs you would have less crossover distortion.

Hi,

I am using 12V.

This circuit only ilustrates what i am intending to do... In reality i have a capacitive load. I want to simulate a ripple current across a capacitor.

Since in databooks most suppliers specify ripple currents for 100 KHz i decided to use MOSFETS to achieve that frequency, since it is hard to get 4A @ 100KHz whith BJT's.

thanks

It would help if you show a picture of the circuit in your simulator.

>I am using 12V.
The circuit you hae shown has three supplies +ve, 0V and -ve.

Hi,

Sorry for my lame post...

Here I provide detailed pictures of the circuit and simulation results.

I see that i have saturation becouse of OPAMP. Its supply rail is +12V /-12V so it is saturating at 10.5V.

The main problem is that i dont understant why a have a such high dc voltage on its output ? So i can see that the problem isn't the mosfets.

I would appreciate any suggestion, becouse i read on articles that if i remove the OPAMP feedback it would give crossover distortion.

Another problem i cant understand how to choose V10 and V11 correctly ?


Thanks in advance
mcoster

try using capacitor between R2 and ground to drop DC gain to 1

You made a mistake connecting M2. D and S pins should be interchanged.