invert a signal to mosfet

[gyula]

When the input (say) 10V pulse coming from a voltage source like a pulse generator is switched off, its amplitude at the MOSFET's gate electrode ought to go down also, to near zero voltage or even below zero with respect to the source electrode, so the voltage source inner resistance must be able to 'sink' the discharge current (the moment the pulse is off the gate-source capacitance is at 10V hence it acts as a static voltage generator).

There are dedicated MOSFET driver circuits which are designed to charge and discharge the gate-source capacitor via their output circuit (normally a P and N channel MOSFET or a PNP and NPN bipolar transistors) and these conduct current towards the gate-source path when the pulse is ON and receive (i.e sink) current from the gate-source path when the pulse is OFF. Unfortunately, the gate-source capacitance has also an equivalent series resistor like any physical capacitor has, this increases losses too.

Here is good read on this subject:
http://focus.ti.com/lit/ml/slup169/slup169.pdf

Here is another paper, calculating the the loss due to the charge-discharge process: http://ww1.microchip.com/downloads/e...tes/00799b.pdf

[dllabarre]

here attatched is a cleaner version of the circuit

Which MOSFETS are you using?

Thanks,

[rave154]

the mosfets are N Channel, IRF 740's