PWM power supplies

[Andy55555]

Hi all

Is any one aware of a power supply that can be pulse width modulated?

The crux of it all is that I'm designing a curve tracer of sorts to do IV characteristics on power Mosfets.

Whilst having the gate open I ideally want to be able to PWM the current across the drain and source as to minimise any heating effects, whilst still achieving currents of up to 300A.

Any input appreciated!

Cheers

 

[3v0]

I do not know of any power supply that has PWM on its output. But any supply can be used to feed a PWM circuit that could feed the transistor.

 

[crutschow]

I would suggest just using another MOSFET as a switch to power the test MOSFET. But you don't need PWM. You just pulse the transistor with a single short pulses of a few tenths of milliseconds each at a low duty-cycle. If you look at the data sheets, that's how they do many of the tests when the devices are manufactured.

What do you mean "having the gate open"? You never want an open gate on a MOSFET.

 

[Andy55555]

Yeah sorry that was me being a dime bar, I meant that the Vth had been reached and the channel between drain and source had formed

 

[crutschow]

Actually you can simplify my suggested technique by just pulsing the transistor you are testing. Use an analog switch, controlled by a pulse generator, to switch the gate voltage to the MOSFET under test. (Note: You need to add a low value gate-source resistor to discharge the gate capacitance when turning the transistor off, or use a gate-driver circuit to reduce the turn-on and turn-off time). You probably should also add a snubber series RC circuit from the transistor drain to source to minimize spikes from stray circuit inductance.