MOSFET interchange help

[mrbuell]

Re: MOSFET help

Thanks for your help Orson. Forgive the newbie question, but what do you mean by the source return? Is that part of the gate drive circuit or the h bridge?

Colin

 

[Orson Cart]

Re: MOSFET help

Yup, part of the gate drive, i.e. check that the gate drive is connected to the gate and the source of each fet. Also check that the H-bridge structure is fully as it was, with no power connections missing to/from the upper devices sources or the lower devices drain connections.

Regards, Orson Cart

 

[kabiru]

Here's what I don't understand...the low side isn't actually ground, its -150 VDC. It is a 240 VAC welder, each leg rectified one positive one negative. So, should the low side still be grounded in this case?

No, the source of your low side will be connected to negetive of your rectifier and i so much belive that their is a capacitor between the pos and neg of the rectifier.

 

[mrbuell]

Yes, you are right.

 

[mrbuell]

Re: MOSFET help

Thanks for the suggestion, Orson. I've double checked and everything is good. My gate signal is only 8 milliamps though. Is this enough to turn on a MOSFET?

 

[Orson Cart]

Re: MOSFET help

Seems pretty low, normally a gate drive is plus 10 to 15 V for turn on via a gate resistor that may be in the region of a few ohms to a hundred or so, 8mA would take a while to turn a device on and would give high switching losses - better check more of the gate drive circuitry...
Regards, Orson Cart.