Should MOSFETs be open all the way?

[stevenmahoney]

I have a question, perhaps a simple one.

In the following schematics driver send a signal to the gates of three MOSFETs. I expected a square signal in the output, but it is straight DC. It looks like one or all MOSFETs is open.

I replaced the driver IC, driver transistors, all MOSFETs, but result is the same.

What am I missing?



Steven

 

[shaiko]

You're saying that you expect a square wave - that exactly what your oscilloscope shows...a square wave with a very high duty cycle.

 

[stevenmahoney]

Yes, it is on the drain, but instead of a square wave at the output I just get a staright line (DC). It looks like MOSFEts are simply not switching...

 

[shaiko]

Disconnect R7 and re-test your circuit.