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Should MOSFETs be open all the way?

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stevenmahoney

New Member
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?

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Steven
 

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ericgibbs

Well-Known Member
Most Helpful Member
hi Steve,
Some component values on the circuit would be helpful, also which driver IC.?

E.
 

audioguru

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Most Helpful Member
The 'scope shows that the duty-cycle forces the Mosfets to be turned on most of the time and they turn off for very short durations.
D8 prevents the rectified AC from being shorted by the Mosfets when they turn on.
The drains of the Mosfets are connected directly to +168V but the 0V of the 168V does not connect to anything.
The ground of the circuit connects to +168V when the Mosfets turn on.
 

audioguru

Well-Known Member
Most Helpful Member
I see... That means that my oscilloscope simply does not see those little gaps...
There are no "gaps".
Your oscilloscope shows that the gate signal is high most of the time and goes low for very short durations because of the duty-cycle.
 
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