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Negative signal for P-Mos

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New Member
Hi Everybody,

Just wondering if someone could point me in the right direction regarding switching a P Channel Mosfet with a 0 to -10v square wave signal.
I want to be able to vary the pulse width as well.

I am not sure which way is best & am having problems?

Use a 555 timer as an oscillator & then use an inverting Op Amp circuit for 0 to - 10v.
Or use an Op Amp oscillator & then an inverting circuit, i'm not sure how to vary the pulse width with this way?.

Or can the 555 timer make a good Negative going 0 to -10v square wave by itself, i have found a few circuits on the net that say they have a negative output but most either don't seem to work or they fall in a heap with a load on them but work fine with no load..

The load is inductive, supply is 12v.


Well-Known Member
Most Helpful Member
Is the PFET on the high side of the load? Post a sketch showing the PFET, the load, and how they connect to the 12V supply.

You can always power the 555 on the same 12V that is running your load. Pin 3 is the 555 output; who says it cannot be wired directly to the gate of a PFET whose source is connected to +12V? The only difference is that the PWM % is defined the other way; i.e. the PFET is ON when the 555 output is LOW and is OFF when the 555 output is HIGH.
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New Member
Thanks MikeMl,

I found a way to do what i needed, i am just experimenting with things trying to learn more--some i should say.


New Member
Why don't you use low side switching using an N-channel Fet?

N-channels have generally a lower RDS(on) than P-channel Fets.
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