I stopped using BJTs for a while and now I cant figure out why this configuration does not give me a 12V PWM at the gate of the mosfet? I am only getting slightly more than my PWM voltage about 4.2V

I have tried resistors at the gate to limit current and different resistors at the PWM for some input impedance but nothing. If I am not mistaken, When the top transistor is on it should effectively close that "switch" and I should get my 12V at the gate. Maybe too much time playing with mosfets and I have forgotten how BJTs work.

Any insight from the more experienced would be appreciated.


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Try adapting this. It's close. \$\endgroup\$ – jonk Nov 2 '18 at 5:10

Your BJTs are configured as followers so the gate signal will be smaller than the drive by a diode drop each way. Perhaps add a common emitter amplifier between the drive signal and Q1/Q2 to boost the amplitude to near 12 V peak to peak.

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  • 2
    \$\begingroup\$ oh I see, I remember that term from a couple of semesters ago. I think I need to hit the textbooks for a refresher to see how that is so. \$\endgroup\$ – Edwin Fairchild Nov 2 '18 at 4:38

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