Basic PWM question

[mazur50]

So I have a basic PWM question. I have a Basic PWM 555 circuit and it controls a N Chanel Mosfet can I control a NPN transistor with that.

[mazur50]

Would this work.

[davemac2]

well, you would be better off using the darlington pair switching the negative lead of the motor vs the positive since your emitter voltage is going to be limited to the base voltage - .65V or so. It could work for a low volatge motor, but you would have substantial losses using the Darlington transistor configuration vs a MOSFET if your currents are large. The darlington configuration has a VCE in saturation of maybe 1.2V best case vs a higher current rated MOSFET which is rated for a RDS resistance at a specific IDS current when on. Losses also occur due to the switching frequency, how fast the circuit can switch, etc.

dave mc

[Chippie]

Switching a mosfet would be better....With its lower 'On' resistance the wasted heat would be smaller

[mazur50]

can i use a n channel. and also what could i do if i wanted to change the rate at at which the duty cycle goes up as i adjust the pot. like how sensitive the pot is thanks.