Simple Linear MOSFET Dimming Circuit + PWM

[WizardG]

The output of that driver chip, and all others I've looked at, is a pair of MOSFETs; one source and one sink. Both are rated for several amps of current. The whole point of these drivers is to stand between microcontrollers or other low power control/logic and high power MOSFET or IGBT output devices. But if you only need a couple amps there's no point in adding in the extra power transistors.

The output pins of a microcontroller aren't capable of much current so they can't drive a power MOSFET at high frequency directly. As the frequency goes higher the current required to drive a MOSFET gate (a capacitor, as far as the driving circuitry is concerned) goes up. That's why you were seeing the sawtooth waveform. It takes a while for the charge to build up on the gate given the limited drive current from the microcontroller.

 

[rajhlinux]

Interesting, thanks for the reply.

This really simplifies things and only a gate driver chip is needed. So I can easily send 5 - 30KHz TTL/PWM to the gate driver chip you provided?

How would I make the circuit? Can you share any simple schematics? Is it heavily involved in designing? I have never heard of anything like this and it is a rare implementation, will be difficult for any resource of information that shows how it is done for a laser diode.

 

[WizardG]

You were planning on using arduino to do PWM, correct? The outputs of these drivers are just MOSFETs, with buffer amplifiers to drive their gates. So just use the output you need (source or sink) and hook it to whatever circuitry you had planned for your discrete parts. If you need schematics, look up some application notes from the manufacturer. They all publish them. After all, they want people buying their chips!

 

[rajhlinux]

Thanks for the reply @WizardG.

Yes, I intend to use an arduino to do the PWM, if it helps I would use pure assembly code and use AVRDUDE to flash the AVR chip or use STM32 chips without using arudino IDE since it bring a lot of latency.

Alright I will look up on application notes and see what comes up. I also assume I would need to use a constant current source such as LM317 along with the gate driver.