Hello,
Electronics is my hobby and I am relatively new to mosfets and switching applications in general, so I'll request some help. I am working on a circuit where a PWM driver (
PCA9634) is used to generate a 97kHz square wave signal of a chosen duty cycle. The chip is a 8-channel driver, but let's assume we're only using a single channel since I can simply replicate the same solution on all 8 channels later. Anyway, I would like to use this PWM signal to drive and dim a certain +24VDC LED light. The outputs of PCA9634 are obviously not strong enough to drive the LED directly since they require a lot more current than the pins can supply (according to datasheet: sink 25 mA and source 10 mA at 5 V), and the fact that the IC runs on 3.3V while the LED requires +24V.
What would be the proper way to drive the LED light with the given PWM frequency?I was thinking of using an intermediate mosfet as an on/off switch. The first thing that came to mind was to use a low-side N-channel mosfet, but that would mean connecting it to the ground rail. That implies that I would have to clamp the positive wire of the LED light to the +24V rail... which is not something that I am a fan of considering this is going to be an outdoor light. The mosfet switch should therefore be located *before* the LED chain (high-side), and the obvious choice is to use a
P-channel mosfet. Unfortunately, this type of mosfet cannot be driven directly by the PWM IC.
So here's where I am stuck. I've seen some circuits where a P-channel mosfet is driven by a N-channel mosfet or even a BJT, but it was also stated that this setup was not meant for high-frequency switching. The mosfets apparently have some parasitic gate capacitance that delays the switching action a bit, and that can be a problem at high frequencies. But honestly, what even is a high frequency at switching? Does 97kHz qualify as a high frequency in a mosfet application? If I use a N-channel mosfet or a BJT to drive the P-channel mosfet, will the circuit be able to cope with the used switching frequency (97kHz)? Should I use a different approach than a n-mos/bjt to drive the p-channel mosfet? Should I use something else instead of a P-channel mosfet to drive/dim my LED?
Thanks in advance for any advice.