I'm trying to PWM a 5 meter RGB LED strip with a microcontroller. With this setup:
I have built it on a breadboard and probed the drain with my (new) scope and saw this huge overshoot:
Why doesn't the diode catch that spike? I though an 1N4148 would be fast enough. The power supply is a 12V 6A switching power supply from eBay. Is that why the voltage drop as low as about 8V?
Here is the gate voltage:
The high frequency spikes are from the 12V rail it seems, here how the 12V supply rail looks like:
I realize that breadboards are crap for signal integrity especially since I have used crappy long jumper wires but I had never guessed it would be this bad.
So why doesn't the diode catch those spikes ? And how can I reduce them? Also, is this power supply a total crap?
I have placed a couple of caps to decouple the power supply, there is still an overshoot:
I've added a 100nF ceramic cap across D4 and the overshoot is totally gone:
It looks good now, but notice the 2nd channel (in yellow). That's the power supply (which is a lot cleaner with the decoupling caps). Now another question comes in mind:
Why is the Drain voltage only about 6v when the leds are off ?