Remove unwanted voltage spike

Thread Starter

qwwwizx

Joined Aug 23, 2014
5
Hi all,

I am trying to make an adjustable power supply. The supply will be attached directly to a computer PSU 12v. I just need to be able to trim the 12v down, to whatever i want and I can do that now.

For adjustment and PWM signal I use an Arduino, switching at 62,5khz. I boost the signal from the Arduino with a mosfet driver (MIC4421), just to be sure I get the mosfet FDB7030BL fully saturated.

Between the outputs I have a schottky diode to protect the mosfet from self inductance coming from the load.

My big problem is that I have a lot of spike voltage, - going to approx 50v, and the spikes seems to be there no matter if I use it to adjust fans, pumps or peltier elements, heavy load and with nearly no load. I have read that this voltage spikes is related to the corrent pushing the mosfets body diode, - not sure if thats the case. But how can I remove it. My mosfet can handle up to 30v, so I am afraid the voltage spikes will kill it.
 

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Last edited:

crutschow

Joined Mar 14, 2008
34,285
The best way to connect a protective Schottky diode is directly from the MOSFET driver output pin to the V+ supply (cathode to V+) bypass capacitor which should be connected to the V+pin on the driver.
 

Thread Starter

qwwwizx

Joined Aug 23, 2014
5
Hi Crutschow,

Thanks for trying helping me out. I dont really get your idea. Do you think the problem is related to the Mosfet gate?

The attached image of the oscilloscope was with the oscilloscope attached over the load.
 

Thread Starter

qwwwizx

Joined Aug 23, 2014
5
Thanks Mike,

Its late here, but I will try it out tomorrow. I am afraid I already ruined the transistor, so I might also need to change that.

Btw. will a normal metalfilm resistor be non-inductive?
 

Thread Starter

qwwwizx

Joined Aug 23, 2014
5
Found out that I soldered a capacitor wrong, and - I ruined something, so i need the weekend to solder a new setup. Damn holeprint makes it so messy.
 
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