Remove unwanted voltage spike

Discussion in 'General Electronics Chat' started by qwwwizx, Aug 26, 2014.

  1. qwwwizx

    Thread Starter New Member

    Aug 23, 2014
    5
    0
    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.
     
    Last edited: Aug 26, 2014
  2. crutschow

    Expert

    Mar 14, 2008
    12,988
    3,226
    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.
     
  3. qwwwizx

    Thread Starter New Member

    Aug 23, 2014
    5
    0
    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.
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Post the complete circuit...
     
  5. qwwwizx

    Thread Starter New Member

    Aug 23, 2014
    5
    0
    The complete circuit looks something like this. Not a big circuit, since I already have a powersupply in front of it.
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Try putting a 10 to 100Ω non-inductive resistor between the Out pin of the MIC4422 and the gate of the FET
     
  7. qwwwizx

    Thread Starter New Member

    Aug 23, 2014
    5
    0
    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?
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Yes..................
     
  9. qwwwizx

    Thread Starter New Member

    Aug 23, 2014
    5
    0
    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.
     
Loading...