H-bridge problem

Discussion in 'General Electronics Chat' started by Atata, Mar 28, 2015.

  1. Atata

    Thread Starter New Member

    Mar 28, 2015
    4
    0
    hello guys,
    i implemented my own hi power h bridge as shown in the attached picture.
    the problem is in the shown pnp mosfet, it is burning each time i test its side in the h-bridge and the other side is working properly. It is not over heating when activated,. The motor does not run and a short circuit occurs. We tested the circuit, this mosfet legs become short circuited when tested using continuity test. I changed it many times and the same thing keeps happening.
    I really need your help and I really appreciate it.
    Copy of h bridge.PNG
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    You are sequencing in1-4 in such a way that you never have the PFET and NFET on the same side of the bridge on at the same time, with some dead time when reversing?

    What are the threshold voltages for the NFETs and PFets? (Part numbers?)

    What is the Vpp of the drive signals in1-4?

    What is the PWM frequency?

    What is the motor current?

    Are the FETs on suitable heatsinks?
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,061
    3,825
    Check the pinout of that P-Mosfet that is getting hot. It looks like it was flipped in a mirror image in your attached drawing (vs the other P-Channel). You cannot fip in mirror image in real life to make your parts look symmetrical. The tabs on the back of each Pchannel should be facing the same direction on your real board. And the N-channels should be facing the opposite way.

    Also, p-channel MOSFETS are normally slower than n-channel. So, to PWM, do not pulse both channels. Just turn on the P-channel you want, then pulse only the n-channel. If you try to pulse both, the p-channel will get hot. As MikeML said, let us know the frequency and other details of your circuit.
     
    Roderick Young and shortbus like this.
  4. Atata

    Thread Starter New Member

    Mar 28, 2015
    4
    0

    hi mikeml
    thanks for your help:D
    1- No p fet and N fet on the same side being enables
    2-The is dead time when reversing about one or 2 seconds
    3- Pmos 100V 35 amps with Vt= -2v to -4v (IRF5210)
    4- Nmos 60v 30amps with vt=2.5 - 5 v (2s K1191)
    5- Input voltage 24 volts which is the drive voltage of the motor, and 5 v for mosfet switching
    6- PWM 15khz
    7-starting current without pwm = 12 amps, current at full voltage 0.7 amps
    8- yes fets are on suitable heat sinks and they are not getting hot just warm.
    thanks
     
  5. Atata

    Thread Starter New Member

    Mar 28, 2015
    4
    0
    hey gophert
    in the real board, pmos are not facing each other unlike Nmoses, they are connected according to G,D,S as shown in the figure.
    thanks
     
  6. Atata

    Thread Starter New Member

    Mar 28, 2015
    4
    0
    i made 2 half bridges and all worked great, but why when adding them to have a full bridge the stated p mos burns??!!
     
  7. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,292
    1,255
    The maximum gate to source voltage of the PFET is 20 volts. It looks like you have 24.
    The NFET would like to have more than 5 voltsg ate to source toturn on hard.
     
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