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The circuit below is a power switch controlled by a push button. Basically, the switch (Q1) is controlled by a On/Off IC controller.

During testing on the real circuit, a DC Electronic Load is connected on Vout (as load) and a DC power supply is connected to the input (Vin).

When the IC (U1) turn off the load, the P channel transistor is damaged in the following conditions:

  • DC electronic load (connected at Vout): 2A
  • DC Power Supply (connected at Vin): 24V (max 4A)

Any suggestions?

Thanks,

Power switch using a ON/OFF IC controller and P MOSFET

Edit: after adding a 40V 15A Schottky diode (SK154-TP) parallel to the load, the following test were performed:

  1. 1A load with 24V input
  2. 2A load with 24V input
  3. 3A load with 24V input

Below the voltage on load during the turn on/off of the transistor.

Output voltage with 1A load with 24V input Output voltage with 2A load with 24V input Output voltage with 3A load with 24V input

Below the setup:

Setup

Performing the same testing (3 cases) without C1 and R2 = 0 the results on Vout

Vout with 1A load without C1 and R2=0 Vout with 2A load without C1 and R2=0 Vout with 3A load without C1 and R2=0

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  • \$\begingroup\$ What is the load? If it is inductive, the current can't stop immediately and causes voltage spike on the transistor- in fact raises the voltage over D ans S until breakdown. Just in case, inductive load may be relay, motor, solenoid, speaker, etc. \$\endgroup\$ – Gregory Kornblum May 24 '15 at 9:36
  • \$\begingroup\$ Hi Gregory, Thanks for your comment. The load is a DC Electronic Load in "CC mode" (prodigit.com/…). I'm not sure about the inductance of this equipment. If this is the case, could you suggest a protection circuit? Thanks \$\endgroup\$ – Julio Cruz May 24 '15 at 9:51
  • \$\begingroup\$ Ok, CC mode is almols like an inductor. You have to add a serious diode with anode on the GND and cathode on the output. The current then will flow through it without damaging the transistor \$\endgroup\$ – Gregory Kornblum May 24 '15 at 10:02
  • \$\begingroup\$ I add a Schottky Diode as you suggested, but still damaged. Do you think a MBRS140 is a serious diode? fairchildsemi.com/datasheets/MB/MBRS140.pdf. Thanks again \$\endgroup\$ – Julio Cruz May 24 '15 at 10:07
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    \$\begingroup\$ It says 1A, you need 2A, so put a 4A diode \$\endgroup\$ – Gregory Kornblum May 24 '15 at 10:14
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Ok, CC mode is almols like an inductor. You have to add a serious diode with anode on the GND and cathode on the output. The current then will flow through it without damaging the transistor.

Upd: Oh, i known what is your problem. Remove the capacitor. And make the resistor between the gate and driver like 100r or even 0. You must close the transistor as quick as you can, otherwise the current times voltage is too high- power that heats it up exists for too long. Keep the diode, of course. In case your transistor's gate voltage is limited, make sue you get the maximum out of it.

Upd: It's still gets burned, but now there is no power or overvoltage on the drain. There is still overvoltage on the gate. Change the resistors so they will be still much smaller than the initial 100k, and at the same time will not drive the gate beyond it's absolute maximum rating. Change R1 to 10k and R2 to 2k.

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