Electrical – Circuit Testing failed (Reverse polarity and Buck-Converter)

buckfailurereverse-polarity

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Hello guys,

today I tested my circuit. Its a simple Reverse Polarity Protection Circuit with a Buck-Converter. As I supplied voltagae to my circuit, everything was well (3.5V output). Going higher with the voltage was okay, too. Until I got to ~30V. Then my power supply gone into current limitation.

I think my TVS Diode (which I choosed too small..) gone to Breakdown Volatge and caused a short circuit (is that possible?). I Supplied voltage only to the pins of the Buck but its still not working, so I think something destroyed the buck but exactly what?

EDIT: With "the buck dont work" I mean, when I supply voltage to my circuit, my power supply goes into current limitation because the circuit wants to drain a lot of current. So if I dont supply from J1 and J5 and supply the IC pins of the buck directlyy its the same failure.

Datasheets:
Buck

PMOS

Bipolar TVS

Schottky

Zener

Best Answer

  1. TVS can fail in shorted mode, it is actually the preferred failure mode as it still protects the circuit against overvoltage.
  2. TVS is (without additional components) usually not suitable to clamp sustained overvoltage. It is intended for clamping voltage spikes (short duration) If you check your datasheet, the 600 W applies to pulse only (it is actually more energy limit than power limit). Sustained power absolute maximum is 3 W only, with 30V drop it is 100 mA only.
  3. It is well possible that your C2 capacitor failed as well. What is its voltage rating? Typical overvoltage failure mode of MLCCs is short circuit.