As seen below, I have a circuit that turns on +12V to the EN pin of a LM53601 buck converter when the +6V DC component in a car speaker wire is detected (bridged output). This works fine.

But I am a bit confused when reading the specifications for the PNP and I need some help understanding how much voltage the 3906 can withstand. In my current circuit, the +12V from the battery has TVS diode protection, clamping the voltage at 36V. It also has a 200V Schottky in series.

Will a transient of 36V at Q2 emitter destroy it?

Switch circuit

enter image description here

  • \$\begingroup\$ <This works fine...> Are you sure? D1&C1do not react to DC only. They actually rectify even null average audio and enable output no matter 6V bias or not. \$\endgroup\$ – carloc Sep 27 '17 at 17:12
  • \$\begingroup\$ @carloc It works fine in the way that the buck converter is turned on when the head unit is turned on and off when the head unit is turned off. What you're saying is that it may also conduct when using an output that is not bridged? \$\endgroup\$ – JohnDonut Sep 27 '17 at 17:31
  • \$\begingroup\$ Yes I think so, it may conduct even when not bridged amplifiers are connected. \$\endgroup\$ – carloc Sep 27 '17 at 20:33

36V causes 35V/3k base current which is ok and is < 40V max

But reverse voltage will exceed Vebo of -5V and damage it instantly and grounding the output will fry it when active high.


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