Hi! I'm working on reverse voltage protection for a battery powered device. I have a bunch of 2N5401 PNP transistors so I was planning to do it like this:
The load is 50mA (max), hfe of the transistor is 50, so a base current of 1mA should turn the transistor fully on.
But now I'm confused... the datasheet of the transistor says that max emitter base voltage is only 5V and I was planning to use a 6V battery pack. Is this a problem?
My theory is that the voltage drop over the emitter-base junction is 1V (= base-emitter saturation voltage in the datasheet), so that the base resistor needs to drop the remaining 5V. So the resistor value should be... R = U/I = 5kohm?
Did I get this all backwards? If so, how do I calculate the correct resistor value, or is 6V too much for the circuit to handle?
(I know I could use a P-channel MOSFET for better results but I don't have the required parts here right now so I'd like to try the PNP transistor circuit first)