ok, so I need to power my usb with 5V but to make sure I dont drain my battery. I want it to only turn on when the remote wire from my amps is activated. I used a IRF510 and a 7805 for this. It does go to 5V when the remote wire is turned on but when the remote wire is off there is ~11.5V still going through the circuit. Obviously no good. So whats wrong with it?
I was using this http://brunningsoftware.co.uk/FET.htm page as a reference.
Assuming the FET switches off, the circuit floats the ground input of the regulator. This causes the regulator output voltage to approach the unregulated input voltage. Subsequently re-attaching the regulator ground (i.e. turning on the FET) can damage the regulator. Check the regulator datasheet for an example.
Yup, what he said,
maybe FET in series with the 7805 input.
I like to see a small gate resistor and a zener to limit Vgs
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