I want to make a circuit which performs these tasks:
1) Protect the load against reverse polarity.
2) Protect the load against over voltage.
Load = Raspberry pi
Reason for this circuit - Pi is not directly being powered through the USB jack. There will be a DC jack where the users are supposed to plug in a 5V 2A power supply with circular pin. Ultimately this will be given to the micro-USB jack. This is being done because Pi is inside a casing and it's not possible to expose the micro-USB port directly.
I have come up with this circuit:
How I think it works:
Mosfet will prevent turn ON in case of reverse polarity.
If polarity is correct, mosfet will turn ON. I have set up a voltage reference to output 5.6 VDC. A comparator will compare this to DCOUT. If DCOUT > 5.6 VDC, OPAMP will generate a HIGH turning the mosfet OFF.
Am I correct?
Possible concern - When OPAMP turns off the mosfet, the entire circuit will lose power and mosfet will turn ON again. I will get a oscillating voltage on DCOUT equal to 5.6 VDC. Am I right?
Should I put another mosfet downstream which will cut off in case of DCOUT > 5.6 VDC? If it's downstream, I can make sure that there is no oscillations. Example:
Is there a better alternative to all this?