Electronic – Managing reverse currents using MOSFETs

currentdesigndiodesmosfet

I'm planning to use a chip with two 5V output pins to provide power to two systems: a MCU (attiny85, operating voltage: ~2V – ~5V) and a USB device (input current: 3A). On top of that, I'll have an alternative 5.3V input source to power these systems.

I think the chip's 5V pins will need to be protected from current flow when the alternative source is active. I believe I could perhaps use two sets MOSFETs back-to-back and two Schottky diodes for the required circuitry. The diode will likely have a 300mA – 400mA voltage drop, which is why the alternative source is boosted to 5.3V to accommodate the voltage drops.

I'm very new to designing transistor circuits, so please bear with me. Is the following a good circuit for the task? I'm thinking of using Si2305CDS, which I just happened to find on Digikey and seems to have the right Vgs.

enter image description here

I added a 100r to each gate and a 1M to GND by following this answer. The idea is to block current flow in PIN 1 and PIN 2 when VDD is active. Is this the entire circuitry required? Are there things one should look out for?

Any advice will be much appreciated.

Thanks

EDIT: Fixed MOSFETS. Thanks to @mkeith.

Best Answer

If you are going to use a mechanical switch anyway,then this one is simple and cheap.　Both your supplies will be mechanically isolated.

Mech

If you want electric circuit, and if you are sure that 5.3V supply will always be greater than (Pin1 - Vf(diode) - Vf(schottky)) and Pin1 & Pin2 supply won't be less than (5.3V - Vf(diode) - Vf(schottky)), then you can use this diode based circuit.You just need to used diode with high forward votlage drop. And schottky aren't that useful in that case.

schematic

simulate this circuit – Schematic created using CircuitLab

Else the @next-hack's Answer is the solution.

Related Topic