Help with MOSFET circuit for turn on/off power

Hi all,

I saw this switching circuit online from a reference design that uses 2 MOSFET to enable or disable power (V+) to the rest of the components .


I don't quite understand how this circuit works. Can anyone help? I have 5V connected to VBAT and VBUS is not connected to anything. Then I have a microcontroller pin connected to POWER. The microcontroller pin switches between 0 and 3.3V.

When the POWER pin is 3.3V, I have 5V coming out from V+ to power up the rest of my circuit. When POWER pin is 0V, I have 3.3V coming out from V+ (shouldn't it be 0V?)

Thanks in advance!

Either something is faulty, or (more likely) the 3.3V is coming back along the V+ rail.

Maybe VBUS/VBAT are source voltage inputs and V+ is actually the load?

eTech said:

Maybe VBUS/VBAT are source voltage inputs and V+ is actually the load?

Click to expand...

Yes. This is the intention. V+ is used to drive the load. So the MOSFETS are used to enable or disable the source voltages from driving the load connected to V+.
I have 5V connected to Vbatt and nothing connected to VUSB. Then I used a multimeter to measure the voltage between V+ and Ground (with no load connected). Its giving me 5V (when POWER is applied with 3.3V) and 3.3V (when POWER is applied with 0V)

Kian said:

Yes. This is the intention. V+ is used to drive the load. So the MOSFETS are used to enable or disable the source voltages from driving the load connected to V+.
I have 5V connected to Vbatt and nothing connected to VUSB. Then I used a multimeter to measure the voltage between V+ and Ground (with no load connected). Its giving me 5V (when POWER is applied with 3.3V) and 3.3V (when POWER is applied with 0V)

Click to expand...

It should be near 0v when POWER is at 0v. Maybe 3.3v is feeding in to V+ from some other part of the circuit.