Charge USB device using a MCU controlled power Mosfet

[Diego_]

Hi there,

I have little experience with power electronics, as my background is software.

Given a USB powered device, I would like to interrupt or allow the USB Vcc using a digital output controlled by e.g. a ESP32.
I read that the USB allowed voltage range is as below as 4.75V, and that the USB can provide up to 2A.
I designed the attached circuit.
The IRFZ44N has a Rds = 0.024 ohm, so it should not cause a drop from the VCC to the USB Vcc.
I think the problem is the Vds: does the Mosfet cause a drop so that the USB Vcc falls below 4.75V?
Thank you.

Best regards,
Diego

 

[Bluejets]

You say IRFZ44N whereas the circuit says IRLZ44N.
Circuit is correct, you are not.

However, I doubt your circuit will work as you will need a P type mosfet for high side switching.

 

[Harald Kapp]

+1 for the PMOS. With an NMOS fet you will need V_gate >>5 V to turn V_USB completely on. Such a high voltage is obviously not available in your circuit.
With a PMOS fet you can turn it on witg V_gate = 0 V. You will need a so called logic level MOSFET with V_th << 5 V.

You can also buy complete USB high side switches with integrated overcurrent protection. Enter "usb high side switch" into your preferred search engine to find these.

 

[Diego_]

You say IRFZ44N whereas the circuit says IRLZ44N.
Circuit is correct, you are not.

However, I doubt your circuit will work as you will need a P type mosfet for high side switching.

Hi Bluejets, thank you for the information.