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I am trying to create a Raspberry Pi Hat which has my usb hub and a mosfet which turn on and off the power on individual port.

There are different way to do this: Transistor, Mosfet, Relay, but I have chosen Mosfet for the lower consumption if the usb has to be on for a long time ( everything runs on battery ).

Unfortunately my knowledge of mosfet made the pcb not working as I was hopping, so I tried to add a transistor PNP and buying different rate ( 500ma, 1A ), the transistor worked but didnt let pass enough current even if it says 1A.

I am a bit confused on what I have made wrong and if my idea to use the VCC rather than GND line is correct. I do understand that PNP should be use on the positive line and NPN on negative lines, right?

This is my schematic: enter image description here

My temporary solution is to connect a relay to switch on and off, which works, but I want to make my pcb as small as possible by using a mosfet ( smd ).

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Might want to swap the source and drain on those P channel mosfets, the source should connect to Vbus and the drain to the port (Otherwise the body diode will conduct).

Also what exact part number is the mosfet? You need a logic level part, because you only have 5V Vgs available.

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  • \$\begingroup\$ I tried to use this mosfet link but I suppose what you said is that I cant trigger with a 3.3V. In the other hand, I am using a expander IO which can operate at 5V, so I could potentially use that 5V output to connect my mosfet. \$\endgroup\$ – max246 Oct 8 '16 at 13:48
  • \$\begingroup\$ The mosfet will switch on if the gate is more then 500mV below the source, so you need 5V if you are switching a 5V rail. Pulling the gate low will switch on the mosfet. \$\endgroup\$ – Dan Mills Oct 8 '16 at 14:52
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The P-Channel MOSFETs require a high side driver, since your GPIOs on the RPi can only go up to 3V3. You need to go up to 5V to switch the MOSFETs off completely.

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  • \$\begingroup\$ So what is the alternative here? Transistor? \$\endgroup\$ – max246 Oct 8 '16 at 13:44
  • \$\begingroup\$ One N-Channel logic level mosfet and one resistor to drive the p-channel gate. \$\endgroup\$ – Turbo J Oct 8 '16 at 14:13
  • \$\begingroup\$ any suggestion? I think I need to find something which can handle up to 1A. I will try to find something and might post here to double check. \$\endgroup\$ – max246 Oct 8 '16 at 14:16
  • \$\begingroup\$ Sopping questions are off topic here. \$\endgroup\$ – Turbo J Oct 8 '16 at 14:18

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