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Topic: Using a transistor as a switch (Read 509 times) previous topic - next topic

leovanasch

Hello forum!

I want to switch the main power supply to a gps reciever(UP501) on and off. The gps reciever uses 1 pin for ground, 1 pin for back up power supply and 1 pin for main power supply. Using plain digital pins doesn't work, because the gps draws about 30mA on 3,3V. The back up power supply pin is always connected to 3,3V.
To make it work I want to use a transistor to switch the main power supply on and off. But my lack of knowledge about transistor isnt helping much. Can anybody help me with this?
Im using an arduino clone based on the arduino pro (3,3V;8MHz) w/ Atmega328.

Regards,

Leo

fungus

You'll need a MOSFET for this. Almost any logic level N-Channel MOSFET will do.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

MarkT

No, this won't work, a p-channel MOSFET or PNP switching transistor to do high-side switching is required.  An n-channel
or NPN device can only do low-side switching on the ground which is incompatible with maintaining the backup 3.3V
supply.  Search for high-side switching, p-channel and/or PNP.
[ I won't respond to messages, use the forum please ]

Magician

Probably, you may "simplify" this circuit, leaving T1 only, than driving LOW to turn on device
http://ruggedcircuits.com/html/circuit_-17.html

MarkT

Indeed - losing Q1 would improve that circuit!
[ I won't respond to messages, use the forum please ]

cjdelphi

I dunno, I think a 2n2222 might be up for the job....

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