Transistor Help

[M4rsH]

Hi guys,

I do not have a whole lot of knowledge concerning electronics so I am turning to the forums for information.
In my circuit I want to control a servo motor. But I only want to power this servo when I am using it.
Here comes the transistor in the picture. With a USB supplying 5V to the collector of the transistor, and a raspberry Pi supplying 2.5V to the Base. I thought the Emitter would pass through about 5V, but it is only passing 2V.

I need to power my server with roughly 5V and be able to control the power to this circuit with my Raspberry Pi.

Is this the right approach? What am I doing wrong

Thanks in advance for your help

 

[duke37]

The transistor needs about 0.6v between base and emitter. Subtract this from 2.5V and you will get close to what you measure.

If you wish to use a common ground, you can use a p channel mosfet in the 5V line and drop its gate to turn it on. The resistance of the fet could be much less than 1Ω.

 

[BobK]

See here, for how to use a transistor as a switch:

https://www.electronicspoint.com/resources/using-a-bipolar-transistor-to-turn-a-load-on-and-off.30/

The problem is where you are putting the transistor. It needs to go between the negative power lead of the servo and ground. You also need a resistor between the Arduino and the base. All is explained in the linked resource.

Bob