Create a controlled 12V output for Raspberry Pi

I had to add a 12V controlled output for my raspberry Pi to connect a radio frequency system to my Pi. This system just need 12V to start transmitting but it needs 12V ! The raspberry can offer 5V or 3.3V. The solution is to use a currant elevator system. The one I built is based on a Texas Instrument component TPS6734, able to deliver 120mA / 12V with a 3.3V input.

This soic-8 component have a Enable signal to activate the 12V generation, when not activated, as the output is connected to Vin through an inductance, the Vout = Vin when the enable pin is connected to the ground. This was nos acceptable for my system so I added in front of the Vin a BC848C NPN transistor to drive the Vin current. This transistor is controlled by a RPI GPIO to enable / disable 12V out.

Here is the schema of this circuit, use it at your own risk.

raspberry pi 12V currant elevator
raspberry pi 12V currant elevator

With this schema the output will be limited to 17mA / 12V ; the input will require about 90mA to deliver this current on output. The BC848C have a Beta coefficient around 20 which limiting the input to 100mA corresponding to what is measured (90mA) assuming different approximations.

 

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