Mixing Voltages

[xenobie]

Hello all,

I have a project at the moment and everything is to work from a single 12V battery. Now I am using an Arduino which has its own 5V regulator. Since I intend to switch some ICs and a relay, I can't just power everything from this poor 5v regulator. Can I for example have a transistor's base switch on using the output from the uC (Arduino), have the emitter connected to GND, and the collector-relay-coil take voltage directly from the battery?

Another similar scenario is to have two 5V regulators (1 on Arduino and 1 for some ICs) both of which taking power from 12V battery and have the Arduino "mix" its 5V with that of the ICs ??

Sorry if this is silly but I know that this might be fatal to some components in certain circumstances.

Thanks
X

 

[Hero999]

The most efficient solution is to power the MCU from the regulator and everything else (relays, lights motors etc.) from the 12V. A 5V linear reglator running off 12V is only 42% efficient. Transistors are normally used in the way you've described to enable the MCU to control 12V appliances and don't forget the diode in reverse parallel with the relay coil.