For example I have a microcontroller running at 3.3v.
I want one GPIO pin to switch a 12v relay and a 5v load. Do I need to use multiple transistors? Or would something like this work?
simulate this circuit – Schematic created using CircuitLab
Electronic – Can a transistor be used to switch two loads with different voltages
transistors
Related Solutions
I believe something like this would work for you:
You will have to play around with the cap and resistor values in order to achieve your desired timing and intensity for the lamp.
The left circuit you show will not work, because the emitter of Q1 will not rise above its base.
The right circuit is a disaster, because when Q2 conducts there is nothing in its path (via the BE of Q4) to limit the current.
A good circuit could be either
- the right circuit, but replace Q4 with an NPN type (but now the circuit inverts)
- the right circuit, but add a 1k resistor in series with the collector of Q2
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Best Answer
Yes, this will work if you change it slightly. Put a resistor and a diode (i.e. 1N4148) in series with the LED so it doesn't die from too much current or reverse voltage. Also put a free-wheeling diode across the relay to protect the transistor from voltage spikes.
simulate this circuit – Schematic created using CircuitLab
If your 5V load isn't a LED, you need at least the diode (D4) in series with it but not the resistor.