using 5v circuit with 12v circuit

[david90]

How do you interface a uC 5V circuit to with a 12V automotive circuit? I can use a relay but it is too big.

How do I use a transistor to let a 5V signal work with 12V circuit? Would using a BJT in open collector configuration work?[/GVideo]

 

[dfullmer]

Hi david90

Yeah the open collector idea can work. You could also use an opto isolator to do the same thing. There are logic level translator or level shifting IC that go from TTL to CMOS level that could do the same thing for you.

Regards

dfullmer

 

[daviddlc]

Be aware that if you use BJT you will only be able to use a NPN transistor.

This is because you will trigger the transistor with a low signal.

If you use a PNP you will need to apply a "HIGH" signal which has to be 12 volts or close. If you apply 5 volts to the base the transistor will not be switched.

So based on this, depending on your needs I will use a NPN BJT or a Optocoupler.

Added after 30 minutes:

See the circuit, you can connect the load on the collector path of the transistor, or you can connect the load between the collector and ground.

Connecting the load between the collector and ground will be inverse the output(NOT), when you apply the voltage (5V) to the transistor the load is not getting the 12 Volts, when you apply "0" to the transistor the load will get aprox 12 volts.

You should calculate the resistances values for proper operation. Also you need to consider if your load is passive ( consuming constant current all the time) or dynamic (current consumption variable).

 

[nikhil_damle]

the circuit discussed is the right answer u can also use 5-12 volt buckup regulator for ti that will be a more smaller shoice

 

[Meridian]

Try this link: **broken link removed**