# Select between two sources with transistors

I'm sorry if this has been asked before but I can't find useful data on this matter.

I have two sources of data and I want to select one of them using transistors.

If I had to guess I'd make the circuit below. Sadly I never had any electronics courses so maybe I'm missing something obvious here but as I can't find anything about my goal on internet I'd rather ask here.

I just heard about SSRs and they seem to be the best solution for my needs, but I still want to know about how to do this with transistors if this is possible.

Thanks

Vout is bottom-right

Edit: The sources are composite video signals

• What kind of “sources” are these? – user2233709 Jan 6 at 11:23
• They are composite video signals – RenéX Jan 6 at 16:38

If you're selecting between two sources of binary digital data, you should be looking for a digital multiplexer. If you're selecting between two analog signals you should be looking for an analog multiplexer. There are dozens of part numbers of either type available from the major IC vendors, depending on the details of your requirements.

Buying either of these circuits as an IC will probably be lower cost (after accounting for assembly costs) and almost certainly be more reliable and give more consistent results than constructing them out of transistors.

• Thanks I'll look at these analog multiplexers. – RenéX Jan 6 at 16:39
• By the time I receive them, is there hope in trying to do something testable (even if far from perfect) with the setup in the OP? I'd like to understand why it doesn't work, be it because of signals stability, frequency response, etc. – RenéX Jan 6 at 16:45
• To be honest, your circuit could more or less work. Whether it works and/or works well depends on the nature of the sources (Source1 and Source 2), and the load (where is the output signal going). Since you haven't shared that information, I can't say why it didn't work for you. – The Photon Jan 6 at 18:39
• I wasn't able to try when I asked and I wanted to be sure the circuit was not something stupid. I finally tried and it works perfectly, I didn't expect that. I sure will buy multiplexers though, thanks – RenéX Jan 7 at 10:37
• @RenéX, now you've shared that these are video signals, I will mention that AFAIK there are ICs specifically sold as video multiplexers. I'm not sure exactly what formats they support or whether they will fit your application. – The Photon Jan 7 at 17:05

Part like this will do for analog or digital switching at 3.3V levels. https://www.analog.com/media/en/technical-documentation/data-sheets/ADG839.pdf

What voltage and current levels are you after?