Electronics help please

[rog8811]

I want to drive 2 lasers from 3 transistor switched inputs, to give red only, green only and red & green together.

Could you cast you eye over the circuit below and tell me if it is a workable scheme please.

Regards rog8811

 

[Hemlock_Mike]

Rog --

I would do the switching on the base side of the driver transisitosrs using this circuit and 1n4148 diodes.  Your design here adds another 0.7 volt drop to your LD's.
I assume you're using NPN transistors for drivers and it's more efficient to switch the low current parts.

Mike

 

[rog8811]

Hi Mike, yes they are NPN transistors, I am adapting an existing circuit so I will need to look to see if I can put this the other side of them....The main thing is though that this looks a possibility.

Thanks for the response,
Regards rog8811

 

[Benm]

What exactly are you connecting on the right hand side of that schematic?

If both devices are the same voltage (e.g. 5V powered laser modules), it would work fine. On the other hand, if one is a red laser diode, and the other is an IR pump diode, it would not work very well, because the IR diode has a lower drop voltage and would consume all the power coming from the middle input.

 

[rog8811]

@ Benm, thanks for the input, I must admit I had not considered that, I will need to have a look at my setup and check that out.

Regards rog8811