Driving 3x red diodes with 2 lithium cells on a case negative host.

[Fiddy]

G'day,

Im going to be building a portable, triple red laser, but im not sure how i am going to drive it properly.

Can anyone recommend a drive method for driving 3x red diodes at 300-400mA, off 2x 18650's in series and a case negative host?

Im thinking LPC-826's, but other diodes are an option, i was looking at the 110mW single mode 638nm's but they are fairly costly.
If you could recommend other diodes with at least 200mW output id like to hear it!

I want to avoid 3 individual drivers too.

Should i opt for a series diode setup?

Any help will be much appreciated!

Cheers! Fiddy.

 

[Blord]

You must put the diodes in series in order to get equal current for each diode.
I don't know if 3xVf diode is lower than than voltage of 2x 18650. I assume it is.

Flexdrive is out of the question due max input voltage of 5V.
You need a linear or buck driver with a low voltage overhead.

ST-driver has low overhead but it isn't continuous negative.

 

[Fiddy]

hmmmmm looks like i will have to isolate the heatsink me thinks.

 

[Cyparagon]

3 in series is about 9V. You'd need a boost driver. Isolating the heat sinks is required, yes. At least two of them anyway.

 

[Fiddy]

is there a driver we know of that boosts to ~9V? from 2 lithium's?

 

[benmwv]

I think the easiest way to do this would be running them in parallel with a 1 or 0.5 ohm balancing resistor on each diode from a linear driver. Not the most efficient way but you won't have to worry about isolating them.

 

[Fiddy]

what linear driver would you recommend?

 

[benmwv]

How about mohgasm 1.25A round?
Mohgasm 1.25A 16mm Round linear driver circuit [MOHR1.25] - $14.99 : Cajunlasers Store

Should give about 420ma to each diode, and since it goes into the contact board area it might save you some room for the balancing resistors.