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I couldn't find this in the search so I hope that I'm not repeating a question that's been asked already. I'm using a driver board that monitors the photodiode feedback in a laser diode to maintain constant power. This works fine with my single LD but I am wondering if it is possible to put more than one LD in series? These are 3 pin LDs (LD anode, LD cathode/PD anode, and PD cathode). Any thoughts on how to wire these? Can I simply put the LD pins in series?

Thanks!

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Any thoughts on how to wire these? Can I simply put the LD pins in series?

Not if you want to monitor the light output using the inbuilt photodiodes and use the light output value to control the laser diode current. In controlling the current for the one you are monitoring you may be overdriving another laser in series.

To do this properly you should consider driving all three independently, each with their monitor and control system.

An alternative is to decide which laser outputs the most laser light (for a given current) and use this as the controlled (master) device. The other lasers in series will be slaves and not quite put-out the same level of light.

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  • \$\begingroup\$ Thanks Andy, that's what I assumed but wanted to see if there were other ideas. I tried wiring 2 LDs in series and both are turned on but they are at much higher power than when using just the single LD. I'll have to double check the arrangement to make sure I'm not making a mistake in the wiring to see what's happening. I may just have to get a driver for each one but wanted to avoid that since they aren't that cheap. Thanks again. \$\endgroup\$ – Dr. Geaux Dec 18 '15 at 20:39

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