Hi,
Been a while since I posted here, off doing work and life etc.. But I'm back with a niggling problem. A while aog I got some UV laser diodes off ebay, some plain diodes, and one in a mount - all around 100-150mW. Inevitably, because the mount had two wires coming out of it directly to the diode - after much plugging and unplugging the diode went. Could be ESD, maybe I plugged it in wrong, or maybe just over current with me lighting candles with it
So, because the inside of the mount is rather small - 16mm long, 9mm wide inside the tube, a micro driver circuit isn't ideal. Instead I would just like to put a protection circuit in there, soldered directly to the diode, with two (maybe 3) wire-lead coming out for plugging into a half decent driver circuit. This way I can use multiple driver circuits, buck, boost, able to adjust the current and therefore output of it.
I still can't decide what would be 'enough' protection, and something to fit onto the very small PCB. I could of course just have a two-track PCB, in parallel with the diode, with a TVS diode and a cap - but I feel I could do more, and this wouldn't provide decent protection.
So, here's my tihnking. This is what can destroy a laser diode:
1.Over-voltage: ESD spikes, from having an exposed lead, over-shoot from supply, accidentally plugging into wrong supply
2. Over-current: being over zealous with current trying to maximise output, plugging into wrong supply etc..
3. Transients: These are covered by the above, but could mean very fast rise times and nanosecond events.
4. Temperature: Caused by too much current.
Ok, As I said, I'm planning on an external driver board which will control current and maximum output voltage, but would like a small proteciton circuit in there to minimise the chanecs of me popping another diode. I don't think temperature would be much of a problem, as its mounted in a brass mount (not ideal as copper, but it'll do, its only 100mW).
Aside from a TVS diode, a cap, would some form of basic current limiter in there be a good idea? I was thinking of using a shunt transistor for over-current, along with a zener for over voltage - but zeners are quite slow, and TVS diodes have a rather vague clamp voltage. Given the small space, SMT is required, but I'm confident I could fit a two-transistor circuit on there, along with diode and some passives.
Perhaps i am just being overly cautious, but as I don't want just 'wires soldered directly to the LED coming out', I'm using a small PCB in there anyway, just to solder wires to for mechanical robustness - seems a pity to waste that PCB space when these diodes are so electrically fragile. Any idea's?
Cheers!
BuriedCode.
Been a while since I posted here, off doing work and life etc.. But I'm back with a niggling problem. A while aog I got some UV laser diodes off ebay, some plain diodes, and one in a mount - all around 100-150mW. Inevitably, because the mount had two wires coming out of it directly to the diode - after much plugging and unplugging the diode went. Could be ESD, maybe I plugged it in wrong, or maybe just over current with me lighting candles with it
So, because the inside of the mount is rather small - 16mm long, 9mm wide inside the tube, a micro driver circuit isn't ideal. Instead I would just like to put a protection circuit in there, soldered directly to the diode, with two (maybe 3) wire-lead coming out for plugging into a half decent driver circuit. This way I can use multiple driver circuits, buck, boost, able to adjust the current and therefore output of it.
I still can't decide what would be 'enough' protection, and something to fit onto the very small PCB. I could of course just have a two-track PCB, in parallel with the diode, with a TVS diode and a cap - but I feel I could do more, and this wouldn't provide decent protection.
So, here's my tihnking. This is what can destroy a laser diode:
1.Over-voltage: ESD spikes, from having an exposed lead, over-shoot from supply, accidentally plugging into wrong supply
2. Over-current: being over zealous with current trying to maximise output, plugging into wrong supply etc..
3. Transients: These are covered by the above, but could mean very fast rise times and nanosecond events.
4. Temperature: Caused by too much current.
Ok, As I said, I'm planning on an external driver board which will control current and maximum output voltage, but would like a small proteciton circuit in there to minimise the chanecs of me popping another diode. I don't think temperature would be much of a problem, as its mounted in a brass mount (not ideal as copper, but it'll do, its only 100mW).
Aside from a TVS diode, a cap, would some form of basic current limiter in there be a good idea? I was thinking of using a shunt transistor for over-current, along with a zener for over voltage - but zeners are quite slow, and TVS diodes have a rather vague clamp voltage. Given the small space, SMT is required, but I'm confident I could fit a two-transistor circuit on there, along with diode and some passives.
Perhaps i am just being overly cautious, but as I don't want just 'wires soldered directly to the LED coming out', I'm using a small PCB in there anyway, just to solder wires to for mechanical robustness - seems a pity to waste that PCB space when these diodes are so electrically fragile. Any idea's?
Cheers!
BuriedCode.
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