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powering a laser off a variable power supply

Kage

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thebucketmouse said:
Alright thanks a lot. But would a test load still work identically to a laser diode, for testing the current settings??
With this PS you are going to get, all you would really need is a resistor. Say you wanted to power up a Bluray like a PHR for example. So you may want to try putting 100mA through it. We know from the data on these that the diode will have something like a little under 5.5V@100mA, so using ohm's law 5.5/.1 = 55 ohms. So, try setting the voltage to around 6V and stick a 56 ohm resistor across the PS output and turn up the current control until you see 100mA. That will give you a good idea where the 100mA setting is on the knob. But with your supply, you could even just short the output and set the current too, I think.
So, then you could put something like 20 or 30 ohms in series with the actual diode when connecting it to the PS, and as you turn up the voltage from around 4V to 7 to 9V you should see the current increase to the 100mA limit you previously set - and you will be pretty safe this way.
The more complex loads made up of a string of diodes and a resistor are more for testing an actual driver.
 

CoZZm0_AU

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I would recommend the following:

Build a simple driver (using the LM317T regulator), with a large variable pot (~50ohms) and power the driver with the power supply in constant voltage mode. That's what i do and its the safest way.

Using Constant voltage mode to supply the driver, you know that you have a stable power source so everytime you switch it on, the driver will put out the same current given the same load.

This also allows you to test new driver designs and with a resistor in series with the pot, you can effectively limit the regulator output just in case you don't have a steady hand while adjusting the pot.

I have found that while having an LCD readout of the current and voltage is great, the resolution isn't "tight" enough to really show you what is flowing through. I still always use a multimeter to confirm the values shown on the power supply (when i need precise setting).
 

Things

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I find that a good way to test current is to put your DMM on the 10A setting, and DIRECTLY SHORT the output of the powersupply. This will tell you the MAX current thhe power supply will EVER give you, which is a good way to make sure the diodes dont go pop.

EDIT: About the resistor across it, that will also slowly drain the filter cap in the power supply every time you turn it off, so there is no charge left in it when you connect the diode. Most power supplies will already have a resistor there already, but better to be safe then sorry.
 

Ironbar

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Kage said:
Partly because, as Explorer877 mentioned - the current control knob may be very sensitive, and partly because if any connection to the diode becomes intermittent - it will prevent your diode from getting killed.   Still, I would recommend keeping a small zip-lock bag to put your dead ones in, I think most of us end up with at least a few - I'm up to about 20 or so now -  ;)
Why not just throw the dead ones away?
 

Kage

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Ironbar said:
[quote author=Kage link=1228854815/0#13 date=1228985104]
Partly because, as Explorer877 mentioned - the current control knob may be very sensitive, and partly because if any connection to the diode becomes intermittent - it will prevent your diode from getting killed. Still, I would recommend keeping a small zip-lock bag to put your dead ones in, I think most of us end up with at least a few - I'm up to about 20 or so now - ;)
Why not just throw the dead ones away?
[/quote]

I guess I'm hoping that if the bag gets big and heavy enough, I'll start taking my own advice seriously, LOL ::)
 




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