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Laser driver to diode resistance.

EvilsConscience

Apr 2, 2016
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Hey! This is my first personal project where I'm adapting a design to my own ideas. I'm taking an infrared laser diode and making a handheld laser engraver with it. Since this is my first build, I want to double check with more experienced people that the resistance I calculated between the driver and the diode is correct.

The driver info page said it had an output of 3.0-4.5V. I'm going to provide 3V.
The page also said the constant current was 8mha, I assume a typo meaning 8mAh, so .8 amps, bring the R to 3.75Ω.

The diode needs only 2.2V and 650mA.I calculated that I need an R of 3.38mA, but I don't see how the R O the diode could be lower than the output from the driver.

I don't want to waste $50 of equipment. Could someone correct me where I went wrong?
 

cjdelphi

Oct 26, 2011
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Cc of 8ma is not 0.8amps :eek:

2.2v 600ma sounds like what it is rated, 3-2.2/ 0.6

0.6ohm resistor to drive it at max current using (at a push) a 1/2w resistor but i'd use a 1w

If you do, be careful 1 splash of IR could do serious damage to eyes
 

cjdelphi

Oct 26, 2011
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Diodes work on current, it should not providing max current (650ma?) Is not reached, when the driver limits the current the voltage will drop to around the foward voltage it's supposed be, if current rises then the voltage across the diode will rise as well

Take a normal LED and stick a 300ohm - 1k in series to the LED, supply 3 - 5v you'll see the voltage stay pretty constant unless you push it past it's current capability
 

cjdelphi

Oct 26, 2011
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Screenshot_2016-04-02-16-19-14.png

Notice how the voltage stays pretty constant? This is a poor mans way of a voltage regulator using an LED, the voltage is passed to a transistor and then regulates a component which requires that level of voltage
 

EvilsConscience

Apr 2, 2016
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View attachment 26020

Notice how the voltage stays pretty constant? This is a poor mans way of a voltage regulator using an LED, the voltage is passed to a transistor and then regulates a component which requires that level of voltage
I see. So, as long as I have the driver set to the proper frequency of my IR laser diode, I won't need a resistor because the driver is already limiting the current.
 

cjdelphi

Oct 26, 2011
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The ir diode could not care about frequency really only current, for example if it was on for 1ms off for 1ms in theory can drive it harder than it's rated current, pwm is merely a way of driving the diode

To test it you could stick resistor on the end of the driver, but as long as the driver does not supply more current than the diode can handle you should be safe...

But please hold out if you must, as others will have more experience than myself with lasers, after almost burning my retina out i decided to stay away from them lol
 

EvilsConscience

Apr 2, 2016
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Apr 2, 2016
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The ir diode could not care about frequency really only current, for example if it was on for 1ms off for 1ms in theory can drive it harder than it's rated current, pwm is merely a way of driving the diode

To test it you could stick resistor on the end of the driver, but as long as the driver does not supply more current than the diode can handle you should be safe...

But please hold out if you must, as others will have more experience than myself with lasers, after almost burning my retina out i decided to stay away from them lol
Thank you for your help! I'll hold out for a bit because I still have to buy goggles, but you've helped.
 
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