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11-02-2014, 10:21 PM #1
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EXO
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How to determine the voltage and current unknown flat diode

Hi, I have two flat laser diode with 3 pin.One is from 24X dvd burner.Other is from unknown xxX dvd burner.How do I know how much current can handle these two diodes.
What is the operating voltage of this flat 3 pin diodes.Can according to their operating voltage to know how much current they need.

For example, if operating voltage is 3V can I rising voltage from 0V to 3V until reached 3V and then I saw how much current flows at 3V.Is this testing method is correct.

11-03-2014, 02:15 AM #2
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Re: How to determine the voltage and current unknown flat diode

Test them with current, not voltage. If you have an LPM chart a graph of input current vs output power, starting at the threshold current.

Calculate the rate of change for the current vs power, and if you see a deviation you've hit the maximum current. If you want to drive the diode for maximum life time use half of the maximum current you determined.

At around 350mA in this chart the power doesn't go up much when the current increases. That would be the point to stop at.

Last edited by ARG; 11-03-2014 at 02:42 PM. Reason: spelling

11-03-2014, 02:24 AM #3
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Re: How to determine the voltage and current unknown flat diode

EXO -
What ARG said !!!! We learned looong ago that
when the PO hits the "knee" of the curve,
BACK OFF !!!
HMike
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11-03-2014, 11:48 AM #4
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Re: How to determine the voltage and current unknown flat diode

Excellent as always Alex. Way to go actually showing an explanation.
Can finally REP you again
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11-03-2014, 09:33 PM #5
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Re: How to determine the voltage and current unknown flat diode

But I dont have light power meter to measure output light power to calculate rate of change.I have today tested this unknown flat diode and he draw 150mA @ 2.5V.Diode is in very small factory heat sink and is not become warm.Now I do not know if this is the maximum current.I'm afraid to increase supply current because I dont want destroy diode.
Can I increase current from 0 mA to point of maximum lighting of diode,and then stop increasing current.Or I can continue increasing current when reached maximum lighting of diode.

11-04-2014, 12:57 AM #6
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Re: How to determine the voltage and current unknown flat diode

in theory, yes. but the eye won't be able to differentiate when the beam has stopped increasing in power until it is too late.

11-04-2014, 12:55 PM #7
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Re: How to determine the voltage and current unknown flat diode

Can I use LDR connected to multimeter to measure resistance,then illuminate it with a laser.And increasing current to laser diode until resistance on LDR stops decreasing.I guess this should mean that laser diode no longer gives more output light.

11-04-2014, 05:00 PM #8
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Re: How to determine the voltage and current unknown flat diode

Could work. But if the LDR is fully saturated then even if there is still an increase of light output, the resistance will barely decrease.

11-04-2014, 09:04 PM #9
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Re: How to determine the voltage and current unknown flat diode

Quote:
 Originally Posted by EXO But I dont have light power meter to measure output light power to calculate rate of change.
You don't need a calibrated LPM to find the rate of change. Since you're reading relative to your past readings you could shine the laser at a TEC and take voltage readings from the TEC to find the rate of change.

11-04-2014, 10:37 PM #10
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Re: How to determine the voltage and current unknown flat diode

Can you tell me what is TEC.

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