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FrozenGate by Avery

Help With Voltage for Red Diode

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Mar 7, 2010
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Hey guys i finally put together a red laser..i got the diode from a DVD burner and im using a driver i got from ebay..
Driver
I didnt have my DMM with me, plus i didnt know what was the required amperage, so i started low and gradually raised the amperage to a satisfactory amount..
Im powering it using two double A batterys..3volts..is this enough?
I noticed that with the batteries it works well, but with my 3volt adapter it works better..so maybe my batterys are a little dead, but now it got me thinking if 3volts is enough..cause i know blue ray diodes require alot more..any advice would be appreciated..thank you..
 





It depends on the driver, more information is neded to say for sure. If it's a linear driver, you need (Diode voltage + Dropout voltage) at the input to power it fully. Diode voltage is 2.7-3.3v for a Red diode at a reasonable current, and dropout of a linear driver can be anywhere from 0.8v to 2.5v depending on the driver - that's why we can't say for sure. "3V" wall adaptors are generally over the rated output, so this may be why.

It's well worth investing a little in tools (multimeter) and getting a good quality driver with good documentation - some, especially cheap ones, are not constant-current, but drift with input voltage - not ideal for a laser diode.Any link to this driver that you have though?
 
Looking at the picture of that PCB i only see an opamp and some resistors and capacitors. This would suggest this is a linear driver, and its power supply voltage must be higher than whatever your laser diode requires.

Most red diodes require between 3 and 4 volts, depending on how hard you drive them, so 2 alkaline or nimh batteries will not suffice - as the driver will have some voltage drop too. Also, the opamp on the board is a smd version of the lm358 opamp, and requires at least 3.0 volts to operate within specifications.

You might be able to get a red running from a lithium cell with this, but even that is on the border of specs. I'd strongly suggest a higher supply voltage - 4 nimh cells or 2 lithiums, to operate reliably.
 
It's a linear driver there. Based on the fact that it's TTL I'd say 5V input ideally for a red diode, you'll have to look up the specs on Aixiz's website to find out the voltage drop, as well as to find out its maximum input voltage.
 
Thank for all the responses..
Can i simply check the output voltage of the driver using a DMM? (i got mine back)
and adjust the input until i get a suitable output? This suitable output should be between 3-4 volts, right?

Another thing is im driving the diode at about 135mA, is this good or too low? Thanks guys..
 
TTL is a way to switch the laser driver on and off rapidly to pulse the laser. This can be used to control the apparent brightness of the laser by if done rapidly, (used in some laser display equipment), or to switch the higher current on with a low current source. TTL stands for Transistor-Transistor Logic.

You may find it difficult to check output voltage directly with the DMM. For one thing, a linear driver supplies enough voltage to maintain the constant current. This means a different component will be supplied with a different voltage to reach the set current. The usual method for setting a driver up is to use a Dummy Test Load that can be set by means of a series of standard diodes to simulate the voltage requirements of a particular laser diode. If this diode was free and you don't mind possibly killing it, in this case you can measure the voltage across the diode pins. Start with a low input voltage into the driver and monitor the output voltage across the pins. (I would also start with a low current setting on the driver for this initial test.) As you increase the input voltage to the level the driver and the diode needs you should see the output voltage stabilise. Any extra voltage input into the driver from here will be dissipated as heat from the driver. Be aware that as you increase the current into the diode, it may require a little more voltage. As Charliebruce says though, you should be able to find the info on the Aixiz website or similar. These are fairly common drivers.

Without knowing which diode it is, it is impossible to say if 135mA is enough or too much but if it was free then I wouldn't worry too much. The practice will be invaluable even if you do kill it eventually. Are you certain it's a visible diode? Caution should be used if it could be NIR. I hope you will or have installed the diode in a suitable module?

Good luck.

M
:)
 
Thanks for the information..
The diode im using is not IR, it a red..since i currently have it working..but im just powering it using 2 AA batterys (3volts)..and about 135mA..
I want to know if that is good or not..
Since im not sure weather the diode is receiving 3volts or less..i know that im supplying driver with 3volt..i just dont know how much is coming out..
My laser is working, so i dont want to mess it up..but at the same time, i would like to get the most out of it..
Can u explain how to set up a test load so that i can test the voltage and current? i dont want to do it with the diode, cause i dont want to ruin it..
I know that after i create the test load i must test in series to get the current..
what about voltage..
i noticed u said that i just can test directly of the driver..how can i do it? thanks again..
 
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