Diode Voltage & Current

[daboss]

Hi All,

I have built a current limiter circuit - DDL's.

What I am trying to work out is what mA and Voltage is ideal for my laser diode that I have salvaged out of a 16X DVD-RW drive. I think the diode is a closed - looks like the senkat ones. It is not from a Pioneer drive which has a open can.

I am monitoring both the current and voltage going to the diode.

At the moment I see 3.0 Volts = 100mA's of current, 2.6Volts = 62mA's of current.

Thanks for your help.

 

[chimo]

If it's a 16x, it's likely in the same range of Senkat's Group Buy laser diodes. There's a safe current recommended by the manufacturer (probably ~ 80-130mA DC) and a current that most folks on the board run them at (~ 150-300mA). There's a risk of burning it out by running it at the higher current.

As far as voltage and current go, you can control one but not the other. Picture a graph that has voltage on one axix and current on the other. The current through a diode and the voltage across it will track on a line on that graph. If you move on one axis the corresponding point on the line will be different on the other axis. The best method to drive a laser diode is to control the current going to it. The voltage across it can only be the corresponding point on the VI curve.

 

[jayrob]

As chimo said, just measure current. As long as the battery supply is over 6 volts. 2 X 3.0 volt CR123 is not enough. It is at first, but as soon as the battery voltage drops just a hair, the LM317 begins to 'drop out'. You need to use 2 X 3.6 volt RCR123 batteries. For the 16 X diodes/DDL driver, a very common current is 250mW's. (5 ohms of resistance - or, 2 X 10 ohm resistors in parallel) This will give you around 160mW's to 170mW's. I have one of the Sony/Senkat diodes (one of the good ones - VL) that I like at 294mA's. That is using a 4.3 ohm resistor. This drives the diode at just over 200mW's. At this power, you would want a pretty good heatsink though...
Jay

 

[daboss]

wouldnt 295ma give the diode a considerably high voltage - i.e around 5 or 6 volts..

if 100ma is 3 volts then I would expect 295ma to be really high...

 

[jayrob]

At that current, the voltage to the LD is between 2.8 and 3.0. At least with this Sony/Senkat diode...
Jay

 

[BlueFusion]

Sort out the current and as long as you have enough input voltage minus the driver's drop, you let the voltage sort itself out. If the current is OK the voltage will regulate itself.-

 

[daboss]

Jayrob = have you measured this? If this is the case then I have something wrong or my diode is not the same.

I would have thought that you should give the diode the correct voltage = i.e if it is rated at 2.8volts then thats all you should give it.

If I wanted to give my diode 150ma + I would expect my voltage to be quite high - but i will check and report back, I will plot an excel graph with a VI curve.

my didoe is from a LG GSA-H31L 16X Sata DVD-RW

 

[chido]

I'll repeat what Blue said, you don't have to worry about voltage, think current.
Every diode draws different amounts of voltage, my SenKat diode (before it died) used to draw 2.5v when running it at 150mA.

 

[jayrob]

Jayrob = have you measured this? If this is the case then I have something wrong or my diode is not the same.

I would have thought that you should give the diode the correct voltage = i.e if it is rated at 2.8volts then thats all you should give it.

If I wanted to give my diode 150ma + I would expect my voltage to be quite high - but i will check and report back, I will plot an excel graph with a VI curve.

my didoe is from a LG GSA-H31L 16X Sata DVD-RW

Yes I have measured it. I don't know about other drivers, but the DDL driver, I am very familiar with. It is true what the others here are telling you. You don't have to worry about voltage, as long as you have 2 X 3.6 volt batteries or more. You can supply up to 37 volts! The LD will still only take what it needs. As long as you have your DDL driver built correctly, all you have to do is measure the current...
Jay

 

[daboss]

These are the stats I have for a SLD1236VL:-

Item Symbol Typ. Unit
Threshold current Ith 50 mA
Operating current Iop 130
Operating voltage Vop 2.5 V
Wavelength [ch955]p 658 nm
Radiation angle Parallel [ch952]// 9.0 deg.
Perpendicular [ch952][ch8869] 17.5


Reason I am scared is because I have already turned one diode into a expesnive LED because I connected it to a powered DDL circuit (fully charged capacitor at battery voltage)

Ill let you know how I go.. I will ramp the current up to 180mA and see


update:-

I have just soldered some wires to a laser diode in the drive. I have burnt a disk at 16x and I am seeing 2.2volts DC durning a 16X burn.. tried flicking the meter to AC to see if I see pulses 3.6-4.0volts ac..

Does that mean a 16X burner that I have isnt using full power of the laser diode?

 

[daboss]

sorry all... i feel like a dill :'(

I have just measured my diode again - directly at the diode 2.8volts 180mA.

If I measure at the output of my DDL circuit I get 3.6volts this when I have one multimeter in series measuring current.