laser diode resistance And two other questions

Thread Starter

Peter basolo

Joined Nov 24, 2014
38
I have laser diode and I'm not sure what the power it with. I contacted the guy I bought it from and he said I could power with 9 volts but when I do I don't get nearly the 150 mW it's rated at. It's an aixiz diode and he said it could have a max input of 180 mah (diode death?). I'm wondering if I put it in the computer heat sink that I have could I put more than 180 mAh in it, and could I put more voltage in it. I have some 18650 batteries laying around but I also have a psu I could mod to use that if it would be better. Well I'm on the subject what on the power supply says -5 Volts? I'm assuming that it works as a ground or negative voltage but how does it affect a positive 5 volts? On a slightly related note, do batteries in parallel charges As one cell?
 

ian field

Joined Oct 27, 2012
6,539
I have laser diode and I'm not sure what the power it with. I contacted the guy I bought it from and he said I could power with 9 volts but when I do I don't get nearly the 150 mW it's rated at. It's an aixiz diode and he said it could have a max input of 180 mah (diode death?). I'm wondering if I put it in the computer heat sink that I have could I put more than 180 mAh in it, and could I put more voltage in it. I have some 18650 batteries laying around but I also have a psu I could mod to use that if it would be better. Well I'm on the subject what on the power supply says -5 Volts? I'm assuming that it works as a ground or negative voltage but how does it affect a positive 5 volts? On a slightly related note, do batteries in parallel charges As one cell?
All the laser drivers I've seen in professional equipment used well deigned (possibly over engineered) constant current generators, while cheap laser pointers rely entirely on the internal resistance of 3 series button cells.

Most of the current limit circuits even used high speed transistors so they could respond to spikes.

With regular LEDs the cell limiting works, but damages the semiconductor - there was a MIB neuraliser toy with a blue LED and a stack of button cells, it works but light output drops off pretty much as quick as a kids attention span. A LED from a discarded toy was tested, it berely lit and the reverse leakage was as much as the forward construction.

A laser diode from a bar code scanner produced dim incoherent light when I had the current limit set to minimum - it suddenly burst into life at about 100mA.
 

Thread Starter

Peter basolo

Joined Nov 24, 2014
38
I have a driver board but it only accepts 10 volts :/ I would like to get Round this, is there another way to get a constant current without a dinky driver board? Maybe something more versatile? Like I said I have a psu I could mod.
 

ian field

Joined Oct 27, 2012
6,539
I have a driver board but it only accepts 10 volts :/ I would like to get Round this, is there another way to get a constant current without a dinky driver board? Maybe something more versatile? Like I said I have a psu I could mod.
Usually you put the LD in the collector of the driver transistor, you have a current sensing resistor between emitter and GND, the voltage developed across the sense resistor is fed back to the inverting input of an op-amp. The non-inverting input is fed by a fixed Vref. The op-amp output directly drives the transistor base.

You can get single supply op amps that work down to 5V, maybe even 3.3V - but that would be cutting it fine for the diode voltage and the sense resistor voltage.
 

ian field

Joined Oct 27, 2012
6,539
If the diode is rated at 180mA max. then you should never exceed that value (that's why it's max.), even with a good heat sink, otherwise the diode will likely blow or deteriorate.
Pulse operation at higher current is usually permitted as long as you keep within a specified average power rating.

But there is still a peak current rating, with LEDs its the fusing current of the bond wire - I'm not entirely sure if laser diodes have one of those.
 

gerty

Joined Aug 30, 2007
1,281
And all of this is irrelevant without proper heat sinking. If you want to run this laser at its max values it's going to get very hot...
 
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