Test load for red

[ped]

Hi guys, to go with these new high power 635's that are available now, what are you using as a test load to set current? does anyone have a diagram?

 

[Flaminpyro]

Some people are using these



and you can get one here> http://laserpointerforums.com/f64/fp-super-3-amp-test-load-62826-4.html#post894284

 

[LaZeRz]

i think hes asking for voltage :thinking:

EDIT: maybe not, but those testloads from FP are awesome

 

[Flaminpyro]

Well first he asked what we were using then he asked for diagrams.
So I showed him something he could use :na:
Now why don't you show him a diagram...

 

[Blord]

I use a selfmade testload, poor-man version.
There are 2x2Ω resistor in parallel to even out the load.

http://www.rog8811.com/laserdriver.htm

 

[ped]

Yeah FP , I just dont have any disposable income at the moment, but your test loads look great. I just wanted to whip something up as iv'e just killed a $70 diode with a faulty flexdrive.

 

[Blord]

Condolences with the loss of the Mitsubitsi 638nm diode. I use my testload with the diode without problem. Few seconds below 1A should be okay as the testload heat up very fast at high current.

 

[ped]

Job done! , with a tap for red

 

[Fiddy]

 

[rhd]

I just want to point out that the normal RED logic fails us with respect to test loads for the 635s.

At 1A, those 1N400X or 1N540X diodes start to drop closer to 1V each. If you're placing 4 of them in series, and also dropping ~1V across the resistor, than you're really talking about something between 4.5 and 5V of simulated Vf.

IIRC, these Mitsubishi reds only have a Vf of something like 3.5, when run at 1A (that's a rough memory though - confirm before taking my word for it)

 

[Benm]

The 400x series gets to about 1 volt drop at 1 amp indeed, so you only need 3 to simulate the laser diode.

If you want to test your driver for consistency just test it with 2, 3 and 4 diodes as the load, the current should be indentical unless the power supply doesnt have enough voltage when you connect 4.

Make sure to use a 1 watt resistor too - a 0.25/0.4 watt standard version will get pretty toasty dissipating 1 watt.

 

[Fiddy]

I just want to point out that the normal RED logic fails us with respect to test loads for the 635s.

At 1A, those 1N400X or 1N540X diodes start to drop closer to 1V each. If you're placing 4 of them in series, and also dropping ~1V across the resistor, than you're really talking about something between 4.5 and 5V of simulated Vf.

IIRC, these Mitsubishi reds only have a Vf of something like 3.5, when run at 1A (that's a rough memory though - confirm before taking my word for it)

So your better off with 2 or 3 diodes at 1A+?

also they are 1.9 - 2.6Vf

 

[Benm]

The forward voltage will be higher close to 1 amp, there is a graph somewhere in the review of the diode.

But 3 diodes + the 1 ohm resistor would be a better representation than using 4 in any case. I think the idea of 4 diodes comes from the 'textbook' voltage drop of 0.6 volts for a silicion diode. That 0.6 volt figure is for small signal diodes operating at 1 mA or so, not for these rectifier diodes operating at the edge of their specs - 0.9-1.0 volts is more realistic.

Also, the maximum current for a 1n400x diode is 1 amp continous. They will tolerate a bit more, but overheat eventually... especially when mounted in a cluster on a pcb like that.

 

[Cyparagon]

At 1A, the 635nm diodes drop about 2.6V. With a test load, 2 diodes should get you about 2.9V (at 1A).

 

[ped]

Thanks for the input guys , i'm driving mine at 800mA IIRC and yeah your not wrong, it gets very warm very quickly , but its long enough to tune the driver.

 

[Benm]

Don't worry about it too much, these components can endure pretty high temperatures. As long as the diodes and resistors stay below boiling they will not be damaged. You could always try the 'wet finger test' to see if it sizzles when you touch it, though i will not be responsible for any burns