On Tue, 15 Mar 2016 12:18:10 -0700, John Larkin wrote: ound. Unless I'm missing anything, of course.
Relax, John. I've ordered a pair of these, which protect against both red
*and* green:
Or use a LM338 or LM350
boosting a regulator like that usually comes with stability warnings similar to LDOs
-Lasse
Voltage bounce on the positive rail. If your voltage regulation is good, and you never get spikes on the supply rails, you are lucky - I've had that when driving ECL but in systems involving TTL the 5V rail pretty much always look grassy.
Think paranoid - the universe is out to blow up your expensive laser diode.
-- Bill Sloman, Sydney
You can boost the 317 current with a P-channel or PNP and still have the 317 perform the current folding.
12Volts 4 amp or more PNP +-----+----+----+ +----------------+ | | v / | /+\ | --- | ( ) | + ____ | 0.5R \-/ | ___ | IN | OUT | ___ LASER DIODE | +|___|-+----+|317 |+------+-|___|++---+->|+----+ === 1.5R |____| | | GND + | | | | | | | | +------------------++ === ADJ GNDJamie
I don't know about the high power stuff, but there's a lot of room between the threshold current and the maximum, you can swing things around as fast as you can within those limits... I've never had a laser diode blow out from over driving it*... then again most of the time the first piece in my optical path is an attenuator.
George H.
*I did blow up some laser diodes doing ESD testing with a piezo butane sparker. I monitored the LD output w/ a PD, A nice spike in light and then less light, an increase in the threshold current.... several sparks would kill it.
A stick some resistance in the lead for good measure.
George H.
What ever, I've never had issues.
As it is, the Reg does ~ 50% of the load while the PNP handles the rest. I suppose if you are high speed switching you may want to use something a little faster.
Jamie
Yeah for goofing around that would be a good start. Maybe we can get report of the threshold current few watt blue LD. The 780 nm diodes I use turn on around 30 mA.
George H.
The threshold current... where it starts to lase, should be a lot less, (the current limit is kinda a safety feature, but it's your diode.)
George H.
Which is why you connect the laser then ramp up the voltage and current pots.
Start at low voltage and there can't be much current. 0.2 volts is not going to hurt a laser diode.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Reminds me of the sign in a lab at Lawrence Livermore.
CAUTION
DO NOT LOOK AT LASER WITH REMAINING EYE
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Ha! Ha! Yeah, you're probably right about that, anyways. :-D
Are you suggesting that there's not much to be gained in terms of light output by increasing the current much beyond the turn-on point?
Oh certainly not. Once you are above threshold the intensity scales with the current. So 2 amps will have something near twice the intensity of
1 amp. But you may not need to whole 2 amps of intensity. (Depends on what you want to do.)George H.
On Tue, 15 Mar 2016 17:43:57 -0500 Jon Elson wrote in Message id: :
Nope, I would not. With the price of a used HP 6632A being about $100, why use a cheap Chinese supply in the first place?
Ramping up a laser, I'd rather turn knobs as compared to pushing buttons on a keypad. And given my bench space, I sure don't want that HP beast taking up half my work area.
And a used 6632A still looks to cost 3x of an Extech supply.
I do like my cute little HP6212 power supply. 0-100 volts is handy for all sorts of stuff. It's ancient and still works great.
The Extech stuff has always been good. Extech is now a FLIR company.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Then a 6642A or 6643A. But they do cost more...
Well, you can stack lots of other equipment on it. Of the left side of my bench I have (from bottom to top)
Fluke 5200A boat anchor Rhode & Schwarz SMT03 HP 6643A Keithley 2000 and HP 5386A (side by side) EDC 521 Various junk on top
With 5X better quality and performance + GPIB. And you can download a full service manual with schematics.
They really only cost $35? I have to admit that's pretty cheap. I still wouldn't trust it to power anything expensive, though.
From the 70's right? It'll probably outlive your Extech.
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