Reply by George Herold April 22, 20162016-04-22
On Friday, April 22, 2016 at 2:57:02 PM UTC-4, Chris wrote:
> On Fri, 22 Apr 2016 08:56:50 -0700, George Herold wrote: > > > The numbers don't make sense... but I don't know cheap diode lasers > > either. > > If it's a bare diode laser then you if you drive it with a current > > source. > > (a resistor and voltage source would work.) then you should see the > > laser output increase linearly with current.... I was just measuring the > > power out of my diode laser. Here's a crappy graph. > > https://www.dropbox.com/s/tcst4f09wf1arth/POWER.BMP?dl=0 > > Maybe we're at cross-purposes here. I was discussing voltage across the > laser diode vs. the current through it. Not sure at all what you've > graphed a photodiode's response into the equation here?
Yeah I'm saying the voltage is not relevant to the light output. (if it's bare LD) (The bottom (X) axis is the LD current, the horizontal (Y) axis is the current from a photodiode looking at the laser. (about 0.6A/W so 20 mA is ~30 mW.) (It just happened to be something I was doing today.) George H.
Reply by Chris April 22, 20162016-04-22
On Fri, 22 Apr 2016 08:56:50 -0700, George Herold wrote:

> The numbers don't make sense... but I don't know cheap diode lasers > either. > If it's a bare diode laser then you if you drive it with a current > source. > (a resistor and voltage source would work.) then you should see the > laser output increase linearly with current.... I was just measuring the > power out of my diode laser. Here's a crappy graph. > https://www.dropbox.com/s/tcst4f09wf1arth/POWER.BMP?dl=0
Maybe we're at cross-purposes here. I was discussing voltage across the laser diode vs. the current through it. Not sure at all what you've graphed a photodiode's response into the equation here?
Reply by George Herold April 22, 20162016-04-22
On Thursday, April 21, 2016 at 4:37:07 PM UTC-4, Chris wrote:
> On Wed, 20 Apr 2016 08:04:23 -0700, George Herold wrote: > > > On Tuesday, April 19, 2016 at 6:15:55 PM UTC-4, Chris wrote: > >> On Mon, 18 Apr 2016 06:22:31 -0700, George Herold wrote: > >> > >> > Those voltage numbers don't make much sense, unless there is some > >> > circuitry driving the diodes already. Are these bare diodes? > >> > >> Yes, I believe so. The only other component is what looks like an SMD > >> capacitor across the diode leads just before it goes into the brass > >> housing. I guess this is to iron out any voltage spikes? > > > > Maybe a diode in reverse to prevent reverse voltage? > > No, it's a cap (unless it's a diode with a junction capacitance of 10nF!) > > >> > >> > The best analogy for a laser diode(LD) is an LED. > >> > The forward voltage is mostly set by the band gap.. color of light. > >> > There should still be an increase in the voltage as you increase the > >> > current (~60 mV for a decade increase in current... (I think)) > >> > >> That's what I'm seeing under test, actually. And despite the > >> description, > >> all the diodes I@ve checked so far go into forward conduction at 3.3V. > > I'm not sure what you mean. There's no current with 3.2 V? > > There is, but the current starts to increase hugely at 3.3V but the > voltage then seems to stick around that level. > > > What's inside the brass case? > > (I'd bet a beer there an APC circuit in there.) > > You owe me a beer. There's nothing but a lens in there. :) It's hardly > surprising, though. These things are like DIRT cheap so I wouldn't expect > any driver.
OK, it is Friday. Can you stop by for Lunch and we'll grab a beer and a burger? The numbers don't make sense... but I don't know cheap diode lasers either. If it's a bare diode laser then you if you drive it with a current source. (a resistor and voltage source would work.) then you should see the laser output increase linearly with current.... I was just measuring the power out of my diode laser. Here's a crappy graph. https://www.dropbox.com/s/tcst4f09wf1arth/POWER.BMP?dl=0 The good news is I can get about 30 mW which is enough to make a MOT with. (MOT- Magneto-optical Trap.) George H.
Reply by Chris April 21, 20162016-04-21
On Wed, 20 Apr 2016 08:04:23 -0700, George Herold wrote:

> On Tuesday, April 19, 2016 at 6:15:55 PM UTC-4, Chris wrote: >> On Mon, 18 Apr 2016 06:22:31 -0700, George Herold wrote: >> >> > Those voltage numbers don't make much sense, unless there is some >> > circuitry driving the diodes already. Are these bare diodes? >> >> Yes, I believe so. The only other component is what looks like an SMD >> capacitor across the diode leads just before it goes into the brass >> housing. I guess this is to iron out any voltage spikes? > > Maybe a diode in reverse to prevent reverse voltage?
No, it's a cap (unless it's a diode with a junction capacitance of 10nF!)
>> >> > The best analogy for a laser diode(LD) is an LED. >> > The forward voltage is mostly set by the band gap.. color of light. >> > There should still be an increase in the voltage as you increase the >> > current (~60 mV for a decade increase in current... (I think)) >> >> That's what I'm seeing under test, actually. And despite the >> description, >> all the diodes I@ve checked so far go into forward conduction at 3.3V. > I'm not sure what you mean. There's no current with 3.2 V?
There is, but the current starts to increase hugely at 3.3V but the voltage then seems to stick around that level.
> What's inside the brass case? > (I'd bet a beer there an APC circuit in there.)
You owe me a beer. There's nothing but a lens in there. :) It's hardly surprising, though. These things are like DIRT cheap so I wouldn't expect any driver.
Reply by George Herold April 20, 20162016-04-20
On Tuesday, April 19, 2016 at 6:15:55 PM UTC-4, Chris wrote:
> On Mon, 18 Apr 2016 06:22:31 -0700, George Herold wrote: > > > Those voltage numbers don't make much sense, unless there is some > > circuitry driving the diodes already. Are these bare diodes? > > Yes, I believe so. The only other component is what looks like an SMD > capacitor across the diode leads just before it goes into the brass > housing. I guess this is to iron out any voltage spikes?
Maybe a diode in reverse to prevent reverse voltage?
> > > The best analogy for a laser diode(LD) is an LED. > > The forward voltage is mostly set by the band gap.. color of light. > > There should still be an increase in the voltage as you increase the > > current (~60 mV for a decade increase in current... (I think)) > > That's what I'm seeing under test, actually. And despite the description, > all the diodes I@ve checked so far go into forward conduction at 3.3V.
I'm not sure what you mean. There's no current with 3.2 V? You can look up bare LD's on DK... check the spec sheet for typical forward voltages.
> > > I'm guess you've got diode with a built in controller (in the brass > > case.) > > I'm pretty sure these ones have no controller. Another batch from another > supplier just arrived. I'll check them tomorrow...
What's inside the brass case? (I'd bet a beer there an APC circuit in there.) George H.
Reply by Chris April 19, 20162016-04-19
On Mon, 18 Apr 2016 06:22:31 -0700, George Herold wrote:

> Those voltage numbers don't make much sense, unless there is some > circuitry driving the diodes already. Are these bare diodes?
Yes, I believe so. The only other component is what looks like an SMD capacitor across the diode leads just before it goes into the brass housing. I guess this is to iron out any voltage spikes?
> The best analogy for a laser diode(LD) is an LED. > The forward voltage is mostly set by the band gap.. color of light. > There should still be an increase in the voltage as you increase the > current (~60 mV for a decade increase in current... (I think))
That's what I'm seeing under test, actually. And despite the description, all the diodes I@ve checked so far go into forward conduction at 3.3V.
> I'm guess you've got diode with a built in controller (in the brass > case.)
I'm pretty sure these ones have no controller. Another batch from another supplier just arrived. I'll check them tomorrow...
Reply by George Herold April 18, 20162016-04-18
On Wednesday, April 13, 2016 at 6:38:47 PM UTC-4, Chris wrote:
> I made a bulk purchase of red laser diodes off Ebay. There are three bags > together unmarked. 25 of them are 3.3V., another 25 are 4.5V and the > other 25 are 5V. But like I say they're not labelled so I don't know what > spec correpsonds with which batch. They're all in brass hosts with > adjustable lenses. > Is there a simple way to tell which is which - establish safe working > current and voltage for each batch? I don't mind blowing a few in the > process if necessary as I can afford to lose some. > thanks.
Those voltage numbers don't make much sense, unless there is some circuitry driving the diodes already. Are these bare diodes? The best analogy for a laser diode(LD) is an LED. The forward voltage is mostly set by the band gap.. color of light. There should still be an increase in the voltage as you increase the current (~60 mV for a decade increase in current... (I think)) I'm guess you've got diode with a built in controller (in the brass case.) Thye probably need ~10's of mA to lase. I'd hook one up to a power supply with a bit of resistance to limit current. (say a volt at 10 mA.. 100 ohms or so.) Turn up the voltage and see what you get. George H.
Reply by Cursitor Doom April 15, 20162016-04-15
On Fri, 15 Apr 2016 10:42:58 -0400, Ralph Mowery wrote:

> I would say more like a zener diode than the rectifying diode. > Not much effect before the device goes into zener type action and it > starts to draw lots more current.
I'm certainly no expert in this area, Ralf, but I don't quite see how the zener analogy works here. These laser diodes require forward voltage to operate and (this bit is the main difference from 1N4*** series diodes) that forward voltage is typically much higher than the 0.6 - 0.7V - less for Schottkys - anything up to about 5V in fact. But the 'knee' shape you would see with a curve tracer will be the same; just further to the right on the x axis than with a conventional diode.
Reply by Ralph Mowery April 15, 20162016-04-15
"Chris" <cbx@noreply.com> wrote in message 
news:neqt8g$nfp$1@dont-email.me...
> On Thu, 14 Apr 2016 13:47:34 -0400, Ralph Mowery wrote: > [...] > > So, just to get this clear, there is basically no difference in the > dynamic behaviour of a laser diode (wrt current and voltage) and an > ordinary run-of-the-mill rectifying diode such as a 1N4001 for example? > The laser diode is very static sensitive; the ordinary diode is not. But > aside from that.... nothing? >
I would say more like a zener diode than the rectifying diode. Not much effect before the device goes into zener type action and it starts to draw lots more current.
Reply by Chris April 15, 20162016-04-15
On Thu, 14 Apr 2016 13:47:34 -0400, Ralph Mowery wrote:
[...]

So, just to get this clear, there is basically no difference in the 
dynamic behaviour of a laser diode (wrt current and voltage) and an 
ordinary run-of-the-mill rectifying diode such as a 1N4001 for example?
The laser diode is very static sensitive; the ordinary diode is not. But 
aside from that.... nothing?