2 Mode Switch Questions

scumbagatheist · May 18, 2013

I understand Ohm's law just fine. It's just very late and I am not exactly uninfluenced, as it were, so I didn't do the calculations..But, thank you. That was very helpful.

What does it mean in practical terms if the driver isn't regulating? Does that mean it's not providing the smooth current to the diode? Is this dangerous for the diode? It's not like we haven't seen multi-mode (switching) lasers before.

Cyparagon · May 18, 2013

The driver will try to increase the current draw until the voltage input drops to the driver's input voltage threshold. If you go by the spec I pulled from here, the voltage threshold is 2.7V. So 1V/6.8Ω is 150mA. That means the diode is going to be below lasing threshold.

Another way you can guess is by using impedance matching. The rule is that for max power at the load, the source impedance must match load impedance. That calculation would be 3.7/(6.8*2) = 270mA at 1.85V or 310mA at 2.1V for a full cell. The theoretical max power input to the driver would therefore be 650mW.

edit: Of course, you're still wasting at least half of the power in that resistor so it isn't a very efficient design at all.

Bionic-Badger · May 18, 2013

csshih said:
From the ones I've used it's On, On (routed through the resistor), and Off.

I guess the off isn't considered a throw?

Actually, that might count too, though it is sometimes called "Center Off" or "Change Over." Overall, I'd check what the defined switch characteristics are for those more exotic switches in the documentation instead of just relying on the pole/throw designations -- especially for push buttons where the switch cycles through multiple settings.

norbyx · May 18, 2013

Ok but is there any microchip switch that could do the same function but without the resistor? I mean I know there is since I have two lasers with different power outputs, but what I am asking is if there is a add on that could be purchased online and adapted to work on lasers....

Bionic-Badger · May 18, 2013

Unless it's one of those specific flashlight drivers with different modes, you'll probably end up having to put in resistors to set the current you want anyway.

scumbagatheist · May 18, 2013

Thanks all for the responses and Cyparagon for the math!
I'm not terribly concerned about the lack of efficiency in the switch. I cannot figure out another way to achieve the same effect w/o running into the same issue. As our batteries are rechargeable, that is of little concern to me, either...As compared to the joy of using my lasers indoors.
I report back what I find when I dismantle the switch.

norbyx · May 18, 2013

Bionic-Badger said:
Unless it's one of those specific flashlight drivers with different modes, you'll probably end up having to put in resistors to set the current you want anyway.

Now the problem with that would be that not all lasers could be fitted with a flashlight driver... correct?

csshih · May 19, 2013

norbyx said:
Now the problem with that would be that not all lasers could be fitted with a flashlight driver... correct?

the main difference between a flashlight driver and a laser driver is that laser drivers takes more care to smooth output spikes.

you could potentially add a chip to PWM the output of a laser for modes, but I would not advise that due to the hazard of a pulsed laser having a higher damaged potential than it actually looks. Adding in another constant current circuit might be a bit difficult.

Lazerbeak · May 19, 2013

My Twintask also has a 2 mode switch I wanted to keep. Could we just solder voltage regulators or capacitors to protect the LD from voltage spikes?

Thanks,

~ LB

Cyparagon · May 19, 2013

csshih said:
...a pulsed laser having a higher damaged potential than it actually looks.

I thought it was the other way around. Persistence of vision and such.

csshih · May 20, 2013

Cyparagon said:
I thought it was the other way around. Persistence of vision and such.

so now the question is - as you said in chat,
"The relationship of pulsed brightness to hazard level - is it linear?"

scumbagatheist · May 20, 2013

No, it isn't linear. After the initial pulse, and the time it takes the human blink reflex to take effect, the eye is much more prepared to protect itself, combined with the period of time the laser isn't flashing, and the additional chances of opportunity for the blink to block the beam, I would have to conclude that there would be no greatly increased chance of harm from a pulsed beam.

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