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Multiple select-power laser?

LazyBeam

LazyBeam

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If a pen or torch style laser pointer were to incorporate simple circuits (with varying resistances) AFTER the driver, wouldn't that decrease power to the diode (creating a dimmer dot) because the current coming out of the driver is fixed?

For example, say you had a 3 position switch that routed power through a 0 ohm, 2 ohm, and 5 ohm post-driver circuit... wouldn't that switch act exactly like a brightness selector by curtailing power available to the diode? You could even use a variable potentiometer. Keep in mind though, even though the output optical mW could vary the driver would still be driving the full mA load. To deal with the heat created by resistors dissapating power the resistors could be located away from the diode and heat sink.

Alternatively, I suppose you could remount the potentiometer of the driver for user acess... but then you run the risk of killing your diode if you accidently crank it up too much.

I was thinking this could be useful for homemade powerful lasers so that if you had a laser, you could use it as a pointer (5mW-30mW), burning and recreation (100-200mW), and roasting (250+mW). One laser, three functions. The only limitation would be the threshold mA for the diode and it's upper limit.
 
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pullbangdead

pullbangdead

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LazyBeam said:
If a pen or torch style laser pointer were to incorporate simple circuits (with varying resistances) AFTER the driver, wouldn't that decrease power to the diode (creating a dimmer dot) because the current coming out of the driver is fixed?

For example, say you had a 3 position switch that routed power through a 0 ohm, 2 ohm, and 5 ohm post-driver circuit... wouldn't that switch act exactly like a brightness selector by curtailing power available to the diode? You could even use a variable potentiometer. Keep in mind though, even though the output optical mW could vary the driver would still be driving the full mA load. To deal with the heat created by resistors dissapating power the resistors could be located away from the diode and heat sink.

Alternatively, I suppose you could remount the potentiometer of the driver for user acess... but then you run the risk of killing your diode if you accidently crank it up too much.

I was thinking this could be useful for homemade powerful lasers so that if you had a laser, you could use it as a pointer (5mW-30mW), burning and recreation (100-200mW), and roasting (250+mW). One laser, three functions. The only limitation would be the threshold mA for the diode and it's upper limit.
Click to expand...

Putting a potentiometer in the sense resistance of a driver like the LM317 driver is fine, just put a fixed resistor in series with the pot to limit the maximum current. That sets a safe limit, so even if the pot skips and goes to zero resistance while you're turning it, you're still limited by the fixed resistor.

You can also do the same switch idea with the sense resistor instead of after the driver, which will save your efficiency and give better control. For example, in the LM317 driver (since it's an easy example). It maintains 1.25V across the sense resistor to set the current, so let's say you have a 10 ohm resistor, that's 125mA. Not you have a second 10 ohm resistor with a switch that acts as a shunt resistor, in parallel to the first 10 ohm resistor. Close the switch, and now now you have both 10 ohm paths active, giving you a 5 ohm resistance and 250mA. Activate a 3rd parallel shunt path with a 5 ohm resistor on it, and now you have a 2.5 ohm resistance and 500mA of current.

Either way, make sure your resistors are rated for the wattages you'll be supplying, which it getting pretty high for these new high power visible diodes.

Both very simple and totally doable.
 
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