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DRIVING 532NM LASER WITH SINGLE 1.5V AAA BATTERY

jim_dojo

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Can someone please help me understand how this circuit works. Its a Lasermax Spartan green laser sight/led light combo. From what I understand, most green lasers require more than 1.5v to operate, however this gun sight uses a single 1.5 v AAA to drive the green laser and the green led light with infinite on time (until battery runs out of course). And you can run both the laser and led simultaneously. This is also the smallest laser housing I've ever seen....its tiny. In the attached images, it shows both sides of the circuit board. The LED is on one side and Laser on the other. I assume it is using some kind of boost converter circuit? Is the laser diode being modulated? Ive googled the electrical component labels without success. Can someone please help me understand how they are achieving this. I greatly appreciate any help. Thanks.
 

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Immo1282

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I couldn't find a part number for the main controller chip there (small rectangular in the top right) but this is no doubt some form of Boost Converter. Switching Converters use a combination of an Inductor (coil), capacitor and switching elements (either a transistor and a diode, or a pair of transistors being switched synchronously) to provide a different output voltage to their input. In the case, of a Boost Converter, the circuit diagram is shown, and I'll do my best to explain in rough terms...

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This diagram shows the converter in it's two states, with the switch ON (top) and OFF (bottom).
1. The supply flows into the Inductor (L, which resists changes in current.) This creates a magnetic field around the inductor, storing energy. In this phase, the load sees only the voltage of which the Capacitor (C, resists changes in voltage by storing charge) is charged to. i.e. Vout = Vc.

2. Now the switch (transistor) is off, the impedance of the current flow in the Inductor increases, so the Inductor (which tries to resist the change of current flow) will use the stored energy to push more current into the load. This reverses the direction of the voltage in the inductor, which adds an extra voltage source to the load. i.e. Vout = Vc+Vl.

The output capacitor also acts to smooth this varying voltage out, so that the load sees a higher steady voltage. The output voltage can be varied by adjusting the duty cycle of the transistor, i.e. how long it remains on compared to how long it is off.

To regulate the current (constant-current) as a laser diode driver does, the operation is the same, but instead of looking at the output voltage, the controller measures the load current and varies the output voltage to keep this constant given a changing Load.

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Laser Diodes require a current-regulated supply (the controller of the supply attempts to keep the current supplied to the diode constant by varying the voltage) as their load on a driver decreases with increasing temperature. This means that for a Voltage-regulated supply, as a Laser Diode heats up, the current in them will increase, further heating the device (and potentially causing a thermal runaway).

Do you know if this is a 532nm laser or a 520/510/505nm? I checked on their website, and it says 510-535nm which is useless...

532nm Lasers are what is called DPSS (Diode-Pumped Solid State), where an infra-red Laser Diode pumps energy into a series of crystals that change the wavelength of light, whereas the others I mentioned all use laser-diodes directly. My guess would be on 532nm as it is the most inexpensive way of making a green beam. IR Pump diodes for DPSS lasers

To me, it seems like a really expensive laser - but I have no idea what normal gun accessories cost so it could be reasonable value.
As to why I gave such a detailed response to a new member who didn't post an introduction thread - I'm bored :)
 




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