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Pulsed Laser Circuit created

happytomato

happytomato

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Nov 19, 2007
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Hey all,
I and another guy have made a circuit that pulses a laser very fast (over 4000hz).

On the diagram, it says LM317, this is not the regulator itself, but is used to represent the regulator circuit daedal made.

Note:Although this has not been tested, it should work.

Please comment
 

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When a LM317 configured to current mode has an open circuit at the load, the output voltage rises pretty close to its input voltage. That's what is likely to happen in the "off-cycle" with this circuit when transistor BC337 is "off". Subject to the switching speed of the transistor and the LM317, when it turns on again, the LD will momentarily see that full voltage (~6V in this case). This "may" be OK for a BLuRay but would not be healthy for a red LD. HTH,

Paul
 
Hmmm, you have a point, I think a zener diode is needed in the driver circuit to control the voltage, or maybe another lm317 circuit in voltage mode ? Or, maybe using a diffrent regulator would be more appropriate
 
i dont know if 4000hz is nearly enough. im pretty sure i saw somewhere about lasers being pulsed at several Mhz. i dont really know anything about it though so im not sure what would be better. ive had a hard time researching it. the faster it pulses the less time it spends off. so im pretty sure youd want to try and use the 555 for all its worth. careful with circuit regulators because they will need to allow higher values in order to get the benefits of the pulse.
 
The Senkat Diodes are driven at 40ns, IIRC.
Thus you'd need 25MHz for that - way out of range of a 555.
 
Adding a shunt resistor from the 317 to ground would keep some regulation working. 5 mA would probably be sufficient but should be tested.

Mike
 
You also can use the transistor to shunt current from the LD (i.e., connect the transistor in parallel with the LD in the normal 317 Ireg circuit) and waste some power.
 
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