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Laser Driver with Fault Protection

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sgpee

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Hi,

I am trying to design a laser driver with fault protection. The diode will be pulsed at 1MHz with low duty cycle. (25%). I use a simple mosfet driver and it works great. I do not utilize the PD inside the diode.

ledDriverQ.PNG

Laser is pulsed above its nominal rating but since the duty cycle is low it works within the safety requirements. However when I send the unit for testing they have shorted DS manually which turned on the Laser on with 100% duty cycle and failed the tests.

I am thinking how to deal with the fault situation. One idea is to detect the lack of pulse and cut the power to the laser. I can do this with a valley detector that is controlling a pMOS to cut the power. If there is a pulse PMOS is on, if not, the PMOS is off. Do you think this idea would work?
 

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