Laser Driver/Modulator Circuit

ericgibbs said:

chris,
Did a rough analysis of the cct, you must have a 8V7 zener on that regulator cct, else the 2.5Vreg CR2 will not be effective.
With a 6V zener on the base, you will have Vrail of approx +5.3V, the CR2 progzener has a current spec of 10mA, there is
a 560R in series with CR2 from the '5.3v' . So you have a voltage drop of 5.6v!!!
Check the CR2 voltage.

Without the Q2 base 2.5V clamp voltage, limiting the current, its most likely that the LD has died.

The reduced Vrail voltage will also adversley effect the control of the photodiode monitoring feedback loop.
The conduction current thru the monitor photodiode and R5, R4, R7 path will be lower, so the switch on voltage of Q1 will be
reduced, hence the current in the LD will be higher than required before the monitor cct responds.

Regards

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ericgibbs said:

Hi Ron,
Sorry about delayed response.

The CR2 device as I understand from the datasheet will sink 10mA, if its not configured in the programmable mode?

The way I see CR2 working is that it acts a base clamp voltage for the LD drive transistor, so that the voltage drop across the 10R shuts off the the driver when the maximum rated current is reached?

I cant see a CR3, do we a different drawing? [Ive attached the one Im using]
Regards

EDIT: attachment.

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