FlexMod bias current can not go down to 0

Hi there,

I got a flexmod and 2W 445nm, I can successfully switch the laser on/off by sending TTL signals (0/5V), but I can not set the standby bias current to 0. I turned the bias pot to the minimum, but i still read around 15ma, any advice or test i can do? Thanks!

TTL inputs usually control the current going into the diode. But not the circuitry of the driver. You will have to use a switch on the driver inputs.

djQUAN said:

TTL inputs usually control the current going into the diode. But not the circuitry of the driver. You will have to use a switch on the driver inputs.

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Hi, djQUAN

Thanks for your answer, but I'm afraid i didn't quite get your point, what switch you are referring to?

Sorry I missed one piece of information in the previous post, I basically shorted the modulation input to ground, which for sure is 0V, but I still read 15ma current.

I think your answer is giving me hints, but could you elaborate more? Thanks!

15mA into the driver, or 15mA out of the driver?

The driver circuitry is always on if you apply power no matter how you mess with the modulation input. The modulation input just controls the amount of current going out of the driver.

So if you set the modulation to zero, your output is zero but the driver circuitry remains operating, waiting for the modulation to change.

You will need a switch for the power input to disconnect the whole thing from the battery to get zero quiescent current draw if you want totally no current consumption when off.

Is it a Flexmod P3 ? ,

The idea is to use the bias pot to set the current to the diode threshold and then the TTL input will take the current from bias set to maximum set diode current

Is there a main reason you need the bias current to be zero , 15ma is quite below the lasing threshold of the 445nm diodes assuming its 15ma though the diode and not just the driver circuit itself pulling current ( more likely the diode is getting the 15ma )

For you the only way to stop this is to remove power fully from the flexmod .

Thanks all, it is 15mA out of the driver, yes, disconnecting the power supply is the best way to cut off the current, but that's not my purpose.

With the 15mA, i can see very dim light coming out of the laser. ionlaser555 is right, 15ma is below the laser threshold, it is fine with my application.