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Help with chip ID?

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I’ll try to keep this short as I lost the long version took too long, timed out, and I lost it :)  I was also thinking g the problem out along the way :)

The chip is to a constant current laser driver (poorly built as evidenced by the zoomed out picture)

Why the request for ID?  I’d like to turn down the current.  The green diode died in maybe 10 minutes of use at 20% power (by pwm). 

What I think I know:
red laser:  900mA.  Driver circuitry is “missing” a 1 ohm resistor vs the others and a diode.  “Suspected sense” resistor 270 ohms.  Suspected sense resistor divided by likely current setting:  300. The other side of the inductor does have a slightly different Zener as well, 2W7 labeled vs 2WC for the green and blue. A separate zener is also different...so I suspect this, plus the “missing” components sets the lower range..

Green laser:  1.8A (claimed, but probably a fake ndg7475).  1 ohm resistor, both diodes, “suspected sense” resistor 240 ohms.  Suspected sense resistor divided by likely current setting: 133.33333

Blue laser: 1.5A (again claimed for max, continuous is 1.2).  1 ohm resistor, both diodes, “suspected sense” resistor 200 ohms.  Resistor divided by likely current setting 133.333333

So, my guesses are:
The missing diode is either a mistake, or since they are  in parallel to one another and across one side of the inductor, maybe the diodes are to just prevent back emf and the higher current setting requires a “bigger” diode (or 2 in parallel).

The 1 ohm resistor has me a bit puzzled.  It is in parallel to the resistor I’m calling the sense resistor, so if we add them up we have less than 1 ohm
As a sense resistor.  That doesn’t make sense much sense...pun not precisely intended :)  they are connected to the other side of the inductor from
the diode(s) through a 10 ohm
Resistor and some filter capacitors.  However, the inductor is also connected on that side via the zener to ground.   

That’s about as far as I got though.  Figured the datasheet might have a reference circuit, and I’d bet this driver would be that reference circuit :)

Anyhow, if you know what this chip is, or have experience with these circuits and can confirm my inferences that would be appreciated :)

It could be QX5241.


That looks really promising...especially considering that the sense circuitry does appear to be connected to the high side....

I kept searching with the lower case r figuring that seemed unique and would get me to the right chip...I feel pretty dumb now :)

When I get home I’ll have a closer look, but I’m pretty sure that solves it.

Hmm, well, the dim pin doesn’t line up, nor do the specs (this will....if the vendor is to be believed, pwm at 30KHz). (Actually Useful in a laser projector). So I guess the hunt is still on...

I think QX Micro Devices is a manufacturer of this IC.


You can contact them for the specifications and the datasheet.


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