Help with chip ID? - Page 1
Forum section: electronics / projects

author: Corryl
author_rank: Newbie
timestamp: December 07, 2021, 05:16:38 am
content: I’ll try to keep this short as I lost the long version took too long, timed out, and I lost itI was also thinking g the problem out along the wayThe 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: 133.33333Blue 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 133.333333So, 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 ohmAs a sense resistor. That doesn’t make sense much sense...pun not precisely intendedthey are connected to the other side of the inductor fromthe diode(s) through a 10 ohmResistor 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 circuitAnyhow, if you know what this chip is, or have experience with these circuits and can confirm my inferences that would be appreciated

author: 8goran8
author_rank: Contributor
timestamp: December 07, 2021, 02:09:14 pm
content: It could be QX5241.https://www.flashled.com.ua/images/pdf/qx5241_en.pdf

author: Corryl
author_rank: Newbie
timestamp: December 07, 2021, 08:04:46 pm
content: 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 nowWhen I get home I’ll have a closer look, but I’m pretty sure that solves it.

author: Corryl
author_rank: Newbie
timestamp: December 08, 2021, 05:42:08 am
content: 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...

author: 8goran8
author_rank: Contributor
timestamp: December 08, 2021, 05:12:01 pm
content: I think QX Micro Devices is a manufacturer of this IC.http://www.qxmd.com.cn/productmores/86/5/30.htmlYou can contact them for the specifications and the datasheet.

author: Corryl
author_rank: Newbie
timestamp: December 09, 2021, 03:23:58 am
content: The logo certainly looks identical. I wonder if the r is a custom chip...I might try to contact them, or spend some more time reverse engineering.