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| Help identify this chip? EM1701G |
| (1/1) |
| MattHollands:
Hi, I was playing around with reverse engineering a broken PIR activated LED lamp and I came across a chip I cannot find a data sheet for. My best guess is that it is a constant current regulator to keep the LEDs at a constant brightness, but I want to know for sure. Attached are photos of the board, the chip and my reverse-engineered schematic. |
| MattHollands:
No suggestions? Does anyone recognise the logo on the chip? |
| SiliconWizard:
Can't find this reference anywhere... but you could always ask those guys: https://www.luceco.com/uk/page/contact ;D Anyway, I think you got it right that it must form a constant current sink. Judging from your schematic, one possible option would be that this is actually a depletion MOSFET, used as a constant current sink, with the 22 ohm resistor setting the constant current. You can have a look at this for more info: https://www.infineon.com/dgdl/Infineon-Application_Note_Applications_for_Depletion_MOSFETs-AN-v01_00-EN.pdf?fileId=5546d4624cb7f111014cd63d1a197d94 Edit: I thought suggesting a depletion MOSFET was kind of fancy and an opportunity for some to learn about them. One other, probably more obvious possibility is that the chip would be an adjustable linear regulator, similar to an LM317 or so. Note the typical ref. voltage of linear regulators is most often 1.25V or less; that would mean here, a current of ~57mA or less. Sounds a bit on the low side for a LED lamp, but I don't know about its rated power at all; it can be perfectly possible: 18 LEDs in series, with say ~3V Vfd each, that's 54V => ~3W. Not sure why they went with a ~200V supply though, it looks largely overkill here? (But maybe it's a basic design to accomodate for many variants of lamps with more LEDs.) Note that a LM317 would not cut it here. You'd need to use a regulator that can take at least 150V or so. A possible replacement candidate would be the TL783. (Additional edit: searches on both Mouser and Digikey gave the TL783 for >= 150V input voltage regulators, but the datasheet says 125V, so we'd probably have to look elsewhere. There are some regs that could be a fit, but not many at all.) The benefit of a linear reg over a depletion MOSFET is that the set current will be easy to set and with little variability from one device to another, so I'd lean towards this. One additional thought - here the regulator (or transistor) would have to dissipate around 150*57e-3 ~8.6W. This thing must be getting pretty hot while ON. (If you're sure about the 200V supply though.) |
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