Infrared 3W LED
- Wavelength: 850nm
- Diameter: 2cm
- Voltage: 1.5V~1.7V
- Current: 1500mA
- Replacement emitter board for flashlight
Well, if that's true [and I'm not sure how you can know it is], then there is a huge issue of power dissipation. Either that HY4D is more like a p-channel MOSFET, with a very low channel resistance [in saturation] AND that 4XY6 is
somehow managing to limit current to 1500mA, without frying, or the HY4D is some mysterious marvel that can cut 3.3V down to the 1.5V~1.7V needed to properly drive that 3W LED...makes no sense what-so-ever!
To drop 3.3V down to even 1.5V [the least worst case condition] would require:
(3.3 - 1.5) * 1.5A = 2.7W!!!!How the heck are either of those tiny little parts going to dissipate that kind of power? I mean, they gotta be linear, 'cuz there are no Switch Mode related parts--anywhere!
BUT, I'm guessing that the HY4D
is a p-channel MOSFET [one with a
very low Gate Threshold Voltage] -- that's the only way, so far, I can see this thing even beginning to function properly. But, that 3k3 resistor is rather odd--really doesn't need to be that low, if all it's doing is pulling up the Gate on a MOSFET [unless, maybe, that MOSFET needs to switch
really fast--which might be the case if that LED
really is 3W]! BUT, really, I doubt it's a 3W LED [or there's more to this circuit than has been revealed]! Another possibility is that the 3k3 resistor was chosen to set the sensitivity of the LDVR [by imposing a greater current load -- but, again, the variability of transistor Beta would seem to make that a rather touchy design decision.
