Simple "LED driver" chip?
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From: Richard H. on 13 Apr 2006 13:46 linnix wrote: >>So far, I've found a discrete 2N7002 MOSFET with great specs (overkill, >>actually) at $0.04 in a similar tiny package; at this price, I could >>afford to buy a reel if I can't find a disti that'll do cut tape. > > We got a few hundreds spare 2N7002 (100mA). If you can't find what you > need, we can send you some. Shipping is probably more than the cost > anyway. Thanks - I really appreciate the offer. What mfr & package type do you have surplus in? Digikey has the "larger" SOT-23 in cut tape, but at least for ON's part# they don't stock the smaller SC-75 package. More digging is in order with alternate disti's and other manufacturers. I had to chuckle that ON would sample 10 for free, but charges $11 shipping. I'd pay for more to make the S&H worthwhile, but they don't offer that option. More vendors should follow Microchip's model of offering all their parts direct; they can offer better selection than the disti's and charging a small premium will keep the disti's happy.
From: Rich Grise on 13 Apr 2006 13:50 On Thu, 13 Apr 2006 16:38:45 +1000, Andrew M wrote: > "Richard H." <rh86(a)no.spam> wrote in message news:31m%f.426$AB3.11(a)fed1read02... >> Rocky wrote: >>> The 2N7002 may be a good fit. FET with low threshold voltage and low on >>> resistance. >> >> Indeed, this looks very promising. In particular, ON Semi's version in a tiny 1.6mm >> SC-75 package for 4 cents. >> >> After wallowing a while in Digikey's search engine, I tried a different approach... >> I jumped over to ON Semi's site and sorted by price (something Digikey won't do). >> Thinking I'd work my way up the price list, I stopped after the first entry, which >> was a 2.7 cent 2N7002. Good enough for my purposes, but the smaller version was >> worth the extra penny. :-) > > Depending where you have stuff manufactured, the LED-specific constant current drivers > are likely to be cost-effective against the loading and procurement cost of all those > discretes, and the reliability issues surrounding so many parts. Part prices are only > part of the picture. > > They're damn easy to use too. Where do you get one? The last time I checked for a constant-current diode (AKA "field-effect diode") they were about five bucks a pop! Thanks, Rich
From: rickman on 13 Apr 2006 17:05 Richard H. wrote: > rickman wrote: > > Interesting that everyone focuses on transistors rather than more > > integrated solutions. An interface chip I use a lot is the NC7WZ17P6X > > dual buffer in a 6 pin SC70 package, about 2 mm square. It will drive > > 24 mA at LVCMOS levels and will handle up to +-7 volts on the input. > > With 5 volt Vcc it will drive up and down at 32 mA. I don't think you > > can touch the density with transistors and we are only paying $0.06 > > each or $0.03 per driver. > > > > I recently removed a bunch of SOT23 transistors from my design and > > replaced them with these, some to drive LEDs. > > Thanks! Half the battle seems to be finding these bargains when you > need them. The other half seems to be getting distributors to talk with > a small guy (even if you're willing to buy a reel). > > I agree with you on using arrays where possible, and this package > certainly seems small. I'll give it a look. Small PCB size is > important to this project, so discretes are attractive because they can > be squeezed into small spaces (even though the overall density is worse). > > So far, I've found a discrete 2N7002 MOSFET with great specs (overkill, > actually) at $0.04 in a similar tiny package; at this price, I could > afford to buy a reel if I can't find a disti that'll do cut tape. Keep in mind that the NC7WZ17P6X has *two* devices in this small package and you can get cut tape from Digikey.
From: linnix on 13 Apr 2006 19:03
Richard H. wrote: > linnix wrote: > >>So far, I've found a discrete 2N7002 MOSFET with great specs (overkill, > >>actually) at $0.04 in a similar tiny package; at this price, I could > >>afford to buy a reel if I can't find a disti that'll do cut tape. > > > > We got a few hundreds spare 2N7002 (100mA). If you can't find what you > > need, we can send you some. Shipping is probably more than the cost > > anyway. > > Thanks - I really appreciate the offer. What mfr & package type do you > have surplus in? We have the SOT-23. I think they are Phillips. > > Digikey has the "larger" SOT-23 in cut tape, but at least for ON's part# > they don't stock the smaller SC-75 package. More digging is in order > with alternate disti's and other manufacturers. > > I had to chuckle that ON would sample 10 for free, but charges $11 > shipping. I'd pay for more to make the S&H worthwhile, but they don't > offer that option. More vendors should follow Microchip's model of > offering all their parts direct; they can offer better selection than > the disti's and charging a small premium will keep the disti's happy. We can send you 50 for $10, including shipping. |