Simple "LED driver" chip?

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.

On Thu, 13 Apr 2006 16:38:45 +1000, Andrew M wrote:
> "Richard H." <rh86@no.spam> wrote in message news:31m%f.426$AB3.11@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

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.

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.