Simple "LED driver" chip?
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From: Rich Grise on 7 Apr 2006 16:13 On Fri, 07 Apr 2006 07:39:59 -0700, Richard H. wrote: .... > That brings me back to the question about the generic part numbers - in > this case, a general-purpose transistor. Is there a book (website?) MMBT2222: http://www.fairchildsemi.com/ds/MM/MMBT2222.pdf Cheers! Rich
From: Jim Granville on 7 Apr 2006 18:35 Richard H. wrote: > That brings me back to the question about the generic part numbers - in > this case, a general-purpose transistor. Is there a book (website?) > that offers a good reference for these part numbers and their > characteristics? (E.g., Lancaster's TTL and CMOS cookbooks have about > 100 pages of reference for logic chips, but it seems there's a lot more, > and there are newer processes.) Resistor Equipped Transistors are now quite common, and cheap. So they are a good digital interface device, where you go outside the uC pins abilities. See the Philips web site, and they also have dual RETs with PNP/NPN designed for level shifting, giving (eg) 12V hi side drive from a uC pin, in a single SOT23-6 style package. -jg
From: Joseph2k on 9 Apr 2006 13:02 Richard H. wrote: > Spehro Pefhany wrote: >> If it's several, as in 2 or 3, just use transistors, BJT or MOSFET. >> Darlington arrays as others have suggested would be better if you have >> more than four... keep in mind that they have significant foward drop >> on a 3-5V circuit (which may be a factor if you're using blue or white >> LEDs). You might also be able to use a HCMOS shift register. > > > Thanks to everyone for the quick comments! > > The need here is very simple, so I'm reluctant to use a feature-rich / > pricey part (we'll be making a lot of these; the forward voltage drop > would also be an issue). We'll probably do 4-5 LEDs per MCU. > > The flexibility of discrete transistors sounds good (and possibly very > cheap); since I'm doing SMT, we could get them pretty small too. Hmmm. > > I'll do some AoE reading and look at the discrete designs offered here. > > > That brings me back to the question about the generic part numbers - in > this case, a general-purpose transistor. Is there a book (website?) > that offers a good reference for these part numbers and their > characteristics? (E.g., Lancaster's TTL and CMOS cookbooks have about > 100 pages of reference for logic chips, but it seems there's a lot more, > and there are newer processes.) > > >> If you're running small LEDs at that high a current you >> may well have reliability and lifetime problems, particularly when the >> ambient temperature gets high. > > No problem here. They're not normal LEDs; they're high intensity > (several hundred mcd, but not the multi-candela ones), and I'll be > running them well below rating. > > Thanks! > Richard Please do not rule out transistor arrays in sot23 packages. Half a dozen transistors in a 14 pin package (emitters tied to pins 7/14).
From: Spehro Pefhany on 9 Apr 2006 14:10 On Fri, 07 Apr 2006 07:39:59 -0700, the renowned "Richard H." <rh86(a)no.spam> wrote: >That brings me back to the question about the generic part numbers - in >this case, a general-purpose transistor. Is there a book (website?) >that offers a good reference for these part numbers and their >characteristics? No, AFAIK. Look at distribution quantities-in-stock and prices or ask. There are thousands of part numbers which will work, and dozens which are close to optimal depending where the product is being built and how many. For low to moderate quantities in North America you can't go far wrong using MMBT4401/4403 for NPN/PNP. Google for data sheets, there are many, many manufacturers. 'Digital' transistors (transistors with base and maybe E-B resistors built-in) and digital transistor arrays were developed originally in Japan by Rohm and are now multiple sourced & are very popular in consumer goods, but generally not quite as cheap and easily available as resistors or resistor networks and discrete parts in low quantities. Generally the transistors 'inside' are referenced to popular Japanese discrete transistor part numbers. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff(a)interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
From: Rocky on 9 Apr 2006 14:30
Spehro Pefhany wrote: > On Fri, 07 Apr 2006 07:39:59 -0700, the renowned "Richard H." > <rh86(a)no.spam> wrote: > > >That brings me back to the question about the generic part numbers - in > >this case, a general-purpose transistor. Is there a book (website?) > >that offers a good reference for these part numbers and their > >characteristics? > > No, AFAIK. Look at distribution quantities-in-stock and prices or ask. > > There are thousands of part numbers which will work, and dozens which The 2N7002 may be a good fit. FET with low threshold voltage and low on resistance. Regards Robert |