In led driving, 8 pins are hardly light up at the same time! Even with some period over current in VDD, that does not mean disarst at all. am I right? BR, ----- Original Message ----- From: To: "Microcontroller discussion list - Public." Sent: Tuesday, February 22, 2005 10:13 AM Subject: Re: [EE] IC Sugestion: serial->parallel shift register > Hello people, > > Jinx wrote: > > Can you add 8 transistors or one of the ULN2xxx family ? > > Perhaps a ULN is a bit over-rated for this. Reliable though > > this is a good idea, but I have space constraints on this PCBs. > Actually, the bigger problem quantity of PCB traces. > > > If you intend using pulses with a short but known maximum width > > then the value of the series resistor can be lowered, maybe you can > > get your 20mA that way. The LEDs in moving signs often have as > > low as 47R with 12V, but only because they are driven with short > > pulses. Normally 12V + 47R would kill a LED stone dead > > I will do some PWMing, but no short-overrated-currente-pulses. Thi= s > is the reason the MAX6966 seens so great: Already can do PWM, 20mA > constant current outputs. > > microsoftwarecontrol wrote: > > read hc595 datasheet: max output is 25mA and just good for you. > > Nope, read it again: "VCC or GND current =B170 mA max". > > 70/8=3D8.75 on each PIN. But it's the max current, and even if > there's no quiescent current, it's very hard to extract all this on a > single HC part. > > Dominic Stratten wrote: > > I use smt 16f627a a fair bit to do this kind of thing. > > You have the added advantage of being able to pwm the display as wel= l > >for dimming. > > Have you been using the F627 output direct to LED without a > resistor? I've made some tests and the PIC drives the LED, directly, > with about 18-19mA. Seens fine. Datasheet says "Maximum current into VD= D > pin 250 mA" so I think this is reliable. > > Tobias wrote: > > how about something old fashioned such as a BC847C Transistor on eac= h > >of the 74HC595 outputs - or something like an BCR108W for lower > >component count. > > Already thought of this, but again I would preffer to have the > lowest component count possible because of my lack of space on the PCB. > Anyway, the BCR108W is a neat part... it's a possibility... > > > > Russell McMahon wrote: > > You can also get driver IC's that combine shift register and latchin= g > > and drivingh functions. usually dearish. > > do you remember the part numbers? > > > I like the MM5450 family. Old but good. 40 pin DIPs usually but MANY > > segments and driven easily with just 2 PIC pins. There are also > > LCD driving versions. > > Very interesting part. Big, so it could be hard to use on my proje= ct. > > Thanks you all, > > Brusque > > -- > --------------------------------------------------------------------- > Edson Brusque C.I.Tronics Lighting Designers Ltda > Research and Development Joinville - SC - Brazil > http://www.ryan.com.br/netiqueta.htm www.citronics.com.br > --------------------------------------------------------------------- > > > -- > --------------------------------------------------------------------- > Edson Brusque C.I.Tronics Lighting Designers Ltda > Research and Development Joinville - SC - Brazil > http://www.ryan.com.br/netiqueta.htm www.citronics.com.br > --------------------------------------------------------------------- > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist