Forums

Most suitable driver chip

Started by Unknown May 22, 2008
I have a matrix of LED's, six rows and seven columns:

    X    X    X    X    X    X    X

    X    X    X    X    X    X    X

    X    X    X    X    X    X    X

    X    X    X    X    X    X    X

    X    X    X    X    X    X    X

    X    X    X    X    X    X    X

Across the rows, the LED's anodes are common, and each row has a
single microcontroller pin.

Down the columns, the LED's cathodes are common, and each column has a
single microcontroller pin.

The row pins have to source 25 mA, which isn't a problem for the =B5C.
The column pins, however, need to sink 150 mA (150 mA =3D the current
that will flow if every LED in a column is lit).

Because the column pins can only sink a maximum of 25 mA, I was going
to use a transistor to provide the extra current. Since I have 7
column pins though, I'm going to need 7 transistors, which is why I'm
thinking of going with a "transistor array".

I'm just wondering is there any "bread and butter" chip that people
use for this? I've had a quick look at the ULN200X family and they
look kind of suitable. If I was picking my own transistors, I'd use
FET's as switches (instead of bi-polars), but I suppose if I the
driver chip has a base resistor inside it, and if there's negligible
current flow when it's turned off, then maybe a BJT array will be OK.

(Of course I'd be wise to switch the rows and columns so that I only
need 6 transistors, but I'll get on to that later)

So what would you use as a "driver chip"? My microcontroller pins work
at 5 V for high and 0 V for low.
Tom�s � h�ilidhe wrote:
> I have a matrix of LED's, six rows and seven columns: > > X X X X X X X > > X X X X X X X > > X X X X X X X > > X X X X X X X > > X X X X X X X > > X X X X X X X
http://www.suckow.de/ralf/ledmatrix4x20/ http://www.suckow.de/ralf/ledmatrix4x20/LEDMATRIX4x20.pdf shows a good example of the 2003 used in LED configuration. I'll bet you will find heaps if you google uln2003 and leds Cheers Don... -- Don McKenzie Site Map: http://www.dontronics.com/sitemap E-Mail Contact Page: http://www.dontronics.com/email Intelligent 2.83" AMOLED with touch screen for micros: http://www.dontronics-shop.com/product.php?productid=16699
Tom�s � h�ilidhe wrote:
> > I have a matrix of LED's, six rows and seven columns: > > X X X X X X X > X X X X X X X > X X X X X X X > X X X X X X X > X X X X X X X > X X X X X X X > > Across the rows, the LED's anodes are common, and each row has a > single microcontroller pin. > > Down the columns, the LED's cathodes are common, and each column > has a single microcontroller pin. > > The row pins have to source 25 mA, which isn't a problem for the > �C. The column pins, however, need to sink 150 mA (150 mA = the > current that will flow if every LED in a column is lit).
You haven't considered limiting the individual LED currents. -- [mail]: Chuck F (cbfalconer at maineline dot net) [page]: <http://cbfalconer.home.att.net> Try the download section. ** Posted from http://www.teranews.com **
Tom&#2013265921;s &#2013265939; h&#2013265929;ilidhe wrote:
> I'm just wondering is there any "bread and butter" chip that people > use for this? I've had a quick look at the ULN200X family and they > look kind of suitable.
The ULN2003 is the NE555 of the Driver market. Widely sourced, and 'cheap as chips'. Great if you can tolerate the Darlington characteristics. -jg
> You haven't considered limiting the individual LED currents.
=B5C pin ---> 150 ohm resistor ---> LED ---> transistor ---
> ground
Tom&#2013265921;s &#2013265939; h&#2013265929;ilidhe wrote:
> >> You haven't considered limiting the individual LED currents. > > &#2013266101;C pin --> 150 ohm resistor --> LED --> transistor --> ground
Yup. How much current flows through the resistor? How much of that flows through each LED. We have known about Ohms law for some time. You have trimmed too much, so other readers can't tell what this is about. -- [mail]: Chuck F (cbfalconer at maineline dot net) [page]: <http://cbfalconer.home.att.net> Try the download section. ** Posted from http://www.teranews.com **
On Mon, 26 May 2008 09:26:34 -0700 (PDT), linnix
<me@linnix.info-for.us> wrote:

>On May 26, 10:23 am, donald <Don...@dontdoithere.com> wrote: >> Tom&#2013265921;s &#2013265939; h&#2013265929;ilidhe wrote: >> >> > Does anyone else see a problem with taking 25 mA from a >> > microcontroller pin that's rated for 25 mA maximum? >> >> I would look at the data sheet directly and see what is says. >> >> Is this micro-controller a secret ? >> >> Lets all take a look at the data sheet involved and see if this >> micro-controller would have a problem with this. >> >> donald > >I read 25mA max per pin and 90mA max per chip. Namely, no more than 3 >leds on at any time.
http://ww1.microchip.com/downloads/en/devicedoc/41202C.pdf I see Abs. Max 25mA/port pin and 200mA max combined port A and C, and a prominent (not that it has to be) note: "This is a stress rating only and functional operation of the device at those or any other conditions above those indicated in the operation listings of this specification is not implied. Exposure to maximum rating conditions for extended periods may affect device reliability." Now, let's look at "operation listings"-- parameter D080 is the highest rating (8.5mA sink). That would be a good number not to exceed. And D090 (-3.0mA source). There's another. Of course if you don't care if device reliability is affected, then it doesn't much matter. In fact there's not much point in looking at the data sheet at all if you're going to only pay attention selectively. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
On Mon, 26 May 2008 10:46:14 -0700 (PDT), linnix
<me@linnix.info-for.us> wrote:

>On May 24, 6:38&#2013266080;pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat> >wrote: >> On Mon, 26 May 2008 09:26:34 -0700 (PDT), linnix >> >> >> >> >> >> <m...@linnix.info-for.us> wrote: >> >On May 26, 10:23 am, donald <Don...@dontdoithere.com> wrote: >> >> Tom&#2013265921;s &#2013265939; h&#2013265929;ilidhe wrote: >> >> >> > Does anyone else see a problem with taking 25 mA from a >> >> > microcontroller pin that's rated for 25 mA maximum? >> >> >> I would look at the data sheet directly and see what is says. >> >> >> Is this micro-controller a secret ? >> >> >> Lets all take a look at the data sheet involved and see if this >> >> micro-controller would have a problem with this. >> >> >> donald >> >> >I read 25mA max per pin and 90mA max per chip. &#2013266080;Namely, no more than 3 >> >leds on at any time. >> >> http://ww1.microchip.com/downloads/en/devicedoc/41202C.pdf >> >> I see Abs. Max 25mA/port pin and 200mA max combined port A and C, > >And a 95mA max Idd and Iss, so you can't do more than 95mA absolutely.
Where are you getting that number from? On page 127 (PDF page 129) Abs. max Idd is 250mA Abs. max Iss is 300mA Abs. max current sunk by PORTA and C combined 200mA Abs. max current sourced by PORTA and C combined 200mA Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
On Mon, 26 May 2008 11:48:30 -0700 (PDT), linnix
<me@linnix.info-for.us> wrote:

>On May 26, 11:35 am, linnix <m...@linnix.info-for.us> wrote: >> On May 24, 6:58 pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat> >> wrote: >> >> >> >> > On Mon, 26 May 2008 10:46:14 -0700 (PDT), linnix >> >> > <m...@linnix.info-for.us> wrote: >> > >On May 24, 6:38 pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat> >> > >wrote: >> > >> On Mon, 26 May 2008 09:26:34 -0700 (PDT), linnix >> >> > >> <m...@linnix.info-for.us> wrote: >> > >> >On May 26, 10:23 am, donald <Don...@dontdoithere.com> wrote: >> > >> >> Tom&#2013265921;s &#2013265939; h&#2013265929;ilidhe wrote: >> >> > >> >> > Does anyone else see a problem with taking 25 mA from a >> > >> >> > microcontroller pin that's rated for 25 mA maximum? >> >> > >> >> I would look at the data sheet directly and see what is says. >> >> > >> >> Is this micro-controller a secret ? >> >> > >> >> Lets all take a look at the data sheet involved and see if this >> > >> >> micro-controller would have a problem with this. >> >> > >> >> donald >> >> > >> >I read 25mA max per pin and 90mA max per chip. Namely, no more than 3 >> > >> >leds on at any time. >> >> > >>http://ww1.microchip.com/downloads/en/devicedoc/41202C.pdf >> >> > >> I see Abs. Max 25mA/port pin and 200mA max combined port A and C, >> >> > >And a 95mA max Idd and Iss, so you can't do more than 95mA absolutely. >> >> > Where are you getting that number from? On page 127 (PDF page 129) >> > >OK, your link is dated 2004: >http://ww1.microchip.com/downloads/en/devicedoc/41202C.pdf > >> > Abs. max Idd is 250mA >> > Abs. max Iss is 300mA >> > Abs. max current sunk by PORTA and C combined 200mA >> > Abs. max current sourced by PORTA and C combined 200mA >> > >My link is dated 2007: > >> Page 131 ofhttp://ww1.microchip.com/downloads/cn/DeviceDoc/cn011811.pdf >> >> That's strange. Are we looking at the same chip, PIC16F684? > >So, I won. This is progress (LOL). Probably process shrink.
Yup, you win, although my suggested conservative numbers of 8.5mA/-3mA (IIRC) would be rather safe in either case (unless you're trying to sink 8.5mA from all 11 port pins at once, in which case it's a bit over). Usually they add an "A" or "B" when they do a process shrink because some characteristics inevitably change a bit. I think they discovered it dies REALLY fast at 200mA, and just revised the data sheet rather than revising the part! Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
On May 22, 11:12=EF=BF=BDpm, Tom=EF=BF=BDs =EF=BF=BD h=EF=BF=BDilidhe <t...@=
lavabit.com> wrote:
> I have a matrix of LED's, six rows and seven columns: > > =EF=BF=BD =EF=BF=BD X =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =
=EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX
> > =EF=BF=BD =EF=BF=BD X =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =
=EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX
> > =EF=BF=BD =EF=BF=BD X =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =
=EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX
> > =EF=BF=BD =EF=BF=BD X =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =
=EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX
> > =EF=BF=BD =EF=BF=BD X =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =
=EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX
> > =EF=BF=BD =EF=BF=BD X =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =
=EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX =EF=BF=BD =EF=BF=BDX
> > Across the rows, the LED's anodes are common, and each row has a > single microcontroller pin. > > Down the columns, the LED's cathodes are common, and each column has a > single microcontroller pin. > > The row pins have to source 25 mA, which isn't a problem for the =EF=BF=BD=
C.
> The column pins, however, need to sink 150 mA (150 mA =3D the current > that will flow if every LED in a column is lit). > > Because the column pins can only sink a maximum of 25 mA, I was going > to use a transistor to provide the extra current. Since I have 7 > column pins though, I'm going to need 7 transistors, which is why I'm > thinking of going with a "transistor array". > > I'm just wondering is there any "bread and butter" chip that people > use for this? I've had a quick look at the ULN200X family and they > look kind of suitable. If I was picking my own transistors, I'd use > FET's as switches (instead of bi-polars), but I suppose if I the > driver chip has a base resistor inside it, and if there's negligible > current flow when it's turned off, then maybe a BJT array will be OK. > > (Of course I'd be wise to switch the rows and columns so that I only > need 6 transistors, but I'll get on to that later) > > So what would you use as a "driver chip"? My microcontroller pins work > at 5 V for high and 0 V for low.
First off 25mA is going to give you a dim display unless you are useing low current leds. ULN200x chips were designed to drive 7Seg led displays, so a perfect choice for you. PNP bjts are cheapest and simplest for the rows. You seem to have the rows/colomns mixed up.