how do you drive leds?

V

valentin tihomirov

Guest
We have to control hundreds of typical colour leds (a couple of mA) and
optocouplers (1mA). The device is not portable; however, I would like 1 -
not to waste energy on the ballast resistors and 2 - reduce amount of the
resistors. Can you point to the guidelines on the issue? In addition, the
optocouplers have open collector outputs; that is, the outputs have to be
pulled up by more power and resistors.
 
valentin tihomirov wrote:

We have to control hundreds of typical colour leds (a couple of mA) and
optocouplers (1mA). The device is not portable; however, I would like 1 -
not to waste energy on the ballast resistors and 2 - reduce amount of the
resistors. Can you point to the guidelines on the issue? In addition, the
optocouplers have open collector outputs; that is, the outputs have to be
pulled up by more power and resistors.
Click to expand...
Hi,

What are you driving the LED's from? Computer, controller board,
microcontroller? Any way you hack it, it will take 1 digital output per
LED/OPTO; and this takes a lot of driver chips.

--
Luhan Monat (luhanis 'at' yahoo 'dot' com)
"The future is not what it used to be..."
http://members.cox.net/berniekm
 
Luhan Monat wrote:

valentin tihomirov wrote:

We have to control hundreds of typical colour leds (a couple of mA) and
optocouplers (1mA). The device is not portable; however, I would like 1 -
not to waste energy on the ballast resistors and 2 - reduce amount of the
resistors. Can you point to the guidelines on the issue? In addition, the
optocouplers have open collector outputs; that is, the outputs have to be
pulled up by more power and resistors.



Hi,

What are you driving the LED's from? Computer, controller board,
microcontroller? Any way you hack it, it will take 1 digital output per
LED/OPTO; and this takes a lot of driver chips.

-- unless you're turning on LED's, Opto's or both in groups -- then you
Click to expand...
could gang things together.

You can get optos with different outputs -- do some web searches.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
On Tue, 22 Feb 2005 00:56:13 +0200, "valentin tihomirov" <spam@abelectron.com>
wroth:

We have to control hundreds of typical colour leds (a couple of mA) and
optocouplers (1mA). The device is not portable; however, I would like 1 -
not to waste energy on the ballast resistors and 2 - reduce amount of the
resistors. Can you point to the guidelines on the issue? In addition, the
optocouplers have open collector outputs; that is, the outputs have to be
pulled up by more power and resistors.
Click to expand...
Welcome to the REAL world.

Jim
 
"valentin tihomirov" <spam@abelectron.com> wrote in message
news:37v6vtF5gki77U1@individual.net...
We have to control hundreds of typical colour leds (a couple of mA) and
optocouplers (1mA). The device is not portable; however, I would like 1 -
not to waste energy on the ballast resistors and 2 - reduce amount of the
resistors. Can you point to the guidelines on the issue? In addition, the
optocouplers have open collector outputs; that is, the outputs have to be
pulled up by more power and resistors.


Use resistor packs to reduce component count. Is the power saving really
Click to expand...
critical enough to worry about? How much do you want to save?

Ken
 
Use resistor packs to reduce component count.
Click to expand...
IMO, the packs violate the main design concept - divide and conquer.



Is the power saving really critical enough to worry about?
How much do you want to save?
Click to expand...
Personally, I do not like useless wastes. As a noob, Im just asking about
adopted practices. The power is 3.3v, diodes drop 1v..1.5v, the rest drops
at the ballast. I suppose 50..100%. In one circuit there are 32 optocoupler
diodes and source voltage is 30v; that is, 30 times more power will be burnt
than required to activate optocoupler. So I think, the total reduction can
be about 4 times.
 
"valentin tihomirov" <spam@abelectron.com> wrote in message
news:37vik6F5ibqsmU1@individual.net...
Use resistor packs to reduce component count.

IMO, the packs violate the main design concept - divide and conquer.
Click to expand...
What do you mean by that/ You didn't mention anything like that before.


Is the power saving really critical enough to worry about?
How much do you want to save?

Personally, I do not like useless wastes. As a noob, Im just asking about
adopted practices. The power is 3.3v, diodes drop 1v..1.5v, the rest drops
at the ballast. I suppose 50..100%. In one circuit there are 32
optocoupler
diodes and source voltage is 30v; that is, 30 times more power will be
burnt
than required to activate optocoupler. So I think, the total reduction can
be about 4 times.

Maybe you should look at the design again and decide if you are approaching
Click to expand...
it correctly. If power usage and component count are so critical you should
look from top down again.

Ken
 
IMO, the packs violate the main design concept - divide and conquer.
What do you mean by that/ You didn't mention anything like that before.
Click to expand...
Nothing special. The major design concept which reduces amount of
information enabling creation of complex systems is hierarchy. The the
partition incapsulates functionality into hierarchy modules. The purpose of
the partition, is to break down a solid block of N elements (complexity =
number of interconnections is about N^2) into loosely interconnected tight
pieces. The resistor packs will increase connectivity between modules. In
addition, my CAD does not support multple sections of a component spread
over design modules enforcing the HW hierarcy.
 
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