FPGA Central - World's 1st FPGA / CPLD Portal

FPGA Central

World's 1st FPGA Portal

 

Go Back   FPGA Groups > NewsGroup > FPGA

FPGA comp.arch.fpga newsgroup (usenet)

Reply
 
LinkBack Thread Tools Display Modes
  #1 (permalink)  
Old 04-27-2006, 04:41 PM
Guest
 
Posts: n/a
Default LED Driver

Hi,
We would like to drive LEDs using Ramp Waveforms using Xilinx CPLDs.
Is it possible to write a driver and control the LED directly from CPLD
or should an external D/A Converter be used?

Reply With Quote
  #2 (permalink)  
Old 04-27-2006, 04:51 PM
Antti
Guest
 
Posts: n/a
Default Re: LED Driver

you can use PWM modulation to control the LED current

Antti

Reply With Quote
  #3 (permalink)  
Old 04-27-2006, 09:13 PM
Jim Granville
Guest
 
Posts: n/a
Default Re: LED Driver

[email protected] wrote:
> Hi,
> We would like to drive LEDs using Ramp Waveforms using Xilinx CPLDs.
> Is it possible to write a driver and control the LED directly from CPLD
> or should an external D/A Converter be used?


Depends on the precision, and if you need linear current, or can
tolerate an average value.

Most common for human-view applications is PWM or PDM to drive the LED,
but that can give EMC issues, if you have large LED currents.

If you want to avoid the EMC, you can do PWM/PDM to a DC voltage,
and add a linear LED driver (now you have thermal issues

-jg

Reply With Quote
  #4 (permalink)  
Old 04-28-2006, 07:10 AM
Kolja Sulimma
Guest
 
Posts: n/a
Default Re: LED Driver

Jim Granville schrieb:

> Most common for human-view applications is PWM or PDM to drive the LED,
> but that can give EMC issues, if you have large LED currents.


You can route the current in alternating loops. That should remove
almost all EMC issues.

Kolja Sulimma
Reply With Quote
  #5 (permalink)  
Old 04-28-2006, 08:14 AM
Jim Granville
Guest
 
Posts: n/a
Default Re: LED Driver

Kolja Sulimma wrote:
> Jim Granville schrieb:
>
>
>>Most common for human-view applications is PWM or PDM to drive the LED,
>>but that can give EMC issues, if you have large LED currents.

>
>
> You can route the current in alternating loops. That should remove
> almost all EMC issues.


Yes, it can mitigate some of the problems, but it also requires
forethought and skill, and probably an EMC test

'LED Driver' covers a very wide range of possible loads, so it is not
easy to advise the best solution.

Between the Digital Switch, and linear drive choices, there is also
soft digital drive ( Typically MOSFETS with high value Rg drive ),
gives less power loss than pure Linear, but better EMC than pure
digital.
If the LEDs are a matrix ( moving signs etc ) you can also ease EMC
by adding a deadband, and design the drive so only one axis needs to be
slow.

Mostly, I use PDM (Pulse Density Modulation) a la Rate Multipliers of
old. That uses the least CPLD resource.

-jg

Reply With Quote
  #6 (permalink)  
Old 05-02-2006, 11:13 AM
mohan
Guest
 
Posts: n/a
Default Re: LED Driver

Hi,
LED's sinking current capacity is in uA.
so tie Anode of LED to port pin of CPLD & Cathode of LED to gnd.
If u do this kind of connection then CPLD will be in sourcing mode.so
to avoid sourcing of CPLD,u can tie Vdc to LED Anode through current
limiting resistor,& cathode of LED should be directly connected to CPLD
port pin.in this case CPLD will be in sinking mode.
I have tried this kind of thing,it woks fine.

Reply With Quote
  #7 (permalink)  
Old 05-02-2006, 03:33 PM
Peter Alfke
Guest
 
Posts: n/a
Default Re: LED Driver

CMOS outputs are fairly symmetrical, they can source or sink similar
amounts of current. But perhaps the sink capability of the n-channel
output is slightly higher than the source capability of the p-channel
pull-up..
The difference is less than 2 : 1
Peter Alfke, Xilinx, from home.

Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
tranif1 always a driver ? [email protected] Verilog 3 08-22-2008 12:27 AM
PCI driver for ARM processor Chanemou FPGA 0 07-27-2004 12:30 PM
device driver Tom FPGA 1 04-27-2004 09:18 AM


All times are GMT +1. The time now is 06:59 AM.


Powered by vBulletin® Version 3.8.0
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.2.0
Copyright 2008 @ FPGA Central. All rights reserved