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Driving LEDs with M series DAQ board

Hello,
 
  In my current application, I'm using a PCI-6289 and BNC-2110.  I need to use several of the outputs to drive an LED in the 0-20 mA range.  I've been given to understand that I'll need to use some type of voltage-to-current converter circuit to have real control over the LED drive current (and also to amplify the 5 mA limit of the DAQ board)
 
  I'm fairly inexpert at analog circuitry design, but unfortunately pre-packaged converters are fairly rare and have to slow a response time for the dynamics I need. I want to drive the circuit from 0-10 V from the board and receive an output current of 0-20 mA.  The voltage will be modulated in amplitude in the 10 kHz range and will be turned on and off completely in the 1 kHz range (dynamic response time of <1 us).  In addition, I'm trying to keep the circuit fairly small profile and power-efficient, as I'll be needing 2-4 of them for the complete system.
 
  Can anyone with more experience in these matters give me any advice or point me in the direction of resources that might help me design this circuit?
 
Many thanks,
Steven Israel

Message Edited by Malenchite on 07-06-2005 11:45 AM

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Hello M.

I would suggest you use PWM to control the average voltage and therefore the average current going through your LED. This is a the same technology used in light dimmers. I have attached below a drawing of the circuit that you would have to build. The maximum current you want to see go through the LED will depend on the value of the resitor and Vcc.
The circuit also allows you to not limit the current to the value that the DAQ specifies since the current is sourced by the external power supply (Vcc).

Hope this helps.
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