LED Driver request

Discussion in 'The Projects Forum' started by LDC3, Apr 29, 2013.

  1. LDC3

    Thread Starter Active Member

    Apr 27, 2013
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    I would like to replace a sodium lamp with an bright LED with a maximum wavelength output of 589 nm. I found such an LED (Mouser 828-OVLGY0C9B9 :)), but in order to use the maximum current (100 mA), it needs a 10% duty cycle. I would also like to have a brightness control to have a lower output if necessary. I have create a circuit that I hope will do the job.

    The CMOS timer gives me a duty cycle of 90%, which grounds the input to the op-amp 90% of the time through Q1. R4 gives me a voltage reference from 0 to 3 V, so that with R7 the maximum current through the LED is 100 mA. D2 is a 12 zener diode to prevent the gate voltage exceeding 20 V. I forgot to put the supply voltage on the top (and the ground on the bottom). Since the voltage drop of the LED is about 2.2 V and the maximum voltage at R7 is 3 V, then the power supply must be at least 6 V. I was going to use a 9 VDC transformer.

    Does anyone have any comments?
     
  2. #12

    Expert

    Nov 30, 2010
    16,278
    6,791
    The drawing looks good, right down the variable current drive on the output stage.
    I'm just baffled at the idea that a 1/4 watt LED is going to compare to a Sodium Lamp.
     
  3. LDC3

    Thread Starter Active Member

    Apr 27, 2013
    920
    160
    The lamp is in a polarimeter and I need to see through 20 cm of solution. It is not to light up a room.
     
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