I am trying to drive a bright 350mA blue LED using an iPhone as the signal generator. Please see the attached circuit. I am using a 350mA BuckPuck (datasheet attached) to drive the LED. I have the reference of the BuckPuck set to a regulated 5v supply. When the CNTRL voltage drops below 4.2v, the LED starts to turn on until it reaches it's max when CNTRL < ~1.5V.
I have an iPhone app that can output square waves at +/- 1.3V (the max an iPhone can output). I want to amplify this to 5v and 0 (Full Off and On for the LED CNTRL signal respectively) so I used an op-amp (TLC2272, datasheet attached) to act as a simple comparator.
When I test the circuit without the BuckPuck, I get a clean 0-5v square wave at TP2 (the output of the OPAMP). However, when I connect the BuckPuck, this square wave drops to 0-3.5v. The LED goes "on" at full brightness, but the "off" state is still rather bright.
I disconnected the OpAmp, and tested the BuckPuck using a POT. The BuckPuck drives the LED until 4.2v, then turns off as the signal approaches 5v. So both systems seem to work independently, but not together. Any suggestions?
Some specific questions:
1) Am I using the OpAmp correctly?
2) Should I be using a Voltage Regulator? I wanted to be sure to keep the REF voltage at 5V. When I used a voltage divider, but I notice the voltage dropped a lot when the LED was drawing current when it was turned on. Will the voltage regulator shorten the 9v battery life?
Thanks,
Greg
I have an iPhone app that can output square waves at +/- 1.3V (the max an iPhone can output). I want to amplify this to 5v and 0 (Full Off and On for the LED CNTRL signal respectively) so I used an op-amp (TLC2272, datasheet attached) to act as a simple comparator.
When I test the circuit without the BuckPuck, I get a clean 0-5v square wave at TP2 (the output of the OPAMP). However, when I connect the BuckPuck, this square wave drops to 0-3.5v. The LED goes "on" at full brightness, but the "off" state is still rather bright.
I disconnected the OpAmp, and tested the BuckPuck using a POT. The BuckPuck drives the LED until 4.2v, then turns off as the signal approaches 5v. So both systems seem to work independently, but not together. Any suggestions?
Some specific questions:
1) Am I using the OpAmp correctly?
2) Should I be using a Voltage Regulator? I wanted to be sure to keep the REF voltage at 5V. When I used a voltage divider, but I notice the voltage dropped a lot when the LED was drawing current when it was turned on. Will the voltage regulator shorten the 9v battery life?
Thanks,
Greg
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