this post was submitted on 03 Jul 2023
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Can I switch this constant current LED driver at 38kHz? (discuss.tchncs.de)
submitted 2 years ago by silvio2402@discuss.tchncs.de to c/askelectronics@discuss.tchncs.de
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My goal is to drive an infrared LED like (this SFH 4727AS) to control IR remote controlled devices (for example a TV).

I can already output the signal on a pin of my microcontroller. The signal has a carrier frequency of 38kHz.

I am however limited to a 5V 1A power supply and would like to drive the LED as close to the 5W psu limit as possible.

I first thought about using a MOSFET like this AO3400A together with a resistor, but decided it was worth using an LED driver, do you agree?

Now I'm looking at this PAM2804 constant current LED driver but I'm not sure if I can just supply my signal to the EN pin. The EN pin is meant for PWM-dimming, so does that mean the output is smoothed to prevent flickering?

I'd love to hear your thoughts about how I should go about this. Thanks

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[–] silvio2402@discuss.tchncs.de 1 points 2 years ago* (last edited 2 years ago) (1 children)

Hey, thanks for your comment. I looked at using a resistor in series with the LED, but if my calculations were correct I could only power the LED less than 3W and 2W would be wasted.

R = (V~s~-V~f~)/I~f~ = (5V-2.8V)/1A = 2.2Ω

P~LED~ = V~f~*I~f~ = 2.8V*1A = 2.8W

P~Resistor~ = V~s~*I~f~-P~LED~ = 5V*1A-2.8W = 2.2W

Let me know if the calculations are correct.

Edit: Calculations

[–] cmnybo@discuss.tchncs.de 1 points 2 years ago

Those calculations are correct.

Since the remote control signals are short and low duty cycle, you could use a capacitor to provide the peak current for the LED without going over the maximum current of the power supply.