power dissipation - IR diode

Hello. I want to find the power dissipation in my IR diode. I'm using pwm/pulses of 1/3 of the time it's on. It can handle 100 milliamps 100% of the time and 1 Amp when pulsing it. I want to know if 1/3 of the time is too short of a pause between pulses (200/400 microseconds)? It's maximum powerdissapation is 190 miliwatt and the resistor i'm using is 1,5 ohm.


Thank you in advance

if you are pulsing it with 1 amp, you need the duty cycle to be 10% or less. the power dissipation limit also de-rates linearly with the device temperature. since it's an IR diode, the voltage drop across it is most likely to be about .7V, so for a power dissipation of 190mW, that's an average current of 270 mA. the device will heat up, lowering the max dissipation limit, so that's why they spec'ed it at 100mA continuous instead of 270. for 1A pulses, like i said your on-time needs to be 10% or less, you didn't actually say you were using 1A pulses, but if you are, 33% duty cycle is too much. do you have a data sheet for the diode? a data sheet could probably tell you what you want to know

1600 Hz is a low frequency for pulsed IR. Most remotes work at ~38kHz. Your on time of 400uS may be too long to count as a pulse. What are you doing that needs such a long on time?

Mike.

metoo25 said:

Hello. I want to find the power dissipation in my IR diode. I'm using pwm/pulses of 1/3 of the time it's on. It can handle 100 milliamps 100% of the time and 1 Amp when pulsing it. I want to know if 1/3 of the time is too short of a pause between pulses (200/400 microseconds)? It's maximum powerdissapation is 190 miliwatt and the resistor i'm using is 1,5 ohm.


Thank you in advance

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To drive a bullet shaped LED at 1Amp, the manufacturers generally recommend less than 10% duty cycle at 1kHz pulse rate (or higher). The thermal time constant of the little bond wires is very short. The datasheets essentially say that 1Amp pulses longer than 10% of 1mSec (i.e. 100uSeconds) will cause the bond wires to overheat. In summary, don't do 0.4 second pulses at 1 amp!