# power dissipation - IR diode

#### Metoo25

Joined Sep 7, 2020
13
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.

#### KeithWalker

Joined Jul 10, 2017
3,149
"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."

Do you mean that the duty cycle is 33.33%?

" 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."

We can not calculate the power dissipation if we do not know what the voltage is, so what is the supply voltage and part number of the diode?

#### Audioguru again

Joined Oct 21, 2019
6,767
The IR diode has no part number for us to see its detailed spec's.
The resistor value is useless without us knowing the LED's forward voltage and your power supply voltage.

#### BobTPH

Joined Jun 5, 2013
9,190
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.

If it can only handle 100mA continuous, you cannot pulse it at 1000mA 1/3 duty cycle. That would be 3.3 times the average power .

Bob

#### crutschow

Joined Mar 14, 2008
34,720
For 100mA continuous rating than you should pulse it at most 10% of the time a 1A, probably more like 5% for reasonable derating.

#### Metoo25

Joined Sep 7, 2020
13
If it can only handle 100mA continuous, you cannot pulse it at 1000mA 1/3 duty cycle. That would be 3.3 times the average power .

Bob
OK. Yes, it might not work in real life. However, I would like to calculate the power dissipation anyways, from this scenario. What formula should I use or how should I do this?

#### Metoo25

Joined Sep 7, 2020
13
Yes. 33.33%
I am not sure about the voltage supply. I was wondering if I could use the formula: I^2*R ?

#### crutschow

Joined Mar 14, 2008
34,720
I am not sure about the voltage supply. I was wondering if I could use the formula: I^2*R ?
You would use I*V where I is the current through the diode and V is the voltage across the diode at that current.

#### sagor

Joined Mar 10, 2019
920
Like crutschow says, try I*V. For example, if the forward voltage drop thru the LED is 2.0V, then 100mA through it would have 200mW dissipation. If forward voltage drop through the IR is higher, like 2.5V or 3.0V, you get 250mW or 300mW respectively.

#### DickCappels

Joined Aug 21, 2008
10,240
Can you please supply the part number and name of the manufacturer, or just post the datasheet here.

The average power dissipation is = (peak current) X (voltage across the diode while that current is passing through it) X (duty cycle).