# What’s the difference between led current draw with and without PWM?

I have a LED that’s rated for 3W (aprox 3V and 1A max current)

Do I get the same result in terms of current draw and led’s durability if I supply the led with a 1A Led Driver (at full current supply, or full PWM signal) or if I supply the led with a 2A led driver, but only allow to the led half the PWM max current?

Attached is the datasheet for the Cree XP-E neutral white led I’m using. XPE-Datasheet

I found this document about over-current pulsed driving leds of this manufacturer: Cree over-current pulsed driving leds

I’m also using a constant led driver, but it only provides 500mA.

I have another led driver that is set for more than 1A. That’s why I thought of using this one but in a lower PWM setting.

• We need to see the datasheet for your LED. Please provide a link. Commented Jan 16, 2020 at 23:41

A led had usually two kind of max current specified in its datasheet: Pulsed and DC operation. Usually, max pulsed current can be much (e.g. 5-10 times) higher than max. DC current.

If you consider only the current, you will have the same result if you operate 1A at 100% or 2A at 50% (Both have 1A mean current).

But because the forward voltage of the LED is higher at 2A, you will generate more heat losses at 2A/50%.

It could be that you have more brightness at 2A/50%, because the current to brightness curve of a led is not linear.

• I think the maximum pulse current ratings for an LED are usually for very low duty factors, much less than 50%, and for very narrow pulse widths. Commented Jan 16, 2020 at 23:40
• @ElliotAlderson Like 10x the continuous current for 0.5% duty cycle at some us pulse width. Commented Jan 17, 2020 at 0:06

LED current draw with PWM has ripple that averages out to a value but instantaneously might have higher and lower voltage/current values. For example, would you rather have the temperature be 25C? Or alternate between 0C and 50C? They both average to be 25C after all. If your LED handles 1A and gets 1A at 100% PWM, then PWMing lets you reduce the visual brightness (to the human eye anyways) more efficiently than using a resistor because you are dissipating less heat.

But if your LED can only handle 1A and gets 2A at 100% and try to PWM at 50% to stay at 1A average, then you are hammering the LED at 200% what it can take half the time.

Not to say you "overdriving" will necessarily destroy the LED. LEDs can handle high power bursts for short periods of time as long as it kept under control, but you have to know what you're doing. It does shorten their life though. You might do this with something like a pulsed laser diode where you need really high power pulses and it's too expensive to just use a bigger diode, but really not worth it to overdrive an LED that is just a visible indicator.

This is all if your driver has no filtering (you're just PWMing the LED to control brightness, not to run something like a constant current driver which has filtering to smooth things out so it's less peak and the actual currents more closely resemble the average current.

The specific LED you have mentioned does not provide any indication in its datasheet that it can be pulsed at a current higher than 1000mA. So, if you choose to operate the LED using PWM at 2A you are using the part beyond the manufacturer's specified maximum ratings. It might work, it might fail immediately, or it might fail next week.