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techneo
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« on: August 07, 2019, 11:24:06 11:24 »


Hi,

 I have an array of white LEDs which is to be used as a street lamp. I am using a PWM signal to switch the leds at 3 Khz, the current varies according to the duty cycle of the control signal. For 100 % PWM or simple DC-high, the current consumed by the LED array is 5 amp and when i reduce the PWM to 20%, the current is also reduced proportionally.
Will operating at low duty cycle affect the life of the LED panel?



-techNeo
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Old_but_Alive
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« Reply #1 on: August 07, 2019, 12:05:35 12:05 »

operating at low duty cycle will greatly increase the operating life( probably exponentialy)

its all about temperature, lower is greater lifetime
« Last Edit: August 07, 2019, 12:08:17 12:08 by Old_but_Alive » Logged

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techneo
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« Reply #2 on: August 07, 2019, 08:52:52 20:52 »

operating at low duty cycle will greatly increase the operating life( probably exponentialy)

its all about temperature, lower is greater lifetime

You seem to be right.... but don't you think that the spikes resulting on the positive and negative transition edges will result into spikes of higher voltage and subsequently affecting the life of the LED?
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CocaCola
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« Reply #3 on: August 07, 2019, 11:32:44 23:32 »

will result into spikes of higher voltage and subsequently affecting the life of the LED?

As a general rule LEDs life span is based on current levels, heat (excess is what kills most LEDs) and obviously duty cycle, if the voltage spikes do not create excess current levels (they shouldn't in a good design) beyond the safe limits of the LED it should not harm the life in any significant way...  LEDs can be supplied with huge amounts of forward voltage (theoretically no limit as long as electrical insulation is maintained) as long as the current is kept in check and their temp is kept in check...  Note they don't tolerate reverse voltage well at all, that really has to be limited...
« Last Edit: August 07, 2019, 11:44:25 23:44 by CocaCola » Logged
Old_but_Alive
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« Reply #4 on: August 07, 2019, 11:45:32 23:45 »

its all about heat.

I remember 15 years ago designing a system using IR leds synced to a Sony electronic camera module.

The led was only on whilst the shutter was open.

We drove the LED at 5X the average current spec since the duty cycle was low.

no problem at all.

its probably limited by the current rating of the internal wiring from the pin to the actual semiconductor layer

so transient currents are not going to cause a problem.  Voltage is irrelevant, its current=heat
« Last Edit: August 07, 2019, 11:48:26 23:48 by Old_but_Alive » Logged

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techneo
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« Reply #5 on: August 10, 2019, 08:41:14 08:41 »

its all about heat.

I remember 15 years ago designing a system using IR leds synced to a Sony electronic camera module.

The led was only on whilst the shutter was open.

We drove the LED at 5X the average current spec since the duty cycle was low.

no problem at all.

its probably limited by the current rating of the internal wiring from the pin to the actual semiconductor layer

so transient currents are not going to cause a problem.  Voltage is irrelevant, its current=heat

I am happy to be in the company of experienced and learned people.....I genuinely appreciate help of all contributors.

I tested my circuit as per the given suggestions and till now there had been no problems.....

-techNeo
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