Pushing LEDs Beyond Ratings: Can My 25ma LED Survive?

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Discussion Overview

The discussion revolves around the operational limits of LEDs, specifically regarding how much current can be applied beyond their rated specifications without causing failure. Participants explore the implications of driving a 25mA LED at 50mA for short durations and the potential for heat dissipation using an aluminum block. The conversation touches on theoretical and practical aspects of LED performance, including pulsed operation and lifetime expectations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions how far LEDs can be pushed beyond their ratings, proposing to run a 25mA LED at 50mA for short durations.
  • Another participant suggests considering a brighter LED or reducing the current, while also humorously proposing a long-duration test to see if the LED lasts.
  • A participant notes the absence of brighter LEDs at the same wavelength with decent response times and mentions having multiple LEDs for testing.
  • Concerns are raised about whether the 25mA rating is a peak or average current, with some suggesting that pulsed operation may allow for higher currents.
  • One participant shares their experience of running an LED at 50mA overnight and discusses the timing of the pulse frequency in relation to phosphor decay time.
  • There is a discussion about the data sheet specifications, including maximum ratings for continuous and pulsed currents, with some participants interpreting these ratings differently.
  • Another participant emphasizes the importance of keeping peak currents below certain thresholds to avoid damage.
  • Discussion includes the concept of a maximum duty cycle versus frequency, noting that the die size affects the ability to dissipate heat.

Areas of Agreement / Disagreement

Participants express varying opinions on the implications of the LED ratings and the feasibility of operating beyond them. There is no clear consensus on the maximum allowable current or the interpretation of the data sheet specifications, indicating ongoing debate and uncertainty.

Contextual Notes

Participants reference specific LED specifications and operational conditions, but there are limitations in the discussion regarding assumptions about heat dissipation and the effects of pulsed versus continuous operation. The conversation also lacks definitive conclusions about the long-term reliability of the proposed operating conditions.

Topher925
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How far can you push most LEDs beyond their recommended rating before they burn out? I currently have a 25ma, 34k mcd LED that I am planning on putting 50ma through for 10ms durations for 30ms periods. The LED is inside of a aluminum block to help dissipate heat. Do you think and LED like this could survive this kind of operation for <100 hours?
 
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Topher925 said:
How far can you push most LEDs beyond their recommended rating before they burn out? I currently have a 25ma, 34k mcd LED that I am planning on putting 50ma through for 10ms durations for 30ms periods. The LED is inside of a aluminum block to help dissipate heat. Do you think and LED like this could survive this kind of operation for <100 hours?

Can you just spec out a brighter LED, or run with less current? You could just leave it on for 3 days and see if it works for that 100 hour spec. I'd bet it'd last less than the stated MTBF, however.
 
No one makes a brighter LED at this wave length that still has a decent response time. I'll put one LED through testing and if it dies then I've still got 9 more.
 
Topher925 said:
How far can you push most LEDs beyond their recommended rating before they burn out? I currently have a 25ma, 34k mcd LED that I am planning on putting 50ma through for 10ms durations for 30ms periods. The LED is inside of a aluminum block to help dissipate heat. Do you think and LED like this could survive this kind of operation for <100 hours?

I googled LED life current power, and got lots of usefful hits. Here's one:

http://www.philipslumileds.com/pdfs/WP12.pdf

.
 
MATLABdude said:
You could just leave it on for 3 days and see if it works for that 100 hour spec.

Good suggestion. Since the OP is a grad student, 33-hour days should not be a problem :biggrin:
 
Redbelly98 said:
Good suggestion. Since the OP is a grad student, 33-hour days should not be a problem :biggrin:

I, too, am a grad student, and could also use 33 hour days!

(Miscalculated 24 x 4 as 72 instead of 96)

EDIT: D'Oh! 24 x 3 as 96 instead of 72
 
Topher925 said:
How far can you push most LEDs beyond their recommended rating before they burn out? I currently have a 25ma, 34k mcd LED that I am planning on putting 50ma through for 10ms durations for 30ms periods. The LED is inside of a aluminum block to help dissipate heat. Do you think and LED like this could survive this kind of operation for <100 hours?

Is 25mA a peak rating or an average rating? If it's an average current rating then there should be no problems. LED's usually don't mind being driven with a pulsed current waveform. It's not uncommon to drive them in pulsed mode with peak currents 2 to 3 times the average rated current.

BTW. Is there any reason why you're using such a low frequency (approx 33Hz) for the pulses? Typically 100 to 1000 Hz would be more usual for LED pulse mode operation.
 
I let one LED run all night at 50ma. I'll check and see if its still alive when I get to campus. 25ma is the rating for its max current, an average current isn't given on the data sheet.

I'm running it at 33Hz because the decay time of the phosphor its exciting is around 4ms and time is required for it to settle. I may end up using a sinusoidal wave form if I can get a decent wave form out of it.
 
25ma is the rating for its max current
Then most likely it's the absolute maximum rating of the continuous current. This is not usually the same thing as the maximum peak current for pulsed operation. Tpyically the data sheet for a LED would contain data something like the snippet shown below.

Code: 
Absolute Maximum Rating (Ta = 25C)

PARAMETER                                MAXIMUM RATING         UNITS

DC Forward Current                       30                       mA

Reverse Voltage (IR = 100mA)             5                        V

Peak Pulse Forward Current               100                      mA

Avg. Forward Current (Pulse Operation)   30                       mA
 
  • #10
The data sheet actually says "Absolute Maximum Rating" which I'm going to assume can either mean DC current or average pulsed current. The data sheet also has data going up to 80ma. I think as long as I stay below 80ma with my current pulse routine it should be fine.
 
  • #11
Yes keep the peak below 80mA and the average below 25mA and it should be fine.
 
  • #12
Typically, any silicon device has a max duty vs. frequency curve, whether it's published or not. I've move often seen this for collector or drain current. The curve depends on the bond-outs and die's ability to dissipate heat before it gets hit with the next pulse.

In general, the larger the die the lower the frequency for any given duty.
 

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