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FrozenGate by Avery

Misconceptions about diode "lifetime" ratings

  • Thread starter Thread starter Deleted member 10578
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It seems that there are some misconceptions/ misunderstandings about laser diode lifetime ie. MTTF/MTBF ratings.
I saw a post in another thread earlier today where people were discussing this, but it wasn't the thread topic and I cannot find the thread now.

Anyway, someone had thought that since their laser or the diode in their laser was rated for 5000 or 8000 hours that it meant that the laser/diode would work for that amount of time; this is not so. Many may in fact last up to or perhaps even longer than the rated, but many will not even last a fraction of that amount of time. MTBF/MTTF numbers are a statistic that are good for determining product quality when many thousands or millions of units are considered, but they mean very little to how long an individual unit will live. For the person buying laser the number can be used for instance to compare the quality of one diode to another in that a diode with a 8000hr MTBF on average will be of higher quality than one of 5000hr MTBF; but it doesn't mean much more.

Here's a link that describes this somewhat and there's more on the web, just do a google search.
Using MTBF and Time Dependent Reliability for disks : Ramblings from Richard's Ranch
One of the interesting things that is used to describe MTBF is that in the USA, the death rate of children between the ages of 5 to 14 is 0.0208% per year, this would equal an MTBF of 4,807 years for these kids.
This article was written about MTBF in disk drives, but it applies to all electronics or anything that uses MTBF as a quality metric.
 





Right on the head Jerry, sounds like he's describing our conversation on that thread.....
 
The way I always understood it was this:

MTTF: Mean Time To Failure
The average time it takes for a piece of hardware to fail out of X number of tested items.

MTBF: Mean Time Between Failures
The average time a piece of hardware will operate between failures and repair.

I never thought of the MTTF as a guarantee of how long a laser diode would "live," but rather an estimate of how long I can expect a laser diode to live on average.
Obviously, in order to get an average figure, you will have some on the high end and some on the low end, with most in the middle range. Variations in production will cause this.
A component with a higher MTTF rating can usually be considered "higher quality" but by no means does it guarantee that an individual item will last longer than an a product with a lower MTTF.

I'm not sure I understand what the 5-14 year old children example has to do with this and where the 5000 year MTBF for a human being came from.
How was that calculated? :thinking:
 
Well, you were a participant so you don't "count".:na:
 
Last edited:
bootleg2go said:
It seems that there are some misconceptions/ misunderstandings about laser diode lifetime ie. MTTF/MTBF ratings.
I saw a post in another thread earlier today where people were discussing this, but it wasn't the thread topic and I cannot find the thread now.

Anyway, someone had thought that since their laser or the diode in their laser was rated for 5000 or 8000 hours that it meant that the laser/diode would work for that amount of time; this is not so. Many may in fact last up to or perhaps even longer than the rated, but many will not even last a fraction of that amount of time. MTBF/MTTF numbers are a statistic that are good for determining product quality when many thousands or millions of units are considered, but they mean very little to how long an individual unit will live. For the person buying laser the number can be used for instance to compare the quality of one diode to another in that a diode with a 8000hr MTBF on average will be of higher quality than one of 5000hr MTBF; but it doesn't mean much more.

Here's a link that describes this somewhat and there's more on the web, just do a google search.
Using MTBF and Time Dependent Reliability for disks : Ramblings from Richard's Ranch
One of the interesting things that is used to describe MTBF is that in the USA, the death rate of children between the ages of 5 to 14 is 0.0208% per year, this would equal an MTBF of 4,807 years for these kids.
This article was written about MTBF in disk drives, but it applies to all electronics or anything that uses MTBF as a quality metric.
Click to expand...

This is very true. Fortunately most last quite awhile.. I'll even go so far as to add that when we push diodes like we do regularly here on LPF, that already shaky MTTF figure goes out the window into the realm of almost complete unpredictability when placed against a time line. The vast majority of diodes we see being overdriven will last for awhile, but nowhere near 5,000 or more hours.
 
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