Voltage ratings of SM resistors

Test some to destruction and derate! That's always fun.

I did a tiny HV supply using 0603 resistors. The ones we tested smoked at 1600 volts, so I felt good using them at 300.

John

A 1206 is rated at 200V and an 0805 is rated at 150V. Under low power conditions (say 2mW for a 10meg resistor), what is the maximum voltage they can handle without a large reduction in reliability? How about at 150C, which is less than the manufacturer max of 175C?

I read in sci.electronics.design that Robert Baer wrote (in ) about 'Voltage ratings of SM resistors', on Fri, 14 Oct 2005:

I think you should ask the manufacturers.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

You do have to be concerned about failure modes that are more subtle, such as long-term drift of resistance value.

Best regards, Spehro Pefhany

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"it\'s the network..."                          "The Journey is the reward"
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Embedded software/hardware/analog  Info for designers:  http://www.speff.com

There is surge voltage and current that the resistor might withstand but not for sustained period. Some datasheet provide that information.

I found it difficult to work out lifetime of the circuit as whole due to lack of failure data on each component. One way is to select part, build up data via qualification test, but may not be valid for later batch as they may move process elsewhere...I seen this happen before.

One of my perennial issues. I specify parts that appear (to others) to be far overrated in SMPS startup circuits, simply because they are so critical.

The one thing I have going for me is my SMPS circuits don't fail long term :)

Cheers

PeteS

I read in sci.electronics.design that Spehro Pefhany wrote (in ) about 'Voltage ratings of SM resistors', on Fri, 14 Oct 2005:

Tell that to the people who specify the start-up resistors in SMPS.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

I would not expect you would get much more voltage at 150C. I recall roughly that the electric field across the microscopic irregularities of the resistor cause tiny areas of overload. I suppose that once a microscopic failure exists, the neighbouring microscopic areas of conduction get overloaded in turn and gradually the whole resistor goes high in value.

You can get away with exceeding the voltage specification - if exposure to the voltage is short or life of the product is limited or you can handle the drift of resistance. Damage seems to be exponential with voltage e.g. running at 3 times the voltage rating shortens the life much more than running 1.5 times. The parts are specd for continuous running for so many

1000s of hours with resistance staying within tolerance, so you may be able to sacrifice some tolerance.

Roger Lascelles

IMHO the place to optimize costs isn't with SMD resistors - been there

- tried that

Regards

Klaus

"Klaus Kragelund" a écrit dans le message de news: snipped-for-privacy@f14g2000cwb.googlegroups.com...

I can remember a design review were 7 engineers discussed for more than an hour the necessity of one SMD resistor for a 20000 board production run. After 10 minutes I got bored and left the meeting room for a coffee break and get back when they were finished with that.

Now, one hour alone taking coffee really seems long...

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Thanks,
Fred.

It sounds like the money they spent debating the part was more expensive than the part.

--
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Michael A. Terrell
Central Florida

an

break

Yep. That what I told after 5 min. After 10, I left.

--
Thanks,
Fred.

"Fred Bartoli"

** Possibly they could compute the total number of angels that can dance on the head of a pin just a tad quicker .

Or are pre-scientific Mediaeval Monks the dudes for that one ?

........ Phil

"12C rise at 100% rated power" is a far, far cry from my 2mW for a

10meg resistor... And the 0805s i use/see are rated at 150V (Rohm, Yaego, Panasonic) not at the 100V (Xicon) you mention.

Thanks for the insight! Very helpful.

...and at room temperature. I run my resistors above the 175 max indicated by the derating (power) curve.

Those meetings make about as much sense as wrestling with a pig. :(

--
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Michael A. Terrell
Central Florida

The ones I like are the daily two-hour meetings to explain why the project is late. I finally made my part of the presentation; "because I'm wasting 25% of my time in these stupid meetings". The big boss didn't think that was funny. It wasn't meant to be.

--
  Keith

He sounds like my station manager at the AFRTS TV station in Alaska. No downtime allowed, a couple thousand dollars a year in spare parts to keep a radio & TV station on the air. He got pissed and tried to have me court martialed for this poster:

- We the willing - - Lead by the unknowing - - Have done so much - - For so long - - That we are now qualified - - To do anything with NOTHING! -

It backfired on him. I was promoted from E3 to E4 before the day was over. ;-)

The meetings remind me of Microdyne prepping the RCB2000 for production. A couple hour meeting several times a week where they promise you anything, followed by being refused access to schematics of some circuit boards because they are still waiting for someone to sign them off for release to production. I made it clear that things were going to change in the next meeting, or there would be a lot of visits to the president of the company to set things straight. On top of that, were were going though ISO 9001 certification with all those stupid meetings. I had to laugh, because to get certified, they had to make the changes I wanted, to start with.

--
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Michael A. Terrell
Central Florida