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Shunt Reg issues (TL431) found in some TRIPP LITE UPS.

J

Jamie

Jan 1, 1970
0
Today, I went through a pile of goodies that were given to me
from a friend that has access to electronic hardware slated for
disposal or defects. (not repair shops).

Any ways, I had problems with my own TRIPP LITE UPS and decided
to use of these offerings as a replacement. I have 5 total TRIPP LITE
UPS, all similar models and fairly new with good batteries.

3 of total had a defective TL431 shunt regulator that runs the uC.

They simply shorted and created almost a 0 ohm load.

Has any one seen these TL431 to have a bad run or does TRIPP LITE have
a design issues ? The replacement does not appear to be operating at any
severe temperature.

P.S.
This circuit is well up the food chain from potential things like
mother nature.. And also, the original is ST, which I think is On Semi/.
 
J

Jim Thompson

Jan 1, 1970
0
Take a good one from that batch and carefully run it on a curve-tracer.
There is a possibility that there is a "N" shaped peak before normal
regulation voltage, where that peak gets higher as temperature goes up.
That peak can be rather large WRT datasheet nominal operating point.
If i remember correctly, one of the National Semiconductor references
gets bad that way from 165C up.

More likely, given the failure mechanism... short, they're running too
much current in the TL431's.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine Sometimes I even put it in the food
 
J

Jim Thompson

Jan 1, 1970
0
That peak in the "N" curve before the operating point can be 10 times
the nominal datasheet spec.
So..assume the peak is low or absent at 25C, the supply powers up,
and after X hours of use gets warm enough to have a large peak.
Continuing, assume the supply is shut off and there is a (relatively)
large capacitor across the TL431.
As the capacitor discharges, the TL431 will follow this new I-V curve
and result in a large current which either degrades or destroys the device.
Without knowing if the particular TL431s exhibit this temperature
sensitive "N" characteristic and without knowing the temperature that
peak starts to grow (assuming there is one) this is all speculation.
However, knowing one possible mechanism might be useful in tracking
down a possible cause of damaged devices.
Be aware that every manufacturer of regulators of this type makes
more than one version and that EVERY version has a different
characteristic, and that if the process is changed, start over again.
Processes may creep over time and will BE DIFFERENT if a new fab is
used to make the "same part".

You completely lost me there. What is this "N" curve of which you
speak? The TL431 is a SHUNT regulator (bandgap-style).

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine Sometimes I even put it in the food
 
H

Hammy

Jan 1, 1970
0
That peak in the "N" curve before the operating point can be 10 times
the nominal datasheet spec.
So..assume the peak is low or absent at 25C, the supply powers up,
and after X hours of use gets warm enough to have a large peak.
Continuing, assume the supply is shut off and there is a (relatively)
large capacitor across the TL431.
As the capacitor discharges, the TL431 will follow this new I-V curve
and result in a large current which either degrades or destroys the device.
Without knowing if the particular TL431s exhibit this temperature
sensitive "N" characteristic and without knowing the temperature that
peak starts to grow (assuming there is one) this is all speculation.
However, knowing one possible mechanism might be useful in tracking
down a possible cause of damaged devices.
Be aware that every manufacturer of regulators of this type makes
more than one version and that EVERY version has a different
characteristic, and that if the process is changed, start over again.
Processes may creep over time and will BE DIFFERENT if a new fab is
used to make the "same part".

Yes I'm lost too!

I use this part a lot so the thread got my attention. I've looked
through all the 431 datasheets I have and I have several and I can't
find any "N" Curve. I've always found them to be pretty robust within
reason. I use mainly TI's and Nationals.

Are you talking about stability curves versus load capacitance?
 
J

Jasen Betts

Jan 1, 1970
0
Today, I went through a pile of goodies that were given to me
from a friend that has access to electronic hardware slated for
disposal or defects. (not repair shops).

Any ways, I had problems with my own TRIPP LITE UPS and decided
to use of these offerings as a replacement. I have 5 total TRIPP LITE
UPS, all similar models and fairly new with good batteries.

3 of total had a defective TL431 shunt regulator that runs the uC.

They simply shorted and created almost a 0 ohm load.

Has any one seen these TL431 to have a bad run or does TRIPP LITE have
a design issues ? The replacement does not appear to be operating at any
severe temperature.

P.S.
This circuit is well up the food chain from potential things like
mother nature.. And also, the original is ST, which I think is On Semi/.

STMicro is OnSemi? AIUI TLxxx is originally a TI part number
 
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