"Sam Goldwasser" bravely wrote to "All" (19 Aug 04 11:23:59)
--- on the heady topic of " Did low voltage cause the pc to fail?"

SG From: Sam Goldwasser

SG (w_tom) writes:

Unervoltage - also known as a brownout - does not damage electronics.
Unfortunately too many take what they learned about motors and
expolate that to knowledge about electronics. One must first learn
basic concept before making assumptions such as low voltage will
damage a computer.

SG In an ideal world this would be so.

SG In the real World, it's quite possible that brownouts can cause
SG switchmode power supplies to fail.

Yes, quite possible. In my experience the critical parameter turns out
to be the HFE of the switching devices. HFE is a tricky parameter in
pwoer transistors. HFE is dependent on Vcc, Ic, and temperature. HFE
tends to drop with Vcc. Worse, HFE tends to peak at some value of Ic
beyond which it drops as well.

It really is a double whammy. For example, suppose the switching
transistor driver circuit is designed to operate with a HFE half of the
transistor ratings. Now add to this a factor like aging, which tends to
cause a loss of HFE over time, and we can have a situation where the
transistor switches sluggishly or even not fully ON. Combine a marginal
HFE with a low Vcc and the supply may fail to regulate properly.

A+s+i+m+o+v

.... Electrical engineers deal with current events.