Re: Varistor question

On Thu, 24 Nov 2005 19:43:54 GMT, Ignoramus10725
<ignoramus10725@xxxxxxxxxxxxxxxxxxxx> wrote:

>I have a question about varistors. Actually two.
>
>Question 1.
>
>Are varistors the sort of devices that cannot be expected to conduct
>many pulses of electricity..

Yes, when operated within their specifications, varistors can be
expected to last as long as any other solid-state device.


>Question 2. Once a breakdown voltage of a varistor is exceeded, and it
>starts conducting, when would it return to a non-conductive state?
>When current falls below some threshold? Or when?

Varistors are not like that. They do not suddenly start conducting.
They do not latch. In fact, they have a very gradual
current-vs-voltage curve. Take a look as some data sheets. You will
see that in order to conduct enough current to protect a circuit at
400 volts, it must also conduct quite a bit of current at 100 volts
too. Even at 50 volts, the current does not drop to zero. A varistor
would be very poor as a voltage regulator.



-Robert Scott
Ypsilanti, Michigan
.

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