EFI

[John Dammeyer]

At 11:49 AM 17/07/1996 +0200, you wrote:
>
>> simple.  They will handle inputs from 6V up to around 60V, and for
>> protection against load dump and other spikes you can just use a MOV and
>> either a fuse or polyswitch electronic fuse in series with the input.  You
>
>What is a MOV?
>
>Forgive me for asking...
>
>Best regards,
>
>-Oliver

A MOV - Metal Oxide Varistor - acts like a high impedance resistor until a
particular breakdown voltage is reached at which point it conducts.

A Transorb is a semiconductor similar to a Zener diode but with self
limiting characteristics so that a series resistor is not required. Number
like PK6E-18 for 18 volt.

A transorb is preferable to a MOV for the following reasons:  

Because it acts like a zener it always conducts in the reverse direction so
that any negative voltage transients are maintained at -0.6 volts.  If you
have negative transients that exceed the forward current capacity of the
Transorb than you need to fix that problem.  A MOV specified for 18 volts is
non-polarized so works for +/- 18 volts

A Transorb can be exposed to multiple hits, like the regular pulse of the
ignition system.  Granted, again better to remove the source but it can take it.

A MOV cannot.  My understanding of the MOV technology is that it works well
and quickly but eventually under repeated transients begin to fail. MOV's
are better for sporadic, rare bursts of noise rather than periodic transients.

regards,

John



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