EFI

[thor at pixie.co.za]

>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
>
>
>
>Pioneers are the ones, face down in the mud,
>with arrows in their backs.
>Automation Artisans Inc.      Ph. 604-544-4950
>6468 Loganberry Place         Fax 604-544-4954
>Victoria BC CANADA V8Z 7E6
>
>
Just one point for correction, there are two types of transorbs, unidirectional,
and bidirectional. You are only correct for unidirectional transorbs, in
stating that they conduct in the reverse direction. However, bidirectional
transorbs, are like two back to back zener diodes in a single package. They
do not have any polarity and can protect for both +ve and -ve transients
(above the rated break-down voltage). MOV's are probably are a bit tougher
if compared as a single entity against a transorb, but transorbs are seldom
used alone in a circuit where frequent / repetative breakdown is expected. A
low value resistor (usually hi wattage) is placed between the source and the
transorb, the resistor acts like a buffer, to disipate some of the energy
when the transorb breaks dowm. The really good thing about transorbs is
their speed. MOV's tend to be a little slow in reacting to a transient,
where as there are some really ultra fast transorbs.

A good automotive transorb, especially for supply inputs is the 1.5KE18CA,
(18 volt) this is availible from numerous sources, Microsemi Corp. Santa
Ana, CA being one of them.

Hope this is of some help.


Gary.