[s-cars] Re: [SOS-cars]POS question

Paul Gailus gailus at mindspring.com
Tue Jun 21 00:39:38 EDT 2005

I don't know the specs on these 2 POS parts, but there are
certainly some differences between various ignition coil
driver stages or transistors. I tend to believe that there was
probably some reason for this different part number, since
it cost Audi some money to set it up and stock it. That being
said, it may still possibly be close enough that it could work OK.
It may be an issue of guaranteed margins over worst case conditions.
It could even be the identical part but graded out during production
tests, possibly for something like a higher breakdown voltage.

On the slim chance someone might be interested, here are just
some of the differences between various available ignition driver
Output peak voltage ratings tend to vary from a little over 300
to as much as 500 volts. Many are intentionally clamped at a
target voltage level to protect the transistor if the secondary
voltage (and therefore primary voltage) is allowed to get too high.
Various clamp voltages are available. Current ratings and
gain (transconductance) curves vary between different parts.
There are also different ratings on the stored coil energy that the
device can safely dissipate if the clamp voltage is reached on the coil
primary before there's a spark on the coil output (due to a defective plug,
too large a plug gap, etc.)
The specific requirements for the coil driver (POS) in a given application
will depend on the maximum spark voltage required, coil turns ratio,
peak primary current, coil primary inductance, and other factors.

----- Original Message -----
From: Lino M. Valadas <l.valadas at rogers.com>
To: <SOS-cars at yahoogroups.com>; s-car-list <s-car-list at audifans.com>
Sent: Monday, June 20, 2005 9:59 PM
Subject: [s-cars] Re: [SOS-cars]POS question

> Hi guys,
> My 93 S4 blew a POS, part number 4A0 905 351 A - about $375 Canadian.
> In trying to debug the problem I used my wife's 2.8 V6's POS (single vs.
> two) on the S4 part  number 4A0 905 351 cost unknown at this point in
> it worked fine at least for the 5 minutes I ran it.
> The question is.  I expect the V6's POS to be much cheaper (made in Japan
> S4's made in Germany).  The V6's worked fine in the S4 even though the
> number is slightly different.  If the V6's is half the cost, which I
> it will be (I'll find out tomorrow) does anybody see a problem with using
> that one instead of the correct part number at a higher cost? Any BTDT? Is
> the function of the POS fairly generic?
> Lino
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