George Richardson wrote:
>
> Sorry Randal, but power is used to drive the ICs in the unit as well as
> supply voltage to the base of the transistor that turns on the coil.
Well, assuming it has ICs, that's exactly what I meant by "the amplifier
for the signal".
> The
> ICs, if they're anything like those in the Piranha ignition system,
> require a minimum of 5 volts to operate.
Right, unless of course they are CMOS equivalents, good to about 3
volts. And they would also require a modest amount of regulation.
Lessee, two diodes, a resistor, and a capacitor or two : Presto ! A
moderately regulated 5v from the _AC_ waveform across the coil,
regardless of whether there is a ballast or not. We're not talking
rocket science here.
> And although it may not make
> any difference in the majority of cases where the connection is made, in
> the case of a coil and resistor that are not matched, there could be a
> problem supplying adequate voltage.
Which is one of the reasons why the instructions specify the ballast
resistor value range. The other reason of course being that there is a
definite limit on how much current the unit can switch. And since the
instructions specifically mention lower resistance aftermarket coils,
IMO it's safe to assume that the designer considered and designed for
this case.
> ( 12 volts/2.8 ohms)*1.1 ohms = 4.714 volts across the coil when the
> ignition is on, not accounting for the voltage drop of the switching
> transistor.
Only when the transistor is on. And if you know how to design something
like this, you know that the voltage is _not_ "4.714", but rather
"approximately 4.7", because the "12 volts" is actually "something
somewhere between 9 volts and 15 volts, maybe". Not accounting for
various transients, etc. which can be hundreds of volts in either
direction ...
> By the way, I designed my first electronic ignition more than 25 years
> ago.
That would be about the time I designed, built, and tested my first
multiple-spark capacitive-discharge ignition in my spare time. One of
the few things I built that worked perfectly, the first time. However,
a missed shift on my Audi cut short the testing, and I never went back
to it, even after I finished the rebuild ...
Tell me, when you pick up a spec sheet that says a particular IC
requires 2.8v to operate correctly, do you immediately say "Oh, I
designed an IC once and it required 5.0v, so I'm going to use that
instead" ???
Randall
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