John Larkin wrote:
[snip]
Actually, it's tricky to get high stepup ratios in circuits like
this. As the boost ratio increases, energy gets lost in the
various parasitics. You're suggesting a 100:1 boost (4v cold
cranking, 400v peak out) and that's pushing things.
John is confused ;-) 0.5*L*I^2 = 0.5*C*V^2
Good thing you smilied that one. I'd have to be seriously drunk to get
confused over anything this simple.
INDUCTIVE charging, so John's ratio is meaningless
Boost step-up ratios are not meaningless. High ratios get expensive,
which is why people tend to prefer transformers for high Vout/Vin
ratios on dc/dc converters.
This circuit is cute and clever, and one could certainly build one and
get it to work (provided the base drive timing assured full energy
transfer at min cranking voltage and didn't fry things at max), but I
don't think it's the way people would do this in production.
Its very cleverness is the danger here.
John
I can't believe you are so confused, John. You are TOTALLY
out-to-lunch on this one.
From a previous post...
"Turning ON the transistor does two things... dumps the capacitor
through the ignition coil primary (firing the plug) and begins
charging L1.
When the L1 current reaches 5A a control circuit (not shown) turns off
the transistor, which dumps the L1 energy into the capacitor.
Next point opening, or star wheel control signal, turns on the
transistor, repeating the cycle."
Did you miss the part where a "control circuit" turns the device off
when 5A is attained? The current is MEASURED!
The device WAS made in production quantities. What is it you think
made it not mass-producible?
(Maybe you missing the point that the control circuit is not shown,
but it's an integrated circuit with bandgap, smarts, etc. I think
you're also missing the point that the capacitor gets discharged
completely each firing cycle.)
Other folk had no trouble understanding it ;-)
...Jim Thompson