Re: How do Atom Computer Ignition modules work?

[legendre]

quote Phil B:

quote debe:

Did some tests on the 3 original Atom modules I dismantled switching transistors. Using a Digitec Component tester. All test as NPN darlington, & Hfe is not accurate due to B-E resistor of 2.2K, all have internal protection diode C-E. Two of the modules had a custom transistor marked A1, Hfe 8 Ic test 2.5Ma B-E 1V. Other one marked A2, Hfe 9 Ic test 2.5Ma B-E 1V.

I’d always assumed higher gain was needed.

It most definitely is an absolute requirement. The power NPN won’t turn-on soon enough with an hfe in the single or double digits, and this is very easy to demonstrate. Even the low hundreds is probably insufficient.

The hfe readings that debe posted are obviously incorrect, some sort of measurement artifact – possibly the result of an overflow error? The gain of a Darlington stage is: HFEd = (HFE1 * HFE2) + (HFE1 + HFE2) so it’s essentially impossible to have a Darlington with single-digit gain figures. Darlington gain is typically in the range of 500-2500 or better.

@debe

Would you have the time to make some manual bench measurements of gain in those Atom A1 and A2 parts? You know, just set up a variable PSU, a couple of ammeters and a resistor or two.. try a range of base currents from (perhaps) 1mA to 50mA, a total of ten points, and record the corresponding BE voltage, base current and emitter current.

Even if the supply is limited to 1A or 2A, that should give you a very solid picture of the current gain figures.