How do Atom Computer Ignition modules work?

[legendre]

Dangit.

Well OK, I figured out why none of my circuits are working. The 2SD1071 I purchased from this eBay listing (item #181052048392) are F*A*K*E! I’ve built three so far, and (as with any good experimenter) in each case I chalked up the failures to my own errors, despite being unable to find any wiring errors in the modules. Solid-state isn’t my world, but even so, they +are+ pretty darned simple!

Recall my asking some time back, why they measured with an hfe of 20-25? Well, that’s because they do have an hfe of 20-25, as opposed to the (min.) 500 of a real 1071. These fakes also lack the internal diode, from E to C.

Be advised.. I’m now taking this up with the seller. I already left them a nice FB – in good faith, as they shipped promptly – so we’ll see how they act. In the meantime, I’d avoid that seller’s offerings.

FYI – Here is how I confirmed it.

15V variable supply. C tied to B+ / E tied to Gnd / B tied to B+ via 1K3 resistor. With the supply cranked full-on, Ib = 10mA and Ie = 200mA.. that’s a 20:1 ratio, which fits nicely with the measured hfe of ~20 for this particular device. I didn’t trust the component tester, but I sure do trust my own separate instruments. And I really doubt the whole batch is defective in exactly the same way.. the missing diode is the final nail.

[mercuryman]

Thaats the same place I got my 2sd1071’s and they don’t work either.

[phil-b]

I went back to parametric search forms. Here are parts currently available from a major manufacturer (ST), all rated 60W or better, Ic 8A or better, Hfe 750 or 1000, but all only Vce 100V:

BDX33C BDW93C BDX53C TIP102 TIP132 TIP142

Could the voltage limitation be overcome with "protection"?

[mercuryman]

How about this transistor BU931T, Max C to E voltage 400, max current 15 a, DC gain 300.. $2.25 from JAMECO Electronics USA
The spec sheet shows a diode across C to E.

[legendre]

quote mercuryman:

Thaats the same place I got my 2sd1071’s and they don’t work either.

Well that pretty much nails it then, doesn’t it? Sorry to hear it.

BTW, are the D1071s obsolete? I can’t find them at Digi-Key or Mouser.

quote Phil B:

Could the voltage limitation be overcome with “protection”?

The circuit as published already has a protection device.. so to me, the question is: "What happens when that protection voltage threshold is further reduced?"…

Would someone with a working module take some measurements, to see how the spark voltage and energy change as the protection diode voltage threshold is progressively reduced?

[legendre]

quote mercuryman:

How about this transistor BU931T, Max C to E voltage 400, max current 15 a, DC gain 300.. $2.25 from JAMECO Electronics USA
The spec sheet shows a diode across C to E.

Possibly.. though the Hfe might be a little shy. But take a look at the ST901T "High voltage NPN Darlington transistor for ignition coil"

It would seem to be a solid candidate, though it lacks the internal diode.. but we’re already planning to add that, so it’s not of much concern. They’re about $1.70/ea from DigiKey or Mouser.

Chinese eBay sellers are offering them at significantly reduced prices.. 😉

[debe]

Very interesting about fake transistors. Cant remember where I bought the original 20 on Ebay but it was China & they work fine. Have since ordered another 20 from China on Ebay, Will be interesting to see if they work when I get them.

[legendre]

quote debe:

Very interesting about fake transistors.

True story.

A few years back, a friend who built specialty guitar amps bought a lot of "100uF / 450V Nichicon" caps off eBay. When they arrived, something was obviously wrong. You know what a typical aluminum electrolytic cap looks like, right? An aluminum can, with a rubber gas seal crimped into one end.

But these caps had a rubber seal on +both+ ends, like you’d see on a non-polar electrolytic. So, get this..

I open one up, and the can is just that.. a hollow can that has a used-pull 360V 100uF no-name Chinese cap inside. The short leads had new, full-length leads tack-welded onto them, and then the whole thing shoved into the can, sealed with two rubber seals and finished with a Nichicon shrink label over it.

Seriously. And apparently someone had a way to +make money+ on this!

[legendre]

Yay, success..

Absent a supply of +real+ D1071, I used a pair of ST 13007A transistors in a Darlington configuration. This is a common part used in switching supplies, motor controllers and even horizontal deflection circuits of small CRTs. It has a Vceb of 850V, Vceo of 400V, Ic of 8A (16A surge) and so far, no snubber diode has been needed. Darlington gain (hfe) is measuring at 1500 for small-signals – this is directly in line with calculated hfe (38 x 40). I also lack 1K5 resistors, so 1K3 are used instead. All resistors are 1/4W.

Anyway, just as expected, Q1 turns on hard, as soon as the coil voltage hits ~1.2V. When the coil voltage rises to ~2.4V (raising the base of Q2 to ~0.6V) Q2 switches on firmly, abruptly switching off Q1 and causing the coil to fire. For this exercise, I’m using a Bosch 6V ignition coil from a moped and a 12V / 1.5A DC bench supply. Coil is in the +ground+ circuit of the module / PSU loop, and the PSU (-) terminal is tied to earth ground.

There is also no cap in the circuit, yet, as it makes little sense at this point, using a manually-controlled DC supply. Once it’s being run on AC, the cap will become much more important.. it would seem to set a time constant allowing the coil voltage to rise +above+ the ~2.4V threshold before Q2’s base current starts to flow. This increases spark energy by permitting coil current to hit higher peaks before the spark is triggered.

[mercuryman]

Is this a valid test for the D1071’s Hooked 14 volt dc supply to a auto tail light , light to collector and Emitter to negative. Connected 300 ohm resistor from collector to base( had .7 volt on base). The light burned dim and 8.1 volts was across the D1071. Should the light burn bright in the test.

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