Finding a replacement transistor

Semiconductor Discrete Semiconductor Products
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1

Hi,

I have a transistor from the igniter of a 90s motorcycle, part 2SD1071.
It doesn’t appear to be made anymore so I need an alternative.

I did see this one that may have done the trick, but looking at the diagram it is lacking a Zener Diode https://www.digikey.co.nz/en/products/detail/stmicroelectronics/BU931T/603822

The datasheet I have been working off is https://alltransistors.com/adv/pdfdatasheet_inchange_semiconductor/2sd1071.pdf

Any suggestions would be appreciated.

2

Hi,
Welcome to the DigiKey tech forum. I wasn’t able to find an option to offer with the zener feature.

3

MJE5742G looks line a pretty similar option that’s in stock. Lacks the zener, but it shouldn’t be much of a task to attach one externally, with the leads being adjacent and whatnot. BZT03C270-TAP is probably the closest in stock at present.

4

Thanks Rick, the MJE5742G looks like a better fit, on the sheet it has 2 power figures 2W and 100W do you know which one would be correct?
Also the hFE value does seem a bit low (200 min vs 500 min), any idea how much of an issue this would be?

Cheers.

5

Both: it depends on whether one stipulates an air temperature or case temperature for the measurement. This resource and its sequel explain the whys, wherefores, and relevant procedures for analysis of such things.

Lacking specific knowledge of the design in question, I can’t say if the difference in min gain would matter much. As sloppy a parameter as hFE is, good designs tended to leave quite a bit of margin. Here’s the longer short list if you wanted to look at some of the other options.

6

Hi blair5032,

Not sure if this helps, but BU941 seems to have a zener embedded. It’s connected to the lower transistor’s base, possibly to offer better isolation to the Base pin.

In an ignition application the transistor is used as a switch, so the small signal gain is not that important parameter. These days IGBT would suit better, but cannot likely be used as a replacement here due to higher base (e.g. gate) threshold voltage.
Cheers,
heke, AsamaLab

7

Thanks @heke, that does look like a good option sadly I could not find any in stock. So I think I will try ordering @rick_1976 suggestion and soldering the zener on.

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