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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 7th Aug 2022, 9:03 pm   #1
river9999uk
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Default 2SD1976 transistor replacement ?

Hi All

Whats a modern replacement for this 2SD1976.....I've been looking at all sorts for hours and my head now hurts as all I can find is just as old no longer made transistors Its in a old computer unit and I need a swap.

Thank you

Last edited by river9999uk; 7th Aug 2022 at 9:09 pm.
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Old 7th Aug 2022, 9:56 pm   #2
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Default Re: 2SD1976 transistor replacement ?

The device is described as having an inbuilt zener diode and resistors so trying to find a modern drop in replacement is not looking straightforward.

https://datasheetspdf.com/pdf/240506...ctor/2SD1976/1
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Old 7th Aug 2022, 10:07 pm   #3
river9999uk
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Default Re: 2SD1976 transistor replacement ?

Yeah I was looking at a 2SD1071 but I am not sure I am right......
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Old 7th Aug 2022, 10:09 pm   #4
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Default Re: 2SD1976 transistor replacement ?

I looked in all my books and nothing, sorry!
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Old 8th Aug 2022, 9:42 am   #5
river9999uk
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Default Re: 2SD1976 transistor replacement ?

Thanks for looking...its a tough one. Think I might get a couple of old stock 1071's and gamble as they look almost the same spec wise.
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Old 8th Aug 2022, 1:21 pm   #6
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Default Re: 2SD1976 transistor replacement ?

Search on ebay.COM $9.48 inc shipping from China
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Old 8th Aug 2022, 1:25 pm   #7
river9999uk
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Default Re: 2SD1976 transistor replacement ?

OK thanks for that link. Do these transistors with Zenners test out different to a normal transistor ? Can you tell if its correct or fake?
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Old 8th Aug 2022, 1:40 pm   #8
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Default Re: 2SD1976 transistor replacement ?

Different, but you have to work at it to see the difference. A little battery powered hand-held tester won't show it.

The zener looks like a normal diode when biased the opposite way, but then so do most MOSFETs across d-s. So nothing unusual. To find the difference you have to take d-s voltage high enough in the normal direction for the zener clamp to act. A normal MOSFET would just let Vds gohigher until damage happened.

MOSFETs made the usual way have an unavoidable diode across drain-source which will turn on if the drain-source pair get reverse biased. In things like SMPS and class D transmitters, great care has to be taken to make sure this diode never gets turned on, because it's rather slow and won't turn off at the speed of the transistor itself... this leads to pops, bangs and smoke. In the case of these transistors, the implicit diode is made to have avalanche characteristics. (Zener is a misnomer, real zener effect diodes are all low voltage)

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Old 8th Aug 2022, 2:03 pm   #9
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Default Re: 2SD1976 transistor replacement ?

What voltage are they working at? I have some 2SD1276's, but they're a lower voltage, 60v as opposed to 300v
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Old 8th Aug 2022, 2:14 pm   #10
river9999uk
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Default Re: 2SD1976 transistor replacement ?

Think its quite high so might break those. Can anyone tell me if a 2SD1071 would be a good swap as to my eyes they look almost identical in the spec sheets and seem to be a few around still.
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Old 8th Aug 2022, 6:14 pm   #11
Cruisin Marine
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Default Re: 2SD1976 transistor replacement ?

I guess if it comes to it, you will have to fit a 300v device and fit an external 300v zener.
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Old 9th Aug 2022, 6:37 am   #12
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Default Re: 2SD1976 transistor replacement ?

Look the same to me, suck it and see as they say.
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Old 9th Aug 2022, 7:36 am   #13
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Default Re: 2SD1976 transistor replacement ?

Hi.
Why not fit a BU2508 line transistor or similar and an external 300v avalanche diode?

Mind you the original transistor has a pretty amazing spec and of course is very fast.
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Old 9th Aug 2022, 7:57 am   #14
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Default Re: 2SD1976 transistor replacement ?

Found this on the internet, maybe an equivalent using two transistors could be used to make a darlington replacement
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Old 9th Aug 2022, 10:27 am   #15
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Default Re: 2SD1976 transistor replacement ?

The protection diode, if you used an external one could be a suitably rated TVS type. A unidirectional one would be fine, you wouldn't need a bi-directional one.

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