2SD2385 + 2SB1556 Transistors

fruittool · 2012-10-25T20:06:24+00:00

I've just been done on ebay. Both output transistors on a Kenwood A-97amplifier had blown. Ordered the pair from ebay, installed them,working, great. Turned it off to put it back together and noticed theheatsink was really hot on the repaired side. I found that the basevoltage on both transistors was low. Swapped both transistors from thegood side to the repaired side and its now fine. Put the new ones in thegood side the and now the good side has got hot and all the voltageshave dropped the same as they did when they were on the repaired side. Does anyone know where i can get a genuine pair of these transistors ata reasonable price?-- fruittool

Oct 25, 2012 25 Replies

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jurb6006 13 years ago

Will wonders never cease ? This place actually has a datasheet ! (they fail ed me so much I no longer bother, but at the end it said "PDF" so I got it)

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If you really cannot get them you can make Darlingtons, but I don't recomme nd it. However when you look at the internal diagram you see the the EB jun ction on a meter is not going to read like a Darlington because of the 100 ihm resistor across the EB junction of the output. You would only see the d rop of the driver EB junction. Depending on your meter it might read 0.100 higher, but will not read 1.2 volts as you might expect.

You are not ordering a million of these things, if the right part is a bit more expensive it is worth it. Like someone said B & D, but then I don't kn ow where you are. If not in the US, dealing internationally can be a PITA.

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Phil Allison 13 years ago

"fruittool"

** But you are an utter idiot.

.... Phil

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Phil Allison 13 years ago

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** Shame the schem in the above omits the reverse diode across the C and E terminals.

Easiest way to pick a power darlington with an ohm meter.

.... Phil

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jurb6006 13 years ago

Actually it might not have one, there is no law.

With two resistors, a DVM and a 12 volt supply you can measure the hfe quite easily.

That 100 ohm resistor is much more important, otherwise the Icex of the first transistor at the very least will always be applied to the base of the second transistor. The Ice leakage numbers for the whole device would look like germanium.

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Phil Allison 13 years ago

** Every darlington power transistor made has a reverse diode from C to E - it is part if the structure of the chip.

All power mosfets have a similar diode.

** But you gotta be real quick or the device will cook.

** Hogwash.

The 100ohm resistor is there to improve the switch off speed of the power transistor plus increase the breakdown voltage a little.

Leakage current in the driver transistor is only a few microamps, at most, a current level the output device can barely amplify at all.

.... Phil

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Sofa Slug 13 years ago

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