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Old 7th January 2005, 02:05 PM   #1
gmarsh is offline gmarsh  Canada
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Default onsemi "thermaltrak" transistors

Just spotted this while part hunting, I think you folks will find this interesting:

http://www.onsemi.com/site/newsItem/...75_985,00.html

On Semi has taken the 1302/3281 transistors and integrated a diode into the case, providing near-instant thermal tracking. Suddenly I've got the urge to build a 4-transistor Leach...
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Old 7th January 2005, 02:59 PM   #2
markp is offline markp  United States
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That's a great idea but will it be too fast? It might cause a 'breathing' effect by making the bias track the output if you know what I mean.
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Old 7th January 2005, 03:00 PM   #3
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i think you will have to overcome the urge for a few months -- they aren't in stock anywhere yet and only limited samples are available from OnSemi -- looks neat, however.
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Old 9th January 2005, 11:59 PM   #4
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That's very interesting, wondering how soon I can lay
my hands on some samples. Looks like the pin spacing
is closer together than the 3-pin packages.

Brian and Jens will have to redesign their Leach amplifier boards.

Well, not necessarily, but it'd be nice to eliminate
the external bias diodes and their wiring. I've been
testing one of Brian's boards and it's great to not
have to deal with the wires and sockets of TO-3
packages.

Taking advantage of the integrated diodes is another
issue; I don't know enough design to understand how
this would lower distortion as claimed. The obvious
benefit would be increased thermal stability and ruggedness,
allowing a designer to maybe use one less pair or
extend reliability with the same number of output devices.
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Old 10th January 2005, 12:52 AM   #5
jaycee is offline jaycee  United Kingdom
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This reminds me of the Sanken SAP power darlington devices commonly used in 5.1 gear and Arcam's DIVA amplifiers. Those devices operate without any VBE multiplier (just a single preset used for bias adjust) but they include about 3-4 diodes in each device or so.
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Old 10th January 2005, 03:06 AM   #6
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It figures... I just got a box from Newark with all my trannies on Friday. Oh well, ther's always next time...
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Old 10th January 2005, 09:58 AM   #7
MikeB is offline MikeB  Germany
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Hmm, what drives me crazy now, how to put multiple devices in paralell ?
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Old 10th January 2005, 03:34 PM   #8
LBHajdu is offline LBHajdu  United States
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Does anybody know if those diodes are drop in replacements for the leach amp ?
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Old 10th January 2005, 03:51 PM   #9
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I'm assuming that the integral diode is just a silicon diode
isolated electrically from the transistor. Each diode would
correspond to one diode in the chain of four diodes used
in the Leach circuit. Thus all four diodes in the four output transistors would be wired in series and to the circuit board,
but otherwise it should work identically.

The only difference is that these diodes will be in intimate
contact with the transistor dies and respond much more
quickly to temperature changes. Hopefully that's benefical
to the operation of the Leach design as it currently exists.

In designs that specifically take advantage of the integral
diode, the designer should be able to opt for more power
and/or more thermal stability under extreme operating
conditions.

The datasheet isn't very specific, but the diode appears to
have characteristics similar to a 1N4002 (200 volt blocking,
1 amp forward current).
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Old 10th January 2005, 04:02 PM   #10
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Well, here's an 'oopsie'.

These new transistors are connected, left to right:

base, emitter, collector, anode, cathode

The standard three-pin package is normally

base, collector, emitter

The center pin is still the collector. Obviously they
are not 'drop-in and solder' replacements. They can
be wired in with appropriate jumpers.
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