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Old 5th January 2007, 02:35 PM   #21
AndrewT is offline AndrewT  Scotland
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Hi,
how does a DIYer measure the capacitance of a BJT?

Method and equipment?
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Old 1st October 2008, 08:32 PM   #22
Xmitr is offline Xmitr  Canada
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I have 3 of the 2SC3281's which I've been testing. I tested hFE and CEO breakdown on a curve tracer and they met spec. The markings can't be removed with acetone. I installed one on a 3"x4" finned heat sink and put 20 volts at 3 amps, that's 60 watts through it. The case reached 130 degrees C. Was this a good test of power dissipation? I don't know what kind of heat sink would be required to allow 150 watts Pd.
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Old 1st October 2008, 09:16 PM   #23
wg_ski is offline wg_ski  United States
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Quote:
Originally posted by AndrewT
Hi,
how does a DIYer measure the capacitance of a BJT?

Method and equipment?
With the capacitance function on a DMM. Because the test frequency and amplitude may vary, expect absolute numbers to vary from meter to meter. But a real device with a large die will always have a larger Cbe than a phony so it's easy to compare a suspect to a known good unit.
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Old 1st October 2008, 09:21 PM   #24
wg_ski is offline wg_ski  United States
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Quote:
Originally posted by Xmitr
I have 3 of the 2SC3281's which I've been testing. I tested hFE and CEO breakdown on a curve tracer and they met spec. The markings can't be removed with acetone. I installed one on a 3"x4" finned heat sink and put 20 volts at 3 amps, that's 60 watts through it. The case reached 130 degrees C. Was this a good test of power dissipation? I don't know what kind of heat sink would be required to allow 150 watts Pd.

The same heat sink with the fins in icewater. You'll easily be able to test 100+ watts. 70V at 1.5A for one second would be a good test for a C3281. Even a 3055 could do 20V/3A at 130C case. You need to push up the voltage where a junker would go into S/B.
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Old 2nd October 2008, 04:18 AM   #25
Xmitr is offline Xmitr  Canada
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Thanks wg_ski, an interesting suggestion. I bit and immersed the heatsink in a tub of cool distilled water, just deep enough that the transistor wasn't wet. I put 75 watts into it and got a case temperature of 80 deg. Then I went for broke and covered the transistor too. Now I couldn't measure the case temp with my IR thermometer but figured if the water is at 25 degrees the case is too. The power derating curve shows it should handle 150 watts at 25 degrees case temp. So I hit it with 5 amps at 30 volts for a couple of minutes. The water was boiling on the transistor leads but she hung in there. After it cooled down it was still working ok. Sounds like Doc Brown in Back to the Future: "Einstein's clock is exactly one minute behind mine and still ticking!"

But an interesting experiment and looks like these Toshiba 2SC3281's are genuine.

Pretty tough little guy considering I way overdrove it with a case temp of 130 degrees at 60 watts.
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Old 2nd October 2008, 06:51 AM   #26
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2SA1302
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Old 2nd October 2008, 08:03 AM   #27
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by Xmitr
I have 3 of the 2SC3281's which I've been testing. I tested hFE and CEO breakdown on a curve tracer and they met spec. The markings can't be removed with acetone. I installed one on a 3"x4" finned heat sink and put 20 volts at 3 amps, that's 60 watts through it. The case reached 130 degrees C. Was this a good test of power dissipation? I don't know what kind of heat sink would be required to allow 150 watts Pd.
Hi,
with Tc = 130degC the temperature derating for a 150degC plstic package is Pmax * [(150-130)/[150-25] = Pmax * 0.16
For a 150W device operating with Tc = 130degC the power should be de-rated to 24W.
You put 60W through it.
Look up the SOA curves for the device and see where 60/0.16 lies. Use 15A and 25V (375W).
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Old 2nd October 2008, 04:27 PM   #28
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The 150 degree max junction temperature limit is mostly because the case epoxy material degrades pretty fast above that temperature. I'm not surprised it can take 60W at 130 degrees case at only 30 volts, that's just 180 degrees junction temperature.

But at higher voltages it won't take as much though...
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Old 5th June 2009, 09:59 PM   #29
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Default Fakes!!! or not?

I have a bunch of Toshiba 2SC3280's and 2SA1301's that I Plan on paralleling in an amplifier, I just have no idea if they will all agree with each other when I do so...

Nextly.... are these Toshiba 2SC3281's and 2SA1302 Fakes? They look genuine, will they work with the others in parallel?
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Old 5th June 2009, 10:02 PM   #30
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Smile Not fakes!

These are definetly genuine Toshiba's, the four with the long pins were from a cheap but working Fisher amp.
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