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bipolar (bjt) transistor families for audio power output stages
bipolar (bjt) transistor families for audio power output stages
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Old 18th December 2009, 01:55 PM   #81
Eva is offline Eva  Spain
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Could you explain the physical diferences between a "switching die" and an "audio die" in bipolar transistors?

I don't get it.

Also, in my opinion bipolar transisros work better in switching applications when:

- They keep good current gain up to high current levels, so that not a too high base current is required to achieve a low saturation Vce
- Capacitances are low, capacitances are evil in switching applications (losses, parasitic turn on, etc...)
- Transition frequency is high, which tends to imply quick saturation and de-saturation, the opposite of storing huge charge in the junctions

In fact, I think the Japanese audio bipolar transistors could be great for switching too...
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Last edited by Eva; 18th December 2009 at 02:00 PM.
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Old 18th December 2009, 02:53 PM   #82
bobodioulasso is offline bobodioulasso  Europe
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The Semi South jfets are made for switching applications. And they are excellent in audio.
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Old 18th December 2009, 03:12 PM   #83
Lumba Ogir is offline Lumba Ogir  Sweden
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bobodioulasso,
Quote:
The Semi South jfets are made for switching applications. And they are excellent in audio.
Right. Video transistors made for CRT screens are the very best you can use in VAS, but there īs much more to say about this issue. In short, you need to choose the devices with extreme care.
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Old 18th December 2009, 03:24 PM   #84
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Lumba Ogir View Post
bobodioulasso,

Right. Video transistors made for CRT screens are the very best you can use in VAS, but there īs much more to say about this issue. In short, you need to choose the devices with extreme care.
Video transistors often have very low gain and very non-linear Ic/Vce curves. Choosing with care also means not to generalize.

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Old 18th December 2009, 04:30 PM   #85
Ultima Thule is offline Ultima Thule  Europe
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Quote:
Originally Posted by AKSA View Post
Wahab,

I note quiescent here is 240mA, pretty deep Class AB; not sure what output, but is that around 20Vp?

Hugh,

was that a reply to sajti's post where he provided an attachment of the test setup for the ON-Semi transistors, then I just wonder how did you come to the conclusion the Iq is 240 mA?

I downloaded the datasheet but couldn't see anything speced.

I would have assumed, according to the theoretical proper biasing for "lowest" crossover distortion, it would be ~52 mA.


Wahab,

could you perhaps simulate with Iq = 52 mA, would be interesting to know the THD figures just out of curiosity, thanks.

Cheers Michael

Last edited by Ultima Thule; 18th December 2009 at 04:33 PM.
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Old 18th December 2009, 04:47 PM   #86
Steve Dunlap is offline Steve Dunlap  United States
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That information is printed on the graphs Wahab posted. It also says 100W at 8 ohm. Post 70.
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Old 18th December 2009, 04:55 PM   #87
wahab is offline wahab  Algeria
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the figures are higher with low quiescent current, furthermore at these
levels, close to clipping , the transfer function is heavily (literaly) distorded,
and there s no feedback to balance it...so the only mean to reduce
distorsion is to increase quiescent current, as the degeneration of
the 0.5R emitter resistance is anecdotic...

here the spectrum for 52 ma quiescent current..
Attached Files
File Type: zip MJL 21193 21194 THD.zip (5.3 KB, 107 views)
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Old 18th December 2009, 04:58 PM   #88
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Steve Dunlap View Post
That information is printed on the graphs Wahab posted. It also says 100W at 8 ohm. Post 70.
yes, steve, but iddle currents are higher in these sims,
about 250 mA...somhow hard class AB...
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Old 18th December 2009, 05:09 PM   #89
Ultima Thule is offline Ultima Thule  Europe
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Quote:
Originally Posted by Steve Dunlap View Post
That information is printed on the graphs Wahab posted. It also says 100W at 8 ohm. Post 70.
Steve,

Yes, but my post concerned post #71, or perhaps do you know what is the Iq?


Quote:
Originally Posted by Wahab
the figures are higher with low quiescent current, furthermore at these
levels, close to clipping , the transfer function is heavily (literaly) distorded,
and there s no feedback to balance it...so the only mean to reduce
distorsion is to increase quiescent current, as the degeneration of
the 0.5R emitter resistance is anecdotic...

here the spectrum for 52 ma quiescent current..
Wahab,

thanks for making the simulation, very kind of you!
Sorry for not understanding, by saying "clipping" did you mean with lower Iq it's closer to "turned off" output device or as in general understood, clipping into the rails voltage?

Cheers Michael
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Old 18th December 2009, 05:20 PM   #90
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Ultima Thule View Post
Steve,

Wahab,

thanks for making the simulation, very kind of you!
Sorry for not understanding, by saying "clipping" did you mean with lower Iq it's closer to "turned off" output device or as in general understood, clipping into the rails voltage?

Cheers Michael
since the rail voltage is +-50V, at 100W RMS,the output is close to clipping..
the emitter 0.5R degeneration bring a 2.5 V /rail loss..
if we add the Vbe at these current, we end with no more than a
margin of 6.5 V before saturation of the conductive device is effective....
the other device has reached switch off state long before the conductive
device hit the 40V peak..
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