Comparing Power BJTs (Sanken, ON Semi, ...) - Page 2 - diyAudio
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Old 31st July 2010, 11:37 PM   #11
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Originally Posted by panson_hk View Post

I measured the Ic/Vce curves of the above BJTs for lower Ic. The DUT has a heatsink (65 x 40 x 20 mm) and cooling fan to avoid over temperature. The setting for curve tracer is written on the white label (mA/div, V/div). Note Ib was 5 mA for MJL21194 whereas Ib was 2 mA for other BJTs. What can see all BJTs have Ic nearly independent to Vce (ideal transistor Ic/Vce curves) when Ic is less than 2.5 A and Vce = 5 V. These are the Ic and Vce levels for a two-pair output stage driving a load consisting of 2 uF // 6 Ohm as shown in the simulation mode below where supply rails is +/- 40 V. The BJTs are nearly "ideal".
From the curves, we can see that the clipping levels (Ic = 2.5 A) for 2SC and NJL are about 10 volts from supply rails. On the other hand, 21193/93 is about 5 V.
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Old 1st August 2010, 08:33 AM   #12
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Douglas Self has also written about this and he coined the term 'load-invariant power amp' IIRC. Basically he looked at the increased linearity with more output pairs.
One way to look at that is that if you double the output pair, it LOOKS for each pair as if the load has doubled from say 8 ohms to 16 ohms as the required Ic for one pair for a certain output level is halved.

If you also want to keep the advantage of lower Vce you would tend to speakers with low impedance (like 4 ohms drivers) for low output signal for a certain sound level, coupled with multiple output pairs.

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Old 1st August 2010, 11:05 AM   #13
wahab is offline wahab  Algeria
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Originally Posted by janneman View Post
One way to look at that is that if you double the output pair, it LOOKS for each pair as if the load has doubled from say 8 ohms to 16 ohms as the required Ic for one pair for a certain output level is halved.


Right.
That s why i use at least two power devices pairs for a 50W/8R amp.
The only drawback is power dissipation at iddle, but since most designs
are AB class, it doesn t really matter.
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Old 28th November 2012, 12:29 PM   #14
catalin is offline catalin  Romania
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Great work Panson !
Congrat's !
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Old 28th November 2012, 09:48 PM   #15
Telstar is offline Telstar  Italy
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I missed this thread. Good work!
It confirms why i prefer the NJL devices.
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Old 29th November 2012, 01:24 AM   #16
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Thank you guys! NJL is also my first choice.
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