how much class A power can be expected with a Pair of 2sc5200 1943 pair at +/-52V - Page 3 - diyAudio
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Old 21st December 2012, 09:13 AM   #21
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I do not understand your post exactly though i suppose you speak about the Vbe multiplier.
If so, for more current into the output stage:

increase Rb2

Refering to:Page 12 of LME49811 datasheet
VBIAS= VBE(1+Rb2/Rb1)

Last edited by bobodioulasso; 21st December 2012 at 09:26 AM.
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Old 21st December 2012, 11:55 AM   #22
qusp is offline qusp  Australia
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I really think you need to spend more time reading datasheets. the LME chips have a VERY well documented amplifier application note that answers all (or at least many) of your questions.
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Old 24th December 2012, 07:42 PM   #23
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Quote:
Originally Posted by bobodioulasso View Post
I do not understand your post exactly though i suppose you speak about the Vbe multiplier.
If so, for more current into the output stage:

increase Rb2

Refering to:Page 12 of LME49811 datasheet
VBIAS= VBE(1+Rb2/Rb1)

so in the above case it can give about 2Amps of output if increasing the Rb2 so what is the maximum bias current that I can achieve with this? what are the limitations?

like I want to bias till 2.5 amps can I do that? what is the max limit on what factor it is dependent?
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Old 24th December 2012, 08:00 PM   #24
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Originally Posted by BachAudioDK View Post
If I was to design a 100W into 8ohm class A, I would consider to make it a balanced design. This reduces the rail voltage to half, but off cause doubles the peak current needed. (Amplifiers see 4ohm in BTL)

Rail voltage on output stage can be reduced to a bit above +/- 20volt.
The bias current needed in each Pushpull stage would be 2.5A (20V into 4 ohm=5A or 40V into 8ohm=5A). Power dissipation in each BJT device will be 2.5Ax20V =50W and a total of 200W for the four transistors. (One balanced channel)


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If using LME49811 the min voltage is +-20v so reducing or coming close to that voltage might shutdown the LME49811 so how did u calculate the voltage to be bit over +-20V?

so using 4 pairs of output devices is enough for safe operation? and no thermal runaway?

but I still have a question that do we need an external driver to feed the base current or Gate current to the output stages?

since according to you each pair requires about 2.5 amps so for all 8 devices its 20 amps of continuous current! the big question is that how considering that this amp would deliver 100W of class A power then what should be the psu rating? 2KVa? preferably safe...

but can you tell me what driver to use to give 2.5 amps for each output device?
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Old 24th December 2012, 08:22 PM   #25
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but technically class A amplifier pow is calculated as I x I x R example in your case 2.5 bias current which is continuous and peak its considered as 5 amps and for 5 x 5 x 8 ohms 200W peak and in RMS its 141W RMS

but my prob is what should be the gate current for each output device example toshiba 2sj201 output mosfet? what driver to use and how many stages to be used for the above power?
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