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Old 12th November 2012, 07:03 PM   #671
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Quote:
Originally Posted by Bogdi12001 View Post
Hello.
This amplifier can be powered from a +/-93v supply?
Thanks.
No, +/-80V is maximum.
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Old 22nd November 2012, 02:38 AM   #672
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hi apex sir,
i set preset to 2vdcv on 10 ohm rail 10w resitor. why the emiter resistor value is different from one one? emiter resitors showing voltage 10mv,4.5mv,15mv,0mv like this.
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Old 22nd November 2012, 06:56 AM   #673
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Quote:
Originally Posted by nazirdigi View Post
hi apex sir,
i set preset to 2vdcv on 10 ohm rail 10w resitor. why the emiter resistor value is different from one one? emiter resitors showing voltage 10mv,4.5mv,15mv,0mv like this.
because of diferent hFE of output transistors,that is the reason why the emitor resistors are used. if they were matched (Ibe /Ie for bipolar or Ugs/Is for fet) before soldiering at pcb than this voltages would be the same and emitor resistors would not be needed.

please someone correct me if im wrong.
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Old 22nd November 2012, 10:22 AM   #674
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correct me if im wrong.
Your wrong !
Can't be hFE. They are mosFETs
Quote:
mosfet-amplifier-irfp240-irfp9240
.

If they were BJTs, then it's variation in Vbe that leads to be variations in Ic and shows when reading the individual Vre (voltage across the emitter resistor).

For mosFET output stage it's variation in Vgs that leads to even bigger variations in Id and that shows when reading individual Vrs (voltage across the source resistor).
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Last edited by AndrewT; 22nd November 2012 at 10:25 AM.
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Old 22nd November 2012, 10:44 AM   #675
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Quote:
Originally Posted by AndrewT View Post
Your wrong !
Can't be hFE. They are mosFETs.

If they were BJTs, then it's variation in Vbe that leads to be variations in Ic and shows when reading the individual Vre (voltage across the emitter resistor).

For mosFET output stage it's variation in Vgs that leads to even bigger variations in Id and that shows when reading individual Vrs (voltage across the source resistor).
thank you for correcting me.
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Old 22nd November 2012, 10:49 AM   #676
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and that variation in Vgs for paralleled mosFETs is why it is absolutely important that devices be selected for very close Vgs at the target operating current for the amplifier output stage.
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Last edited by AndrewT; 22nd November 2012 at 10:58 AM.
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Old 22nd November 2012, 10:55 AM   #677
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Originally Posted by AndrewT View Post
and that variation in Vds for paralleled mosFETs is why it is absolutely important that devices be selected for very close Vds at the target operating current for the amplifier output stage.
Vds or Vgs?
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Old 22nd November 2012, 10:57 AM   #678
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Sorry. Yes, Vgs
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Old 22nd November 2012, 11:25 AM   #679
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Thumbs up 0k

its 0k Andrew,we learn with you!

Last edited by 44250; 22nd November 2012 at 11:36 AM.
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Old 22nd November 2012, 11:26 AM   #680
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No,
I get accused of being unhelpful.
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