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Old 1st July 2004, 03:40 PM   #1
wensan is offline wensan  United States
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Default Excellent SRPP power amp of MOSFET

SRPP circuit is very popular in vacuum tube circuits.
It also can apply to MOSFET power amp with extraordinary performance.
So I modify Aleph5 of Mr. Pass become a SRPP power amp.

Circuit and simulation result shown below:
Click the image to open in full size.
Click the image to open in full size.
The upper MOSFETs of output stage can sense the current of the lower MOSFETS to adjust the current of themselves.
In this circuit,the AC current ratio between upper and lower MOSFETs set to about 1:1.

If the AC current ratio set to 2:1 or higher,
it can perform some kind of Class AB like below:
Click the image to open in full size.
Click the image to open in full size.

In fact,SRPP circuit is a feedback control circuit.
But its open loop gain is too low to do a precise control.
Add a small transistor providing high open loop gain can improve its performance.
Circuit and simulation result shown below:
Click the image to open in full size.
Click the image to open in full size.

Another artful SRPP circuit shown below:
Click the image to open in full size.
Click the image to open in full size.
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Old 2nd July 2004, 10:22 AM   #2
wensan is offline wensan  United States
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Such SRPP circuit has extremely the same effect as Active Current Source of Mr. Pass.
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Old 2nd July 2004, 04:48 PM   #3
X.G. is offline X.G.  China
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The Great idea!!!

Quote:
Originally posted by wensan
Such SRPP circuit has extremely the same effect as Active Current Source of Mr. Pass.
I second you


BTW:My name is Đ¡¹íÍ· in Chinese forums


X.G.
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Old 2nd July 2004, 07:07 PM   #4
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You will find, though, that when you run this sort of circuit
in Class AB, the distortion is excessive.
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Old 3rd July 2004, 12:36 AM   #5
wensan is offline wensan  United States
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Running such circuit in Class AB is not my point.
I just find it has the same characters as Active Current Source.
Active Current Source senses output current.
SRPP circuit senses the MOSFET's current of the other side.

Aleph5's simulation result shown below:
Click the image to open in full size.
Click the image to open in full size.
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Old 4th July 2004, 05:19 AM   #6
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Your drawing is full of numbers, cannot see the original schematic clearly. From what I see, there is no fundamental difference from the Master's original design.
If you can make class AB Aleph, please draw more clean schematic, without sim numbers
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Old 4th July 2004, 07:50 AM   #7
wensan is offline wensan  United States
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This is Aleph5's circuit:
Click the image to open in full size.


This is original MOSFET's SRPP circuit like vacuum tube SRPP circuit:
Click the image to open in full size.


This is enhanced MOSFET's SRPP circuit:
Click the image to open in full size.


This is MOSFET's SRPP voltage follower:
Click the image to open in full size.


The major difference between MOSFET's SRPP and Acitve Current Source of Mr. Pass is the position of sensor resistor.
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Old 4th July 2004, 07:57 AM   #8
uli is offline uli  Austria
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Default difference

Main difference is that in the master´s circuit the ccs is controled by current to the load and in this SRPP circuit the ccs is controled by the voltage seen at the uotput node.

Uli

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Old 4th July 2004, 01:24 PM   #9
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Default Damn, I still dont get it

I still dont understand this SRPP concept. Do you have simpler design, like tube design to explain what it wants to achieve and how it works?
In the Master's active current source, this active current source is not controlling 100% fluctuation. The active part is some percent of output current, not 100%, there always steady number, added with some more bias following the drop in the output resistor.
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Old 4th July 2004, 02:15 PM   #10
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Default Re: difference

Quote:
Originally posted by uli
Main difference is that in the master´s circuit the ccs is controled by current to the load and in this SRPP circuit the ccs is controled by the voltage seen at the uotput node.

Uli

The BJT of wensan' ccs works in the CB stage,amplifies voltage.The BJT of the master's ccs works in the CE stage,amplifies voltage and current.but......the MOSFET is the ampflies-current- controlled-by- voltage device.

the result of both ccs maybe the same?

sorry for my poor English

X.G.
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