Excellent SRPP power amp of MOSFET

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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:
An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

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:
An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.


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:
An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.


Another artful SRPP circuit shown below:
An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.
 
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:
An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.
 
This is Aleph5's circuit:
An externally hosted image should be here but it was not working when we last tested it.



This is original MOSFET's SRPP circuit like vacuum tube SRPP circuit:
An externally hosted image should be here but it was not working when we last tested it.



This is enhanced MOSFET's SRPP circuit:
An externally hosted image should be here but it was not working when we last tested it.



This is MOSFET's SRPP voltage follower:
An externally hosted image should be here but it was not working when we last tested it.



The major difference between MOSFET's SRPP and Acitve Current Source of Mr. Pass is the position of sensor resistor.
 
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.
 
Re: difference

uli said:
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

:nod: :nod: :nod:

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.
 
wensan said:

The major difference between MOSFET's SRPP and Acitve Current Source of Mr. Pass is the position of sensor resistor.

In the SRPP circuit there is no current sensing resistor.

The current source is controled entirely by the voltage swing
occuring at the very output node.

NP circuitry is a bit more sophisticated as the current source is
controled by the current flowing through the sense resistor.

This leads to better damping factor and less distortion.

I would not call the Aleph current source to be a CCS as the
current is not constant except some amount of DC bias.

Uli

:nod: :nod: :nod:
 
In this SRPP circuit,R22 is current sensing resistor.
An externally hosted image should be here but it was not working when we last tested it.



In this SRPP circuit,R2//R4//R22//R24 are current sensing resistor.
An externally hosted image should be here but it was not working when we last tested it.



In this SRPP circuit,R14 is current sensing resistor.
An externally hosted image should be here but it was not working when we last tested it.



The output current is equal to upper MOSFET's current plus lower MOSFET's current.
The Active Current Source of Mr. Pass monitors the output current to adjust upper MOSFET's current.
The SRPP circuit monitors lower MOSFET's current to adjust upper MOSFET's current.
 
:eek: :eek: :eek:

The output current is equal to upper MOSFET's AC current plus lower MOSFET's AC current.
The Active Current Source of Mr. Pass monitors the output current to adjust upper MOSFET's AC current.
The SRPP circuit monitors lower MOSFET's AC current to adjust upper MOSFET's AC current.
 
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I see only two real distinctions between the above circuits and
the Aleph, and that is where the Aleph doesn't have to run
the DC bias through 2 sets of resistors, raising the efficiency
slightly, and is set up to independently adjust the DC and AC
characteristics without a hassle. :cool:
 
Nelson Pass said:
I see only two real distinctions between the above circuits and
the Aleph, and that is where the Aleph doesn't have to run
the DC bias through 2 sets of resistors, raising the efficiency
slightly, and is set up to independently adjust the DC and AC
characteristics without a hassle. :cool:

To the control circuits,The AC signal and DC bias mix together anyway.
The relationship among upper,lower MOSFET's current and output current are interdependent.
To discriminate brtween AC signal and DC bias just convenient to calculate with a pencil.

About the statement of raising the efficiency slightly,
it is not tenable to this SRPP circuit.
An externally hosted image should be here but it was not working when we last tested it.
 
IMO(I just got:D ):

the master's circuit can correct the ouptput of CCS,cause the sense cover the 'correct' and 'error' signal.Tn the other words ,it can reduce the error from the sense resister.

wensan's circuit just amplifies the the sennse signal,including the 'error' signal from the sense resister.

I think that is the main difference. :cool:
 
Either Active Current Source or SRPP circuit,
The relationship among upper,lower MOSFET's current and output current are interdependent tightly.
The output current is equal to upper MOSFET's AC current plus lower MOSFET's AC current.
Towards these control systems,Active Current Source and SRPP circuit both,
Lower MOSFET's AC current is the input singal source in the control system.
The control system can not distinguish the distortion of the input singal,
just can adjust a right ratio with the input singal.
And the output current is totally passive.
In the case of Active Current Source,
Upper MOSFETs adjust AC current of themselves a ratio with output current.
The output current includes upper MOSFET's AC current and lower MOSFET's AC current.
The lower MOSFET's AC current is the input signal in this control system.
And the other ingredient of output current,upper MOSFET's AC current,cause positive feedback!
Positive feedback is not an advantage in control system.
But in the case of SRPP circuit,
Upper MOSFETs adjust AC current of themselves a ratio with input signal directly,
and their own current will not hassle input signal in current sensing resistor like Active Current Source.
 
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