F5X -- the EUVL Approach

[EUVL]

For those who like analysing circuits, this is essentially one (bottom) half of a single ended F5, fed by current sources.
Except for the output stage which has a JFET phase Splitter to drive it as quasi Push-pull.

All FET JLH Class A

Performance quite OK in Spice at least.




Patrick


PS

No, I have not built, and it probably would not be a new project.
Too many on the queue already.

[luvdunhill]

Originally Posted by EUVL

The schematics will be made public.
It's just a MOSFET follower with 2x RC filter from the rectifier.
Nothing special.

Patrick:

In your opinion, what's the better "use" of the voltage drop, the follower as you propose or cap multiplier?

[EUVL]

The follower I proposed is essentially a cap multiplier using UHC MOSFETs.
You can always use a Darlington instead.
But I like FETs as they allow high impedance at the gate.

Whether follower is better or feedback regulator or CRCis a matter of taste.
My current reference system has CRCRC.


Happy New Year to all,
Patrick

[luvdunhill]

Originally Posted by EUVL

The follower I proposed is essentially a cap multiplier using UHC MOSFETs.
You can always use a Darlington instead.
But I like FETs as they allow high impedance at the gate.

Whether follower is better or feedback regulator or CRCis a matter of taste.
My current reference system has CRCRC.


Happy New Year to all,
Patrick

Interesting. Which capacitor gets multiplied? I'm used to seeing a capacitor on the base of a high gain transistor, such that the "perceived" (I'm not sure what the proper word is) capacitance is a function of the beta of the device times the base capacitor value.

In this case using a MOSFET, what is the value of the resulting capacitance?

[EUVL]

> I'm used to seeing a capacitor on the base of a high gain transistor, such that the "perceived" (I'm not sure what the proper word is) capacitance is a function of the beta of the device times the base capacitor value.

IMHO this is not the correct interpretation.

The BJT CM is nothing more than a emitter follower with its base locked at a filter voltage by an upstream RCRC filter. Whether you use a BJT (Darlington) or MOSFET is immaterial. Usually MOSFETs have a lower transconductance than BJT with the same current, hence higher output impedance. This is why people prefer BJTs. The MOSFETs I chose has a transconductance of 10S at 4A, which I consider sufficient.

So the input cap gets "multiplied not because of current gain of the pass device, but by the additional filtering action of the RCRC (and if you so wish R-C-R-ZD//C) which appears to act like a much larger bank of caps.

At least this is my understanding.


Happy New Year,
Patrick

[qusp]

Patrick, thankyou for that simple and logical explanation of the capX, I have implemented them, but have been a little confused by the naming and they were a bit of a mystery to me, but thinking of them as multiplying the smoothing effect of the filter in the loop is much easier to understand. so 'in effect' the filtering is as of a larger bank of caps, but if you were to draw on them you wouldnt get the added storage of the extra capacitance. so it only amplifies the smoothing aspect, not the storage.

[EUVL]

It is just another name of an open loop floating regulator.


Patrick

[buzzforb]

PAtrick,
How does this version compare to your 2sj201 version?

[EUVL]

I do not recall publishing a regulator using 2SJ201 ??

But in any case, you can pretty much use any MOSFET in those positions.
Only two factors need to be consider :

1. The Vgs at operating current will determine the minimum voltage drop.
2. The transconductance will determine the output impedance.


Patrick

[luvdunhill]

Patrick, on the PSU schematic. If the relay K1 is omitted, can R4-R7 go as well?