Help to understand full wave CW multiplier w/o center-tapped driver?

Thread Starter

Aleph(0)

Joined Mar 14, 2015
597
So I just always understood principle of full wave Cockroft Walton multiplier to be basically running two halfwave multipliers on opposite sides of a center-tap so the 180° phase difference develops a composite output with low ripple and better load regulation?

Anyhow HP suggested I just use three stage full wave CW multiplier cuz I'm having problems with xfmr voltage stress using just doubler. She sent me schematic of circuit (like attached pic). She said it doesn't need center tap and that performance is not degraded without it (which is good cuz most HV winding aren't tapped).

Well the more I thought abt it the more convinced I got that she had to be mistaken so I modeled it in Ltspice and it totally agrees with what HP is saying:confused:!

So K1 is just 1:1 transformer that I added so grounded tap vs floating tap operation can be easily compared.

Now I'm feeling totally dumber than usual:oops: cuz I can't understand how grounded tap and non-grounded tap operation are identical! There's just no difference in output current, voltage, ripple, buildup time and like that! And input current waveshape, _inrush_ magnitude and duration are same also:confused:

So I get that the circuit somehow sees a totally solid virtual midpoint when running w/o center-tap (which explains why output is Pk input * number of stages (instead usual CW factor of 2*pk input * number of stages) but I just can't get my mind around how:(!

So to put fine point on it here's questions:
◊How can grounded center-tap operation be exactly the same as when it's not connected?
◊Why isn't there a single solitary mention or example of non center-tapped operation anywhere on the net (I've looked for hours!)

HP isn't available to ask right now and anyhow maybe hearing explanation in other words will help clear _block_ Anyhow I hope it's just mental block and not plain stupidity:eek::oops:

Here's schematic: Also I've attached .asc file so for standard connection just ground node "T":)

So tnx in advance for helping me recapture my sanity:eek::)!

PS R1 and R3 are just to keep Ltspice happy:cool:!

FWCW.png
 

Attachments

Hypatia's Protege

Joined Mar 1, 2015
3,226
◊Why isn't there a single solitary mention or example of non center-tapped operation anywhere on the net
It's a plot to confound little Alephs and make them 'all sick and crazy inside'!:p

@Aleph(0) Noting that the '.asc file' has received only a single view (probably yours) -- I suggest that this thread is 'misplaced' in General Chat?-- Perhaps you should ask a mod to move it to 'Power Electronics'?

Failing all else (i.e. a constructive response) I'll try to post a 'walk-through' sometime tomorrow/early Wed -- Please understand I've a lot on in preparation for/prior to Dayton (Including completion of the 'Indicator mini-turorial':rolleyes:)

Very best regards
HP:)
 

tcmtech

Joined Nov 4, 2013
2,867
Hmm... Did you want a single ended voltage multiplier or a split rail one, (Common and V+ out ) DC Vs a dual rail center tapped (-V Com - V+) DC multiplier? o_O

Interesting circuit but as you have found out it's pretty limited applications hence the reason so little explanations behind it. Either you need one and you build it or you don't need it and could care less. :oops:

I would like to put it in better words but at the moment I can't come up with a written explanation that makes sense without it coming off like a Dr Who space-time explanation that's summed up with, " It's just time travel. Don't overthink it." and doesn't really answer anything in general. :p

If you want to understand how it's doing it the simplest way I can think of is draw multi line current flow lines on the circuit in different colors for the various current flows and their magnitudes of each half of the input AC cycle.
 

Hypatia's Protege

Joined Mar 1, 2015
3,226
If you want to understand how it's doing it the simplest way I can think of is draw multi line current flow lines on the circuit in different colors for the various current flows and their magnitudes of each half of the input AC cycle.
Thanks @tcmtech - In contemplation of my explanation of the circuit to @Aleph(0) it occurs to me that a powerful conceptual/educational tool could be realized via a simulation feature whereby the appearance of component symbols on the schematic change at simulation time with varying electrical conditions. For example, diodes could show as green to indicate (unbiased/'off') and red for (biased/'on'), capacitors could change hue based on percentage of charge, etc... IIRC I've seen something of the sort on the web - somewhere? At any rate it seems you're describing something similar?

Interesting circuit but as you have found out it's pretty limited applications hence the reason so little explanations behind it. Either you need one and you build it or you don't need it and could care less.
:oops:
FWIW, as I understand it, @Aleph(0) 'problem' is merely that she can't get past the fact that the circuit operates equally with or without a center-tap to ground connection... --- A matter more readily comprehended than explained to another (at least by me:oops:) -- Seems I'm destined to be a 'frustrated instructor' 'till my 'dyin day!:rolleyes::oops:

Hmm... Did you want a single ended voltage multiplier or a split rail one, (Common and V+ out ) DC Vs a dual rail center tapped (-V Com - V+) DC multiplier? o_O
She (Aleph) posted the 'positive side' of a 'split supply', the 'negative side' is precisely the same configuration save that all diodes are reversed... Note also that, in actual construction, the transformer is an 'AC' TV Flyback driven by a resonant Royer power oscillator... Aleph wished to reduce stress on the transformer, hence my suggestion of the above circuit (which being a tripler) as opposed to the Delon rectifier (full wave doubler)... Please note: Despite CW topology, the cascade in question is indeed a tripler (as opposed to a sextupler) owing to effective 'halving' of the excitation EMF each side of 'ground'...

Very best regards
HP:)
 

Thread Starter

Aleph(0)

Joined Mar 14, 2015
597
@tcmtech it's like HP says I totally understand circuit if center-tap (which is node T) is grounded but circuit works perfectly good without any center-tap at all! Also if I run simulator with center-tap disconnected it doesn't follow ground which means something should change when it's connected:confused:!

So anyhow tnx for reply cuz sound of crickets gets too depressing!:)
 

Hypatia's Protege

Joined Mar 1, 2015
3,226
Also if I run simulator with center-tap disconnected it doesn't follow ground which means something should change when it's connected:confused:!
---Emphasis Added---

Aleph - I daresay this matter has you speaking in tongues!:eek: -- Relax! I've yet to be 'beaten up' by a cascade!:D

As I understand the (emphasized) text quoted above, you are advising that ungrounded, the center-tap does not remain at ground potential during simulation? -- Indeed not! Ungrounded, the center-tap fluctuates between Ca. 8kv and 8.25kV above ground at twice the input frequency. More to the point, provided a low Z current path to ground, the center-tap to ground current manifests as a train of complex ≈ 3us, 350ma (pk-pk) pulses recurrent at twice the input frequency...

which means something should change when it's connected:confused:!
Well indeed grounding the center-tap alters the 'charging pattern' howbeit, as you have seen, sans change of circuit parameters - as would be obvious were you to merely behold the 'big picture' en masse, as it were...:rolleyes:

Best regards
HP:)
 

AnalogKid

Joined Aug 1, 2013
9,639
"FWIW, as I understand it, @Aleph(0) 'problem' is merely that she can't get past the fact that the circuit operates equally with or without a center-tap to ground connection..."

"equally" is a relative term. Real world, the output voltage will vary between the two conditions. As a test, increase C1 by 25% and decrease C2 by 25%, and see what happens at the output.

ak
 

Hypatia's Protege

Joined Mar 1, 2015
3,226
"equally" is a relative term. Real world, the output voltage will vary between the two conditions.
FWIW experience has shown that the 'real world' implementation exhibits no difference in output or drive parameters whatever (grounded secondary vs. non-grounded secondary) -- of course the 'internal behaviour' (i.e. capacitor charging patterns) are quite different albeit 'equivalent' (i.e. productive of equal 'external' parameters):cool:

As a test, increase C1 by 25% and decrease C2 by 25%, and see what happens at the output.
Aye! Such 'tinkering' would indeed provide a glimpse inside the 'black box' -- To wit: Symmetry is the soul of transparency via balance:) You getting this @Aleph(0)?:cool:

The secondary is already center tapped. With the load.
Please note that, as shown, the center-tap (i.e. node 'T') is not grounded and needn't be grounded for proper circuit operation...

But to continue...
The load is placed between Node 'Ea' and the ground node (i.e. across the central capacitor 'stack' formed by C3, C8 and C9) -- grounding of the center tap is without effect beyond internal cascade operation -- in point of fact the circuit does not require a tapped secondary at all...

On the other hand, if your assertion is merely that the circuit is self-balancing - correct! -- Howbeit such does not imply correspondence of mid-secondary and ground node potentials in a non tapped or otherwise non grounded secondary configuration (please see post #6)

Apologies if I'm missing your point:oops: -- But then our being, as you claim, of disparate 'species', communications issues are only to be expected;):p

Sincerely many thanks and very best regards all around!
HP:cool:
 
@Aleph(0)

Well hey! Following some 'soul-searching', I suppose I've let you 'stew' upon (i.e. obsessively overthink) this one for long enough;):cool:

So...
By way of exposition, please consider the fact that (with reference to the diagram shown in your OP) C1 & C2 (i.e. the leftmost 'input capacitors') may be omitted (i.e. replaced by conductors) if a center-tap connection is not used. -- Get it? The cascade may be regarded as a string of 'bridge rectifiers' each charging one of C3, C8 and C9 to peak input EMF while effectively placing same in series across the load:) The function of the other caps being merely provision of DC isolation...

◊Why isn't there a single solitary mention or example of non center-tapped operation anywhere on the net (I've looked for hours!)
I submit that your confusion owes to the (above) quoted consideration alone! To render one of your favorite 'refrains' 'truth is not consensus based' -- Well indeed not! But then neither is common sense!:rolleyes: The sad, sad fact that the 'web' (and, for that matter, the world) is replete with lazy (I daresay, even, 'cowardly') folk happy to outsource their perception and interpritation of reality would seem irrelevant! While one hesitates to advise you to 'walk your talk', It seems I just did:eek::D

It is sincerely hoped that your 'struggle' in this matter will be taken as a lesson in the 'virtues' of independent thought!:cool:

Expository diagram of cascade 'optimized' for 'tap-less' operation (via omission of C1 and C2) -- Please note: For your convenience I have attached an LtSpice model ('.asc') of this circuit
FWCW_Expo.png

As always, sincerely, very best regards
HP:)
 

Attachments

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Thread Starter

Aleph(0)

Joined Mar 14, 2015
597
@Aleph(0)

Well hey! Following some 'soul-searching', I suppose I've let you 'stew' upon (i.e. obsessively overthink) this one for long enough;):cool:

So...
By way of exposition, please consider the fact that (with reference to the diagram shown in your OP) C1 & C2 (i.e. the leftmost 'input capacitors') may be omitted (i.e. replaced by conductors) if a center-tap connection is not used. -- Get it? The cascade may be regarded as a string of 'bridge rectifiers' each charging one of C3, C8 and C9 to peak input EMF while effectively placing same in series across the load:) The function of the other caps being merely provision of DC isolation...


I submit that your confusion owes to the (above) quoted consideration alone! To render one of your favorite 'refrains' 'truth is not consensus based' -- Well indeed not! But then neither is common sense!:rolleyes: The sad, sad fact that the 'web' (and, for that matter, the world) is replete with lazy (I daresay, even, 'cowardly') folk happy to outsource their perception and interpritation of reality would seem irrelevant! While one hesitates to advise you to 'walk your talk', It seems I just did:eek::D

It is sincerely hoped that your 'struggle' in this matter will be taken as a lesson in the 'virtues' of independent thought!:cool:

Expository diagram of cascade 'optimized' for 'tap-less' operation (via omission of C1 and C2) -- Please note: For your convenience I have attached an LtSpice model ('.asc') of this circuit
View attachment 126410

As always, sincerely, very best regards
HP:)
HP it's totally intriguing cuz when tap is tied to ground (on circuit with leading caps) it's just just back to back 1/2 wave multipliers which are just stacked 1/2 wave rectifiers!

So circuit w/o tap is totally beautiful in functionality and concept as well as being better circuit!

Now I'm going to say something! I think it's awesome how circuit w/o tap is actually better design cuz of simpler transformer and also reducing impedance by removing two caps! HP I admit I was psyched into not thinking for myself cuz there was no mention of untapped design anywhere! Not even on industry and trade sites! So it just goes to show how most professionals are educated idiots who just parrot anything from what they consider reliable source w/o any critical thinking for themselves and I say that's worse than lame cuz it's revoltingly lazy!

So anyhow thanks cuz now I have my mind right abt the multipliers and also abt not accepting rubbish based on consensus which I'm realizing is always wrong until proven otherwise! But ppl with proof and truth on their side don't need consensus so consensus is just a crutch for feeble minded, lazy and ppl who like whistling in the dark! So anyhow you can see I'm learning but it can be like you say slowly but slowly sometimes:oops:
 
I admit I was psyched into not thinking for myself cuz there was no mention of untapped design anywhere! Not even on industry and trade sites! So it just goes to show how most professionals are educated idiots who just parrot anything from what they consider reliable source w/o any critical thinking for themselves and I say that's worse than lame cuz it's revoltingly lazy!

So anyhow thanks cuz now I have my mind right abt the multipliers and also abt not accepting rubbish based on consensus which I'm realizing is always wrong until proven otherwise! But ppl with proof and truth on their side don't need consensus so consensus is just a crutch for feeble minded, lazy and ppl who like whistling in the dark! So anyhow you can see I'm learning but it can be like you say slowly but slowly sometimes:oops:
...And once again! Truth is not consensus based! Congratulations on your epiphany! - albeit a tad late;):D

Best regards
HP:cool:
 
hi
what is application of it?
The circuit shown in the OP (if the center-tap is grounded) is a full-wave Cockcroft-Walton cascade -- Whereas the ungrounded secondary configuration (as shown in post #10) is a variant therof offering (slightly) superior performance and greater versatility as regards transformer/driver selection...

Best regards
HP:)
 
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Thread Starter

Aleph(0)

Joined Mar 14, 2015
597
@Aleph(0)

Well hey! Following some 'soul-searching', I suppose I've let you 'stew' upon (i.e. obsessively overthink) this one for long enough;):cool:

So...
By way of exposition, please consider the fact that (with reference to the diagram shown in your OP) C1 & C2 (i.e. the leftmost 'input capacitors') may be omitted (i.e. replaced by conductors) if a center-tap connection is not used. -- Get it? The cascade may be regarded as a string of 'bridge rectifiers' each charging one of C3, C8 and C9 to peak input EMF while effectively placing same in series across the load:) The function of the other caps being merely provision of DC isolation...


I submit that your confusion owes to the (above) quoted consideration alone! To render one of your favorite 'refrains' 'truth is not consensus based' -- Well indeed not! But then neither is common sense!:rolleyes: The sad, sad fact that the 'web' (and, for that matter, the world) is replete with lazy (I daresay, even, 'cowardly') folk happy to outsource their perception and interpritation of reality would seem irrelevant! While one hesitates to advise you to 'walk your talk', It seems I just did:eek::D

It is sincerely hoped that your 'struggle' in this matter will be taken as a lesson in the 'virtues' of independent thought!:cool:

Expository diagram of cascade 'optimized' for 'tap-less' operation (via omission of C1 and C2) -- Please note: For your convenience I have attached an LtSpice model ('.asc') of this circuit
View attachment 126410

As always, sincerely, very best regards
HP:)
HP I say maybe is not a good move to omit leading caps cuz then there's DC path across secondary if output is shorted? Just sayin'
 
HP I say maybe is not a good move to omit leading caps cuz then there's DC path across secondary if output is shorted? Just sayin'
Granting that it's less than 'elegant', it slightly increases performance and saves the builder ≈ $50 (Small quantity pricing on 10 nf HV disks ≈ $25 apiece) -- Yes I know!:rolleyes: Howbeit, as you point out, we must strive to 'meet them half way':)

For the benefit of interested readers I've prepared the following illustration of the DC path through the multiplier.

DCpathExpo.png

Very best regards
HP:)
 
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