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Why is full wave voltage doubler not used more?
Why is full wave voltage doubler not used more?
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Old 11th October 2017, 01:36 AM   #21
infinia is offline infinia  United States
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Quote:
Originally Posted by Elvee View Post
but it still covers a good number of real-life situations
I wouldn't go that far & call your model "real life".
Get a dual winding XFMR and build it, you know with a central measurement ground point. Show equal Vripple 1st, then measure current or better yet power factor.
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Old 11th October 2017, 03:58 AM   #22
LuigiDJ is offline LuigiDJ  Colombia
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I found one panasonic subwoofer (sb-wa330) that uses this circuit for a 2-step power supply feeding a rsn311w64 ic for the power output.
Check page 12 and 13 on the service manual : http://diagramas.diagramasde.com/aud...0subwoofer.pdf
Filter caps were 4700 and 3300 uF and this was a 5.1 channel setup.
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Old 11th October 2017, 04:07 PM   #23
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by infinia View Post
I wouldn't go that far & call your model "real life".
I do not call the model "real life", I just say that the majority of real life loads are either floating (thus inherently balanced) or balanced: amplifiers and opamps circuits fall into that category.

A few other circuits require a main (often positive) supply, and an auxiliary supply of opposite polarity.
These will let DC pass through the transformer and aren't suitable candidates for doubler supply: the effects will be unpleasant and unpredictable, and delving into the gory details is a waste of time.

With balanced outputs, the behavior of both circuits will be very similar, if sizing is made fairly: same total CV product for the capacitance, etc.

There will be some minor differences: diodes will see twice the current (but they are 2 instead of 4) and the filter caps will see a ripple at Fmains instead of 2*Fmains.
This in turn will be reflected in the output voltages, and the total output voltage will also be slightly smaller

If you have doubts, feel free to experiment for yourself...
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Old 12th October 2017, 11:22 AM   #24
infinia is offline infinia  United States
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Quote:
Originally Posted by Elvee View Post
There will be some minor differences: diodes will see twice the current (but they are 2 instead of 4) and the filter caps will see a ripple at Fmains instead of 2*Fmains.
This in turn will be reflected in the output voltages, and the total output voltage will also be slightly smaller

If you have doubts, feel free to experiment for yourself...
You now admit doubler operation is infact only half wave rectification with all that implies on adding capacitance across the load to compensate ...thus reactive current has increased over the 4 diode version (with equal ripple on the loads ). I'm sorry XFMER utilization is not the same or better for half wave rectification. I don't call it a minor difference on some real designs esp. with small transformers. You can see for yourself on your model if you care to show the output ripple voltages as magnitudes, not simply dismiss it as mains or 2x mains frequencies.

The supply in Question is a dual with a central ground. On your simulation you modified the circuit.. The waveform you showed was a single balanced system operating as full wave which was/is very deceiving, not accurate at all.
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Last edited by infinia; 12th October 2017 at 11:24 AM.
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Old 12th October 2017, 11:27 AM   #25
mchambin is offline mchambin  France
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Old 12th October 2017, 12:16 PM   #26
infinia is offline infinia  United States
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Originally Posted by mchambin View Post
+1
That's the problem with simulating designs, at some point you have to build it. That's when the "minor" problems smack you upside the head. Little dual regulated linear supplies are hidden with many gotchas. Starting with this doubler topology youll either have live with higher ripple and more 3T regulator headroom / heatsinks or buying bigger caps, in either case the XFMR will running at hotter VA's.
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Last edited by infinia; 12th October 2017 at 12:18 PM.
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Old 12th October 2017, 12:20 PM   #27
Merlinb is offline Merlinb  United Kingdom
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Originally Posted by ivanlukic View Post
Yes, that's what I ment.
Ripple frequency is halved = harder to filter.
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Old 12th October 2017, 04:12 PM   #28
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by infinia View Post
You now admit doubler operation is infact only half wave rectification....
I am not admitting it now: if you cared to read the previous posts, I mentionned it from the very beginning:

Quote:
Originally Posted by Elvee View Post
The differences between a FW doubler and a FW rectifier using a winding of twice the voltage is very subtle indeed, and could be missed in a first analysis, but they do exist: in a FW rectifier, two sets of diodes replenish a single filter capacitor twice per cycle, whereas in a (so-called) FW voltage doubler, two times one diode replenish two caps once per cycle, and the cap voltages are later added.

The result looks superficially similar, but it isn't: adding two half-wave rectifiers isn't equivalent to a true full wave rectifier.
The ripple seen by each half-wave cap is somewhat higher,
....
Here are the individual V+ outputs for each case, and also the voltages sum:

Why is full wave voltage doubler not used more?-compdoubrect-png

For this situation, the transformers currents are comparable:


Why is full wave voltage doubler not used more?-compdoubrect1-png

Quote:
with all that implies on adding capacitance across the load to compensate ...thus reactive current has increased over the 4 diode version (with equal ripple on the loads ). I'm sorry XFMER utilization is not the same or better for half wave rectification. I don't call it a minor difference on some real designs esp. with small transformers. You can see for yourself on your model if you care to show the output ripple voltages as magnitudes, not simply dismiss it as mains or 2x mains frequencies.
We can increase the filter caps to compensate for the higher ripple:

Why is full wave voltage doubler not used more?-compdoubrect2-png

This does practically not change the peak currents compared to the previous case (it looks counter-intuitive), because the average output current remains practically identical, as is the diodes conduction angle.

What about the individual ripple voltages? They are now practically identical:

Why is full wave voltage doubler not used more?-compdoubrect3-png


Thus, there is a penalty to be paid (twice the C*V product), but it remains relatively acceptable.
Of course, if you start designing a supply from scratch, it would be silly to opt for the doubler solution, but if you already have a suitable transformer of half the voltage, it is certainly cheaper to use it with a doubler rather than buying a new transformer
Attached Images
File Type: png CompDoubRect.png (78.3 KB, 55 views)
File Type: png CompDoubRect1.png (64.7 KB, 55 views)
File Type: png CompDoubRect2.png (88.2 KB, 55 views)
File Type: png CompDoubRect3.png (62.2 KB, 55 views)
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Old 12th October 2017, 05:32 PM   #29
infinia is offline infinia  United States
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I saw & agreed with your 1st post. but disagreed with your conclusions about XFMR utilization in later posts.
Now I still have issues with your last sim on the actual circuit. Strangely you added caps to the full wave side correcting the current angle, when we both know it should of been added to the half wave side. right?
Realizing the reactive current is C*dV/dt looking at the ripple voltage
Quote:
Of course, if you start designing a supply from scratch, it would be silly to opt for the doubler solution,
I fully agree 100% on this but your sim results and other statements don't support this view.
Quote:
but if you already have a suitable transformer of half the voltage, it is certainly cheaper to use it with a doubler rather than buying a new transformer
Of course , also keeping the loads from being too lopsided E.g balanced.
Nothing wrong with the topology. its just not ideal for the smallest iron and copper.
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Last edited by infinia; 12th October 2017 at 05:47 PM.
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Old 12th October 2017, 05:37 PM   #30
ivanlukic is offline ivanlukic  Serbia
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Originally Posted by Elvee View Post
Of course, if you start designing a supply from scratch, it would be silly to opt for the doubler solution, but if you already have a suitable transformer of half the voltage, it is certainly cheaper to use it with a doubler rather than buying a new transformer
That's exactly the reason why I used it for some preamps.
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