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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 12th October 2017, 07:55 PM   #31
Elvee is offline Elvee  Belgium
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Originally Posted by infinia View Post
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?
There must be some misunderstanding, because I added the capacitors to the half-wave side (I think), where the voltages have a D suffix:
I repost the same picture here, to eliminate possible confusions:

Why is full wave voltage doubler not used more?-compdoubrect4-png

C4 and C5 have been added to compensate for the weakness of the doubler; without them, the comparison is completely fair, ie. identical circuits elements are rearranged in a different manner.
Note that the current angle will only have a minuscule effect on the power factor: most of it stems from the high peak to average ratio, inherent to this type of supply, not the I-V phase shift.

Realizing the reactive current is C*dV/dt looking at the ripple voltage I fully agree 100% on this but your sim results and other statements don't support this view.
I do not see where.
The peak current remains ~the same, because the positive slope of the ripple is halved, but the capacitance is doubled.
The area under the peak must remain the same, because the average current is identical.
Note that in all of the cases, the current is measured on one winding, even though the windings are paralleled in the doubler's case. That's to respect the fairness condition:
The primary winding will always see both windings in front of him, be they series or paralleled.
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.
If the loads are unbalanced, the doubler topology should be avoided: some transformers, like loosely packed EI might tolerate it very well, but a high perm toroidal or R-core could be unhappy with only a few % unbalance, and there is no way to know without trying.
For pure doubler (no GND out) applications, the doubler is only very marginally inferior (for the same components investment).
For dual supplies, the capacitors would need to be larger to keep the same ripple (without impact on the transformer's utilization), but the total component count is 4 against 6, even if the 4 need to be larger.

If one is aware of these limitations, the topology can be useful, especially for DIY purposes (I don't see any valid justification for OEM's)
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