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I know it may be sounds silly! But I can not figure out where from it comes - the second half-wave (let's say positive) in full-wave rectification. Is there any key to understand it? I mean: there is only one cycle at a time, and we currently see it's positive half, but when the cycle going down to minus V, where from the second positive half-wave appears?

enter image description here

I may guess where it comes from in the case of two secondary windings with common center where the signal of the second coil acts in anti phase 180° (I'am right?). But when there is only 1 secondary winding, what is the trick to double the frequency?

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A full-wave rectifier is a specific arrangement of diodes. It has nothing to do with windings, frequency doubling, etc.

The diodes are arranged so that whichever of the two AC wires is most positive, this positive voltage passes through to to the same rectified output node. I've marked up a diagram to show the current paths. Please forgive the crudeness of my artwork!

fullbridge

As you can see, when the "upper" AC node is positive, it drives current through the load from top to bottom. When the the "lower" AC node is positive (which is the same as saying that the "upper" node is negative), the current is still driven through the load from top to bottom. The load never sees a negative voltage.

Does this help?

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Think of it in terms of current moving through the bridge rectifier, rather than voltages. If you must think about it in voltages, think about the fact that the ground can flop around in a strange manner that maintains the relationship you see.

schematic

simulate this circuit – Schematic created using CircuitLab

Note that the way the diodes point, no matter what the transformer does, the 'ground' symbol is always going to be getting current 'sucked' from it, and the wire on the right is always getting current deposited onto it. This means that the ground symbol will always be the lowest voltage in the circuit (on the secondary side) and the wire on the right will always be the highest voltage (on the secondary side).

Note that this pump action happens on BOTH positive and negative wave cycles!

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  • \$\begingroup\$ I like the option of comparison with pump ) \$\endgroup\$ – Roman Feb 11 '16 at 23:57

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