In a Full Wave Rectifier circuit, the two diodes are now used, each one is used for each half wave of the cycle. In full wave rectifier a multiple winding transformer is used whose secondary winding is divided equally into two half waves with a common center-tapped connection.
Full Wave Rectifier
Each diode is conducting when its anode terminal is attached to the positive terminal with respect to the transformer center point C so that it produces an output during both half-cycles.. so its efficiency is 100%.
Full Wave Rectifier Circuit
This circuit consists of two power diodes that connected with a single load resistance (RL) with each diode taking it in turn to supply current to the load.
When point A of the transformer is positive with respect to point C ( the point c acts as a negative terminal), diode D1 conducts in the forward direction.
When point B is positive (in the negative half of the cycle) with respect to point C so point c acts as a negative terminal,
diode D2 conducts in the forward direction and the current is flowing through resistor R in the same direction for both half-cycles.
The output voltage across the resistor R is the phasor sum, where the two waveforms combined, this type of full wave rectifier circuit is also known as a “bi-phase” circuit.
We can see this effect quite clearly if we run the circuit in the Partsim Simulator Circuit with the smoothing capacitor removed.
Partsim Simulation Waveform
As the spaces between each half-wave developed by each diode are now being filled by the other diode.
So the average DC output voltage across the load resistor is now double that of the single half-wave rectifier circuit and that is about 0.637Vmax of the peak voltage with assuming no losses.
Where VMAX is the maximum peak value in one half of the secondary winding and VRMS is the root mean square (rms) value.
The peak voltage of the output waveform is the same as the input of the half-wave rectifier provided each half of the transformer windings have the same rms voltage value.
To obtain different values of DC voltage output different transformer ratios can be used.
The main and big disadvantage of this type of full wave rectifier circuit is that a larger transformer for given high power output is required
with two separate but identical secondary windings transformer, so making this type of full wave rectifying circuit costly compared to the Full Wave Bridge Rectifier circuit equivalent.