The rectifier circuit in Figure 1 is called full-wave because it makes use of both the positive and negative half-cycles of the sinusoidal AC source voltage wave in powering a DC load.
As a result, there is less ripple voltage seen at the load than in a half-wave rectifier. It relies on the center-tapped transformer and two diodes to always provide a positive voltage to the load.
It is essential for this experiment that the low-voltage AC power supply is equipped with a center tap. A transformer with a non-tapped secondary winding simply will not work for this circuit.
Step 1: First, build the circuit illustrated in Figure 2.
Note that our low-voltage AC power supply contains inside it the center-tapped step-down transformer that was shown in the schematic diagram of Figure 1. This transformer converts the 120 VAC wall voltage down to the 12 VAC (± 6 VAC) output by our supply.
Step 2: Use a voltmeter to measure both the DC and AC voltage delivered to the motor. The RMS (root-mean-square) value of this full-wave rectifier’s output is also greater for this circuit than for the half-wave rectifier.
You should notice the advantages of the full-wave rectifier immediately by the greater DC output voltage and lower, undesirable AC voltage fluctuations, as compared to the half-wave rectifier experiment. In addition, this full-wave rectifier design has only a single-diode voltage drop in the conduction path. This is better than the two-diode voltage drops of the full-wave bridge rectifier.
Step 3: An experimental advantage of this circuit is the ease with which it may be converted to a half-wave rectifier. Simply disconnect the short jumper wire connecting the two diodes’ cathode ends together on the terminal strip (Figure 2). Better yet, for a quick comparison between half and full-wave rectification, you can add a switch in the circuit to open and close this connection at will using the circuit of Figures 3 and 4.
With the ability to quickly switch between half- and full-wave rectification, you may easily perform qualitative comparisons between the two different operating modes.
Step 4 (Optional): You can use the audio signal detector to listen to the ripple voltage present between the motor terminals for half-wave and full-wave rectification modes, noting both the intensity and the quality of the tone. Remember to use a coupling capacitor in series with the detector, as illustrated in Figure 5, so that it only receives the AC ripple voltage and not the DC voltage.
We can simulate the full-wave center-tap rectifier, as illustrated in Figure 6, using SPICE.
Netlist (make a text file containing the following text, verbatim):
Fullwave center-tap rectifier v1 1 0 sin(0 8.485 60 0 0) v2 0 3 sin(0 8.485 60 0 0) rload 2 0 10k d1 1 2 mod1 d2 3 2 mod1 .model mod1 d .tran .5m 25m .plot tran v(1,0) v(2,0) .end
Learn more about the fundamentals behind this project in the resources below.
Textbook:
Worksheets:
In Partnership with NXP Semiconductors
by Jeff Child
by Jake Hertz
