Full-Wave Rectifiers

In the half-wave rectifier the voltage is zero for half of the cycle. Full-wave rectifiers are designed using two or more diodes so that voltage is produced over the whole cycle.

Figure 83 shows a full-wave rectifier designed using two diodes and a center-tapped AC supply (i.e. center-tapped transformer).

**Figure 83:** Center-tapped full-wave rectifier.
$\begin{figure} \begin{center} \epsfig{file=images/diodeimg18.eps}\end{center}\end{figure}$

The waveforms are shown in Figure 84. The center tapping implies that the two source voltages v₁ and v₂ are a half cycle out of phase. We see that diode D₁ conducts when source v₁ is positive, and D₂ conducts when v₂ is positive, giving the waveform v_out.

**Figure 84:** Full-wave rectifier waveforms.
$\begin{figure} \begin{center} \epsfig{file=images/diodeimg20.eps}\end{center}\end{figure}$

The average or DC value of the waveform v_out is now

$\begin{displaymath}V_{AVE} = \frac{2V_{m(out)}}{\pi} \end{displaymath}$

(79)

since the waveform is non-zero twice as much as in the half-wave case. Here, V_m(out) equals V_m if we regard the diodes as ideal, and equal to V_m -0.7 V if we use the practical model.

The peak inverse voltage is

$\begin{displaymath}PIV = 2V_m -0.7 \ V \end{displaymath}$

(why?)

Figure 85 shows a bridge rectifier built from four diodes and a single AC source. The waveform of v_out is the same as for the center-tapped full-wave rectifier.

**Figure 85:** Bridge full-wave rectifier.
$\begin{figure} \begin{center} \epsfig{file=images/diodeimg19.eps}\end{center}\end{figure}$

The average voltage for the bridge rectifier is the same as in (79) but the peak inverse voltage is

$\begin{displaymath}PIV = V_m - 0.7\ V \end{displaymath}$

(again, why?)

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