Electrical Power Systems Technology

Direct Current Power Systems 193

Vr(rms)

% ripple = ——— = 100

Vdc

Sample Problem:

Given: a power supply has an AC input of 24 volts (rms) and a p-p

ripple of 1.5 volts at its output, as measured with an oscilloscope.

Find: DC voltage output of the power supply.

Solution:

Vr(p–p)

VDC = Vmax – ———

2

1.5 V

= (24 V × 1.41) – ———

2

VDC = 33.09 volts

A full-wave rectified voltage has a lower percentage of ripple than a

half-wave rectified voltage. When a DC supply must have a low amount

of ripple, a full-wave rectifier circuit should be used.

Capacitor Filter

A simple capacitor filter may be used to smooth the AC ripple of a rec-

tifier output. Figure 7-28 shows the result of adding a capacitor across the

output of a single-phase, full-wave bridge rectifier. The output waveform

after the capacitor has been added is shown in Figure 7-28C.

Figure 7-27. Rectifier output voltage