TC 9-62
of time that the anode is positive in respect to the cathode (in other words, for the first 180
degrees of the input sine wave).
Figure 4-3. Simple Half-wave Rectifier
4-9.
During the negative alternation of input voltage (dotted polarity signs), the anode
is driven negative and the diode cannot conduct. When conditions such as these exist, the
diode is in cutoff and remains in cutoff for 180 degrees. During this time, no current flows
in the circuit. The circuit current therefore has the appearance of a series of positive pulses
(see shaded areas on the waveform in Figure 4-3, view (B)). Notice that although the
current is in the form of pulses, the current always flows in the same direction. Current that
flows in pulses in the same direction is called PULSATING DC. The diode has thereby
RECTIFIED the AC input voltage.
Root Mean Square, Peak, and Average Values
4-10. Figure 4-4, view (A) shows a comparison of the root mean square, peak, and
average values of the types of waveforms associated with the half-wave rectifier. AC
voltages are normally specified in terms of their RMS values. Therefore, when a 115-volt
AC power source is mentioned in this chapter, it is specifying the RMS value of 115 volts
AC. Use the following formula to compute peak values:
Erms = Epeak x .707
The peak value is always higher than the RMS value. To compute this, use the following
formula:
Epeak = Erms x 1.414
4-4
TC 9-62
23 June 2005
Previous Page
