EEE 360 LAB 23

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Johns Hopkins University *

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360

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Electrical Engineering

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Apr 3, 2024

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docx

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EEE 360 Lab 23 Experiment 23. Diode Bridge Rectifier cf4c3cad91289812d1a9005f1afc056067777ff9.docx 23-1

OBJECTIVE  To study the operation of a single-phase diode bridge rectifier. DISCUSSION Rectifiers are a class of power converters which convert alternating current (AC) to direct current (DC). Rectifiers are classified as either controlled or uncontrolled. Today, we will be exploring the uncontrolled, single-phase, full-wave, diode bridge rectifier. It should be noted that many of the concepts discussed can be extended to the three-phase power system. This bridge rectifier circuit is comprised of four diodes usually followed by a filter capacitor as illustrated in Figure 23-1. The diode is a two-terminal device, which permits current flow in a single direction. The forward current of a large diode can be can be several thousand amperes. The reverse current is only few milliamperes. The forward rated current produces potential drop of a few volts. In the reverse current direction, the increase of the voltage beyond the rated value produces breakdown and destruction of the device. The single-phase bridge type rectifier is widely used in low power appliances because of simplicity and low cost. A transformer is also usually placed before the rectifier to first step the voltage down. cf4c3cad91289812d1a9005f1afc056067777ff9.docx 23-2

Figure 23-1. Bridge rectifier circuit with a filter capacitor. In many cases, the four diodes are contained in a single package as shown in Figure 23-2. Figure 23-2. Diode bridge components. The bridge rectifier, without a filter capacitor, functions as follows. When the AC voltage is positive relative to earth ground, current will flow through diode D1, through the load, and back through diode D4, as shown in Figure 23-3. Diodes D2 and D3 will be off during this first half of the cycle. Figure 23-3. The current through D1 and D4 in diode bridge rectifier. When the input swings negative, current will flow through diode D2, through the load, and back through diode D3, as shown in Figure 23-4. Diodes D1 and D4 will be off in this second half of the cycle. Current will always only flow in the same direction through the load. cf4c3cad91289812d1a9005f1afc056067777ff9.docx 23-3

Figure 23-4. The current through D2 and D3 in diode bridge rectifier. Figure 23-5 shows a typical voltage waveform applied to a resistive load without the filter capacitor. The DC output voltage is pulsed at twice the line frequency (120 Hz). Figure 23-5. Typical output voltage waveform without a filter capacitor. The average DC output voltage is related to the peak of the input AC waveform with the following expression: V DC = 2 V P π (1) With the filter capacitor included, the DC output waveform is smoother and has a greater average value as illustrated in Figure 23-6. cf4c3cad91289812d1a9005f1afc056067777ff9.docx 23-4

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