11.9
Vollweggleichrichter
Ein Vollweggleichrichter ist ein Gerät, das Wechselstrom (AC) in Gleichstrom (DC) umwandelt und effizienter ist als sein Halbweg-Gegenstück. Er enthäl…
Stellen Sie sich eine Vollwellengleichrichterschaltung vor, die aus einem Transformator mit mittlerem Abgriff, zwei Dioden in einer mittig abgegriffenen Konfiguration und einem Lastwiderstand besteht.
Die Sekundärwicklung des Transformators liefert zwei gleiche Eingangsspannungen mit entgegengesetzten Polaritäten über die beiden Hälften der Sekundärwicklung
.Während der positiven Halbzyklen des Eingangssignals, wenn die Spannung den Durchlassspannungsabfall der Diode erreicht oder gleich ist, leitet die Diode D1, während D2 in Sperrrichtung vorgespannt ist. Die Ausgangswellenform ähnelt der eines Halbwellengleichrichters.
Umgekehrt wird während des negativen Halbzyklus, wenn die Eingangsspannung niedriger ist als der Durchlassspannungsabfall der Diode, die Diode D1 abgeschaltet, während D2 leitet. Auch hier spiegelt die Ausgangswellenform die eines Halbwellengleichrichters wider.
Der Strom durch den Widerstand fließt konstant in die gleiche Richtung, was zu einem unipolaren Ausgang führt.
Die erhöhte Gleichrichtereffizienz eines Vollwellengleichrichters ermöglicht den Einsatz in Netzteilen, Batterieladegeräten, Audioverstärkern und der Signalverarbeitung.
Die inverse Spitzenspannung ist doppelt so hoch wie die Spitzeneingangsspannung abzüglich des Durchlassspannungsabfalls der Diode, der etwa doppelt so hoch ist wie beim Halbwellengleichrichtergehäuse.
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Q1: How does a full-wave rectifier convert AC to DC?
A full-wave rectifier converts alternating current to direct current by using a center-tapped transformer and two diodes that conduct on alternate half-cycles. During the positive half-cycle, diode D1 becomes forward-biased and conducts while D2 is reverse-biased. During the negative half-cycle, D1 is reverse-biased and D2 conducts, flipping the negative voltage to positive. This ensures unidirectional current through the load resistor, producing a unipolar DC output.
Q2: What is the role of the center-tapped transformer in a full-wave rectifier?
The center-tapped transformer is the pivotal element of full-wave rectification. Its secondary winding is divided to provide two equal voltages of opposite polarities across the two halves. This dual-voltage configuration allows each diode to conduct during alternate half-cycles of the AC input, enabling the circuit to utilize the full cycle of the AC waveform rather than just half of it.
Q3: Why is a full-wave rectifier more efficient than a half-wave rectifier?
A full-wave rectifier has higher rectification efficiency because it utilizes both the positive and negative half-cycles of the AC input signal, whereas a half-wave rectifier uses only one half-cycle. Additionally, the full-wave rectifier produces lower ripple voltage at double the ripple frequency, yielding smoother DC output with less filtering requirement compared to a half-wave rectifier.
Q4: What is peak inverse voltage in a full-wave rectifier?
Peak inverse voltage (PIV) is the maximum reverse voltage a diode must withstand in the circuit. In a full-wave rectifier, the PIV equals twice the maximum input AC voltage minus the diodes' forward voltage drop. This PIV is approximately double that encountered in a half-wave rectifier, requiring diodes that can sustain higher reverse voltages to ensure safe operation.
Q5: What are the main applications of full-wave rectifiers?
Full-wave rectifiers are extensively used in power supply units, battery chargers, audio amplifiers, and signal-processing applications. Their increased rectification efficiency and smoother DC output make them ideal for these applications where stable, continuous direct current is required. The reduced ripple voltage and higher ripple frequency minimize the need for additional filtering components.
Q6: How does the output waveform differ between the two diodes in a full-wave rectifier?
Each diode in a full-wave rectifier produces an output waveform resembling that of a half-wave rectifier during its respective conduction period. When D1 conducts during positive half-cycles, it generates a positive output. When D2 conducts during negative half-cycles, it flips the negative voltage to positive. Combined, these alternating outputs create a continuous unipolar waveform with current flowing consistently in the same direction through the load resistor.
Q7: What determines when each diode conducts in a full-wave rectifier?
Diode conduction is determined by the input signal polarity and the diode's forward voltage drop threshold. During positive half-cycles, when voltage exceeds the diode's forward voltage drop, D1 conducts while D2 is reverse-biased. During negative half-cycles, when input voltage is lower than the forward voltage drop, D1 is cut off while D2 conducts. This alternating conduction pattern ensures full-wave rectification of the AC signal.