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What is Rectifier circuit?

A circuit that converts AC into current flowing in one direction (DC). Types include the half-wave rectifier, which removes the negative half cycles with a diode, the full-wave rectifier, which turns both half cycles the same way with a bridge of four diodes, and the three-phase full-wave rectifier, which rectifies three-phase AC with six diodes. The output contains ripple, so a smoothing capacitor or an inductor brings it closer to DC. Using thyristors instead of diodes lets the firing angle adjust the output voltage.

Read the beginner explainer: What Is a Diode? How It Lets Current Flow Only One Way

Japanese name: 整流回路

Rectifier circuit appears in 8 practice questions across 2 topics, including Power Electronics Circuits, PN junctions and diodes.

Field: Power Electronics Circuits

Average value and ripple

The average of a full-wave rectified sine wave of RMS value V is (2√2/π) × V ≈ 0.90V; for half-wave rectification it is about 0.45V. The fundamental ripple frequency equals the supply frequency for half-wave, twice it for full-wave and six times it for three-phase full-wave rectification, and the higher the frequency, the easier the smoothing. The average output of a three-phase full-wave rectifier is about 1.35 times the RMS line voltage, so 200 V three-phase AC gives about 270 V DC.

Input current with capacitor smoothing

With a large smoothing capacitor after the diodes, the output stays near the peak voltage, but the diodes conduct only for a short time near the peaks, when the input voltage exceeds the capacitor voltage. The input current therefore takes the form of narrow pulses, rich in harmonics, and the power factor falls sharply. Power factor correction (PFC) circuits are used to counter this.

Choosing the devices

General-purpose silicon rectifier diodes are used at mains frequency. High-frequency rectification in switching power supplies uses fast-recovery diodes with quick reverse recovery or Schottky barrier diodes with a low forward voltage, and synchronous rectification with MOSFETs where losses must be cut further. In a bridge the current always passes through two diodes, so at high currents the forward-voltage loss and the thermal design become important.

Try it: questions about Rectifier circuit

What does a bridge rectifier made of four diodes do?

  1. AConverts DC to AC
  2. BAmplifies a signal
  3. CFull-wave rectifies AC into a current flowing in one direction (pulsating DC)
Show answer and explanation

Answer: C. Full-wave rectifies AC into a current flowing in one direction (pulsating DC)

In a bridge rectifier, a different pair of diodes conducts on the positive and negative half-cycles, so current flows through the load in the same direction either way (full-wave rectification). Current always passes through two diodes, costing about 1.4 V. The output still pulses and is smoothed with a capacitor for DC use. The ripple frequency is twice the input (100 Hz for 50 Hz mains), making it easier to smooth than half-wave rectification.

When a sinusoidal AC signal is applied to a half-wave rectifier made of one diode and a resistor, what is the output?

  1. AThe AC signal passes through unchanged
  2. BThe negative half-cycles are also flipped and output as positive
  3. COnly one half-cycle, either positive or negative, is output
Show answer and explanation

Answer: C. Only one half-cycle, either positive or negative, is output

In a half-wave rectifier, current flows only during the half-cycle when the diode is forward-biased; the other half is blocked, so only one half-cycle appears at the output. The output peak is lower than the input peak by the diode drop (about 0.7 V). It needs just one diode, but it uses only half the input and its ripple has the same frequency as the input, making it hard to smooth, so power supplies mainly use full-wave rectification.

FAQ

Which is better, full-wave or half-wave rectification?

Almost all power supplies use full-wave rectification. Using both half cycles doubles the average value and the ripple frequency, which makes smoothing easier, and no DC component flows in the transformer to magnetize its core in one direction. Half-wave rectification, which needs fewer parts, is used only for very small currents.

What does a DC voltmeter read on a rectified voltage?

A typical DC voltmeter, which indicates the average, reads about 90 V on an unsmoothed full-wave rectified output from a 100 V RMS input. With a smoothing capacitor and a light load, the output approaches the peak value of about 141 V.

Rectifier circuit in the explanations

Questions that mention Rectifier circuit (8)

  1. What does a bridge rectifier made of four diodes do?
  2. When a sinusoidal AC signal is applied to a half-wave rectifier made of one diode and a resistor, what is the output?
  3. When AC is applied to a single-phase bridge rectifier made of four diodes, which of the following correctly describes the path of the current during one half cycle?
  4. Which of the following correctly describes the output of a three-phase full-wave rectifier that rectifies three-phase AC with a bridge of six diodes?
  5. A 200 V RMS single-phase AC supply feeds a resistive load through a single-phase full-wave rectifier using thyristors, with phase control. Which of the following is closest to the average output voltage at a firing angle of 60°?
  6. What is the property of a diode that lets current flow easily in one direction but hardly at all in the other called?
  7. A sinusoidal AC voltage of 100 V RMS is full-wave rectified with an ideal diode bridge. Without a smoothing capacitor, which of the following is closest to the average output voltage?
  8. Estimate on the assumption that the capacitor supplies all of the load current for one full ripple period. When 50 Hz AC is full-wave rectified, smoothed with a 10,000 µF capacitor, and a constant 2 A flows to the load, which of the following is the approximate peak-to-peak output voltage ripple?

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