Introduction
Diodes play a crucial role in rectifiers, converting AC signals into unidirectional signals.
Rectifiers are a type of AC to DC converter, also known as absolute value converters.
The output voltage waveform (\(V_0\)) of a rectifier mirrors the shape of the AC input voltage (\(V_s\)), but negative portions become positive, represented as \(V_0 = |V_s|\)
Rectifiers are classified into single-phase and three-phase types based on the input supply.
Single-phase rectifiers can be half-wave or full-wave.
Single-phase half-wave rectifiers, though simplest, are not commonly used in industrial applications.
In this context, diodes are assumed to be ideal, meaning negligible reverse recovery time (\(t_{rr} = 0\)) and forward voltage drop (\(V_D = 0\)).
Performance Parameters
Practical rectifiers produce output voltage with harmonics or ripples despite aiming for pure DC output.
Rectifiers are power processors striving for minimal harmonic content in DC output while maintaining input current sinusoidal and in phase with input voltage for near unity power factor.
Assessing rectifier quality involves analyzing harmonic contents of input current, output voltage, and output current.
Fourier series expansions are utilized to determine harmonic contents of voltages and currents.
The performance parameters of a rectifier: \[\begin{aligned} &\text{Average output (load) voltage and current,}~ V_{dc};~I_{dc}\\ & \text{Output dc power}~ P_{dc} = V_{dc} \cdot I_{dc}\\ & \text{RMS output voltage and current,}~ V_{rms};~ I_{rms} \\ & \text{Output ac power}~ P_{ac} = V_{rms} \cdot I_{rms}\\ \end{aligned}\]
The efficiency (or rectification ratio) of a rectifier: \[\eta = \dfrac{P_{dc}}{P_{ac}}\]
Measure of the quality of the output waveform, indicating how effectively the rectifier converts input power to a pure DC output.
For a pure DC output, the conversion efficiency would be unity.
Output voltage = dc value + ac (or ripple) component
The effective (rms) value of the ac component of output voltage: \[V_{ac} = \sqrt{V_{rms}^2-V_{dc}^2}\]
Form Factor: Measure of the shape of the output voltage waveform \[\text{FF} = \dfrac{V_{rms}}{V_{dc}}\]
Ripple Factor: Measure of the ripple content in the output voltage waveform \[\mathrm{RF}=\sqrt{\left(\frac{V_{\mathrm{rms}}}{V_{\mathrm{dc}}}\right)^2-1}=\sqrt{\mathrm{FF}^2-1}\]
Transformer utilization factor: \[\mathrm{TUF}=\frac{P_\mathrm{dc}}{V_sI_s}\] \(V_s,~I_s\) rms voltage and rms current of the transformer secondary
Power Factor: \[\mathrm{PF}=\frac{P_\mathrm{ac}}{V_sI_s}\]
Crest Factor (CF): commonly used to specify the peak current ratings of devices and components, providing insight into the peak-to-average ratio of the waveform. \[\mathrm{CF}=\frac{I_{s(\mathrm{peak})}}{I_s}\]
Diode Rectifiers
Conversion of AC voltage from mains to DC voltage for electronic products.
AC voltage converted to pulsating DC voltage using diodes or thyristors.
Pulsating DC voltage filtered to provide smooth DC voltage.
Classification of Rectifiers
Uncontrolled rectifiers.
Controlled rectifiers.
Uncontrolled Rectifiers
Use diodes as power switch.
Turn-ON and turn-OFF of diode is uncontrolled.
Diode-based rectifier topologies termed uncontrolled rectifiers.
Controlled Rectifiers
Utilize controllable power semiconductor switches.
Power Generation, Distribution, and Utilization
Electrical power generation and distribution predominantly in AC form.
Many electronic devices require DC sources, necessitating rectification and filtering of AC voltage.
AC Input Sources
obtained from
Single-phase supply for low-to-medium power needs.
Three-phase supply for medium-to-high power requirements.
Role of Transformer & Limitations
Scale voltage or Isolate input from rectifier output.
Increases cost, size, and weight of rectifier.
Uncontrolled Rectifier Circuits
Primarily utilize diode semiconductor switches.
Diodes connected in various topological configurations.
Input Sources and Classification
Source for rectifier circuits considered as sinusoidal voltage source like mains/grid.
Classified based on input source:
Single-phase rectifier circuits.
Three-phase rectifier circuits.
Single-Phase vs. Three-Phase
Rectifier circuit topologies designed for single-phase or three-phase grid applications.
Single-Phase Rectifier Circuits
Half-wave rectifier
Full-wave center-tapped rectifier
Full-wave bridge rectifier