Power Supply Units and Rectifiers

Power Supply Unit (PSU)

• Converts AC or DC line power into the required DC voltage for a system.

Rectifiers

• Convert AC voltage into pulsating DC voltage.
• Half-wave rectifiers allow current flow during only one half-cycle of AC input.
• Full-wave rectifiers allow current to flow during both half-cycles of AC input.
• Rectifier efficiency is the ratio of useful DC power output to AC power input.
• Peak Inverse Voltage (PIV) is the maximum voltage a rectifier diode can withstand without breakdown.
• Load Resistor (RL) is where the DC output voltage is applied in a rectifier circuit.
• Center-tap transformers have a middle connection on the secondary winding for full-wave rectifiers.
• Bridge Rectifiers use four diodes in a bridge arrangement for full-wave rectification.

Filtering

• Reduces AC ripple in a DC output signal.
• Filter circuits smooth out pulsating DC voltage.
• Capacitor filters use a capacitor in parallel with the load to reduce ripple voltage.
• Inductor filters use an inductor to smooth out ripple current.
• Choke input filters use an inductor before a capacitor to smoothen rectified voltage.
• Pi filters (CLC) use a capacitor, inductor, and another capacitor in a π configuration.

Voltage Regulation

• Maintains constant output voltage despite variations in input voltage or load current.
• Voltage regulators are responsible for maintaining a constant output voltage.
• Line regulation measures the percentage change in output voltage due to input voltage change.
• Load regulation measures the percentage change in output voltage due to load current change.
• Thermal regulation measures the percentage change in output voltage due to power dissipation change over time.
• Ripple rejection is the ability to reduce ripple voltage from input to output.
• Stabilization factor measures how well a voltage regulator maintains constant output voltage.
• Zener diode voltage regulators rely on a Zener diode to maintain a stable output voltage.
• Switching regulators use high-speed switching components for efficient output voltage control.
• Linear regulators provide constant output voltage using a resistive method.
• PWM switching regulators control output voltage using pulse-width modulation.
• Shunt regulators divert excess current to maintain output voltage stability.
• Series regulators control voltage drop across a pass transistor to maintain regulation.

DC-DC Converters and Topologies

• Buck converters step down the input voltage.
• Boost converters step up the input voltage.
• Buck-boost converters can either step up or step down voltage.
• Cuk converters provide an inverted output voltage.
• Flyback and forward converters use transformers for isolation and energy transfer.
• Push-pull converters use center-tapped transformers.
• Full-bridge converters use four switches to control power flow through a transformer.
• Duty Cycle (D) refers to the ratio of switch ON time to the total period.

AC-DC and DC-AC Conversion

• Rectifiers convert AC to DC.
• Inverters convert DC to AC.
• Cycloconverters convert AC power from one frequency to another without an intermediate DC link.
• Voltage Source Inverters (VSI) primarily control output voltage.
• Current Source Inverters (CSI) primarily control output current.
• Single-phase and three-phase are common inverter configurations.
• Half-bridge and full-bridge are inverter topologies.
• H-bridge circuits are used in full-bridge inverters and motor control.
• Multilevel inverters generate stepped output waveforms for higher applications.
• Grid-tied inverters feed AC power into the utility grid.
• Off-grid inverters operate independently from the utility grid.
• Uninterruptible Power Supplies (UPS) provide backup AC power using an inverter.

Filters

• Ripple Factor measures the ratio of RMS ripple component to DC output voltage.
• Bleeder resistors discharge filter capacitors when no load is connected.
• Capacitor filters use capacitance to reduce ripple.
• Inductor filters use inductance to reduce current ripple.
• Choke-input filters place an inductor before a capacitor.
• Pi filters combine a capacitor, inductor, and capacitor.

Key Parameters

• Ripple Frequency is the AC ripple's frequency in the rectified output voltage.
• Ripple Voltage is the AC component remaining in the rectified DC voltage.
• Utilization Factor describes transformer secondary power usage.
• Voltage Regulation is the ability to maintain steady output voltage.
• Holding Current (IH) is the minimum current to maintain conduction.
• Latching Current (IL) is the minimum current to turn on and maintain conduction.
• Forward Voltage Drop appears across a conducting diode.
• Reverse Leakage Current flows through a reverse-biased diode.
• Surge Current Rating is the maximum allowable peak current a rectifier can handle briefly.
• Transformer Efficiency measures output power relative to input power.
• Dynamic Resistance of a Diode is the small resistance when conducting.
• Breakdown Voltage is the voltage causing reverse bias conduction and failure.

Silicon Controlled Rectifiers (SCRs) and Thyristors

• Silicon Controlled Rectifier (SCR) is a four-layer, three-terminal semiconductor switch allowing current flow in one direction when triggered.
• SCRs belong to the thyristor family of semiconductor devices.
• Anode, Cathode, and Gate are the three SCR terminals.
• Forward Blocking Mode is when an SCR is forward-biased but not conducting.
• Forward Conduction Mode is when an SCR is turned ON and conducts current.
• Reverse Blocking Mode is when an SCR is reverse-biased and not conducting.
• Breakover Voltage (V_BO) is the minimum forward voltage to trigger conduction without a gate signal.
• Gate Triggering is the most common method for turning an SCR ON.
• Gate Turn-off Thyristors (GTO) can be turned off by a negative gate signal.
• Commutation is the process of turning off an SCR.
• Natural Commutation uses the natural zero crossing of AC current to turn off an SCR.
• Forced Commutation externally forces the current to zero in DC circuits.
• Reverse Recovery Time (t_rr) is the time for an SCR to fully turn off.
• Gate Trigger Current (I_GT) is the minimum current needed to turn on an SCR.
• On-State Voltage Drop (V_T or V_on) is the small voltage drop across a conducting SCR.
• Average ON-State Current (I_T(AV)) is the average current an SCR can handle when ON
• Peak Reverse Voltage (PRV or V_RRM) is the maximum reverse voltage an SCR can withstand before breakdown.
• Turn-on Losses are the power lost during the turn-on transition.
• Turn-off Losses are the power lost during the turn-off transition.

SCR Ratings

• Repetitive Peak Reverse Voltage (V_RRM) is its highest repeatedly handled reverse voltage.
• Non-Repetitive Peak Reverse Voltage (V_RSM) is its maximum one-time reverse voltage.
• dv/dt Rating is the maximum rate of voltage increase without unintended turn-on.
• di/dt Rating is the maximum current increase rate without junction damage.
• SCR Turn-on Time (t_on) is the time to transition from OFF to ON after a gate signal.
• SCR Turn-off Time (t_off) is the total time to switch off completely.

SCR Operation

• Conduction involves minority carrier injection and regenerative feedback.
• Voltage Triggering occurs due to excessively high anode-cathode voltages.
• Thermal Runaway is overheating and failure due to excessive current and temperature.
• Radiation Triggering uses light (LASCRs).
• Pulse Triggering uses a unijunction transistor (UJT).
• Pulse Width Modulation (PWM) controls SCR switching.
• Gate Pulse Amplification ensures reliable triggering.
• Static Switch uses an SCR in place of mechanical relays.
• Saturable Reactors are used in SCR gate control circuits.

Power Electronics Switching Devices

• Power Electronics deals with electrical power conversion and control.
• Switching Devices control power flow by rapidly turning circuits on and off.
• MOSFETs are voltage-controlled switches for high-frequency applications.
• IGBTs combine MOSFET and BJT advantages.
• BJTs are current-controlled switches.
• Thyristors include SCRs, TRIACs, and DIACs.
• TRIACs are bidirectional switches for AC control.
• DIACs are triggering devices used with TRIACs.
• Gate Turn-off (GTO) Thyristors can be turned off via a gate signal.

Circuit Protection

• Snubber circuits protect power switches from high dv/dt and di/dt stress.
• Overvoltage Protection prevents excessive voltage damage to devices.
• Overcurrent Protection (OCP) limits excessive current. Short Circuit Protection (SCP) prevents current during short circuits.
• Thermal Shutdown turns off a device above safe temperatures.
• Gate Drive Protection prevents overvoltage or overcurrent damaging MOSFET and IGBTs.
• Clamping Circuits limit voltage spikes by absorbing excess energy.
• Transient Voltage Suppressors (TVS) absorb high-energy transients.

Power System Mitigation Techniques

• Soft Switching reduces losses by minimizing voltage and current overlap.
• Resonant Converters reduce losses by operating at resonance.
• Flicker rapid voltage fluctuations, causes lights to dim inconsistently
• Harmonic Filters reduce unwanted harmonics.
• Noise Immunity is ability of a system to operate correctly despite electrical noise.

Components

• Inductors store and release energy to smooth out voltage and current variations.
• Capacitors filter out voltage ripple.
• Diodes prevent reverse current flow.

AC-AC converters

• Convert AC power from one voltage level or frequency to another.
• Cycloconverters directly convert AC from one frequency to a lower frequency without an intermediate DC stage.
• Matrix converter use bidirectional switches for frequency and voltage conversion.
• Phase Control is a technique used to control the output voltage and frequency.
• Space Vector Modulation (SVM) modulation technique used in matrix converters to improve efficiency and waveform quality.
• Four-Quadrant Operation allows operation in all power flow directions.

Power Conditioning and Isolation

• Improves electrical power to quality and safety standards
• Transformer Isolation provides electrical between input and output circuits.
• Optocouplers transfer electrical information while maintaining isolation.

DC choppers

• Convert fixed DC voltage to a variable DC voltage.
• Step-Down Chopper or Buck Converter reduces the DC output voltage compared to the input.
• Step-Up Chopper or Boost Converter increases the DC output voltage compared to the input.
• Regenerative Chopper returns energy to the power source instead of dissipating it.

DC motor control

• Used in many industrial equipment.
• Used to control, power and perform precision movement.

Power and Thermal Considerations for Semiconductors

• Power Dissipation generates heat energy.
• On-State Resistance is conduction resistance when the device is conducting current.
• Thermal Runaway causes failure due to excessive heat.
• Total Switching Losses are the sum of turn-on and turn-off losses .
• Thermal Management prevents overheating.
• Heat Sinks dissipate heat to the environment.
• Junction Temperature is the semiconductor heat temperature.
• Case Temperature is the device outer casing temperature.

Renewable Energy

• Solar Inverters convert DC power from solar panels into AC power.
• Wind Turbine Generators (WTG): Converts wind energy into electrical energy.
• Maximum Power Point Tracking (MPPT): Used to extract the maximum solar energy.

Electric Vehicles (EVs)

• EVs are powered entirely or partially by electric energy.
• Battery Management Systems (BMS) monitors and controls battery charging and discharging.
• Traction Inverters convert DC battery power into AC for driving the electric motor.

Smart Grids

• Smart Transformer with digital controls improve grid performance.
• Advanced Metering Infrastructure (AMI) uses smart meters for real-time energy monitoring.
• Supervisory Control and Data Acquisition (SCADA) monitors and controls grid operations remotely.
• Dynamic Voltage Restorer (DVR) compensates for sags and swells.

Emerging Technologies

• Wide Bandgap Semiconductors (WBG): Silicon Carbide (SiC) and Gallium Nitride (GaN) enable higher efficiency, power density.
• Wireless Power Transfer (WPT): Enables energy transfer without physical connections, using magnetic fields or microwaves.
• Artificial Intelligence in Power Systems: Optimize efficiency, predictive maintenance, grid management.