2. Power Semiconductor Devices and Characteristics

Introduction and Context

Power electronic systems control and convert electrical energy by operating semiconductor devices as controlled switches, rectifiers, or, in some applications, linear regulating elements. The performance of a converter is therefore strongly determined by the selected power semiconductor. Device choice influences efficiency, switching frequency, electromagnetic interference, thermal design, control bandwidth, reliability, cost, and the physical size of passive components.

A power device differs from a small-signal semiconductor not merely because it handles greater power. Its structure is deliberately designed to withstand high blocking voltage, conduct substantial current, remove heat, and survive repetitive electrical and thermal stress. These requirements create an important trade-off: structures optimized for high voltage generally exhibit greater conduction resistance, while structures optimized for rapid switching may have reduced voltage or current capability.

This chapter develops the operating principles and practical characteristics of power diodes, thyristors, gate turn-off thyristors (GTOs), bipolar junction transistors (BJTs), power MOSFETs, insulated-gate bipolar transistors (IGBTs), and wide-bandgap devices based on silicon carbide (SiC) and gallium nitride (GaN). Static characteristics describe voltage-current behavior in steady states; dynamic characteristics describe switching transitions. Loss models, thermal limits, and safe operating areas connect device physics with engineering design.

Learning Objectives

After studying this chapter, the reader should be able to:

1. Explain the construction and operating principles of major power semiconductor devices.

2. Interpret forward, reverse, blocking, switching, and gate characteristics from device data sheets.

3. Develop first-order conduction, switching, and thermal-loss models.

4. Explain reverse-recovery, charge-storage, parasitic, and gate-drive effects.

5. Compare thyristors, MOSFETs, IGBTs, SiC devices, and GaN devices for voltage, current, frequency, and thermal requirements.

6. Use safe-operating-area concepts and derating principles in converter design.

7. Select a suitable device for an applied power-electronic system and identify associated risks.

2.1 Device Classes and the Switching Function

A power semiconductor normally operates in one of three states: forward conduction, reverse or forward blocking, and transition between these states. An ideal switch has zero voltage in the on-state, zero current in the off-state, instantaneous transitions, and no power loss. Real devices depart from this ideal model because they possess conduction voltage or resistance, finite switching times, stored charge, parasitic capacitance, leakage current, and thermal limitations.

Devices may also be classified by controllability. An uncontrolled device, such as a conventional diode, changes state according to the applied circuit voltage and current. A semi-controlled device, such as a thyristor, can be turned on by a gate signal but normally requires the external circuit to reduce its current below the holding value for turn-off. A fully controlled device, such as a MOSFET or IGBT, can generally be turned on and off by its control terminal, subject to gate-drive and commutation constraints.

The principal device terminals are the anode and cathode of a diode or thyristor, the collector, emitter, and base of a BJT or IGBT, and the drain, source, and gate of a MOSFET. The gate of a MOSFET, IGBT, and many thyristor variants is insulated or highly isolated from the main current path. This allows low-power control circuits, but it does not eliminate the need for careful management of voltage, current, insulation, and parasitic coupling.

2.2 Power Diodes: The Uncontrolled Rectifying Element

A power diode is a two-terminal device that conducts predominantly in one direction. In forward bias, carriers cross the junction and the device supports current with a voltage drop. In reverse bias, the depletion region widens and only a small leakage current flows until breakdown is approached.

Static characteristics

The forward characteristic is commonly represented by

V_D approximately equal to V_{D0} + I_D r_D,

where V_{D0} is an effective threshold or junction-voltage term and r_D is a differential or slope resistance. This is a convenient engineering approximation, not a complete physical law. At high current, the effective voltage drop may depend significantly on temperature and current density.

The reverse characteristic includes leakage current and a maximum repetitive reverse voltage, often designated V_RRM. Exceeding the rated blocking voltage can cause avalanche breakdown, localized heating, and failure unless the device is specifically designed for controlled avalanche operation.

Dynamic characteristics

When a forward-conducting diode is reverse biased, it does not block immediately. Stored minority carriers must be removed. The reverse-recovery current commonly consists of a rising interval followed by a decaying interval. Important parameters include reverse-recovery time t_rr, peak reverse-recovery current I_RRM, and reverse-recovery charge Q_rr. A simplified recovery loss estimate is

E_rr approximately equal to integral of v_D(t)i_D(t)dt,

and the average recovery power is P_rr = f_s E_rr, where f_s is switching frequency.

Reverse recovery can produce voltage overshoot through circuit stray inductance. If current changes at a rate di/dt, the parasitic inductive voltage is approximately L_sigma di/dt. Snubbers, soft-recovery diodes, controlled commutation, and reduced loop inductance are common mitigation measures.

Power diodes include general-purpose line-frequency types, fast-recovery diodes, ultrafast diodes, Schottky diodes, and SiC Schottky diodes. A Schottky diode uses a metal-semiconductor junction and has negligible minority-carrier storage, which gives very fast switching. Silicon Schottky devices are usually limited in reverse-voltage capability, whereas SiC Schottky diodes offer substantially higher voltage capability and low reverse-recovery charge.

2.3 Thyristors and GTOs

A conventional thyristor, or silicon-controlled rectifier (SCR), is a four-layer p-n-p-n device with anode, cathode, and gate terminals. It has forward-blocking, forward-conducting, and reverse-blocking regions. In the forward-blocking state, a positive gate pulse can initiate regenerative action and switch the device into conduction. Once latched, the gate generally cannot turn the device off.

The latching current I_L is the minimum anode current required immediately after triggering for the device to remain on when the gate signal is removed. The holding current I_H is the minimum current below which the device returns to the blocking state. Usually I_L is greater than I_H. Triggering may be affected by gate current, anode-cathode voltage, temperature, dv/dt, and light or noise coupling.

The on-state voltage of a thyristor is relatively low for its voltage and current rating, making it attractive in line-frequency rectifiers, soft starters, controlled AC regulators, high-power motor drives, and HVDC converters. Its major limitation is turn-off. A forced-commutation circuit or a naturally reversing AC current is required. Excessive dv/dt can cause unintended turn-on through junction capacitances, while excessive di/dt can create localized current concentration before the entire junction becomes conductive.

A GTO is a thyristor that can be turned off by applying a substantial reverse gate current. Compared with an SCR, it offers greater controllability but requires a powerful, low-inductance gate-drive circuit. GTOs have historically been used in high-power traction and industrial converters, although IGBTs and integrated gate-commutated thyristors have displaced them in many applications. Their switching frequency is generally lower than that of MOSFETs and modern IGBTs.

2.4 BJTs, MOSFETs, and IGBTs: Controlled Power Switches

Power BJTs

A power BJT is a current-controlled device. Collector current is related to base current through an effective current gain, but the gain varies with current, temperature, and operating region. To force a BJT into saturation, sufficient base current must be supplied. Saturation reduces conduction voltage but stores charge in the base, increasing turn-off delay and switching loss.

Power BJTs have largely been replaced by insulated-gate devices in many switching applications because their drive circuits consume continuous base current and their gain falls at high current. Nevertheless, their operating principles remain important because the IGBT combines a MOS-controlled input with bipolar conduction.

Power MOSFETs

A power MOSFET is a voltage-controlled majority-carrier device. When the gate-to-source voltage exceeds the threshold under specified conditions, an inversion channel permits current between drain and source. Since conduction does not require minority-carrier storage, MOSFETs can switch rapidly.

In the on-state, a useful approximation is

P_cond = I_D,rms^2 R_DS(on).

The resistance R_DS(on) generally increases with junction temperature. It also varies with gate voltage, drain current, manufacturing process, and device temperature. At high voltage ratings, the drift region needed to support blocking voltage contributes significantly to R_DS(on), creating a silicon high-voltage trade-off.

The MOSFET gate is capacitive. Gate-drive requirements are therefore characterized by total gate charge Q_g, input capacitance, Miller charge Q_gd, and the required gate voltage. A first-order gate-drive current estimate is I_g approximately equal to Q_g/t_g. During the drain-voltage transition, the Miller effect causes the gate voltage to remain nearly constant while charge is transferred through the gate-drain capacitance. A low-impedance driver, suitable dead time, and controlled turn-on and turn-off speeds are essential.

The intrinsic body diode provides an important current path, but it may have substantial reverse-recovery charge in silicon MOSFETs. In bridge converters, body-diode recovery can produce loss and voltage stress; an external fast diode or a device with improved reverse-conduction behavior may be preferable.

IGBTs

An IGBT combines a MOS gate structure with a bipolar output path. The insulated gate provides voltage-controlled drive, while minority-carrier injection lowers the on-state voltage at medium and high voltage ratings. The approximate conduction loss is often represented as

P_cond approximately equal to V_CE0 I_C,avg + r_CE I_C,rms^2,

or, more simply, P_cond approximately equal to V_CE(sat) I_C,avg for a specified operating condition.

The bipolar conduction mechanism gives IGBTs a lower conduction loss than a comparable high-voltage silicon MOSFET at moderate switching frequencies. However, stored minority carriers produce a current tail during turn-off. This tail increases turn-off energy and limits high-frequency operation. Modern field-stop and trench IGBTs reduce tail current and improve the trade-off between conduction and switching losses.

An IGBT requires a gate-emitter voltage above threshold for turn-on and commonly uses a positive gate voltage such as +15 V in industrial drives, although the exact value is data-sheet dependent. A negative turn-off voltage may improve immunity to dv/dt-induced turn-on, but it increases driver complexity. Short-circuit withstand time is limited; protection must detect and interrupt a fault rapidly.

2.5 Wide-Bandgap Devices: SiC and GaN

Silicon carbide and gallium nitride have wider bandgaps than silicon. This enables operation at higher electric field, higher temperature, and, depending on construction, higher switching frequency. Wide-bandgap devices are not automatically superior in every application: gate-drive requirements, packaging, insulation, electromagnetic compatibility, cost, and reliability must also be considered.

SiC devices

SiC Schottky diodes have negligible minority-carrier reverse recovery and are particularly valuable in boost converters, power-factor-correction stages, and high-voltage bridge circuits. SiC MOSFETs provide high blocking voltage, low output capacitance in suitable operating ranges, and rapid switching. Their voltage-controlled gates require careful limits on positive and negative gate voltage. The common-source inductance and gate-loop inductance must be minimized because high dv/dt and di/dt can cause unwanted gate excursions and overshoot.

SiC devices can reduce switching loss and heatsink size, but their high-speed transitions may increase common-mode currents, bearing currents in motor drives, radio-frequency emissions, and insulation stress. A design that replaces a silicon IGBT with a SiC MOSFET must therefore reconsider layout, gate resistance, filtering, isolation, and measurement methods.

GaN devices

GaN transistors are especially attractive at high switching frequency and relatively low-to-medium voltage. Enhancement-mode GaN devices use a normally-off structure, while some cascode arrangements combine a normally-on GaN transistor with a low-voltage silicon MOSFET. GaN devices generally have very low gate charge and low parasitic capacitance, enabling fast transitions and high power density.

Their advantages are accompanied by narrow gate-voltage margins, sensitivity to layout inductance, demanding commutation behavior, and potentially high electromagnetic interference. GaN is widely considered for compact adapters, data-center power supplies, wireless-power systems, and high-frequency DC-DC converters. The appropriate choice depends on whether the system can exploit high frequency without allowing switching stress and EMI to dominate the design.

2.6 Static, Dynamic, Loss, and Thermal Models

Device selection begins with a static model but cannot end there. Static voltage and current ratings indicate whether a device can survive steady conditions. Dynamic parameters determine whether it can switch safely and efficiently.

The principal loss components are:

• Conduction loss, caused by forward voltage or on-state resistance.
• Turn-on and turn-off switching loss, caused by simultaneous device voltage and current.
• Diode reverse-recovery loss.
• Gate-drive loss, approximately P_gate = Q_g V_drive f_s.
• Output-capacitance and commutation loss.
• Leakage and snubber loss.

For a hard-switched transistor, a first-order switching-energy model is

P_sw approximately equal to f_s(E_on + E_off).

The actual energies depend on bus voltage, current, gate resistance, junction temperature, commutation partner, stray inductance, and switching waveform. Data-sheet energy curves should be scaled cautiously rather than treated as universal constants.

The total semiconductor loss is converted into temperature through a thermal network. A basic steady-state relation is

T_J = T_A + P_loss R_theta JA,

or, when a case and heatsink are modeled separately,

T_J = T_C + P_loss R_theta JC.

In a practical assembly,

T_J = T_A + P_loss(R_theta JC + R_theta CS + R_theta SA),

where the terms represent junction-to-case, case-to-sink, and sink-to-ambient thermal resistance. Transient thermal impedance is needed for pulsed loads because the junction temperature does not instantly follow the average power. Thermal cycling can cause bond-wire fatigue, solder degradation, and package failure even when the average temperature appears acceptable.

2.7 Safe Operating Area and Reliability

The safe operating area (SOA) specifies combinations of voltage, current, pulse duration, and temperature within which the device can operate without damage. The forward-bias SOA is especially important for BJTs and IGBTs during abnormal switching or short circuits. MOSFET SOA must account for drain current, drain-source voltage, pulse duration, temperature, and possible secondary effects such as thermal instability.

The reverse-bias SOA of IGBTs and thyristors describes their ability to withstand voltage during turn-off or commutation. Repetitive avalanche ratings, short-circuit withstand time, peak gate current, di/dt, dv/dt, and maximum junction temperature are equally relevant. A rating is not a design target: voltage and current derating are required because tolerance, temperature, transients, aging, and measurement uncertainty reduce practical margin.

Failure mechanisms include electrical overstress, thermal runaway, avalanche breakdown, gate-oxide damage, bond-wire lift-off, solder fatigue, cosmic-ray-induced failure in high-voltage devices, and excessive electromagnetic stress. Protection may include fuses, desaturation detection, current sensors, active gate control, soft shutdown, clamp networks, snubbers, and coordinated overtemperature protection.

2.8 Comparative Device Selection

No single device is best across all applications. Thyristors remain strong candidates for very high current and line-frequency conversion where natural commutation is available. GTOs are suitable only where their controllability and high-power capability justify complex drive and lower frequency.

MOSFETs are usually favored at low and medium voltage with high switching frequency because of their fast majority-carrier operation. Their conduction resistance becomes increasingly important at high voltage and high current. IGBTs are often appropriate for medium- and high-power converters operating at moderate frequency, especially motor drives, uninterruptible power supplies, and traction systems. SiC MOSFETs extend high-frequency capability into high-voltage applications, while GaN is particularly attractive when extremely low switching charge and compact high-frequency conversion are central objectives.

A disciplined selection procedure should evaluate:

1. Maximum blocking voltage, including overshoot and derating.

2. Continuous, pulsed, and RMS current under the actual thermal conditions.

3. Switching frequency and allowable switching energy.

4. Conduction loss at the operating temperature.

5. Reverse-conduction and recovery behavior.

6. Gate-drive voltage, charge, isolation, and protection requirements.

7. SOA, short-circuit behavior, and fault response.

8. Package parasitics, cooling method, cost, availability, and qualification.

Applied Case Study: Selecting a Switch for a 5 kW Motor Inverter

Background

Consider an illustrative three-phase inverter supplying a 400 V DC link to a 5 kW induction motor. The inverter is required to operate at 10 kHz, with high reliability and moderate acoustic noise. The design team is considering a 650 V silicon MOSFET, a 650 V IGBT, and a 650 V SiC MOSFET.

Situation and analysis

The 650 V rating appears adequate only if switching overshoot is controlled and a design margin is maintained. The motor current is not purely sinusoidal at the device level; each switch experiences pulsed current, diode commutation, and temperature-dependent conduction. A silicon MOSFET may switch rapidly, but its R_DS(on) at elevated temperature can produce substantial conduction loss. The IGBT may offer favorable conduction at the expected current but incurs turn-off tail loss at 10 kHz. The SiC MOSFET can reduce both turn-on and turn-off energy, although its higher component cost and fast-edge EMI require attention.

Engineering approach

The team first obtains data-sheet conduction and switching curves at comparable junction temperatures. It estimates

P_total = P_cond + f_s(E_on + E_off) + P_gate + P_reverse,

for each candidate. It then models the gate loop and power loop, selects a low-inductance package, and adds a controlled gate resistor. Desaturation or overcurrent protection is coordinated with the device’s short-circuit capability. The thermal design uses the worst-case ambient temperature and transient load profile rather than nominal laboratory conditions.

Solution and outcome

For the illustrative design, the SiC MOSFET is selected when the efficiency and heatsink reduction justify its cost. The gate driver is placed close to the device, a Kelvin source connection is used where available, and common-mode filtering is added to control motor-cable emissions. If the application were cost-sensitive, operated at a lower switching frequency, and had a larger permitted heatsink, the IGBT could be the more rational choice.

Learning points

The case demonstrates that voltage rating alone cannot determine selection. Switching frequency, thermal impedance, gate-drive behavior, EMI, fault response, and total system cost must be considered together. A device with the lowest data-sheet loss may not produce the lowest system cost if it demands expensive filtering, specialized layout, or difficult protection.

Design Challenges, Professional Practice, and Emerging Directions

A common mistake is to compare devices using only nominal on-state voltage or resistance. Ratings are conditional: R_DS(on), V_CE(sat), switching energy, and current capability depend on temperature and waveform. Another mistake is to ignore the commutation loop. Stray inductance can create voltage spikes that exceed the nominal device rating even when the average bus voltage is safe.

Measurement itself requires professional care. High-voltage differential probes, current probes, bandwidth limits, probe-loop inductance, and grounding arrangements can distort switching waveforms or create safety hazards. Gate-driver isolation, creepage and clearance, protective earthing, and compliance with applicable electrical and electromagnetic-compatibility standards are part of responsible engineering practice.

Digital design tools increasingly support electrothermal simulation, parasitic extraction, lifetime estimation, automated gate-drive optimization, and condition monitoring. Data-driven monitoring can identify increases in on-state voltage, switching time, or thermal resistance that indicate aging. Such tools assist engineering judgment but do not replace validated device models, laboratory tests, or manufacturer qualification data.

Current development emphasizes higher-voltage SiC MOSFETs, improved GaN packaging, integrated drivers and protection, double-sided cooling, advanced sintered interconnects, and intelligent power modules. Research also addresses normally-off GaN reliability, dynamic on-resistance, high-temperature operation, electromagnetic compatibility, and standardized characterization. The central design trend is not simply faster switching; it is the coordinated optimization of semiconductor, package, gate driver, magnetics, thermal path, control algorithm, and protection system.

Best-Practice Checklist

A sound device-selection study should:

• Begin with worst-case voltage, current, temperature, and transient conditions.
• Separate conduction, switching, gate-drive, recovery, and auxiliary losses.
• Use temperature-dependent data rather than room-temperature values alone.
• Check SOA, short-circuit limits, dv/dt, di/dt, and repetitive avalanche capability.
• Design the gate loop and commutation loop for minimum parasitic inductance.
• Provide protection that acts within the device’s fault withstand time.
• Verify thermal performance under real load cycles and ambient conditions.
• Test EMI, insulation stress, and switching overshoot before finalizing the design.
• Maintain derating and document assumptions, tolerances, and test evidence.

Chapter Summary

Power semiconductor devices are selected according to their controllability, voltage and current capability, conduction behavior, switching performance, thermal path, SOA, and system-level constraints. Diodes provide uncontrolled rectification but may suffer reverse-recovery loss. Thyristors offer low conduction loss and high power capability, but conventional devices require circuit-assisted turn-off. GTOs add turn-off control at the expense of complex drive and lower frequency.

MOSFETs are fast majority-carrier devices whose loss is strongly related to on-resistance and gate charge. IGBTs combine insulated-gate control with bipolar conduction and are effective at moderate switching frequencies, although tail current increases turn-off loss. SiC devices provide high-voltage, high-temperature, and low-recovery advantages, while GaN devices enable very high-frequency, high-power-density conversion with demanding layout and gate-drive requirements.

Static models must be combined with dynamic switching-energy models and thermal networks. Safe design requires SOA verification, derating, controlled parasitics, fault protection, and attention to electromagnetic compatibility. The best device is the one that minimizes total system risk and cost while meeting electrical, thermal, frequency, reliability, and regulatory requirements.

Key Terms

Power semiconductor device: A semiconductor designed to control or convert substantial electrical power.

Forward blocking: The state in which a device supports positive voltage without conducting significant current.

Reverse recovery: The transient process by which a conducting diode regains reverse-blocking capability.

Reverse-recovery charge: The charge removed from a diode during reverse recovery.

Thyristor: A latching four-layer semiconductor switch controlled principally at turn-on by a gate signal.

Latching current: The minimum current needed immediately after triggering to maintain thyristor conduction.

Holding current: The minimum current below which a conducting thyristor turns off.

GTO: A gate turn-off thyristor that can be turned off using reverse gate current.

MOSFET: A voltage-controlled, majority-carrier transistor with an insulated gate.

R_DS(on): The drain-source resistance of a MOSFET in its conducting state.

IGBT: An insulated-gate bipolar transistor combining MOS gate control with bipolar conduction.

Tail current: The decaying turn-off current caused by stored minority carriers in an IGBT.

Wide-bandgap semiconductor: A semiconductor such as SiC or GaN with a larger energy bandgap than silicon.

Switching energy: Energy dissipated during a device turn-on or turn-off transition.

Safe operating area: The permitted combinations of voltage, current, duration, and temperature for reliable operation.

Thermal resistance: A parameter relating temperature rise to dissipated power.

Gate charge: The charge required to change a transistor’s gate voltage and operating state.

Miller effect: The influence of gate-drain or gate-collector capacitance during voltage transitions.

Derating: Operating a component below its absolute rating to provide reliability margin.

Commutation: The transfer of current between semiconductor devices or circuit paths.

Review Questions

Short Answer Questions

1. Distinguish between uncontrolled, semi-controlled, and fully controlled power devices.

2. What are latching current and holding current in an SCR?

3. Why does a power diode produce reverse-recovery current?

4. State the principal difference between MOSFET and IGBT conduction mechanisms.

5. What information does a device safe operating area provide?

Long Answer Questions

1. Explain the static and dynamic characteristics of a power diode and discuss methods of reducing reverse-recovery stress.

2. Describe the operating principle, triggering, turn-off limitations, and applications of an SCR and a GTO.

3. Compare power MOSFETs and IGBTs in terms of conduction loss, switching loss, gate drive, and application range.

4. Explain the conduction, switching, gate-drive, and thermal-loss models used in power-device selection.

5. Discuss the advantages and design challenges of SiC and GaN devices compared with silicon devices.

Analytical / Application Questions

1. A converter operates at high voltage and 10 kHz with a restrictive heatsink volume. Develop a reasoned procedure for choosing between an IGBT and a SiC MOSFET.

2. A bridge circuit experiences voltage overshoot when a diode turns off. Identify the physical cause and propose circuit, layout, and device-level remedies.

3. A MOSFET’s measured on-resistance is much higher at elevated temperature than its room-temperature data-sheet value. Explain the effect on loss, thermal stability, and device selection.

22. Multiple Choice Questions with Answers

Question 1

Which characteristic most directly explains why a conventional SCR cannot normally be turned off by removing its gate signal?

A. Its gate is insulated from the anode

B. It is a latching device requiring current reduction below the holding current

C. Its forward voltage is independent of current

D. It has no reverse-blocking capability

Correct Answer: B. It is a latching device requiring current reduction below the holding current

Question 2

A diode in a hard-switched converter causes a large voltage spike when it recovers. Which mechanism most directly produces the spike?

A. Gate-charge variation

B. Parasitic inductance interacting with rapid current change

C. Reduction of junction temperature

D. Increase in MOSFET threshold voltage

Correct Answer: B. Parasitic inductance interacting with rapid current change

Question 3

For a MOSFET operated at a fixed RMS current, which change most directly increases conduction loss?

A. Reduction in R_DS(on)

B. Reduction in switching frequency

C. Increase in junction temperature that raises R_DS(on)

D. Reduction in gate charge

Correct Answer: C. Increase in junction temperature that raises R_DS(on)

Question 4

Why does an IGBT generally have greater turn-off loss than a comparable MOSFET?

A. It requires continuous base current

B. It stores minority carriers that produce a current tail

C. It cannot block forward voltage

D. Its gate is electrically connected to the collector

Correct Answer: B. It stores minority carriers that produce a current tail

Question 5

Which device is generally most suitable for very high-frequency, relatively low-to-medium-voltage conversion when extremely low gate charge is important?

A. Line-frequency SCR

B. GTO

C. GaN transistor

D. Power BJT in deep saturation

Correct Answer: C. GaN transistor

Question 6

A designer estimates semiconductor temperature using T_J = T_A + P_loss R_thetaJA. What does this model primarily represent?

A. Electrical switching gain

B. Steady-state thermal temperature rise

C. Reverse-recovery charge

D. Gate-drive current

Correct Answer: B. Steady-state thermal temperature rise

Question 7

Which statement best describes a principal advantage of a SiC Schottky diode?

A. It requires minority-carrier storage for conduction

B. It has negligible minority-carrier reverse recovery

C. It can only operate at line frequency

D. It must be triggered by a gate pulse

Correct Answer: B. It has negligible minority-carrier reverse recovery

Question 8

A design uses a high-voltage silicon MOSFET at high current. Which trade-off is especially important?

A. The voltage-supporting drift region can increase R_DS(on)

B. The device cannot be voltage controlled

C. The device always has a current tail

D. The body diode has no effect on commutation

Correct Answer: A. The voltage-supporting drift region can increase R_DS(on)

Question 9

Which factor should be included when comparing switching energies from two device data sheets?

A. Only the package color

B. The test voltage, current, temperature, and gate resistance

C. Only the nominal blocking voltage

D. The number of control terminals alone

Correct Answer: B. The test voltage, current, temperature, and gate resistance

Question 10

A SiC MOSFET replacement reduces switching loss but increases electromagnetic interference. What is the most appropriate engineering response?

A. Ignore EMI because semiconductor loss is lower

B. Increase the DC-link voltage without testing

C. Optimize layout and gate speed and reassess filtering and insulation stress

D. Remove all gate protection

Correct Answer: C. Optimize layout and gate speed and reassess filtering and insulation stress