13. Power Semiconductor Devices and Power Circuits

Introduction and context

Power semiconductor devices are the controlled valves through which electrical energy is converted, regulated, and delivered in modern power-electronic systems. Unlike small-signal devices, they are designed to withstand substantial voltage, conduct high current, dissipate heat, and switch repeatedly with acceptable loss. They are found in motor drives, renewable-energy interfaces, uninterruptible power supplies, electric vehicles, industrial controllers, battery chargers, traction systems, medical equipment, and high-efficiency power supplies.

The central engineering problem is not simply to select a device with a suitable voltage and current rating. The designer must coordinate semiconductor characteristics with topology, switching frequency, gate-drive requirements, thermal paths, electromagnetic compatibility, protection, reliability, insulation, and applicable safety standards. A device that appears suitable from its catalogue ratings may fail because of voltage overshoot, excessive junction temperature, uncontrolled di/dt, inadequate gate control, or repetitive avalanche stress.

This chapter develops a device-to-system perspective. It begins with the operating behaviour of power diodes, MOSFETs, IGBTs, thyristors, and wide-bandgap devices, and then relates them to rectifiers, regulators, inverters, commutation circuits, gate drivers, protection networks, and thermal design. The objective is informed engineering selection rather than memorisation of isolated specifications.

Learning objectives

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

1. Explain the electrical and switching characteristics of major power semiconductor devices.

2. Select power diodes, MOSFETs, IGBTs, thyristors, and wide-bandgap devices for a specified application.

3. Estimate conduction and switching losses and relate them to thermal limits.

4. Analyse the operation of rectifiers, dc-dc converters, inverters, and controlled power circuits.

5. Design the essential functions of gate-drive, snubber, clamp, current-sensing, and protection circuits.

6. Evaluate trade-offs involving efficiency, frequency, cost, EMI, reliability, and manufacturability.

7. Apply professional safety and verification practices to high-energy power circuits.

The power-device operating envelope

A power semiconductor is normally operated in one of three states: blocking, conducting, or transitioning between them. In the blocking state, leakage current must remain small while the device supports a specified voltage. In the conducting state, voltage drop and power dissipation must be limited. During transition, both voltage and current can be significant, producing switching loss and electrical stress.

Important ratings include repetitive peak off-state voltage, drain-source or collector-emitter voltage, continuous and pulsed current, surge current, gate voltage, junction temperature, safe operating area (SOA), short-circuit withstand time, and avalanche capability. Ratings are conditional: current depends on temperature, cooling, duty cycle, package, and waveform. The designer should distinguish absolute maximum ratings from recommended operating values and should apply derating rather than designing at the limit.

The switching frequency affects several competing quantities. Increasing frequency can reduce the size of inductors, transformers, and filters, but increases switching loss, gate-drive loss, displacement current, and EMI. Reducing conduction resistance or forward drop may require a larger die, which can increase capacitance and switching loss. Device selection is therefore a system optimisation problem.

Power diodes

A power diode conducts when forward biased and blocks when reverse biased. Its principal parameters are forward voltage, reverse-recovery charge, reverse-recovery time, leakage current, surge-current capability, and repetitive reverse-voltage rating. The forward drop causes conduction loss approximately given by

P_D \approx V_F I_{D,avg}

or, for a more accurate model, by

P_D \approx V_{F0}I_{avg}+r_d I_{rms}^{2}.

The ordinary pn-junction diode has useful voltage and surge-current capability but may exhibit substantial reverse recovery. When a conducting diode is suddenly reverse biased, stored charge must be removed. The resulting reverse current can produce voltage overshoot, switching loss, and severe EMI. Fast-recovery diodes reduce this interval. Schottky diodes have low forward voltage and essentially no minority-carrier reverse recovery, but conventional silicon Schottky devices have higher leakage and limited high-voltage capability. Silicon-carbide Schottky diodes combine low recovery charge with high-voltage capability and are especially useful in high-frequency and high-temperature converters.

Power diodes are used as rectifiers, freewheeling paths, clamp elements, commutation components, and antiparallel devices across switches. Their dynamic behaviour must be evaluated together with the switch. A slow diode paired with a fast MOSFET can create a damaging current spike even if both devices satisfy static ratings.

Power MOSFETs

The power MOSFET is a voltage-controlled, majority-carrier device. Its gate is insulated, so steady-state gate current is very small, although transient current is required to charge and discharge gate capacitances. It can switch rapidly and is particularly effective at low and medium voltages and high frequencies.

The main conduction parameter is the on-state resistance, R_DS(on). Conduction loss is approximately

P_cond = I_{rms}^{2}R_{DS(on)}.

R_DS(on) increases significantly with junction temperature, so thermal feedback must be considered. Switching behaviour is influenced by gate charge, output capacitance, reverse-transfer capacitance, internal gate resistance, and the Miller plateau. A low gate charge does not necessarily imply low total switching loss; capacitances and the applied voltage-current trajectory also matter.

MOSFET body diodes provide an intrinsic reverse-current path, but their reverse-recovery behaviour may be unsuitable for hard-switched bridge operation. In synchronous buck converters, a MOSFET may be deliberately turned on during the interval that would otherwise use a diode, reducing conduction loss. Dead time is required to prevent simultaneous conduction of the high-side and low-side switches. Excessive dead time increases body-diode conduction; insufficient dead time causes shoot-through.

IGBTs

The insulated-gate bipolar transistor combines MOS gate control with bipolar conduction. It generally offers lower conduction loss than a high-voltage silicon MOSFET at moderate switching frequencies and high voltage, but it has a relatively slow turn-off tail caused by stored minority carriers. Consequently, IGBTs are common in motor drives, industrial inverters, traction converters, and medium-frequency high-power systems, while silicon MOSFETs dominate many lower-voltage, high-frequency converters.

An approximate IGBT conduction model is

P_cond \approx V_{CE0}I_{avg}+r_{CE}I_{rms}^{2}.

IGBTs require a suitable antiparallel diode in bridge circuits. Gate voltage must be controlled carefully because a false turn-on caused by Miller coupling can produce shoot-through. Short-circuit protection is important: an IGBT may tolerate a short circuit only for a specified, often brief, interval.

Thyristors and controlled rectifiers

The thyristor, or silicon-controlled rectifier (SCR), is a latching device with an anode, cathode, and gate. A forward-biased SCR turns on when an adequate gate pulse is applied, but it remains on after the gate signal is removed until current falls below the holding current or reverse bias is applied. This makes it highly suitable for line-frequency and high-power controlled rectifiers, soft starters, AC voltage controllers, and some high-power transmission applications.

A thyristor cannot normally be turned off through its gate. Commutation may be natural, as in an AC supply, or forced through auxiliary capacitors, inductors, and switches. Important ratings include latching current, holding current, turn-on di/dt, turn-off time, critical dv/dt, surge current, and repetitive blocking voltage. Excessive dv/dt can cause unwanted turn-on, while excessive di/dt can produce nonuniform current distribution and local heating.

Gate-turn-off thyristors, integrated gate-commutated thyristors, and related devices extend controllability to high-power applications. They offer high current and voltage capability but require substantial gate-drive energy and careful mechanical and thermal design.

Wide-bandgap devices

Silicon carbide (SiC) and gallium nitride (GaN) have larger bandgaps than silicon. This enables higher critical electric field, lower intrinsic carrier concentration, higher-temperature operation, and potentially lower charge-related losses. SiC MOSFETs and diodes are established choices in high-voltage solar inverters, electric-vehicle chargers, industrial drives, and high-power dc-dc converters. GaN HEMTs are especially attractive for high-frequency, relatively lower-voltage applications such as compact adapters, server supplies, and high-density converters.

Wide-bandgap devices do not remove design difficulties. Their fast transitions expose parasitic inductance, common-source inductance, package limitations, gate-loop layout errors, and measurement-probe problems. Gate-voltage margins may be narrower, and dynamic behaviour can be strongly affected by layout and driver impedance. Their higher switching speed can reduce magnetic size, but it can also increase common-mode current and radiated EMI. The correct question is not whether wide-bandgap technology is intrinsically superior, but whether its switching, thermal, cost, and system benefits justify the additional design discipline.

From device physics to circuit function

Rectifiers and freewheeling paths

An uncontrolled single-phase bridge rectifier uses four diodes to convert AC into pulsating DC. A capacitor-input filter raises the dc output near the peak of the AC waveform, but causes narrow, high-amplitude input-current pulses and poor power factor. An inductive or actively controlled front end produces a more continuous current and can improve power factor and harmonic performance.

In a buck converter, the freewheeling device conducts when the main switch is off. In a boost converter, the diode transfers inductor energy to the output when the switch turns off. In bridge inverters, antiparallel diodes carry current when the load current direction differs from the commanded switch state. Diode selection must therefore consider current direction, commutation, reverse recovery, and the switching node voltage—not only average current.

PWM dc-dc converters

The ideal buck converter produces

V_o = D V_{in},

where D is the duty ratio. The ideal boost converter produces

V_o = \frac{V_{in}}{1-D},

and the ideal inverting buck-boost converter produces

V_o = -\frac{D}{1-D}V_{in}.

Real converters depart from these expressions because of switch resistance, diode drop, inductor resistance, capacitor ESR, dead time, and finite transition times. Continuous-conduction operation generally reduces peak current but introduces right-half-plane dynamics in boost-derived stages. Discontinuous conduction may simplify some control behaviour but increases peak and RMS currents.

At postgraduate level, the converter should be treated as a dynamic plant rather than merely a voltage-ratio circuit. Small-signal models, current-mode control, loop compensation, slope compensation, soft switching, and digital control determine transient response and stability. Zero-voltage switching and zero-current switching reduce overlap loss, although they may introduce circulating current and additional conduction loss.

Inverters and motor-drive bridges

A half bridge contains two controlled switches and a split dc link; a full bridge contains two half bridges. Complementary PWM signals synthesize an AC voltage, while dead time prevents cross-conduction. In a voltage-source inverter, dc-link capacitors absorb switching ripple and provide a low-impedance source for pulsed current. Their ripple-current rating and lifetime are often system-limiting factors.

Motor drives add current regulation, rotor-position or sensorless estimation, regeneration, braking, and fault management. The power stage must withstand regenerative energy and short-circuit events. Space-vector PWM can use the dc bus efficiently, but its switching states and common-mode voltage must be evaluated for bearing currents, insulation stress, and EMI.

Loss estimation and thermal design

Total semiconductor loss is commonly divided into conduction, switching, gate-drive, reverse-recovery, and sometimes output-capacitance loss:

P_loss = P_cond + P_sw + P_gate + P_rr + P_other.

A first estimate of hard-switching loss is

P_sw \approx \frac{1}{2}VI(t_r+t_f)f_s,

where t_r and t_f are effective voltage-current overlap times. More reliable estimates use measured or manufacturer-supplied turn-on and turn-off energies, often corrected for current, voltage, and temperature. Diode reverse-recovery energy should be included in the appropriate device or system loss budget.

The gate-drive loss is approximately Q_g V_{drive} f_s, with refinements for driver supply current and charging losses. In multi-device converters, gate-drive power can become substantial at high frequency.

Thermal design begins with the junction-temperature limit:

T_J = T_A + P_loss R_{\theta JA},

or, for a heatsinked package,

T_J = T_A + P_loss(R_{\theta JC}+R_{\theta CS}+R_{\theta SA}).

Here, case-to-sink and sink-to-ambient resistances depend on interface material, mounting pressure, airflow, orientation, and contamination. Transient thermal impedance is needed for pulsed loads. Designers should account for simultaneous device operation, heatsink temperature gradients, thermal interface ageing, and worst-case ambient conditions. Reliability generally improves when junction temperature excursions and maximum temperature are kept below their rated limits.

Gate drivers, protection, and layout

A gate driver must deliver controlled source and sink current, establish a defined off-state, tolerate common-mode voltage, and maintain adequate isolation where required. High-side switches may use bootstrap, isolated, or isolated-power drivers. Bootstrap circuits are economical but cannot maintain a high-side gate indefinitely at 100% duty ratio and require suitable refresh conditions.

Important protection functions include overcurrent detection, desaturation detection for IGBTs, cycle-by-cycle current limiting, short-circuit shutdown, undervoltage lockout, overtemperature sensing, dc-link overvoltage protection, and shoot-through interlock. A fault should be turned off in a controlled manner; an excessively fast shutdown can create large voltage overshoot through stray inductance.

Snubbers and clamps control switching stress. An RC or RCD snubber absorbs energy and damps ringing. Active clamps recycle or limit energy more efficiently in selected topologies. The required component values should be based on measured parasitic inductance, ringing frequency, peak current, and acceptable voltage. A snubber that is selected without waveform measurement may merely shift the resonance or create continuous loss.

Layout is part of the circuit. High di/dt loops should be physically compact; power and gate-return paths should be separated where appropriate; the driver should be close to the gate; Kelvin source or emitter connections should be used when available; and control-ground references should not share uncontrolled high-current paths. Wide-bandgap designs are particularly sensitive to common-source inductance and gate-loop inductance.

EMI, insulation, and safety

Fast switching produces conducted and radiated emissions through differential-mode and common-mode paths. Remedies include controlled gate resistance, slew-rate control, spread-spectrum modulation where appropriate, input and output filters, common-mode chokes, shielding, snubbers, careful grounding, and minimisation of switching-node copper area. EMI control must be designed alongside the power stage because a filter added late may interact with converter control or create resonance.

High-voltage converters require reinforced or basic insulation as dictated by the application. Creepage and clearance, insulation coordination, touch-safe construction, precharge circuits, discharge resistors, fusing, interlocks, emergency shutdown, and safe measurement procedures are essential. Oscilloscope probes must have suitable voltage and common-mode ratings; an ordinary grounded probe can create a short circuit across a floating switching node.

Professional practice requires documented design margins, traceable component ratings, fault analysis, thermal testing, production tests, and compliance evaluation. Standards depend on the equipment category and jurisdiction, but the underlying principles—protection against electric shock, fire, excessive temperature, and stored energy—are universal.

Device-selection framework

A useful selection sequence is:

1. Define the electrical envelope: maximum blocking voltage, current waveform, switching frequency, duty cycle, overload, and fault energy.

2. Identify the dominant operating regime: low-voltage/high-frequency, high-voltage/moderate-frequency, line-frequency/high-power, or extreme-temperature operation.

3. Compare conduction and switching losses at actual temperature and waveform, not only at room-temperature catalogue conditions.

4. Check gate-drive, reverse-current, short-circuit, avalanche, and commutation requirements.

5. Verify package, thermal path, isolation, creepage, parasitics, availability, cost, and manufacturing constraints.

6. Simulate and measure double-pulse or representative switching waveforms.

7. Apply voltage, current, thermal, and lifetime derating, followed by fault and compliance testing.

A MOSFET is often preferred where switching frequency is high and voltage is relatively low. An IGBT may be advantageous where voltage and power are high but switching frequency is moderate. A thyristor remains compelling in very high-power, line-commutated systems. SiC is attractive when high voltage, high temperature, or high-frequency switching justifies its cost; GaN is attractive where very high frequency and compact magnetics dominate the design.

Illustrative case study: a 10 kW solar inverter leg

Background

Consider an illustrative 10 kW photovoltaic inverter with a 700 V dc link, a three-phase output, and a switching frequency of 20 kHz. The design team initially proposes silicon IGBTs because they are familiar and economical.

Situation and problem

Prototype testing shows that efficiency is below the target, the heatsink is large, and turn-off voltage overshoot approaches the device limit. The measured switching-node waveform contains ringing, and common-mode current is higher than predicted.

Analysis

The dc-link voltage and 20 kHz switching frequency place the design in a region where IGBT conduction performance is useful but turn-off tail loss is significant. The antiparallel diode also contributes reverse-recovery loss. Stray inductance in the commutation loop produces overshoot according to the approximate relationship V_L = L_s di/dt. The original thermal estimate used nominal switching energy and did not include worst-case temperature or diode recovery.

Approach and solution

The team compares three alternatives: improved silicon IGBTs with faster diodes, 1200 V SiC MOSFETs, and a modified switching frequency. Double-pulse testing is used to measure actual turn-on, turn-off, and recovery energies. A laminated dc-link connection reduces commutation inductance. The gate driver is redesigned with isolated power, Miller control, undervoltage lockout, and separate turn-on and turn-off resistances. An RC snubber limits the remaining overshoot, while the PWM strategy is adjusted to reduce unnecessary switching during low-current intervals. The thermal model includes semiconductor, interface, and heatsink resistances and is verified with thermocouples and junction-temperature estimation.

Outcome

The final choice is made from measured energy per switching event, total loss, thermal margin, EMI performance, and cost—not from device technology alone. The SiC option offers lower switching loss and a smaller heatsink but requires tighter layout, a more carefully controlled gate voltage, and a higher component cost. The improved IGBT option is retained for a cost-sensitive product variant. Both variants receive independent overcurrent protection, dc-link discharge, insulation verification, and conducted-emissions testing.

Learning points

The case demonstrates that a device rating is not a design solution. Switching energy, parasitic inductance, diode behaviour, gate-drive control, thermal impedance, EMI, and commercial constraints must be evaluated together. It also illustrates the value of double-pulse testing and of maintaining more than one technically viable architecture during early design.

Challenges and common design errors

Frequent errors include selecting a device from average current alone, ignoring peak and RMS current, using maximum voltage ratings without overshoot margin, omitting diode recovery loss, assuming a heatsink temperature equals ambient temperature, and placing the gate resistor far from the device. Other failures arise from inadequate dead time, poorly controlled Miller turn-on, insufficient short-circuit response, excessive probe-loop inductance during measurement, and failure to test at high temperature.

Digital control and simulation are valuable but cannot replace measurement. SPICE models may not represent layout-dependent parasitics, nonlinear capacitances, driver saturation, or temperature-dependent recovery. Automated data acquisition can support efficiency maps, thermal monitoring, predictive maintenance, and fault trending, but the measurement chain must be calibrated and isolated. Machine-learning methods may help classify abnormal waveforms, yet protection must remain deterministic and independently validated.

Emerging developments include higher-voltage SiC devices, enhancement-mode GaN devices, advanced sintered and embedded packages, integrated current sensing, intelligent power modules, solid-state circuit breakers, and converter topologies designed for soft switching. These developments improve power density but increase the importance of packaging, control co-design, reliability physics, and electromagnetic compatibility.

Best-practice design checklist

A robust design normally includes the following practices:

• Use worst-case voltage, current, temperature, tolerance, and fault conditions.
• Select the diode and switch as a commutating pair rather than as independent parts.
• Calculate losses from actual waveforms and manufacturer energy data.
• Keep high-current and gate-drive loops short and use appropriate Kelvin returns.
• Provide defined gate turn-off, interlock, undervoltage lockout, and fast fault handling.
• Measure switching waveforms with properly rated differential and current probes.
• Verify thermal performance under steady-state and transient loading.
• Design EMI filtering, insulation, precharge, discharge, and touch protection from the beginning.
• Validate prototypes using double-pulse, short-circuit, overload, thermal, humidity, vibration, and compliance tests as appropriate.
• Document assumptions, margins, revision history, and production-test limits.

Chapter Summary

Power semiconductor design links device physics to converter topology, control, thermal management, protection, EMI, safety, and reliability. Power diodes differ mainly in forward drop, recovery behaviour, and voltage capability. MOSFETs provide rapid majority-carrier switching and are effective at high frequency; IGBTs serve higher-voltage, moderate-frequency applications but exhibit tail current; thyristors provide economical high-power latching control; and SiC and GaN devices enable higher-frequency and higher-temperature operation when layout and gate-drive requirements are satisfied.

Rectifiers, dc-dc converters, and inverters depend on correct commutation paths, dead time, PWM control, and energy storage. Conduction and switching losses must be estimated together and translated into junction temperature through a complete thermal path. Gate drivers, snubbers, clamps, current limits, isolation, and careful layout are essential for safe operation. The appropriate device is selected by evaluating the complete operating envelope and system trade-offs, then verifying the design experimentally under electrical, thermal, EMI, and fault conditions.

Key Terms

Power diode: A diode designed to block high voltage and conduct substantial current.

Reverse recovery: The transient reverse current required to remove stored charge from a conducting diode.

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

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

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

Thyristor: A latching semiconductor switch that remains on until its current is sufficiently reduced.

Holding current: The minimum thyristor current required to keep it conducting.

Safe operating area: The permitted combinations of voltage, current, time, and temperature for a device.

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

Miller plateau: The gate-voltage interval associated with rapid drain or collector-voltage transition.

Dead time: The intentional interval between turning one bridge switch off and its complementary switch on.

Shoot-through: Direct cross-conduction between upper and lower switches of a bridge leg.

Snubber: A network used to damp ringing or limit voltage and current transients.

Wide-bandgap semiconductor: A semiconductor material such as SiC or GaN with a large energy bandgap.

Conduction loss: Power dissipated because of on-state voltage drop or resistance.

Switching loss: Power dissipated during voltage-current transitions.

Thermal resistance: Temperature rise per unit dissipated power between two defined points.

Common-mode current: Current driven through parasitic capacitances by switching-node voltage changes.

Double-pulse test: A controlled test used to characterise switching and commutation behaviour.

Derating: Operating a component below its maximum rating to improve margin and reliability.

Review Questions

Short Answer Questions

1. Why can reverse recovery of a power diode increase both switching loss and EMI?

2. Distinguish the turn-off mechanisms of a MOSFET, an IGBT, and a thyristor.

3. What is the purpose of dead time in a half bridge?

4. Identify the main elements of a semiconductor thermal resistance path.

5. Why are wide-bandgap devices especially sensitive to layout parasitics?

Long Answer Questions

1. Explain the operating characteristics, advantages, and limitations of power diodes, MOSFETs, IGBTs, and thyristors.

2. Derive the principal loss components in a hard-switched PWM converter and explain how each can be reduced.

3. Describe the construction and operation of a protected half-bridge gate-drive system.

4. Compare silicon, SiC, and GaN devices for high-frequency power conversion.

5. Explain how EMI, insulation, thermal design, and safety requirements influence converter architecture.

Analytical / Application Questions

1. A 600 V converter operates at 25 kHz and shows excessive turn-off overshoot. Propose a measurement and redesign procedure involving layout, gate drive, and snubber selection.

2. Select a device technology for a 400 V, 100 kHz, 2 kW dc-dc converter and justify the choice using conduction loss, switching loss, thermal, and cost considerations.

3. An inverter experiences shoot-through only at high temperature. Analyse possible causes involving gate threshold, Miller coupling, dead time, driver supply, and thermal parameter variation.

22. Multiple Choice Questions with Answers

Question 1

Which characteristic most directly makes a power MOSFET suitable for high-frequency switching?

A. Minority-carrier storage during turn-off

B. Majority-carrier operation with low stored charge

C. Latching conduction after gate removal

D. Requirement for natural commutation

Correct Answer: B. Majority-carrier operation with low stored charge

Question 2

In a hard-switched converter, switching loss is most directly associated with which condition?

A. Voltage and current overlapping during transitions

B. Zero current and zero voltage simultaneously

C. Gate leakage in the off-state only

D. Heatsink temperature being below ambient

Correct Answer: A. Voltage and current overlapping during transitions

Question 3

What is the principal function of dead time in a bridge leg?

A. Increase diode reverse recovery

B. Prevent simultaneous conduction of complementary switches

C. Maintain continuous gate current

D. Raise the dc-link voltage

Correct Answer: B. Prevent simultaneous conduction of complementary switches

Question 4

Which device normally remains on after its gate pulse is removed until current falls below the holding current?

A. Power MOSFET

B. IGBT

C. SCR thyristor

D. Schottky diode

Correct Answer: C. SCR thyristor

Question 5

For a MOSFET with RMS current I and on-resistance RDS(on), the approximate conduction loss is

A. I RDS(on)

B. I squared RDS(on)

C. RDS(on) divided by I

D. I divided by RDS(on)

Correct Answer: B. I squared RDS(on)

Question 6

A major advantage of a silicon-carbide Schottky diode is

A. Very large minority-carrier reverse recovery

B. Low recovery charge with high-voltage capability

C. Need for a thyristor gate pulse

D. Permanent forward blocking

Correct Answer: B. Low recovery charge with high-voltage capability

Question 7

Which design change most directly reduces voltage overshoot caused by commutation-loop inductance?

A. Increasing the high-current loop area

B. Reducing parasitic inductance and controlling switching speed

C. Removing all gate resistance

D. Increasing probe-loop inductance

Correct Answer: B. Reducing parasitic inductance and controlling switching speed

Question 8

Why can a bootstrap high-side gate driver be unsuitable for indefinite 100% duty-ratio operation?

A. It cannot conduct gate current at any time

B. It requires refresh conditions to recharge its floating supply

C. It always produces thyristor latching

D. It eliminates the need for isolation

Correct Answer: B. It requires refresh conditions to recharge its floating supply

Question 9

Which expression best represents a simple thermal estimate for junction temperature?

A. TJ = TA minus P Rtheta

B. TJ = TA plus P Rtheta

C. TJ = P divided by TA

D. TJ = Rtheta divided by P

Correct Answer: B. TJ = TA plus P Rtheta

Question 10

A double-pulse test is primarily used to

A. Measure switching and commutation behaviour under controlled conditions

B. Determine the colour of a semiconductor package

C. Replace all thermal testing

D. Set the nominal AC grid frequency

Correct Answer: A. Measure switching and commutation behaviour under controlled conditions