Today, Our Communication Elements Are: - Thyristor: Structure, Working & Applications, Power MOSFET: Structure, Characteristics, Operation, Ratings, Protections & Thermal Aspects, IGBT: Structure, Characteristics, Operation, Ratings, Protections & Thermal Considerations, TRIAC, MOS Controlled Thyristor (MCT), Power Integrated Circuit (PIC) – Smart Power, Commutation and Snubber Circuits for Thyristors, Power MOSFETs and IGBTs (Discrete and IC Based), Concept of Fast Recovery and Schottky Diodes as Freewheeling and Feedback Diodes.
Thyristor: Structure, Working & Applications: -
Thyristine structure
- Anode (A) – Bahari is connected to the P layers.
- Cathode (K) -Bahari is connected to N-layers.
- Gate (G) – Lines are connected to the P layer, which is used to trigger.
Working principle
Thyristine application
- Controlled rectifiers – Used in AC to DC conversion.
- Motor speed control – DC is widely used in motor stations.
- Light dimmers and fan controllers – For controlling household appliances.
- Transmitters and converters – used in UPS, SMP, and HVDC transfer.
- Output protection – as a cutting circuit to protect sensitive devices.
Conclusion
Power MOSFET: Structure, Characteristics, Operation, Ratings, Protections & Thermal Aspects: -
Structure of Power MOSFET
- Source region (N+ layer) – Provides carriers (electrons or holes).
- Channel (P-body) – Controls current conduction.
- Drain (N-drift region) – Collects carriers and handles high voltage.
- Gate (metallic contact with oxide insulation) – Controls the conductivity of the channel.
Characteristics of Power MOSFET
- High Input Impedance – Needs very low gate drive power.
- Fast Switching Speed – Suitable for high-frequency operation.
- Low On-State Resistance (RDS-ON) – Reduces conduction losses.
- Unipolar Conduction – Depends only on majority carriers, making it faster than BJTs.
- High Efficiency – Lower switching and conduction losses.
Operation of Power MOSFET
The working of a MOSFET depends on the Gate-to-Source Voltage (VGS):
- OFF State (VGS < Vth) – No current flows between drain and source.
- ON State (VGS > Vth) – An inversion layer (channel) is formed, allowing current to flow.
- Linear & Saturation Region – In linear mode, the MOSFET acts as a resistor, while in saturation, it acts as a switch.
Ratings of Power MOSFET
When selecting a MOSFET for applications, key ratings must be considered:
- VDS (Drain-to-Source Voltage) – Maximum voltage it can withstand.
- ID (Continuous Drain Current) – Maximum current-carrying capacity.
- RDS-ON (On-State Resistance) – Affects conduction losses and heating.
- VGS (Gate Drive Voltage) – Typical range 5V–20V.
- Ptot (Power Dissipation) – Maximum heat the device can handle.
Protection of Power MOSFET
Power MOSFETs are sensitive to voltage and temperature stresses. Common protections include:
- Gate Protection – Using Zener diodes or gate resistors to limit gate voltage.
- Overcurrent Protection – Fuses or current-sensing circuits.
- Overvoltage Protection – Snubber circuits and TVS diodes.
- Short-Circuit Protection – Fast response circuits to cut off current.
Thermal Aspects of Power MOSFET
Heat management is crucial for MOSFET reliability:
- Heat Sink & Cooling Fans – Reduce junction temperature.
- Thermal Resistance (RθJA, RθJC) – Specifies how efficiently heat flows.
- Safe Operating Area (SOA) – Defines limits for voltage, current, and temperature.
- Safe Operating Area (SOA) – Defines limits for voltage, current, and temperature.
Conclusion
Power MOSFETs are vital devices for modern power conversion and control systems. Their fast switching speed, high efficiency, and simple gate drive make them superior to BJTs in most power applications. However, proper protection and thermal management are essential for ensuring long life and reliability.
IGBT: Structure, Characteristics, Operation, Ratings, Protections & Thermal Considerations: -
Structure of IGBT
An IGBT has a four-layer structure (P+ - N- - P - N+) with three main terminals:
- Collector (C) – Connected to the P+ substrate.
- Emitter (E) – Connected to the N+ region
- Gate (G) – Insulated by a thin oxide layer, used to control conduction.
Essentially, it combines the MOSFET’s gate structure with the BJT’s conduction mechanism, making it efficient for both low- and high-power applications.
Characteristics of IGBT
- High Input Impedance – Requires very low gate drive power (similar to MOSFET).
- Low Conduction Losses – Due to the conductivity modulation of the BJT section.
- High Voltage Capability – Can withstand up to 6.5 kV in modern devices.
- Moderate Switching Speed – Faster than BJT but slightly slower than MOSFET.
- Latch-up Free Designs – Modern IGBTs are designed to prevent unwanted latch-up conditions.
- Current Handling – Suitable for applications from a few amperes to several kiloamperes.
Operation of IGBT
The operation of an IGBT depends on the Gate-to-Emitter
Voltage (VGE):
- OFF State (VGE < Vth): No channel is formed, and the device blocks current between collector and emitter.
- ON State (VGE > Vth): A channel is formed, allowing electrons to flow, which in turn activates the PNP transistor section. This leads to a large collector current flow with very low on-state resistance.
- Switching: Turn-on is faster, but turn-off may involve tail current due to stored charge in the drift region.
Ratings of IGBT
When selecting an IGBT, important ratings to consider are:
- VCES (Collector-Emitter Voltage): Maximum blocking voltage, typically 600V to 6.5kV.
- IC (Continuous Collector Current): The maximum current it can handle continuously.
- VGE (Gate-Emitter Voltage): Maximum gate drive voltage, usually ±20V.
- Ptot (Total Power Dissipation): Indicates how much heat it can safely handle.
- Switching Frequency: Generally limited to 20–50 kHz due to tail currents.
Protections in IGBT
- Overcurrent Protection: Using fast-acting fuses or current sensors.
- Overvoltage Protection: Snubber circuits, clamping diodes, or TVS diodes.
- Short-Circuit Protection: Necessary in motor drives to avoid catastrophic failure.
- Gate Protection: Zener diodes to prevent excessive gate voltage.
- Thermal Protection: Sensors and shutdown circuits for overheating prevention.
Thermal Considerations
- Conduction Losses (IC × VCE(sat)): Caused by current flow in the ON state.
- Switching Losses: Due to finite rise and fall times and tail current.
- Safe Operating Area (SOA): Defines allowable limits of current, voltage, and temperature.
- Heat Dissipation: Managed using heat sinks, fans, or liquid cooling.
- Thermal Resistance (RθJC, RθJA): Specifies how well the device conducts heat from junction to case or ambient.
- Junction Temperature (Tj): Must always be kept below maximum (usually 150–175°C).
Conclusion
TRIAC: Structure, Characteristics, Operation & Applications: -
Structure of TRIAC
The TRIAC is a five-layer, three-terminal device. Its
terminals are:
- MT1 (Main Terminal 1)
- MT2 (Main Terminal 2)
- Gate (G)
Internally, the TRIAC can be thought of as two SCRs (Silicon
Controlled Rectifiers) connected in parallel but opposite directions, sharing a
common gate terminal.
Characteristics of TRIAC
Ø Bidirectional
Conduction – Can control both positive and negative half cycles of AC.
Ø Gate
Triggering – A small gate pulse can turn it ON in both directions.
Ø Latching
and Holding Current – Similar to SCR, once triggered, it continues to
conduct until the current falls below a threshold.
Ø Low
Gate Drive Requirement – Needs a small gate current to trigger.
Ø Suitable
for AC Applications – Unlike SCR, which conducts only in one direction,
TRIAC is ideal for AC switching.
Operation of TRIAC
When a gate pulse is applied, the TRIAC starts conducting
between MT1 and MT2. It remains ON until the AC cycle current drops below the holding
current. Since it is conducted in both half cycles, it provides full control of AC
power.
- Positive Half Cycle: Gate current triggers conduction from MT1 to MT2.
- Negative Half Cycle: Gate current triggers conduction from MT2 to MT1.
This bidirectional property makes it highly versatile in AC
circuits.
Applications of TRIAC
TRIACs are used in a variety of household, industrial, and
commercial applications:
- Light
Dimmers – Smooth brightness control in lamps.
- Fan
Regulators – Speed control of ceiling fans.
- Motor
Speed Control – In washing machines and drills.
- Heater
Control – In temperature regulation systems.
- AC
Switches – General-purpose power switching.
Conclusion
MOS Controlled Thyristor (MCT): -
Introduction
The MOS Controlled Thyristor (MCT) is a modern power
semiconductor device that combines the high current and voltage handling
capability of a thyristor with the easy gate control of a MOSFET.
In simple words, it gives the best of both worlds:
- Like a thyristor, it can handle large amounts of power.
- Like a MOSFET, it can be controlled by a small voltage signal at the gate.
This makes MCTs very attractive for high-power and
high-speed applications such as motor drives, inverters, and power converters.
Structure of MCT
1. The MCT is built on the four-layer PNPN thyristor structure.
2. On top of this, two MOSFETs are integrated:
- One MOSFET is used to turn the device ON.
- Another MOSFET is used to turn it OFF.
3. This dual MOSFET arrangement gives the MCT its unique
ability to be both switched ON and OFF using a gate signal, unlike a normal
SCR.
Working Principle
1. Turning ON the MCT
- When a negative voltage pulse is applied to the gate terminal, the first MOSFET turns ON.
- This injects current into the base of the internal thyristor, switching it ON.
- Once ON, the device can carry a very large current just like a normal SCR.
2. Turning OFF the MCT
- When a positive voltage pulse is applied to the gate terminal, the second MOSFET turns ON.
- This bypasses the base current of the thyristor and forces it to switch OFF.
- Thus, unlike an SCR, no external commutation is required.
Key Features
- Gate control similar to a MOSFET → easy voltage-driven switching.
- High current and voltage handling like a thyristor.
- Fast switching speeds → suitable for modern power electronics.
- Low conduction losses (low voltage drop in ON state).
- Can be both turned ON and OFF by gate signals.
Applications
- AC and DC motor control (variable speed drives).
- Inverters and choppers for power conversion.
- Switch Mode Power Supplies (SMPS).
- Induction heating and welding equipment.
- Uninterruptible Power Supplies (UPS).
Advantages
- Combines the ruggedness of thyristors with the easy drive requirements of MOSFETs.
- Compact and efficient → reduces the need for bulky commutation circuits.
- Lower switching and conduction losses.
Limitations
- Relatively complex structure compared to SCRs or MOSFETs.
- Limited commercial availability compared to IGBTs and MOSFETs.
- Performance is sensitive to gate drive design.
Conclusion
The MOS Controlled Thyristor (MCT) is a remarkable device in
power electronics that simplifies control while handling huge power levels.
Although not as popular as IGBTs and MOSFETs today, it laid the foundation for
combining MOS gate control with high-power thyristor performance, and it still
finds use in specialized applications requiring fast, reliable, and efficient
switching.
Power Integrated Circuit (PIC) – Smart Power: -
Introduction
The Power Integrated Circuit (PIC), often called Smart Power
Technology, is a class of integrated circuits that combine power devices (such
as MOSFETs, IGBTs, thyristors) and control circuits (such as logic gates,
protection circuits, and drivers) on a single chip.
In other words, a PIC is not just a power switch — it is a complete
intelligent power management solution, capable of handling power as well as
controlling and protecting itself.
This makes them highly useful in modern electronics, where
compactness, efficiency, and reliability are very important.
Structure of a Power Integrated Circuit
A PIC is built by combining two main sections on the same
chip:
Power Stage –
- Includes high-voltage/high-current devices like MOSFETs or IGBTs.
- Responsible for switching or controlling large power loads.
Control/Logic Stage –
- Contains CMOS or bipolar circuits for logic, sensing, and protection.
- Includes features such as gate drivers, current limiters, thermal sensors, undervoltage lockout, and protection circuits.
Thus, a PIC is like combining a power device, + driver
circuit + protection circuit into a single package.
Working Principle
- The control unit (logic circuits) continuously monitors the input signal, supply voltage, current, and temperature.
- Based on this monitoring, it generates a suitable gate signal to the power device (MOSFET/IGBT).
- The power device then switches ON/OFF or regulates power flow according to the input control and protection rules.
- If abnormal conditions occur (e.g., overcurrent, overheating, short-circuit), the control unit immediately shuts down the power stage to protect the device and load.
This is why PICs are often referred to as intelligent or
smart power devices.
Key Features of Smart Power ICs
- Integration of power and logic on a single chip.
- High efficiency and reduced losses.
- Self-protection features such as overcurrent, overvoltage, and thermal shutdown.
- Compact design → reduces external circuitry.
- Can handle both analog and digital control signals.
- Reliable operation even under harsh conditions.
Applications
Smart Power ICs are used in almost every modern electronic
system where power control + intelligence is needed. Examples include:
- Automotive electronics → ignition systems, motor control, lighting control, ABS, fuel injection.
- Consumer electronics → washing machines, refrigerators, air conditioners.
- Industrial drives → robotics, servo drives, process control.
- Telecommunication systems → power supplies, switching equipment.
- Switch Mode Power Supplies (SMPS) and battery chargers.
Advantages
- Combines multiple functions in one chip → reduces external component count.
- Smaller size and lighter weight compared to discrete circuits.
- Improved reliability due to fewer interconnections.
- Built-in protection mechanisms extend device and system life.
- Higher system efficiency and cost-effectiveness in mass production.
Limitations
- Design complexity is higher compared to discrete circuits.
- Heat dissipation may be challenging since power and control are on the same chip.
- Initial development cost is high.
- May not be as flexible as using discrete devices for some specialized applications.
Conclusion
The Power Integrated Circuit (PIC), or Smart Power Technology, represents a major advancement in power electronics by integrating power handling and intelligent control into a single device. With their ability to control, monitor, and protect themselves, PICs are widely used in automotive.Triggering/Driver: -
Introduction
A thyristor (SCR) is a powerful semiconductor device used in
converters, inverters, and motor drives.
Unlike transistors or MOSFETs, a thyristor cannot turn ON by just applying a
voltage across its terminals. It requires a small current pulse at its gate
terminal to start conduction. This process is called triggering.
Once triggered, the thyristor remains ON until the current
through it naturally goes to zero (AC circuits) or is forced to zero (DC
circuits).
Because thyristors are usually connected in high-voltage and
high-current circuits, special driver circuits are needed to provide safe,
reliable, and isolated gate pulses.
Requirements of a Good Triggering/Driver Circuit
A good driver circuit must:
- Deliver a sharp gate pulse (high enough amplitude and short duration).
- Provide electrical isolation between control (low-power) and power circuits.
- Be capable of triggering multiple thyristors in sequence (for converters and inverters).
- Avoid false triggering due to noise or leakage currents.
Methods of Triggering
Forward Voltage Triggering
- When the forward voltage across the thyristor exceeds the breakover voltage, it turns ON.
- Rarely used, as it stresses the device.
dv/dt Triggering
- A rapid increase in voltage can cause unwanted turn-on.
- Prevented using snubber circuits.
Light Triggering (LASCR)
- A light pulse is used to trigger.
- Useful in HVDC transmission.
Gate Triggering (Most Common)
- A positive current pulse is applied to the gate.
- This is the standard method used in practical circuits.
Driver Circuits for Thyristors
1. RC Triggering Circuit
- Uses a resistor and a capacitor to shape a triggering pulse.
- Simple but not suitable for precise control.
2. Pulse Transformer Driver
- A pulse transformer is used to send gate pulses.
- Provides galvanic isolation between control and power sides.
- Multiple thyristors can be triggered by multiple secondary windings.
3. Opto-Isolated Driver
- Uses an LED and photodiode/phototransistor pair to send the triggering signal.
- Provides excellent electrical isolation.
- Widely used in modern power electronic circuits.
4. Microcontroller/IC-Based Drivers
- Modern systems use driver ICs that can directly trigger thyristors with controlled pulse width and timing.
- These ICs are often combined with opto-isolation.
Gate Pulse Waveform
- A sharp current pulse is preferred rather than a continuous gate current.
- Gate pulse amplitude: 2–5 V.
- Gate current: tens of milliamps (depends on thyristor rating).
- Sometimes multiple pulses are applied to ensure reliable firing under noisy conditions.
Applications of Triggering/Driver Circuits
- Controlled rectifiers (AC → DC converters).
- Inverters (DC → AC for UPS and drives).
- Cycloconverters (AC → AC with variable frequency).
- Motor control (speed and torque control).
- HVDC transmission (long-distance power transfer).
Conclusion
Triggering and driver circuits are the heart of thyristor
control.
They ensure that the device receives the correct gate pulse at the right time,
with proper isolation and protection.
In modern systems, opto-isolated and IC-based drivers are most popular,
ensuring safe, reliable, and noise-free triggering of thyristors in power
electronic applications.
Commutation and Snubber Circuits for
Thyristors: -
Introduction
A thyristor (SCR) is a controlled semiconductor device that
can easily be turned ON using a gate pulse. However, turning it OFF
(commutation) is not as simple. Once it starts conducting, it will remain ON as
long as the current is above its holding current.
To bring the device back to the OFF state, the anode current
must be reduced to zero (or even slightly negative for a short time). The
circuits used for this purpose are called commutation circuits.
Additionally, thyristors are highly sensitive to rapid
changes in voltage (dv/dt) or current (di/dt). To protect them, we use snubber
circuits.
Commutation in Thyristors
Types of Commutation
Natural Commutation (Line Commutation)
- Occurs automatically in AC circuits.
- At the end of each half cycle, the AC current naturally goes to zero, turning the SCR OFF.
- Common in controlled rectifiers.
Forced Commutation
- Needed in DC circuits, where current does not naturally fall to zero.
- An external circuit forces current through the SCR to zero.
- Widely used in choppers and inverters.
Classification of Forced Commutation
Class A – Load Commutation
- The load current itself becomes zero using resonant LC circuits.
Class B – Resonant Commutation
- An LC resonant circuit creates reverse current through the SCR to turn it OFF.
Class C – Complementary Commutation
- One thyristor turns OFF another by applying reverse voltage.
Class D – Auxiliary Commutation
- Uses an auxiliary SCR and commutating capacitor.
Class E – External Pulse Commutation
- An external pulse source is used to force turn-off.
 |
| CLASS C |
Snubber Circuits for Thyristors
Need for Snubbers
When a thyristor is OFF, if the applied voltage rises very
fast (high dv/dt), it may accidentally turn ON without a gate signal.
Similarly, at turn-on, a high di/dt may cause localized heating and device
damage.
To prevent such failures, snubber networks are used.
Typical Snubber Circuit
- A series combination of a resistor (R) and a capacitor (C) is connected across the thyristor.
- The capacitor absorbs sudden voltage changes (dv/dt).
- The resistor dissipates stored energy and limits current.
Working of Snubber
- When the voltage across the thyristor tries to rise sharply, the capacitor charges first, delaying the voltage rise across the device.
- The resistor prevents oscillations and limits capacitor current during discharge.
- This ensures safe turn-off and turn-on conditions for the thyristor.
Applications of Commutation and Snubbers
- Choppers and DC-DC converters (use forced commutation).
- Inverters and cycloconverters (need reliable commutation).
- Power factor control circuits.
- Industrial drives and motor controllers.
- Protection of thyristors in rectifiers, SMPS, and HVDC systems.
Advantages
- Commutation circuits ensure proper turn-off of thyristors in DC circuits.
- Snubber circuits increase reliability by protecting against false triggering.
- Together, they extend the life of thyristors and improve system stability.
Conclusion
Commutation and snubber circuits are essential companions of
thyristors in power electronics. While commutation ensures proper turn-off of
the device, snubbers protect against dv/dt and di/dt stresses. Without these
supporting circuits, thyristors would be unreliable in practical high-power
applications.
Thus, every power electronic system using SCRs — from
converters and inverters to drives and HVDC transmission — relies on carefully
designed commutation and snubber networks for safe and efficient operation.
Power MOSFETs and IGBTs (Discrete and IC
Based): -
Introduction
In power electronics, Power MOSFETs and Insulated Gate
Bipolar Transistors (IGBTs) are two of the most widely used semiconductor
devices.
- Power MOSFETs are preferred for high-frequency, low-to-medium power applications (like SMPS, inverters, UPS).
- IGBTs are best for medium-to-high power applications where efficiency and switching speed both matter (like motor drives, traction systems, and renewable energy converters).
Both are available as discrete components (single device
packages) and also integrated into ICs (smart power modules with multiple
devices + drivers + protections).
Power MOSFET
Structure
- Has a drain, source, and gate.
- The gate is insulated by an oxide layer, giving it high input impedance.
- Current flows through a channel controlled by the gate voltage.
Characteristics
- Voltage-controlled device (requires very little gate current).
- Very fast switching speed → suitable for high-frequency converters (up to hundreds of kHz).
- Low conduction losses at low voltage but higher resistance at higher voltage.
- Excellent thermal stability.
Operation
- When a positive gate-to-source voltage (Vgs) is applied, a conductive channel forms.
- Current flows from drain to source.
- Removing the gate voltage switches the MOSFET OFF instantly.
Applications
- Switch Mode Power Supplies (SMPS).
- DC-DC converters.
- Low-voltage motor drives.
- Consumer electronics (laptops, chargers, TVs).
IGBT
Structure
- Combines the MOSFET input stage with a BJT output stage.
- Has terminals: Collector, Emitter, and Gate.
- Offers the voltage-controlled gate of MOSFET + low conduction losses of BJT.
Characteristics
- Voltage-controlled like MOSFET → simple drive circuit.
- Handles higher voltages (600V to >6kV) and higher currents.
- Moderate switching speed (slower than MOSFETs but faster than BJTs).
- High power handling capability.
Operation
- Applying a positive gate-to-emitter voltage turns ON the device.
- Current flows from collector to emitter.
- When gate voltage is removed, the device turns OFF, but a tail current flows for a short time (slower turn-off than MOSFET).
Applications
- Motor control (VFDs, traction, robotics).
- Renewable energy systems (solar inverters, wind converters).
- HVDC transmission.
- Induction heating and welding.
Discrete vs. IC-Based Implementation
Discrete Devices
- Single Power MOSFET or IGBT packaged individually.
- Used when only one switching element is needed.
- Advantages: flexibility, easy replacement, cost-effectiveness.
- Example: MOSFETs in SMPS circuits.
IC-Based (Smart Power Modules / IPMs)
- Combine multiple MOSFETs/IGBTs with gate drivers, protection circuits, and sometimes diodes.
- Used in motor drives, industrial automation, UPS, and EV inverters.
- Advantages: compact, reliable, easier to design.
- Example: 6-pack IGBT modules for 3-phase inverters.
Comparison Between MOSFET and IGBT
|
Feature |
Power
MOSFET |
IGBT |
|
Control |
Voltage |
Voltage |
|
Switching
Speed |
Very High
(100 kHz–1 MHz) |
Medium (up to
50 kHz) |
|
Voltage
Handling |
Up to 600V |
600V –
>6kV |
|
Conduction
Loss |
Higher at
high voltages |
Lower at high
voltages |
|
Best
Application |
Low/medium
voltage, high frequency |
Medium/high
voltage, high power |
Conclusion
Both Power MOSFETs and IGBTs are essential in power
electronics:
- MOSFETs dominate low-voltage, high-frequency circuits.
- IGBTs dominate high-voltage, high-power applications.
- With the availability of discrete devices and IC-based smart modules, engineers can choose the right solution depending on power level, frequency, and system requirements.
Together, they form the backbone of modern power electronics
used in everything from small chargers to large industrial drives and renewable
energy systems.
Concept of Fast Recovery and Schottky Diodes
as Freewheeling and Feedback Diodes: -
Introduction
In power electronic circuits, diodes are not only used for
rectification but also for energy recovery and protection.
When inductive loads (such as motors, solenoids, or
transformers) are switched OFF, they generate a reverse voltage spike due to
stored magnetic energy. This surge can damage power devices (like MOSFETs,
IGBTs, or thyristors).
To protect the circuit and ensure continuous current flow, freewheeling
diodes (also called flyback diodes or feedback diodes) are used.
Two important types of diodes commonly used in this role
are:
- Fast Recovery Diodes
- Schottky Diodes
1. Fast Recovery Diodes
Definition
A Fast Recovery Diode (FRD) is a PN-junction diode specially
designed to switch OFF very quickly, with short reverse recovery time (trr).
- In normal PN diodes, when current switches from forward to reverse, the stored charge carriers take time to recombine, causing a delay called reverse recovery time.
- FRDs minimize this delay, making them suitable for high-frequency power converters.
Characteristics
- Reverse recovery time: typically < 500 ns.
- Forward voltage drop: ~0.7–1.2 V (slightly higher than normal diodes).
- Can handle moderate to high currents.
Applications as a Freewheeling Diode
- Used in inverters and choppers, where fast switching is required.
- Provides a smooth path for current during switch OFF.
- Prevents voltage spikes and improves efficiency.
2. Schottky Diodes
Definition
A Schottky Diode is a metal–semiconductor junction diode.
Unlike PN diodes, it does not rely on charge carrier recombination, so it
switches extremely fast.
Characteristics
- Very low forward voltage drop (0.2–0.4 V) → reduces conduction losses.
- Negligible reverse recovery time (almost zero).
- Limited reverse voltage rating (typically up to 200 V).
- Higher leakage current than PN diodes.
Applications as Freewheeling/Feedback Diode
- Ideal for high-frequency switching power supplies (SMPS).
- Used with MOSFETs and IGBTs to provide a low-loss current path.
- Widely used in DC–DC converters, synchronous rectifiers, and motor drivers.
Comparison: Fast Recovery vs Schottky Diodes
|
Feature |
Fast
Recovery Diode (FRD) |
Schottky
Diode |
|
Forward
Voltage Drop |
~0.7–1.2 V |
~0.2–0.4 V |
|
Reverse
Recovery Time |
Few 100 ns |
Almost Zero |
|
Reverse
Voltage Rating |
Up to kV
range |
Limited
(<200 V) |
|
Efficiency |
Moderate |
Very High
(low loss) |
|
Typical Use |
Medium/high
voltage, high power |
Low/medium
voltage, high-frequency circuits |
Role in Power Electronics
- As Freewheeling Diode: Provides a safe current path for inductive loads when the switch is OFF.
- As a Feedback Diode: Returns excess energy back to the source, improving efficiency.
- Protects switching devices (MOSFETs, IGBTs, SCRs) from overvoltage stress.
- Ensures smooth operation in rectifiers, inverters, SMPS, and motor drives.
Conclusion
Both Fast Recovery Diodes and Schottky Diodes play a crucial
role in modern power electronics.
- Fast Recovery Diodes are best for high-voltage, high-power applications where switching losses must be reduced.
- Schottky Diodes are preferred in low-voltage, high-frequency applications due to their ultra-fast switching and low forward drop.
Together, they ensure safe, efficient, and reliable
operation of power electronic systems by acting as freewheeling and feedback
diodes.
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