IGBTs and Thyristors have a lot in common, which is why we’re so commonly asked to compare them! Both are types of semiconductor devices, both are used to control currents, both have a ‘gate’, etc. However, there are a few differences including their applications and their advantages and disadvantages.
To help you understand the similarities and differences between them, we’ve created a helpful guide covering IGBT Vs Thyristors. Let’s get stuck in!
What are Thyristors?
Thyristors are a type of semiconductor device consisting of four layers in the form of P-N-P-N. This PNPN structure is essentially two transistors coupled together – one PNP and one NPN.
They have three terminals:
- Anode – positive terminal
- Cathode – negative terminal
- Gate – control terminal
The gate, located at the inner P-type semiconductor layer is the part of the device that controls the flow of current between the anode and the cathode. During operation, the thyristor only acts when a pulse is applied to the gate.
A thyristor has three modes of operation:
- Reverse blocking mode
- Forward blocking mode
- Forward conducting mode
Essentially, the primary purpose of a thyristor is to act as a switch – controlling electric power and alternating currents.
Once the device is triggered by a pulse, the thyristor shifts into forward conducting mode. It will remain in this conducting state until the forward current becomes less than the threshold ‘holding current’.
The forward blocking state occurs when the NP junction blocks the flow of positive current from moving from the anode to the cathode. Whereas the reverse blocking state is the opposite; in this mode the PN junctions block the flow of negative current.
What are IGBTs?
An IGBT is an Insulated Gate Bipolar Transistor. They are also a type of semiconductor device; however, they work a bit differently to thyristors. They combine features from traditional Bipolar Transistors with attributes from MOSFETs (Metal Oxide Semiconductor Field Effect Transistors).
Originally introduced to the market in the 1980s, IGBTs consist of three terminals:
With the gate controlling the device and the emitter and collector linked to the current and the conductance path.
Taking the high-speed switching abilities of MOSFETs and the high voltage and current handling capabilities of Bipolar Transistors, IGBTs are capable of handling large currents with a very low gate current drive.
Unlike Thyristors, IGBTs are unidirectional, which means they can only switch current in the forward direction. They also differ from thyristors in terms of power supply, as IGBTs require a continuous supply of gate voltage to run – although it is worth mentioning that only a small voltage is required for the gate to maintain conduction throughout the device.
Uses of Thyristors
Thyristors have a wide range of applications and are used across a variety of industries. Generally, thyristors are categorised into three varieties; thyristors with turn-on capabilities, thyristors with turn-off capabilities, and bi-directional control thyristors.
Thyristors with turn-on capabilities:
- Silicone Controlled Rectifiers (SCRs) – used in DC motor drives, AC/DC static switches, switching and inverting circuits
- Reverse Conducting Thyristors (RCTs) – used in inverters and DC motor drives for high-powered machinery
- Light Activated Silicone Controlled Rectifiers (LASCRs) – used in reactive power compensators, high-powered pulse generators and transmission equipment
Thyristors with turn-off capabilities:
- Gate Turn-off Thyristor (GTOs) – used in DC and AC motor drives, AC Power stabilisers, and high-powered inverters
- MOS Turn-off Thyristor (MTOs) – predominantly used in high voltage applications of up to 20 MVA, motor drives, Voltage Inverters, and flexible AC line transmissions
- Emitter Turn-off Thyristors (ETOs) – Voltage inverters for high powered applications, Static Synchronous Compensators, and Flexible AC line Transmissions.
Bi-directional control Thyristors:
- Triode for Alternating Current (TRIAC) – Low-power TRIACs are commonly used as speed controls for fans and other electric motors, light dimmers, and in computerised control circuits of household appliances
- Diode for Alternating Current (DIAC) – commonly used in light bulb dimmers
- Silicone Diode for Alternating Current (SIDAC) – used in a range of special-purpose devices and relaxation oscillators
Uses of IGBTs
Predominantly IGBTs are used as switching devices for applications with high voltages and moderate speeds, thanks to their fast switching abilities and high-efficiency rates. They’re used in the same situations that Bipolar Transistors are favoured for as they have similar current and voltage ratings; however, because of their isolated gate, they require less drive power!
Common uses of IGBTs include:
- Frequency Converters
- DC-AC inverters
- Switch-mode power supplies (SMPS)
- Variable speed control
- Pulse-width modulation (PWM)
- AC & DC motor drives
- Traction Motor Control
- Driving inductive loads
Benefits of Thyristors
Thyristors offer a wide range of advantages, making them an incredibly popular choice for a number of applications. These advantages include:
- High reliability
- Easy to maintain
- Ability to switch currents in microseconds
- Capable of working with high voltages
- Ability to control direct current devices
- Fast activation
- Easy to use
- Small dimensions
Benefits of IGBTs
IGBT modules have a number of unique advantages over other types of transistors, including:
- Fast switching speeds
- Low resistance
- Low power dissipation (on-state)
- Simplicity of drive
- High voltage capabilities
Hopefully this clears things up regarding the difference between IGBTs and Thyristors and the reasons why each device is chosen for specific applications thanks to their unique benefits and characteristics. For further queries on this topic, please don’t hesitate to contact us!
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