29.11.16
29.11.16
A power semiconductor is used to switch or control power (or current) in electrical circuits. These include the power diode, power MOSFET, Bipolar Junction Transistor, Thyristor and Insulated Gate Bipolar Transistor (IGBT). They can be categorised as either 2-terminal, or 3-terminal devices.
Power diodes are 2-terminal devices, made up of two type of semiconductor material (commonly Silicon P-type and N-type), which either block or conduct current in one direction depending upon the circuit configuration and how a voltage is applied. Diodes are used in rectifiers to convert alternating current (AC) to direct current (DC).
The 3-terminal devices are classified as Controlled Power Semiconductors and these can switch current flow on and off between two of the terminals (ANODE and CATHODE) by the application of a signal voltage or current to the third terminal, usually referred to as the GATE. One of the most widely used for high power applications is the Thyristor, which is used to switch current on and off at frequencies up to 100 Hz.
A Thyristor is a semiconductor with four layers of alternating N and P-type material. This can be represented as two diodes in series:
Or as two transistors connected together:
As new applications developed requiring higher frequency switching devices, power semiconductors advanced accordingly. Where high voltages and currents were required the Bipolar Junction Transistor (BJT) was a suitable choice, operating at frequencies above 100 Hz. For much higher frequency applications, above 100 kHz, the MOSFET became a better and more cost effective option. The principles of their operation differed, each having distinct advantages and disadvantages, but both had relatively low maximum voltage ratings compared to thyristors. The development of the IGBT for high frequency applications narrowed the gap with Thyristors in voltage terms, effectively replacing Bipolar Junction Transistors. MOSFETs are still used at frequencies above 100 kHz.
Further advances are required to increase power density and improve thermal management for key future technologies, including Rail Traction and Electric Vehicle applications. By moving from Silicon based semiconductor materials to a wide band-gap material such as Silicon Carbide, power semiconductor manufacturers will address the need for higher voltages, power density improvements, and allow devices to operate at much higher temperatures – Silicon Carbide can operate at temperatures up to 400°C, compared to a practical limit for silicon of around 175°C. Although these devices are still relatively expensive, costs will come down as yields improve and volumes increase.
Power Products are the Main UK Franchised Distributor for Semikron devices, including diode & thyristor products, IGBT Modules and SiC Modules. Our in house sales team can provide assistance with design issues, and have direct access to the Semikron technical support team in the UK. We are ready to assist with all of your power system requirements.
