For decades, there has been a greater awareness of the need for energy-saving and power consumption reductions, which increased the demand for semiconductors that reduce power loss. After a series of research, power semiconductors were manufactured.
Power semiconductors are specially designed to handle high power applications. In recent years, they have been used in a variety of applications globally, thanks to their structure, which enables them to handle large currents and high voltages without damage.
Power semiconductors are continuously improving to attain improved efficiency, higher power, better controllability, and reliability.
Power Semiconductor Devices
High power semiconductor devices are becoming a necessity. They are devices with high current and high voltage ratings. They are classified into different categories depending on their turn ON/OFF capability, gate signal type needed, voltage withstand capacity and current conduction ability.
There are high power semiconductors and lower power semiconductors devices. High power semiconductor devices like Insulated Gate Bipolar Transistors (IGBT) or Thyristor switches are used for high power applications like HVDC transmission.
They vary slightly in their operating principle from the low power semiconductors, but their operating characteristics remain the same.
Category Of Power Semiconductors
Generally, power semiconductors are categorized as having a current rating of 1A and above. They can either be 2-terminal or 3-terminal devices:
• 2-terminal devices – Power diode, a 2-terminal device, is used in rectifiers to convert AC to DC. It consists of two types of semiconductor materials that either conduct or block current in a direction, depending on the voltage applied and the circuit configuration.
• 3-terminal devices – They are classified as Controlled Power Semiconductors and can switch current flow on/off between two of the terminals. A signal current or voltage is applied to the third terminal, which is usually referred to as the GATE.
Where Power Semiconductors Are Used
Power semiconductors are mostly used in power conversions, such as in changing AC to DC (and vice versa) as well as changing frequencies and voltages. They are used to control current (or power) in electrical circuits, including the power MOSFET (Metal Oxide Semiconductor Field Effect Transistor), power diode, Thyristor, Bipolar Junction Transistor (BJT) and Insulated Gate Bipolar Transistor (IGBT).
Where high currents and voltages are necessary, the BJT may be a suitable choice, operating at frequencies over 100 Hz. For higher frequency applications above 100 kHz, the MOSFET is a better and more affordable option.
Power semiconductors also play a significant role in driving motors accurately from lower to higher speeds, delivering power grids with energy generated from solar cells with fewer power losses, and offering a steady electricity source to different electrical equipment and home appliances.
Are Power Semiconductors Reliable?
According to Alexander Lubka, “An undue operating voltage or excessive current can lead to the failure of power semiconductors, due to a temperature rise resulting from the heat generated from handling high power applications. This high temperature will not only destroy devices, but even operations at non-destructive temperature can demean their functionality.”
A worse situation occurs when a power semiconductor has high current and high voltage concurrently. All things being equal, the majority of power semiconductor datasheets specify the max voltage that can be applied. Datasheets indicate a maximum junction voltage of about 100°C and 200oC for silicon. Most power transistors feature a maximum junction rating between 125°C and 150°C inclusive. However, a safe and reliable operating temperature should be much lower.
Applying Caution with Power Semiconductors
When applying the supply voltage, it is not ideal reversing the polarities in some power semiconductor devices. If you apply negative voltage to the positive terminal and positive voltage to the negative terminal, the device will be damaged since there is no reverse-voltage protection. Alternatively, some power semiconductor devices are capable of enduring bipolar voltage.