Thyristors:What They Are and How They Work

Posted on November 1, 2021 David Atkinson Aviation News

Thyristors are a type of solid-state semiconductor device featuring four P- and N-type material layers that alternate. When placed within varying types of circuits, a thyristor will act as a bistable switch. As such, it will conduct when a current trigger is received, continuing until the voltage is either removed or becomes reverse biased. Two thyristor variations are common, each of which differs in the way that its conductive state is triggered. In this blog, we will discuss the thyristor and its functionality, allowing you to better understand their importance and the applications that they commonly serve.

Typically, a standard thyristor will exhibit three terminals, those of which are the anode, cathode, and gate. While the anode and cathode serve as the positive and negative terminal respectively, the gate manages the current that flows between each. Despite their compact size and low weight, thyristors are often capable of acting as a switch for more robust applications, providing optimal protection for circuits that feature large current and voltage values. One of their major benefits is the speed at which they can switch between a conducting state and a state of non-conduction. Additionally, they can last a long amount of time in standard operating conditions, allowing them to avoid faults and drive down maintenance costs. With such attributes, thyristors find implementation within power-switching circuits, relay-replacement circuits, inverter circuits, oscillator circuits, level-detector circuits, chopper circuits, and much more.
With their design and capabilities, thyristors may operate in three possible states. While in a forward blocking mode, the thyristor is switched off as no current is flowing into the gate. As such, no current can move across the anode to the cathode, and the junction in the center is reversed biased. As thyristors are often compared to the action of two diodes, the upper diode and lower diode would both be forward biased in such a state. By reversing the anode and cathode connections, the component would become reverse-biased and continue to prevent current from flowing. This state is known as reverse blocking, and it is analogous to the reverse bias state of a diode.
The final state that a thyristor can be in is forward conducting. To reach this state, the anode will need to be positive while the cathode is negative. As current flows into the gate, the lower transistor will be switched on, causing the upper transistor to switch before a back and forth process of switching carries out. In the forward conducting state, the thyristor may stay on permanently. Removing the current from the gate would also not end this process, and the main current moving between the anode and cathode would need to be disrupted for the thyristor to be switched off. Generally, this is achieved by removing power from the entire circuit.
Thyristors are  important components due to their various characteristics and states, thus, it is important that you understand their use so that you may correctly implement them within your particular systems as needed. Just like an NPN transistor or MOSFET component, thyristors will require regular inspection and replacement when issues occur. When it comes time to begin sourcing the various electronic components that you need, there is no better alternative to ASAP Parts 360.
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