Working of Thyristor
A thyristor also can function as a circuit breaker in device power circuits. They prevent power supply disruptions by connecting a Zener diode at the thyristor gate. When power supply voltage levels exceed the Zener voltage, the thyristor turns off the power supply output to the ground and activates circuit breakers or fuses upstream from the power supply. This is called a crowbar effect and protects devices being served by the power supply from damage.
- Thyristors operate in one of the following three states, depending on the requirements:
- Thyristors consists of four layers(i.e., p, n, p and n) three terminals A(Anode), K(Cathode) and G(Gate) and three junction J1 , J2 , and J3.
- In thyristors there are three junctions J1, J2 and J3 .
- These junctions play a very important role in the operation of thyristor.
- Depending on whether the junctions are forward biased or reverse biased, the thyristor will either conduct the current or will not be conduct. For thyristor to conduct current, all the three junctions must be forward biased. If any one of the junctions is reverse biased the thyristor will not conduct any current and hence acts as an open switch.
Reverse Blocking
- Current attempts to pass through the thyristor in the opposite direction. However, a diode blocks it, and the thyristor is not activated.
- In this case, the junction J1 and J3 are reverse biased, whereas J2 is forward biased. Hence, thyristor does not conduct and acts as an open switch.
Forward Blocking
- The thyristor blocks the flow of current, despite voltage being applied in the direction that would signal a diode to conduct it.
- In this case, the junction J2 is reverse biased, whereas junctions J1 and J3 are forward biased, again due to which the thyristor does not conduct and acts as an open switch.
Forward Conduction
- This is a thyristor’s primary operating mode. It is switched to conducting mode and stays that way until the current falls below a specific level, called the holding current.
- In this case, all the three junctions are forward biased and hence gets turned ON and starts conducting. Here, the thyristor acts as a closed switch.
Hence, from the above cases, it is clear that all the three junctions play important role in the operation of thyristor and they all must be forward biased in order to turn ON the thyristor.
What is Thyristors in Power Electronics ?
Thyristors in Power Electronics are used as power semiconductor devices which are used as on/off switches in power control circuits. A power semiconductor device is a semiconductor device used as a switch or rectifier in power electronics for example in a switch-mode power supply. A thyristor is the most important type of power semiconductor device. They are extensively used in power electronic circuits. They are operated as bi-stable switches from non-conducting to conducting state. Thyristors are high speed switches that can be used to replace electromechanical relays in many circuits as they have no moving parts, no contact arcing, or suffer from corrosion or dirt. But in addition to simply switching large currents “ON” and “OFF”, thyristors can be made to control the mean value of an AC load current without dissipating large amounts of power.
Table of Content
- What is a Thyristor?
- Properties of Thyristors
- Construction of Thyristor
- Working of Thyristor
- V-I characteristics of thyristor
- Types of Thyristors in Power Electronics
- Examples of Thyristors in Power Electronics