T707123054BY

Thyristors - SCRs: Application Field and Working PrincipleThyristors - SCRs are a special type of switch device that can control high currents, also known as power controlling devices. They can be used as switches for both AC and DC electrical systems. SCRs can be used for a wide range of applications, from lighting control systems to motor speed and AC power control, triggering usage in high-voltage circuits, and switching high-current applications.The SCR has three terminal: Anode, Cathode, and Gate. The SCRs are triggered into action using an electric current in the Gate lead. When this current is present, an avalanche breakdown occurs due to heavy ion current flowing between the Anode and Cathode, resulting in a high current flow between them.  When the gate current is removed, the SCR is unable to switch off and turn off until the current between the Anode and Cathode drops to zero. Otherwise, the high current flow between the Anode and Cathode will persist and not turn off. This is known as the SCR\'s latching characteristic, and is an advantage over other types of switches.One of the main uses for SCRs is to control the speed of electric motors. This is achieved by connecting the SCR in series with the motor and using varying gate currents to regulate the current flow between the Anode and Cathode. This allows the speed of the motor to be adjusted in a predictable manner. SCRs can also be used to control the power used by a motor by controling the current flow between the Anode and Cathode.SCRs are also commonly used in lighting control systems. This is because they are able to turn light sources on and off. When used in combination with a timer, SCRs can be used to create a "dimmer switch" effect where a light source is steadily turned up and down, depending on the timer\'s settings.Additionally, SCRs are used in AC power control in order to reduce the amount of power used. For example, if an AC system is powered by an AC generator, SCRs can be used to control the flow of current, allowing the user to reduce the amount of power consumed.The working principle of SCRs is based on the charge storage effect. When a voltage is applied to the Gate, the electric field generated by the Gate overcomes the potential barrier, allowing the electrons to travel from the Anode to the Cathode. This process results in a current flow between the Anode and Cathode, which is known as “polarization”.When the flow of current between the Anode and Cathode reaches a certain level, it causes a voltage drop on the Gate that is referred to as "holding voltage". This voltage drop eliminates the electric field, thus preventing the current flow. The amount of current that is necessary for the Gate to activate, turn on, and maintain this “latching” position is referred to as the “gate trigger current”.Once the SCR is turned on, it will remain on until the current between the Anode and Cathode drops to zero. This is known as “quasi-saturation”, and this is where the SCR gets its power-controlling capabilities.In conclusion, SCRs are a special type of switch device with three terminals – Anode, Cathode, and Gate. They are used for power controlling purposes, because of their ability to switch on and off in a predictable manner. The working principle of SCRs is based on the charge storage effect, where a voltage is applied to the Gate, and a current flow between the Anode and Cathode is created. This current flow is necessary to maintain a voltage drop on the Gate and prevent further current flow. SCRs can be used in various applications, including lighting control systems, motor speed and AC power control, and triggering usage in high-voltage circuits.