Thyristor Devices Silicon Controlled Rectifiers (SCR)
Objectives•Draw and explain the i-v characteristics of a thyristor. •Explain the operating principle of a thyristor in terms of the “two transistor analogy”. •Draw and explain the switching characteristics of a thyristor.
Power Semiconductor Switches Power Diodes Power Transistors Thyristors 2 layer device 3 layer Device 4 layer Device • Thyristor devices can convert and control large amounts of power in AC or DC systems while using very low power for control. • Thyristor family includes 1- Silicon controlled Rectifier (SCR) 2- Gate-turnoff thyristor (GTO) 3- Triac 4- Diac 5- Silicon controlled switch (SCS) 6- Mos-controlled switch (MCT)
Introduction • SCR is most popular of thyristor family due to its • Semi switching action , small size and high voltage and current ratings.(300V, 25A-----6kV, 4kA) • SCR has 3 terminals (gate provides control) • SCR is turned on by applying +ve gate signal when anode is +ve with respect to cathode. • SCR is turned off by interrupting anode current. PNPN structure Symbol
Operation of SCR • The SCR has two states : a high-current low- impedance ON state and a low-current high- impedance OFF state. • The basic transistor action in a four-layer p–n–p–n structure is analysed first with only two terminals, and then the third control input is introduced.
Ideal Characteristic Of SCR
Physical Operation and Characteristics: • The physical operation of the SCR can be explained clearly with reference to the current–voltage characteristics. • Forward blocking Forward Conduction Reverse blocking