07-07-2014, 03:18 PM
SILICON CONTROLLED RECTIFIER
[attachment=65698]
INTRODUCTION
The term ‘thyristor’ has been adopted by the International Electrotechnical Commission(IEC) for SCR.
Silicon unilateral switch(SUS), light activated SCR(LASCR), silicon bilateral switch(SBS) all are designated by this term.
An SCR (Thyristor) is a “controlled” rectifier (diode). It is a four-layer solid state current controlling device. The name “silicon controlled rectifier” or SCR is General Electric’s trade name for a type of thyristor. It consists of four layer three terminal device in which the end P-layer acts as anode, the end N-layer acts as cathode and P-layer nearer to cathode acts as gate. As leakage current in silicon is very small compared to germanium, SCRs are made of silicon and not germanium
SCRConstruction
The Silicon Control Rectifier SCR is consist of four layer of semiconductor which forms PNPN or NPNP structure, it has tree junction J1.
J2 and J3 and also three terminals, the anode terminal of SCR is connected to the P-type of material of PNPN structure and the cathode terminal is connected to the N-type layer of the Silicon Control Rectifier while the gate of the Silicon Control Rectifier is connected to the P-type of material near to the cathode, as shown in the given figure
SCR Operation / Working
The Silicon Control Rectifier SCR start conduction when it is forward biased. For this purpose the cathode is kept at negative and anode at positive. When positive clock pulse is applied at the gate the SCR turns ON.
When forward bias voltage is applied to the Silicon Control Rectifier SCR, the junction J1 and J3 become forward bias while the junction J2 become reverse bias. When we apply a clock pulse at the gate terminal, the junction J2 become forward bias and the Silicon Control Rectifier SCR start conduction.
The Silicon Control Rectifier SCR turn ON and OFF very quickly, At the OFF state the Silicon Control Rectifier SCR provide infinity resistance and in ON state, it offers very low resistance, which is in the range of 0.01O to 1O.
SCR Applications- Power Control
When the voltage across the capacitor reaches the “trigger-point” voltage of the device, the SCR turns ON, current flows in the Load for the remainder of the positive half-cycle.
Current flow stops when the applied voltage goes negative
Applications of SCR
SCRs are mainly used in devices where the control of high power, possibly coupled with high voltage, is demanded. Their operation makes them suitable for use in medium to high-voltage AC power control applications such as lamp diming, regulators and motor control.
[attachment=65698]
INTRODUCTION
The term ‘thyristor’ has been adopted by the International Electrotechnical Commission(IEC) for SCR.
Silicon unilateral switch(SUS), light activated SCR(LASCR), silicon bilateral switch(SBS) all are designated by this term.
An SCR (Thyristor) is a “controlled” rectifier (diode). It is a four-layer solid state current controlling device. The name “silicon controlled rectifier” or SCR is General Electric’s trade name for a type of thyristor. It consists of four layer three terminal device in which the end P-layer acts as anode, the end N-layer acts as cathode and P-layer nearer to cathode acts as gate. As leakage current in silicon is very small compared to germanium, SCRs are made of silicon and not germanium
SCRConstruction
The Silicon Control Rectifier SCR is consist of four layer of semiconductor which forms PNPN or NPNP structure, it has tree junction J1.
J2 and J3 and also three terminals, the anode terminal of SCR is connected to the P-type of material of PNPN structure and the cathode terminal is connected to the N-type layer of the Silicon Control Rectifier while the gate of the Silicon Control Rectifier is connected to the P-type of material near to the cathode, as shown in the given figure
SCR Operation / Working
The Silicon Control Rectifier SCR start conduction when it is forward biased. For this purpose the cathode is kept at negative and anode at positive. When positive clock pulse is applied at the gate the SCR turns ON.
When forward bias voltage is applied to the Silicon Control Rectifier SCR, the junction J1 and J3 become forward bias while the junction J2 become reverse bias. When we apply a clock pulse at the gate terminal, the junction J2 become forward bias and the Silicon Control Rectifier SCR start conduction.
The Silicon Control Rectifier SCR turn ON and OFF very quickly, At the OFF state the Silicon Control Rectifier SCR provide infinity resistance and in ON state, it offers very low resistance, which is in the range of 0.01O to 1O.
SCR Applications- Power Control
When the voltage across the capacitor reaches the “trigger-point” voltage of the device, the SCR turns ON, current flows in the Load for the remainder of the positive half-cycle.
Current flow stops when the applied voltage goes negative
Applications of SCR
SCRs are mainly used in devices where the control of high power, possibly coupled with high voltage, is demanded. Their operation makes them suitable for use in medium to high-voltage AC power control applications such as lamp diming, regulators and motor control.