SCR

Semiconductor Devices

AIM

To study the VI characteristics of SCR.

APPARATUS

  • NV6530 SCR Characteristics Trainer
  • Wires

THEORY

SCR is a four-layered semiconductor device that is alternative of P-type and N-type semiconductor silicon. Junction J1, J2 and J3 (J1, J2 and J3 operate in forward direction while middle operates in reverse direction) and three terminals known as anode A, cathode K and gate G. The function of the gate is to trigger the device into conduction by the application of a small voltage.

CIRCUIT DIAGRAM

PROCEDURE

  1. Connect terminal 1 to terminal 4, terminal 2 to terminal 8, and terminal 3 to terminal 12.
  2. Connect a voltmeter across terminals 7 and 8 and an ammeter across terminals 9 and 10.
  3. Make short terminals 5 and 6.
  4. Rotate the knob P1 and P2 fully in counter clockwise.
  5. Switch on the Power Supply.
  6. Set the value of the anode voltage at 35V by using the knob P1.
  7. Increase the gate current, and the voltmeter reading falls to almost zero. This action indicates the firing of SCR.
  8. Note the gate’s current value at this position.
  9. Keep the current constant by shorting terminals 9 with 10 and connecting the ammeter to terminals 5 and 6.
  10. Rotate the potentiometer P1 fully in counter-clockwise.
  11. Rotate knob P1 gradually and record the anode current for the respective value of anode voltage.

OBSERVATION TABLE

Anode Voltage Anode Current [Gate Current = 7mA]

RESULT

VI Characteristic graphs of SCR are obtained where the gate current is Ig = 7mA. Thus, it is observed that the current increases after V.

PRECAUTIONS

  • Avoid double connections, if possible.
  • The connection should be proper and tight.