R, RC & UJT GATE TRIGGERINGCIRCUITS

AIM:

To study the performance of various turn-on methodsof thyristors, using R, RC and UJT triggering.

APPARATUS:

1. RC-Firing circuit study unit.

2. UJT-Firing circuit study unit

3. Thyristor-TYN612

4. Rheostat-50 ohms

5. CRO

6. Connecting wires

  1. R-FIRING CIRCUIT

Theory :The circuit operates as follows:

  • As Es goes positive scr becomes fwd biased from anode to cathode however it will not coduct until its gate current exceeds minimum gate current
  • The positive Es also fwd biases the diode and the scrs gate cathode junction.this causes flow of Ig
  • Ig will increase as Es increases towards the peak value. When Ig reaches a value which is equal to Igmin, the scr turns on. And will approximately equals Es

CIRCUIT DIAGRAM:

PROCEDURE:

1. Connections are made as per the circuit diagram.

2. The main supply is switched ON andtriggering circuit is switched ON

3. Wave forms across the load are observed in CRO values are noted down and tabulatedfor different firing angles.

4. The output wave forms are plotted on the graph sheet.

TABULAR COLUMN:

Vm=

Sl.no. / Firing angle(α) / Vdc
(theoretical) / Vdc
(practical) / Vrms
(theoretical) / Vrms
(practical)

2. RC-FIRING CIRCUIT

CIRCUIT DIAGRAM:

WAVEFORMS:

PROCEDURE:

1. Connections are made as per the circuit diagram.

2. The main supply is switched ON andtriggering circuit is switched ON

3. Wave forms across the load are observed in CRO values are noted down and tabulatedfor different firing angles.

4. The output wave forms are plotted on the graph sheet.

TABULAR COLUMN:

Vm=

Sl.no. / Firing angle(α) / Vdc
(theoretical) / Vdc
(practical) / Vrms
(theoretical) / Vrms
(practical)

3. UJT-FIRING CIRCUIT

CIRCUIT DIAGRAM:

WAVEFORMS:

PROCEDURE:

1. Connections are made as per the circuit diagram.

2. The main supply is switched ON andtriggering circuit is switched ON

3. Wave forms across the load are observed in CRO values are noted down and tabulatedfor different firing angles.

4. The output wave forms are plotted on the graph sheet.

TABULAR COLUMN:

Vm=

Sl.no. / Firing angle(α) / Vdc
(theoretical) / Vdc
(practical) / Vrms
(theoretical) / Vrms
(practical)

RESULT:

The performance of R, RC &UJT Firing circuits with R -loads are studied and outputwave forms for different firing angles are drawn on thegraph sheet.