Thyristor turn on methods

Different Turn on methods of SCR is Explained

1. 1 THYRISTOR Turn on/Triggering methods Dr. A. Ravi Professor/EEE FRANCIS XAVIER ENGINEERING COLLEGE TIRUNELVELI Tamil Nadu - India

2. Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli 2 SCR Turn ON Methods (SCR Triggering) What is triggering Process of Turn on the SCR To Break the Junction J2 which is Reverse Bias

3. Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli 3 SCR Turn ON Methods (SCR Triggering) Forward voltage triggering Temperature triggering dv / dt triggering Light triggering Gate triggering AC triggering Pulse triggering Different Methods

4. Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli 4 SCR Turn ON Methods (SCR Triggering) Forward voltage triggering by increasing the forward anode to cathode voltage. By doing this, the depletion layer width is also increasing at junction J2. This further leads to an avalanche breakdown of the junction J2 at a forward breakover voltage VBO . In practice this is not employed because it needs a very large anode to cathode voltage.

5. Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli 5 SCR Turn ON Methods (SCR Triggering) Temperature Triggering The reverse leakage current depends on the temperature. If the temperature is increased to a certain value, the number of hole-pairs also increases. Increase the leakage current and further it increases the current gains of the SCR. This starts the regenerative action inside the SCR since the (α1 + α2) value approaches to unity practically not employed because it causes the thermal runaway . SCR may be damaged.

6. Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli 6 SCR Turn ON Methods (SCR Triggering) dv / dt Triggering In forward blocking state junctions J1 and J3 are forward biased and J2 is reverse biased. T he junction J2 behaves as a capacitor . I = C dv/ dt produce very high voltage spikes across the SCR so there will be considerable damage to it. dv / dt is the rate of change of applied voltage C is the junction capacitance . Rate of change of the applied voltage is large that leads to increase the charging current which is enough to increase the value of α. Hence SCR ON

7. Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli 7 SCR Turn ON Methods (SCR Triggering) Light Triggering An SCR turned ON by light radiation is also called as Light Activated SCR (LASCR). light rays with appropriate wavelength and intensity are allowed to strike the junction J2. It consist a niche in the inner p-layer. Therefore, when the light struck on this niche, electron-hole pairs are generated at the junction J2 which provides additional charge carriers at the junction leads to turn ON the SCR .

8. Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli 8 SCR Turn ON Methods (SCR Triggering) Light Triggering It consist a niche in the inner p-layer. Therefore, when the light struck on this niche, electron-hole pairs are generated at the junction J2 which provides additional charge carriers at the junction leads to turn ON the SCR .

9. Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli 9 SCR Turn ON Methods (SCR Triggering) DC Gate Triggering Gate triggering is the method in which positive gate current is flown in forward biased SCR to make it ON.   reliable, simple and efficient way to turn on SCR positive gate voltage between gate and cathode terminals are applied in forward biased SCR which establishes gate current from gate terminal to cathode

10. Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli 10 SCR Turn ON Methods (SCR Triggering) DC Gate Triggering When the gate current I g  is zero, the forward breakover voltage is V BO . As gate current increases from zero to I g1 , the forward breakover voltage reduces from V BO  to V 1 . Similarly, its value reduces from V 1  to V 3  as the gate current increases from I g1  to I g3 .

11. Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli 11 SCR Turn ON Methods (SCR Triggering) AC Triggering most commonly used method for AC applications. With the proper isolation between the power and control circuit, the SCR is triggered by the phase-shift AC voltage derived from the main supply . 

12. Dr.A.Ravi, Francis Xavier Engineering College,Tirunelveli 12 SCR Turn ON Methods (SCR Triggering) Pulse Triggering Gate is supplied with single pulse or a train of pulses is given into the SCR ADVANTAGE gate drive is discontinuous or doesn’t need continuous pulses to turn the SCR.  

13. THANK YOU 13