Turn ON methods of an SCR
Triggering is nothing but switching the device from a non-conducting(OFF) state to a conducting (ON) state. The various methods of thyristor triggering are as follows,
- Forward Voltage Triggering
- Gate triggering
- Thermal triggering
- Light triggering
- dv / dt triggering
Forward Voltage Triggering
With the gate circuit opens, the thyristor will not start conducting with the normal value of forward anode to cathode voltage. However, if this voltage is increased beyond the forward break over voltage VB an avalanche will occur and hence the SCR starts conducting. However, this method of triggering is never recommended, as it may damage the SCR or the whole circuit.
Gate Triggering
Gate triggering is the most efficient and the most commonly used method of triggering the SCR. In this method, small gate pulse is applied between gate and cathode along with the normal anode to cathode. With this, a gate current will be established which will J2 will be forward biased. As the other two junctions J1 and J3 was already forward biased, the SCR starts conducting.
Thermal Triggering
During forward blocking mode of SCR, junctions J1 and J3 will be forward biased and hence acts as a short circuit; whereas, junction J2 will be reverse biased, which acts as an open circuit. Due to this, the applied voltage will appear across the open terminals of junction J2 along with some leakage current. This leakage current will increase the temperature of the junction J2 (because of junction resistance) which in turn increases the mobile charges and hence the current. This process is cumulative and hence may turn ON the SCR at point.
Light Triggering
In this method, the inner p-layer is radiated with a light ray of an appropriate wavelength and intensity. With this, free charge carriers will be injected in the junction J2 and the junction J2 will be forward biased and hence the SCR gets turned ON. SCRS, employing this technique, are called as LASCR (Light Activated SCR).
dv/dt (V) Triggering
We know that under forward blocking mode, junction J1 and J3 are forward biased; whereas, junction J2 is reverse biased. The junction J2 acts as a capacitor because of the opposite polarity carriers present at its two terminals. Hence, the leakage current through the junction is nothing but the capacitor current given by,
ic = C dv / dt
Where, C = Junction capacitance
V = Anode to cathode voltage
If the rate of rise of the voltage V is very high i.e., the voltage across the SCR increases within no time ic will very large (from above equation ). This large value of current will turn ON the SCR immediately.
Silicon Controlled Rectifier
The SCR or thyristor is one type of semiconductor device and using in high-power switching applications is exceptionally planned. The working of this device should be possible in a switching mode only and acts as a switch. When the SCR is triggered by its gate terminal into the transmission, then it will supply the current constantly. While planning a SCR or Thyristor circuit, exceptional focus ought to be expected for enacting the circuit. This article examines various techniques for SCR setting off or SCR turn ON strategies or setting off of Thyristors. There are different setting off strategies are accessible in light of different substances which incorporate temperature, voltage, and so on.
Table of Content
- Silicon Controlled Rectifier
- Key Terminologies
- Construction
- Operation
- Modes of Operation
- Types
- Advantages of SCR