Figure: SCR Characteristics It is the curve between anode-cathode voltage (V) and anode current (I) of an at constant gate SCR current. Fig. 20.7 shows the characteristics of a typical V-I SCR. Forward characteristics. When anode is positive cathode, the curve between and is w.r.t. V I called the forward characteristic. In Fig. 20.7, is the forward characteristic of at = 0. If OABC SCR IG the supply voltage is increased from zero, a point is reached (point when the starts A) SCR conducting. Under this condition, the voltage across suddenly drops as shown by dotted curve SCR and most of supply voltage appears across the load resistance If proper gate current is made to AB RL. flow, can close at much smaller supply voltage. SCR Reverse characteristics. When anode is negative cathode, the curve between and is w.r.t. V I known as The reverse voltage does come across when it is operated with reverse characteristic. SCR a.c. supply. If the reverse voltage is gradually increased, at first the anode current remains small (i.e. leakage current) and at some reverse voltage, avalanche breakdown occurs and the starts SCR conducting heavily in the reverse direction as shown by the curve This maximum reverse voltage DE. at which starts conducting heavily is known as SCR reverse breakdown voltage.
Figure: SCR Characteristics It is the curve between anode-cathode voltage (V) and anode current (I) of an SCR at constant gate current. Fig. 20.7 shows the V-I characteristics of a typical SCR. Forward characteristics. When anode is positive w.r.t. cathode, the curve between V and I is called the forward characteristic. In Fig. 20.7, OABC is the forward characteristic of SCR at IG = 0. If the supply voltage is increased from zero, a point is reached (point A) when the SCR starts conducting. Under this condition, the voltage across SCR suddenly drops as shown by dotted curve AB and most of supply voltage appears across the load resistance RL. If proper gate current is made to flow, SCR can close at much smaller supply voltage. Reverse characteristics. When anode is negative w.r.t. cathode, the curve between V and I is known as reverse characteristic. The reverse voltage does come across SCR when it is operated with a.c. supply. If the reverse voltage is gradually increased, at first the anode current remains small (i.e. leakage current) and at some reverse voltage, avalanche breakdown occurs and the SCR starts conducting heavily in the reverse direction as shown by the curve DE. This maximum reverse voltage at which SCR starts conducting heavily is known as reverse breakdown voltage.
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