Draw and Explain the SCR V-I characteristic?
(i) When a positive voltage is applied to anode with respect to cathode, the junctions J1 and J3 are forward biased, but the junction J2 is reverse biased.
(ii) The SCR is in its forward blocking state. At this time the Gate signal is not applied.
(iii) As shown in figure a small amount of forward leakage current is flows through the device.
Vak = + & Vg = +ve
(i) When the small amount of positive voltage is applied, while positive voltage is applied to anode with respect to cathode, the junction J3 becomes forward biased.
(iv) The thyristor will only turn off when the forward current drops below holding current. The holding current is defined as the minimum current required to hold the SCR in the forward conduction state.
(ii) As shown in figure a small amount of reverse leakage current flows through the device.
(ii) The difference between the input and output voltage is applied to inductor as shown in the below waveform.
(iii) When the switch is turned off, the inductor current will flow in the same direction to load. It is inductor property to maintain the current flow in the same direction.
(iv) The freewheeling diode D1 is forward biased at this time and completes the inductor current path.
The output of the buck converter with continuous output current is
Vout = D*VIN
D = Duty cycle = TON / [TON + TOFF]