Steady State Characteristics

By using v-I faculties we could explain the procedure effortlessly SCR, you can find three modes of procedure. v-I characteristics of SCR is just a graph of anode present we A on y-axis & anode to cathode Voltage plotted on x-axis traits that are be put into v-I two parts especially ahead traits & Reverse Characteristics Steady State Characteristics of SCR:

The circuit symbol in the hand that is left inset describes the polarity conventions associated with the factors found in this figure. You will find three modes of operation for an SCR depending upon the biasing given to it:

Forward blocking mode

In this mode of operation the anode is given a positive potential while the cathode is given a negative voltage keeping the gate at zero potential i.e. disconnected. In this case junction J1 and J3 are forward biased while J2 is reversed biased due to which only a small leakage current flows from the anode to the cathode until the applied voltage reaches its breakover value at which J2 undergoes avalanche breakdown and at this breakover voltage it starts conducting but below breakover voltage it offers very high resistance to the flow of current and is said to be in off state.

Forward conduction mode

SCR can be brought from blocking mode to conduction mode in two ways - either by increasing the voltage across anode to cathode beyond breakover voltage or by applying of positive pulse at gate. Once it starts conducting no more gate voltage is required to maintain it in on state. There is one way to turn it off i.e. Reduce the current flowing through it below a minimum value called holding current.

Reverse blocking mode

SCR are available with reverse blocking capability. Reverse blocking capability adds to

the forward voltage drop because of the need to have a long, low doped P1 region. (If one

cannot determine which region is P1, a labeled diagram of layers and junctions can help).

Usually, the reverse blocking voltage rating and forward blocking voltage rating are the

same. The typical application for reverse blocking SCR is in current source inverters.