Constructional Features of a Thyristor
Constructional Features of a Thyristor:
Fig:Constructional features of a thyristor (a) Circuit Symbol, (b) Schematic Construction
- The primary crystal is of lightly doped n- type on either side of which two p type layers with doping levels higher by two orders of magnitude are grown.
- As in the case of power diodes and transistors depletion layer spreads mainly into the lightly doped n- region. The thickness of this layer is therefore determined by the required blocking voltage of the device.
- However, due to conductivity modulation by carriers from the heavily doped p regions on both side during ON condition the “ON state” voltage drop is less.
- The outer n layers are formed with doping levels higher then both the p type layers. The top p layer acts as the “Anode” terminal while the bottom n layers acts as the “Cathode”. The “Gate” terminal connections are made to the bottom p layer.
- For better switching performance it is required to maximize the peripheral contact area of the gate and the cathode regions.
- Therefore, the cathode regions are finely distributed between gate contacts of the p type layer. An “Involute” structure for both the gate and the cathode regions is a preferred design structure.