Comparison of Thyristor and Transistor
As already mentioned, transistors and thyristors are both semiconductor devices. They are now widely employed in switching operations because of their numerous advantages such as noiseless operation owing to absence of moving parts, very high switching speed (say 109 operations per second), high efficiency, low maintenance, small size, little weight and trouble free service for long period, large control current range (say from 30 A to 100 A) with small gate current of few mA over mechanical switches or electro-mechanical relays. However, transistors and thyristors both have their own areas of applications. Thyristors have some advantages over transistors, as enumerated below :
1. Thyristor is a four-layer device while the transistor is a three-layer device.
2. Due to difference in fabrication and operation it is possible to have thyristors with higher voltage and current ratings.
3. Rating of a transistor is always in watts while that of a thyristor is in kWs i.e. thyristors having better power handling capacity.
4. A thyristor needs only a pulse to make it conducting and thereafter it remains conducting. On the other hand a transistor needs a continuous current for keeping it in a conducting state.
5. Internal power losses in a thyristor are much smaller than those in a transistor. Transistors, however, have lower voltage drop, and need no turn-off circuit. Power transistors are linear devices better suited for some linear power applications such as audio and high frequency power amplifiers, regulator systems etc.
which on was invented first and which one nowadays is commonly used.