Symbols of SCR and TRIAC
The symbol of SCR is
The symbol of TRIAC is
The difference between SCR and TRIAC is given below:
| SCR | TRIAC |
| It is a unidirectional device, i.e., it can conduct current in forward direction only. | It is a bidirectional device, i.e. it can conduct current in forward as well as reverse direction. |
| It is available with a large current and voltage ratings. | It is available for lower current rating as compared to that of SCR. |
| It has a fast turn-OFF and therefore can be used to switch a.c. supply frequencies upto few kHz. | It has comparatively longer turn-OFF time than SCR and therefore its use is limited to a.c. supply frequencies upto 400 Hz. |
| It is triggered by positive gate pulses. | It is triggered by a positive or negative pulse |
| It has high (di/dt) and (dv/di) ratings. | It has low (di/di) and (dv/di) ratings. |
| It has more reliability. | It has less reliability. |