This is AC mode universal motor drive circuit. This circuit is suitable for large range of application. It uses the microcontroller to interpret the user interface that is used to select the four operating modes that are defined in hardware. Here is the circuit :
As power switch, this circuit use “SNUBBERLESS” TRIAC BTA 12-600BW with a maximum specified gate trigger current of 50mA at 25°C. It is driven by pulse. A small signal transistor interfaces the “SNUBBERLESS” TRIAC and the microcontroller. If spurious triggering is prohibited in case of mains perturbation we should implement a small filter RfCf, although no snubber is needed in nominal operations.
For synchronization, this circuit uses zero voltage detection across the mains. we can change operation from 50Hz to 60Hz by changing the EPROM/ROM table defining TRIAC conduction angle versus power level. It can be self-adapted by software or hardware programmed. [Source: STMicroelectronics Application Note]