Interface circuit diagram for controlling AC load

The MC6820 external interface adapter drives four "NAND gates" 7400. The output signal of the 7400 is fed to the MOC 3011 photoelectric isolator, which controls the three-terminal triac of the pharmaceutical factory, and then the thyristor controls the AC resistance of the pharmaceutical factory. load or AC inductive load.

The second input end of the "NAND gate" in the 7400 is connected to a transistor timing circuit, and the thyristor can only be turned on when the AC input voltage crosses zero. Doing so can extend the service life of the incandescent lamp, reduce the impact of surge current on the triac, and reduce the back electromotive force generated when the load is switched.