AC power supply non-stop switching circuit using transistors c

AC and DC power supply non-stop switching circuits are usually used in load circuits such as lighting. Once the power grid is cut off or power is restored, the backup
power supply will automatically switch immediately. The automatic switching circuit
    using transistors is shown in the figure, and the automatic switching time is less than Is. Figure (a) is suitable for DC 12V backup power supply; Figure (b) is suitable for DC 24V backup power supply; Figure (c) is suitable for AC backup power supply.