AC and DC inflow automatic switching circuit diagram

The figure below shows the AC/DC inflow automatic switching circuit. After the mains voltage is stepped down by transformer T1, it is then rectified, filtered, and stabilized before being output for load operation. At the same time, another DC voltage generated through rectification and filtering is divided by RP and added to the base of VT2. VT2 is turned on and VT1 is turned off. When the mains power is interrupted, VT2 changes from on to off. At this time, the power field effect transistor VT1 is on, and the battery is added to the voltage stabilizing circuit through VT1 to output a stable DC voltage for negative interception. Due to the use of MOSFET for fast electronic switching, this circuit achieves the purpose of uninterrupted power supply.