This be power supply variable regulator circuit, since 5V to 13V that current about 1A. By use IC LM7805 (3-Terminal 1A Positive Voltage Regulator) perform maintain one’s position voltage, be stable that 5V. And have op-amp IC number CA3140 , help fine decorate voltage go out can modify 5V to 13V from get, by use VR1 in fining decorates. It takes current from output feed come back still a pin GND of LM7805 control the level voltage get efficiently better using resistor R1 only. See little detail in the circuit.