This transformer converts 110 volt AC to 18 volt AC which is converted to DC by the gate control board. This voltage then charges the batteries of the gate operator. The RB570 is the factory replacement for GTO SW2000/3000/4000 series, SL-1000/2000 using the AQ251 control board, MM350/500 series, GTO PRO -SW3000/4000 and duals of the XL and XLS series. Cannot be used with Pre UL operators.