the configurations of a buck type and a buck / boost type converter systems and a controlling method thereof are provided in the present invention . the proposed buck / boost type converter system includes a rectifier bridge , a first auxiliary circuit including a first unidirectional switch coupled to the rectifier bridge and a second unidirectional switch coupled to the first unidirectional switch , a first capacitor coupled to the first unidirectional switch and the rectifier bridge , a buck / boost converter having a first input terminal coupled to the first unidirectional switch , a second input terminal coupled to the first capacitor , a first output terminal coupled to the second unidirectional switch and a second output terminal , a second capacitor electrically connected to the first and the second output terminals in parallel , and a dc source coupled to the second unidirectional switch .