This paper presents novel resonant techniques in controlling the output power of a half-bridge series-parallel load-resonant and a quasi-resonant converter operating at true resonance using simple power electronics techniques. A mathematical model of the load-resonant converter has been designed, analyzed and developed, leading to the building of a practical circuit with multi-resonant frequencies. Operation of the circuit over the entire resonant frequency range maintains essentially zero-current switching, and unity-power factor while operating at high-frequency operation. Different power levels can be delivered to the load at each distinct resonant frequency. Different curves have been drawn to assist the process. The quasi-resonant converter has been constructed using a pair of back-to-back power switches switching around 100kHz. The resonant components consist of only an inductor and a capacitor. Another pair of switches is inserted in the circuit to avoid slip-frequency problems when the load is an induction motor and variable speed operation is desired.