This paper presents small signal ac analysis of LLC current resonant converter. Equivalent source model that represents a switching element as an equivalent source having averaged current and voltage is employed and described in detail. From analysis, the transfer function of the switching frequency to the output voltage of the converter becomes a quadratic system. Resonant capacitor and inductor do not affect directly to the small signal characteristics. However they affect a dc gain and an internal resistance. The analysis method is confirmed by experiments, and experimental results are relatively consistent with the analytical results.

Vehicles employing idle reduction system need a step up DC-DC converter which operates stably for a voltage drop of a battery during engine restart. This paper proposes a power supply for idle reduction system employing a ripple regulator having an excellent transient performance and stability without using electrolytic capacitors which results in long life. The feedforward circuit is employed in order to improve transient response for large input voltage change. The prototype converters were experimentally examined to verify the transient performance for the large variations of the load current and input voltage.

Control characteristics and power losses of magnetic amplifier used as a pulse-width modulator are discussed for a typical forward converter driven high-frequency switching. The control region of the magnetic amplifier is analyzed by modeling the DC magnetizing characteristics of the core and the reverse recovery of the diode in the converter circuit, and the dynamic characteristics of the regulated converter are examined analytically. The iron loss and switching loss of the magnetic amplifier are derived as functions of the switching frequency and the load current, with five states of the magnetic amplifier taken into consideration.>