is turned off if the first switch qerh is turned off therefore the resonance is not generated and a current path comprising the second diode dc 2 the first inductor lr 1 the first diode dc 1 and the external capacitor ce is formed to recover and store energy in the external capacitor ce in the period of t2 the current ir 1 is decreased to 0 rapidly and linearly in the period of t3 state of each switch is sustained as the period of t2 in order to sustain the voltage vp of the panel capacitor cp to the voltage vsus in the period of t4 the pull up switch qh in the driving unit 32 is turned off and the second switch qerl in the energy recovery unit 30 is turned on to form a current path comprising the panel capacitor cp the discharge path diode derl biased to the forward the second inductor lr 2 and the second switch qerl and the voltage of the one electrode of the panel capacitor cp is discharge to the ground voltage by the resonance current ir 2 owing to the u00bc resonance of the second inductor lr 2 and the panel capacitor cp at this time the voltage vp of the panel capacitor cp is decreased rapidly to the ground voltage with the u00bc resonance of the second inductor lr 2 and the panel capacitor cp in the period of t5 the second switch qrl is.