| 摘要 |
PROBLEM TO BE SOLVED: To simplify a switching circuit located between a first control mode in a light load and a second one in a heavy load. SOLUTION: A switching element 3 is connected between a pair of output terminals 12 and 13 in a rectifying smoothing circuit 1 via a transformer 2. A capacitor 5 for resonance is connected to the switching element 3 in parallel. A rectifying smoothing circuit 6 is connected to the transformer 2. A control circuit 7 is provided to perform the on/off-control of the switching element 3 so that the output voltage can be controlled to be constant. In the control circuit 7, a circuit for determining the end point of an on period, a circuit for detecting a flyback voltage generation period, and a circuit for forming control signals and for switching modes are provided. In the circuit for forming control signals and switching modes, a pulse generator and a control pulse formation circuit are provided. The control pulse formation circuit has the function of switching modes by using the output of the pulse generator which is other than a function for forming the control pulse of the switching element. COPYRIGHT: (C)2003,JPO
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