| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply which can reduce an inrush current at turn-on and -off of a contact in a relay. SOLUTION: A rectifying and smoothing circuit, a switching element 5, a pulse width control circuit 6 for delaying the switching element under control are connected on the primary side of a converter transformer 11. A first diode 12 and a smoothing capacitor 13 are connected in series on the secondary side of the converter transformer 11, and a relay 15 connected to the smoothing capacitor 13 is connected to the pulse width control circuit 6 in the switching power supply. A serial circuit made up of a first resistor 19 and a first transistor 20, and a parallel circuit of a second transistor 25 and a second diode 22 along with a second resistor 21 connected in serial with the parallel circuit, are connected in parallel between the smoothing capacitor 13 and the relay 15, and a cathode of the second diode 22 is connected to a base of the second diode 22 to form an inrush current control circuit 14. At the same time, resistance between the collector and emitter of the second transistor 25 is made small than that of the transistor 20.
|
