| 摘要 |
PURPOSE:To prevent an influential accident from happening, by interrupting the outflow of secondary current for output at a switching transistor, when a load short-circuiting accident happens. CONSTITUTION:A switching power supply device is composed of a DC power source 1, an input capacitor 2, a switching transformer 3, a switching transistor 4, a control circuit 5 generating the output of drive signal 5a, a rectifying transis tor 7 for a secondary winding 36 for output, a smoothing circuit 23, an arithme tic circuit 14, and the like, and specified DC voltage E0 is fed to a load 13. In this case, in place of smoothing coils, a current transformer 16 is set, and an excess current monitoring circuit 17 including the transformer 16 is set. At the transformer 16, a primary winding 16a having a winding N1 is set to be worked in the same manner as the smoothing coils are worked, and to both the ends of a secondary winding 16b, a resistor R3 is connected. As a result, when a secondary current value exceeds a specified value to get excessive, then the flowing passage of secondary current at the rectifier circuit 23 is inter rupted, and an influence accident is prevented from happening.
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