| 摘要 |
PROBLEM TO BE SOLVED: To make the current entering a control terminal of a switching element constant to further reduce a loss and prevent destruction of the switching element when the output is short-circuited, by installing a constant-current circuit between one end of a primary winding and a control circuit or the control terminal of the switching element. SOLUTION: A switching power circuit 20 comprises a transformer 3 having a primary winding 4, a secondary winding 5, and a feedback winding 6, a DC power supply with one end connected to one end of the primary winding 4, and a switching element serially connected between the other end of the DC power supply and the other end of the primary winding 4. Between the feedback winding 6 and a control circuit 8, a rectifier circuit 22 for supplying DC voltage for a control circuit is connected. Between one end of the primary winding 4 and a contact between the rectifier circuit 22 and the control circuit 8, a constant-current circuit 21 for supplying bias current for driving to the control circuit 8 is connected. Due to this structure, the current entering the control terminal can be made constant regardless of a change in the power of the DC power supply.
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