| 摘要 |
PROBLEM TO BE SOLVED: To provide a power circuit which is so structured as to keep the output voltage constant by indirectly detecting the voltage on the secondary side insulated from the primary side and therefore can provide the constant output voltage with high reliability. SOLUTION: This power circuit 1 is provided with a current detection resistor 70 serially connected to a switching transistor 13 which is a main switch. When the switching transistor 13 is conducting, the voltage across the current detection resistor 70 is detected. Based on the detected voltage, the power circuit 1 so controls that the detected voltage may be increased and thereby the voltage generated between terminals (f) and (g) of a secondary winding 43 may be increased. Thus, by increasing the voltage generated between the terminals (f) and (g) of the secondary winding so as to compensate for a line voltage drop caused when the load current is large, the output voltage can be kept constant.
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