| 摘要 |
PROBLEM TO BE SOLVED: To provide a self-exciting switching power unit, which provides an output voltage with highly accurate stability and enables a precise over current control. SOLUTION: A feedback winding 13 biases the switching element 2 in the conductive direction with a voltage induced during the on-period of a switching element 2. An output rectification and smoothing circuit 3 rectifies and smoothes a voltage induced during the off-period of the switching element 2 and output the voltage. An output voltage detection circuit 4 including a photo coupler PD4 supplies an output voltage signal to a control circuit 5. A time constant circuit 51 is connected between both ends of the feedback winding 13. A transistor 53 for controlling the time constant, whose base receives incoming output voltage signal, controls the time constant of the time constant circuit 51. A transistor 54 for switching control has a control electrode connected to a capacitor C5 of the time constant circuit 51, and a main electrode connected to the control output side of the switching element 2.
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