| 摘要 |
PURPOSE:To check variation in the operating frequency against changes in the load by employing for the output transformer so designed as to be large in the primary inductance when the flux density of the magnetic path is small while becoming small with saturation when the flux density is large. CONSTITUTION:As the output voltage Eo exceeds the specified level, the error amplifying circuit 40, the photocoupler 50 and the control circuit 60 combine to raise the operating frequency of the blocking oscillation circuit 10 whereby the output voltage is controlled to reduce. Here, a core chip 74 having the sectional area smaller than that of the central leg 74 is provided at the gap part G of the magnetic path and a saturatable transformer is used having such a characteristic that when the flux density of the magnetic path is small, the primary inductance is large while when it is large, the density becomes small with a saturation of the chip. This enables the operating frequency to be reduced within the variation range to a level lower than that in the past against changes in the load condition from light to heavy thereby further stabilizing the output voltage. |
