| 摘要 |
PROBLEM TO BE SOLVED: To provide a compact and highly safe switching power supply device that dispenses with a photo-coupler and controls an output voltage without adding to the number of windings of a main transformer.SOLUTION: An auxiliary winding 26 is provided between a Vs line 28 and a GND line 18 to generate a positive voltage V(+) substantially proportional to an output voltage Vo. An auxiliary rectifying/smoothing circuit 34 is provided to convert the positive voltage V(+) to an auxiliary voltage Vo1. A first transistor 50 and a second transistor 52 are provided to pull a gate of a main switching element 32 up to a Vo1 line 36 and down to a low level, respectively. A feedback circuit 58 is provided between the Vs line 28 and a base of the second transistor 52. A third, grounded base transistor 60 has an emitter connected to the second transistor 52 and drives the first transistor 50 via a collector terminal voltage. A modulating capacitor 62 provided to turn on the second transistor 52 is charged/discharged by a charge/discharge circuit 66 and an output voltage control circuit 68. |
