| 摘要 |
PURPOSE:To prevent the DC output voltage of a switching regulator from becoming unstabilized by a method wherein an analog output from an error amplifier is converted into a digital signal and, thereafter, is transmitted to a primary side while the digital signal is taken out by a D/A converting circuit as the analog signal. CONSTITUTION:When a DC output voltage has become higher compared with a reference voltage Vref, the output voltage of an error amplifying circuit 8 is reduced. Accordingly, the output of an A/D converting circuit 11 is changed in accordance with an input. Subsequently, the output of the A/D converting circuit 11 is transmitted to the input of a D/A converting circuit 12 through a photocoupler 7. The level of the output of the D/A converting circuit 12 is changed in accordance with the input of a digital signal. Accordingly, the level of the voltage of the analog signal at a point (b) becomes higher than before. Then, the voltage of the analog signal at the point (b) is compared with a reference triangular wave or a saw-teeth wave by a comparing circuit 9 whereby the pulse width of the output of the comparing circuit 9 is narrowed and the DC output voltage is reduced.
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