| 摘要 |
PURPOSE:To send current similar with an input voltage waveform and keep the output electric power constant by detecting the alteration of the effective value of an input a.c. voltage and correcting the standard bias based on the detected signal. CONSTITUTION:The output signal from an output terminal OUT of a switching control IC 28 is integrated in a time constant circuit for integration composed of resistors 36, 38 and a capacitor 37 and in the case the effective value of the input voltage lowers and the duty ratio of the output control signal of the IC 28 becomes high as a whole, the integration value becomes high and to the contrary, in the case the duty ratio becomes low, the integration value becomes low. The integration value is subtraction-processed by the standard bias determined by bias adjusting resistors 24, 2 5 and a computation amplifier 35. The resultant output is sent to a computation amplifier 21 as a bias component and, together with the current detected value of a switching device 12, it is subtraction-processed and further after compounded with a triangular wave, it is sent to a current detecting terminal ISENS of the IC 28. As a result, high power efficiency is achieved and at the same time the output electric power is made to be constant. |
