| 摘要 |
PURPOSE:To miniaturize step-up circuits, in which two kinds are constituted in parallel, and to decrease the number of components by sharing the coils and diodes of the step-up circuits at a first stage and a second stage without damaging the smooth operation of the step-up circuits in the step-up circuits in a voltage conversion circuit stepping up DC voltage and outputting the stepped-up DC voltage. CONSTITUTION:A power supply 20 is turned on, the MOS transistor 25 of a first switching circuit 21 is operated in response to the control pulses of an oscillation circuit 43 first, and induced voltage is generated at both ends of a coil 23, and output to an external output terminal 54 through a diode 27 and a smoothing circuit 31. The comparator 36 of a comparison circuit 35 outputs changeover pulses Vcont when output voltage Vout reaches reference voltage Vref, and the control pulses of the MOS transistor 25 from a frequency dividing circuit 42 are stopped. Operation by the output signal of a PWM circuit 44 using the output voltage Vout of the MOS transistor 29 of a second switching circuit 22 as feedback is started, and the step-up operation of a step-up circuit 28 is continued. |
