| 摘要 |
PROBLEM TO BE SOLVED: To prevent an interference noise which is generated from a switching element by providing a switching power circuit and a phase-locked loop device which synchronizes phase of a triangular wave generator that constitutes power of the circuit with prescribed frequency. SOLUTION: Switching power compares error voltage for reference voltage of output voltage 21 with a reference triangular wave (being fHH2 here) which is produced by a triangular wave generator 18 in a comparator 16 and controls the error voltage with a DWM. When the output voltage 21 decreases, the switching voltage operates to increase duty of output pulse of the comparator 16 and an on period of a switching transistor 13. Also, it performs the opposite operation and outputs stabilized voltage when the output voltage 21 increases. At this time, basic triangular wave frequency synchronizes with fH/2 by means of a phase-locked loop device 19 and is interleaved in frequency because it is integer double of the fH/2 . Thereby, interference of switching frequency can not be seen on a screen to human beings' vision. |
