POWER SUPPLY CIRCUIT FOR VACUUM FLUORESCENT DISPLAY CAPABLE OF GENERATING AC FILAMENT VOLTAGE BY USING PERIODIC ON/OFF OPERATION OF SWITCHING ELEMENT

摘要

PURPOSE: A power supply circuit is provided to eliminate the necessity of using a filament driving transformer and reduce noise by generating an AC filament voltage through the use of periodic on/off operation of a switching element. CONSTITUTION: A power supply circuit(100) comprises an induction element(L), an input terminal(Pin) for a DC voltage(Vin), a switching element(TR), a control circuit(15), a boosting circuit(13), a first terminal(F1), and a second terminal(F2). The induction element is arranged in a current path(Lin) so as to generate an induced voltage in accordance with changes in current flow. The input terminal for the DC voltage is connected to one terminal(Pa) of the induction element. The switching element is interposed between the other terminal(Pb) of the induction element and a ground line(GND). The control circuit periodically turns on/off the switching element. The boosting circuit generates a boosted voltage(VDD2) on the basis of an induced voltage(V0) generated from the other terminal of the induction element when the switching element is switched from ON to OFF. The first terminal is connected to a node(P1) arranged between the other terminal of the induction element and the switching element. The second terminal is applied with a DC voltage(Vin) lower than the induced voltage generated from the other terminal of the induction element.