| 摘要 |
PURPOSE:To make it possible to supply proper warm-up current to a filament with a simple circuit structure by increasing the output voltage of a chopper during warm-up time, that is, to increase the direct current input voltage for an inverter and also controlling a switching element to on state. CONSTITUTION:When a DC power supply 16 is switched on by the on operation of a switch 15, though a charging of capacitor C4 starts in a timer circuit 14, a transistor Q7 remains in its off state because the voltage between its both ends does not reach a fixed value for a certain time. Because of this, a chopper 13 generates a high DC output voltage and a inverter 11 generates an output voltage for supplying a warm-up current. At this time, a photo coupler PC1 is in off state. And, a voltage, which is induced in the auxiliary winding 21d of an output transformer 21, rectified by a diode D2 and smoothed by a capacitor C5, is divided by resistors R11 and R12 and is applied to the base of a transistor Q1 for turning the transistor on. Consequently, a circuit 17 for warm-up becomes electrically conductive, thus proper warm-up current flows through the filaments. |
