Voltage smoothing circuit

摘要

Even if the internal resistance of a smoothing capacitor varies, voltage higher than or equal to the rated voltage of the smoothing capacitor is prevented from being applied to the capacitor by a simple configuration. Further, the balance of the voltage applied to the smoothing capacitor is maintained by a simple configuration. Specifically, a voltage smoothing circuit (14) is provided with a first smoothing capacitor (C1), a second smoothing capacitor (C2), a balance resistance (R3) and a zener diode (RZ4). The first smoothing capacitor (C1) and the second smoothing capacitor (C2) are connected in series to each other and connected in parallel to a power supply unit (13). The balance resistance (R3) is connected in parallel to the first smoothing capacitor (C1). The zener diode (RZ4) is connected in a current path (I4) that is in parallel to the second smoothing capacitor (C2). The zener diode (RZ4) passes a current through the current path (I4) in one direction when the voltage higher than or equal to zener voltage (Vr4) is applied.