Battery charger, voltage monitoring device and self-diagnosis method of reference voltage circuit

A self-diagnosis method of a reference voltage circuit supplying an A/D conversion reference voltage to an A/D converter comprising:

• connecting an A/D converting section to a first divided voltage output section outputting a first divided voltage of the reference voltage of the reference voltage generating circuit, obtaining a first A/D conversion value by A/D converting the first divided voltage via the A/D converter using the reference voltage, and comparing the first A/D conversion value with a first reference value obtained by A/D converting the first divided voltage via the A/D converter using the reference voltage when the A/D converter is normal;
• and
• connecting the A/D converting section to the first divided voltage output section outputting the first divided voltage of the reference voltage of the reference voltage generating circuit when the first A/D conversion value is equal to the first reference value, obtaining a second A/D conversion value by A/D converting the first divided voltage via the A/D converter using a second reference voltage of a second reference voltage generating circuit generating the second reference voltage equal to the reference voltage, and comparing the second A/D conversion value with a second reference value obtained by A/D converting the first divided voltage via the A/D converter using the reference voltage when the reference voltage circuit is normal in the case where the A/D converter and the reference voltage generating circuit are normal.