Patent ID: 7315095

Claim:
A voltage regulating apparatus comprising: a voltage supplying circuit which applies a drive voltage to a first end of each of a plurality of loads; a mount checking circuit which checks, load by load, to determine whether each of the plurality of loads is mounted; a monitoring circuit which monitors a voltage occurring at a second end of each of the plurality of loads as a result of applying the drive voltage or which monitors an associated voltage, the monitoring being done load by load; and a boost control circuit which increases the drive voltage output from the voltage supplying circuit when it is determined as a result of the monitoring by the monitoring circuit that the monitored voltage drops below a preset voltage, wherein the monitoring circuit invalidates the monitoring on the load determined to be unmounted as a result of the checking by the mount checking circuit, so as to prevent a result of monitoring on the load unmounted from affecting the control on the drive voltage by the boost control circuit, wherein the mount checking circuit is provided with a plurality of voltage comparators which compare, for each of the plurality of loads, the voltage at the monitored terminal with a predetermined threshold voltage supplied commonly to the plurality of voltage comparators, the mount checking circuit determining that a load is not connected to the monitored terminal when the voltage at the monitored terminal is lower; the mount checking circuit and the monitoring circuit time-share a single comparator for a given one of the plurality of loads; and the voltage at the monitored terminal is input to one input terminal of the single comparator for the given one of the plurality of loads, and one of a reference voltage to be used in the monitoring circuit and a reference voltage to be used in the mount checking circuit is switchably input to the other input terminal.