A power source control chip which is a high voltage controlling portion is added
to an ASIC for sequence control constituting a sequence control unit. A PWM signal
is sent from the high voltage controlling portion to a high voltage producing portion
constituting a high voltage unit, and an output detection signal is sent from the
high voltage producing portion to the high voltage controlling portion, thereby
effecting feedback control. At that time, a modulated wave PWM/detection signal
amplitude-modulated with the PWM signal as a carrier wave and with the output detection
signal as a modulating wave is produced and is transmitted onto a signal line,
whereby the number of signal lines can be decreased.
