A drive arrangement for a switched output stage, such as an output stage of a gradient intensifier of a tomography apparatus has a pulse-width modulator and drive logic for producing at least two drive signals. The drive logic produces, for each drive signal, an edge of each on-phase pulse at a time made fixed corresponding to a time reference clock signal thereby allowing a fine adjustment of the on-phase of the power transistors of the switched output stage with low components costs, and a prescribed dead time between the individual on-phases is reliably adhered to.

A semiconductor integrated circuit according to an aspect of the invention comprises a first storage circuit, second storage circuit, adder circuit, timer, first comparator circuit and waveform-generating circuit. The first storage circuit stores a first value used to set a dead time. The second storage circuit stores a second value used to set a pulse width. The adder circuit adds the first value stored in the first storage circuit and the second value stored in the second storage circuit, thereby outputting an addition result. The timer measures an elapsed time and outputs a count value indicative of the elapsed time. The first comparator circuit compares the count value output from the timer with the addition result output from the adder circuit. The waveform-generating circuit generates a pulse on the basis of a comparison result of the first comparator circuit.

In an embodiment of this invention, if a state, in which duty ratio of a PWM signal is kept equal to or greater than a predetermined value, has been maintained for a first time period, the duty ratio of the PWM signal of a digital power amplifier is adjusted downward. Furthermore, the duty ratio of the PWM signal is maintained without change when the duty ratio of the PWM signal is adjusted downward for a second time period, and the duty ratio of the PWM signal is adjusted downward only when volume is set to a maximum value allowable in the power amplifier. Accordingly, the temperature of the power amplifier can be prevented from rapidly increasing, the internal temperature of an electronic apparatus can be efficiently prevented from increasing, and damage to the power amplifier resulting from increased temperature can be prevented.

A pulse width modulation apparatus includes a load circuit, a signal switch, a shunt switch, and a resistor. The signal switch isolates the load circuit from a voltage source along a signal path. The shunt switch is connected to the signal path at a point between the signal switch and the load circuit. The shunt switch isolates the signal path from a ground voltage. A resistor is connected in series between the signal switch and the shunt switch.

A transformerless driver circuit for an EL device has a battery or other source of dc power, and a microcontroller that is suitably programmed with associated firmware, so that a first switch control signal appears at a first output and a second switch control signal appears at a second output. A flyback circuit is connected to the first microcontroller output and, through a diode, to a charge storage device, e.g., a capacitor. This charges the capacitor stepwise to a relatively high voltage. The flyback circuit includes an inductor having one end connected to a first terminal of the dc power source, and another end coupled to a transistor or similar switch element. The transistor is coupled to the second dc power terminal, and has a base or gate coupled to the first output of the microcomputer. A controlled discharge arrangement bridges across the charge storage device to discharge the same periodically, and create an alternating current to drive the EL device. A second transistor has its base or gate coupled to the microcontroller second output. An isolating capacitor can be positioned in series between the diode and the charge storage device to eliminate the dc offset to the EL element. In one alternative arrangement, two or more flyback circuits are gated on and off sequentially. In a power-saver arrangement, the discharge circuit returns charge back to the battery.