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In a power supply device including a PWM-controlled DC/DC converter which changes an output voltage on the basis of a setting signal, and a control unit, the DC/DC converter includes a circuit for changing a dead-time control voltage in accordance with a control signal. A dead-time control circuit

In a power supply device including a PWM-controlled DC/DC converter which changes an output voltage on the basis of a setting signal, and a control unit, the DC/DC converter includes a circuit for changing a dead-time control voltage in accordance with a control signal. A dead-time control circuit is arranged, which sets the ON duty of a PWM main switching element at a predetermined time constant in accordance with the dead-time control voltage. The control unit outputs the setting signal and control signal. In this arrangement, an input rush current generated in changing the output voltage during operation can be reduced, and the time required for causing the output voltage to reach the setting value can also be shortened.

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What is claimed is: 1. A power supply device comprising: a PWM-controlled DC/DC converter capable of changing an output voltage on the basis of a setting signal, the DC/DC converter including a voltage change circuit configured to change a dead-time control voltage in accordance with a control sign

What is claimed is: 1. A power supply device comprising: a PWM-controlled DC/DC converter capable of changing an output voltage on the basis of a setting signal, the DC/DC converter including a voltage change circuit configured to change a dead-time control voltage in accordance with a control signal and a dead-time control circuit which sets an upper limit value of an ON duty of a PWM main switching element at a predetermined time constant in accordance with the dead-time control voltage; and a control unit configured to output the setting signal instructing a change from a first voltage, which is presently being output, to a second voltage, and the control signal of a pulse width according to the first or second voltage; wherein said control unit outputs the control signal so as to set the upper limit value of the ON duty to a given value larger than a mean value of an ON duty corresponding to the first voltage and an ON duty corresponding to the second voltage. 2. The device according to claim 1, wherein said dead-time control circuit includes a capacitor which determines the time constant, and said voltage change unit includes a discharge switching element connected parallel to said capacitor to discharge said capacitor in accordance with the control signal. 3. The device according to claim 2, wherein said voltage change unit controls an ON time of said discharge switching element in accordance with the control signal, thereby changing the dead-time control voltage. 4. The device according to claim 1, further comprising an output capacitance discharge circuit formed from a resistor and switching element arranged between output terminals of said DC/DC converter, wherein said control unit outputs a discharge control signal which operates said output capacitance discharge circuit for a predetermined period of time in synchronism with the setting signal which changes the output voltage. 5. The device according to claim 4, wherein said control unit outputs the discharge control signal only when the output voltage is set lower than the present value.