Patent ID: 7489975

Claim:
A power supply device comprising: a power converting unit that switches DC power on the basis of a pulse signal having a predetermined ON-pulse time and a predetermined pulse period, as pulse elements, thereafter smoothes the switched power, and outputs a predetermined power-supply voltage; a control unit that calculates a new pulse-element on the basis of an output of the power converting unit; and a pulse generating unit that generates the pulse signal on the basis of the new pulse-element instructed from the control unit, wherein the pulse generating unit generates the pulse signal of the new pulse-element from the instructed timing without waiting for a new pulse-period, irrespective of the ON-pulse time and an OFF-pulse time, even if the instructed timing is at any timing during the pulse period, wherein the pulse generating unit comprises: a counter that inputs a predetermined clock signal and counts the number of clocks; a pulse period storing portion that stores a value of the pulse period; a pulse period generating portion that compares a count value of the counter with the pulse period stored in the pulse period storing unit and resets the count value of the counter every pulse period; a first pulse-width storing portion that stores a value of the ON-pulse time; a second pulse-width storing portion that receives the value of the ON-pulse time transferred from the first pulse-width storing portion and stores the value of the ON-pulse time, when the count value is reset; and a pulse width generating portion that compares the count value of the counter with the value of the ON-pulse time stored in the second pulse-width storing portion, determines the ON-pulse time on the basis of the comparison of both the values, and generates the pulse signal on the basis of the determined ON-pulse time, and wherein the control unit stores the value of the ON-pulse time to the first pulse-width storing portion, directly stores a value of a pulse width to be changed to the second pulse-width storing portion not via the first pulse-width storing portion, upon issuing an instruction for changing the pulse with during the ON-pulse time, and forcedly resets the count value of the counter upon issuing the instruction for changing the pulse width during the OFF-pulse time.