Patent ID: 7710175
Filing Date: 2010-05-04
Classification: H03F

Abstract:
1. A pulse width modulation circuit comprising: a reference-clock generator which generates a reference clock; a first electric-charge accumulator which accumulates an electric charge; a second electric-charge accumulator which accumulates an electric charge; a first current generator which generates, from an input AC voltage, a first current with a current value varying with the amplitude of this AC voltage; a second current generator which generates a second current with a constant current value; a first current supply controller which, during high-level half cycles of said reference clock, supplies said first current to said first electric-charge accumulator during the high-level time intervals, in order to change the voltage across said first electric-charge accumulator from a first voltage to a second voltage corresponding to the amplitude of said AC voltage; a second current supply controller which, during low-level half cycles subsequent to the half cycles during which said first current is supplied, supplies said second current to said first electric-charge accumulator, in the opposite direction from that of said first current, until a predetermined time is elapsed after the voltage across the first electric-charge accumulator is changed from said second voltage to a predetermined threshold value between the second voltage and said first voltage; a first pulse-signal generator which, during the low-level half cycles subsequent to the half cycles during which said first current is supplied, generates pulse signals with a pulses width corresponding to the time interval required for changing the voltage across said first electric-charge accumulator from said second voltage to said threshold voltage; a third current supply controller which, during the low-level half cycles of said reference clock, supplies said first current to said second electric-charge accumulator during the low-level time intervals, in order to change the voltage across said second electric-charge accumulator from said first voltage to said second voltage; a fourth current supply controller which, during the high-level half cycles subsequent to the half cycles during which said first current is supplied, supplies said second current to said second electric-charge accumulator, in the opposite direction from that of said first current, until said predetermined time is elapsed after the voltage across the second electric-charge accumulator is changed from said second voltage to said threshold value; a second pulse-signal generator which, during the high-level half cycles subsequent to the half cycles during which said first current is supplied, generates pulse signals with a pulses width corresponding to the time interval required for changing the voltage across said second electric-charge accumulator from said second voltage to said threshold voltage; and a pulse modulated signal generator which synthesizes the pulse signals generated by said first pulse-signal generator and the pulse signals generated by said second pulse-signal generator to generate a pulse-width modulated signal; wherein there is provided a current limiter which limits the first current generated by said first current generator to a third current with a predetermined current value, if the amplitude of said AC voltage in the negative side exceeds a predetermined level.