Integrated circuit for power supply and power supply system
An integrated circuit for a power supply is provided that is connected to an AC power supply via an input circuit including a capacitor, comprising: a voltage dividing unit that divides an input voltage to generate a divided voltage; a shutoff detection unit that compares the divided voltage with a predetermined reference voltage to detect shutoff of the AC power supply; and a discharge unit that discharges accumulated charge in the capacitor when shutoff of the AC power supply is detected, wherein the voltage dividing unit sets a ratio of the divided voltage to the input voltage to a first voltage division ratio when no shutoff of the AC power supply is detected, and sets a ratio of the divided voltage to the input voltage to a second voltage division ratio greater than the first voltage division ratio when shutoff of the AC power supply is detected.
1 . An integrated circuit for a power supply that is connected to an AC power supply via an input circuit including a capacitor, comprising:
a voltage dividing unit that divides an input voltage to generate a divided voltage;
a shutoff detection unit that compares the divided voltage with a predetermined reference voltage to detect shutoff of the AC power supply; and
a discharge unit that pulse-discharges accumulated charge in the capacitor in pulses when shutoff of the AC power supply is detected,
wherein the voltage dividing unit sets a ratio of the divided voltage to the input voltage to a first voltage division ratio when no shutoff of the AC power supply is detected, and sets a ratio of the divided voltage to the input voltage to a second voltage division greater than the first voltage division ratio when shutoff of the AC power supply is detected, and
wherein when the shutoff detection unit outputs an output signal to the voltage dividing unit and the discharge unit, the voltage dividing unit changes the ratio of the divided voltage to the input voltage from the first voltage division ratio to the second voltage division ratio according to the output signal, and the discharge unit pulse-discharges accumulated charge in the capacitor in pulses according to the output signal.
2 . The integrated circuit for a power supply according to claim 1 , wherein the voltage dividing unit includes:
a first voltage dividing resistor having a resistance value Rdiv 1 connected between a first node and a second node;
a second voltage dividing resistor having a resistance value Rdiv 2 connected between the second node and a ground;
a third voltage dividing resistor having a resistance value Rdiv 3 connected at one end to the second node and connected in parallel with the second voltage dividing resistor; and
a first switch connected between another end of the third voltage dividing resistor and a ground.
3 . The integrated circuit for a power supply according to claim 1 , wherein the shutoff detection unit controls the first switch to be in an on state according to the output signal when no shutoff of the AC power supply is detected, and controls the first switch to be in an off state according to the output signal when shutoff of the AC power supply is detected.
4 . The integrated circuit for a power supply according to claim 1 , wherein
the discharge unit includes
a discharge resistor having a resistance value Rdis connected at one end to the first node and connected in parallel with the first voltage dividing resistor, and
a second switch connected between another end of the discharge resistor and a ground, and
wherein the shutoff detection unit controls the second switch to be in an off state according to the output signal when no shutoff of the AC power supply is detected, and controls the second switch to be in an on state according to the output signal when shutoff of the AC power supply is detected.