Signal calculator

A signal calculator comprising:

• a capacitor;
• a variable current source that is configured to:
• charge the capacitor,
• generate a current corresponding to a predetermined voltage during a first period, wherein a first voltage is generated using a voltage of the capacitor charged during an enable period of a first signal in the first period, a second voltage is generated using a voltage of the capacitor charged during the first period, and
• generate a current corresponding to the second voltage during a second period, wherein a second signal is generated according to a result of comparing the first voltage with the voltage of the capacitor during the second period, and a fourth voltage is generated by generating and sampling a third voltage which is increased according to a first current during an enable period of the second signal in the second period.

A power supply comprising:

• a transformer;
• a power switch coupled to the transformer;
• and
• a switch control circuit configured to control a switching operation of the power switch based on a voltage detected when the power switch is turned on,
• wherein the switch control circuit comprises a signal calculator, the signal calculator comprising:
• a capacitor;
• and
• a variable current source that is configured to:
• charge the capacitor,
• generate a current corresponding to a reference voltage during a first period, wherein a first voltage is generated using a voltage of the capacitor charged during an enable period of a first signal in the first period, and a second voltage is generated using a voltage of the capacitor charged during the first period, and
• generate a current corresponding to the second voltage during a second period, wherein a second signal is generated according to a result of comparing the first voltage with the voltage of the capacitor in the second period, and a fourth voltage is generated by generating and sampling a third voltage which is increased according to a first current during an enable period of the second signal,
• wherein the third voltage increases according to the first current during a third period,
• wherein after a period for the third voltage to reach the fourth voltage has passed, the variable current source generates a current corresponding to a predetermined voltage, and
• wherein the voltage of the capacitor is sampled at an end time point of the third period.

A power supply comprising:

• a transformer;
• a power switch coupled to the transformer;
• and
• a switch control circuit configured to control a switching operation of the power switch based on a voltage detected when the power switch is turned on,
• wherein the switch control circuit comprises a signal calculator, the signal calculator comprising:
• a capacitor;
• a variable current source that is configured to:
• charge the capacitor,
• generate a current corresponding to a predetermined voltage during a first period, wherein a first voltage is generated using a voltage of the capacitor charged during an enable period of a first signal in the first period, a second voltage is generated using a voltage of the capacitor charged during the first period, and
• generate a current corresponding to the second voltage during a second period, wherein a second signal is generated according to a result of comparing the first voltage with the voltage of the capacitor during the second period, and a fourth voltage is generated by generating and sampling a third voltage which is increased according to a first current during an enable period of the second signal in the second period.