Switch control circuit and power supply device including the same

1. A power supply device, comprising:

a power switch on a primary side of the power supply;

a rectification diode on a secondary side of the power supply, the rectification diode being configured to rectify a supplied current in accordance with a switching operation of the power switch to generate an output current;

a sensing resistor from which a sensing voltage is detected on the primary side of the power supply; and

a switch control circuit configured to generate an output current estimating voltage corresponding to the output current by supplying the sensing voltage to a low pass filter in the switch control circuit during a discharging period when a current flows through the rectification diode during a switching cycle of the power switch and averaging the detected sensing voltage during the switching cycle of the power switch.

2. The power supply device of claim 1 , wherein the switch control circuit is configured to generate the detected sensing voltage, by detecting a peak of the sensing voltage for every switching cycle of the power switch.

3. The power supply device of claim 1 , wherein the switch control circuit is configured to generate the detected sensing voltage by at least one of calculating or detecting an average of the sensing voltage for every turn-on period of the power switch.

4. The power supply device of claim 1 , wherein the switch control circuit is configured to divide the detected sensing voltage using first and second resistors in the switch control circuit, and to supply a resistively divided detected sensing voltage to the low pass filter in the switch control circuit during the discharging period, wherein the low pass filter is configured to generate the output current estimating voltage by averaging the resistively divided detected sensing voltage during the switching cycle of the power switch.

5. The power supply device of claim 1 , wherein the switch control circuit is configured to supply the detected sensing voltage to the low pass filter in the switch control circuit during the discharging period, wherein the low pass filter is configured to average the detected sensing voltage during the switching cycle of the power switch and to provide the average detected sensing voltage to first and second resistors in the switch control circuit configured to generate the output current estimating voltage by dividing the average detected sensing voltage using the first and second resistors.

6. The power supply device of claim 1 , wherein the switch control circuit is configured to supply the detected sensing voltage to an amplifying unit in the switch control circuit, wherein the amplifying unit is configured to amplify the detected sensing voltage and to supply an amplified detected sensing voltage to the low pass filter in the switch control circuit during the discharging period, wherein the low pass filter is configured to generate the output current estimating voltage by averaging the amplified detected sensing voltage during the switching cycle of the power switch.

7. The power supply device of claim 1 , wherein the switch control circuit is configured to supply the detected sensing voltage to the low pass filter in the switch control circuit during the discharging period, wherein the low pass filter is configured to average the detected sensing voltage during the switching cycle of the power switch and to provide the average detected sensing voltage to an amplifying unit in the switch control circuit, wherein the amplifying unit is configured to generate the output current estimating voltage by amplifying the average detected sensing voltage.

8. The power supply device of claim 1 , wherein the switch control circuit includes a current mirror configured to:

generate a second current by copying a first current corresponding to the detected sensing voltage at a predetermined ratio;

generate a copied voltage corresponding to the second current; and

supply the copied voltage to the low pass filter during the discharging period; and

wherein the low pass filter is configured to generate the output current estimating voltage by averaging the copied voltage during the switching cycle of the power switch.

9. A switch control circuit which controls a switching operation of a power switch of a power supply, the circuit comprising:

a sensing voltage detector configured to generate a detected sensing voltage based on a sensing voltage in accordance with a current which flows through the power switch on a primary side of the power supply; and

an output current estimator configured to generate an output current estimating voltage corresponding to an output current which is controlled in accordance with a switching operation of the power switch by averaging the detected sensing voltage,

wherein the output current estimator includes:

a low pass filter; and

a first switch,

wherein the first switch is configured to supply the detected sensing voltage to the low pass filter during a discharging period, and the discharging period is a period when the output current flows through a rectification diode on a secondary side of the power supply.

10. The switch control circuit of claim 9 , wherein the sensing voltage detector is configured to generate the detected sensing voltage by detecting a peak of the sensing voltage for every switching cycle of the power switch.

11. The switch control circuit of claim 9 , wherein the sensing voltage detector is configured to generate the detected sensing voltage by at least one of calculating or detecting an average of the sensing voltage for every turn-on period of the power switch.

12. The switch control circuit of claim 9 , wherein the output current estimator further includes a second switch that is configured to supply a predetermined reference voltage during a remaining period except for the discharging period in the switching cycle of the power switch.

13. The switch control circuit of claim 9 , wherein the output current estimator further includes first and second resistors configured to resistively divide the detected sensing voltage and supply the detected sensing voltage which is resistively divided to the low pass filter through the first switch during the discharging period.

14. The switch control circuit of claim 9 , wherein the output current estimator further includes first and second resistors configured to generate the output current estimating voltage by resistively dividing an output of the low pass filter.

15. The switch control circuit of claim 9 , wherein the output current estimator further includes an amplifying unit configured to amplify the detected sensing voltage and supply the amplified detected sensing voltage to the low pass filter during the discharging period.

16. The switch control circuit of claim 9 , wherein the output current estimator further includes an amplifying unit configured to generate the output current estimating voltage by amplifying an output of the low pass filter.

17. The switch control circuit of claim 9 , wherein the output current estimator further includes a current mirror configured to copy the first current corresponding to the detected sensing voltage at a predetermined ratio to generate a second current, generate a copied voltage corresponding to the second current, and supply the copied voltage to the low pass filter during the discharging period.

18. The switch control circuit of claim 9 , wherein the switching operation of the power switch is controlled in accordance with a result of comparing a comparison voltage obtained by amplifying a difference between the output current estimating voltage, a predetermined reference voltage and any one of the sensing voltage and a triangular wave.

19. A switch control circuit which controls a switching operation of a power switch, the circuit comprising:

a sensing voltage detector configured to generate a detected sensing voltage corresponding to a sensing voltage in accordance with a current which flows through the power switch;

an error amplifier configured to amplify a difference between the detected sensing voltage and the predetermined reference voltage;

a capacitor coupled to an output terminal of the error amplifier to act as a low pass filter, wherein an output of the error amplifier is averaged by the capacitor;

a first switch; and

a second switch,

wherein the first switch is configured to supply the detected sensing voltage to the low pass filter during a discharging period, the discharging period is a period when a current flows through a rectification diode to generate the output current, and the second switch is configured to provide a predetermined reference voltage during a remaining period except for the discharging period in a switching cycle of the power switch.