Output current estimating method and power supply device using the same

1. A power supply device comprising:

a power switch;

a rectification diode configured to generate an output current by rectifying a current supplied according to a switching operation of the power switch; and

a switch control circuit configured to generate an output current estimation voltage corresponding to the output current using a detection sense voltage corresponding to a sense voltage that depends on a switch current flowing to the power switch and a compensated discharge period,

wherein the compensated discharge period is a period from the peak of a discharge current flowing to the rectification diode to an instant at which the discharge current becomes zero current, and the peak of the discharge current occurs when a snubber current flowing to a snubber circuit has decreased to zero current.

2. The power supply device of claim 1 , wherein the switch control circuit generates the detection sense voltage by detecting a peak of the sense voltage for every switching cycle of the power switch.

3. The power supply device of claim 1 , wherein the switch control circuit generates the detection sense voltage by calculating an average of the sense voltage for every switching cycle of the power switch.

4. The power supply device of claim 1 , further comprising:

a primary winding coupled to the power switch;

a secondary winding coupled to the rectification diode;

an auxiliary winding coupled to the secondary winding in an insulated manner; and

a delay voltage generator configured to generate a delay voltage delaying an auxiliary voltage generated in the auxiliary winding during a turn-off period of the power switch.

5. The power supply device of claim 4 , wherein the delay voltage generator comprises:

a first resistor and a second resistor coupled to the auxiliary winding;

a capacitor coupled to a first node to which the first resistor and the second resistor are coupled, wherein the delay voltage is a voltage of the first node.

6. The power supply device of claim 4 , wherein the switch control circuit comprises a discharge period detector configured to determine a start instant of the compensated discharge period according to a result of comparison between the delay voltage and a predetermined first reference voltage.

7. The power supply device of claim 6 , wherein the discharge period detector determines an instant at which the delay voltage rising from a turn-off instant of the power switch reaches the first reference voltage as a start instant of the compensated discharge period.

8. The power supply device of claim 6 , wherein the first reference voltage is determined by multiplying a predetermined first ratio by a maximum voltage of the delay voltage.

9. The power supply device of claim 8 , wherein the first ratio is changed according to a peak of the switch current.

10. The power supply device of claim 6 , wherein the discharge period detector is further configured to determine a termination instant of the compensated discharge period according to a result of comparison between the delay voltage and a predetermined second reference voltage.

11. The power supply device of claim 10 , wherein the discharge period detector determines an instant at which the delay voltage starts to decrease and then reaches the second reference voltage as the termination instant of the compensated discharge period.

12. The power supply device of claim 10 , wherein the second reference voltage is determined by multiplying a predetermined second ratio by a maximum voltage of the delay voltage.

13. The power supply device of claim 12 , wherein the second ratio is changed according to a peak of the switch current.

14. The power supply device of claim 1 , further comprising:

a primary winding coupled to the power switch,

wherein a current of the primary winding flows to the snubber circuit from a turn-off instant of the power switch, wherein the switch control circuit determines a start instant of the compensated discharge period using the snubber current flowing to the snubber circuit.

15. The power supply device of claim 14 , wherein the snubber circuit comprises:

a snubber diode of which an anode is coupled to a node to which a first end of the power switch and the primary winding are coupled; and

a snubber resistor and a snubber capacitor coupled in parallel between a cathode of the snubber diode and a second end of the power switch.

16. The power supply device of claim 14 , wherein the snubber circuit comprises:

a snubber diode of which an anode is coupled to a first end of the primary winding; and

a snubber resistor and a snubber capacitor coupled in parallel between a cathode of the snubber diode and a first end of the power switch, wherein the first end of the power switch and a second end of the primary winding are electrically coupled, while an input voltage is supplied to a second end of the power switch.

17. The power supply device of claim 14 , wherein the switch control circuit is configured to determine an instant at which the snubber current flowing to the snubber circuit becomes zero current as a start instant of the compensated discharge period.

18. A method for estimating an output current of a power supply device including a power switch coupled to a primary winding and a rectification diode coupled to a secondary winding, comprising:

detecting a compensated discharge period from an instant at which a discharge current flowing to the rectification diode reaches a peak after a turn-off instant of the power switch to an instant at which the discharge current becomes zero current, wherein the peak of the discharge current occurs when a snubber current flowing to the snubber circuit has decreased to zero current;

multiplying the compensated discharge period by a detection sense voltage that depends on a sense voltage that corresponds to a switch current flowing to the power switch; and

dividing a result of the multiplication by a switching cycle of the power switch.

19. The method of claim 18 , wherein detecting the compensated discharge period comprises:

generating a delay voltage by delaying an auxiliary voltage of an auxiliary winding coupled in an insulated manner to the secondary winding; and

determining a start instant of the compensated discharge period by comparing the delay voltage and a predetermined first reference voltage.

20. The method of claim 19 , wherein detecting the compensated discharge period further comprises determining a termination instant of the compensated discharge period by comparing the delay voltage and a predetermined second reference voltage.

21. The method of claim 18 , wherein the detecting the compensated discharge period comprises determining a start instant of the compensated discharge period to be an instant at which the snubber current flowing from the turn-off instant of the power switch becomes zero current.