Power converter and driving method thereof

1. A power converter comprising:

a primary coil configured to receive an input voltage;

a switch, including a first electrode, a second electrode coupled to the primary coil, and a control electrode;

an output unit, including a secondary coil, the output unit configured to output an output voltage, the primary coil and the secondary coil forming a transformer, and the input voltage being converted to the output voltage by the transformer; and

a controller configured

to receive a sensing voltage corresponding to a switch current flowing between the first electrode and the second electrode of the switch;

to detect a maximum value of the switch current based on the sensing voltage;

to detect a valley point of a voltage between the first electrode and the second electrode of the switch based on the sensing voltage; and

to transmit a control signal having a first voltage for turning on the switch and a second voltage for turning off the switch to the control electrode of the switch in accordance with the valley point,

wherein an off period in which the control signal has the second voltage includes a first period and a second period, and

wherein the controller is configured to calculate the first period of the off period based on the maximum value of the switch current, and to detect the valley point by using a third period in which the control signal has the first voltage, the calculated first period, and the second period.

2. The power converter of claim 1 , wherein the valley point is a time when the voltage between the first electrode and the second electrode of the switch substantially reaches a valley.

3. The power converter of claim 1 , wherein

the controller is configured to set the control signal to the first voltage in response to the valley point.

4. The power converter of claim 1 , wherein

the first period is substantially the same as a period in which the magnetizing current is changed from the maximum value to 0 A; and

the off period is substantially the same as a sum of the first period and the second period.

5. The power converter of claim 1 , wherein the controller is configured to calculate the second period based on a magnetizing inductance component of the transformer and a capacitance component of the switch.

6. The power converter of claim 5 , wherein the second period is substantially the same as a half resonance cycle between the magnetizing inductance component and the capacitance component.

7. The power converter of claim 1 , wherein the first period is determined by a magnetizing inductance component of the transformer, the maximum value, the output voltage, and a ratio of the number of turns of the primary coil to the number of turns of the secondary coil.

8. The power converter of claim 7 , wherein the first period is substantially the same as a value obtained by dividing a product of an inductance of the magnetizing inductance component and the maximum value by a product of the output voltage and the ratio.

9. The power converter of claim 1 , wherein the first period is determined by a magnetizing inductance component of the transformer, the maximum value, and a voltage of the primary coil when the switch is turned off.

10. The power converter of claim 1 , wherein the controller comprises:

an oscillator configured to generate a clock signal in response to the valley point;

a comparator configured to output a first signal according to a comparison between the sensing voltage and the feedback voltage;

a flip-flop configured to output a second signal in accordance with the first signal and the clock signal;

a logic circuit configured to output a third signal by a logic operation of the clock signal and the second signal; and

a gate driver configured to generate the control signal in response to the third signal.

11. A power converter comprising:

a primary coil configured to receive an input voltage;

a switch, including a first electrode, a second electrode coupled to the primary coil, and a control electrode;

an output unit, including a secondary coil, and configured to output an output voltage, the primary coil and the secondary coil forming a transformer, and the input voltage being converted to the output voltage by the transformer; and

a controller comprising

a first current source configured to output a first current corresponding to the input voltage when the switch is turned on; and

a second current source configured to output a second current corresponding to a voltage of the primary coil of the transformer when the switch is turned off, and

configured

to receive the input voltage;

to detect a valley point of a voltage between the first electrode and the second electrode of the switch by using the first current source and the second current source; and

to transmit a control signal to the control electrode of the switch in accordance with the valley point.

12. The power converter of claim 11 , wherein the valley point is a time when the voltage between the first electrode and the second electrode of the switch substantially reaches a valley.

13. The power converter of claim 11 , wherein

the control signal has a first voltage for turning on the switch or a second voltage for turning off the switch; and

the controller is configured to set the control signal to the first voltage in response to the valley point.

14. The power converter of claim 13 , wherein

an off period in which the control signal has the second voltage includes a first period and a second period;

the controller further comprises a capacitor configured to be charged during a third period in which the control signal has the first voltage, and to be discharged by the second current during the first period; and

the controller is configured to detect a sum of the first period and the third period based on a voltage of the capacitor to detect the valley point.

15. The power converter of claim 14 , wherein the first period is substantially the same as a period in which the magnetizing current is changed from the maximum value to 0 A, and the off period is substantially the same as a summation of the first period and the second period.

16. The power converter of claim 14 , wherein

the controller further comprises a comparator including an inverse terminal coupled to the capacitor and a non-inverse terminal receiving a reference voltage; and

the controller is configured to detect the sum based on an output of the comparator.

17. The power converter of claim 16 , wherein the controller is configured to delay the output of the comparator by the second period to detect the valley point.

18. The power converter of claim 16 , wherein the controller is configured to calculate the second period based on a magnetizing inductance component of the transformer and a capacitance component of the switch.

19. The power converter of claim 18 , wherein the second period is substantially the same as a half resonance cycle between the magnetizing inductance component and the capacitance component.

20. The power converter of claim 11 , wherein the controller comprises:

an oscillator configured to generate a clock signal in response to the valley point;

a comparator configured to output a first signal according to a comparison between a sensing voltage and a feedback voltage, the sensing voltage corresponding to a current flowing between the first electrode and the second electrode of the switch, and the feedback voltage corresponding to the output voltage;

a flip-flop configured to output a second signal in accordance with the first signal and the clock signal;

a logic circuit configured to output a third signal by a logic operation of the clock signal and the second signal; and

a gate driver configured to generate the control signal in response to the third signal.

21. A method of driving a power converter, the converter comprising a transformer including a primary coil receiving an input voltage and a second coil transmitting an output voltage, and a switch including a first electrode, a second electrode coupled to the primary coil, and a control electrode receiving a control signal, the method comprising:

turning on the switch in response to a first voltage of the control signal;

turning off the switch in response to a second voltage of the control signal for an off period;

detecting a maximum value of a current flowing between the first electrode and the second electrode of the switch;

calculating a first period of the off period based on a voltage of the primary coil of the transformer when the switch is turned off and the maximum value of the current;

detecting a second period based on a magnetizing inductance component of the transformer and a capacitance component of the switch;

determining a valley point of a voltage between the first electrode and the second electrode of the switch based on the calculated first period and the second period; and

setting the control signal to the first voltage in response to the valley point.

22. The method of claim 21 , wherein the valley point is a time when the voltage between the first electrode and the second electrode of the switch substantially reaches a valley.

23. The method of claim 21 ,

wherein

the valley point is determined by the first period, the second period, and a third period in which the control signal has the first voltage.

24. A method of driving a power converter, the converter comprising a transformer including a primary coil receiving an input voltage and a second coil transmitting an output voltage, and a switch including a first electrode, a second electrode coupled to the primary coil, and a control electrode receiving a control signal, the method comprising:

turning on the switch in response to a first voltage of the control signal;

turning off the switch in response to a second voltage of the control signal;

determining a valley point of a voltage between the first electrode and the second electrode of the switch based on a first current and a second current, the first current corresponding to the input voltage when the control signal has the first voltage and the second current corresponding to the voltage of the primary coil when the control signal has the second voltage; and

setting the control signal to the first voltage in response to the valley point.

25. The method of claim 21 , wherein the second period is substantially the same as a half resonance cycle between the magnetizing inductance component and the capacitance component.

26. The method of claim 24 , wherein determining the valley point comprises:

charging the first current to a capacitor during a first period in response to the first voltage of the control signal;

discharging the second current to the voltage of the primary coil from the capacitor during a second period in response to the second voltage of the control;

detecting a sum of the first period and the second period based on a voltage of the capacitor; and

determining the valley point by using the sum.

27. The method of claim 26 , further comprising detecting a third period based on a magnetizing inductance component of the transformer and a capacitance component of the switch, and

wherein the valley point is determined by a sum of the first period, the second period, and the third period.