Protection circuit, resonant converter including the protection circuit, and protecting method of the resonant converter

1. A resonance converter having first and second switches, comprising:

a sense resistor coupled to receive a first current flowing through the first switch; and

a protection circuit coupled to the sense resistor, the protection circuit measuring a sense voltage developed on the sense resistor by the first current to determine a direction of the first current through the first switch based on a polarity of the sense voltage, determining a length of a time period during which the first current is detected to be flowing in a negative direction through the first switch, comparing the length of the time period to a predetermined reference time period when the first switch is turned off, and detecting a zero voltage switching (ZVS) failure when the length of the time period is shorter than the predetermined reference time period.

2. The resonance converter of claim 1 , further comprising:

stopping switching of the first and second switches upon detection of a ZVS failure.

3. The resonance converter of claim 1 , wherein the protection circuit comprises:

a width measurement comparator comparing the sense voltage and a first reference voltage to generate a level detection signal;

a timer using the level detection signal to generate a width detection voltage corresponding to the length of the time period during which the first current is detected to be flowing in the negative direction through the first switch; and

a ZVS determination comparator comparing the width detection voltage and a second reference voltage when the first switch is turned off to determine a ZVS failure according to the comparison result.

4. The resonance converter of claim 3 , wherein the protection circuit further comprises a ZVS detection controller detecting turn-on/off of the first switch, controlling the ZVS determination comparator to compare the width detection voltage and the second reference voltage when the first switch is turned off, and resetting the width detection voltage after a predetermined delay period from a turn-off time of the first switch.

5. The resonance converter of claim 4 , wherein the timer comprises:

a charge switch being turned on/off according to the level detection signal;

a current source connected to a first end of the charge switch;

a capacitor having a first end connected to a second end of the charge switch; and

a discharge switch connected in parallel with the capacitor,

wherein a voltage at the first end of the capacitor is the width detection voltage.

6. The resonance converter of claim 5 , wherein the ZVS detection controller turns on the discharge switch after the predetermined delay period.

7. The resonance converter of claim 6 , wherein the ZVS determination comparator comprises:

a first input terminal;

a second input terminal to which the second reference voltage is input; and

a switch having a first end connected to the first input terminal, transmitting the width detection voltage to the first input terminal during a predetermined comparison period from the turn-off time of the first switch, and transmitting a source voltage to the first input terminal during a turn-on period of the first switch.

8. The resonance converter of claim 3 , wherein the protection circuit further comprises a protection signal generator receiving a ZVS failure signal from the ZVS determination comparator and generating a protection signal to stop switching of the first and second switches, and

the resonance converter further comprises a gate driver that stops switching of the first and second switches according to the protection signal.

9. The resonance converter of claim 3 , wherein the protection circuit further comprises a protection signal generator receiving a ZVS failure signal from the ZVS determination comparator and generating a protection signal for increasing switching frequencies of the first and second switches, and

the resonance converter further comprises a gate driver that increases the switching frequencies of the first and second switches according to the protection signal.

10. A protection method of a resonance converter having first and second switches, comprising:

generating a sense voltage indicative of direction of a first current flowing through the first switch;

using the sense voltage to measure a length of a time period during which the first current is flowing in a negative direction through the first switch; and

detecting a zero voltage switching (ZVS) failure when the length of the time period during which the first current is flowing in the negative direction through the first switch is shorter than a predetermined reference time period.

11. The protection method of claim 10 , wherein using the sense voltage to measure the length of the time period during which the first current is flowing in the negative direction through the first switch comprises:

generating a level detection signal by comparing the sense voltage and a predetermined first reference voltage; and

using the level detection signal to generate a width detection voltage corresponding to the length of the time period during which the first current is flowing in the negative direction through the first switch.

12. The protection method of claim 11 , wherein detecting the zero voltage switching (ZVS) failure comprises comparing the width detection voltage and a second reference voltage when the first switch is turned off.

13. The protection method of claim 12 , further comprising turning off the first and second switches when the ZVS failure is detected.

14. The protection method of claim 13 , further comprising increasing operation frequencies of the first and second switches when the ZVS failure is detected.