Power supply apparatus with drive control signal inversion based upon resonance current level detection

1. A switching power supply apparatus, comprising:

a DC power supply including a high-side terminal and a low-side terminal;

a first switching element and a second switching element, connected in series between the high-side terminal and the low-side terminal of the DC power supply;

a resonance inductor and a resonance capacitor, connected in series to an connection point for the first and second switching elements;

an output circuit configured to supply power to a load based on a resonance current provided by the resonance inductor and the resonance capacitor;

a current detection unit configured to detect a resonance current passing through at least one of the first switching element and the second switching element; and

a control circuit configured

to generate a drive control signal at levels at which the first switching element and the second switching element are alternately turned on or off,

to control a cycle of the drive control signal according to the detection signal from the current detection unit so that the output power from the output circuit is maintained constant,

to perform at least one of

detecting whether or not the resonance current detected by the current detection unit is beyond a first detection level over a predetermined time period, and detecting, in a case of detecting that the resonance current is beyond the first detection level over the predetermined time period, that the resonance current falls below a second detection level, and

detecting whether or not the resonance current detected by the current detection unit is below a first detection level over a predetermined time period, and detecting, in a case of detecting that the resonance current is below the first detection level over the predetermined time period, that the resonance current exceeds a second detection level, and

to invert, in a case of detecting that the resonance current falls below or exceeds the second detection level, the levels of the drive control signal at which the first switching element and the second switching element are turned on or off.

2. The switching power supply apparatus according to claim 1 , wherein

the control circuit includes a phase control unit and a pulse shaping unit,

the phase control unit including

a first level detection unit configured to detect at least one of

whether or not the resonant current detected by the current detection unit is beyond the first detection level, and

whether or not the resonant current detected by the current detection unit is below the first detection level,

a level-duration detection unit configured to detect whether or not one of a state in which the resonance current is beyond the first detection level and a state in which the resonance current is below the first detection level remains over the predetermined time period, and

a second level detection-and-output unit configured

to perform at least one of

detecting, in a case where the state in which the resonance current is beyond the first detection level remains over the predetermined time period, whether or not the resonance current falls below the second detection level, and

detecting, in a case where the state in which the resonance current is below the first detection level remains over the predetermined time period, whether or not the resonance current exceeds the second detection level, and

to output a detection signal according to the detected result,

the pulse shaping unit being configured

to shape a drive control pulse as the drive control signal turning on or off the first switching element and the second switching element,

to receive the detection signal from the second level detection-and-output unit of the phase control unit, the detection signal indicating that the resonance current falls below or exceeds the detection level, and

to invert the levels of the drive control pulse in response to the detection signal.

3. The switching power supply apparatus according to claim 2 , further comprising:

a first positive level detection unit configured to detect whether or not the resonance current detected by the current detection unit is beyond the first positive detection level;

a second positive level detection-and-output unit configured to detect whether or not the resonance current falls below the second positive detection level, in a case where the resonance current is beyond the first positive detection level over the predetermined time period;

a first negative level detection unit configured to detect whether or not the resonance current detected by the current detection unit is below the first negative detection level; and

a second negative level detection-and-output unit configured to detect whether or not the resonance current exceeds the second negative detection level, in a case where the resonance current is below the first negative detection level over the predetermined time period.

4. The switching power supply apparatus according to claim 3 , wherein

the second positive level detection-and-output unit includes

a second positive level detection unit configured to detect whether or not the resonance current falls below the second positive detection level, and

an output unit configured to output the detection signal according to the detection result from the level-duration detection unit and the result from the second positive level detection unit, to the pulse shaping unit,

the second negative level detection-and-output unit includes

a second negative level detection unit configured to detect whether or not the resonance current exceeds the second negative detection level, and

an output unit configured to output the detection signal according to the detection result from the level-duration detection unit and the result from the second negative level detection unit, to the pulse shaping unit, and

the output unit is shared by the first positive level detection unit, the second positive level detection unit, the first negative level detection unit, and the second negative level detection unit, the output unit supplying the signals according to the detection result from the level-duration detection unit and the detection results from the second positive and negative level detection units.

5. The switching power supply apparatus according to claim 3 , wherein

the pulse shaping unit in the control circuit is configured

to generate a first drive control pulse for driving the first switching element connected to the high-side terminal, and

to generate a second drive control pulse for driving the second switching element connected to the low-side terminal, the second drive control pulse having a complementary level to a level of the first drive control pulse, and

the phase control unit is configured

to select and process a signal from the first positive level detection unit and a signal from the second positive level detection-and-output unit, in a case where the first drive control pulse is at a level at which the first switching element is turned on, and

to select and process a signal from the first negative level detection unit and a signal from the second negative level detection-and-output unit, in a case where the second drive control pulse is at a level at which the second switching element is turned on.

6. The switching power supply apparatus according to claim 1 , wherein

the first detection level and the second detection level are equal to each other.

7. The switching power supply apparatus according to claim 1 , wherein

the predetermined time period varies according to a frequency of the first switching element and a frequency of the second switching element.

8. The switching power supply apparatus according to claim 1 , wherein

the control circuit employs, as the predetermined time period for an off-resonance valid condition, a predetermined latter time period of each pulse, the off-resonance state being detected by performing at least one of

detecting whether or not the resonance current detected by the current detection unit is beyond a first detection level over a predetermined time period, and detecting, in a case of detecting that the resonance current is beyond the first detection level over the predetermined time period, that the resonance current falls below a second detection level, and

detecting whether or not the resonance current detected by the current detection unit is below a first detection level over a predetermined time period, and detecting, in a case of detecting that the resonance current is below the first detection level over the predetermined time period, that the resonance current exceeds a second detection level as off-resonance.