Switching power supply including threshold based permissions
Aspects of the invention provide a switching power supply that exhibits an improved conversion efficiency. In aspects of the invention, a load condition detecting circuit sets a threshold voltage for determining the magnitude of the load on the DC-DC converter based on the maximum value of the output voltage of the power factor correction converter in a suspended period of the power factor correction converter. An operation permission signal is delivered when a feedback voltage that indicates the magnitude of the load of the DC-DC converter exceeds the threshold voltage. When the feedback voltage exceeds a threshold voltage that is set at a value higher than the threshold voltage, the operation permission signal is delivered.
1. A switching power supply comprising:
a power factor correction converter that conducts switching of an input AC voltage to obtain a DC voltage;
a DC-DC converter that conducts switching of an output voltage of the power factor correction converter to obtain a specified DC output voltage; and
a load condition detecting circuit that delivers an operation permission signal to the power factor correction converter corresponding to a load condition of the DC-DC converter and permits or stops operation of the power factor correction converter;
wherein the load condition detecting circuit
sets a second threshold voltage and a third threshold voltage for determining a magnitude of the load on the DC-DC converter based on the maximum value of the output voltage of the power factor correction converter in a suspended state of operation of the power factor correction converter;
delivers the operation permission signal when a signal indicating the magnitude of the load on the DC-DC converter changes from being below the second threshold voltage to exceeding the second threshold voltage for a specified period of time in a suspended state of operation of the power factor correction converter; and
delivers the operation permission signal when the signal indicating the magnitude of the load on the DC-DC converter changes from being below the third threshold voltage to exceeding the third threshold voltage in a suspended state of operation of the power factor correction converter.
2. The switching power supply according to claim 1 , wherein the DC-DC converter is a quasi-resonance converter.
3. A switching power supply comprising:
a power factor correction converter that conducts switching of an input AC voltage to obtain a DC voltage;
a DC-DC converter that conducts switching of an output voltage of the power factor correction converter to obtain a specified DC output voltage; and
a load condition detecting circuit that delivers an operation permission signal to the power factor correction converter corresponding to a load condition of the DC-DC converter and permits or stops operation of the power factor correction converter;
wherein the load condition detecting circuit
sets a second threshold voltage and a third threshold voltage for determining a magnitude of the load on the DC-DC converter based on the maximum value of the output voltage of the power factor correction converter in a suspended state of operation of the power factor correction converter;
delivers the operation permission signal when a signal indicating the magnitude of the load on the DC-DC converter exceeds the second threshold voltage for a specified period of time in a suspended state of operation of the power factor correction converter; and
delivers the operation permission signal when the signal indicating the magnitude of the load on the DC-DC converter exceeds the third threshold voltage in a suspended state of operation of the power factor correction converter wherein
the load condition detecting circuit comprises, in a suspended state of operation of the power factor correction converter,
a voltage detecting means that detects the maximum value of the output voltage of the power factor correction converter,
the load condition detecting circuit sets the second threshold voltage and the third threshold voltage for determining the magnitude of the load on the DC-DC converter corresponding to the maximum value of the output voltage that is detected by the voltage detecting means.
4. A switching power supply comprising:
a power factor correction converter that conducts switching of an input AC voltage to obtain a DC voltage;
a DC-DC converter that conducts switching of an output voltage of the power factor correction converter to obtain a specified DC output voltage; and
a load condition detecting circuit that delivers an operation permission signal to the power factor correction converter corresponding to a load condition of the DC-DC converter and permits or stops operation of the power factor correction converter;
wherein the load condition detecting circuit
sets a second threshold voltage and a third threshold voltage for determining a magnitude of the load on the DC-DC converter based on the maximum value of the output voltage of the power factor correction converter in a suspended state of operation of the power factor correction converter;
delivers the operation permission signal when a signal indicating the magnitude of the load on the DC-DC converter exceeds the second threshold voltage for a specified period of time in a suspended state of operation of the power factor correction converter; and
delivers the operation permission signal when the signal indicating the magnitude of the load on the DC-DC converter exceeds the third threshold voltage in a suspended state of operation of the power factor correction converter wherein
the second threshold voltage and the third threshold voltage are set as threshold voltages for a feedback voltage that is used for controlling a DC output voltage in the DC-DC converter, and
the load condition detecting circuit comprises:
a flip-flop that delivers the operation permission signal when the flip-flop is reset;
a light load detecting circuit that sets the flip-flop when the feedback voltage falls below a predetermined first threshold voltage;
a middle load detecting circuit that resets the flip-flop when the feedback voltage exceeds, for a specified period of time, the second threshold voltage that is higher than the first threshold voltage and determined based on the maximum value of an input voltage to the DC-DC converter; and
a heavy load detecting circuit that resets the flip-flop forcedly when the feedback voltage exceeds the third threshold voltage that is set at a value higher than the second threshold voltage.
5. The switching power supply according to claim 4 , wherein the specified period of time set in the middle load detecting circuit is about a half period of the AC power or longer.
6. A switching power supply comprising:
a power factor correction converter that conducts switching of an input AC voltage to obtain a DC voltage;
a DC-DC converter that conducts switching of an output voltage of the power factor correction converter to obtain a specified DC output voltage; and
a load condition detecting circuit that delivers an operation permission signal to the power factor correction converter corresponding to a load condition of the DC-DC converter and permits or stops operation of the power factor correction converter;
wherein the load condition detecting circuit
sets a second threshold voltage and a third threshold voltage for determining a magnitude of the load on the DC-DC converter based on the maximum value of the output voltage of the power factor correction converter in a suspended state of operation of the power factor correction converter;
delivers the operation permission signal when a signal indicating the magnitude of the load on the DC-DC converter exceeds the second threshold voltage for a specified period of time in a suspended state of operation of the power factor correction converter; and
delivers the operation permission signal when the signal indicating the magnitude of the load on the DC-DC converter exceeds the third threshold voltage in a suspended state of operation of the power factor correction converter wherein
the second threshold voltage and the third threshold voltage are set as threshold voltages for a periodic voltage that is proportional to a period of time of an ON/OFF driving period of an switching element in the DC-DC converter, and
the load condition detecting circuit comprises:
a flip-flop that delivers the operation permission signal when the flip-flop is reset;
a light load detecting circuit that sets the flip-flop when the periodic voltage falls below a predetermined first threshold voltage;
a middle load detecting circuit that resets the flip-flop when the periodic voltage exceeds, for a specified period of time, the second threshold voltage that is higher than the first threshold voltage and determined based on the maximum value of an input voltage to the DC-DC converter; and
a heavy load detecting circuit that resets the flip-flop forcedly when the periodic voltage exceeds the third threshold voltage that is set at a value higher than the second threshold voltage.
7. The switching power supply according to claim 6 , wherein the specified period of time set in the middle load detecting circuit is about a half period of the AC power or longer.