Converter and power adapter
This application discloses a converter and a power adapter, to reduce an energy loss of the power adapter. The converter includes a direct current power supply, a main power transistor, an auxiliary power transistor, a first capacitor, a transformer, and a control circuit. The first capacitor and the transformer are connected in series to form a series circuit. The series circuit is connected to a first terminal and a second terminal of the auxiliary power transistor in parallel. The control circuit is configured to: when the main power transistor is in a cutoff state and a target voltage reaches a target valley voltage, control the main power transistor to be conducted. The target voltage is a voltage between the first terminal of the main power transistor and the ground.
1. A converter, comprising:
a direct current power supply;
a main power transistor;
an auxiliary power transistor
a first capacitor
a transformer
a control circuit; and
wherein:
the first capacitor and the transformer are connected in series to form a series circuit, the series circuit is connected to a first terminal and a second terminal of the auxiliary power transistor in parallel, a first terminal of the main power transistor is connected to the second terminal of the auxiliary power transistor, a second terminal of the main power transistor is connected to one of a positive electrode or a negative electrode of the direct current power supply, the first terminal of the auxiliary power transistor is connected to the other electrode of the direct current power supply, and the negative electrode is grounded; and
the control circuit is configured to:
when the main power transistor is in a cutoff state and a target voltage reaches a target valley voltage, control the main power transistor to be conducted, wherein the target voltage is a voltage between the first terminal of the main power transistor and the ground, and the target valley voltage is a voltage of at least one waveform valley in the target voltage when the converter operates;
detect an excitation current in the transformer when the excitation current in the transformer is discontinuous and the auxiliary power transistor is conducted; and
when the excitation current is equal to 0, control the auxiliary power transistor to be cut off.
2. The converter according to claim 1 , wherein the control circuit is configured to:
detect the target voltage when the main power transistor is in the cutoff state;
determine, based on a preset policy, whether the target voltage reaches the target valley voltage;
if the target voltage reaches the target valley voltage, control the main power transistor to be conducted; and
after the main power transistor is cut off and a dead time period passes, control the auxiliary power transistor to be conducted, wherein the dead time period is a time period in which the main power transistor is cut off and the auxiliary power transistor is not conducted.
3. The converter according to claim 1 , wherein
the control circuit is further configured to:
determine a comparison result between the target voltage and a preset voltage threshold, and
adjust conduction duration of the auxiliary power transistor based on the comparison result.
4. The converter according to claim 3 , wherein the second terminal of the main power transistor is connected to the negative electrode, and the first terminal of the auxiliary power transistor is connected to the positive electrode; and
the control circuit is further configured to: lengthen next conduction duration of the auxiliary power transistor based on current conduction duration of the auxiliary power transistor when the comparison result indicates that the target voltage is greater than the preset voltage threshold; or shorten next conduction duration of the auxiliary power transistor based on current conduction duration of the auxiliary power transistor when the comparison result indicates that the target voltage is less than the preset voltage threshold.
5. The converter according to claim 3 , wherein the second terminal of the main power transistor is connected to the positive electrode, and the first terminal of the auxiliary power transistor is connected to the negative electrode; and
the control circuit is further configured to:
shorten next conduction duration of the auxiliary power transistor based on current conduction duration of the auxiliary power transistor when the comparison result indicates that the target voltage is greater than the preset voltage threshold; or
lengthen next conduction duration of the auxiliary power transistor based on current conduction duration of the auxiliary power transistor when the comparison result indicates that the target voltage is less than the preset voltage threshold.
6. The converter according to claim 3 , wherein
the control circuit is further configured to: repeatedly adjust the conduction duration of the auxiliary power transistor based on an adaptive policy, and
adjust the target voltage to the preset voltage threshold when the target voltage reaches a first valley voltage in an operating waveform of the target voltage.
7. The converter according to claim 1 , wherein when the converter operates, an operating waveform of the excitation current in the transformer comprises at least one of a continuous waveform or a discontinuous waveform;
if the operating waveform of the excitation current is a continuous waveform when the target voltage reaches the first valley voltage, the control circuit controls, when the target voltage reaches the first valley voltage, the main power transistor to be conducted; and
if the operating waveform of the excitation current is a discontinuous waveform when the target voltage reaches the first valley voltage, the control circuit maintains the main power transistor in the cutoff state, and when the target voltage reaches an m th valley voltage, controls the main power transistor to be conducted, wherein m is an integer greater than 1.
8. The converter according to claim 1 , wherein the control circuit comprises a detection circuit, a power transistor control circuit, a first drive circuit, and a second drive circuit, wherein the power transistor control circuit is separately connected to the detection circuit, the first drive circuit, and the second drive circuit; the first drive circuit is connected to the main power transistor; and the second drive circuit is connected to the auxiliary power transistor;
the detection circuit is configured to detect the target voltage;
the power transistor control circuit is configured to send a drive signal for the first drive circuit or the second drive circuit based on a detection result of the detection circuit;
the first drive circuit is configured to drive, based on the drive signal, the main power transistor to be conducted or cut off; and
the second drive circuit is configured to drive, based on the drive signal, the auxiliary power transistor to be conducted or cut off.
9. The converter according to claim 1 , wherein the converter further comprises a second capacitor, and two terminals of the second capacitor are respectively connected to the positive electrode and the negative electrode.
10. The converter according to claim 1 , wherein the transformer comprises a primary-side winding and a secondary-side winding, a dotted terminal of the primary-side winding is connected to the first capacitor, and a dotted terminal of the secondary-side winding is grounded.
11. The converter according to claim 1 wherein the transformer comprises a primary-side winding and a secondary-side winding, a dotted terminal of the primary-side winding is connected to the first capacitor, and a dotted terminal of the secondary-side winding is connected to a secondary-side synchronous rectifier.
12. A converter, comprising:
a direct current power supply;
a main power transistor;
an auxiliary power transistor;
a first capacitor;
a transformer;
a control circuit;
wherein:
the first capacitor and the auxiliary power transistor are connected in series to form a series circuit, the series circuit is connected to two terminals of the transformer in parallel, a first terminal of the main power transistor is connected to a second terminal of the auxiliary power transistor, a second terminal of the main power transistor is connected to one of a positive electrode or a negative electrode of the direct current power supply, one terminal that is of the first capacitor and that is connected to the transformer is connected to the other electrode of the direct current power supply, and the negative electrode is grounded; and
the control circuit is configured to:
when the main power transistor is in a cutoff state and a target voltage reaches a target valley voltage, control the main power transistor to be conducted, wherein the target voltage is a voltage between the first terminal of the main power transistor and the ground, and the target valley voltage is a voltage of at least one waveform valley in the target voltage when the converter operates;
detect an excitation current in the transformer when the excitation current in the transformer is discontinuous and the auxiliary power transistor is conducted; and
control the auxiliary power transistor to be cut off when the excitation current is equal to 0.
13. The converter according to claim 12 , wherein the transformer comprises a primary-side winding and a secondary-side winding, a dotted terminal of the primary-side winding is connected to the positive electrode or the first terminal of the main power transistor, and a dotted terminal of the secondary-side winding is grounded.
14. A power adapter, comprising:
a converter,
an alternating current-direct current conversion circuit,
a filter circuit,
wherein:
the filter circuit is separately connected to the alternating current-direct current conversion circuit and the converter;
the alternating current-direct current conversion circuit is configured to convert an alternating current in a power grid into a direct current;
the converter is configured to supply a direct current voltage to a load, wherein the converter comprises a direct current power supply, a main power transistor, an auxiliary power transistor, a first capacitor, a transformer, and a control circuit,
the first capacitor and the transformer are connected in series to form a series circuit,
the series circuit is connected to a first terminal and a second terminal of the auxiliary power transistor in parallel, a first terminal of the main power transistor is connected to the second terminal of the auxiliary power transistor, a second terminal of the main power transistor is connected to one of a positive electrode or a negative electrode of the direct current power supply, the first terminal of the auxiliary power transistor is connected to the other electrode of the direct current power supply, and the negative electrode is grounded; and
the control circuit is configured to:
when the main power transistor is in a cutoff state and a target voltage reaches a target valley voltage, control the main power transistor to be conducted, wherein the target voltage is a voltage between the first terminal of the main power transistor and the ground, and the target valley voltage is a voltage of at least one waveform valley in the target voltage when the converter operates;
the filter circuit is configured to filter out noise in the alternating current-direct current conversion circuit and the converter;
detect an excitation current in the transformer when the excitation current in the transformer is discontinuous and the auxiliary power transistor is conducted; and
control the auxiliary power transistor to be cut off when the excitation current is equal to 0.
15. The converter according to claim 14 , wherein
the control circuit is configured to: detect the target voltage when the main power transistor is in the cutoff state; determine, based on a preset policy, whether the target voltage reaches the target valley voltage; if the target voltage reaches the target valley voltage, control the main power transistor to be conducted; and after the main power transistor is cut off and a dead time period passes, control the auxiliary power transistor to be conducted, wherein the dead time period is a time period in which the main power transistor is cut off and the auxiliary power transistor is not conducted.
16. The converter according to claim 14 , wherein the control circuit is further configured to: determine a comparison result between the target voltage and a preset voltage threshold, and adjust conduction duration of the auxiliary power transistor based on the comparison result.
17. The converter according to claim 16 , wherein the second terminal of the main power transistor is connected to the negative electrode, and the first terminal of the auxiliary power transistor is connected to the positive electrode; and
the control circuit is configured to:
lengthen next conduction duration of the auxiliary power transistor based on current conduction duration of the auxiliary power transistor when the comparison result indicates that the target voltage is greater than the preset voltage threshold; or
shorten next conduction duration of the auxiliary power transistor based on current conduction duration of the auxiliary power transistor when the comparison result indicates that the target voltage is less than the preset voltage threshold.
18. The converter according to claim 16 , wherein the second terminal of the main power transistor is connected to the positive electrode, and the first terminal of the auxiliary power transistor is connected to the negative electrode; and
the control circuit is configured to: shorten next conduction duration of the auxiliary power transistor based on current conduction duration of the auxiliary power transistor when the comparison result indicates that the target voltage is greater than the preset voltage threshold; or lengthen next conduction duration of the auxiliary power transistor based on current conduction duration of the auxiliary power transistor when the comparison result indicates that the target voltage is less than the preset voltage threshold.
19. The converter according to claim 16 , wherein
the control circuit is configured to: repeatedly adjust the conduction duration of the auxiliary power transistor based on an adaptive policy, and adjust the target voltage to the preset voltage threshold when the target voltage reaches a first valley voltage in an operating waveform of the target voltage.