Power conversion circuit and control method thereof

Abstract

A power conversion circuit includes a first transformer, a second transformer, a first switch, a second switch, an extension switch, and a control circuit. The first transformer includes a first primary coil and a second primary coil that generates a first primary current. The second transformer includes a second primary coil and a second primary coil that generates a second primary current. The first switch is coupled between the first primary coil and a first output voltage. The second switch is coupled between the second primary coil and a second output voltage. The extension switch is coupled between the first switch and the second switch. The control circuit magnetizes the first and second transformers in a time-division multiplexing manner.

Claims

1. A power conversion circuit, comprising: A first transformer includes a first primary coil and a second primary winding, wherein the first primary coil receives an input voltage and the second primary winding generates a first primary current; a first primary switch electrically connects the first primary coil to a ground terminal based on a first primary control signal; a second transformer includes a second primary coil and a second secondary coil, wherein the second primary coil receives the input voltage and the second secondary winding generates a second secondary current; a second primary switch electrically connects the second primary coil to the ground terminal based on a second primary control signal; a first switch coupled between the first primary winding and a first output voltage; a second switch coupled between the second secondary winding and a second output voltage; an extension switch coupled between the first switch and the second switch; and a control circuit that drives the first primary switch and the second primary switch to magnetize the first transformer and the second transformer respectively, and operates in a first mode and a second mode; When the control circuit operates in the first mode, both the first switch and the extension switch are turned on and the second open relationship is turned off, so that both the primary current and the secondary current supply power to the first output voltage. When the control circuit operates in the second mode, both the first switch and the second switch are turned on and the extension open relationship is turned off, so that the primary current and the secondary current supply power to the first output voltage and the second output voltage, respectively. The operating circuit uses a switching frequency to time-division turn on the first primary switch and the second primary switch.

2. The power conversion circuit of claim 1, wherein the switching frequency is adjustable; wherein there is a phase difference between the conduction of the first primary switch and the conduction of the second primary switch; wherein the control circuit adjusts the phase difference so that the conduction time of the first primary switch and the conduction time of the second primary switch are staggered.

3. The power conversion circuit of claim 1 further includes: A first synchronous rectification unit is coupled between the first primary coil and the first switch, so that the first primary current flows unidirectionally to the first switch or the extension switch. A second synchronous rectification unit is coupled between the second stage coil and the second switch, such that the second stage current flows unidirectionally to the second switch or the extension switch.

4. The power conversion circuit of claim 1, wherein when the control circuit operates in the first mode, the first switch and the extended open relationship are turned on and the second open relationship is turned off, such that the first stage current and the second stage current both supply power to the first output voltage.

5. The power conversion circuit of claim 1, wherein when the control circuit operates in the second mode, the first switch and the second open relationship are turned on and the extended open relationship is turned off, such that the first stage current independently supplies power to the first output voltage and the second stage current independently supplies power to the second output voltage.

6. The power conversion circuit of claim 1, wherein when the control circuit operates in a third mode, the second switch and the extended open relationship are turned on and the first open relationship is turned off, such that both the first stage current and the second stage current supply power to the second output voltage.

7. The power conversion circuit of claim 6, wherein the control circuit further includes: A first error amplifier compares a first output voltage with a first reference voltage to generate a first error signal; a second error amplifier compares a second output voltage with a second reference voltage to generate a second error signal; a first multiplexer outputs one of the first error signal and the second error signal as a first selection signal based on the states of the first switch, the second switch, and the extension switch; a second multiplexer outputs one of the first error signal and the second error signal as a second selection signal based on the states of the first switch, the second switch, and the extension switch; a first isolation circuit generates a first feedback signal based on the first selection signal; a second isolation circuit generates a second feedback signal based on the second selection signal; a first signal generation circuit drives the first primary switch based on the first feedback signal; and a second signal generation circuit drives the second primary switch based on the second feedback signal.

8. The power conversion circuit of claim 7, wherein when the control circuit operates in the first mode, both the first signal generating circuit and the second signal generating circuit extend the conduction time of the first primary switch and the second primary switch based on the first output voltage being less than the first reference voltage; wherein when the control circuit operates in the first mode, both the first signal generating circuit and the second signal generating circuit shorten the conduction time of the first primary switch and the second primary switch based on the first output voltage being not less than the first reference voltage.

9. The power conversion circuit of claim 7, wherein when the control circuit operates in the second mode, the first signal generating circuit turns on the first primary switch based on the first output voltage being less than the first reference voltage, and the second signal generating circuit turns on the second primary switch based on the second output voltage being less than the second reference voltage; wherein when the control circuit operates in the second mode, the first signal generating circuit shortens the on-time of the first primary switch based on the first output voltage being not less than the first reference voltage, and the second signal generating circuit shortens the on-time of the second primary switch based on the second output voltage being not less than the second reference voltage; wherein when the control circuit operates in the second mode, the first signal generating circuit extends the on-time of the first primary switch based on the first output voltage being less than the first reference voltage, and the second signal generating circuit extends the on-time of the second primary switch based on the second output voltage being less than the second reference voltage.

10. The power conversion circuit of claim 7, wherein when the control circuit operates in the third mode, both the first signal generating circuit and the second signal generating circuit extend the conduction time of the first primary switch and the second primary switch based on the second output voltage being less than the second reference voltage; wherein when the control circuit operates in the third mode, both the first signal generating circuit and the second signal generating circuit shorten the conduction time of the first primary switch and the second primary switch based on the second output voltage being not less than the second reference voltage.

11. The power conversion circuit of claim 1 further includes: A third switch is coupled between the first stage coil and a third output voltage; wherein when the third switch is turned on, the first stage current supplies power to the third output voltage.

12. The power conversion circuit of claim 11 further includes: A fourth switch is coupled between the second stage coil and a fourth output voltage; wherein when the fourth switch is turned on, the second stage current supplies power to the fourth output voltage.

13. The power conversion circuit of claim 12 further includes: An additional extension switch is coupled between the third switch and the fourth switch.

14. A control method for controlling a power conversion circuit to convert an input voltage into a first output voltage and a second output voltage, wherein the power conversion circuit includes a first transformer and a second transformer, and wherein the control method includes: The first transformer is magnetized using the input voltage for a first magnetization time; when the first transformer is demagnetized, a primary current generated by the secondary coil of the first transformer is used to supply power to one of the first output voltage and the second output voltage; the second transformer is magnetized using the input voltage for a second magnetization time; and when the second transformer is demagnetized, a secondary current generated by the secondary coil of the second transformer is used to supply power to one of the first output voltage and the second output voltage.

15. The control methods as described in Request 14 further include: The power conversion circuit is determined to be operating in one of a first mode, a second mode, and a third mode; when operating in the first mode, the first output voltage is powered by the first stage current and the second stage current; when operating in the second mode, the first output voltage is powered by the first stage current and the second output voltage is powered by the second stage current; and when operating in the third mode, the second output voltage is powered by the first stage current and the second stage current.

16. The control methods described in Request 15 further include: When operating in the first mode, the relationship between the first output voltage and a first reference voltage is determined; when the first output voltage is less than the first reference voltage, the first magnetization time and the second magnetization time are extended based on the difference between the first output voltage and the first reference voltage; and when the first output voltage is not less than the first reference voltage, the first magnetization time and the second magnetization time are shortened based on the difference between the first output voltage and the first reference voltage.

17. The control methods described in Request 15 further include: When operating in the second mode described above, the relationship between the first output voltage and a first reference voltage, and the relationship between the second output voltage and a second reference voltage are determined; when the first output voltage is less than the first reference voltage, the first magnetization time is extended based on the difference between the first output voltage and the first reference voltage; when the first output voltage is not less than the first reference voltage, the first magnetization time is shortened based on the difference between the first output voltage and the first reference voltage; when the second output voltage is less than the second reference voltage, the second magnetization time is extended based on the difference between the second output voltage and the second reference voltage; and when the second output voltage is not less than the second reference voltage, the second magnetization time is shortened based on the difference between the second output voltage and the second reference voltage.

18. The control methods described in Request 15 further include: When operating in the third mode described above, the relationship between the second output voltage and a second reference voltage is determined; when the second output voltage is less than the second reference voltage, the first magnetization time and the second magnetization time are extended based on the difference between the second output voltage and the second reference voltage; and when the second output voltage is not less than the second reference voltage, the first magnetization time and the second magnetization time are shortened based on the difference between the second output voltage and the second reference voltage.

19. The control method of claim 14, wherein there is an interval between the first magnetization time and the second magnetization time; wherein the interval is not less than zero.

20. The control methods as described in request item 14 further include: The first magnetization time ends when the first primary current flowing through the first primary coil of one of the first transformers is not less than a first threshold value; and the second magnetization time ends when the second primary current flowing through the second primary coil of one of the second transformers is not less than a second threshold value.

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