US-12627224-B2 - Resonant power convertor and control method thereof

US12627224B2US 12627224 B2US12627224 B2US 12627224B2US-12627224-B2

Abstract

A resonant power converter includes a resonant capacitor, a transformer, a high-side transistor, a low-side transistor, a divider, a full-wave rectification device, a control circuit, and a rectifying circuit. The resonant capacitor is coupled between a resonant node and a ground. The transformer includes a primary coil coupled between a switch node and the resonant node and a secondary coil. The high-side transistor provides an input voltage to the switch node and the low-side transistor couples the switch node to the ground. The divider divides a voltage of the resonant node to generate a divided signal. The full-wave rectification device full-wave rectifies the divided signal to generate a full-wave rectified signal. The control circuit compares the full-wave rectified signal to a feedback voltage related to an output voltage to drive the high-side transistor and the low-side transistor. The rectifying circuit generates the output voltage.

Inventors

Ta-Yung Yang
Yu-Chang Chen
Kuo-Chi Liu
Tzu-Chen Lin

Assignees

RICHTEK TECHNOLOGY CORPORATION

Dates

Publication Date: 20260512
Application Date: 20240724
Priority Date: 20240506

Claims (20)

1 . A resonant power converter, comprising: a resonant capacitor, coupled between a resonant node and a ground; a transformer, comprising a primary coil and a secondary coil, wherein the primary coil is coupled between a switch node and the resonant node; a high-side transistor, providing an input voltage to the switch node based on a high-side driving signal; a low-side transistor, coupling the switch node to the ground based on a low-side driving signal; a first voltage divider, dividing a voltage of the resonant node to generate a voltage-divided signal; a full-wave rectification device, full-wave rectifying the voltage-divided signal to generate a full-wave rectified signal; a control circuit, comparing the full-wave rectified signal to a feedback voltage to generate the high-side driving signal and the low-side driving signal; a rectifying circuit, coupled to the secondary coil and converting a current flowing through the secondary coil into an output voltage; and a feedback circuit, generating the feedback voltage based on the output voltage.
2 . The resonant power converter as claimed in claim 1 , wherein the full-wave rectification device uses a basic voltage as a DC level and full-wave rectifies the voltage-divided signal to generate the full-wave rectified signal; wherein the basic voltage is equal to a sum of a divided voltage and an offset voltage; wherein the divided voltage is equal to the input voltage multiplied by a first ratio; wherein the full-wave rectification device further compares the full-wave rectified signal with a first threshold voltage to generate a crossover signal; wherein the first threshold voltage slightly exceeds the basic voltage.
3 . The resonant power converter as claimed in claim 2 , wherein when the full-wave rectified signal is less than the first threshold voltage, the full-wave rectification device sets the crossover signal to a disabled state; wherein when the full-wave rectified signal is not less than the first threshold voltage, the full-wave rectification device sets the crossover signal to an enabled state; wherein in response to the crossover signal changing from the disabled state to the enabled state, the control circuit sets a phase signal to the enabled state; wherein in response to the full-wave rectified signal exceeding the feedback voltage, the control circuit sets the phase signal to the disabled state based on a high-side dead time signal or a low-side dead time signal; wherein the high-side dead time signal controls a high-side dead time of the high-side driving signal; wherein the low-side dead time signal controls a low-side dead time of the low-side driving signal.
4 . The resonant power converter as claimed in claim 3 , wherein when the high-side driving signal turns on the high-side transistor and the phase signal is in the enabled state, the control circuit disables the high-side driving signal in response to the full-wave rectified signal exceeding the feedback voltage; wherein when the high-side signal turns off the high-side transistor, the control circuit enables the low-side driving signal to turn on the low-side transistor after the low-side dead time; wherein when the low-side driving signal turns on the low-side transistor and the phase signal is in the enabled state, the control circuit disables the low-side driving signal in response to the full-wave rectified signal exceeding the feedback voltage; wherein when the low-side driving signal turns off the low-side transistor, the control circuit enables the high-side driving signal to turn on the high-side transistor after the high-side dead time.
5 . The resonant power converter as claimed in claim 3 , wherein the control circuit further limits an enable period of the high-side driving signal and an enable period of the low-side driving signal to no greater than a maximum enable period.
6 . The resonant power converter as claimed in claim 3 , wherein the offset voltage is determined based on a difference between an enable period of the high-side driving signal and an enable period of the low-side driving signal; wherein the offset voltage is configured to adjust the enable period of the high-side driving signal and the enable period of the low-side driving signal so that the enable period of the high-side driving signal is close to the enable period of the low-side driving signal.
7 . The resonant power converter as claimed in claim 3 , further comprising: a second voltage divider, configured to divide the input voltage to generate the divided voltage; wherein the full-wave rectification device comprises: a first resistor, coupled between the divided voltage and the basic voltage, wherein a voltage across the first resistor generates the offset voltage; a first current source, providing a first current flowing to the basic voltage; and an automatic adjustment circuit, sinking an adjustment current from the basic voltage based on the high-side driving signal, the low-side driving signal, the high-side dead time signal, and the low-side dead time signal.
8 . The resonant power converter as claimed in claim 7 , wherein in response to the first current exceeding the adjustment current, the offset voltage is positive and the basic voltage exceeds the divided voltage; wherein in response to the first current being less than the adjustment current, the offset voltage is negative and the basic voltage is less than the divided voltage; wherein in response to the first current being equal to the adjustment current, the basic voltage is equal to the divided voltage.
9 . The resonant power converter as claimed in claim 7 , wherein the automatic adjustment circuit comprises: a time-to-voltage conversion circuit, configured to respectively convert an enable period of the high-side driving signal and an enable period of the low-side driving signal into a high-side enable-period voltage and a low-side enable-period voltage; wherein the time-to-voltage conversion circuit comprises: a second current source, providing a second current; a first switch, providing the second current to a charge node based on the high-side driving signal or the low-side driving signal being enabled; a second switch, coupling the charge node to the ground in the high-side dead time and the low-side dead time; a first capacitor, coupled between the charge node and the ground; a second capacitor, coupled between a high-side enable-period voltage and the ground; a third capacitor, coupled between a low-side enable-period voltage and the ground; a third switch, coupling the charge node to the high-side enable-period voltage based on the high-side driving signal being enabled; and a fourth switch, coupling the charge node to the low-side enable-period voltage based on the low-side driving signal being enabled; wherein the high-side enable-period voltage represents the enable period of the high-side driving signal, and the low-side enable-period voltage represents the enable period of the low-side driving signal.
10 . The resonant power converter as claimed in claim 9 , wherein the automatic adjustment circuit further comprises: a comparison circuit, comparing the high-side enable-period voltage to the low-side enable period to generate an up-count signal and a down-count signal; a plurality of registers, configured to latch the up-count signal and the down-count signal in the high-side dead time and the low-side dead time; a counter, up-counting a digital code based on the up-count signal being enabled and down-counting the digital code based on the down-count signal being enabled; and a digital-to-analog converter, generating the adjustment current based on the digital code; wherein when the high-side enable-period voltage exceeds the low-side enable-period voltage, the comparison circuit enables the up-count signal and disables the down-count signal; wherein when the high-side enable-period voltage does not exceed the low-side enable-period voltage, the comparison circuit disables the up-count signal and enables the down-count signal.
11 . The resonant power converter as claimed in claim 7 , wherein in response to the output voltage increasing, the feedback voltage decreases; wherein in response to the feedback voltage being less than a low-power threshold voltage, a low-side dead time signal enables a burst signal, so that the control circuit operates in a burst mode based on the burst signal being enabled; wherein when the control circuit operates in the burst mode, the high-side transistor and the low-side transistor are turned off; wherein a duration of the burst mode increases as output power of the output voltage decreases.
12 . The resonant power converter as claimed in claim 11 , wherein the control circuit comprises: a first amplifier, comprising a first positive input terminal, a first negative input terminal, and a first output terminal, wherein the first positive input terminal receives the feedback voltage, and the first negative input terminal is coupled to the first output terminal; a second amplifier, comprising a second positive input terminal, a second input terminal, and a second output terminal, wherein the second positive input terminal receives a feedback threshold voltage; a second resistor, coupled between the second negative input terminal and the first output terminal and generating a difference current; an N-type transistor, comprising a gate terminal, a drain terminal, and a source terminal, wherein the gate terminal is coupled to the second output terminal and the source terminal is coupled to the second negative input terminal; and a current mirror, mapping the difference current to a mapping current; wherein the feedback threshold voltage is a lower limit of the feedback voltage; wherein the mapping current is configured to adjust the duration.
13 . A control method configured to control a resonant power converter, wherein the resonant power converter comprises a resonant capacitor coupled between a resonant node and a ground, a transformer comprising a primary coil and a secondary coil, a high-side transistor providing an input voltage to a switch node, a low-side transistor coupling the switch node to the ground, a rectifying circuit converting a current flowing through the secondary coil into an output voltage, and a feedback circuit generating a feedback voltage based on the output voltage, wherein the primary coil is coupled between the switch node and the resonant node, wherein the control method comprises: dividing a voltage across the resonant capacitor to generate a voltage-divided signal by using a first voltage divider; full-wave rectifying the voltage-divided signal to generate a rectified a full-wave rectified signal; and comparing the full-wave rectified signal with the feedback voltage to drive the high-side transistor and the low-side transistor.
14 . The control method as claimed in claim 13 , further comprising: full-wave rectifying the voltage-divided signal with a basic voltage as a DC level to generate the full-wave rectified signal; and comparing the full-wave rectified signal with a first threshold voltage to generate a crossover signal; wherein the basic voltage is equal to a sum of a divided voltage and an offset voltage; wherein the divided voltage is equal to the input voltage multiplied by a first ratio; wherein the first threshold voltage is slightly greater than the basic voltage.
15 . The control method as claimed in claim 14 , further comprising: when the full-wave rectified signal is less than the first threshold voltage, setting the crossover signal to a disabled state; when the full-wave rectified signal is not less than the first threshold voltage, setting the crossover signal to an enabled state; in response to the crossover signal changing from the disabled state to the enabled state, setting a phase signal to the enabled state; and in response to the full-wave rectified signal exceeding the feedback voltage, setting the phase signal to the disabled state in a high-side dead time or a low-side dead time; wherein the low-side dead time is a period between a point at which the high-side transistor is turned off and a point at which the low-side transistor is turned on; wherein the high-side dead time is a period between a point at which the low-side transistor is turned off and a point at which the high-side transistor is turned on.
16 . The control method as claimed in claim 15 , further comprising: when the high-side transistor is turned on and the phase signal is in the enabled state, turning off the high-side transistor in response to the full-wave rectified signal exceeding the feedback voltage; when the high-side transistor is turned off, turning on the low-side transistor after the low-side dead time; when the low-side transistor is turned on and the phase signal is in the enabled state, turning off the low-side transistor in response to the full-wave rectified signal exceeding the feedback voltage; and when the low-side transistor is turned off, turning on the high-side transistor after the high-side dead time.
17 . The control method as claimed in claim 15 , further comprising: limiting an enable period of the high-side transistor and an enable period of the low-side transistor so as not to exceed a maximum enable period.
18 . The control method as claimed in claim 15 , further comprising: determining the offset voltage based on a difference between an enable period of the high-side transistor and an enable period of the low-side transistor; wherein the offset voltage is configured to adjust the enable period of the high-side transistor and the enable period of the low-side transistor so that the enable period of the high-side transistor is close to the enable period of the low-side transistor.
19 . The control method as claimed in claim 15 , further comprising: generating the offset voltage by using a voltage across a first resistor, wherein the first resistor is coupled between the divided voltage and the basic voltage; providing a first current flowing to the basic voltage; sinking an adjustment current from the basic voltage based on the high-side transistor and the low-side transistor being turned on and off, the high-side dead time, and the low-side dead time by using an automatic adjustment circuit; wherein the offset voltage is positive and the basic voltage exceeds the divided voltage in response to the first current exceeding the adjustment current; wherein the offset voltage is negative and the basic voltage does not exceed the divided voltage in response to the first current not exceeding the adjustment current; wherein the first current is equal to the adjustment current, and the basic voltage is equal to the divided voltage.
20 . The control method as claimed in claim 19 , wherein the step of sinking the adjustment current from the basic voltage based on the high-side transistor and the low-side transistor being turned on and off, the high-side dead time, and the low-side dead time by using the automatic adjustment circuit further comprises: converting an enable period of the high-side transistor into a high-side enable-period voltage by using a time-to-voltage conversion circuit; converting an enable period of the low-side transistor into a low-side enable-period voltage by using the time-to-voltage conversion circuit; comparing the high-side enable-period voltage and the low-side enable-period voltage to generate an up-count signal and a down-count signal; when the high-side enable-period voltage exceeds the low-side enable-period voltage, increasing the adjustment voltage; and when the high-side enable-period voltage does not exceed the low-side enable-period voltage, decreasing the adjustment voltage.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63/609,904, filed on Dec. 14, 2023, the entirety of which is incorporated by reference herein. This application claims priority of Taiwan Patent Application No. 113116723, filed on May 6, 2024, the entirety of which is incorporated by reference herein. BACKGROUND OF THE INVENTION Field of the Invention The present invention is generally related to a resonant power convertor and a control method thereof, and more particularly it is related to a resonant power convertor and a control method thereof, for controlling the high-side transistor and the low-side transistor by comparing the full-wave rectified signal generated by full-wave rectifying a signal related to a voltage across the resonant capacitor with the feedback signal. Description of the Related Art With the continuous advancements being made in portable electronic devices, the development of power conversion circuits, like most power products, is trending in the direction of high efficiency, high power density, high reliability, and low cost. Since the resonant power convertor (including LLC resonant power convertor, etc.) has the advantages of achieving zero-voltage switching (ZVS) on the primary side and zero-current switching (ZCS) of the rectifier diode on the secondary side within the full load range, causing the duty cycle of the high-side and low-side transistors to both be 50% by frequency control, no output inductor required, using low-voltage transistors on the secondary side leading to cost reductions and efficiency improvements, the resonant power convertor has been increasingly used for DC voltage conversion in recent years. The duty cycles of the high-side transistor and the low-side transistor are not both 50%, however. The current transmitted to the secondary side is uneven and the conversion efficiency is reduced. Therefore, it is necessary to improve the balance between the duty cycles of the high-side transistor and the low-side transistor. BRIEF SUMMARY OF THE INVENTION In an embodiment, a resonant power converter is provided. The resonant power converter comprises a resonant capacitor, a transformer, a high-side transistor, a low-side transistor, a first voltage divider, a full-wave rectification device, a control circuit, a rectifying circuit, and a feedback circuit. The resonant capacitor is coupled between a resonant node and a ground. The transformer comprises a primary coil and a secondary coil, wherein the primary coil is coupled between a switch node and the resonant node. The high-side transistor provides an input voltage to the switch node based on a high-side driving signal. The low-side transistor couples the switch node to the ground based on a low-side driving signal. The first voltage divider divides a voltage of the resonant node to generate a voltage-divided signal. The full-wave rectification device full-wave rectifies the voltage-divided signal to generate a full-wave rectified signal. The control circuit compares the full-wave rectified signal to a feedback voltage to generate the high-side driving signal and the low-side driving signal. The rectifying circuit is coupled to the secondary coil and converts a current flowing through the secondary coil into an output voltage. The feedback circuit generates the feedback voltage based on the output voltage. According to an embodiment of the present invention, the full-wave rectification device uses a basic voltage as a DC level and full-wave rectifies the voltage-divided signal to generate the full-wave rectified signal. The basic voltage is equal to a sum of a divided voltage and an offset voltage. The divided voltage is equal to the input voltage multiplied by a first ratio. The full-wave rectification device further compares the full-wave rectified signal with a first threshold voltage to generate a crossover signal. The first threshold voltage slightly exceeds the basic voltage. According to an embodiment of the present invention, when the full-wave rectified signal is less than the first threshold voltage, the full-wave rectification device sets the crossover signal to a disabled state. When the full-wave rectified signal is not less than the first threshold voltage, the full-wave rectification device sets the crossover signal to an enabled state. In response to the crossover signal changing from the disabled state to the enabled state, the control circuit sets a phase signal to the enabled state. In response to the full-wave rectified signal exceeding the feedback voltage, the control circuit sets the phase signal to the disabled state based on a high-side dead time signal or a low-side dead time signal. The high-side dead time signal controls a high-side dead time of the high-side driving signal. The low-side dead time signal controls a low-side dead time of the low-side driving signal. According to an embodiment of the present invention, when the