US-12620898-B2 - Power converter and control circuit thereof

US12620898B2US 12620898 B2US12620898 B2US 12620898B2US-12620898-B2

Abstract

A control circuit for a power converter includes an error amplifier, a compensation circuit, a comparator, and a controller. The error amplifier generates an error amplification signal according to a first reference signal and a feedback signal. The compensation circuit compensates the error amplification signal to obtain a compensation signal that is a ripple signal, The controller generates a switching control signal according to a predetermined clock pulse signal and a comparison signal of the compensation signal and the feedback signal. The clock pulse signal being used to determine a frequency of the switching control signal, and the comparison signal being used to determine a duty cycle of the switching control signal.

Inventors

Linjue Li

Assignees

JoulWatt Technology (Shanghai) Co., Ltd.

Dates

Publication Date: 20260505
Application Date: 20240228
Priority Date: 20230410

Claims (15)

1 . A control circuit of a power converter for generating a switching control signal to control a switching transistor in the power converter, wherein the control circuit comprises: an error amplifier that receives a first reference signal and a feedback signal and outputs an error amplification signal, the feedback signal being obtained according to an output signal of the power converter; a compensation circuit that compensates the error amplification signal to obtain a compensation signal, the compensation signal being a ripple signal; a comparator that compares the feedback signal and the compensation signal to obtain a comparison signal; a controller that generates the switching control signal according to a predetermined clock pulse signal having a first frequency and the comparison signal, the clock pulse signal being used to determine a frequency of the switching control signal, and the comparison signal being used to determine a duty cycle of the switching control signal, wherein the compensation circuit is configured to: generate a triangular wave signal according to a second reference signal and the switching control signal, the triangular wave signal representing inductor current information of the power converter, superimpose the triangular wave signal onto the error amplification signal in the compensation circuit to achieve compensation for the error amplification signal.
2 . The control circuit according to claim 1 , wherein the controller is configured to: switch the switching control signal from an invalid state to a valid state according to a rising edge of the clock pulse signal; and switch the switching control signal from a valid state to an invalid state according to a rising edge of the comparison signal, wherein a rising edge of the comparison signal occurs when the compensation signal drops to less than the feedback signal.
3 . The control circuit according to claim 1 , wherein the controller is configured to: switch the switching control signal from an invalid state to a valid state according to a rising edge of the comparison signal; and switch the switching control signal from a valid state to an invalid state according to a rising edge of the clock pulse signal, wherein a rising edge of the comparison signal occurs when the compensation signal rises to be greater than the feedback signal.
4 . The control circuit according to claim 2 , wherein a falling slope of the compensation signal is positively correlated with an input voltage of the power converter.
5 . The control circuit according to claim 3 , wherein a falling slope of the compensation signal is positively correlated with difference between an input voltage and an output voltage of the power converter, and a rising slope of the compensation signal is positively correlated with a sum of the input voltage and the output voltage of the power converter.
6 . The control circuit according to claim 1 , wherein the compensation circuit comprises: a triangular wave signal generating branch coupled between an output of the error amplifier and a reference ground, the triangular wave signal generating branch is configured to discharge a compensation capacitor according to a first discharge current and the second reference signal during a valid period of the switching control signal, and to charge the compensation capacitor with a second reference signal during an invalid period of the switching control signal, thereby generating the triangular wave signal.
7 . The control circuit according to claim 6 , wherein the first discharge current is controlled by an input voltage of the power converter.
8 . The control circuit according to claim 6 , wherein the triangular wave signal generating branch comprises: a first capacitor, a first switch and a current source sequentially coupled in series between an output of the error amplifier and a reference ground, the first current source being used to provide the first discharge current; a first resistor coupled between an intermediate node of the first capacitor and the first switch and a receiving terminal of the second reference signal, wherein the first switch is in an on state during a valid period of the switching control signal and is in an off state during an invalid period of the switching control signal.
9 . The control circuit according to claim 1 , wherein the compensation circuit further generates a sawtooth wave signal according to the second reference signal and the switch control signal; the compensation circuit further superimposes the sawtooth wave signal onto the error amplification signal to achieve compensation for the error amplification signal.
10 . The control circuit according to claim 9 , wherein the compensation circuit further comprises: a first sawtooth wave signal generating branch coupled between an output of the error amplifier and a reference ground; wherein the first sawtooth wave signal generation branch is configured to discharge a compensation capacitor according to a second discharge current during a valid period of the switching control signal, and to couple the compensation capacitor to the second reference signal during an invalid period of the switching control signal, thereby generating the sawtooth wave signal.
11 . The control circuit of claim 10 , wherein the second discharge current is controlled by an output voltage of the power converter.
12 . The control circuit according to claim 10 , wherein the first sawtooth wave signal generation branch comprises: a second capacitor and a second current source sequentially coupled in series between an output of the error amplifier and a reference ground, the second current source being used to provide the second discharge current; a second switch coupled between an intermediate node of the second capacitor and the second current source and a receiving terminal of the second reference signal, wherein the second switch is in an off state during a valid period of the switching control signal and is in an on state during an invalid period of the switching control signal.
13 . The control circuit according to claim 9 , wherein the compensation circuit further comprises: a second sawtooth wave signal generating branch coupled between an output of the error amplifier and a reference ground, wherein the second sawtooth wave signal generation branch is configured to generate the sawtooth wave signal by coupling the compensation capacitor to a reference ground during a valid period of the switching control signal, and to charge the compensation capacitor with a first charging current during an invalid period of the switching control signal; the first charging current is controlled by an input voltage of the power converter.
14 . The control circuit according to claim 13 , wherein the second sawtooth wave signal generation branch comprises: a third current source coupled to an output of the error amplifier through a second capacitor, the third current source being used for providing the first charging current; a third switch coupled between an intermediate node of the second capacitor and the third current source, and a reference ground; wherein the third switch is in an on state during a valid period of the switching control signal and is in an off state during an invalid period of the switching control signal.
15 . A power converter, comprising: at least one power stage circuit, each of the power stage circuits comprising an inductor and a switching transistor coupled to the inductor; a control circuit for providing a switching control signal to the at least one power stage circuit to control the switching transistor in each power stage circuit, wherein the control circuit comprises: an error amplifier that receives a first reference signal and a feedback signal and outputs an error amplification signal, the feedback signal being obtained according to an output signal of the power converter; a compensation circuit that compensates the error amplification signal to obtain a compensation signal, the compensation signal being a ripple signal; a comparator that compares the feedback signal and the compensation signal to obtain a comparison signal; a controller that generates the switching control signal according to a predetermined clock pulse signal having a first frequency and the comparison signal, the clock pulse signal being used to determine a frequency of the switching control signal, and the comparison signal being used to determine a duty cycle of the switching control signal, wherein the compensation circuit is configured to: generate a triangular wave signal according to a second reference signal and the switching control signal, the triangular wave signal representing inductor current information of the power converter, superimpose the triangular wave signal onto the error amplification signal in the compensation circuit to achieve compensation for the error amplification signal.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present disclosure claims priority to a Chinese patent application No. 202310376440.6, filed on Apr. 10, 2023, and entitled “POWER CONVERTER AND CONTROL CIRCUIT THEREOF”, the entire contents of which are incorporated herein by reference, including the specification, claims, drawings and abstract. TECHNICAL FIELD The present application relates to the technical field of power supply, and more particularly, to a power converter and its control circuit. BACKGROUND With the demand for power electronics and the development of semiconductor technology, power supply management chips are widely used in communication, consumption, computing and other fields. Taking a DC-DC converter as an example, a DC-DC converter is one of the most common among power management chips and typically includes one or more switches that are selectively turned on or off to provide a controlled output voltage according to a received input voltage. The output power of the circuit is regulated by controlling a duty cycle of the signal provided to the one or more switching transistors of the converter. The control circuit in a DC-DC converter has many control modes. Typically, there are: voltage control mode, current control mode, and constant on-time control mode (COT). Here, referring to FIG. 1a, there is shown a schematic diagram of a DC-DC converter in a conventional current control mode, such as a peak current control mode. The converter includes: a control circuit 210, a driving circuit 220, and a power stage circuit 230. The control circuit 210 comprises: an error amplifier 211, a current sensing circuit 212, a signal generator 213, an adder 214, a PWM comparator 215, and an RS flip-flop 216. The error amplifier 211 receives a feedback signal FB of an output voltage Vout and a reference signal Vref, and outputs a compensation signal COMP by using a compensation capacitor Ccom. The current sensing circuit 212 detects a current flowing through a switching transistor in the power stage circuit 230 and obtains a sensing voltage signal Vsense accordingly. The signal generator 213 generates both a sawtooth wave signal ramp and a clock pulse signal CLK with the same frequency. The adder 214 superimposes the sensed voltage signal Vsense with the sawtooth wave signal ramp onto obtain a sum signal SUM. The PWM comparator 215 compares the feedback signal FB and the sum signal SUM and provides a pulse signal to a reset terminal of the RS flip-flop 216. A set terminal of the RS flip-flop 216 receives a clock pulse signal CLK. The RS flip-flop 216 generates a PWM signal for the driving circuit 220 according to signal changes at the set terminal and the reset terminal. The driving circuit 220 outputs complementary driving signals HS and LS to the power stage circuit 230 according to the received PWM signal. Referring to FIG. 1b, a schematic diagram of a DC-DC converter in a constant on-time control mode is shown. The converter includes: a control circuit 310, a driving circuit 320, and a power stage circuit 330. The control circuit 210 comprises: a loop comparator 311, a timer 312, and an RS flip-flop 313. The loop comparator 311 receives a feedback signal FB of an output voltage Vout and a reference signal Vref. When the feedback signal FB is less than the reference signal Vref, the loop comparator 311 outputs a pulse signal to the set terminal of the RS flip-flop 313. The pulse signal from the loop comparator 311 further controls the timer 312 to start timing, and after a predetermined time period Ton, a triggering signal is output to the reset terminal of the RS flip-flop 313. The RS flip-flop 313 generates a PWM signal for the driving circuit 320 according to signal changes at its set terminal and reset terminal. The driving circuit 320 outputs complementary drive signals HS and LS to the power stage circuit 330 according to the received PWM signal. However, the conventional DC-DC converter has the following problems: 1. On one hand, the DC-DC converter in a conventional peak current control mode needs to sample a current through the switching transistor to achieve control, and on the other hand, it needs a high-bandwidth error amplifier to achieve fast dynamic response. The circuit is more complex, and a current sampling circuit is not easy to use for a high-frequency circuit control.2. Although the conventional DC-DC converter in a constant conduction time control mode has a fast dynamic response speed, a frequency error is large, and the frequency error will increase with the increase of the switching frequency, which is not easy to synchronize with an external clock. Therefore, it is necessary to provide improved technical solutions to overcome the above technical problems in the existing technology. SUMMARY In order to solve the above technical problems, the present disclosure provides a power converter and its control circuit, which can solve the problem of achieving a fast dynamic response and