CN111431392A - Constant on-period controller and buck converter using same - Google Patents

Constant on-period controller and buck converter using same Download PDF

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Publication number
CN111431392A
CN111431392A CN201910022478.7A CN201910022478A CN111431392A CN 111431392 A CN111431392 A CN 111431392A CN 201910022478 A CN201910022478 A CN 201910022478A CN 111431392 A CN111431392 A CN 111431392A
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voltage
period
controller
reference voltage
signal
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CN111431392B (en
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许哲玮
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Elite Semiconductor Memory Technology Inc
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Elite Semiconductor Memory Technology Inc
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1584—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load with a plurality of power processing stages connected in parallel

Abstract

A constant on-period controller for controlling an off-period and an on-period of a buck regulator includes a comparator, an on-timer, a reference voltage controller, and a switch switching device. The comparator is used for comparing a feedback voltage generated based on the output voltage of the buck regulator with a reference voltage so as to generate a closing termination signal for terminating the closing period. The start timer determines the start-up period according to the input voltage and the output voltage of the buck regulator, and accordingly generates a start-up termination signal for terminating the start-up period. The reference voltage controller is electrically connected with the comparator and generates a reference voltage according to the feedback voltage and a predetermined voltage. The switch switching device is electrically connected with the reference voltage controller, and instantly pulls down the reference voltage to the node voltage of the electronic switch device of the buck regulator at the beginning of the closing period.

Description

Constant on-period controller and buck converter using same
Technical Field
The present invention relates to a controller of a buck converter, and more particularly, to a constant on-time controller and a buck converter using the same.
Background
The on-period controller may be configured to control an on-period and an off-period of the buck regulator. When the buck regulator is turned on (i.e., during the turn-on period), the input voltage charges the energy storage inductor of the buck regulator through the turn-on of the electronic switching device (e.g., the switching transistor) of the buck regulator, and an output voltage related to the input voltage is generated at the output terminal of the buck regulator. When the buck regulator is turned off (i.e., during the turn-off period), the input voltage is isolated from the energy storage inductor and the output terminal of the buck regulator due to the electronic switching device of the buck regulator being turned off, so that the energy storage inductor of the buck regulator transmits the stored energy to the output terminal of the buck regulator to provide the output voltage of the buck regulator.
The constant on-period controller has a circuit for determining the constant on-period through an input voltage and an output voltage, so that the buck regulator is turned on at a constant frequency even though a duty cycle varies.
Disclosure of Invention
Embodiments of the present invention provide a constant on-period controller and a buck converter using the same, so as to solve the technical problem that when ripple of an output voltage of a buck regulator is relatively small, the constant on-period controller is easily affected by noise to reduce stability of the constant on-period controller.
To achieve the above object, the constant on period controller according to an embodiment of the present invention is used for controlling an off period and an on period of a buck regulator, and includes a comparator, an on timer, a reference voltage controller, and a switch switching device. The comparator is used for comparing a feedback voltage generated based on the output voltage of the buck regulator with a reference voltage so as to generate a closing termination signal for terminating the closing period. The start timer determines the start-up period according to the input voltage and the output voltage of the buck regulator, and accordingly generates a start-up termination signal for terminating the start-up period. The reference voltage controller is electrically connected with the comparator and generates a reference voltage according to the feedback voltage and a predetermined voltage. The switch switching device is electrically connected with the reference voltage controller, and instantly pulls down the reference voltage to the node voltage of the electronic switch device of the buck regulator at the beginning of the closing period.
Alternatively, the switch switching device provides a ground voltage as a reference voltage of the reference voltage during the turn-on period and provides a node voltage as a reference voltage of the reference voltage during the turn-off period.
Optionally, the switch switching device includes a first switch and a second switch, wherein a first end of the first switch and a first end of the second switch are electrically connected to the reference voltage controller, a second end of the first switch and a second end of the second switch are respectively electrically connected to the ground voltage and the node voltage, and the first switch and the second switch are respectively turned on in response to the stop close signal and the stop open signal.
Optionally, the reference voltage controller includes an error amplifier, an RC compensation circuit, a transconductance amplifier, and a current sensing resistor. The error amplifier is used for outputting an error amplification signal according to the feedback voltage and a predetermined voltage. The RC compensation circuit is electrically connected to the output end of the error amplifier for reducing the phenomenon of high-frequency oscillation. The transduction amplifier is electrically connected with the output end of the error amplifier and used for converting the error amplification signal passing through the RC compensation circuit into a current signal. The current sensing resistor is electrically connected between the output end of the error amplifier and the switch switching device and used for converting the current signal into a reference voltage.
Optionally, the reference voltage controller further comprises a ramp signal generator and an adder. The ramp signal generator is used for generating a ramp signal. The adder is electrically connected to the output end of the transconductance amplifier, the output end of the ramp signal generator and the comparator, and is used for adding the ramp signal to the stream signal.
Optionally, the constant on period controller further comprises two switches. The two switches are respectively electrically connected with the positive input end and the negative input end of the comparator and controlled by the stop opening signal, so that the comparator only carries out comparison in the closing period.
Optionally, the constant on period controller further comprises an RS flip-flop. The RS flip-flop is electrically connected with the comparator, the start timer and the buck regulator and used for receiving the stop close signal and the stop open signal so as to generate a control signal and a reverse control signal.
Optionally, the constant on period controller further comprises a voltage divider. The voltage divider is electrically connected with the reference voltage controller, the comparator and the buck regulator and used for generating feedback voltage according to the output voltage.
To achieve the above objective, a buck converter according to an embodiment of the present invention includes one of the constant on period controller and the buck regulator.
In summary, the constant on-period controller and the buck converter provided by the embodiments of the present invention have higher noise margin and faster response speed.
For a better understanding of the nature and technical content of the present invention, reference should be made to the following detailed description of the invention, taken in conjunction with the accompanying drawings, which are set forth to illustrate, but are not to be construed to limit the scope of the invention.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive labor. The drawings of the invention are briefly described as follows:
FIG. 1 is a schematic diagram of a buck converter according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a reference voltage controller of a constant on period controller according to an embodiment of the present invention;
FIG. 3 is a waveform diagram of node voltage, node current, reference voltage and feedback voltage in a buck converter using the constant on period controller of FIG. 2;
FIG. 4 is a schematic diagram of a buck converter according to another embodiment of the present invention; and
fig. 5 is a waveform diagram of a node voltage, a node current, a voltage at the positive input terminal of a comparator and a feedback voltage in a buck converter using the constant on period controller of fig. 4.
List of reference numerals
1. 1': step-down converter
10: step-down regulator
101: predriver circuit
11. 11': constant on period controller
111: voltage divider
112: start timer
113: RS flip-flop
114: comparator with a comparator circuit
115: reference voltage controller
1151: error amplifier
1152: transduction amplifier
1153: ramp signal generator
116: switch switching device
ADD 1: adder
C1、CF: capacitor with a capacitor element
CO: output capacitor
LX: energy storage inductor
NM1, PM 1: transistor with a metal gate electrode
ISW: node current
RFBH、RFBL、R1、R2、RF: resistance (RC)
RLOAD: load resistance
S1-S4: switch with a switch body
TOFF: terminate the shutdown signal
VFB: feedback voltage
VIN: input voltage
VOUT: output voltage
VREFX: reference voltage
V’REFX: voltage at positive input of comparator
VSW: node voltage
R: reset input terminal
S: setting input terminal
Q: positive output terminal
QB: reverse output end
RAMP _ SIG: ramp signal
Detailed Description
Embodiments of the present invention provide a constant on-period controller for enlarging a difference between a feedback voltage and a reference voltage to thereby extend a noise margin (noisemargin), and a buck converter using the same. Therefore, the technical problem that when the ripple of the output voltage of the buck regulator is relatively small, the stability of the controller is easily influenced by noise during the constant starting period can be solved.
Further, the constant on-period controller includes an on-timer, a comparator, a reference voltage controller and a switch switching device, wherein the reference voltage controller is electrically connected to the comparator and the switch switching device. The start timer is used for determining a start-up period according to the receiving voltage and the output voltage and outputting a start-up termination signal for terminating the start-up period. The reference voltage controller compares a feedback voltage generated based on the output voltage with a predetermined voltage to generate a reference voltage. The switch switching device switches to the ground voltage and the node voltage of the electronic switching device of the buck regulator according to the stop start signal and the stop close signal, so that the reference voltage is pulled down instantly when the closing period begins, and the difference between the feedback voltage and the reference voltage is increased. During the turn-off period, the pulled-down reference voltage gradually rises to a predetermined voltage and the feedback voltage gradually falls, and when the feedback voltage is lower than the reference voltage, the comparator outputs a turn-off termination signal for terminating the turn-off period.
In an embodiment of the present invention, the reference voltage controller may further include a ramp signal generator. The ramp signal generator can further pull down the reference voltage and adjust the rising slope of the pull-down reference voltage through the generated ramp signal. Therefore, the sensitivity of the controller to noise during the constant on period can be further reduced and the stability thereof can be maintained, and the technical problem of insufficient stability of the controller during the constant on period due to signal jitter (jitter) can be further solved.
The above is the inventive concept of the constant on period controller and the buck converter using the same provided by the present invention, and the following will describe in detail different embodiments of the constant on period controller and the buck converter using the same, and the functions and details of each component in conjunction with the drawings.
First, referring to fig. 1, fig. 1 is a schematic diagram of a buck converter according to an embodiment of the invention. The buck converter 1 includes a buck regulator 10 and a constant on-period controller 11, wherein the buck regulator 10 is electrically connected to the constant on-period controller 11. The buck regulator 10 is controlled by a constant on-period controller 11, and is turned on during on-periods and turned off during off-periods. The constant on-period provided by the controller 11 is a constant on-period, and the constant on-period is determined by the input voltage VINAnd an output voltage VOUTAnd (6) determining. When the buck regulator 10 is turned on, the input voltage VINFor the energy storage inductor L of the buck regulator 10XCharging and generating a voltage V related to the input voltageINOutput voltage V ofOUT. When the buck regulator 10 is turned off, the input voltage VINAnd energy storage inductor LXAnd the output terminal of the buck regulator 10, the energy storage inductor LXDischarge and accordingly generate an output voltage VOUT。
Further, the constant on period controller 11 generates a stop on signal at the end of the on period to control the buck regulator 10 to enter the off period. During the off period, the constant on period controller 11 compares the output voltage V from the buck regulator 10OUTGenerated feedback voltage VFBAnd a reference voltage VREFXTo generate a stop closing signal T for stopping the closing periodOFFTo allow the buck regulator 10 to be controlled to enter the turn-on period. During the on period, the parameters generated by the controller 11 during the constant on periodReference voltage VREFXIs a predetermined voltage, but at the end of the on period and at the beginning of the off period (i.e., when the off-on signal is generated), the constant on period controller 11 will generate the reference voltage VREFXMomentarily pulled down to the node voltage V of the electronic switching device of the buck regulator 10SWThen, the reference voltage VREFXGradually increasing to a predetermined voltage during the shutdown period. Thus, by applying the reference voltage V at the beginning of the OFF periodREFXInstantaneously pulled down to the node voltage VSWMay allow the noise margin to be extended to account for the output voltage V of the buck regulator 10OUTWhen the ripple is relatively small, the constant on period controller 11 is susceptible to noise and thus has a problem of reducing its stability. On the other hand, optionally, the constant on period controller 11 may generate a ramp signal during the off period, and change the reference voltage V through the ramp signalREFXTo further solve the problem of insufficient stability of the controller 11 due to jitter (jitter) during the constant on period.
The implementation of the buck regulator 10 is described below, but the implementation of the buck regulator 10 described below is not intended to limit the invention, and other types of implementations of the buck regulator 10 are possible.
In this embodiment, the buck regulator 10 includes a pre-driver circuit 101, switching transistors PM1 and NM1 as electronic switching devices, and an energy storage inductor LXAn output capacitor COAnd a load resistance RLOAD. The pre-driver circuit 101 is electrically connected to the constant on-period controller 11, the gates of the switching transistors PM1 and NM1 are electrically connected to the pre-driver circuit 101, and the source of the switching transistor PM1 receives the input voltage VINThe source of the switching transistor NM1 is coupled to the ground voltage, and the drains of the switching transistors PM1 and NM1 are electrically coupled to the energy storage inductor LXAnd an energy storage inductor LXThe other end of the first and second capacitors are connected in parallel with each other through a capacitor COAnd a load resistance RLOADCoupled to a ground voltage and used as an output terminal of the buck regulator 10 (also the output terminal of the buck converter 1) to output an output voltage VOUT. In addition, the first and second substrates are,the voltages at the drains of the switching transistors PM1, NM1 are the node voltage V of the electronic switching deviceSW。
The pre-driver circuit 101 receives a signal T associated with terminating the shutdownOFFAnd a control signal for terminating the turn-on signal and generating a gate control signal for controlling the turn-on and turn-off of the switching transistors PM1 and NM1, wherein the pre-driver circuit 101 may be a logic circuit including a plurality of logic gates, but the invention is not limited thereto. In this embodiment, the switch transistors PM1 and NM1 are PMOS transistors and NMOS transistors, respectively, but the invention is not limited thereto.
The controller 11 generates the stop off signal T during the constant on periodOFFThe control signal has a logic high level voltage, so that the pre-driver circuit 101 controls the PMOS transistor and the NMOS transistor to be turned on according to the control signal to let the input voltage VINTo energy storage inductance LXCharging and generating a voltage V related to the input voltage at the output terminalINOutput voltage V ofOUTWhen the controller 11 generates the stop-on signal during the constant-on period, the control signal has a voltage of a logic low level, so that the pre-driver circuit 101 controls the PMOS transistor and the NMOS transistor to be turned off according to the control signal to enable the energy storage inductor LXTo discharge the output to generate an output voltage V at the output terminalOUT. Further, during the turn-on period, the output voltage VOUTWill gradually rise and during the turn-off period, the output voltage VOUTWill gradually fall.
The implementation of the constant on period controller 11 is described below, but the implementation of the constant on period controller 11 described below is not intended to limit the present invention, and other types of implementations of the constant on period controller 11 are possible.
The constant on period controller 11 includes a voltage divider 111, an on timer 112, an RS buffer 113, a comparator 114, a reference voltage controller 115, and a switch switching device 116. The voltage divider 111 is electrically connected to the output terminal of the buck regulator 10 for receiving the output voltage VOUT. The reference voltage controller 115 and the voltage divider 111 are electrically connected to the comparator 114. Switch switchingThe device 116 is electrically connected to the RS register 113 and the reference voltage controller 115. The RS register 113 is electrically connected to the comparator 114, the start timer 112 and the pre-driver circuit 101 of the buck regulator 10.
The voltage divider 111 is used for dividing the output voltage VOUTGenerating a feedback voltage VFBThe voltage divider 111 may be composed of a plurality of resistors RFBHAnd RFBLRealization of, in which the resistance RFBHOne terminal of receives the output voltage VOUTResistance RFBHAnother terminal of (1) and a resistor RFBLIs electrically connected to output a feedback voltage VFBAnd a resistance RFBLThe other end of the first terminal is electrically connected to a ground voltage. The start timer 112 is used for receiving the input voltage VINAnd an output voltage VOUTAnd according to the input voltage VINAnd an output voltage VOUTA constant turn-on period is determined, and a termination turn-on signal for terminating the turn-on period is output after the buck regulator 10 is turned on for a turn-on period. The start timer 112 may be a one-shot on-timer (one-shot on-timer), but the invention is not limited thereto.
The reset input terminal R and the set input terminal S of the RS flip-flop 113 receive the stop-on signal and the stop-off signal T, respectivelyOFFAnd the levels of the control signal output from the positive output terminal Q and the inverted control signal output from the inverted output terminal QB of the RS flip-flop 113 are based on the on-stop signal and the off-stop signal TOFFAnd then determined. Further, when the stop start signal is at a logic high level, the levels of the control signal output by the positive output terminal Q and the inverted control signal output by the inverted output terminal QB of the RS flip-flop 113 are at a logic low level and a logic high level, respectively; when T is turned offOFFThe signal is at a logic high level, and the levels of the control signal output by the positive output terminal Q and the inverted control signal output by the inverted output terminal QB of the RS flip-flop 113 are at a logic high level and a logic low level, respectively.
The positive input terminal and the negative input terminal of the comparator 114 respectively receive the reference voltage VREFXAnd a feedback voltage VFBAnd comparing the reference voltage VREFXAnd a feedback voltage VFBTo provide a feedback voltage VFBBelow the reference voltage VREFXGenerating a closing termination signal T for terminating the closing periodOFF. The reference voltage controller 115 receives the feedback voltage VFBAnd generates a feedback voltage VFBAnd a predetermined voltage. Then, the reference voltage controller 115 converts the error amplification signal into a current signal. Thereafter, the reference voltage controller 115 converts the current signal into a reference voltage V through a resistorREFX. It should be noted that, alternatively, the reference voltage controller 115 may add a ramp signal to the current signal to solve the technical problem of signal jitter, but the invention is not limited thereto.
The switch switching device 116 is used for providing a ground voltage as a reference voltage (baseline) during the turn-on period and providing a node voltage V during the turn-off periodSWAs a reference voltage. Thus, at the beginning of the turn-off period, the reference voltage VREFXWill be instantaneously pulled down to the node voltage VSWAnd then gradually rises to a predetermined voltage. The switch switching device 116 may be implemented by two switches S1 and S2, but the invention is not limited thereto. One terminal of the switch S1 is electrically connected to the reference voltage controller 115, the other terminal of the switch S1 is electrically connected to the ground voltage, one terminal of the switch S2 is electrically connected to the reference voltage controller 115, and the other terminal of the switch S2 is electrically connected to the node voltage VSW. The switches S1 and S2 are controlled by the control signal and the inverted control signal, respectively, and further, the switch S2 is turned on (i.e., turned on) when the end-on signal is at a logic high level, and the switch S1 is turned on when the end-off signal is at a logic high level.
Next, referring to fig. 2, fig. 2 is a schematic diagram of a reference voltage controller of a constant on-period controller according to an embodiment of the invention. One implementation of the reference voltage controller 115 of the constant on period controller 11 is shown in fig. 2, but the following implementation of the reference voltage controller 115 is not intended to limit the present invention, and other types of implementations of the reference voltage controller 115 are possible.
In the embodiment of fig. 2, the reference voltage controller 115 includes an error amplifier 1151, resistors R1, R2, a capacitor C1, an adder AAD1, a transconductance amplifier 1152, and a ramp signal generator 1153. The error amplifier 1151 is electrically connected to the voltage divider 111, one end of the resistor R1, and the input end of the transconductance amplifier 1152. The output terminal of the transconductance amplifier 1152 is electrically connected to the input terminal of the adder ADD1, and the output terminal of the ramp signal generator is electrically connected to the other input terminal of the adder ADD 1. One end of the resistor R2 is electrically connected to the positive input terminal of the comparator 114 and the output terminal of the adder ADD1, and the other end of the resistor R2 is electrically connected to one end of the switch S1 and one end of the switch S2. Two ends of the capacitor C1 are electrically connected to the other end of the resistor R1 and the ground voltage, respectively.
The negative input terminal and the positive input terminal of the error amplifier 1151 respectively receive the feedback voltage VFBWith a predetermined voltage VREF(e.g., 0.6 volts, but not limited thereto) and generates the feedback voltage V accordinglyFBWith a predetermined voltage VREFThe error amplification signal of (1). The capacitor C1 and the resistor R1 form an RC compensation circuit, and the RC compensation circuit has the effect of stabilizing the circuit and reducing the phenomenon of high-frequency oscillation. The error amplified signal after passing through the RC compensation circuit is converted into a current signal by the transconductance amplifier 1152. The adder ADD1 ADDs the RAMP signal RAMP _ SIG to the current signal, and the resistor R2 is used for current sensing purpose, so as to generate the reference voltage V according to the current signal of the added RAMP signal RAMP _ SIGREFX。
It is noted that the ramp generator 1153 and the adder ADD1 are added to the reference voltage controller 115 to solve the problem of jitter. Therefore, if there is no serious signal jitter, the ramp signal generator 1153 and the adder ADD1 can be removed from the reference voltage controller 115.
Referring to fig. 1 to 3, fig. 3 is a waveform diagram of a node voltage, a node current, a reference voltage and a feedback voltage in a buck converter using the constant on-period controller of fig. 2. In this embodiment, at time T0, the electronic switching device of the buck regulator 10 is turned on, and the turn-on period P01 is terminated at time T1, i.e., the buck regulator 10 is turned on during the turn-on period P01. During the turn-on period P01, the input voltage VINGenerating associated output powerPressure VOUTAnd node voltage VSWDue to pair of storage inductors LXReason for charging, node voltage VSWGradually decreases and node current ISWGradually rising. During the turn-on period P01, the reference voltage provided by the switch switching device 116 is the ground voltage, and the reference voltage V isREFXWill be approximately equal to the predetermined voltage VREFAnd the feedback voltage VFBCorresponding to the output voltage VOUTRises as a result of the rise of (c).
At a time point T1, a termination turn-on signal is generated, and thus, the electronic switching devices of the buck regulator 10 are turned off, and the node voltage V of the electronic switching devices of the buck regulator 10SWWill be pulled down instantaneously and the energy storage inductor LXBegins discharging to the output of the buck regulator 10 to produce the output voltage VOUTP12 during off period because of the energy storage inductor LXContinuously discharging to the output terminal, so that the node current ISWWill gradually drop and the node voltage V after being pulled downSWWill gradually rise, and the feedback voltage VFBCorresponding to the output voltage VOUTAnd falls at the feedback voltage VFBBelow the reference voltage VREFXAt time (i.e., at time T2), a stop close signal for stopping the close period P12 is generated. At time T1, the reference voltage provided by the switching device 116 is changed to the node voltage VSWThus, the reference voltage VREFXWill be instantaneously pulled down to the node voltage VSWAnd then, a reference voltage VREFXWill gradually rise to the predetermined voltage V during the closing period P12REF. Since the constant on-period controller 10 of the embodiment of the present invention uses the switch switching device 116 to change the supplied reference voltage to pull down the reference voltage V instantaneouslyREFXTherefore, in addition to improving the noise margin, it has an advantage of fast response speed.
Next, referring to fig. 4, fig. 4 is a schematic diagram of a buck converter according to another embodiment of the invention. Compared to the embodiment of fig. 1, the constant on period controller 11 'of the buck converter 1' of fig. 4 additionally has two switches S3 and S4. One end of the switch S3 is electrically connected to the feedback voltage VFBThe other end of the switch S3 is electrically connected to ground, and one end of the switch S4 is electrically connected to the reference voltage VREFXThe other end of the switch S4 is electrically connected to the positive input terminal of the comparator 114 through an RC filter circuit. The RC filter circuit includes a resistor RFAnd a capacitor CFResistance RFIs connected to the switch S4, resistor RFIs connected to the positive input of the comparator 114, the capacitor CFOne end of which is connected to ground, a capacitor CFAnd the other end thereof is connected to the positive input of the comparator 114. The switches S3 and S4 are controlled by the control signal and the inverted control signal QB, respectively, such that the switches S3 and S4 are turned on only during the turn-off period, and the comparator 114 compares the reference voltage V only during the turn-off periodREFXAnd a feedback voltage VFB。
Referring to fig. 4 and 5, fig. 5 is a waveform diagram of a node voltage, a node current, a voltage at the positive input terminal of the comparator and a feedback voltage in the buck converter using the constant on-period controller of fig. 4. Since the switch S4 is turned on only during the turn-off period P12, the comparator 114 compares the reference voltage VREFXAnd a feedback voltage VFBTherefore, during the turn-on period P01, the switch S3 is turned on, so that the voltage V 'at the positive input terminal of the comparator 114'REFXIs below a predetermined voltage VREFLower voltage. During the turn-off period P12, the switch S3 turns off and the switch S4 turns on, so that the voltage V 'at the positive input terminal of the comparator 114'REFXWill be subject to a reference voltage VREFXIs effected to gradually increase from a lower voltage to a predetermined voltage VREF. Thus, by adding the switches S3 and S4 to the positive input terminal and the negative input terminal of the comparator 114, the feedback voltage V can be further pulled openFBAnd voltage V'REFXThereby increasing the noise margin even more.
In summary, the constant on-period controller and the buck converter provided by the embodiments of the invention have a higher noise tolerance, so that the technical problem that the stability of the constant on-period controller is easily affected by noise when the ripple of the output voltage of the buck regulator is relatively small can be solved. Preferably, in one embodiment, during the off period, the slope of the reference voltage is changed by the ramp signal, so as to further improve the jitter problem. In addition, the controller switches the reference voltage corresponding to the reference voltage by using the switch switching device during the constant on period, so that the controller has the advantage of faster response speed.
The above description is only an example of the present invention, and is not intended to limit the scope of the present invention.

Claims (9)

1. A constant on-period controller for controlling an off-period and an on-period of a buck regulator, comprising:
a comparator for comparing a feedback voltage generated based on an output voltage of the buck regulator with a reference voltage to generate a termination turn-off signal for terminating the turn-off period;
a start timer for determining the start period according to the input voltage and the output voltage of the buck regulator and generating a start termination signal for terminating the start period;
a reference voltage controller electrically connected to the comparator for generating the reference voltage according to the feedback voltage and a predetermined voltage; and
and the switch switching device is electrically connected with the reference voltage controller and instantly pulls down the reference voltage to the node voltage of the electronic switching device of the buck regulator at the beginning of the closing period.
2. The constant on-period controller according to claim 1, wherein the switch switching device provides a ground voltage as a reference voltage of the reference voltage during the on-period and provides the node voltage as a reference voltage of the reference voltage during the off-period.
3. The constant on period controller according to claim 2, wherein the switching means comprises:
the first terminal of the first switch and the first terminal of the second switch are electrically connected to the reference voltage controller, the second terminal of the first switch and the second terminal of the second switch are electrically connected to the ground voltage and the node voltage, respectively, and the first switch and the second switch are turned on in response to the termination-off signal and the termination-on signal, respectively.
4. The constant on-period controller of claim 1, wherein the reference voltage controller comprises:
an error amplifier for outputting an error amplified signal according to the feedback voltage and the predetermined voltage;
the RC compensating circuit is electrically connected to the output end of the error amplifier;
the transduction amplifier is electrically connected with the output end of the error amplifier and used for converting the error amplification signal passing through the RC compensation circuit into a current signal; and
and the current sensing resistor is electrically connected between the output end of the error amplifier and the switch switching device and used for converting the current signal into the reference voltage.
5. The constant on-period controller of claim 4, wherein the reference voltage controller further comprises:
a ramp signal generator for generating a ramp signal; and
and the adder is electrically connected with the output end of the transduction amplifier, the output end of the ramp signal generator and the comparator and is used for adding the ramp signal to the current signal.
6. The constant on period controller of claim 1, further comprising:
an RC filter circuit;
the first switch and the second switch are controlled by the stop-start signal, so that the comparator only performs comparison during the closing period.
7. The constant on period controller of claim 1, further comprising:
and the RS flip-flop is electrically connected with the comparator, the start timer and the buck regulator and used for receiving the stop close signal and the stop start signal so as to generate a control signal and a reverse control signal.
8. The constant on period controller of claim 1, further comprising:
the voltage divider is electrically connected with the reference voltage controller, the comparator and the buck regulator and used for generating the feedback voltage according to the output voltage.
9. A buck converter, comprising:
the constant on period controller of one of claims 1 to 8; and
the buck regulator.
CN201910022478.7A 2019-01-10 2019-01-10 Constant on-period controller and buck converter using same Active CN111431392B (en)

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