CN113612392B - Switching power supply and control circuit thereof - Google Patents

Switching power supply and control circuit thereof Download PDF

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Publication number
CN113612392B
CN113612392B CN202110655953.1A CN202110655953A CN113612392B CN 113612392 B CN113612392 B CN 113612392B CN 202110655953 A CN202110655953 A CN 202110655953A CN 113612392 B CN113612392 B CN 113612392B
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signal
voltage
switching
module
power supply
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CN113612392A (en
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张钦阳
洪益文
廖小军
詹桦
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Hangzhou Silan Microelectronics Co Ltd
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Hangzhou Silan Microelectronics Co Ltd
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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
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The application discloses control circuit of switching power supply includes: the demagnetization detection module obtains the demagnetization time of the switching power supply according to the voltage feedback signal; the control module outputs a current peak signal and a slope signal in a time-sharing mode according to the demagnetizing time, the clock signal and the driving signal of the switching tube, and outputs the current peak signal in the conducting period of the switching tube; outputting a ramp signal during the off period of the switching tube; the conducting signal generating module is used for sampling and holding the voltage feedback signal to obtain a first sampling signal, generating an error signal according to the first sampling signal and the reference voltage and generating a conducting signal according to the error signal and the ramp signal; and the turn-off signal generating module is used for generating a turn-off signal according to the current sampling signal and the current peak value signal. The constant voltage output is realized through the digital control module and the digital-to-analog converter, and a complex ramp signal is generated, wherein the ramp signal has a plurality of falling slopes.

Description

Switching power supply and control circuit thereof
Technical Field
The invention relates to the technical field of switching power supplies, in particular to a switching power supply and a control circuit thereof.
Background
The primary side controlled switching power supply can adopt an auxiliary winding of the transformer to obtain a feedback signal related to output voltage, so that electronic elements such as an optical coupler and a precise voltage source for feeding back the feedback signal from a secondary side to the primary side can be saved, and a signal feedback path is simplified. The primary-side controlled switching power supply is easy to form a modularized and miniaturized integrated circuit, and has been widely used in various charging power supplies of electronic digital products such as mobile phones, tablet computers and portable media players, and in power supplies for driving Light Emitting Diodes (LEDs).
However, in the existing control process of the switching power supply, the signal sampled by the auxiliary winding is amplified by the error amplifier, then the analog control technology is adopted to control the frequency and the current peak value, and the defects that the control circuit is complex, the area of the compensation component is too large, the number of components is large, the control circuit can only aim at a specific loop and the like exist, so that the control circuit is not beneficial to the miniaturization and the integration application of the switching power supply.
Disclosure of Invention
In view of the foregoing, an object of the present invention is to provide a switching power supply and a control circuit thereof, which combine digital control and analog control together, optimize a control manner, and achieve performance and cost optimization.
According to a first aspect of the present invention, there is provided a control circuit of a switching power supply, comprising: the demagnetization detection module obtains the demagnetization time of the switching power supply according to the voltage feedback signal representing the output voltage; the control module outputs a current peak value signal and a slope signal in a time-sharing mode according to the demagnetizing time, the clock signal and the driving signal of the switching tube, and the control module outputs the current peak value signal in the conducting period of the switching tube; during the off period of the switching tube, the control module outputs the ramp signal; the conducting signal generating module is used for carrying out sampling and holding on the voltage feedback signal to obtain a first sampling signal, generating an error signal according to the first sampling signal and a reference voltage, and generating a conducting signal according to the error signal and the slope signal; and the turn-off signal generating module is used for generating a turn-off signal according to the current sampling signal representing the current flowing through the switching tube and the current peak value signal.
Preferably, the ramp signal has at least one slope during the switching off of the switching tube.
Preferably, during the off period of the switching tube, the ramp signal comprises a plurality of sections of slopes, wherein the ramp signal is reduced from an initial voltage or a preset voltage with different slopes to form a plurality of sections of slopes; the ramp signal is turned up to a preset voltage to form a folding slope.
Preferably, the ramp signal has a multi-segment transition slope between a first segment slope and the folding slope.
Preferably, the switching frequency of the switching power supply at least includes a maximum switching frequency, a folding frequency and an intermediate frequency, wherein the maximum switching frequency is the highest switching frequency of the switching power supply, the folding frequency is the switching frequency corresponding to when the ramp signal is turned up to a preset voltage, and the intermediate frequency is between the maximum switching frequency and the folding frequency.
Preferably, the control module is a digital control module, and the ramp signal and the current peak signal are generated in a time sharing way in a digital control mode.
Preferably, the control module includes: the digital control unit outputs a digital ramp signal and a digital current peak value signal in a time-sharing manner according to the demagnetizing time, the clock signal and the driving signal of the switching tube; and the digital-to-analog converter is used for carrying out digital-to-analog conversion on the digital ramp signal and the digital current peak signal so as to output the ramp signal and the current peak signal in a time-sharing mode.
Preferably, the control circuit further includes: and the threshold switching module is used for receiving the first threshold voltage and the second threshold voltage and outputting the first threshold voltage or the second threshold voltage as the reference voltage according to a switching signal.
Preferably, the control circuit further includes: and the third comparator is connected with the control module and generates the switching signal according to the ramp signal and the reference voltage.
Preferably, the threshold switching module outputs the first threshold voltage as the reference voltage when the ramp signal is greater than the reference voltage; when the ramp signal is equal to the reference voltage, the threshold switching module outputs the second threshold voltage as the reference voltage according to the switching signal, wherein the first threshold voltage is smaller than the second threshold voltage.
Preferably, the control module generates the switching signal according to the clock signal and a preset time.
Preferably, the threshold switching module outputs the first threshold voltage as the reference voltage when the count period of the clock signal does not reach a preset time; and when the counting period of the clock signal reaches a preset time, the threshold switching module outputs the second threshold voltage as the reference voltage.
Preferably, the control module outputs the first threshold voltage or the second threshold voltage as the reference voltage according to the switching signal.
Preferably, the control circuit further includes: and the third comparator is connected with the control module and generates the switching signal according to the ramp signal and the reference voltage.
Preferably, the control module outputs the first threshold voltage as the reference voltage when the ramp signal is greater than the reference voltage; when the ramp signal is equal to the reference voltage, the control module outputs the second threshold voltage as the reference voltage according to the switching signal, wherein the first threshold voltage is smaller than the second threshold voltage.
Preferably, when the reference voltage is the first threshold voltage, the control module controls the ramp signal to gradually decrease from an initial voltage; when the reference voltage is switched from the first threshold voltage to the second threshold voltage, the control module controls the ramp signal to be turned up to a preset voltage and then gradually reduced.
Preferably, the on signal generating module includes: the sampling and holding module samples and holds the voltage feedback signal to obtain a first sampling signal; the error amplifier is connected with the sampling and holding module and generates an error signal according to the first sampling signal and the reference voltage; and the first comparator is respectively connected with the error amplifier and the digital-to-analog converter and generates a constant voltage conduction signal according to the error signal and the ramp signal.
Preferably, the conduction signal generating module generates a conduction signal according to the constant voltage conduction signal.
Preferably, the control module is connected with the sample-and-hold module, and controls the sample-and-hold module to sample the voltage feedback signal in the demagnetizing time.
Preferably, the shutdown signal generation module includes: the front edge blanking module receives a current sampling signal representing the current flowing through the switching tube and blanking burrs generated by the current sampling signal at the moment of switching tube conduction; and the second comparator is connected with the leading edge blanking module and the digital-to-analog converter and generates a turn-off signal according to the current sampling signal and the current peak value signal.
Preferably, the shutdown signal generation module includes: and the second comparator is connected with the digital-to-analog converter and generates a turn-off signal according to the current sampling signal and the current peak value signal.
Preferably, the control circuit further includes: and an oscillator for generating a clock signal.
Preferably, the control module further comprises: and the constant current control unit generates a constant current conduction signal according to the demagnetizing time.
Preferably, the control module further comprises: and the constant current control unit generates a constant current conduction signal according to the demagnetizing time and the current peak value signal.
Preferably, the conduction signal generation module generates the conduction signal according to a constant voltage conduction signal and the constant current conduction signal.
Preferably, the on signal generating module includes: the first sampling and holding module samples and holds the voltage feedback signal and outputs a first sampling signal; the error amplifier is connected with the sampling and holding module and the digital-to-analog converter and generates an error signal according to the first sampling signal and the reference voltage; the first comparator is connected with the error amplifier and generates a constant-voltage conduction signal according to the error signal and the ramp signal; the AND gate is connected with the first comparator and the digital control module and generates the conduction signal according to the constant voltage conduction signal and the constant current conduction signal; the second sample and hold module is connected in series between the output end of the error amplifier and the ground end.
Preferably, the control circuit further includes: the RS trigger generates a switch control signal according to the on signal and the off signal; and the driving module generates a driving signal according to the switch control signal.
Preferably, the switching tube and the control circuit are integrated on the same chip.
According to another aspect of the present invention, there is provided a switching power supply comprising: a main circuit including a power conversion circuit for converting an ac input voltage to a dc output voltage; a control circuit; wherein the control circuit includes: the demagnetization detection module obtains the demagnetization time of the switching power supply according to the feedback signal representing the output voltage; the control module outputs a current peak signal and a slope signal in a time-sharing mode according to the demagnetizing time, the clock signal and the driving signal of the switching tube, and the control module outputs the current peak signal in the conducting period of the switching tube; during the off period of the switching tube, the control module outputs the ramp signal; the conducting signal generating module is used for carrying out sampling and holding on the voltage feedback signal to obtain a first sampling signal, generating an error signal according to the first sampling signal and a reference voltage, and generating a conducting signal according to the error signal and the slope signal; and the turn-off signal generating module is used for generating a turn-off signal according to the current sampling signal representing the current flowing through the switching tube and the current peak value signal.
Preferably, the ramp signal has at least one slope during the switching off of the switching tube.
Preferably, during the off period of the switching tube, the ramp signal comprises a plurality of sections of slopes, wherein the ramp signal is reduced from an initial voltage or a preset voltage with different slopes to form a plurality of sections of slopes; the ramp signal is turned up to a preset voltage to form a folding slope.
Preferably, the ramp signal has a multi-segment transition slope between a first segment slope and the folding slope.
Preferably, the switching frequency of the switching power supply at least includes a maximum switching frequency, a folding frequency, and an intermediate frequency, where the maximum switching frequency is the highest switching frequency of the switching power supply, the folding frequency is a switching frequency corresponding to when the ramp signal is turned up to a preset voltage, and the intermediate frequency is between the maximum switching frequency and the folding frequency.
Preferably, the control module is a digital control module, and the ramp signal and the current peak signal are generated in a time sharing way in a digital control mode.
Preferably, the control module includes: the digital control unit outputs a digital ramp signal and a digital current peak value signal in a time-sharing manner according to the demagnetizing time, the clock signal and the driving signal of the switching tube; and the digital-to-analog converter is used for carrying out digital-to-analog conversion on the digital ramp signal and the digital current peak signal so as to output the ramp signal and the current peak signal in a time-sharing mode.
Preferably, the control circuit further includes: and the threshold switching module is used for receiving the first threshold voltage and the second threshold voltage and outputting the first threshold voltage or the second threshold voltage as the reference voltage according to a switching signal.
Preferably, the control circuit further includes: and the third comparator is connected with the control module and generates the switching signal according to the ramp signal and the reference voltage.
Preferably, the threshold switching module outputs the first threshold voltage as the reference voltage when the ramp signal is greater than the reference voltage; when the ramp signal is equal to the reference voltage, the threshold switching module outputs the second threshold voltage as the reference voltage according to the switching signal, wherein the first threshold voltage is smaller than the second threshold voltage.
Preferably, the control module generates the switching signal according to the clock signal and a preset time.
Preferably, the threshold switching module outputs the first threshold voltage as the reference voltage when the count period of the clock signal does not reach a preset time; and when the counting period of the clock signal reaches a preset time, the threshold switching module outputs the second threshold voltage as the reference voltage.
Preferably, the control module generates the first threshold voltage or the second threshold voltage as the reference voltage according to a switching signal.
Preferably, the control circuit further includes: and the third comparator is connected with the control module and generates the switching signal according to the ramp signal and the reference voltage.
Preferably, the control module outputs the first threshold voltage as the reference voltage when the ramp signal is greater than the reference voltage; when the ramp signal is equal to the reference voltage, the control module outputs the second threshold voltage as the reference voltage according to the switching signal, wherein the first threshold voltage is smaller than the second threshold voltage.
Preferably, when the reference voltage is the first threshold voltage, the control module controls the ramp signal to gradually decrease from an initial voltage; when the reference voltage is switched from the first threshold voltage to the second threshold voltage, the control module controls the ramp signal to be turned up to a preset voltage and then gradually reduced.
Preferably, the on signal generating module includes: the sampling and holding module samples and holds the voltage feedback signal to obtain a first sampling signal; the error amplifier is connected with the sampling and holding module and generates an error signal according to the first sampling signal and the reference voltage; and the first comparator is respectively connected with the error amplifier and the digital-to-analog converter and generates a constant voltage conduction signal according to the error signal and the ramp signal.
Preferably, the conduction signal generating module generates a conduction signal according to the constant voltage conduction signal.
Preferably, the control module is connected with the sample-and-hold module, and controls the sample-and-hold module to sample the voltage feedback signal in the demagnetizing time.
Preferably, the shutdown signal generation module includes: the front edge blanking module receives a current sampling signal representing the current flowing through the switching tube and blanking burrs generated by the current sampling signal at the moment of switching tube conduction; and the second comparator is connected with the leading edge blanking module and the digital-to-analog converter and generates a turn-off signal according to the current sampling signal and the current peak value signal.
Preferably, the shutdown signal generation module includes: and the second comparator is connected with the digital-to-analog converter and generates a turn-off signal according to the current sampling signal and the current peak value signal.
Preferably, the control circuit further includes: and an oscillator for generating a clock signal.
Preferably, the control module further comprises: and the constant current control unit generates a constant current conduction signal according to the demagnetizing time.
Preferably, the control module further comprises: and the constant current control unit generates a constant current conduction signal according to the demagnetizing time and the current peak value signal.
Preferably, the conduction signal generation module generates the conduction signal according to a constant voltage conduction signal and the constant current conduction signal.
Preferably, the on signal generating module includes: the first sampling and holding module samples and holds the voltage feedback signal and outputs the first sampling signal; the error amplifier is connected with the sampling and holding module and the digital-to-analog converter and generates an error signal according to the first sampling signal and the reference voltage; the first comparator is connected with the error amplifier and generates a constant-voltage conduction signal according to the error signal and the ramp signal; the AND gate is connected with the first comparator and the digital control module and generates a conduction signal according to the constant voltage conduction signal and the constant current conduction signal; the second sample and hold module is connected in series between the output end of the error amplifier and the ground end.
Preferably, the control circuit further includes: the RS trigger generates a switch control signal according to the on signal and the off signal; and the driving module generates a driving signal according to the switch control signal.
Preferably, the switching tube and the switching power supply are integrated on the same chip.
Preferably, the power conversion circuit of the main circuit is any one selected from the following topologies: a floating-type Buck-Boost topology, a field-type Buck-Boost topology, a floating-type Buck topology, a field-type Buck topology, a Boost topology, and a flyback topology.
The control circuit of the switching power supply provided by the embodiment of the invention realizes constant voltage output and generates complex slope signals through the digital control module and the digital-to-analog converter, the slope signals have a plurality of descending slopes, and the slope signals descend from an initial voltage or a preset voltage to form a plurality of sections of slopes with different slopes; the ramp signal is turned up to a preset voltage to form a folding slope. The digital control and the analog control are combined together, the control mode is optimized, and the performance and the cost are optimized.
Further, the present embodiment realizes multiplexing of the digital-to-analog converter, generates the threshold voltage, the current peak signal and the ramp signal with multiple slopes in a time-sharing manner, and reduces the area of the analog circuit.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the present invention with reference to the accompanying drawings.
Fig. 1 shows a circuit diagram of a prior art primary side controlled switching power supply.
Fig. 2 shows a schematic circuit diagram of a control circuit employed in a prior art switching power supply.
Fig. 3 shows a schematic circuit diagram of a control circuit of a switching power supply provided according to a first embodiment of the present invention.
Fig. 4a and 4b are schematic diagrams showing the relationship between the switching frequency and the output current and the peak current and the output current of the switching power supply according to the embodiment of the invention.
Fig. 5 shows a waveform diagram of signals of a switching power supply according to an embodiment of the present invention.
Fig. 6 shows a schematic circuit diagram of a control circuit of a switching power supply provided according to a second embodiment of the present invention;
fig. 7 shows a schematic circuit diagram of a control circuit of a switching power supply according to a third embodiment of the present invention.
Detailed Description
Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. The same reference numbers will be used throughout the drawings to refer to the same or like parts. For clarity, the various features of the drawings are not drawn to scale.
Fig. 1 shows a circuit diagram of a prior art primary side controlled switching power supply. As shown in fig. 1, the switching power supply 100 includes a transformer T1, a switching tube M1 located on the primary side of the transformer T1, a current sampling resistor Rs, a rectifier bridge 101, an input holding capacitor Cin, a voltage feedback circuit 102, a control circuit 103, a flywheel diode D0 located on the secondary side of the transformer T1, an output holding capacitor Co, and an equivalent resistance Req of an output cable.
The rectifier bridge 101 includes diodes D1 to D4. The two inputs of the rectifier bridge 101 receive an ac input voltage Vac from an external ac power source. The input holding capacitor Cin is connected between the two output terminals of the rectifier bridge 101, thereby providing a dc input voltage Vin. The transformer T1 includes a primary winding Np, a secondary winding Ns, and an auxiliary winding Naux, and the primary winding Np, the switching tube M1, and the current sampling resistor Rs of the transformer T1 are sequentially connected in series between the high potential end of the input holding capacitor Cin and the ground. A current sampling signal VCS characterizing the current flowing through the switching tube M1 is obtained at an intermediate node between the switching tube M1 and the current sampling resistor Rs. The auxiliary winding Naux of the transformer T1 is connected to a voltage feedback circuit 102, in this example the voltage feedback current 102 comprising a voltage divider network of a first resistor R1 and a second resistor R2. The feedback signal VFB characterizing the output voltage Vo of the switching power supply 100 is obtained at an intermediate node between the first resistor R1 and the second resistor R2. The control circuit 103 receives the sampling signal VCS and the voltage feedback signal VFB at its two inputs, and provides the driving signal GD of the switching transistor M1 at its output.
On the secondary side of the transformer T1, a flywheel diode D0 and an output holding capacitor Co are connected in series across the secondary side winding Ns of the transformer T1. The flywheel diode D0 has an anode connected to the homonymous terminal of the secondary winding Ns and a cathode connected to one terminal of the output holding capacitor Co. The output voltage Vo is generated across the output holding capacitor Co to supply power to the load.
During operation of the switching power supply 100, the control circuit 103 controls the off time of the switching tube M1 according to the sampling signal VCS, and controls the sampling switching period of the switching tube M1 according to the voltage feedback signal VFB, thereby realizing constant current and/or constant voltage output. During the off-period of the switching tube M1, the secondary winding Ns of the transformer T1 transfers energy to the output terminal through the freewheel diode D0.
Fig. 2 shows a schematic circuit diagram of a control circuit in a prior art switching power supply. The control circuit 103 is used in the switching power supply shown in fig. 1, for example.
The control circuit 103 comprises two input terminals (voltage sampling terminal FB and current sampling terminal CS) for receiving the feedback signal VFB and the sampling signal VCS, respectively, and the control circuit 103 further comprises an output terminal for providing the driving signal GD of the switching tube M1. Further, the control circuit 103 includes a sample-and-hold module 104, an error amplifier 105, an oscillator 106, a demagnetizing time detection module 107, an exponential sawtooth wave signal generation module 108, a comparator 109, a constant current control module 110, an and gate 111, a shutdown signal generation module 112, an RS flip-flop 113, and a driving module 114.
The sample-hold module 104 samples and holds a feedback signal VFB representing the output voltage of the switching power supply, and the output end outputs a first sampling signal Vsample obtained after the sampling and holding; an inverting input terminal of the error amplifier 105 receives the first sampling signal Vsample, a non-inverting input terminal of the error amplifier 105 receives the reference voltage Vref0, and an output terminal of the error amplifier 105 outputs an error signal VEA obtained by amplifying an error between the first sampling signal Vsample and the reference voltage Vref 0; the oscillator 106 generates an oscillation signal, the demagnetizing time detection module 107 obtains the demagnetizing time TDS of the switching power supply by detecting the voltage feedback signal VFB, and the exponential sawtooth wave signal generation module 108 generates a ramp signal Vramp according to the oscillation signal and the demagnetizing time TDS. The comparator 109 generates a constant voltage on signal ONV based on the error signal VEA and the ramp signal Vramp. The constant current control module 110 calculates the peak current or the switching frequency of the next period according to the demagnetizing time TDS, the peak current and the switching frequency of the switching tube M1, and generates a constant current on signal ONC as another control signal for controlling the switching tube M1 to be turned on. The OFF signal generating module 112 generates OFF signal OFF according to the error signal VEA and the sampling signal VCS.
The two input ends of the AND gate 111 respectively receive a constant voltage conduction signal ONV and a constant current conduction signal ONC, and the constant voltage conduction signal ONV and the constant current conduction signal ONC are combined by the AND gate 111 to generate a conduction signal ON, and output the conduction signal ON to the setting end of the trigger 113 for controlling the conduction of the switching tube M1; the OFF signal OFF generated by the OFF signal generating module 112 is output to the reset end of the RS trigger 113, and is used for controlling the switching OFF of the switching tube M1; the output signal of the output terminal of the RS flip-flop 113 generates the driving signal GD after the driving capability is enhanced by the driving module 114.
Fig. 3 shows a schematic circuit diagram of a control circuit of a switching power supply according to a first embodiment of the invention. The control circuit 203 is used in the switching power supply shown in fig. 1, for example.
As shown in fig. 3, the control circuit 203 of the switching power supply includes a demagnetization detection module 207, a control module 221, a digital-to-analog converter (DAC) 210, an on signal generation module 220, an off signal generation module 212, an RS flip-flop 213, and a driving module 214.
The demagnetization detection module 207 is connected to the voltage sampling terminal FB, and detects the feedback signal VFB representing the output voltage to obtain the demagnetization time TDS of the switching power supply.
In this embodiment, the demagnetization detecting module 207 is connected to the voltage sampling terminal FB.
The control module 221 outputs the ramp signal Vramp and the current peak signal Vipk in a time-sharing manner according to the demagnetization time TDS, the clock signal CLK, and the driving signal GD of the switching transistor M1.
In the present embodiment, during the on period of the switching tube M1, the control module 211 outputs the current peak signal Vipk; during the off period of the switching transistor M1, the control module 211 outputs a ramp signal Vramp. The ramp signal Vramp has at least one slope, for example, includes a plurality of slopes, and the ramp signal Vramp is dropped from the initial voltage V0 or the preset voltage Vm with different slopes to form a plurality of slopes; the ramp signal Vramp forms a folding slope when turned up to a preset voltage. The ramp signal Vramp has a multi-segment transition slope between a first segment slope and the folding slope.
In the present embodiment, the switching tube M1 and the control circuit 203 are integrated in the same chip, but not limited thereto.
In this embodiment, the control module 221 is a digital control module, which uses a digital control method to generate the ramp signal Vramp and the current peak signal Vipk in a time-sharing manner.
The control module includes a digital control unit 208 and a digital-to-analog converter 210, where the digital control unit 208 outputs a digital ramp signal and a digital current peak signal in a time-sharing manner according to the demagnetization time TDS, the clock signal CLK, and the driving signal GD of the switching transistor M1. The digital-to-analog converter 210 performs digital-to-analog conversion on the digital ramp signal and the digital current peak signal to output a ramp signal Vramp and a current peak signal Vipk in a time-sharing manner.
In the present embodiment, the clock signal CLK is generated by the oscillator 206. The clock signal CLK is used to control the output waveform of the dac 210 after the demagnetization time TDS and the count of the system operating frequency. The digital control unit 208 starts timing when the switching tube M1 is turned on according to the driving signal GD, performs data operation according to the count value, and generates a control signal; and generating the current peak signal Vipk and the ramp signal Vramp in a time-sharing manner according to the control signal. Specifically, during the on period of the switching transistor M1, the digital-to-analog converter 210 outputs a current peak signal Vipk; during the off period of the switching transistor M1, the digital-to-analog converter 210 outputs a ramp signal Vramp. Wherein, referring to FIG. 5, the output voltage of the digital-to-analog converter 210 is denoted as V DAC . The control module 221 calculates a current peak voltage according to the driving signal GD; the control module 221 starts timing from the rising edge of the driving signal GD, that is, from the time when the switching tube M1 is turned on, and the timing time is T. When the timing time T is in the on period (on time is denoted as Ton) of the switching tube M1, i.e. 0 < T < Ton, the output voltage V of the DAC 210 DAC For the current peak signal Vipk, i.e. V DAC =vipk, current peak signal vipk=vp 1 or VP2, where VP1 and VP2 are peak voltages corresponding to the output current set at different loads. When the timing time T is within the off period of the switching tube (the off time is denoted as Toff), i.e. Ton < T < ton+toff, the output voltage V of the DAC 210 DAC The ramp signal Vramp has at least one slope. Output voltage V of D/A converter 210 DAC The formula of (2) is as follows:
wherein tmin=1/Fmax, fmax is the maximum switching frequency of the switching power supply, and the maximum switching frequency is the highest switching frequency of the switching power supply; tflod=1/fford, wherein fford is a folding frequency, and the ramp signal Vramp is turned up to a corresponding switching frequency when a preset voltage is reached; tmid=1/Fmid, fmid is the intermediate frequency, the switching frequency slightly larger than the gamut 20K, fford < Fmid < Fmax.
Specifically, when the timing time T is from the end of conduction to Tmin, i.e., ton < T < Tmin, the control module 221 causes the output voltage V of the digital-to-analog converter 210 according to the clock signal CLK DAC A first ramp signal Vramp1 which is fixed, i.e. V at this time DAC =vramp 1. At the instant when the timing time is equal to 1/Fmax, i.e., t=1/Fmax, the control module 221 digitally controls the output voltage V according to the clock signal CLK DAC A second ramp signal Vramp2 having a first slope L1, V DAC =vramp 2. During the time T between Tmin and Tmid, i.e. Tmin < T < Tmid, the control module 221 causes the output voltage V of the digital-to-analog converter 210 to be controlled digitally in dependence on the clock signal CLK DAC Is a third ramp signal Vramp3 having a second slope L2, at which time V DAC =vramp 3. At the instant when the timing time is equal to Tmid, i.e., t=tmid, the control module 221 causes the output voltage V of the digital-to-analog converter 210 to be output according to the clock signal CLK and the digital control DAC A fourth ramp signal Vramp4 having a third slope L3, at which time V DAC =vramp 4. During the time T between Tmid and Tflod, i.e. Tmid < T < Tflod, the control module 221 causes the output voltage V of the digital-to-analog converter 210 to be controlled digitally in dependence on the clock signal CLK DAC A fifth ramp signal Vramp5 having a fourth slope L4, at which time V DAC =vramp 5. During Tflod < T < Toff, the control module 221 causes the output voltage V of the digital-to-analog converter 210 to be based on the clock signal CLK and digital control DAC Is the sixth ramp signal Vramp6 having the fifth slope L5. During the off period of the switching tube M1, the digital-to-analog converter 210 outputs ramp signals Vramp with various slopes, i.e. generates down-conversion curves with various slopes.
The conducting signal generating module 220 samples and holds the voltage feedback signal VFB representing the output voltage to obtain a first sampling signal Vsample, generates an error signal VEA according to the first sampling signal Vsample and the reference voltage, generates a constant voltage conducting signal ONV according to the error signal VEA and the ramp signal Vramp, and uses the constant voltage conducting signal ONV as a conducting signal ON.
In this embodiment, the on signal generating module 220 includes a sample-and-hold module 204, an error amplifier 205, and a first comparator 209, where the sample-and-hold module 204 samples and holds the voltage feedback signal VFB and outputs a first sampling signal Vsample; an error amplifier 205 is connected to the sample-and-hold module 204, and generates an error signal VEA according to the first sample signal Vsample and a reference voltage; the first comparator 209 is connected to the error amplifier 205 and generates a constant voltage on signal ONV based on the error signal VEA and the ramp signal Vramp.
The non-inverting input terminal of the error amplifier 205 receives the reference voltage, the inverting input terminal receives the first sampling signal Vsample, and the output terminal outputs the error signal VEA. The first comparator 209 has a non-inverting input terminal receiving the error signal VEA, an inverting input terminal receiving the ramp signal Vramp, and an output terminal outputting the constant voltage on signal ONV.
Referring to fig. 5, during a first period T1, when demagnetization begins, the output voltage V of the dac 210 DAC The fixed first ramp signal Vramp1 is output, and the value of the first ramp signal Vramp1 is the initial voltage V0. After the highest switching frequency Fmax, i.e. after the demagnetization is finished, the output voltage V of the digital-to-analog converter 210 DAC From the initial voltage V0. At the falling instant, i.e. at the instant Tmin corresponding to the highest switching frequency Famx, the output voltage V of the digital-to-analog converter 210 DAC When the error signal VEA is equal, the constant voltage on signal ONV outputted by the first comparator 209 becomes a logic high level, and the RS flip-flop 213 and the driving module 214 generate the driving signal GD for controlling the on of the switching transistor M1, so that the switching transistor M1 is turned on.
During the second period T2, when demagnetization begins, the output voltage V of the DAC 210 DAC The fixed first ramp signal Vramp1 is output, and the value of the first ramp signal Vramp1 is the initial voltage V0. After the highest switching frequency Fmax, i.e. after the demagnetization is finished, the output voltage V of the digital-to-analog converter 210 DAC From the initial voltage V0 not toThe same slope decreases in turn. At some point around the intermediate frequency Fmid, the output voltage V of the digital-to-analog converter 210 DAC The constant voltage on signal ONV outputted by the first comparator 209 becomes logic high level equal to the error signal VEA, and the RS flip-flop 213 and the driving module 214 generate the driving signal GD for controlling the on of the switching transistor M1, so that the switching transistor M1 is turned on.
In the third period T3, when demagnetization starts, the output voltage V of the DAC 210 DAC The fixed first ramp signal Vramp1 is output, and the value of the first ramp signal Vramp1 is the initial voltage V0. After the highest switching frequency Fmax, i.e. after the demagnetization is finished, the output voltage V of the digital-to-analog converter 210 DAC Sequentially from the initial voltage V0 as a function of 4 segments of time. At some point after folding frequency fford, the output voltage V of digital-to-analog converter 210 DAC When the error signal VEA is equal, the constant voltage on signal ONV outputted by the first comparator 209 becomes a logic high level, and the RS flip-flop 213 and the driving module 214 generate the driving signal GD for controlling the on of the switching transistor M1, so that the switching transistor M1 is turned on.
The OFF signal generating module 212 generates an OFF signal OFF for turning OFF the switching tube M1 based on the current sampling signal VCS representing the current flowing through the switching tube M1 and the current peak signal Vipk.
In this embodiment, the shutdown signal generation module 212 is connected to the current sampling terminal CS. The shutdown signal generation module 212 includes a leading edge blanking module 217 and a second comparator 218. The leading edge blanking module 217 receives a current sampling signal VCS representing a current flowing through the primary winding Np of the transformer T1, and blanks burrs generated by the current sampling signal VCS at the instant when the switching tube M1 is turned on; the second comparator 218 is connected to the leading edge blanking module 217 and the digital-to-analog converter 210, and generates a turn-OFF signal OFF according to the current sampling signal VCS and the current peak signal Vipk.
When the switching tube M1 is turned on, the primary winding Np starts to store energy, and the current of the primary winding Np rises with a certain slope, that is, the sampling signal VCS rises with a certain slope. When the sampling signal VCS is greater than the output voltage V of the DAC 210 DAC At the time, a second comparator218 becomes a logic high level, and generates a driving signal for controlling the switching tube M1 to be turned OFF through the RS flip-flop 213 and the driving module 214, so that the switching tube M1 is turned OFF.
The RS flip-flop 213 generates a switching control signal according to the ON signal ON and the OFF signal OFF.
The driving module 214 generates a driving signal GD according to the switch control signal.
In a preferred embodiment, the control module 221 is further connected to the sample-and-hold module 204, and controls the sample-and-hold module 204 to sample the voltage feedback signal VFB.
The control circuit 203 of the switching power supply further includes a third comparator 216 connected to the digital-to-analog converter 210, and generates a switching signal Swp according to the ramp signal Vramp and the reference voltage Vref.
The control circuit 203 of the switching power supply further includes a threshold switching module 215 connected to the third comparator 216, and configured to receive the first threshold voltage CV1 and the second threshold voltage CV2 with different magnitudes, and output the first threshold voltage CV1 or the second threshold voltage CV2 as a reference voltage according to the switching signal Swp.
In the present embodiment, the threshold switching module 215 implements threshold switching using, for example, a single pole double throw switch, but is not limited thereto. The switching signal Swp controls the single pole double throw switch to connect the first threshold voltage CV1 and the second threshold voltage CV2 to achieve threshold switching.
The control module 221 outputs the current peak signal Vipk or the ramp signal Vramp in a time-sharing manner according to the switching signal Swp, the demagnetizing time TDS, the clock signal CLK, and the driving signal GD of the switching transistor M1.
In this embodiment, when the ramp signal Vramp is greater than the reference voltage Vref, the threshold switching module 215 outputs the first threshold voltage CV1 as the reference voltage, and the control module 221 controls the ramp signal Vramp to gradually decrease from the initial voltage V0 (i.e., the fixed first ramp signal Vramp 1); when the ramp signal Vramp is equal to the reference voltage Vref, the threshold switching module 215 outputs a second threshold voltage CV2 as a reference voltage according to the switching signal, and the control module 221 controls the ramp signal Vramp to restore to the preset voltage Vm, wherein the first threshold voltage CV1 is smaller than the second threshold voltage CV2. The corresponding point in time when the ramp signal Vramp is equal to the reference voltage Vref may be taken as the corresponding point in time of the folding frequency fford.
When the reference voltage is the first threshold voltage CV1, the error signal output by the error amplifier 205 is VEA1; when the reference voltage is the second threshold voltage CV2, the error signal outputted by the error amplifier 205 is VEA2, wherein VEA2 > VEA1 and VEA2-VEA 1= (CV 2-CV 1) K EA . Wherein K is EA Is the closed loop gain of the error amplifier 205.
In the threshold switching, for example, when the reference voltage is switched from the first threshold voltage CV1 to the second threshold voltage CV2, the first sampling signal Vsample at the negative terminal of the error amplifier 205 does not need to be changed, and the output voltage is smoothly transited. The output of the error amplifier 205 is changed from small to large, the ramp signal Vramp is also changed from low to high, the falling slope curve of the ramp signal can be redesigned in a larger range, the loop gain near light load or no load is reduced, and the system stability is improved. For example, a point with the working frequency of 1Khz can be selected as a threshold switching point, the range of a frequency-reducing curve from the working frequency of 1Khz to the minimum frequency (for example, 0.3 Khz) after switching can be improved by 10 times, the loop compensation capacitance is greatly reduced, and the area is simplified.
Referring to FIG. 4a, when I1 is less than or equal to Iout < I2, the switching frequency Fsw changes with the output current Iout, i.e., the switching frequency Fsw increases linearly with the output current Iout; when I2 is less than or equal to Iout and less than I3, the switching frequency Fsw is basically unchanged along with the output current Iout; when I3 is less than or equal to Iout and less than I4, the switching frequency Fsw changes along with the output current Iout, namely, the switching frequency Fsw increases linearly along with the increase of the output current Iout; when I4 is less than or equal to Iout and less than I5, the switching frequency Fsw is basically unchanged along with the output current Iout.
Referring to FIG. 4b, when I1 is less than or equal to Iout < I2, the peak current Ieak per cycle is unchanged with the output current Iout; when I2 is less than or equal to Iout and less than I3, the peak current Ieak of each period changes along with the output current Iout, namely, the peak current Ieak of each period linearly increases along with the increase of the output current Iout; when I3 is less than or equal to Iout and less than I4, the peak current Ieak of each period is unchanged along with the output current Iout; when I4 is less than or equal to Iout < I5, the peak current Ieak of each period changes along with the output current Iout, namely, the peak current Ieak of each period increases linearly along with the increase of the output current Iout.
The larger the output current Iout, the larger the error signal VEA becomes (the switching frequency is larger than the folding frequency), so that the switching frequency of the switching transistor M1 becomes higher and higher. The smaller the output current Iout, the smaller the error signal VEA becomes (the switching frequency is larger than the folding frequency), so that the switching frequency of the switching transistor M1 becomes lower. The smaller the output current Iout, the smaller the error signal VEA becomes (the switching frequency is larger than the folding frequency), the higher the reference voltage of the switching error amplifier becomes and the output voltage V of the digital-to-analog converter is controlled at the same time DAC Becomes higher so that the switching frequency of the switching tube M1 is lower.
During the on period of the switching transistor M1, the peak magnitude of the current sampling signal VCS is defined, such as the output voltage V of the digital-to-analog converter 210 DAC As the output current Iout increases, the on-time of the switching tube M1 and the peak magnitude of the current sampling signal VCS both increase with the output current Iout, see I2-I3 and I4-I5 in fig. 4 b.
Output voltage V of digital to analog converter 210 DAC The magnitude of (2) does not vary with the output current Iout, so the on-time of the switching tube M1 and the peak magnitude of the current sampling signal VCS remain constant, see I1-I2 and I3-I4 in fig. 4 b.
According to the control circuit of the switching power supply, constant voltage output is achieved by sampling a voltage feedback signal representing output voltage and adjusting the switching frequency of a switching tube according to the change of the voltage feedback signal, and peak current. Reducing the output voltage, for example by reducing the switching frequency or reducing the peak current or both the switching frequency and the peak current when the output voltage becomes large; when the output voltage becomes smaller, constant voltage output is realized by increasing the output voltage by increasing the switching frequency or increasing the peak current or both.
The control circuit of the switching power supply provided by the embodiment of the invention realizes constant voltage output and generates complex voltage through the digital control module and the digital-to-analog converter
A ramp signal having a plurality of falling slopes, the ramp signal falling from an initial voltage or a preset voltage with different slopes to form a multi-section slope; the ramp signal is turned up to a preset voltage to form a folding slope. The digital control and the analog control are combined together, the control mode is optimized, and the performance and the cost are optimized.
Further, the present embodiment realizes multiplexing of the digital-to-analog converter, generates the threshold voltage, the current peak signal and the ramp signal with multiple slopes in a time-sharing manner, and reduces the area of the analog circuit.
Fig. 6 shows a schematic circuit diagram of a control circuit of a switching power supply according to a second embodiment of the invention. The control circuit 303 is used in the switching power supply shown in fig. 1, for example. Compared to the first embodiment, the control module 321 of the present embodiment further includes a constant current control unit 319, which generates a constant current on signal ONC according to the demagnetizing time TDS and the current peak signal Vipk.
In one example, the output current iout=np×vipk×tds×fsw/(2×ns×rs), where Np is the number of turns of the primary winding, ns is the number of turns of the secondary winding, vipk is the current peak signal, TDS is the demagnetization time, fsw is the switching frequency, and Rs is the current sampling resistor. Since the current peak signal Vipk is generated by the digital control of the control module 321, the demagnetizing time TDS is generated by the demagnetizing detection module 307, and the switching frequency Fsw can be obtained by counting the oscillator 306, the current peak signal vipk×tds×fsw is constant, and a constant current can be realized. The output voltage V of the D/A converter 310 at this time DAC =vref-cc TDS/T. Wherein Vref-cc is constant current reference voltage, TDS is demagnetizing time TDS, and T is counting period T of the oscillator. Correspondingly, the conducting signal generating module 320 further includes an and gate 311, which is connected to the output end of the first comparator 309 and the control module 321, and the and gate 311 generates the conducting signal ON according to the constant voltage conducting signal ONV and the constant current conducting signal ONC.
The non-inverting input of the error amplifier 305 is directly coupled to the output of the digital-to-analog converter 310, receiving either the first threshold voltage CV1 or the second threshold voltage CV2.
The control module 321 of the present embodiment also generates the first threshold voltage CV1 or the second threshold voltage as the reference voltage CV2 according to the switching signal Swp.
When the ramp signal Vramp is greater than the reference voltage Vref, the control module 321 outputs a first threshold voltage CV1 as a reference voltage; when the ramp signal Vramp is equal to the reference voltage Vref, the control module 321 outputs a second threshold voltage CV2 as the reference voltage, wherein the first threshold voltage CV1 is smaller than the second threshold voltage CV2.
In a preferred embodiment, referring to fig. 4a, the magnitude of the output current Iout determines the magnitude of the line loss compensation. At least when I2 is less than or equal to Iout and less than I5, a certain proportional relationship exists between the output current and the line loss compensation. In the constant voltage process, the compensation voltage Vcomp may be expressed as vcomp=kc×vipk×tds×fsw, where Kc is a compensation coefficient.
In a preferred embodiment, the control circuit further comprises a sampling switch K and a holding capacitance C. The sampling switch K is connected between the output of the error amplifier 305 and the non-inverting input of the first comparator 309. The holding capacitance C is connected between the non-inverting input terminal of the first comparator 309 and the ground terminal.
During the on period of the switching tube M1, the digital-to-analog converter 310 outputs a current peak signal Vipk to control the magnitude of the peak current. During the demagnetization time TDS, the control module 321 generates a first threshold voltage CV1 or a second threshold voltage CV2 as a reference voltage according to the compensation voltage Vcomp, where the first threshold voltage cv1=cva+vcomp; the second threshold voltage cv2=cvb+vcomp, where CVa is the threshold voltage before switching and CVb is the threshold voltage after switching, so as to implement line loss compensation; after demagnetization is finished, the sampling switch K and the holding capacitor C start to work, the sampling switch K is disconnected, the output signal VEA of the error amplifier is sampled and held on the holding capacitor C, and after the highest frequency Fmax is finished, the digital-to-analog converter 310 outputs a ramp signal Vramp to control the switching frequency of the switching tube M1.
The rest of the contents are the same as those of the first embodiment, and will not be described again here.
The control circuit of the switching power supply provided by the embodiment of the invention realizes constant voltage and constant current output and generates a complex down-conversion curve through the digital control module and the digital-to-analog converter. The digital control and the analog control are combined together, the control mode is optimized, and the performance and the cost are optimized.
Further, the present embodiment realizes multiplexing of digital-to-analog converters, generates a threshold voltage, a current peak signal and a ramp signal with multiple slopes in a time-sharing manner, and reduces the area of an analog circuit by multiplexing of the digital-to-analog converters.
Fig. 7 shows a schematic circuit diagram of a control circuit of a switching power supply according to a third embodiment of the present invention. The control circuit 403 is used in the switching power supply shown in fig. 1, for example. In contrast to the first embodiment, the third comparator is not employed in the control circuit 403 to generate the switching signal Swp.
The control circuit 403 directly generates the switching signal Swp according to the clock signal CLK generated by the oscillator 406, the demagnetizing time and the preset time T0.
According to the counting period of the clock signal CLK, the threshold switching module 415 takes the first threshold voltage CV1 as the reference voltage when the preset time T0 is not reached; when the preset time T0 is reached, the threshold switching module 415 uses the second threshold voltage CV2 as a reference voltage according to the switching signal Swp.
The rest of the contents are the same as those of the first embodiment, and will not be described again here.
Embodiments of the invention are described above without exhaustive details, nor without limiting the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various modifications as are suited to the particular use contemplated. The scope of the invention should be determined by the following claims.

Claims (55)

1. A control circuit for a switching power supply, comprising:
the demagnetization detection module obtains the demagnetization time of the switching power supply according to the voltage feedback signal representing the output voltage;
the control module outputs a current peak value signal and a slope signal in a time-sharing manner according to the demagnetizing time, the clock signal and the driving signal of the switching tube;
the conducting signal generating module is used for carrying out sampling and holding on the voltage feedback signal to obtain a first sampling signal, generating an error signal according to the first sampling signal and a reference voltage, and generating a conducting signal according to the error signal and the slope signal;
The turn-off signal generating module generates a turn-off signal according to a current sampling signal representing the current flowing through the switching tube and the current peak value signal;
wherein, during the on period of the switching tube, the control module outputs the current peak value signal; during the off period of the switching tube, the control module outputs the slope signal, wherein the slope signal has at least one section of slope.
2. The control circuit of claim 1, wherein the ramp signal includes a multi-segment slope during a switching off period of the switching tube, wherein the ramp signal is dropped from an initial voltage or a preset voltage with different slopes to form the multi-segment slope; the ramp signal is turned up to a preset voltage to form a folding slope.
3. The control circuit of claim 2, wherein the ramp signal has a multi-segment transition slope between a first segment slope and the folding slope.
4. The control circuit of claim 1, wherein the switching frequency of the switching power supply includes at least a maximum switching frequency, a folding frequency, and an intermediate frequency, wherein the maximum switching frequency is a highest switching frequency of the switching power supply, the folding frequency is a switching frequency corresponding to when the ramp signal is turned up to a preset voltage, and the intermediate frequency is between the maximum switching frequency and the folding frequency.
5. The control circuit of claim 1, wherein the control module is a digital control module that generates the ramp signal and the current peak signal in a digitally controlled manner.
6. The control circuit of claim 1, wherein the control module comprises:
the digital control unit outputs a digital ramp signal and a digital current peak value signal in a time-sharing manner according to the demagnetizing time, the clock signal and the driving signal of the switching tube;
and the digital-to-analog converter is used for carrying out digital-to-analog conversion on the digital ramp signal and the digital current peak signal so as to output the ramp signal and the current peak signal in a time-sharing mode.
7. The control circuit of claim 1, further comprising:
and the threshold switching module is used for receiving the first threshold voltage and the second threshold voltage and outputting the first threshold voltage or the second threshold voltage as the reference voltage according to a switching signal.
8. The control circuit of claim 7, further comprising:
and the third comparator is connected with the control module and generates the switching signal according to the ramp signal and the reference voltage.
9. The control circuit of claim 8, wherein the threshold switching module outputs the first threshold voltage as the reference voltage when the ramp signal is greater than the reference voltage; when the ramp signal is equal to the reference voltage, the threshold switching module outputs the second threshold voltage as the reference voltage according to the switching signal, wherein the first threshold voltage is smaller than the second threshold voltage.
10. The control circuit of claim 7, wherein the control module generates the switching signal based on a clock signal and a preset time.
11. The control circuit according to claim 10, wherein the threshold switching module outputs the first threshold voltage as the reference voltage when a count period of the clock signal does not reach a preset time; and when the counting period of the clock signal reaches a preset time, the threshold switching module outputs the second threshold voltage as the reference voltage.
12. The control circuit of claim 7, wherein the control module outputs the first threshold voltage or the second threshold voltage as the reference voltage according to the switching signal.
13. The control circuit of claim 12, further comprising:
and the third comparator is connected with the control module and generates the switching signal according to the ramp signal and the reference voltage.
14. The control circuit of claim 13, wherein the control module outputs the first threshold voltage as the reference voltage when the ramp signal is greater than the reference voltage; when the ramp signal is equal to the reference voltage, the control module outputs the second threshold voltage as the reference voltage according to the switching signal, wherein the first threshold voltage is smaller than the second threshold voltage.
15. The control circuit according to claim 7 or 12, wherein the control module controls the ramp signal to gradually decrease from an initial voltage when the reference voltage is the first threshold voltage; when the reference voltage is switched from the first threshold voltage to the second threshold voltage, the control module controls the ramp signal to be turned up to a preset voltage and then gradually reduced.
16. The control circuit of claim 1, wherein the turn-on signal generation module comprises:
the sampling and holding module samples and holds the voltage feedback signal to obtain a first sampling signal;
the error amplifier is connected with the sampling and holding module and generates an error signal according to the first sampling signal and the reference voltage;
and the first comparator is respectively connected with the error amplifier and the digital-to-analog converter in the control module, and generates a constant voltage conduction signal according to the error signal and the ramp signal.
17. The control circuit of claim 16, wherein the turn-on signal generation module generates a turn-on signal based on the constant voltage turn-on signal.
18. The control circuit of claim 16, wherein the control module is coupled to the sample-and-hold module to control the sample-and-hold module to sample the voltage feedback signal during a demagnetization time.
19. The control circuit of claim 1, wherein the shutdown signal generation module comprises:
the front edge blanking module receives a current sampling signal representing the current flowing through the switching tube and blanking burrs generated by the current sampling signal at the moment of switching tube conduction;
and the second comparator is connected with the front edge blanking module and the digital-to-analog converter in the control module and generates a turn-off signal according to the current sampling signal and the current peak value signal.
20. The control circuit of claim 1, wherein the shutdown signal generation module comprises:
and the second comparator is connected with a digital-to-analog converter in the control module and generates a turn-off signal according to the current sampling signal and the current peak value signal.
21. The control circuit of claim 1, further comprising:
and an oscillator for generating a clock signal.
22. The control circuit of claim 16, wherein the control module further comprises:
and the constant current control unit generates a constant current conduction signal according to the demagnetizing time.
23. The control circuit of claim 16, wherein the control module further comprises:
and the constant current control unit generates a constant current conduction signal according to the demagnetizing time and the current peak value signal.
24. The control circuit according to claim 22 or 23, wherein the turn-on signal generating module generates a turn-on signal according to a constant voltage turn-on signal and the constant current turn-on signal.
25. The control circuit of claim 24, wherein the turn-on signal generation module comprises:
the first sampling and holding module samples and holds the voltage feedback signal and outputs a first sampling signal;
the error amplifier is connected with the sampling and holding module and the digital-to-analog converter and generates an error signal according to the first sampling signal and the reference voltage;
the first comparator is connected with the error amplifier and generates a constant-voltage conduction signal according to the error signal and the ramp signal;
the AND gate is connected with the first comparator and the control module and generates the conduction signal according to the constant voltage conduction signal and the constant current conduction signal;
the second sample and hold module is connected in series between the output end of the error amplifier and the ground end.
26. The control circuit of claim 1, further comprising:
the RS trigger generates a switch control signal according to the on signal and the off signal;
and the driving module generates a driving signal according to the switch control signal.
27. The control circuit of claim 1, wherein the switching tube and the control circuit are integrated on the same chip.
28. A switching power supply, comprising:
a main circuit including a power conversion circuit for converting an ac input voltage to a dc output voltage; a control circuit;
wherein the control circuit includes:
the demagnetization detection module obtains the demagnetization time of the switching power supply according to the feedback signal representing the output voltage;
the control module outputs a current peak value signal and a slope signal in a time-sharing manner according to the demagnetizing time, the clock signal and the driving signal of the switching tube;
the conducting signal generating module is used for carrying out sampling and holding on the voltage feedback signal to obtain a first sampling signal, generating an error signal according to the first sampling signal and a reference voltage, and generating a conducting signal according to the error signal and the slope signal;
The turn-off signal generating module generates a turn-off signal according to a current sampling signal representing the current flowing through the switching tube and the current peak value signal;
wherein, during the on period of the switching tube, the control module outputs the current peak value signal; during the off period of the switching tube, the control module outputs the slope signal, wherein the slope signal has at least one section of slope.
29. The switching power supply of claim 28 wherein said ramp signal includes a multi-segment slope during switching off of the switching tube, wherein said ramp signal drops from an initial voltage or a preset voltage with different slopes to form a multi-segment slope; the ramp signal is turned up to a preset voltage to form a folding slope.
30. The switching power supply of claim 29 wherein said ramp signal has a multi-segment transition slope between a first segment slope and said folding slope.
31. The switching power supply of claim 28 wherein the switching frequency of the switching power supply includes at least a maximum switching frequency, a folding frequency, and an intermediate frequency, wherein the maximum switching frequency is a highest switching frequency of the switching power supply, the folding frequency is a switching frequency corresponding to when the ramp signal is folded up to a preset voltage, and the intermediate frequency is between the maximum switching frequency and the folding frequency.
32. The switching power supply of claim 28 wherein said control module is a digital control module that time-shares said ramp signal and said current peak signal in a digital control manner.
33. The switching power supply of claim 28 wherein said control module comprises:
the digital control unit outputs a digital ramp signal and a digital current peak value signal in a time-sharing manner according to the demagnetizing time, the clock signal and the driving signal of the switching tube;
and the digital-to-analog converter is used for carrying out digital-to-analog conversion on the digital ramp signal and the digital current peak signal so as to output the ramp signal and the current peak signal in a time-sharing mode.
34. The switching power supply of claim 28 wherein said control circuit further comprises:
and the threshold switching module is used for receiving the first threshold voltage and the second threshold voltage and outputting the first threshold voltage or the second threshold voltage as the reference voltage according to a switching signal.
35. The switching power supply of claim 34 wherein said control circuit further comprises:
and the third comparator is connected with the control module and generates the switching signal according to the ramp signal and the reference voltage.
36. The switching power supply of claim 35 wherein said threshold switching module outputs said first threshold voltage as said reference voltage when said ramp signal is greater than said reference voltage; when the ramp signal is equal to the reference voltage, the threshold switching module outputs the second threshold voltage as the reference voltage according to the switching signal, wherein the first threshold voltage is smaller than the second threshold voltage.
37. The switching power supply of claim 34 wherein the control module generates the switching signal based on a clock signal and a preset time.
38. The switching power supply of claim 37 wherein said threshold switching module outputs said first threshold voltage as said reference voltage when a count period of said clock signal does not reach a preset time; and when the counting period of the clock signal reaches a preset time, the threshold switching module outputs the second threshold voltage as the reference voltage.
39. The switching power supply of claim 33 wherein the control module generates either a first threshold voltage or a second threshold voltage as the reference voltage based on a switching signal.
40. The switching power supply of claim 39 wherein said control circuit further comprises:
and the third comparator is connected with the control module and generates the switching signal according to the ramp signal and the reference voltage.
41. The switching power supply of claim 40 wherein said control module outputs said first threshold voltage as said reference voltage when said ramp signal is greater than said reference voltage; when the ramp signal is equal to the reference voltage, the control module outputs the second threshold voltage as the reference voltage according to the switching signal, wherein the first threshold voltage is smaller than the second threshold voltage.
42. The switching power supply of claim 34 or 39 wherein said control module controls said ramp signal to gradually decrease from an initial voltage when said reference voltage is said first threshold voltage; when the reference voltage is switched from the first threshold voltage to the second threshold voltage, the control module controls the ramp signal to be turned up to a preset voltage and then gradually reduced.
43. The switching power supply of claim 28 wherein said on signal generating means comprises:
The sampling and holding module samples and holds the voltage feedback signal to obtain a first sampling signal;
the error amplifier is connected with the sampling and holding module and generates an error signal according to the first sampling signal and the reference voltage;
and the first comparator is respectively connected with the error amplifier and the digital-to-analog converter in the control module, and generates a constant voltage conduction signal according to the error signal and the ramp signal.
44. The switching power supply of claim 43 wherein said turn-on signal generating module generates a turn-on signal based on said constant voltage turn-on signal.
45. The switching power supply of claim 43 wherein said control module is coupled to said sample-and-hold module for controlling the sample-and-hold module to sample said voltage feedback signal during a demagnetization time.
46. The switching power supply of claim 28 wherein said shutdown signal generation module comprises:
the front edge blanking module receives a current sampling signal representing the current flowing through the switching tube and blanking burrs generated by the current sampling signal at the moment of switching tube conduction;
and the second comparator is connected with the front edge blanking module and the digital-to-analog converter in the control module and generates a turn-off signal according to the current sampling signal and the current peak value signal.
47. The switching power supply of claim 28 wherein said shutdown signal generation module comprises:
and the second comparator is connected with a digital-to-analog converter in the control module and generates a turn-off signal according to the current sampling signal and the current peak value signal.
48. The switching power supply of claim 28 wherein said control circuit further comprises:
and an oscillator for generating a clock signal.
49. The switching power supply of claim 28 wherein said control module further comprises:
and the constant current control unit generates a constant current conduction signal according to the demagnetizing time.
50. The switching power supply of claim 28 wherein said control module further comprises:
and the constant current control unit generates a constant current conduction signal according to the demagnetizing time and the current peak value signal.
51. The switching power supply according to claim 49 or 50, wherein the on signal generating module generates the on signal according to a constant voltage on signal and the constant current on signal.
52. The switching power supply of claim 51 wherein said on signal generating means comprises:
The first sampling and holding module samples and holds the voltage feedback signal and outputs the first sampling signal;
the error amplifier is connected with the digital-to-analog converter in the sampling and holding module and the control module and generates an error signal according to the first sampling signal and the reference voltage;
the first comparator is connected with the error amplifier and generates a constant-voltage conduction signal according to the error signal and the ramp signal;
the AND gate is connected with the first comparator and the control module and generates a conduction signal according to the constant voltage conduction signal and the constant current conduction signal;
the second sample and hold module is connected in series between the output end of the error amplifier and the ground end.
53. The switching power supply of claim 28 wherein said control circuit further comprises:
the RS trigger generates a switch control signal according to the on signal and the off signal;
and the driving module generates a driving signal according to the switch control signal.
54. The switching power supply of claim 28 wherein said switching tube and switching power supply are integrated on the same chip.
55. The switching power supply of claim 28 wherein the power conversion circuit of the main circuit is any one selected from the following topologies: a floating-type Buck-Boost topology, a field-type Buck-Boost topology, a floating-type Buck topology, a field-type Buck topology, a Boost topology, and a flyback topology.
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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103151943A (en) * 2013-03-30 2013-06-12 深圳市富满电子有限公司 Dual-threshold control system and method for switch power supply
CN106533214A (en) * 2016-12-21 2017-03-22 无锡硅动力微电子股份有限公司 Switching power supply converter control circuit and control method thereof

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103151943A (en) * 2013-03-30 2013-06-12 深圳市富满电子有限公司 Dual-threshold control system and method for switch power supply
CN106533214A (en) * 2016-12-21 2017-03-22 无锡硅动力微电子股份有限公司 Switching power supply converter control circuit and control method thereof

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