CN117477913A - Switching power supply device, control method, integrated control circuit - Google Patents

Abstract

The embodiment of the application provides a control method of a switching power supply device, an integrated control circuit and the switching power supply device, wherein the integrated control circuit comprises: a switching element and a control circuit for controlling on and off of the switching element, characterized in that the control circuit comprises: a soft start circuit for performing soft start during power supply start and outputting a soft start signal; and the frequency control circuit is used for controlling the switching frequency of the switching element to be reduced to a first frequency when the power supply is started according to the soft start signal during soft start.

Description

Switching power supply device, control method, integrated control circuit

Technical Field

The application relates to the technical field of circuits.

Background

In a pulse width modulation (pulse width modulation, PWM)) switching power supply device, when a switching power supply is started, an output voltage is low, and if a flyback mode is adopted, a slope of a rectifying current of a secondary side rectifying diode of a transformer in the switching power supply is gentle, and if a chopper mode is adopted, a slope of a regenerative current of a flywheel diode is gentle, and thus the current is in a continuous state.

In this continuous current state, when switching is performed, switching current flows from a state where energy of the transformer remains or a state where energy is flowing through the reactance coil, and thus, a current of the primary side metal-oxide semiconductor field effect transistor (MOSFET) of the transformer increases, and a large surge voltage is generated in the rectifier diode or the flywheel diode. Therefore, in the primary side MOSFET, a MOSFET that can allow a large switching current is required, and in the rectifying diode, a diode of high withstand voltage is required.

In order to suppress the occurrence of a large surge voltage caused by the overlapping of drain currents at the time of starting the switching power supply, the switching power supply in the related art (patent document 1: japanese patent No. 6829957) performs control to reduce the switching frequency by detecting a condition that the output voltage is low.

It should be noted that the foregoing description of the background art is only for the purpose of facilitating a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. The above-described solutions are not considered to be known to the person skilled in the art simply because they are set forth in the background section of the present application.

Disclosure of Invention

The inventors have found that in the low-voltage state detection circuit for detecting a condition in which the output voltage is low in the related art, it is necessary to additionally provide a resistor for detecting the output voltage and a dedicated terminal for detection, and it is necessary to add components and design the dedicated terminal.

In order to solve at least one of the above problems or other similar problems, embodiments of the present application provide a switching power supply device and a control method, and an integrated control circuit.

According to a first aspect of embodiments of the present application, there is provided an integrated control circuit of a switching power supply device, the integrated control circuit including: a switching element and a control circuit for controlling on and off of the switching element, the control circuit comprising:

a soft start circuit for performing soft start during power supply start and outputting a soft start signal;

and the frequency control circuit is used for controlling the switching frequency of the switching element to be reduced to a first frequency when the power supply is started according to the soft start signal during soft start.

According to a second aspect of embodiments of the present application, there is provided a control method of a switching power supply device, the method including:

performing soft start control during power supply starting and outputting a soft start signal;

during soft start, the switching frequency of a switching element in the switching power supply device at the time of starting the power supply is controlled to be reduced to a first frequency according to the soft start signal.

According to a third aspect of embodiments of the present application, there is provided a switching power supply device, including the integrated control circuit of the first aspect.

One of the beneficial effects of the embodiment of the application is that: during soft start, the switching frequency of the switching element at the time of power supply start (during a period when the output voltage is low) is lowered in accordance with the soft start signal, whereby the duty ratio is reduced in a current continuous state at the time of start without adding additional components and dedicated terminals, overlap of the switching current is avoided, OFF time required in resetting of excitation energy of the transformer or the reactance coil is ensured, surge voltage generated on the secondary side rectifying diode or the flywheel diode is suppressed, and the installation space of the printed circuit board is reduced.

Specific embodiments of the present application are disclosed in detail below with reference to the following description and drawings, indicating the manner in which the principles of the present application may be employed. It should be understood that the embodiments of the present application are not limited in scope thereby. The embodiments of the present application include many variations, modifications and equivalents within the scope of the terms of the appended claims.

Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments in combination with or instead of the features of the other embodiments.

It should be emphasized that the term "comprises/comprising" when used herein is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps or components.

Drawings

Elements and features described in one drawing or one implementation of an embodiment of the present application may be combined with elements and features shown in one or more other drawings or implementations. Furthermore, in the drawings, like reference numerals designate corresponding parts throughout the several views, and may be used to designate corresponding parts as used in more than one embodiment.

The accompanying drawings, which are included to provide a further understanding of the embodiments of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. It is apparent that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art. In the drawings:

FIG. 1 is a schematic diagram of an integrated control circuit of a switching power supply device according to an embodiment of the present application;

FIG. 2 is a schematic diagram of a switching frequency change according to a feedback control signal according to an embodiment of the present application;

FIG. 3 is a schematic diagram of the action waveforms during power-on of the embodiments of the present application;

fig. 4 is a schematic diagram showing an internal structure of an integrated control circuit of the switching power supply device according to the embodiment of the present application;

fig. 5 is a schematic diagram of a switching power supply device according to an embodiment of the present application;

fig. 6 is a schematic diagram of a switching power supply device according to an embodiment of the present application;

fig. 7 is a schematic diagram of a control method of the switching power supply device according to the embodiment of the present application;

fig. 8 is a schematic diagram of a control method of the switching power supply device according to the embodiment of the present application.

Detailed Description

The foregoing and other features of the present application will become apparent from the following description, with reference to the accompanying drawings. In the specification and drawings, there have been specifically disclosed specific embodiments of the present application which are indicative of some of the embodiments in which the principles of the present application may be employed, it being understood that the present application is not limited to the described embodiments, but, on the contrary, the present application includes all modifications, variations and equivalents falling within the scope of the appended claims. Various embodiments of the present application are described below with reference to the accompanying drawings. These embodiments are merely exemplary and are not limiting of the present application.

In the embodiments of the present application, the terms "first," "second," "upper," "lower," and the like are used to distinguish between different elements from their names, but do not denote a spatial arrangement or temporal order of the elements, which should not be limited by the terms. The term "and/or" includes any and all combinations of one or more of the associated listed terms. The terms "comprises," "comprising," "including," "having," and the like, are intended to reference the presence of stated features, elements, components, or groups of components, but do not preclude the presence or addition of one or more other features, elements, components, or groups of components.

In the embodiments of the present application, the singular forms "a," an, "and" the "include plural referents and should be construed broadly to mean" one "or" one type "and not limited to" one "or" another; furthermore, the term "comprising" is to be interpreted as including both the singular and the plural, unless the context clearly dictates otherwise. Furthermore, the term "according to" should be understood as "at least partially according to … …", and the term "based on" should be understood as "based at least partially on … …", unless the context clearly indicates otherwise.

Example of the first aspect

Embodiments of a first aspect of the present application provide an integrated control circuit for a switching power supply device. Fig. 1 is a schematic diagram of an integrated control circuit of a switching power supply device according to an embodiment of the present application.

As shown in fig. 1, the integrated control circuit includes: a switching element 111 and a control circuit for controlling on and off of the switching element, the control circuit comprising: a soft start circuit 121 for performing soft start during power supply start-up and outputting a soft start signal; and a frequency control circuit 122 for controlling the switching frequency of the switching element to be reduced to a first frequency at the time of starting the power supply according to the soft start signal during soft start.

In some embodiments, the switching element 111 may be an element capable of performing conduction control between an input and an output by controlling a voltage applied to a control terminal of a switching tube. For example, the switching transistor may be an N-channel type power MOSFET, a bipolar transistor, or the like, which is not exemplified herein.

In some embodiments, the soft start circuit 121 performs soft start during the power start, and the output voltage is slowly increased to the set voltage by performing soft start operation, and the configuration of the soft start circuit 121 may refer to the prior art, for example, including a resistor, a capacitor, a diode, and the like, which is not limited in this embodiment.

In some embodiments, the control circuit may further include a start circuit 123 connected to the soft start circuit 121 for outputting a start signal Vcc (on) to the soft start circuit 121, the start circuit 123 (shown in FIG. 4) including a regulator 13 and a hysteresis comparator COMP4, the comparator COMP4 being a pair V _cc Supply voltage V for integrated control circuit of terminal _cc And variable voltage V _R And a comparison circuit for performing comparison. Comparator COMP4 has its non-inverting input terminal connected to V _cc The terminals are connected, the inverting input terminal is connected with a variable voltage V _R And (5) connection. When the power supply voltage V for the integrated control circuit _cc Exceeding the 1 st reference voltage V _on When (for example, 15V), the output signal of the comparator COMP4 becomes high level (output start signal Vcc (on)), and constant current supply from the high voltage resistant element is stopped, when V _cc When the reference voltage Voff is 2 nd (e.g., 10V) or less, the output signal of the comparator COMP4 becomes low level (stop start signal Vcc (on)), and constant current supply from the high voltage-resistant element is started again. Soft start powerUpon receiving the start signal Vcc (on), the circuit 121 performs soft start during power supply start.

In some embodiments, the frequency control circuit 122 is an Oscillator (OSC) that can control the switching frequency of the switching element, the frequency control circuit 122 is based on the PWM mode, i.e. the oscillation frequency during PWM control is determined, and the configuration of the frequency control circuit 122 is referred to in the prior art and will not be described in detail herein. In the normal oscillation operation, the frequency control circuit 122 may control the switching frequency (oscillation frequency) of the switching element according to the feedback control (FB) signal. The feedback control (FB) signal will be described in the later-described embodiment.

Fig. 2 is a schematic diagram of changing the switching frequency according to the feedback control signal in the embodiment of the present application, as shown in fig. 2, the frequency control circuit 122 controls the switching frequency of the switching element to rise from the first frequency to a fixed frequency (green mode function) when the load is constant according to the feedback control signal from the light load to the heavy load according to the FB signal. The first frequency is the lowest frequency f1, the fixed frequency is the highest frequency f0, the lowest frequency may be 20kHZ, that is, sound at a frequency just audible to humans, and the highest frequency may be 150kHZ, which is merely illustrative and the embodiments of the present application are not limited thereto.

As shown in fig. 2, when the feedback signal voltage is VFB1 or less, the frequency control circuit 122 controls the switching frequency to be the normal minimum frequency f1. When the feedback signal voltage is VFB2 or higher, the frequency control circuit 122 sets the switching frequency to the normal highest frequency f0. When the FB voltage is within the range of VFB1 to VFB2, the frequency control circuit 122 increases the oscillation frequency from the lowest frequency f1 to the highest frequency f0 according to the feedback signal voltage VFB. Although fig. 3 shows an example in which the switching frequency is linearly increased, the switching frequency may be increased stepwise or non-linearly.

In the embodiment of the present application, during the power supply start-up, the soft start circuit 121 performs soft start, during which the feedback control signal is switched to the soft start signal and output to the frequency control circuit 122, that is, during the soft start-up, the frequency control circuit 122 controls the switching frequency not according to the FB signal but according to the soft start signal to reduce the switching frequency of the switching element at the time of the power supply start-up to the first frequency. Therefore, the duty ratio is reduced in a current continuous state at the time of starting without adding additional components and special terminals, the overlapping of switching currents is avoided, the OFF time required in the resetting of the excitation energy of the transformer or the reactance coil is ensured, the surge voltage generated on the secondary rectifying diode or the flywheel diode is restrained, and the installation space of the printed circuit board is reduced.

In some embodiments, during soft start, the frequency control circuit 122 controls the switching frequency fn (switching frequency during soft start) to gradually increase from the first frequency in a manner close to the fixed frequency, but lower than the fixed frequency f0 when the load is constant, that is, the switching frequency fn during soft start is shifted from the low frequency fn set to be in a range greater than or equal to the first frequency and less than the fixed frequency, in a range greater than or equal to the first frequency (e.g., the lowest frequency) and less than the fixed frequency (e.g., the highest frequency) in accordance with the soft start signal. Therefore, in the initial stage of soft start, the switching frequency fn is reduced to the first frequency f1, and thus, overlapping of switching currents can be avoided, and as the time elapsed for starting the power supply becomes longer (the middle and later stages of soft start), the switching frequency of the switching element is gradually increased from the first frequency, for example, the switching frequency of the switching element is increased linearly or non-linearly or stepwise from the first frequency. The law (waveform) concerning this rise may be determined by the waveform generation section, and will be described in detail in the later-described embodiment.

FIG. 3 is a schematic diagram of the waveform of the operation during the power-on period in the embodiment of the present application, as shown in FIG. 3, at t _START The integrated control circuit is started, the power supply is started in the stage t1, and the power supply voltage V for the integrated control circuit is used _cc Exceeding the 1 st reference voltage V _on At (e.g., 15V), the soft start circuit performs a soft start during which time t2 (e.g., may be 8.75ms, but is shown here onlyFor example), the soft start circuit outputs a soft start signal (high level H signal), where f0=equal to the maximum frequency, the frequency is fixed, and in the embodiment of the present application, the switching frequency fn during soft start rises from f1 to near f0.

As can be seen from the above embodiments, during the power start, the soft start circuit 121 performs soft start, and during the soft start, switches from the feedback control signal to the soft start signal and outputs the soft start signal to the frequency control circuit 122, and in order to achieve the above functions, the control circuit further includes: a feedback signal detection circuit 124 and a switching circuit 125; the feedback signal detection circuit 124 is connected to the frequency control circuit 122 via the switching circuit 125, and transmits a feedback control signal to the frequency control circuit; the switching circuit 125 intercepts the feedback control signal sent from the feedback signal detection circuit to the frequency control circuit during the soft start.

In some embodiments, in the normal case (during non-soft start), the feedback signal detection circuit 124 is connected to the FB/OLP terminal according to the voltage V as FB _FB And a feedback signal inputted to the FB/OLP terminal to control the duty ratio of the switching element Q1. The structure of the feedback signal detecting circuit 124 can refer to the prior art, and is not described herein, for example, the feedback signal detecting unit 124 includes a comparator, etc., and switches the current signal (i.e. the voltage signal V _ocp ) With FB voltage V _FB Comparing when the switch current signal is greater than V _FB When the switching element is turned OFF (OFF), the switching frequency of the switching element 111 is controlled based on the FB signal by outputting a high-level output signal (i.e., a feedback control signal-FB signal) and driving the switching element driving circuit based on the output signal.

In some embodiments, the switching circuit 125 (as shown in fig. 4) includes a logic circuit (inverter) INV1 and a first switch SW1, the feedback signal detection circuit 124 and the first switch SW1 are connected to the frequency control circuit 122, the logic circuit INV1 is used to control the ON or OFF of the first switch SW1, the logic circuit INV1 is connected to the soft start circuit 121, when the soft start circuit 121 receives the start signal Vcc (ON), the soft start signal is performed during the power start, the soft start signal (high level signal) is output to the logic circuit INV1, the logic circuit INV1 turns OFF (OFF) the first switch SW1 only during the soft start, so that the feedback control signal from the feedback signal detection circuit 124 is cut OFF, the signal input to the frequency control circuit 122 is switched from the FB signal to the soft start signal, and during the non-soft start period, the soft start circuit 121 outputs the low level signal to the logic circuit INV1, so that the feedback control signal from the feedback signal detection circuit 124 is input to the frequency control circuit 122 to control the switching frequency, and the switching frequency is performed, which is not illustrated in fig. 4.

In some embodiments, in order to more flexibly control the change (rising law, etc.) of the switching frequency, a frequency at which the drain current does not overlap may be generated, and the control circuit may further include a waveform generation unit 127 connected to the soft start circuit 121 and the frequency control circuit 122, wherein the soft start circuit 121 performs soft start during the power supply start when receiving the start signal Vcc (on), outputs a soft start signal (high level signal) to the waveform generation unit 127, the waveform generation unit 127 generates a frequency rising waveform signal based on the soft start signal, and inputs the frequency rising waveform signal to the frequency control circuit 122, and the frequency control circuit 122) controls the switching frequency to gradually increase from the first frequency to approach the fixed frequency in accordance with the frequency rising waveform signal, but to be lower than the fixed frequency f0 at which the load is constant, for example, the frequency rising waveform is a stepwise rising waveform from f1, the switching frequency rises from f1 in accordance with a linear rising waveform, the frequency rising from f1 in accordance with a linear rising waveform, the switching frequency rises from f1 in accordance with a nonlinear rising waveform, for example, and the non-linear rising waveform is not exemplified here. During the non-soft start period, the soft start circuit 121 outputs a low level signal to the waveform generating section 127, the waveform generating section 127 does not generate a frequency rising waveform signal, and the specific circuit configuration of the waveform generating section 127 can refer to the prior art, and the embodiment of the present application is not limited thereto.

In some embodiments, the control circuit further comprises: an overcurrent protection circuit 126 connected to the soft start circuit 121 (or the waveform generation section 127) and configured to raise the maximum current threshold value during overcurrent protection according to the soft start signal. As shown in fig. 3, the maximum current threshold in the overcurrent protection process is raised to Io. Thereby, an OFF time at which the leakage current does not overlap at the time of starting is ensured.

In some embodiments, the waveform generation unit 127 outputs a signal obtained by inverting the polarity of the frequency-up waveform signal to the overcurrent protection circuit during the soft start period, and superimposes a bias voltage on the switching current signal according to the signal, thereby advancing the operation start time of the overcurrent protection circuit, and limiting the current at the time of start.

In some embodiments, the soft start circuit 121 controls the frequency reduction and the existing frequency reduction function (i.e., the green mode function that controls the frequency reduction according to the FB signal) to be set to the OR mode, i.e., both cannot be simultaneously performed, thereby causing no competition with the existing steady-state green mode function and no collision.

Fig. 4 is a schematic diagram of an internal structure of an integrated control circuit of a switching power supply device according to an embodiment of the present application, and as shown in fig. 4, the integrated control circuit includes:

a switching element Q1 composed of an N-channel power MOSFET or the like, a feedback signal detection circuit 11, a frequency control circuit 12, a soft start circuit 14, a Leading Edge Blanking (LEB) circuit 15, a start circuit 10, a switching current waveform correction circuit 16, an over-current protection circuit (OCP) 17, a switching element driving circuit (DRV) 18, a waveform generation section (MODE) 19, a plurality of logic circuits, a flip-flop, and the like. The embodiments of the feedback signal detection circuit 11, the frequency control circuit 12, the soft start circuit 14, the Leading Edge Blanking (LEB) circuit 15, the start circuit 10, the over-current protection circuit (OCP) 17, and the frequency control circuit 12 are as described above and will not be repeated here.

The integrated control circuit has: D/ST (MOSFET drain/start current input) terminals; an S/OCP (MOSFET source/over-current protection) terminal; a Vcc (integrated control circuit power supply voltage input) terminal; FB/OLP (feedback signal input/overload protection signal input) terminal; and a GND (ground) terminal. A feedback signal detection circuit 11 is connected to the FB/OLP terminal connected to the light receiving transistor PC2. The source of the switching element Q1 is connected to the S/OCP terminal, and is connected to the primary GND via an external resistor Rocp.

The starting circuit 10 is connected between the D/ST terminal and the Vcc terminal, and turns on/off a constant current to the Vcc terminal via a high withstand voltage element of the rectifying circuit DB, which is not shown in the rectified voltage.

The Leading Edge Blanking (LEB) circuit 15 is connected to the switching current waveform correction circuit 16 AND the feedback signal detection circuit 11 AND the S/OCP terminal, AND is configured to control the switching current waveform correction circuit 16 AND the feedback signal detection circuit 11 after the switch is turned on for a period of leading edge blanking time, wherein the feedback signal detection circuit 11 is further connected to the FB/OLP terminal, inputs a voltage drop signal of an external resistor Rocp, which is a switching current signal of a switching element Q1 of the S/OCP terminal, through the Leading Edge Blanking (LEB) circuit 15, AND compares the voltage drop signal with a feedback signal from the FB/OLP terminal, AND when the switching current signal is greater than the feedback signal, transmits an H signal to the logic circuit AND2, AND resets the flip-flop circuit FF 1. Thereby, the switching element Q1 is turned OFF (OFF) via the logic circuits AND1, AND3 AND the switching element driving circuit 18.

As described above, the frequency control circuit 12 is connected to the feedback signal detection circuit 11 via the switch SW1, and is connected to the waveform generation unit (MODE) 19, and during soft start, the switching frequency is controlled to gradually increase from the first frequency to a fixed frequency in a manner close to the fixed frequency in response to a signal (soft start signal) from the waveform generation unit, but is lower than the fixed frequency f0 at the time of constant load, and during non-soft start, the switching frequency is controlled to increase from the first frequency to the fixed frequency in response to a feedback control signal (FB signal) from the feedback signal detection circuit 11.

In addition, for example, the frequency control circuit 12 generates a ramp wave based on a constant current circuit and a capacitor, and outputs a one-shot signal to the set terminal of the flip-flop circuit FF1 according to the ramp wave. Thereby, the switching element Q1 is turned ON (turned ON) via the logic circuits AND1, AND3 AND the switching element driving circuit 18.

The switching current waveform correction circuit 16 is connected to the waveform generation unit 19, the Leading Edge Blanking (LEB) circuit 15, and the overcurrent protection circuit 17, and the waveform generation unit 19 outputs a signal obtained by inverting the polarity of the frequency-up waveform signal to the switching current waveform correction circuit 16 during the soft start period, and superimposes a bias voltage on the switching current signal from the Leading Edge Blanking (LEB) circuit 15 to advance the operation start time of the overcurrent protection circuit (OCP) 17, thereby limiting the current at the time of start.

In addition, optionally, the integrated control circuit may further include an overload protection OLP circuit, an overvoltage protection OVP circuit, a thermal shutdown TSD circuit, and the like, where specific connection relationships and functions thereof may refer to the prior art, and are not described herein in detail.

It should be noted that, the integrated control circuit of the embodiment of the present application may further include other structures according to actual needs, or may not include some of the structures shown in the drawings, specifically including which structures may be set according to actual needs with reference to related technologies, which is not limited in this embodiment of the present application.

As is apparent from the above-described embodiments, during soft start, the switching frequency of the switching element at the time of power supply startup (during a period when the output voltage is low) is reduced in accordance with the soft start signal, whereby the duty ratio is reduced in the current continuous state at the time of startup without adding additional components and dedicated terminals, overlapping of the switching currents is avoided, the OFF time required in resetting of the excitation energy of the transformer or the reactance coil is ensured, and thus the surge voltage generated on the secondary side rectifying diode or the flywheel diode is suppressed, and the installation space of the printed circuit board is reduced.

Embodiments of the second aspect

An embodiment of a second aspect of the present application provides a switching power supply device, where the switching power supply device of the embodiment of the present application includes the integrated control circuit according to the embodiment of the first aspect. Since in the embodiment of the first aspect, the structure and function of the integrated control circuit have been described in detail, the contents thereof are incorporated herein, and the description thereof is omitted herein.

Fig. 5 is a schematic diagram of a switching power supply device according to an embodiment of the present application, as shown in fig. 5, a switching power supply device 500 includes:

a rectifying circuit DB; a smoothing capacitor Cin, co, cd; a transformer T; an integrated control circuit 501; rectifier diodes D1, D2; a shunt regulator Z1; a light emitting diode PC1 and a light receiving transistor PC2 constituting a photocoupler; a current detection resistor Rocp; resistance Rb, rc; capacitor C4.

The commercial AC power AC is connected to AC input terminals ACin1 and ACin2 of the rectifier circuit DB configured by a diode bridge, and an AC voltage input from the commercial AC power AC is full-wave rectified and output from the rectifier circuit DB. A smoothing capacitor Cin is connected between the rectifying output positive terminal and the rectifying output negative terminal of the rectifying circuit DB. The rectifying output negative terminal of the rectifying circuit DB is connected to the ground terminal. Thus, a direct current power supply (input voltage) obtained by rectifying and smoothing the commercial alternating current power supply AC by the rectifying circuit DB and the smoothing capacitor Cin is obtained.

The transformer T for supplying electric power from the primary side (input side) to the secondary side (load side) is configured by a primary winding P, an auxiliary winding D, and a secondary winding S, a rectifying output positive terminal of the rectifying circuit DB is connected to one end portion of the primary winding P of the transformer T, the other end portion of the primary winding P of the transformer T is connected to a D/ST terminal of the integrated control circuit 501, and an S/OCP terminal of the integrated control circuit 501 is connected to a ground terminal via a resistor Rocp. As a result, on/off control is performed by the switching element incorporated in the integrated control circuit 501, and electric power supplied to the primary winding P of the transformer T is transmitted to the secondary winding S of the transformer T, so that a pulse voltage is generated in the secondary winding S of the transformer T. The current detection resistor Rocp is connected as a resistor that detects a current flowing through a switching element incorporating the integrated control circuit 501 as the voltage signal Vocp. The integrated control circuit 501 has an overcurrent protection (OCP) function, and limits the power supplied to the secondary side when the voltage signal Vocp corresponding to the current flowing through the switching element is equal to or greater than a preset overcurrent threshold.

A snubber circuit composed of a diode D3, a capacitor Ca, and a resistor Ra is connected between both ends of the primary winding P of the transformer T. The diode D3 and the capacitor Ca are connected in series between both ends of the primary winding P of the transformer T, and the resistor Ra and the capacitor Ca are connected in parallel. The diode D3 is connected in a forward bias direction based on a voltage generated at the primary winding P of the transformer T when the switching element incorporated in the integrated control circuit 501 is turned off.

A smoothing capacitor Co is connected between both terminals of the secondary winding S of the transformer T via a rectifier diode D1. The voltage induced by the secondary winding S of the transformer T is rectified and smoothed by the rectifier diode D1 and the smoothing capacitor Co, and the inter-terminal voltage of the smoothing capacitor Co is output from the output terminal as the output voltage Vo. The line connected to the positive electrode terminal of the smoothing capacitor Co serves as a power supply line, and the line connected to the negative electrode terminal of the smoothing capacitor Co serves as a GND line connected to the ground terminal.

A shunt regulator Z1 functioning as a light emitting diode PC1 and an error amplifier is connected in series between the output power supply line and GND line. The output power line is connected with the positive electrode of the light emitting diode PC1, the negative electrode of the light emitting diode PC1 is connected with the negative electrode of the shunt regulator Z1, and the positive electrode of the shunt regulator Z1 is connected with the GND line. Further, a resistor Rb for voltage division and a resistor Rc are connected in series between the power supply line and the GND line, and a connection point of the resistor Rb and the resistor Rc is connected to the control terminal a of the shunt regulator Z1. The output voltage Vo divided by the resistor Rb and the resistor Rc is input to the control terminal a of the shunt regulator Z1, and is compared with the internal reference voltage of the shunt regulator Z1. Accordingly, a current corresponding to the error voltage flows through the light emitting diode PC1, and the current flowing through the light emitting diode PC1 is outputted from the light emitting diode PC1 to the primary-side light receiving transistor PC2 as a feedback signal. The integrated control circuit 501 controls the duty ratio and the switching frequency of the switching element according to the feedback signal input to the FB/OLP terminal, thereby controlling the amount of electric power supplied to the secondary side.

A smoothing capacitor Cd is connected between both terminals of the auxiliary winding D of the transformer T via a rectifier diode D2, and a connection point between the rectifier diode D2 and the smoothing capacitor Cd is connected to the Vcc terminal of the integrated control circuit 501. Thus, the voltage generated in the auxiliary winding D is rectified and smoothed by the rectifying diode D2 and the smoothing capacitor Cd, and then supplied to the Vcc terminal of the integrated control circuit 501 as the power supply voltage Vcc for the integrated control circuit 501.

Fig. 6 is a schematic diagram of a switching power supply device according to an embodiment of the present application, and the same points as those in fig. 5 are not repeated, and the switching power supply device in fig. 6 is a non-insulated buck converter, which does not include a transformer, and current flows to a load terminal through an inductor, and meanwhile, the inductor L1 also stores electric energy, at this time, a switching element between a D/ST terminal and an S/OCP terminal is turned on, and when D1 is turned off, electric energy is supplied to the load terminal through the inductor L1. The regenerative current of the inductor L1 flows through the diode D1 and is supplied to the capacitor Co, and the regenerative current flows through the diode D2 and is supplied to the capacitor Cd. For the specific structure of the non-isolated buck converter, please refer to the prior art, for example, the diode D1 may also be formed by a switching element, which is not described herein.

It should be noted that, the switching power supply device according to the embodiment of the present application may further include other structures according to actual needs, or may not include part of the structures shown in the drawings, and specifically include which structures may be set according to actual needs with reference to the related art, which is not limited in this embodiment of the present application.

As is apparent from the above-described embodiments, during soft start, the switching frequency of the switching element at the time of power supply startup (during a period when the output voltage is low) is reduced in accordance with the soft start signal, whereby the duty ratio is reduced in the current continuous state at the time of startup without adding additional components and dedicated terminals, overlapping of the switching currents is avoided, the OFF time required in resetting of the excitation energy of the transformer or the reactance coil is ensured, and thus the surge voltage generated on the secondary side rectifying diode or the flywheel diode is suppressed, and the installation space of the printed circuit board is reduced.

Embodiments of the third aspect

An embodiment of a third aspect of the present application provides a control method of a switching power supply device. Since the integrated control circuit structure and functions of the switching power supply device have been described in detail in the embodiments of the first aspect, the same is incorporated herein, and the description thereof is omitted.

Fig. 7 is a schematic diagram of a control method of the switching power supply device according to the embodiment of the present application, as shown in fig. 7, the control method includes:

701, performing soft start control during power supply start, and outputting a soft start signal;

702, during soft start, controlling a switching frequency of a switching element in the switching power supply device to be reduced to a first frequency at the time of starting the power supply according to the soft start signal.

For the implementation manners of 701-702, please refer to the example of the first aspect, and are not repeated here.

Fig. 8 is a schematic diagram of a control method of the switching power supply device in the embodiment of the present application, and reference may be made to the embodiment of the first aspect for implementation of the integrated control circuit, as shown in fig. 8, where the control method includes:

801, power supply start, power supply voltage V for IC circuit _cc Exceeding the 1 st reference voltage V _on When the starting circuit outputs a starting signal Vcc (on);

802, the soft start circuit performs soft start according to the output start signal, and outputs a soft start signal to the waveform generation unit and the switching circuit;

803, the waveform generation unit generates a frequency-up waveform signal from the soft start signal, and sends the frequency-up waveform signal to the frequency control circuit;

804, the switching circuit cuts off the FB signal from the feedback signal detection circuit according to the soft start signal;

805, during soft start, the frequency control circuit controls the switching frequency to gradually increase from the first frequency to a fixed frequency, but to be lower than a fixed frequency f0 at which the load is constant, in accordance with the signal from the waveform generation section;

806, after the soft start is completed, the soft start circuit outputs a low level signal to the waveform generating section and the switching circuit;

807, the switching circuit transmits the FB signal from the feedback signal detecting circuit to the frequency control circuit based on the low level signal;

808, during the non-soft start, the frequency control circuit controls the switching frequency in accordance with the feedback control signal (FB signal) from the feedback signal detection circuit 11.

It is noted that fig. 7-8 above are only illustrative of embodiments of the present application, but the present application is not limited thereto. For example, the order of execution among the operations may be appropriately adjusted, and other operations may be added or some of the operations may be reduced. Those skilled in the art can make appropriate modifications in light of the above, and are not limited to the description of fig. 7.

As is apparent from the above-described embodiments, during soft start, the switching frequency of the switching element at the time of power supply startup (during a period when the output voltage is low) is reduced in accordance with the soft start signal, whereby the duty ratio is reduced in the current continuous state at the time of startup without adding additional components and dedicated terminals, overlapping of the switching currents is avoided, the OFF time required in resetting of the excitation energy of the transformer or the reactance coil is ensured, and thus the surge voltage generated on the secondary side rectifying diode or the flywheel diode is suppressed, and the installation space of the printed circuit board is reduced.

The above embodiments are merely illustrative of the embodiments of the present application, but the present application is not limited thereto, and appropriate modifications may be made on the basis of the above embodiments. For example, each of the above embodiments may be used alone, or one or more of the above embodiments may be combined.

Moreover, while those skilled in the art may have great effort and many design choices are made by, for example, available time, current technology, and economic considerations, they can readily generate such software instructions and programs and Integrated Circuits (ICs) with minimal experimentation, given the guidance of the concepts and principles disclosed herein.

In general, the various embodiments of the invention may be implemented in software or special purpose circuits, hardware, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device.

While embodiments of the invention have been illustrated and described in block diagrams, flow charts, or using some other pictorial representation, it is well understood that blocks, apparatus, systems, or methods described herein may be implemented in, without limitation, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or combinations thereof.

Also, while the above description contains details of several embodiments, these should not be construed as limitations on the scope of the invention, but rather as descriptions of features specific to particular embodiments. Certain features that are described in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of separate embodiments can also be implemented in multiple embodiments separately or in suitable combination.

Although the invention has been described in language specific to structural features and/or methodological acts, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

The present application has been described in connection with specific embodiments, but it should be apparent to those skilled in the art that these descriptions are intended to be illustrative and not limiting. Various modifications and alterations of this application may occur to those skilled in the art in light of the spirit and principles of this application, and are to be seen as within the scope of this application.

Claims (10)

1. An integrated control circuit of a switching power supply device, the integrated control circuit comprising: a switching element and a control circuit for controlling on and off of the switching element, characterized in that the control circuit comprises:

a soft start circuit for performing soft start during power supply start and outputting a soft start signal;

and the frequency control circuit is used for controlling the switching frequency of the switching element to be reduced to a first frequency when the power supply is started according to the soft start signal during soft start.

2. The integrated control circuit according to claim 1, wherein the frequency control circuit controls the switching frequency of the switching element to gradually increase from the first frequency as the elapsed time from the start-up of the power supply becomes longer.

3. The integrated control circuit of claim 2, wherein the frequency control circuit controls the switching frequency of the switching element to increase linearly or to increase non-linearly or to increase stepwise from the first frequency.

4. An integrated control circuit according to any one of claims 1 to 3, wherein during the soft start the frequency control circuit controls the switching frequency of the switching element to be lower than a fixed frequency at which the load is constant.

5. The integrated control circuit of claim 1, wherein the control circuit further comprises: a feedback signal detection circuit and a switching circuit;

the feedback signal detection circuit is connected with the frequency control circuit through the switching circuit and sends a feedback control signal to the frequency control circuit;

the switching circuit cuts off the feedback control signal sent to the frequency control circuit by the feedback signal detection circuit during the soft start.

6. The integrated control circuit of claim 5, wherein the frequency control circuit controls the switching frequency of the switching element in accordance with the feedback control signal during non-soft start.

7. The integrated control circuit of claim 6, wherein the frequency control circuit controls the switching frequency of the switching element to rise from the first frequency to a fixed frequency at which the load is constant in accordance with the feedback control signal.

8. The integrated control circuit of claim 1, wherein the control circuit further comprises:

and the overcurrent protection circuit is used for increasing the maximum current threshold according to the soft start signal.

9. A control method of a switching power supply device, the method comprising:

performing soft start control during power supply starting and outputting a soft start signal;

during soft start, the switching frequency of a switching element in the switching power supply device at the time of starting the power supply is controlled to be reduced to a first frequency according to the soft start signal.

10. A switching power supply device comprising the integrated control circuit of any one of claims 1 to 8.