阅读说明：本技术 同时防止输出过压和欠压的开关电源控制电路及控制芯片 (Switch power supply control circuit and control chip capable of preventing output overvoltage and undervoltage simultaneously ) 是由 唐波 向磊 马强 许刚颖 王磊 于 2020-06-22 设计创作，主要内容包括：本发明公开了一种同时防止输出过压和欠压的开关电源控制电路及控制芯片。开关电源控制电路包括：模式切换检测模块用于对开关电源的CC/CV模式的切换进行检测；有效时间设置模块用于在模式切换检测模块检测到开关电源切换至CC模式或CV模式时,设置有效控制时间；输出电压检测模块用于在有效控制时间内检测开关电源的输出电压的变化方向和变化速率；自适应控制模块用于在有效控制时间内根据输出电压的变化方向和变化速率自动调节CV模式的调整方向和响应速度,其中,变化方向与调整方向成反比例关系,变化速率与响应速度成正比例关系。本发明能够在CC/CV模式切换后及时、准确响应输出电压变化。(The invention discloses a switching power supply control circuit and a control chip for simultaneously preventing output overvoltage and undervoltage. The switching power supply control circuit includes: the mode switching detection module is used for detecting the switching of the CC/CV mode of the switching power supply; the effective time setting module is used for setting effective control time when the mode switching detection module detects that the switching power supply is switched to the CC mode or the CV mode; the output voltage detection module is used for detecting the change direction and the change rate of the output voltage of the switching power supply within effective control time; the self-adaptive control module is used for automatically adjusting the adjusting direction and the response speed of the CV mode according to the changing direction and the changing speed of the output voltage within effective control time, wherein the changing direction and the adjusting direction are in an inverse proportional relation, and the changing speed and the response speed are in a direct proportional relation. The invention can timely and accurately respond to the output voltage change after the CC/CV mode is switched.)

1. A switch power supply control circuit capable of preventing output overvoltage and undervoltage simultaneously is characterized by comprising a mode switching detection module, an effective time setting module, an output voltage detection module and a self-adaptive control module;

the mode switching detection module is used for detecting the switching of the CC/CV mode of the switching power supply;

the effective time setting module is used for setting effective control time when the mode switching detection module detects that the switching power supply is switched to the CC mode or the CV mode;

the output voltage detection module is used for detecting the change direction and the change rate of the output voltage of the switching power supply within the effective control time;

the self-adaptive control module is used for automatically adjusting the adjusting direction and the response speed of the CV mode according to the changing direction and the changing speed of the output voltage within the effective control time, wherein the changing direction and the adjusting direction are in an inverse proportional relation, and the changing speed and the response speed are in a direct proportional relation.

2. The switching power supply control circuit according to claim 1, wherein the switching scenario of the CC/CV mode of the switching power supply comprises a CC/CV mode switching caused by a change in the output load state, a CC/CV mode switching during the startup of the switching power supply, and a CC/CV mode switching caused by a change in the operating state of the switching power supply.

3. The switching power supply control circuit according to claim 1, wherein the adaptive control module is further configured to stop adjusting the adjustment direction and the response speed of the CV mode outside the active control time.

4. The switching power supply control circuit according to claim 1 or 3, wherein the adaptive control module is specifically configured to automatically adjust the operating frequency and the primary winding current of the switching power supply according to a change direction and a change rate of the output voltage within the effective control time, wherein the operating frequency and the primary winding current increase when the change direction is smaller, and the increase rate of the operating frequency and the primary winding current increases when the change rate is larger; the operating frequency and the primary winding current decrease as the direction of change becomes larger, and the greater the rate of change, the greater the rate of decrease in the operating frequency and the primary winding current.

5. The switching power supply control circuit according to claim 1, wherein the output voltage detection module is specifically configured to compare the FB sample voltage of the switching power supply in the current period with the FB sample voltage of the previous period within the effective control time, determine a change direction of the output voltage according to voltage values of the FB sample voltage of the current period and the previous period, and determine a change rate of the output voltage according to a voltage difference between the FB sample voltage of the current period and the previous period.

6. A control chip for a switching power supply, characterized in that the control chip integrates a switching power supply control circuit according to any one of claims 1 to 5.

Technical Field

The invention relates to the technical field of switching power supplies, in particular to a switching power supply control circuit and a control chip for preventing overvoltage and undervoltage output at the same time.

Background

With the application of the switching power supply becoming more and more common, the requirements of the power supply control chip on the aspects of reducing cost, increasing functions, optimizing performance and the like are more strict, and particularly, higher requirements are provided for the variation range of the output voltage. Especially, in some applications that easily cause output overvoltage or undervoltage problems in the switching process of the CC/CV mode, users have made explicit requirements for the output overvoltage range and the undervoltage range.

For the problem of output overvoltage or undervoltage, the prior art generally adjusts the response speed of CC/CV mode switching by adjusting the change rate of the output voltage of the error amplifier, and the disadvantages are as follows: 1. because the output response of the error amplifier has certain delay, the error amplifier cannot respond to the change of the output voltage timely and accurately; 2. because the working frequency of the output voltage regulation power supply of the error amplifier and the rate of the primary winding current are relatively fixed, the prior art can only adopt a compromise scheme between the working frequency of the power supply and the change rate of the primary winding current in an acceleration or deceleration way, and cannot simultaneously take the application problems of overvoltage and undervoltage output into consideration.

Disclosure of Invention

The invention mainly solves the technical problem of providing a switching power supply control circuit capable of preventing output overvoltage and undervoltage simultaneously, and the switching power supply control circuit can timely and accurately respond to output voltage change after CC/CV mode switching.

In order to solve the technical problems, the invention adopts a technical scheme that: the switch power supply control circuit capable of preventing output overvoltage and undervoltage simultaneously comprises a mode switching detection module, an effective time setting module, an output voltage detection module and a self-adaptive control module; the mode switching detection module is used for detecting the switching of the CC/CV mode of the switching power supply; the effective time setting module is used for setting effective control time when the mode switching detection module detects that the switching power supply is switched to the CC mode or the CV mode; the output voltage detection module is used for detecting the change direction and the change rate of the output voltage of the switching power supply within the effective control time; the self-adaptive control module is used for automatically adjusting the adjusting direction and the response speed of the CV mode according to the changing direction and the changing speed of the output voltage within the effective control time, wherein the changing direction and the adjusting direction are in an inverse proportional relation, and the changing speed and the response speed are in a direct proportional relation.

Preferably, the switching scene of the CC/CV mode of the switching power supply includes switching of the CC/CV mode caused by a change of the output load state, switching of the CC/CV mode during startup of the switching power supply, and switching of the CC/CV mode caused by a change of the operating state of the switching power supply.

Preferably, the adaptive control module is further configured to stop adjusting the adjustment direction and the response speed of the CV mode outside the effective control time.

Preferably, the adaptive control module is specifically configured to automatically adjust the operating frequency and the primary winding current of the switching power supply according to a change direction and a change rate of the output voltage within the effective control time, where the operating frequency and the primary winding current increase when the change direction is smaller, and the increase rate of the operating frequency and the primary winding current increases when the change rate is larger; the operating frequency and the primary winding current decrease as the direction of change becomes larger, and the greater the rate of change, the greater the rate of decrease in the operating frequency and the primary winding current.

Preferably, the output voltage detection module is specifically configured to compare the FB sample voltage of the switching power supply in the current period with the FB sample voltage of the previous period within the effective control time, determine a change direction of the output voltage according to voltage values of the FB sample voltage of the current period and the previous period, and determine a change rate of the output voltage according to a voltage difference between the FB sample voltage of the current period and the previous period.

In order to solve the technical problem, the invention adopts another technical scheme that: the control chip is used for a switching power supply and is integrated with any one of the switching power supply control circuits.

Different from the prior art, the invention has the beneficial effects that: in the CC/CV mode switching process, on the basis of adjusting the response speed of CC/CV mode switching by adjusting the change rate of the output voltage of the error amplifier, the detection of the change direction and the change rate of the output voltage is increased to automatically adjust the adjustment direction and the response speed of the CV mode, so that the adjustment direction and the response speed of the CV mode are increased, the output voltage change can be timely and accurately responded after the CC/CV mode switching, and the application problem that output overvoltage or undervoltage is difficult to take into account simultaneously is solved.

Drawings

Fig. 1 is a schematic structural diagram of a switching power supply control circuit for preventing output overvoltage and undervoltage at the same time according to an embodiment of the present invention;

fig. 2 is a schematic view of an application scenario of the switching power supply control circuit according to the embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Fig. 1 is a schematic structural diagram of a switching power supply control circuit capable of preventing output overvoltage and undervoltage according to an embodiment of the present invention. The switching power supply control circuit is integrated with a prior art output voltage change rate adjustment system, which includes a sample-and-hold circuit, an error amplifier, a low-pass filter, a logic control circuit, and the like. The switching power supply control circuit comprises a mode switching detection module 1, an effective time setting module 2, an output voltage detection module 3 and a self-adaptive control module 4.

The mode switching detection module 1 is used for detecting the switching of the CC/CV mode of the switching power supply. The switching scene of the CC/CV mode of the switching power supply comprises the switching of the CC/CV mode caused by the change of the output load state, the switching of the CC/CV mode in the starting process of the switching power supply and the switching of the CC/CV mode caused by the change of the working state of the switching power supply. The switching power supply can be detected as long as it switches from the CC mode to the CV mode, or from the CV mode to the CC mode. Preferably, the mode switch detection module 1 can detect the switching of the CC/CV mode according to the magnitude of the output signal VEA _ RC of the low-pass filter.

The effective time setting module 2 is configured to set an effective control time when the mode switching detection module detects that the switching power supply is switched to the CC mode or the CV mode.

The output voltage detection module 3 is used for detecting the change direction and the change rate of the output voltage of the switching power supply within the effective control time. Preferably, the output voltage detection module 3 may determine the change direction and the change rate of the output voltage by the change of the voltage value output by the sample-and-hold circuit. For example, the output voltage detection module 3 is specifically configured to compare the FB sample voltage in the current period with the FB sample voltage in the previous period in an effective control time, determine a change direction of the output voltage according to the voltage values of the FB sample voltage in the current period and the previous period, and determine a change rate of the output voltage according to the voltage difference between the FB sample voltage in the current period and the previous period. Such as: if the FB sampling voltage of the current period is greater than the FB sampling voltage of the previous period, the change direction of the output voltage is increased; if the FB sample voltage of the current period is smaller than the FB sample voltage of the last period, the change direction of the output voltage is smaller. And the larger the voltage difference value between the FB sampling voltage of the current period and the FB sampling voltage of the previous period is, the larger the change rate of the output voltage is. In the figure, the signal FB _ SH represents the FB sample voltage and the output voltage detection block 3 indicates the direction and rate of change of the output voltage by sending a signal FB _ EA to the adaptive control block 4.

The self-adaptive control module 4 is used for automatically adjusting the adjusting direction and the response speed of the CV mode according to the changing direction and the changing speed of the output voltage within the effective control time, wherein the changing direction and the adjusting direction are in an inverse proportional relation, and the changing speed and the response speed are in a direct proportional relation. The changing direction has two directions of increasing and decreasing, when the changing direction is increasing, the adjusting direction is decreasing, otherwise, the adjusting direction is increasing. The greater the rate of change, the greater the response speed, and conversely, the smaller the response speed. In this embodiment, the adaptive control module 4 is further configured to stop adjusting the adjustment direction and the response speed of the CV mode in addition to the effective control time. At this time, the adjustment direction and the response speed of the CV mode are adjusted only by the prior art output voltage change rate adjustment system.

In this embodiment, the adaptive control module 4 is specifically configured to automatically adjust the operating frequency and the primary winding current of the switching power supply according to the change direction and the change rate of the output voltage within the effective control time, where the operating frequency and the primary winding current increase when the change direction is smaller, and the increase rate of the operating frequency and the primary winding current increases when the change rate is larger; the operating frequency and the primary winding current decrease as the direction of change becomes larger, and the greater the rate of change, the greater the rate of decrease in the operating frequency and the primary winding current.

Referring to fig. 1 and 2, in this application scenario, the switching power supply system is a typical primary side feedback detection flyback power converter system, and the system includes a control chip 101, a power NMOS transistor 102, a primary winding peak current limiting resistor 103, an auxiliary winding voltage division upper end resistor 104, an auxiliary winding voltage division lower end resistor 105, a transformer 106, an output rectifier diode 107, a VDD rectifier diode 108, and an output capacitor 109. The control chip 101 integrates the switching power supply control circuit of the foregoing embodiment, and also integrates a prior art change rate adjustment system of the output voltage.

During the period of controlling the power NMOS tube 102 to be conducted at the GATE terminal, the primary winding inductance Lp of the transformer 106 controls the rising slope of the current flowing through the primary winding of the transformer together with the rectified DC power supply voltage VinThe current flows through the primary winding peak current limiting resistor 103 and generates a fixed slope rising voltage signal at the terminal CSWhen the voltage at the CS terminal reaches the set voltage value, the control chip 101 controls the power NMOS 102 to turn off through the GATE terminal. During the turn-off period of the power NMOS tube 102, the output rectifier diode 107 is in forward conduction, the secondary winding of the transformer 106 and the output capacitor 109 together provide energy to the output, and the current of the secondary winding follows a certain slopeAnd gradually reducing, and obtaining the FB demagnetization time when the current of the secondary winding is reduced from the maximum value to 0. Under the condition that the FB demagnetization time is sampled at a fixed proportional point to obtain the FB sampling voltage and other influencing factors are ignored, the relation between the output voltage Vout and the FB sampling voltage can be represented by the following equation:

where N is the ratio of the number of turns of the primary winding and the secondary winding of the transformer 106, Vout is the output voltage, Vd is the forward conduction voltage of the output rectifier diode 107, N_FNumber of turns of auxiliary winding coil for transformer 106, N_SNumber of turns of secondary winding of transformer 106, R₁₀₄And R₁₀₅The resistance values V of the upper resistor 104 and the lower resistor 105 of the auxiliary winding voltage division are respectively_FBThe voltage is sampled for FB.

It should be noted that the switching power supply control circuit of the present invention can also be used in other types of switching power supplies, such as a secondary-side feedback switching power supply, and the operation of the switching power supply with different topologies is slightly different, and the invention should be within the scope of protection without departing from the spirit and scope of the present invention.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.