Switching power supply control circuit with constant working frequency

Abstract

The utility model relates to a switching power supply control circuit with constant working frequency, which is characterized in that a linear voltage stabilizing module is used for adjusting the working voltage of a primary winding of a transformer, the input end of the linear voltage stabilizing module is connected with the input end of an open-end power supply, and the control end of the linear voltage stabilizing module is connected with the output end of a negative feedback module; the output end of the linear voltage stabilizing module is connected with the first end of a primary winding coil of the transformer; the transformer is used for voltage conversion, the PWM switch module is connected to the second end of a primary winding coil of the transformer and used for controlling the working frequency of the transformer, and a multi-side winding coil of the transformer is connected with the input end of the rectifying and filtering module; the output end of the rectification filtering module is connected with the output end of the switching power supply. The negative feedback module is used for collecting the voltage of the output end of the switching power supply, controlling the working voltage of the transformer primary winding coil through the linear voltage stabilization module and adjusting the stability of the output voltage, and the input end of the negative feedback module is connected with the output end of the switching power supply. The working frequency of the switching power supply always keeps consistent.

Description

Technical Field

[0001] The utility model relates to a switching power supply control circuit with a constant operating frequency. Background Art

[0002] Piezoelectric ceramics are widely used in micro-machinery, micro-electronics, precision machining, biomedicine, robotics, aerospace and other fields due to their high electro-mechanical coupling efficiency, high displacement resolution, fast response and other advantages, and have attracted increasing attention from the academic and engineering communities.

[0003] In a piezoelectric ceramic drive system, it generally includes a low-voltage control circuit and a high-voltage drive circuit, and the system is usually powered by a low-voltage power supply of 12V to 24V. Among them, the power supply of the high-voltage drive circuit is direct current with an output voltage as high as several hundred volts, which is generally obtained by boosting the system power supply through a switching power supply. Due to the too high boosting ratio, it is necessary to add a high-frequency transformer in the switching power supply to achieve boosting.

[0004] For most switching power supply chips, in the standby mode of no load or light load, in order to reduce the overall loss of the system as much as possible, they will enter an intermittent working mode. In this mode, the transformer will work at a lower frequency. If the transformer operating frequency is within the audible range of the human ear, the human ear may hear the howling generated by the current in the transformer. This howling that should not exist will seriously affect the user experience. Summary of the Utility Model

[0005] The purpose of the utility model is to overcome the deficiencies of the prior art, provide a switching power supply control circuit with a constant operating frequency, solve the problem of transformer howling in the switching power supply under no load or light load conditions, keep the operating frequency of the transformer in the switching power supply always constant and outside the audible range of the human ear, and improve the user experience.

[0006] The purpose of the utility model is realized by the following technical solutions:

[0007] A switching power supply control circuit with a constant operating frequency, characterized in that: it includes a linear voltage regulator module, a transformer, a PWM switching module, a negative feedback module and a rectifying and filtering module. The linear voltage regulator module is used to adjust the operating voltage of the primary winding of the transformer. The input end of the linear voltage regulator module is connected to the starting power input end, the control end of the linear voltage regulator module is connected to the output end of the negative feedback module, and the output end of the linear voltage regulator module is connected to the first end of the primary winding coil of the transformer;

[0008] The transformer is used for voltage conversion. The PWM switching module is connected to the second end of the primary winding coil of the transformer to control the operating frequency of the transformer. The secondary winding coil of the transformer is connected to the input end of the rectifying and filtering module;

[0009] The output terminal of the rectifying and filtering module is connected to the output terminal of the switching power supply;

[0010] The negative feedback module is used to collect the voltage at the output terminal of the switching power supply and control the operating voltage of the primary winding coil of the transformer through the linear voltage stabilizing module to adjust the stability of the output voltage. The input terminal of the negative feedback module is connected to the output terminal of the output terminal of the switching power supply.

[0011] Further, for the above-mentioned switching power supply control circuit with a constant operating frequency, wherein the linear voltage stabilizing module includes an NPN-type triode, a first electrolytic capacitor, and a second electrolytic capacitor. The positive electrode of the first electrolytic capacitor is connected to the collector of the NPN-type triode, the negative electrode of the first electrolytic capacitor is connected to the ground plane of the primary side of the transformer, the base of the NPN-type triode is connected to the fourth terminal of the linear optocoupler, the emitter of the NPN-type triode is connected to the first end of the primary winding coil of the transformer, the positive electrode of the second electrolytic capacitor is connected to the emitter of the NPN-type triode, and the negative electrode of the second electrolytic capacitor is connected to the ground plane of the primary side of the transformer.

[0012] Further, for the above-mentioned switching power supply control circuit with a constant operating frequency, wherein the PWM switching module includes a PWM output module and an N-channel power MOS transistor. The PWM output module is connected to the gate of the N-channel power MOS transistor, the drain of the N-channel power MOS transistor is connected to the second end of the primary winding coil of the transformer, and the source of the N-channel power MOS transistor is connected to the ground plane of the primary side of the transformer.

[0013] Further, for the above-mentioned switching power supply control circuit with a constant operating frequency, wherein the transformer is a flyback transformer.

[0014] Further, for the above-mentioned switching power supply control circuit with a constant operating frequency, wherein the rectifying and filtering module includes a rectifying diode and a third electrolytic capacitor. The positive electrode of the rectifying diode is connected to the first end of the secondary winding coil of the transformer, the negative electrode of the rectifying diode is connected to the positive electrode of the third electrolytic capacitor, the positive electrode of the third electrolytic capacitor is connected to the output terminal of the switching power supply, the negative electrode of the third electrolytic capacitor is connected to the second end of the secondary winding coil of the transformer, and the second end of the secondary winding coil of the transformer is connected to the ground plane of the secondary side of the transformer.

[0015] Furthermore, for the above-mentioned switching power supply control circuit with a constant operating frequency, the negative feedback module includes a first resistor, a second resistor, a third resistor, a fourth resistor, a linear optocoupler, and a voltage regulator TL431. The first end of the first resistor is connected to the first power supply VCC, the second end of the first resistor is connected to the fourth end of the linear optocoupler, the third end of the linear optocoupler is connected to the ground plane of the primary side of the transformer, the first end of the second resistor is connected to the second power supply VDD, the second end of the second resistor is connected to the first end of the linear optocoupler, the second end of the linear optocoupler is connected to the first end of the voltage regulator TL431, the second end of the voltage regulator TL431 is connected to the first end of the fourth resistor, the third end of the voltage regulator TL431 is connected to the ground plane of the secondary side of the transformer, the first end of the third resistor is connected to the output terminal of the switching power supply, the second end of the third resistor is connected to the second end of the voltage regulator TL431, and the second end of the fourth resistor is connected to the ground plane of the secondary side of the transformer.

[0016] Furthermore, for the above-mentioned switching power supply control circuit with a constant operating frequency, the first resistor and the second resistor are current-limiting resistors, and the third resistor and the fourth resistor are feedback sampling resistors.

[0017] Furthermore, for the above-mentioned switching power supply control circuit with a constant operating frequency, the corresponding relationship between the output voltage VOUT and the third resistor and the fourth resistor is:

[0018] VOUT = 2.5×(R3 + R4) / R4.

[0019] The utility model has remarkable advantages and beneficial effects compared with the prior art, which are specifically embodied in the following aspects:

[0020] The utility model ensures that the operating frequency of the controlled switching power supply always remains consistent and is greater than the upper limit of human ear hearing, solving the problem that the transformer whistles due to the switching power supply entering the intermittent working mode under no-load and light-load modes. By changing the turns ratio of the transformer, both step-up and step-down can be achieved. It is applicable to various switching power supply topologies.

[0021] Other features and advantages of the utility model will be described in the subsequent description, and part of them will become obvious from the description, or be understood by implementing the specific embodiments of the utility model. The objectives and other advantages of the utility model can be achieved and obtained by the structures specifically pointed out in the written description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] To more clearly illustrate the technical solutions of the embodiments of the present utility model, the accompanying drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following accompanying drawings only show some embodiments of the present utility model, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other relevant accompanying drawings can also be obtained based on these drawings.

[0023] Figure 1 : Circuit block diagram of the present utility model;

[0024] Figure 2 : Circuit schematic diagram of the present utility model;

[0025] Figure 3 : Schematic diagram of the voltage waveform at the working node of the switching power supply;

[0026] Figure 4 : Circuit diagram of the switching power supply based on the forward transformer;

[0027] Figure 5 : Circuit diagram of the switching power supply based on the push-pull transformer. Specific embodiments

[0028] The technical solutions in the embodiments of the present utility model will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all the embodiments. Usually, the components of the embodiments of the present utility model described and shown in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present utility model provided in the accompanying drawings is not intended to limit the scope of the present utility model to be protected, but only represents the selected embodiments of the present utility model. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present utility model.

[0029] It should be noted that similar reference numerals and letters indicate similar items in the following accompanying drawings. Therefore, once an item is defined in one accompanying drawing, it does not need to be further defined and explained in subsequent accompanying drawings. At the same time, in the description of the present utility model, orientation terms and order terms are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0030] Such as Figure 1As shown in the figure, a switching power supply control circuit with a constant operating frequency includes a linear voltage regulator module 102, a transformer 103, a PWM switching module 105, a negative feedback module 106, and a rectifier and filter module 104. The linear voltage regulator module 102 is used to regulate the operating voltage of the primary winding of the transformer 103. The input end of the linear voltage regulator module 102 is connected to the starting power input end 101. The control end of the linear voltage regulator module 102 is connected to the output end of the negative feedback module 106. The output end of the linear voltage regulator module 102 is connected to the first end of the primary winding coil of the transformer 103;

[0031] The transformer 103 is used for voltage conversion. The PWM switching module 105 is connected to the second end of the primary winding coil of the transformer 103 and is used to control the operating frequency of the transformer 103. The secondary winding coil of the transformer 103 is connected to the input end of the rectifier and filter module 104;

[0032] The output end of the rectifier and filter module 104 is connected to the switching power supply output end 107;

[0033] The negative feedback module 106 is used to collect the voltage of the switching power supply output end 107 and control the operating voltage of the primary winding coil of the transformer 103 through the linear voltage regulator module 102 to adjust the stability of the output voltage. The input end of the negative feedback module 106 is connected to the output end of the switching power supply output end 107.

[0034] As Figure 2 , the linear voltage regulator module 102 includes an NPN transistor Q1, a first electrolytic capacitor C1, and a second electrolytic capacitor C2. The positive electrode of the first electrolytic capacitor C1 is connected to the collector of the NPN transistor Q1. The negative electrode of the first electrolytic capacitor C1 is connected to the ground plane of the primary side of the transformer T1. The base of the NPN transistor Q1 is connected to the fourth end of the linear optocoupler U1. The emitter of the NPN transistor Q1 is connected to the first end of the primary winding coil of the transformer T1. The positive electrode of the second electrolytic capacitor C2 is connected to the emitter of the NPN transistor Q1. The negative electrode of the second electrolytic capacitor C2 is connected to the ground plane of the primary side of the transformer T1.

[0035] The PWM switching module 105 includes a PWM output module and an N-channel power MOS transistor Q2. The PWM output module is connected to the gate of the N-channel power MOS transistor Q2. The drain of the N-channel power MOS transistor Q2 is connected to the second end of the primary winding coil of the transformer T1. The source of the N-channel power MOS transistor is connected to the ground plane of the primary side of the transformer T1.

[0036] The transformer 103 is a flyback transformer T1.

[0037] The rectifying and filtering module 104 includes a rectifying diode D1 and a third electrolytic capacitor C3. The positive electrode of the rectifying diode D1 is connected to the first end of the secondary winding coil of the transformer T1, the negative electrode of the rectifying diode D1 is connected to the positive electrode of the third electrolytic capacitor C3, the positive electrode of the third electrolytic capacitor C3 is connected to the output terminal of the switching power supply, the negative electrode of the third electrolytic capacitor C3 is connected to the second end of the secondary winding coil of the transformer T1, and the second end of the secondary winding coil of the transformer T1 is connected to the ground plane of the secondary side of the transformer T1.

[0038] The negative feedback module 106 includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a linear optocoupler U1, and a voltage regulator TL431. The first end of the first resistor R1 is connected to the first power supply VCC, the value of which is usually equal to VIN. The second end of the first resistor R1 is connected to the fourth end of the linear optocoupler U1. The third end of the linear optocoupler U1 is connected to the ground plane of the primary side of the transformer T1. The first end of the second resistor R2 is connected to the second power supply VDD, the value of which is usually equal to VIN. The second end of the second resistor R2 is connected to the first end of the linear optocoupler U1. The second end of the linear optocoupler U1 is connected to the first end of the voltage regulator TL431. The second end of the voltage regulator TL431 is connected to the first end of the fourth resistor R4. The third end of the voltage regulator TL431 is connected to the ground plane of the secondary side of the transformer. The first end of the third resistor R3 is connected to the output terminal of the switching power supply. The second end of the third resistor R3 is connected to the second end of the voltage regulator TL431. The second end of the fourth resistor R4 is connected to the ground plane of the secondary side of the transformer T1.

[0039] The first resistor R1 and the second resistor R2 are current-limiting resistors, and the third resistor R3 and the fourth resistor R4 are feedback sampling resistors.

[0040] The corresponding relationship between the output voltage VOUT and the third resistor R3 and the fourth resistor R4 is as follows:

[0041] VOUT = 2.5×(R3 + R4) / R4.

[0042] The turns ratio of the secondary winding coil to the primary winding coil of the transformer T1 is N. The duty cycle of the PWM output waveform is 50%, and the frequency is much greater than the upper limit of human ear hearing. The operating frequency of the transformer is the same as the PWM frequency.

[0043] The transformer T1 is a flyback transformer. The working waveforms of its primary winding coil and secondary winding coil are both PWM waves, and they have the same frequency and duty cycle, with a phase difference of 180°. Its working process is the same as that of a common flyback transformer.

[0044] The switching input voltage VIN and the output voltage VOUT satisfy the following relationship with the turns ratio N of the secondary winding coil to the primary winding coil of the transformer T1:

[0045] VIN=(VOUT+VF) / N+V3

[0046] V3 is the voltage difference between the collector and emitter of the NPN transistor Q1. This parameter affects the load regulation rate of the switching power supply. When the switching power supply is working normally, the NPN transistor Q1 works in the amplification state. The power supply system controls V3 through the negative feedback module to adjust the working voltage V1 of the primary winding coil of the transformer T1, thereby adjusting the induced voltage V2 of the secondary winding coil of the transformer T1 to maintain the output voltage of the switching power supply stable at the set value VOUT.

[0047] When no-load, the induced voltage of the secondary winding coil of transformer T1 is V2=VOUT+VF, where VF is the tube voltage drop of diode D1. Ignoring the influence of the no-load current of the switching power supply and the parasitic parameters of the circuit, the amplitude of the PWM waveform input to the primary winding of the transformer is V1=V2 / N.

[0048] When the load is added to the output end of the power supply, the switch output voltage VOUT decreases, the voltage at the second end of the voltage regulator TL431 decreases, the current flowing through the first and third ends of the voltage regulator TL431 decreases, the current flowing through the light-emitting diode in the linear optocoupler U1 decreases, and the current flowing through the transistor in the linear optocoupler U1 decreases at the same time. The base voltage of the NPN transistor Q1 increases, the emitter voltage of the NPN transistor Q1 increases, and the working voltage V1 of the primary winding of the transformer T1 increases, so that the induced voltage V2 of the secondary winding coil of the transformer T1 increases, and the output voltage of the switching power supply increases, and finally stabilizes at the set value VOUT; if the load continues to increase, the voltage V3 between the collector and emitter of the NPN transistor Q1 will continue to decrease, and eventually the NPN transistor Q1 will be saturated, and the switching power supply will lose its voltage regulation function. Therefore, V3 cannot be set too small, otherwise the load adjustment rate of the switching power supply will be too low. But it cannot be set too large, otherwise the heat generated by the NPN transistor Q1 will be too large.

[0049] like Figure 3 , the voltage waveform of the working node of the switching power supply, the circuit parameters are as follows: the input voltage is 15V, the output voltage is 25V, the transformer is a flyback transformer, the number of turns of the primary winding coil of the transformer is 10, the number of turns of the secondary winding coil of the transformer is 25, and the operating frequency of the transformer is 100kHz; among them, V1 is the operating voltage of the primary winding coil of the transformer T1, VIN is the input voltage of the switching power supply, and VOU is the output voltage of the switching power supply.

[0050] In summary, the utility model controls the operating frequency of the switching power supply to remain consistent and greater than the upper limit of human hearing, solving the problem of transformer howling caused by the switching power supply entering intermittent working mode under no-load and light-load modes. By changing the turns ratio of the transformer, both voltage boost and voltage reduction can be achieved.

[0051] The present invention is applicable to a variety of switching power supply topologies, Figure 4 the circuit structure of a switching power supply based on a forward transformer, Figure 5 the circuit structure of a switching power supply based on a push-pull transformer, and the negative feedback module is different from Figure 2 and Figure 4 , and there is no electrical isolation between the primary winding coil and the secondary winding coil of the transformer.

[0052] The above are only the preferred embodiments of the present utility model and are not used to limit the present utility model. For those skilled in the art, the present utility model can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present utility model shall be included within the protection scope of the present utility model. It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0053] The above are only the specific embodiments of the present utility model, but the protection scope of the present utility model is not limited thereto. Any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present utility model, and all of them should be covered by the protection scope of the present utility model.

[0054] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising a..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

Claims

1. A switching power supply control circuit with a constant operating frequency, characterized in that: It includes a linear voltage regulator module (102), a transformer (103), a PWM switch module (105), a negative feedback module (106) and a rectifier filter module (104). The linear voltage regulator module (102) is used to regulate the operating voltage of the primary winding of the transformer (103). The input end of the linear voltage regulator module (102) is connected to the starting power input end (101). The control end of the linear voltage regulator module (102) is connected to the output end of the negative feedback module (106). The output end of the linear voltage regulator module (102) is connected to the first end of the primary winding coil of the transformer (103). The transformer (103) is used for voltage conversion. The PWM switch module (105) is connected to the second end of the primary winding coil of the transformer (103) and is used to control the operating frequency of the transformer (103). The secondary winding coil of the transformer (103) is connected to the input end of the rectifier filter module (104). The output end of the rectifier filter module (104) is connected to the switching power supply output end (107). The negative feedback module (106) is used to collect the voltage of the switching power supply output end (107) and control the operating voltage of the primary winding coil of the transformer (103) through the linear voltage regulator module (102) to adjust the stability of the output voltage. The input end of the negative feedback module (106) is connected to the output end of the switching power supply output end (107).

2. The switching power supply control circuit with a constant operating frequency according to claim 1, characterized in that: The linear voltage regulator module (102) includes an NPN transistor (Q1), a first electrolytic capacitor (C1) and a second electrolytic capacitor (C2). The positive pole of the first electrolytic capacitor (C1) is connected to the collector of the NPN transistor (Q1). The negative pole of the first electrolytic capacitor (C1) is connected to the ground plane of the primary side of the transformer T1. The base of the NPN transistor (Q1) is connected to the fourth end of the linear optocoupler (U1). The emitter of the NPN transistor (Q1) is connected to the first end of the primary winding coil of the transformer T1. The positive pole of the second electrolytic capacitor (C2) is connected to the emitter of the NPN transistor (Q1). The negative pole of the second electrolytic capacitor (C2) is connected to the ground plane of the primary side of the transformer T1.

3. The switching power supply control circuit with a constant operating frequency according to claim 1, characterized in that: The PWM switch module (105) includes a PWM output module and an N-channel power MOS transistor (Q2). The PWM output module is connected to the gate of the N-channel power MOS transistor (Q2). The drain of the N-channel power MOS transistor (Q2) is connected to the second end of the primary winding coil of the transformer T1. The source of the N-channel power MOS transistor (Q2) is connected to the ground plane of the primary side of the transformer T1.

4. The switching power supply control circuit with a constant operating frequency according to claim 1, wherein: The transformer (103) is a flyback transformer.

5. The switching power supply control circuit with a constant operating frequency according to claim 1, characterized in that: The rectifier filter module (104) includes a rectifier diode (D1) and a third electrolytic capacitor (C3). The positive pole of the rectifier diode (D1) is connected to the first end of the secondary winding coil of the transformer T1. The negative pole of the rectifier diode (D1) is connected to the positive pole of the third electrolytic capacitor (C3). The positive pole of the third electrolytic capacitor (C3) is connected to the switching power supply output end. The negative pole of the third electrolytic capacitor (C3) is connected to the second end of the secondary winding coil of the transformer T1. The second end of the secondary winding coil of the transformer T1 is connected to the ground plane of the secondary side of the transformer T1.

6. The switching power supply control circuit with a constant operating frequency according to claim 1, characterized in that: The negative feedback module (106) includes a first resistor (R1), a second resistor (R2), a third resistor (R3), a fourth resistor (R4), a linear optocoupler (U1), and a voltage regulator TL431. The first end of the first resistor (R1) is connected to the first power supply VCC. The second end of the first resistor (R1) is connected to the fourth end of the linear optocoupler (U1). The third end of the linear optocoupler (U1) is connected to the ground plane of the primary side of the transformer T1. The first end of the second resistor (R2) is connected to the second power supply VDD. The second end of the second resistor (R2) is connected to the first end of the linear optocoupler (U1). The second end of the linear optocoupler (U1) is connected to the first end of the voltage regulator TL431. The second end of the voltage regulator TL431 is connected to the first end of the fourth resistor (R4). The third end of the voltage regulator TL431 is connected to the ground plane of the secondary side of the transformer. The first end of the third resistor (R3) is connected to the output end of the switching power supply. The second end of the third resistor (R3) is connected to the second end of the voltage regulator TL431. The second end of the fourth resistor (R4) is connected to the ground plane of the secondary side of the transformer T1.

7. The switching power supply control circuit with a constant operating frequency according to claim 6, wherein: The first resistor (R1) and the second resistor (R2) are current-limiting resistors. The third resistor (R3) and the fourth resistor (R4) are feedback sampling resistors.

8. The switching power supply control circuit with a constant operating frequency according to claim 7, wherein: The corresponding relationship between the output voltage VOUT and the third resistor (R3) and the fourth resistor (R4) is as follows: VOUT = 2.5×(R3 + R4) / R4.

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