A circuit for improving the output load cross-regulation of a switching power supply and the switching power supply itself.

Abstract

This invention discloses a circuit and a switching power supply for improving the output load cross-regulation of a switching power supply. The switching power supply includes a main output circuit and an auxiliary output circuit. The circuit includes a voltage detection module and an equalization module. The voltage detection module is connected in series in the auxiliary output circuit and outputs a conduction voltage signal when the output voltage of the auxiliary output circuit is greater than a set threshold. The equalization module is connected across the voltage output terminals of the main output circuit and the auxiliary output circuit and receives the conduction voltage signal. When the equalization module receives the conduction voltage signal, it connects the voltage output terminals of the main output circuit and the auxiliary output circuit to improve the output regulation of the switching power supply while ensuring the efficiency of the switching power supply.

Description

Technical Field

[0001] This invention relates to the field of power supply design technology, and specifically to a circuit and a switching power supply for improving the output load cross-regulation of a switching power supply. Background Technology

[0002] In switching power supplies with multiple outputs, closed-loop feedback regulation is typically used only for the main output circuit, while the auxiliary output circuit uses open-loop regulation without feedback. The auxiliary output voltage is achieved by adding an auxiliary output winding to the output side of the transformer. Furthermore, the number of turns in this auxiliary output winding is proportional to the main output voltage, and the number of turns in the main output winding is proportional to the auxiliary output voltage, and vice versa.

[0003] Ideally, the auxiliary output voltage and the main output voltage satisfy the transformer's turns ratio relationship. As long as the main output voltage remains stable, the auxiliary output voltage will also remain stable. However, since the transformer in a switching power supply is not an ideal device, it also has parameters such as leakage inductance and parasitic capacitance. Therefore, the output voltage of the auxiliary output circuit will change with the output load. In particular, when one of the main output circuit and the auxiliary output circuit is fully loaded while the other (or multiple circuits) is lightly loaded or unloaded, the output voltage of the lightly loaded or unloaded circuit will rise and far exceed the device's withstand voltage, thus damaging the device. To prevent this from happening, existing switching power supplies often add a Zener diode to the transformer's auxiliary output circuit to stabilize the auxiliary output voltage. However, since power loss occurs across the Zener diode when it is connected in parallel with the output load, the Zener diode will affect the efficiency of the switching power supply, thus reducing its efficiency.

[0004] In summary, existing switching power supplies still require further improvement. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned defects or problems in the prior art and to provide a circuit and a switching power supply that improve the output load cross-regulation of the switching power supply, so as to ensure the efficiency of the switching power supply while improving the output regulation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A circuit for improving the cross-regulation of the output load of a switching power supply is disclosed. The switching power supply includes a main output circuit, an auxiliary output circuit, a voltage detection module, and an equalization module. The voltage detection module is connected in series in the auxiliary output circuit and outputs a conduction voltage signal when the output voltage of the auxiliary output circuit is greater than a set threshold. The equalization module is connected across the voltage output terminals of the main output circuit and the auxiliary output circuit and receives the conduction voltage signal. When the equalization module receives the conduction voltage signal, it connects the voltage output terminals of the main output circuit and the auxiliary output circuit.

[0008] Furthermore, the voltage detection module includes a first resistor, a second resistor, and a first transistor; the first resistor is connected in series between the voltage output terminal of the auxiliary output circuit and the base of the first transistor; the second resistor is connected in series between the base of the first transistor and ground; the collector of the first transistor is grounded, and its emitter is used to output a conduction voltage signal.

[0009] Furthermore, the equalization module consists of one or two shunt circuits connected in parallel; the shunt circuit is used to bridge the voltage output terminals of the main output circuit and the auxiliary output circuit, and the shunt circuit consists of transistors and resistors.

[0010] Furthermore, the equalization module consists of a first shunt circuit; the first shunt circuit includes a third resistor and a second transistor; the base of the second transistor is used to receive the conduction voltage signal and is connected to the voltage output terminal of the auxiliary output circuit through the third resistor, its emitter is connected to the voltage output terminal of the main output circuit, and its collector is connected to the voltage output terminal of the auxiliary output circuit.

[0011] Furthermore, the equalization module consists of two parallel shunt circuits: a second shunt circuit and a third shunt circuit. The second shunt circuit includes a fourth resistor and a third transistor. The base of the third transistor receives the conduction voltage signal and is connected to the voltage output terminal of the auxiliary output circuit via the fourth resistor. Its emitter is connected to the voltage output terminal of the main output circuit, and its collector is connected to the input terminal of the third shunt circuit. The third shunt circuit includes a fifth resistor and a fourth transistor. The base of the fourth transistor serves as the input terminal of the third shunt circuit and is connected to the voltage output terminal of the auxiliary output circuit via the fifth resistor. Its collector is connected to the voltage output terminal of the main output circuit, and its emitter is connected to the voltage output terminal of the auxiliary output circuit.

[0012] A switching power supply includes a transformer, a main output circuit, an auxiliary output circuit, a pulse width modulation circuit, a voltage regulator circuit, a switching circuit, and a circuit for improving the output load cross-regulation of the switching power supply as mentioned in any of the above technical solutions. The transformer includes a primary winding and a main output winding and an auxiliary output winding respectively connected in series in the main output circuit and the auxiliary output circuit. The voltage regulator circuit is connected in series between the voltage output terminal of the main output circuit and the voltage signal feedback terminal of the pulse width modulation circuit. The pulse width modulation circuit is used to control the switching circuit to open and close according to the electrical signal received at its voltage signal feedback terminal. The output terminal of the switching circuit is connected to the corresponding terminal of the primary winding. A voltage detection module is connected in series in the auxiliary output circuit and outputs a conduction voltage signal when the output voltage of the auxiliary output circuit is greater than a set threshold. An equalization module is connected between the voltage output terminals of the main output circuit and the auxiliary output circuit and receives the conduction voltage signal. When the equalization module receives the conduction voltage signal, it connects the voltage output terminals of the main output circuit and the auxiliary output circuit.

[0013] Furthermore, it also includes a first-stage rectifier-filter rectifier circuit and a second-stage rectifier-filter circuit; the first-stage rectifier-filter circuit includes a first rectifier module and a first filter module; the input terminal of the first rectifier module is connected to the same-name terminal of the auxiliary output winding, and its output terminal is connected to the first filter module connected in series in the auxiliary output circuit; the second-stage rectifier-filter circuit includes a second rectifier module and a second filter module; the input terminal of the second rectifier module is connected to the same-name terminal of the main output winding, and its output terminal is connected to the second filter module connected in series in the main output circuit.

[0014] Furthermore, it also includes a primary filter rectifier circuit and an RCD snubber circuit; the primary filter rectifier circuit is used to receive and filter out interference signals in the mains power and convert the mains power into a DC signal to the non-same-name terminal of the primary winding; the RCD snubber circuit is used to absorb the spike voltage generated by the switching transistor in the switching circuit during the switching process, and it is connected in series between the non-same-name terminal of the primary winding and the drain of the switching transistor in the switching circuit.

[0015] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. By incorporating a voltage detection module and an equalization module into the circuit, the output regulation of the switching power supply is improved, and the efficiency of the switching power supply is ensured. The specific working principle to achieve this effect is as follows: Since the voltage detection module is connected in series in the auxiliary output circuit, it can determine whether the output voltage of the auxiliary output circuit has increased by checking if the output voltage exceeds a set threshold. Furthermore, because the voltage detection module only outputs a conduction voltage signal when the output voltage of the auxiliary output circuit exceeds the set threshold, and the equalization module only connects the voltage output terminals of the main output circuit and the auxiliary output circuit when it receives the conduction voltage signal, when the output voltage of the auxiliary output circuit fluctuates within a small range, the equalization module will not connect the voltage output terminals of the two output circuits, reducing losses and improving the stability and efficiency of the switching power supply. When the equalization module connects the two voltage output terminals, the current in the auxiliary output circuit can flow into the main output circuit through the equalization module to stabilize the output voltage of the auxiliary output circuit, preventing the output voltage of the auxiliary output circuit from increasing due to load changes.

[0017] 2. By configuring the voltage detection module with a first resistor, a second resistor, and a first transistor, the equalization module only connects the voltage output terminals of the main output circuit and the auxiliary output circuit when the output voltage of the auxiliary output circuit exceeds a set threshold. This improves the output regulation rate of the switching power supply while ensuring its efficiency. The specific working principle is as follows: Since the base of the first transistor is connected to the voltage output terminal of the auxiliary output circuit and ground through the first and second resistors respectively, the first and second resistors provide bias current to the base of the first transistor, ensuring that the first transistor remains in a conducting state and detects whether the output voltage of the auxiliary output circuit rises. When the output voltage of the auxiliary output circuit rises, the voltages of both the base and emitter of the first transistor rise. Under the switching characteristics, the emitter junction of the first transistor is forward biased, and the collector junction is reverse biased. This avoids the situation where the emitter of the first transistor outputs a conduction voltage signal when the output voltage of the auxiliary output circuit fluctuates only slightly. This configuration helps improve the stability and efficiency of the power supply.

[0018] 3. By configuring the equalization module to consist of one or more shunt circuits connected in parallel, and configuring each shunt circuit to consist of transistors and resistors connected in series at the voltage output terminals of the main output circuit and the auxiliary output circuit, the user can select the number of shunt circuits according to the voltage difference between the voltage output terminals of the main output circuit and the auxiliary output circuit. When the difference between the two output voltages is large, multiple shunt circuits can be connected in parallel at the voltage output terminals of the two circuits to stabilize the output voltage of the auxiliary output circuit.

[0019] 4. By configuring the equalization module as a first shunt circuit, and setting the first shunt circuit as a third resistor and a second transistor, the equalization module only connects the voltage output terminals of the two output circuits when the output voltage of the auxiliary output circuit rises to a certain level, thus improving the output regulation rate. Specifically, since the emitter of the second transistor is connected to the voltage output terminal of the main output circuit, and its base is connected to the emitter of the first transistor, and when the two output voltages are stable, the voltage at the emitter of the first transistor (the base voltage of the second transistor) is less than the output voltage of the main output circuit (the emitter voltage of the second transistor); therefore, when the output voltages of the two output circuits are stable, the second transistor is in the off state, not connecting the voltage output terminals of the two output circuits to reduce losses and improve efficiency. When the output voltage of the auxiliary output circuit rises, the emitter voltage of the first transistor outputs a conduction voltage signal to turn on the second transistor. At this time, the current at the voltage output terminal of the auxiliary output circuit flows through the second transistor to the voltage output terminal of the main output circuit to maintain the output voltage of the auxiliary output circuit. Furthermore, since transistors have amplification capabilities, only a small current needs to be injected into the base of the second transistor to generate a large current through the transistor's amplification effect. That is, when the equalization module is working (i.e., when the second transistor is conducting), only a small current loss is needed to generate a large current flowing from the voltage output terminal of the auxiliary output circuit to the voltage output terminal of the main output circuit. Therefore, the internal circuit structure of this equalization module not only improves the output regulation of the switching power supply but also further ensures the efficiency of the switching power supply.

[0020] 5. By configuring the equalization module as consisting of two parallel second shunt circuits and a third shunt resistor, and configuring the second shunt circuit as a fourth resistor and a third transistor, and the third shunt circuit as a fifth resistor and a fourth transistor, when the voltage difference between the main output circuit and the auxiliary output circuit is large, a larger current can flow from the voltage output terminal of the auxiliary output circuit to the voltage output terminal of the main output circuit, thereby further improving the effect of the switching power supply output regulation and ensuring the efficiency of the switching power supply.

[0021] 6. By setting a voltage regulator circuit between the voltage output terminal of the main output circuit and the voltage signal feedback terminal of the pulse width modulation circuit, the output voltage of the main output circuit is stabilized. This setting can prevent the main output voltage from rising and damaging the device when the auxiliary output circuit is increased while the main output circuit is still lightly loaded or unloaded. When the output voltage of the main output circuit rises, the voltage regulator circuit will feed the output voltage back to the voltage signal feedback terminal of the pulse width modulation circuit. The pulse width modulation circuit adjusts the on and off time of the switching transistor in the switching circuit according to the voltage value at its voltage signal feedback terminal to stabilize the output voltage of the main output circuit.

[0022] 7. By setting a first-stage filter and rectifier circuit and a second-stage rectifier and filter circuit between the auxiliary output circuit and the main output circuit and the output side of the transformer, respectively, the signal on the output side of the transformer is rectified and interference signals are further filtered out to improve the stability of the power supply.

[0023] 8. By setting a primary filter rectifier circuit and an RCD snubber circuit on the input side of the transformer, interference signals are further filtered out to improve the stability of the switching power supply. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments are briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the module connection of a circuit for improving the cross-regulation of the output load of a switching power supply according to the present invention.

[0026] Figure 2 This is a circuit schematic diagram of a first embodiment of a circuit for improving the load cross-regulation of a switching power supply output according to the present invention.

[0027] Figure 3 This is a circuit schematic diagram of a second embodiment of the circuit for improving the load cross-regulation of a switching power supply output according to the present invention.

[0028] Figure 4 This is a circuit diagram of a switching power supply according to the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise expressly defined, the use of terms such as "first," "second," or "third" in the claims, description, and accompanying drawings of this invention is for distinguishing different objects and not for describing a specific order.

[0031] Unless otherwise expressly defined, in the claims, description, and accompanying drawings of this invention, the use of directional terms such as "center," "lateral," "central," "horizontal," "vertical," "top," "bottom," "inner," "outer," "upper," "lower," "front," "rear," "left," "right," "clockwise," and "counterclockwise" to indicate orientation or positional relationships is based on the orientation and positional relationships shown in the accompanying drawings and is only for the convenience of describing the invention and simplifying the description. It does not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the specific scope of protection of this invention.

[0032] Unless otherwise expressly defined, the terms "fixed connection" or "fixed connection" used in the claims, description and drawings of this invention should be interpreted broadly to refer to any connection in which there is no displacement or relative rotation relationship between the two parties, including non-removable fixed connection, detachable fixed connection, integral connection and fixed connection by other means or components.

[0033] In the claims, description and accompanying drawings of this invention, the terms "comprising," "having," and variations thereof are used to mean "including but not limited to."

[0034] See Figures 1 to 4 As shown, this invention discloses a circuit for improving the output load cross-regulation of a switching power supply and a switching power supply in general. The switching power supply includes a transformer T1, a main output circuit, an auxiliary output circuit, a circuit for improving the output load cross-regulation of the switching power supply, a voltage regulator circuit, a pulse width modulation circuit, an auxiliary power supply circuit, a switching circuit, an RCD snubber circuit, a first-stage filter and rectifier circuit, a second-stage filter and rectifier circuit, and a primary filter and rectifier circuit. In an embodiment of this invention, the output voltage of the main output circuit is +5V; the output voltage of the auxiliary output circuit is +7V.

[0035] Transformer T1 includes a primary winding, a feedback winding, a main output winding, and an auxiliary output winding; the main output winding is connected in series with the main output circuit; the auxiliary output winding is connected in series with the auxiliary output circuit.

[0036] like Figure 1 As shown, the circuit for improving the cross-regulation of the output load of the switching power supply includes a voltage detection module 1 and an equalization module 2.

[0037] The voltage detection module 1 is connected in series in the auxiliary output circuit and outputs a conduction voltage signal CV when the output voltage of the auxiliary output circuit is greater than a set threshold. In an embodiment of the present invention, the voltage detection module 1 includes a first resistor R1, a second resistor R2, and a first transistor Q1. The first resistor R1 is connected in series between the voltage output terminal of the auxiliary output circuit and the base of the first transistor Q1. The second resistor R2 is connected in series between the base of the first transistor Q1 and ground. The collector of the first transistor Q1 is grounded, and its emitter is used to output the conduction voltage signal CV.

[0038] In an embodiment of the present invention, the first transistor Q1 is a PNP transistor. The first resistor R1 and the second resistor R2 provide bias current to the base of the first transistor Q1, ensuring that the first transistor Q1 is always in a conducting state and detecting whether the output voltage of the auxiliary output circuit rises. Specifically, when the output voltage of the auxiliary output circuit rises, the voltages at both the base and emitter of the first transistor Q1 rise. Furthermore, due to the switching characteristics, the emitter junction of the first transistor Q1 is forward biased, and the collector junction is reverse biased. This avoids the situation where the emitter of the first transistor Q1 outputs a conduction voltage signal CV when the output voltage of the auxiliary output circuit fluctuates only within a small range. This configuration is beneficial for improving the stability and efficiency of the power supply.

[0039] The equalization module 2 is used to connect between the voltage output terminals of the main output circuit and the auxiliary output circuit and receive the conduction voltage signal CV. When the equalization module 2 receives the conduction voltage signal CV, it connects the voltage output terminals of the main output circuit and the auxiliary output circuit. The equalization module 2 consists of one or more shunt circuits connected in parallel. Each shunt circuit consists of a transistor and a resistor connected in series between the voltage output terminals of the main output circuit and the auxiliary output circuit. This configuration allows the user to select the number of shunt circuits to be connected in parallel based on the voltage difference between the voltage output terminals of the main output circuit and the auxiliary output circuit. When the difference between the two output voltages is large, multiple shunt circuits can be connected in parallel at the two voltage output terminals to stabilize the output voltage of the auxiliary output return current.

[0040] like Figure 2As shown, in Embodiment 1 of the present invention, the equalization module 2 consists of a first shunt circuit; the first shunt circuit includes a third resistor R3 and a second transistor Q2; the base of the second transistor Q2 is used to receive the conduction voltage signal CV and is connected to the voltage output terminal of the auxiliary output circuit through the third resistor R3, its emitter is connected to the voltage output terminal of the main output circuit, and its collector is connected to the voltage output terminal of the auxiliary output circuit. When the output voltages of the two output circuits are stable, the second transistor Q2 is cut off, not connecting the voltage output terminals of the two output circuits to reduce losses and improve efficiency; when the output voltage of the auxiliary output circuit rises, the emitter of the first transistor Q1 outputs a conduction voltage signal CV (the voltage value of the conduction voltage signal CV is greater than the output voltage value of the main output circuit) to turn on the second transistor Q2; at this time, the current at the voltage output terminal of the auxiliary output circuit flows through the second transistor Q2 to the voltage output terminal of the main output circuit to maintain the output voltage of the auxiliary output circuit. Furthermore, since transistors have amplification capabilities, only a small current needs to be injected into the base of the second transistor Q2 to generate a large current through the transistor's amplification effect. That is, when the equalization module 2 is working (i.e., when the second transistor Q2 is turned on), only a small current loss is needed to generate a large current flowing from the voltage output terminal of the auxiliary output circuit to the voltage output terminal of the main output circuit. Therefore, the setting of the equalization module 2 can not only improve the output regulation rate of the switching power supply but also further ensure the efficiency of the switching power supply.

[0041] like Figure 3 As shown, in Embodiment 2 of the present invention, the equalization module 2 consists of two parallel second shunt circuits and a third shunt circuit; the second shunt circuit includes a fourth resistor R4 and a third transistor Q3; the base of the third transistor Q3 is used to receive the conduction voltage signal CV and is connected to the voltage output terminal of the auxiliary output circuit through the fourth resistor R4, its emitter is connected to the voltage output terminal of the main output circuit, and its collector is connected to the input terminal of the third shunt circuit; the third shunt circuit includes a fifth resistor R5 and a fourth transistor Q4; the base of the fourth transistor Q4 serves as the input terminal of the third shunt circuit and is connected to the voltage output terminal of the auxiliary output circuit through the fifth resistor R5, its collector is connected to the voltage output terminal of the main output circuit, and its emitter is connected to the voltage output terminal of the auxiliary output circuit; and as... Figure 4 As shown, the switching power supply circuit in the embodiments of the present invention takes the equalization module 2 in Embodiment 2 as an example.

[0042] In this circuit, the base of the third transistor Q3 is connected to the emitter of the first transistor Q1, and the emitter of the third transistor Q3 is connected to the +5V main output voltage. Assuming that when both output voltages are stable, the voltage of the first voltage signal received by the base of the first transistor Q1 is 3.5V, then the voltage at its emitter is 4.2V. Since the third transistor Q3 is an NPN transistor, 4.2V is less than its emitter's +5V voltage. Therefore, when both output voltages are stable, the emitter of the first transistor Q1 can clamp the base voltage of the third transistor Q3 to 4.2V, thus cutting off the third transistor Q3 when both output circuits are stable. The same applies to the fourth transistor Q4. When the output voltage of the auxiliary output circuit is stable, the voltage output terminals of the two output circuits are cut off and not connected. However, when the auxiliary output voltage rises and the emitter voltage of the first transistor Q1 is greater than the voltage output terminal voltage of the main output circuit (i.e., the emitter voltage of the third transistor), the emitter of the first transistor Q1 outputs a conduction voltage signal CV, so that the third transistor Q3 and the fourth transistor Q4 are turned on. In this way, the equalization module can connect the two voltage output terminals only when the output voltage of the auxiliary output circuit rises to a set threshold to reduce losses and improve efficiency. Moreover, compared with a single shunt circuit, the arrangement of two parallel shunt circuits allows a larger current to flow, thereby better improving the output regulation of the switching power supply.

[0043] It should be noted that when there are multiple main output circuits or multiple auxiliary output circuits in the circuit, the output load cross-regulation of the switching power supply can be improved by setting a circuit consisting of voltage detection module 1 and equalization module 2 in each of any two main output circuits and auxiliary output circuits.

[0044] like Figure 4 As shown, the voltage regulator circuit is connected in series between the voltage output terminal of the main output circuit and the voltage signal feedback terminal of the pulse width modulation circuit, and is used to feed back the output voltage of the main output circuit to the pulse width modulation module.

[0045] In an embodiment of the present invention, the voltage regulator circuit consists of a sixth resistor R6, an optocoupler PH1, a three-terminal voltage regulator chip IC1, a seventh resistor R7, a first capacitor C1, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a first Zener diode Z1, and a second capacitor C2. One end of the sixth resistor R6 serves as the input terminal of the voltage regulator circuit and is connected to the voltage output terminal of the main output circuit. One end of the twelfth resistor R12 serves as the output terminal of the voltage regulator circuit and is connected to the voltage signal feedback terminal of the pulse width modulation circuit.

[0046] A pulse width modulation circuit is used to control the switching circuit to open or close based on the electrical signal received at its voltage signal feedback terminal. In an embodiment of the present invention, the pulse width modulation circuit comprises a main control chip IC2, a thirteenth resistor R13, a fourteenth resistor R14, a first electrolytic capacitor CD1, a fifteenth resistor R15, a sixteenth resistor R16, a seventeenth resistor R17, a first diode D1, an eighteenth resistor R18, a third capacitor C3, a nineteenth resistor R19, a twentieth resistor R20, a fourth capacitor C4, a fifth capacitor C5, and a second Zener diode Z2. In this embodiment, the main control chip IC2 is model OB2281. The second pin of the main control chip IC2 serves as the voltage signal feedback terminal of the pulse width modulation circuit, and its fourth pin serves as the current signal feedback terminal, detecting the source current of the switching transistor Q5 in the switching circuit via the nineteenth resistor R19 and the twentieth resistor R20. Its fifth pin serves as the power input terminal, sequentially connected to the power supply voltage signal via the fourteenth resistor R14 and the thirteenth resistor R13. One end of the sixteenth resistor R16 serves as the pulse signal output terminal, connected to the gate of the switching transistor Q5 in the switching circuit.

[0047] The auxiliary power supply circuit is connected in series with the feedback winding and is used to power the main control chip IC2. In an embodiment of the present invention, the auxiliary power supply circuit consists of a first inductor L1, a second diode D2, a third diode D3, and a second electrolytic capacitor CD2. One end of the first voltage is connected to the same-named end of the feedback winding as the input terminal of the auxiliary power supply voltage, and the other end is connected to the anode of the second diode D2. The cathode of the second diode D2 is grounded through the second electrolytic capacitor CD2 and is also connected to the anode of the third diode D3. The anode of the third diode D3 is connected to the fifth pin of the main control chip IC2 as the output terminal of the auxiliary power supply circuit.

[0048] The output terminal of the switching circuit is connected to the same terminal of the primary winding. In an embodiment of the present invention, the switching circuit includes a switching transistor Q5, a sixth capacitor C6, and a twenty-first resistor R21. The drain of the switching transistor Q5 serves as the output terminal of the switching circuit and is connected to its source via the sixth capacitor C6. The gate of the switching transistor Q5 serves as the input terminal of the switching transistor Q5 and is connected to the pulse signal output terminal of the pulse width modulation circuit. The source of the switching transistor Q5 is grounded via the twenty-first resistor R21.

[0049] The RCD snubber circuit is used to absorb the spike resistance generated by the switching transistor Q5 during the switching process and is connected in series between the non-same-name terminals of the primary winding and the drain of the switching transistor Q5. In the embodiment of the present invention, the RCD snubber circuit consists of the twenty-second resistor R22, the twenty-third resistor R23, the twenty-fourth resistor R24, the twenty-fifth resistor R25, the seventh capacitor C7, the twenty-sixth resistor R26, the twenty-seventh resistor R27, and the fourth diode D4. The non-same-name terminals of the primary winding are connected to the cathode of the fourth diode D4 through the twenty-second resistor R22 and the twenty-third resistor R23 connected in series. The twenty-fourth resistor R24 ​​is connected in parallel with the twenty-second resistor R22. The twenty-fifth resistor R25 is connected in parallel with the twenty-third resistor R23. The anode of the fourth diode D4 is connected to the drain of the switching transistor Q5, and its cathode is connected to the non-same-name terminals of the primary winding through the seventh capacitor C7 and the twenty-sixth resistor R26 connected in series. The twenty-seventh resistor R27 is connected in parallel with the twenty-sixth resistor R26.

[0050] The first-stage filter rectifier circuit includes a first rectifier module and a first filter module; the input terminal of the first rectifier module is connected to the same-name terminal of the auxiliary output winding, and its output terminal is connected to the first filter module connected in series in the auxiliary output circuit.

[0051] In an embodiment of the present invention, the first rectifier module is composed of a fifth diode D5, a twenty-eighth resistor R28 and an eighth capacitor C8; the first filter module is composed of a third electrolytic capacitor CD3; wherein, the anode of the fifth diode D5 is connected to the same terminal of the auxiliary output winding; the third electrolytic capacitor CD3 is connected in series in the auxiliary output circuit, and its positive terminal is connected to the auxiliary output voltage terminal.

[0052] The second-stage filter rectifier circuit includes a second rectifier module and a second filter module; the input terminal of the second rectifier module is connected to the same-name terminal of the main output winding, and its output terminal is connected to the second filter module connected in series in the main output circuit.

[0053] In an embodiment of the present invention, the second rectifier module is composed of a sixth diode D6, a twenty-ninth resistor R29 and a ninth capacitor C9; the second filter module is composed of a fourth electrolytic capacitor CD4; wherein, the anode of the sixth diode D6 is connected to the same terminal of the main output winding; the fourth electrolytic capacitor CD4 is connected in series in the main output circuit, and its positive terminal is connected to the main output voltage terminal.

[0054] The primary filter rectifier circuit is used to receive and filter interference signals in the mains power and convert the mains power into a DC signal to the non-same-name terminal of the primary winding. In an embodiment of the present invention, the primary filter rectifier circuit includes an EMC circuit and a rectifier filter circuit. The EMC circuit consists of a fuse F1, a thermistor RT1, a varistor VDR1, a tenth capacitor C10, a thirtieth resistor R30, a thirty-first resistor R31, and an inductor LF1. The end where the thirtieth resistor R30 and the thirty-first resistor R31 are connected together is used to output the supply voltage signal and is connected to the fifth pin of the main control chip IC2 through the thirteenth resistor R13 and the fourteenth resistor R14. In an embodiment of the present invention, the rectifier filter circuit consists of a rectifier bridge DB1, a thirty-second resistor R32, a thirty-third resistor R33, and a fifth electrolytic capacitor CD5. The second pin of the rectifier bridge DB1 is connected to the second pin of the inductor LF1. The positive terminal of the fifth electrolytic capacitor CD5 is connected to the non-same-name terminal of the primary winding.

[0055] In summary, the present invention provides a circuit and a switching power supply that improve the output load cross-regulation of a switching power supply, which can improve the output regulation of the switching power supply while ensuring the efficiency of the switching power supply.

[0056] The foregoing description of the specifications and embodiments is intended to explain the scope of protection of this invention, but does not constitute a limitation on the scope of protection of this invention. Modifications, equivalent substitutions, or other improvements to the embodiments of this invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation, based on the teachings of this invention or the foregoing embodiments, in conjunction with common knowledge, general technical knowledge, and / or existing technology, should all be included within the scope of protection of this invention.

Claims

1. A circuit for improving the output load cross-regulation of a switching power supply, the switching power supply comprising a main output circuit and an auxiliary output circuit, characterized in that, include: A voltage detection module is used to be connected in series in the auxiliary output circuit and to output a conduction voltage signal when the output voltage of the auxiliary output circuit is greater than a set threshold. An equalization module is used to connect between the voltage output terminals of the main output circuit and the auxiliary output circuit and to receive the conduction voltage signal; wherein, when the equalization module receives the conduction voltage signal, it connects the voltage output terminals of the main output circuit and the auxiliary output circuit; the equalization module consists of one shunt circuit or two shunt circuits connected in parallel; the shunt circuit is used to connect between the voltage output terminals of the main output circuit and the auxiliary output circuit, and the shunt circuit consists of a transistor and a resistor; The switching power supply further includes: a pulse width modulation circuit, a voltage regulator circuit, a transformer, a switching circuit, and a circuit for improving the output load cross-regulation of the switching power supply. The transformer includes a primary winding and a main output winding and an auxiliary output winding respectively connected in series in the main output circuit and the auxiliary output circuit; The voltage regulator circuit is connected in series between the voltage output terminal of the main output circuit and the voltage signal feedback terminal of the pulse width modulation circuit; wherein, the voltage regulator circuit includes: a sixth resistor R6, an optocoupler PH1, a three-terminal voltage regulator chip IC1, a seventh resistor R7, a first capacitor C1, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a first Zener diode Z1, and a second capacitor C2; one end of the sixth resistor R6 serves as the input terminal of the voltage regulator circuit and is connected to the voltage output terminal of the main output circuit; one end of the twelfth resistor R12 serves as the output terminal of the voltage regulator circuit and is connected to the voltage signal feedback terminal of the pulse width modulation circuit; The pulse width modulation circuit is used to control the switching circuit to open or close based on the electrical signal received at its voltage signal feedback terminal. The output terminal of the switching circuit is connected to the terminal of the primary winding with the same name. The voltage detection module is connected in series in the auxiliary output circuit, and outputs a conduction voltage signal when the output voltage of the auxiliary output circuit is greater than a set threshold. The equalization module is connected between the voltage output terminals of the main output circuit and the auxiliary output circuit and receives the conduction voltage signal; wherein, when the equalization module receives the conduction voltage signal, it connects the voltage output terminals of the main output circuit and the auxiliary output circuit.

2. The circuit for improving the output load cross-regulation of a switching power supply as described in claim 1, characterized in that: The voltage detection module includes a first resistor, a second resistor, and a first transistor; The first resistor is connected in series between the voltage output terminal of the auxiliary output circuit and the base of the first transistor; The second resistor is connected in series between the base of the first transistor and ground; The collector of the first transistor is grounded, and its emitter is used to output the conduction voltage signal.

3. The circuit for improving the output load cross-regulation of a switching power supply as described in claim 1, characterized in that: The equalization module consists of a first shunt circuit; the first shunt circuit includes a third resistor and a second transistor. The base of the second transistor is used to receive the conduction voltage signal and is connected to the voltage output terminal of the auxiliary output circuit through the third resistor. Its emitter is connected to the voltage output terminal of the main output circuit, and its collector is connected to the voltage output terminal of the auxiliary output circuit.

4. The circuit for improving the output load cross-regulation of a switching power supply as described in claim 1, characterized in that: Each equalization module consists of two parallel second shunt circuits and a third shunt circuit; The second shunt circuit includes a fourth resistor and a third transistor; The base of the third transistor is used to receive the conduction voltage signal and is connected to the voltage output terminal of the auxiliary output circuit through the fourth resistor. Its emitter is connected to the voltage output terminal of the main output circuit, and its collector is connected to the input terminal of the third shunt circuit. The third shunt circuit includes a fifth resistor and a fourth transistor; The base of the fourth transistor serves as the input terminal of the third shunt circuit and is connected to the voltage output terminal of the auxiliary output circuit via the fifth resistor. Its collector is connected to the voltage output terminal of the main output circuit, and its emitter is connected to the voltage output terminal of the auxiliary output circuit.

5. A switching power supply, characterized in that: It includes a transformer, a main output circuit, an auxiliary output circuit, a pulse width modulation circuit, a voltage regulator circuit, a switching circuit, and a circuit as described in any one of claims 1 to 4 for improving the output load cross-regulation of a switching power supply. The transformer includes a primary winding and a main output winding and an auxiliary output winding respectively connected in series in the main output circuit and the auxiliary output circuit; The voltage regulator circuit is connected in series between the voltage output terminal of the main output circuit and the voltage signal feedback terminal of the pulse width modulation circuit; wherein, the voltage regulator circuit includes: a sixth resistor R6, an optocoupler PH1, a three-terminal voltage regulator chip IC1, a seventh resistor R7, a first capacitor C1, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a first Zener diode Z1, and a second capacitor C2; one end of the sixth resistor R6 serves as the input terminal of the voltage regulator circuit and is connected to the voltage output terminal of the main output circuit; one end of the twelfth resistor R12 serves as the output terminal of the voltage regulator circuit and is connected to the voltage signal feedback terminal of the pulse width modulation circuit; The pulse width modulation circuit is used to control the switching circuit to open or close based on the electrical signal received at its voltage signal feedback terminal. The output terminal of the switching circuit is connected to the terminal of the primary winding with the same name. The voltage detection module is connected in series in the auxiliary output circuit, and outputs a conduction voltage signal when the output voltage of the auxiliary output circuit is greater than a set threshold. The equalization module is connected between the voltage output terminals of the main output circuit and the auxiliary output circuit and receives the conduction voltage signal; wherein, when the equalization module receives the conduction voltage signal, it connects the voltage output terminals of the main output circuit and the auxiliary output circuit.

6. A switching power supply as described in claim 5, characterized in that: It also includes a primary rectifier-filter rectifier circuit and a secondary rectifier-filter circuit; The first-stage filter rectifier circuit includes a first rectifier module and a first filter module; the input terminal of the first rectifier module is connected to the same-name terminal of the auxiliary output winding, and its output terminal is connected to the first filter module connected in series in the auxiliary output circuit. The second-stage filter rectifier circuit includes a second rectifier module and a second filter module; the input terminal of the second rectifier module is connected to the same terminal of the main output winding, and its output terminal is connected to the second filter module connected in series in the main output circuit.

7. A switching power supply as described in claim 6, characterized in that: It also includes a primary filter rectifier circuit and an RCD absorption circuit; The primary filter rectifier circuit is used to receive and filter out interference signals in the mains power and convert the mains power into a DC signal to the non-same-name terminals of the primary winding; The RCD snubber circuit is used to absorb the voltage spikes generated by the switching transistor in the switching circuit during the switching process, and it is connected in series between the non-same-name terminal of the primary winding and the drain of the switching transistor in the switching circuit.

Images