secondary feedback circuit

Abstract

The application relates to a secondary feedback circuit. The secondary feedback circuit comprises a sampling unit, a signal transmission unit and a stabilizing unit, the sampling unit comprises a voltage stabilizer U6 and a capacitor C5, the voltage stabilizer U6 is electrically connected with the capacitor C5; the voltage stabilizer U6 is electrically connected with the signal transmission unit; and the stabilizing unit is electrically connected with the signal transmission unit. The scheme provided by the application can replace a voltage stabilizing tube and actively provide amplification and compensation functions.

Description

Technical Field

[0001] This utility model relates to the field of circuit design technology, and in particular to a secondary feedback circuit. Background Technology

[0002] The secondary feedback circuit is a key component in a switching power supply. Its main function is to continuously monitor minute changes in the output voltage and make rapid corrections through a negative feedback mechanism, thereby ensuring that the final output voltage to the load is stable and accurate.

[0003] In related technologies, the secondary feedback circuits used in switching power supplies at present typically employ a simple Zener diode in conjunction with an optocoupler. Since the Zener diode is only a nonlinear device, it cannot provide active amplification and compensation functions. Utility Model Content

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a secondary feedback circuit that can replace the Zener diode and actively provide amplification and compensation functions.

[0005] The objective of this utility model is achieved through the following technical solution: The first aspect of this application provides a secondary feedback circuit, comprising: a sampling unit including a voltage regulator U6 and a capacitor C5, wherein the voltage regulator U6 is electrically connected to the capacitor C5; a signal transmission unit, wherein the voltage regulator U6 is electrically connected to the signal transmission unit; and a stabilization unit, which is electrically connected to the signal transmission unit.

[0006] The signal transmission unit includes an optocoupler U2, which is electrically connected to the voltage regulator U6.

[0007] The stabilizing unit includes resistor R3 and resistor R11. The first end of resistor R3 is electrically connected to the optocoupler U2, and resistor R11 is electrically connected to the optocoupler U2.

[0008] The sampling unit further includes resistors R4 and R5. The first end of resistor R4 is electrically connected to the second end of resistor R3, the second end of resistor R4 is electrically connected to the first end of resistor R5, and the second end of resistor R5 is grounded.

[0009] It also includes capacitor C4, the first end of which is electrically connected to the optocoupler U2, and the second end of which is grounded.

[0010] The resistor R4 has the same resistance value as the resistor R5.

[0011] The resistance of resistor R4 is 2.7 kΩ.

[0012] The stabilizing unit also includes a resistor R12, the first end of which is electrically connected to the voltage regulator U6, and the second end of which is electrically connected to the optocoupler U2.

[0013] Compared with the prior art, the present invention has at least the following advantages: This application employs a Zener diode U6 and a capacitor C5. The Zener diode U6 is used as an error amplifier and voltage reference. By connecting the capacitor C5 between its cathode and reference electrode, a compensation network is formed, which can accurately adjust the bandwidth and phase margin of the feedback loop. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of this utility model, the accompanying drawings used in the embodiments will be briefly described below.

[0015] Figure 1 This is a functional block diagram of the secondary feedback circuit in one embodiment of the present invention; Figure 2 This is a circuit diagram of the secondary feedback circuit in one embodiment of the present invention. Detailed Implementation

[0016] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While embodiments of this application are shown in the drawings, it should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0017] It should be understood that although the terms "first," "second," "third," etc., may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0018] Unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0019] The secondary feedback circuit is a crucial component of a switching power supply. Its main function is to continuously monitor minute changes in the output voltage and quickly correct them through a negative feedback mechanism, thereby ensuring a stable and accurate voltage output to the load. Currently, secondary feedback circuits used in switching power supplies typically employ simple Zener diodes in conjunction with optocouplers. However, since a Zener diode is merely a nonlinear device, it cannot provide active amplification and compensation functions.

[0020] To address the aforementioned issues, embodiments of this application provide a secondary feedback circuit that can replace the Zener diode and actively provide amplification and compensation functions.

[0021] The technical solutions of the embodiments of this application are described in detail below with reference to the accompanying drawings.

[0022] See Figure 1 and Figure 2 A secondary feedback circuit includes: a sampling unit 100, a signal transmission unit 200, and a stabilization unit 300. The sampling unit 100 includes a voltage regulator U6 and a capacitor C5. The voltage regulator U6 is electrically connected to the capacitor C5. The voltage regulator U6 is electrically connected to the signal transmission unit 200. The stabilization unit 300 is electrically connected to the signal transmission unit 200.

[0023] It should be noted that the sampling unit 100 is used to set the reference voltage of the voltage regulator U6 to determine the output voltage, and the signal transmission unit 200 is used to achieve electrical isolation and signal transmission between the primary and secondary sides. Furthermore, the voltage regulator U6 is a TL431, a programmable precision parallel voltage regulator with a typical reference voltage of 2.495V, high accuracy, and very small temperature drift. This means that the output voltage is very stable throughout the entire operating temperature range. Conventional Zener diodes, on the other hand, have lower accuracy and are greatly affected by temperature. The regulated voltage will also change under different currents, causing the output voltage to drift with temperature and load variations. Secondly, the voltage regulator U6 itself is an error amplifier. A compensation network can be formed by connecting capacitor C5 between its cathode and reference electrode. This can precisely adjust the bandwidth and phase margin of the feedback loop, making the system both fast-responding and stable without oscillation. Conventional Zener diodes, however, are merely nonlinear devices and cannot provide active amplification and compensation functions. The response characteristics of the feedback loop formed by them are fixed and usually poor. It is difficult to optimize and is prone to large overshoot / undershoot, or even instability, under sudden load changes. Furthermore, the open-loop gain of the operational amplifier inside the U6 regulator is very high, and the gain of the entire feedback loop is also large. High gain means that the system can produce a strong correction effect for even small output voltage changes. This results in excellent load regulation and line regulation of the power supply.

[0024] See Figure 2 In one embodiment, the signal transmission unit 200 includes an optocoupler U2, which is electrically connected to a voltage regulator U6.

[0025] It should be noted that the optocoupler U2 includes U2A and U2B, which are used to achieve electrical isolation and signal transmission between the primary and secondary sides.

[0026] See Figure 2 In one embodiment, the stabilizing unit 300 includes resistor R3 and resistor R11. The first end of resistor R3 is electrically connected to optocoupler U2, and resistor R11 is electrically connected to optocoupler U2.

[0027] It is understandable that resistors R3 and R11 are current-limiting resistors used to control the current of the optocoupler.

[0028] See Figure 2 In one embodiment, the sampling unit 100 further includes resistors R4 and R5. The first end of resistor R4 is electrically connected to the second end of resistor R3, the second end of resistor R4 is electrically connected to the first end of resistor R5, and the second end of resistor R5 is grounded.

[0029] It can be understood that resistors R4 and R5 are sampling resistors.

[0030] See Figure 2 In one embodiment, a capacitor C4 is also included. The first end of the capacitor C4 is electrically connected to the optocoupler U2, and the second end of the capacitor C4 is grounded.

[0031] It is understandable that capacitor C4 is a filter capacitor.

[0032] See Figure 2 In one embodiment, resistors R4 and R5 have the same resistance value. Specifically, resistor R4 has a resistance of 2.7 kΩ.

[0033] See Figure 2 In one embodiment, the stabilizing unit 300 further includes a resistor R12, the first end of which is electrically connected to the voltage regulator U6, and the second end of which is electrically connected to the optocoupler U2.

[0034] It should be noted that resistor R12 is used to ensure the stability of the bias value of voltage regulator U6.

[0035] The circuit principle of this application is explained below: The external output voltage of 5V is divided by resistors R4 (2.7kΩ) and R5 (2.7kΩ) and fed to the reference terminal (Ref) of voltage regulator U6. The reference voltage of voltage regulator U6 is 2.5V. When the voltage after voltage division equals 2.5V, voltage regulator U6 enters linear regulation mode. The output voltage calculation formula is: Vout = 2.5V × (1 + R4 * R5) = 2.5 × (1 + 2.7k * 2.7k) = 5V. Furthermore, when the output voltage increases, the voltage at the Ref terminal of voltage regulator U6 increases, and the cathode-anode current of voltage regulator U6 increases. This current flows through the primary side of the LED of optocoupler PC817B, enhancing its luminous intensity. The phototransistor on the secondary side of the optocoupler receives more light, increasing its conductivity and reducing the equivalent resistance between the collector and emitter. Furthermore, the secondary side of the optocoupler is used to connect to the feedback pin of the control chip on the primary side. Changes in the secondary resistance of the optocoupler alter the level of the FB pin, thereby adjusting the PWM duty cycle and controlling the on-time of the switching transistor. When the output voltage is too high, the optocoupler conduction increases, the voltage at the feedback pin decreases, the PWM duty cycle decreases, causing the output voltage to drop, thus achieving closed-loop voltage regulation.

[0036] The solution of this application has been described in detail above with reference to the accompanying drawings. In the above embodiments, the descriptions of each embodiment have different focuses; for parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments. Those skilled in the art should also understand that the actions and modules involved in the specification are not necessarily essential to this application. Furthermore, it is understood that the steps in the method of this application embodiment can be adjusted, combined, and deleted according to actual needs, and the modules in the device of this application embodiment can be combined, divided, and deleted according to actual needs. The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A secondary feedback circuit, characterized in that, include: The sampling unit includes a voltage regulator U6 and a capacitor C5, wherein the voltage regulator U6 is electrically connected to the capacitor C5; The voltage regulator U6 is electrically connected to the signal transmission unit. The stabilizing unit is electrically connected to the signal transmission unit.

2. The secondary feedback circuit according to claim 1, characterized in that, The signal transmission unit includes an optocoupler U2, which is electrically connected to the voltage regulator U6.

3. The secondary feedback circuit according to claim 2, characterized in that, The stabilizing unit includes resistor R3 and resistor R11. The first end of resistor R3 is electrically connected to the optocoupler U2, and resistor R11 is electrically connected to the optocoupler U2.

4. The secondary feedback circuit according to claim 3, characterized in that, The sampling unit further includes resistors R4 and R5. The first end of resistor R4 is electrically connected to the second end of resistor R3, the second end of resistor R4 is electrically connected to the first end of resistor R5, and the second end of resistor R5 is grounded.

5. The secondary feedback circuit according to claim 2, characterized in that, It also includes capacitor C4, the first end of which is electrically connected to the optocoupler U2, and the second end of which is grounded.

6. The secondary feedback circuit according to claim 4, characterized in that, The resistor R4 has the same resistance value as the resistor R5.

7. The secondary feedback circuit according to claim 6, characterized in that, The resistance of resistor R4 is 2.7 kΩ.

8. The secondary feedback circuit according to claim 5, characterized in that, The stabilizing unit also includes a resistor R12, the first end of which is electrically connected to the voltage regulator U6, and the second end of which is electrically connected to the optocoupler U2.

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