Linear voltage stabilizer and switching power supply

Abstract

The application discloses a linear voltage stabilizing circuit and a switching power supply. The linear voltage stabilizing circuit comprises a power switch tube and a driving control circuit thereof, an inductor connected in series in a voltage output loop, a sampling resistor for sampling loop current in the voltage output loop, and a voltage regulating circuit for regulating the gate voltage of the power switch tube according to the loop current sampled by the sampling resistor to control the switching state of the power switch tube when surge current occurs in the circuit. When surge current occurs in the circuit, the inductor is used to reduce the change rate of the loop current in the voltage output loop. The application can prolong the energy release time of the surge current in the loop, greatly reduce the surge energy in the loop per unit time, reduce the loop impedance of the circuit, effectively meet the high surge protection requirement of the switching power supply, and improve the output load capacity of the power supply under low voltage input.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a linear voltage stabilizing circuit and a switching power supply. BACKGROUND

[0002] In the electric power meter industry, in the early power supply system of electric meter, the power frequency transformer is usually used for power supply. With the development of technology, the function of electric meter is gradually increased, and the power supply of electric meter system has higher demand. The power frequency transformer is difficult to meet the requirements in terms of volume and efficiency, and then the design scheme of replacing the power frequency transformer with the switching power supply is gradually adopted. However, the application of switching power supply brings new problems. According to the requirements of the national power grid, the ground fault of electric meter needs to meet 1.9 times of Un (the rated voltage of electric meter), that is, the highest can reach 3*420Vac. In order to leave some margin, the electric meter should not be damaged under the harsh input condition of 3*440Vac. The peak voltage of the converted direct current voltage is nearly 1100V. At present, the ordinary switching power supply is difficult to meet such high voltage input, and at the same time needs to meet the surge protection requirement of differential mode 6.6KV.

[0003] However, although the existing clamping circuit can solve the problem of high voltage input, it needs to increase the high-impedance current limiting resistor in the whole circuit to absorb the surge energy and achieve high surge protection. However, such a large resistor in series in the circuit will consume a lot of energy, affecting the working efficiency of the circuit, especially when the electric meter has requirements on standby power consumption. The influence is particularly obvious. And this large resistor will produce obvious voltage drop on the resistor in wide range application, especially in low voltage 36Vac input, which seriously affects the output load capacity of the power supply.

[0004] Therefore, it is necessary to provide an improved technical scheme to overcome the above technical problems in the prior art. SUMMARY

[0005] In order to solve the above technical problems, the present application provides a linear voltage stabilizing circuit and a switching power supply, which can prolong the energy release time of the surge current in the circuit, greatly reduce the surge energy in the circuit per unit time, reduce the circuit impedance, effectively meet the high surge protection requirement of the switching power supply, improve the working efficiency of the circuit and the output load capacity of the power supply under low voltage input, and at the same time, under the condition of super high voltage input, the clamping protection of the later stage circuit can also be realized, the stress of the later stage device is reduced, thereby the cost is reduced.

[0006] According to a first aspect of the present disclosure, a linear voltage stabilizing circuit is provided, comprising: a power switch tube and a driving control circuit thereof, the power switch tube being connected in series in a voltage output loop of the linear voltage stabilizing circuit, and the driving control circuit adjusting the power switch tube to output a preset output voltage, wherein the linear voltage stabilizing circuit further comprises:

[0007] an inductor connected in series in the voltage output loop and connected to a drain of the power switch tube;

[0008] a sampling resistor connected in series in the voltage output loop and connected to a source of the power switch tube to sample a loop current in the voltage output loop;

[0009] a voltage regulating circuit configured to regulate a gate voltage of the power switch tube according to the loop current sampled by the sampling resistor to control a switching state of the power switch tube when a surge current occurs in the circuit,

[0010] wherein the inductor is configured to reduce a rate of change of the loop current in the voltage output loop when the surge current occurs in the circuit.

[0011] Further, the voltage regulating circuit regulating the gate voltage of the power switch tube to control the switching state of the power switch tube at least comprises pulling down the gate voltage of the power switch tube to make the power switch tube work in a switching mode.

[0012] Optionally, the voltage regulating circuit comprises:

[0013] a bipolar transistor having a base connected to the sampling resistor through a seventh resistor and a collector connected to the gate of the power switch tube to regulate the gate voltage of the power switch tube according to the loop current.

[0014] Optionally, the voltage regulating circuit further comprises:

[0015] a feedback unit connected between the inductor and the base of the bipolar transistor to perform current positive feedback on the base of the bipolar transistor based on the inductor.

[0016] Optionally, the feedback unit comprises: an eighth resistor and a fourth capacitor,

[0017] a first end of the eighth resistor being connected to the drain of the power switch tube, a second end of the eighth resistor being connected to a first end of the fourth capacitor, and a second end of the fourth capacitor being connected to the base of the bipolar transistor.

[0018] Optionally, the linear voltage stabilizing circuit further comprises:

[0019] a fourth diode, an anode of which is connected to an emitter of the bipolar transistor, and a cathode of which is connected to a base of the bipolar transistor.

[0020] Optionally, the linear voltage stabilizing circuit further comprises:

[0021] a voltage-sensitive resistor connected between a drain and a source of the power switch tube, for discharging at least part of surge energy when a drain voltage of the power switch tube is higher than a voltage-sensitive voltage of the voltage-sensitive resistor.

[0022] Optionally, the sampling resistor is connected in parallel with a first clamping unit at two ends of the sampling resistor, for clamping a voltage at the two ends of the sampling resistor.

[0023] Optionally, the linear voltage stabilizing circuit further comprises:

[0024] a second clamping unit connected between a gate of the power switch tube and an emitter of the bipolar transistor, for clamping a gate voltage of the power switch tube.

[0025] Optionally, the linear voltage stabilizing circuit further comprises:

[0026] a power supply unit receiving an input voltage of the linear voltage stabilizing circuit, for providing a power supply voltage for the driving control circuit and the power switch tube according to the input voltage.

[0027] Optionally, the first clamping unit comprises a first diode and a second diode,

[0028] an anode of the first diode is connected to a source of the power switch tube, a cathode of the first diode is connected to an anode of the second diode, and a cathode of the second diode is connected to an emitter of the bipolar transistor.

[0029] Optionally, the second clamping unit comprises a first resistor and a first voltage-stabilizing diode,

[0030] a first end of the first resistor is connected to a gate of the power switch tube, a second end of the first resistor is connected to a cathode of the first voltage-stabilizing diode, and an anode of the first voltage-stabilizing diode is connected to an emitter of the bipolar transistor.

[0031] Optionally, the power supply unit comprises:

[0032] a second voltage-stabilizing diode, an anode of which receives the input voltage, and a cathode of which is connected to a first node through a second resistor;

[0033] a first capacitor connected between the first node and a reference ground; and

[0034] a third resistor and a second capacitor connected in series between the cathode of the second voltage stabilizing diode and a reference ground,

[0035] wherein the power supply unit outputs the power supply voltage at the first node.

[0036] Optionally, the power supply unit comprises:

[0037] a fourth resistor having a first end receiving the input voltage;

[0038] a fifth resistor having a first end connected to a second end of the fourth resistor;

[0039] a third diode having an anode connected to a second end of the fifth resistor and a cathode connected to a second node;

[0040] a third capacitor connected in parallel to the fourth resistor,

[0041] wherein the power supply unit outputs the power supply voltage at the second node.

[0042] Optionally, the linear voltage stabilizing circuit further comprises:

[0043] a sixth resistor connected between a gate of the power switch tube and a drain of the power switch tube;

[0044] a seventh resistor connected between a source of the power switch tube and a base of the bipolar transistor.

[0045] Optionally, the power switch tube and the driving control circuit are integrated in the same chip.

[0046] Optionally, the chip comprises:

[0047] a first pin receiving the power supply voltage;

[0048] a second pin connected to a collector of the bipolar transistor;

[0049] a third pin connected to the inductor;

[0050] a fourth pin connected to the sampling resistor;

[0051] a fifth pin connected to the fourth pin.

[0052] Optionally, the chip comprises:

[0053] a sixth pin receiving the power supply voltage and connected to a collector of the bipolar transistor;

[0054] a seventh pin connected to the inductor;

[0055] The eighth pin is connected with the sampling resistor.

[0056] The ninth pin.

[0057] Optionally, the linear voltage stabilizing circuit further comprises:

[0058] The sixth resistor is connected between the second pin and the third pin.

[0059] Optionally, the linear voltage stabilizing circuit further comprises:

[0060] The ninth resistor is connected between the ninth pin and the reference ground.

[0061] Optionally, the resistance of the sampling resistor is less than a preset value.

[0062] Optionally, the inductor is connected between the output of the linear voltage stabilizing circuit and the drain of the power switch tube, or the inductor is connected between the input of the linear voltage stabilizing circuit and the drain of the power switch tube.

[0063] According to the second aspect of the present disclosure, a switching power supply is provided, comprising: a three-phase conversion circuit, receiving a grid voltage and outputting a first voltage signal;

[0064] The linear voltage stabilizing circuit as described above is connected with the three-phase conversion circuit, receives the first voltage signal, and outputs a preset second voltage signal.

[0065] The present disclosure has at least the following beneficial effects:

[0066] The linear voltage stabilizing circuit disclosed in the present disclosure has the following beneficial effects: by connecting the inductor in series in the output loop of the linear voltage stabilizing circuit, the change rate of the current in the loop can be reduced when the inrush current occurs, so that the inrush current increases slowly; by setting the sampling resistor and the voltage regulating circuit, the current in the loop is sampled by the sampling resistor, and the voltage regulating circuit is triggered to control the gate voltage of the power switch tube to control the switching state of the power switch tube, for example, the gate voltage of the power switch tube is pulled down to control the power switch tube to work in the switching mode, thereby prolonging the energy release time of the inrush current in the loop during the continuous on-off process of the power switch tube, greatly reducing the inrush energy in the loop per unit time, reducing the current in the output loop, so that the linear voltage stabilizing circuit also has the inrush current protection function. Moreover, the impedance of the inductor is relatively low, which helps to improve the working efficiency of the circuit and the output load capacity of the switching power supply under low voltage input.

[0067] The switching power supply disclosed in the present application can reduce the resistance value requirement of the surge protection resistor needed in the front-stage circuit (such as a three-phase conversion circuit) of the linear voltage stabilizing circuit in the switching power supply based on the surge protection capability of the linear voltage stabilizing circuit, greatly reduces the loop impedance in the switching power supply while enabling the switching power supply to meet the specified surge protection requirement.

[0068] It should be noted that the foregoing general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 A structure schematic diagram of an existing three-phase conversion circuit is shown;

[0070] Figure 2 A structure schematic diagram of an existing linear voltage stabilizing circuit is shown;

[0071] Figure 3 A structure schematic diagram of a three-phase conversion circuit provided according to an embodiment of the present application is shown;

[0072] Figure 4 A structure schematic diagram of a linear voltage stabilizing circuit provided according to a first embodiment of the present application is shown;

[0073] Figure 5 A structure schematic diagram of a linear voltage stabilizing circuit provided according to a second embodiment of the present application is shown. DETAILED DESCRIPTION

[0074] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be realized in different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0075] In a switching power supply, such as a power meter switching power supply, there is usually a three-phase conversion circuit and a linear voltage stabilizing circuit. The three-phase conversion circuit is the front-stage circuit of the linear voltage stabilizing circuit, and the linear voltage stabilizing circuit is the back-stage circuit of the three-phase conversion circuit. The three-phase conversion circuit is used to receive a grid voltage and output a first voltage signal after conversion. The linear voltage stabilizing circuit is connected to the output end of the three-phase conversion circuit, receives the first voltage signal, and outputs a preset second voltage signal according to the first voltage signal.

[0076] As Figure 1The diagram shows a schematic of a conventional three-phase converter circuit. This three-phase converter circuit includes a three-phase rectifier circuit 1, a filter capacitor CX1, and a common-mode inductor LF1. The three-phase rectifier circuit 1 is connected to the first-phase input terminal L1, the second-phase input terminal L2, the third-phase input terminal L3, and the neutral input terminal N to perform three-phase rectification of the grid voltage input from these terminals. The rectified voltage is then filtered by the filter capacitor CX1 and the common-mode inductor LF1, and converted into a first voltage signal Vdc, which is output from the output terminal of the three-phase converter circuit.

[0077] Figure 1 In the three-phase rectifier circuit 1, each of the first phase input terminals L1, the second phase input terminal L2, and the third phase input terminal L3 is connected in series with wire-wound resistors RX1, RX2, and RX3, respectively. A wire-wound resistor RX4 is also connected in series between the common-mode inductor LF1 and one of the output terminals of the three-phase converter circuit. These multiple wire-wound resistors are used to limit the current in the three-phase converter circuit. At the same time, each of the first phase input terminals L1, the second phase input terminal L2, and the third phase input terminal L3 is connected to the neutral input terminal N with varistors RV1, RV2, and RV3, respectively.

[0078] like Figure 2 The diagram shows a schematic of a conventional linear voltage regulator circuit. This circuit includes a clamping chip controller U1 with a power switch Q1 connected to the low end of the load output. When the input voltage Vdc of the linear regulator circuit is higher than a set voltage, the clamping chip controller U1 adjusts the drive voltage of the power switch Q1 through its internal circuitry, ensuring that Q1 is in the linear region. The higher the input voltage Vdc, the lower the control terminal voltage of the power switch Q1, and the higher the voltage between the drain and source of Q1, thus ensuring the stability of the output voltage Vout.

[0079] The above Figure 1 and Figure 2 When combined, this results in the structure of a current type of electricity meter switching power supply, in which... Figure 1 The wire-wound resistors RX1, RX2, RX3, and RX4, along with the varistors RV1, RV2, and RV3, in the shown three-phase converter circuit collectively provide surge protection for the switching power supply. However, existing switching power supplies, in order to meet ideal surge protection requirements, incorporate wire-wound resistors before and after rectification in the three-phase rectifier circuit 1. This results in a high loop impedance, affecting the switching power supply's efficiency, especially under low-voltage input conditions. Furthermore, the high loop impedance also limits the switching power supply's load-carrying capacity under low-voltage input conditions.

[0080] In view of the problems in the prior art, the three-phase conversion circuit and the linear voltage stabilizing circuit in the switching power supply are optimized and improved respectively, so that the improved switching power supply can meet the high surge protection requirement, and the impedance in the loop is reduced, and the working efficiency and the output load capacity of the power supply under low voltage input are improved.

[0081] As shown in Figure 3 , it is a structure schematic diagram of the three-phase conversion circuit in the switching power supply provided by the embodiment of the present application. Compared with the three-phase conversion circuit shown in Figure 1 , the first phase input end L1, the second phase input end L2 and the third phase input end L3 in the three-phase conversion circuit 10 in the embodiment are respectively connected in series with the line winding resistors RX1, RX2 and RX3 between the three-phase rectifier circuit 1, which are replaced by the first line winding resistor RX11, the second line winding resistor RX21 and the third line winding resistor RX31, wherein the impedance of the first line winding resistor RX11, the second line winding resistor RX21 and the third line winding resistor RX31 is smaller than that of the line winding resistors RX1, RX2 and RX3. At the same time, the line winding resistor RX4 connected in series between the common mode inductor LF1 and one of the output ends of the three-phase conversion circuit is removed in the embodiment of the present application, so that the optimized three-phase conversion circuit of the present application greatly reduces the loop impedance and improves the output load capacity of the power supply under low voltage input.

[0082] For example, if the resistance values of the line winding resistors RX1, RX2 and RX3 in Figure 1 are all 22 ohms, and the resistance value of the line winding resistor RX4 in Figure 1 is 47 ohms, the resistance values of the first line winding resistor RX11, the second line winding resistor RX21 and the third line winding resistor RX31 in the optimized three-phase conversion circuit of the present application can be reduced to 10 ohms, that is to say, the loop impedance in the optimized three-phase conversion circuit of the present application can be changed from the original 91 ohms to 20 ohms, which is less than 1 / 4 of the original.

[0083] At the same time, the present application also provides a linear voltage stabilizing circuit in the switching power supply which is used in conjunction with Figure 3 . The linear voltage stabilizing circuit has an inductor connected in series in the output loop, so that when the circuit has a surge current, the change rate of the current in the loop can be reduced, so that the surge current increases slowly. At the same time, a corresponding sampling resistor and a voltage regulating circuit are also provided, the current in the loop is sampled by the sampling resistor and the voltage regulating circuit is triggered to control the gate voltage of the power switch tube to control the working state of the power switch tube (at least including pulling down the gate voltage of the power switch tube to make the power switch tube work in the switching mode), so as to reduce the current in the output loop, so that the linear voltage stabilizing circuit can also have a surge current protection function, which makes up for Figure 3The application discloses a switching power supply with a power switch tube and a drive control circuit, the power switch tube is connected in series in a voltage output loop of the switching power supply, and the drive control circuit is connected with the power switch tube and outputs a preset output voltage Vout by adjusting a switching state of the power switch tube.

[0084] Reference Figure 4 And Figure 5 The linear voltage stabilizing circuit 20 comprises a power switch tube Q1 and a drive control circuit thereof, the power switch tube Q1 is connected in series in a voltage output loop of the linear voltage stabilizing circuit 20, and the drive control circuit is connected with the power switch tube Q1 and outputs a preset output voltage Vout by adjusting a switching state of the power switch tube Q1. In the application, the linear voltage stabilizing circuit comprises a first input end, a second input end, a first output end and a second output end, the first input end and the second input end are used to receive a first voltage signal Vdc, the linear voltage stabilizing circuit receives an input voltage (for example, a first voltage signal output by a three-phase conversion circuit) Vdc from the first input end and the second input end, and outputs a preset second voltage signal, that is, a preset output voltage Vout from the first output end and the second output end. For example, the first input end of the linear voltage stabilizing circuit 10 is a high-voltage input end, the second input end of the linear voltage stabilizing circuit 20 is a low-voltage input end, the first output end of the linear voltage stabilizing circuit 10 is a high-voltage output end, the second output end of the linear voltage stabilizing circuit 10 is a low-voltage output end, and the low-voltage input end and the low-voltage output end of the linear voltage stabilizing circuit 20 are connected with a reference ground. For example, the power switch tube Q1 is an NMOS transistor.

[0085] In the application, two embodiments are adopted to describe the linear voltage stabilizing circuit 20 in detail. In the first embodiment of the application, as shown in Figure 4 , an implementation scheme of the linear voltage stabilizing circuit 20 of the application is shown, in which the power switch tube Q1 is connected in series between the low-voltage input end and the low-voltage output end of the linear voltage stabilizing circuit 20. In the second embodiment of the application, as shown in Figure 5 , an implementation scheme of the linear voltage stabilizing circuit 20 of the application is shown, in which the power switch tube Q1 is connected in series between the high-voltage input end and the high-voltage output end of the linear voltage stabilizing circuit 20. It can be understood that Figure 4 and Figure 5 The first embodiment and the second embodiment shown in the drawings are based on the same inventive concept, have basically the same working principle, and only have differences in specific circuit implementation.

[0086] Optionally, the power switch Q1 and the drive control circuit in the present application can be independent elements or modules in the linear voltage stabilizing circuit 20, or can be integrated in the same chip U1, which is not limited in the present application. Therefore, it can be understood that the corresponding drawings in the description (such as Figure 4 and Figure 5 ) are only based on the consideration of simplifying the drawings, and the power switch Q1 and the drive control circuit are integrated in the same chip U1 as an example, which should not be a limitation of the present application. For example, when the power switch Q1 and the drive control circuit are integrated in the same chip, in the embodiment shown in Figure 4 , the chip U1 includes at least five pins, including a first pin VCC for receiving a supply voltage; a second pin G connected to the collector of the bipolar transistor Q2 in the voltage regulating circuit 26, and also connected to the gate of the power switch Q1 through the controller 25; a third pin D connected to the inductor L1; a fourth pin S connected to the low voltage output of the circuit 20, i.e. the reference ground, through a sampling resistor Rs1; and a fifth pin GND connected to the fourth pin S. Figure 4 In the first embodiment shown, a sixth resistor R6 is connected between the second pin G and the third pin D, which is used to sample the output voltage Vout of the circuit 20 to realize the adjustment of the gate voltage of the power switch Q1 when the circuit is working normally. In the embodiment shown in Figure 5 , the chip U1 includes at least four pins, including a sixth pin G connected to the gate of the power switch Q1 through the controller 25, receiving a supply voltage, and connected to the collector of the bipolar transistor Q2 in the voltage regulating circuit 26; a seventh pin D connected to the inductor L1; an eighth pin S connected to the high voltage output of the circuit 20 through a sampling resistor Rs1; and a ninth pin Isen connected to the low voltage output of the circuit 20, i.e. the reference ground, through a ninth resistor Rs2, which is used to sample the output voltage Vout of the circuit 20 to realize the adjustment of the gate voltage of the power switch Q1 when the circuit is working normally.

[0087] Optionally, the controller 25 can be a drive control circuit or a sub-circuit of the drive control circuit, or can be a circuit module parallel to the drive control circuit in the chip U1, which can be set according to the actual integration process and circuit needs, which is not limited in the present application.

[0088] In the application, the linear voltage stabilizing circuit 20 further comprises an inductor L1, a sampling resistor Rs1 and a voltage regulating circuit 26. The inductor L1 is connected in series in the voltage output loop and connected to the drain of the power switch tube Q1. The sampling resistor Rs1 is connected in series in the voltage output loop and connected to the source of the power switch tube Q1, for sampling the loop current in the voltage output loop. The voltage regulating circuit 26 is used to regulate the gate voltage of the power switch tube Q1 according to the loop current. Based on the inductor L1, the sampling resistor Rs1 and the voltage regulating circuit 26, when a surge current occurs in the circuit, the inductor L1 is used to reduce the change rate of the loop current in the voltage output loop, and the voltage regulating circuit 26 controls the gate voltage of the power switch tube Q1 according to the loop current sampled by the sampling resistor Rs1 to control the switching state of the power switch tube Q1, at least including pulling down the gate voltage of the power switch tube Q1 to make the power switch tube Q1 work in the switching mode, thereby realizing the protection of the surge current.

[0089] In a possible embodiment of the application, the voltage regulating circuit 26 comprises a bipolar transistor Q2, the base of the bipolar transistor Q2 is connected to the sampling resistor Rs1 through a seventh resistor R7, and the collector of the bipolar transistor Q2 is connected to the gate of the power switch tube Q1. The seventh resistor R7 is used to limit the current on the base of the bipolar transistor Q2 to protect the bipolar transistor Q2.

[0090] In the application, the resistance of the sampling resistor Rs1 is less than a preset value, so as to realize the sampling effect while reducing the influence of the impedance of the sampling resistor Rs1 on the overall loop impedance as much as possible.

[0091] In Figure 4 In the first embodiment shown, the inductor L1 is connected in series between the drain of the power switch tube Q1 and the low-voltage output end of the linear voltage stabilizing circuit 20, the sampling resistor Rs1 is connected between the source of the power switch tube Q1 and the low-voltage input end of the linear voltage stabilizing circuit 20, and the base of the bipolar transistor Q2 is connected to the common connection point of the sampling resistor Rs1 and the source of the power switch tube Q1 through the seventh resistor R7, the collector of the bipolar transistor Q2 is connected to the gate of the power switch tube Q1, and the emitter of the bipolar transistor Q2 is connected to the low-voltage input end of the linear voltage stabilizing circuit 20. In Figure 5In the second embodiment shown, the inductor L1 is connected in series between the drain of the power switch Q1 and the high voltage input of the linear voltage regulator 20, the sampling resistor Rs1 is connected between the source of the power switch Q1 and the high voltage output of the linear voltage regulator 20, and the base of the bipolar transistor Q2 is connected to the common connection point of the sampling resistor Rs1 and the source of the power switch Q1 via the seventh resistor R7, the collector of the bipolar transistor Q2 is connected to the gate of the power switch Q1, and the emitter of the bipolar transistor Q2 is connected to the high voltage output of the linear voltage regulator 20.

[0092] Further, the linear voltage regulator 20 further comprises a voltage-dependent resistor RV4 connected between the drain and the source of the power switch Q1, for discharging at least part of the surge energy when the voltage at the drain of the power switch Q1 is higher than the voltage-dependent voltage of the voltage-dependent resistor RV4.

[0093] Further, the linear voltage regulator 20 further comprises a first clamping unit 21 connected in parallel across the sampling resistor Rs1, for clamping the voltage across the sampling resistor Rs1 to protect the sampling resistor Rs1 and the bipolar transistor Q2 from being damaged when a surge current occurs in the circuit. In an example, the first clamping unit 21 comprises a first diode D1 and a second diode D2, wherein the anode of the first diode D1 is connected to the source of the power switch Q1, the cathode of the first diode D1 is connected to the anode of the second diode D2, and the cathode of the second diode D2 is connected to the emitter of the bipolar transistor Q2.

[0094] Further, the linear voltage regulator 20 further comprises a second clamping unit 22 connected between the gate of the power switch Q1 and the emitter of the bipolar transistor Q2, for clamping the voltage at the gate of the power switch Q1 to protect the power switch Q1 from being damaged due to an excessively high gate voltage. In an example, the second clamping unit 22 comprises a first resistor R1 and a first zener diode ZV1, wherein the first end of the first resistor R1 is connected to the gate of the power switch Q1, the second end of the first resistor R1 is connected to the cathode of the first zener diode ZV1, and the anode of the first zener diode ZV1 is connected to the emitter of the bipolar transistor Q2.

[0095] Further, the linear voltage regulator 20 further comprises a power supply unit 23 receiving the input voltage Vdc of the linear voltage regulator 20, for providing a supply voltage for the chip U1 (including the driving control circuit and the power switch Q1) according to the input voltage Vdc.

[0096] In Figure 4In the first embodiment shown, the power supply unit 23 is connected to the first pin VCC of the chip U1 at the first node a, and outputs the power supply voltage at the first node a. In an example, the power supply unit 23 includes a second voltage stabilizing diode ZV2, a second resistor R2, a first capacitor C2, a third resistor R3, and a second capacitor C4. The anode of the second voltage stabilizing diode ZV2 receives the input voltage Vdc, and the cathode of the second voltage stabilizing diode ZV2 is connected to the first node a through the second resistor R2; the first capacitor C2 is connected between the first node a and the reference ground; and the third resistor R3 and the second capacitor C4 are connected in series between the cathode of the second voltage stabilizing diode ZV2 and the reference ground. Figure 5 In the second embodiment shown, the power supply unit 23 is connected to the sixth pin G of the chip U1 at the second node b, and outputs the power supply voltage at the second node b. In an example, the power supply unit 23 includes a fourth resistor R4, a fifth resistor R5, a third diode D3, and a third capacitor C6. The first end of the fourth resistor R4 receives the input voltage Vdc; the first end of the fifth resistor R5 is connected to the second end of the fourth resistor R4; the anode of the third diode D3 is connected to the second end of the fifth resistor R5, and the cathode of the third diode D3 is connected to the second node b; and the third capacitor C6 is connected in parallel to the fourth resistor R4.

[0097] The specific working principle of the linear voltage stabilizing circuit 20 provided by the present application is as follows:

[0098] When a large surge current appears in the loop of the circuit due to lightning strike, the surge current will generate a large voltage across the sampling resistor Rs1, but the maximum voltage across the sampling resistor Rs1 can be clamped to about 1.4V due to the presence of the first clamping unit 21, thereby protecting the sampling resistor Rs1 and the bipolar transistor Q2 from being damaged. At the same time, since the inductor L1 is connected in series in the loop of the circuit, based on the principle that the inductor current cannot change abruptly, the surge current in the loop will only increase slowly. With the increase of the current in the loop, the voltage across the sampling resistor Rs1 also gradually begins to increase, and when it increases to a certain extent, for example, when the current on the sampling resistor Rs1 satisfies I limitWhen the value of the voltage across the sampling resistor Rs1 is greater than or equal to the value of the voltage across the seventh resistor R7, the current starts to flow from the seventh resistor R7 to the base of the bipolar transistor Q2, and the current flowing to the base of the bipolar transistor Q2 also increases with the increase of the inrush current in the loop. At this time, based on the connection relationship between the bipolar transistor Q2 and the power switch tube Q1, the voltage at the gate of the power switch tube Q1 is gradually pulled down by the bipolar transistor Q2, so that the power switch tube Q1 is gradually turned off. When the power switch tube Q1 is turned off, the voltage at the common node where the drain of the power switch tube Q1 and the inductor L1 are connected starts to gradually increase, and when it increases to be higher than the voltage of the voltage-sensitive resistor RV4, the voltage-sensitive resistor RV4 starts to act, so that at least part of the surge energy of the inrush current is consumed from the path of the voltage-sensitive resistor RV4. In other words, the highest voltage between the drain and the source of the power switch tube Q1 can be clamped by the voltage-sensitive resistor RV4, thereby protecting the power switch tube Q1 from being damaged by a large voltage stress.

[0099] At the same time, after the power switch tube Q1 is turned off, the current in the loop starts to decrease, the voltage across the sampling resistor Rs1 also decreases, and the current at the base of the bipolar transistor Q2 also starts to gradually decrease, so that the degree of pull-down of the gate voltage of the power switch tube Q1 by the bipolar transistor Q2 starts to weaken, and the power switch tube Q1 starts to gradually exit the off state, and the current in the loop starts to increase, so that the power switch tube Q1 forms a switching oscillation at a certain frequency, and gradually discharges the surge energy. If the surge energy of the standard lightning strike 8 / 20us time is discharged in this way, the energy release time of the inrush current in the loop can be extended to hundreds or even thousands of microseconds, the surge energy in the loop per unit time is greatly weakened, the device stress is reduced, thereby the devices in the circuit can be protected from being damaged, and the purpose of reducing the inrush current in the loop is achieved.

[0100] On the other hand, referring to Figure 2 , the existing linear voltage regulator circuit, when a single-phase low-voltage input is input, especially when an AC input lower than 36V is input, only relies on the resistor R11 to supply power, the voltage provided to the supply end VCC of the chip U1 at the bottom of the sine wave will be lower, and it is difficult to ensure the fully on state of the power switch tube Q1. Due to the insufficient VCC power supply, the power switch tube Q1 is in a linear state at this time, and a large voltage drop will be generated between the drain and the source of the power switch tube Q1, which affects the load carrying capacity of the output stage of the circuit. Based on this, referring to Figure 4In the first embodiment of the present application, the second voltage stabilizing diode ZV2, the third resistor R3 and the second capacitor C4 are added in the power supply unit 23, so that in a sine wave cycle, at the voltage peak, the input voltage Vdc can supply power to the chip U1 through the second voltage stabilizing diode ZV2, and at the same time, the second capacitor C4 can be charged through the third resistor R3, while at the bottom of the voltage valley, the second capacitor C4 can discharge the power supply end VCC of the chip U1 through the third resistor R3. In this way, the minimum voltage of the power supply end VCC of the chip U1 is raised, so that the power switch tube Q1 can be fully turned on even at the bottom of the sine wave, thereby reducing the voltage drop between the drain and the source of the power switch tube Q1, and improving the output load capacity of the linear voltage stabilizing circuit and the switching power supply at low voltage.

[0101] Reference Figure 5 In the second embodiment of the present application, the power supply unit 23 is used not only to supply power to the chip U1, but also to provide a driving level for the power switch tube Q1, so that the power switch tube Q1 can work normally after the circuit 20 is started. At the same time, based on the above description of the working principle of the linear voltage stabilizing circuit 20, the power supply unit 23 in the second embodiment shown in the figure can reduce the number of pins of the chip U1 in this embodiment, thereby helping to reduce the manufacturing cost of the chip U1. Figure 5

[0102] Further, the linear voltage stabilizing circuit 20 provided by the present application further comprises a feedback unit 24 connected between the drain of the power switch tube Q1 and the base of the bipolar transistor Q2. When a surge current occurs in the circuit, the feedback unit 24 can perform current positive feedback on the base of the bipolar transistor Q2 based on the inductor L1. When a large surge current occurs in the circuit due to lightning strike, based on the above description of the working principle of the linear voltage stabilizing circuit 20, when the voltage at the gate of the linear power tube Q1 is gradually pulled down by the bipolar transistor Q2, due to the fact that the inductor current cannot change abruptly, the voltage at the common node of the inductor L1 and the drain of the linear power tube Q1 will continue to rise, but at this time, due to the presence of the feedback unit 24 in the circuit, the current at the base of the bipolar transistor Q2 will still slowly increase, forming a positive feedback, so that the power switch tube Q1 is turned off deeper, thereby enhancing the protection capability of the linear voltage stabilizing circuit 20 against surge current.

[0103] For example, the feedback unit 24 comprises an eighth resistor R8 and a fourth capacitor C5. The first end of the eighth resistor R8 is connected to the drain of the power switch tube Q1, the second end of the eighth resistor R8 is connected to the first end of the fourth capacitor C5, and the second end of the fourth capacitor C5 is connected to the base of the bipolar transistor Q2.

[0104] ​Further, the linear voltage stabilizing circuit 20 at this time further comprises a fourth diode D4. The anode of the fourth diode D4 is connected with the emitter of the bipolar transistor Q2, and the cathode of the fourth diode D4 is connected with the base of the bipolar transistor Q2.

[0105] Further, at the instant of starting up, the surge energy in the loop is also large, and the linear voltage stabilizing circuit works in the switching oscillation mode. At this time, the fourth capacitor C5 in the feedback unit 24 exists in the charging and discharging process. In the discharging stage of each oscillation period, the current on the fourth capacitor C5 mainly forms a discharging loop through the sampling resistor Rs1 and the seventh resistor R7, so that a small voltage difference is formed on the sampling resistor Rs1 and the seventh resistor R7, that is, a small negative voltage Vbe is generated between the base and the emitter of the bipolar transistor Q2. The present application can clamp the negative voltage below 0.7V by arranging the fourth diode D4 between the base and the emitter of the bipolar transistor Q2, so as to protect the bipolar transistor Q2 from being damaged by the negative voltage, and improve the reliability of the circuit.

[0106] In summary, on the one hand, the present application can reduce the change rate of the current in the loop when the circuit appears surge current by connecting the inductor in series in the output loop of the linear voltage stabilizing circuit, so as to slowly increase the surge current. At the same time, the sampling resistor and the voltage regulating circuit are arranged, the current in the loop is sampled by the sampling resistor, and the voltage regulating circuit is triggered to control the gate voltage of the power switch tube to control the switching state of the power switch tube, so as to prolong the energy release time of the surge current in the loop in the continuous on-off process of the power switch tube, greatly reduce the surge energy in the loop per unit time, reduce the current in the output loop, and enable the linear voltage stabilizing circuit to also have surge current protection function. Moreover, the impedance of the inductor is relatively low, which helps to improve the working efficiency of the circuit and the output load capacity of the switching power supply under low voltage input.

[0107] On the other hand, based on the surge protection capability of the linear voltage stabilizing circuit, the switching power supply disclosed by the present application can reduce the resistance value requirement of the surge protection resistor required in the front-stage circuit (such as a three-phase conversion circuit) of the linear voltage stabilizing voltage in the switching power supply, greatly reduce the loop impedance in the switching power supply, and reduce the cost while enabling the switching power supply to meet the specified surge protection requirements.

[0108] Finally, it should be noted that: obviously, the above embodiments are only examples for clearly illustrating the present application, and are not limitations on the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A linear voltage regulator circuit comprising: A power switch tube and a driving control circuit thereof, the power switch tube is connected in series in a voltage output loop of the linear voltage stabilizing circuit, the driving control circuit adjusts the power switch tube to output a preset output voltage, wherein the linear voltage stabilizing circuit further comprises: an inductor connected in series in the voltage output loop; a sampling resistor connected in series in the voltage output loop to sample a loop current in the voltage output loop; a voltage regulating circuit for regulating a gate voltage of the power switch tube according to the loop current sampled by the sampling resistor to control a switching state of the power switch tube when an inrush current occurs in the circuit, the voltage regulating circuit comprising: a bipolar transistor for regulating the gate voltage of the power switch tube according to the loop current; a feedback unit connected between the inductor and a base of the bipolar transistor for current positive feedback of the base of the bipolar transistor based on the inductor; wherein the inductor is used to reduce a change rate of the loop current in the voltage output loop when the inrush current occurs in the circuit.

2. The linear voltage regulator circuit of claim 1, wherein, The base of the bipolar transistor is connected with the sampling resistor through a seventh resistor, and the collector is connected with the gate of the power switch tube through a controller.

3. The linear voltage regulator circuit of claim 1, wherein, The feedback unit comprises an eighth resistor and a fourth capacitor, a first end of the eighth resistor is connected with a drain of the power switch tube, a second end of the eighth resistor is connected with a first end of the fourth capacitor, and a second end of the fourth capacitor is connected with the base of the bipolar transistor.

4. The linear voltage regulator circuit of claim 3, wherein, The linear voltage stabilizing circuit further comprises: a fourth diode, an anode of which is connected with an emitter of the bipolar transistor, and a cathode of which is connected with the base of the bipolar transistor.

5. The linear voltage regulator circuit of claim 1, wherein, The linear voltage stabilizing circuit further comprises: a voltage-dependent resistor connected between a drain and a source of the power switch tube to discharge at least part of the inrush energy when the drain voltage of the power switch tube is higher than a voltage-dependent voltage of the voltage-dependent resistor.

6. The linear voltage regulator circuit of claim 2, wherein, A first clamping unit is connected in parallel across the sampling resistor to clamp a voltage across the sampling resistor.

7. The linear voltage regulator circuit of claim 6, wherein, The linear voltage stabilizing circuit further comprises: a second clamping unit connected between the gate of the power switch tube and the emitter of the bipolar transistor to clamp the gate voltage of the power switch tube.

8. The linear voltage regulator circuit of claim 2, wherein, The linear voltage stabilizing circuit further comprises: a power supply unit receiving an input voltage of the linear voltage stabilizing circuit to provide a power supply voltage for the driving control circuit and the power switch tube according to the input voltage.

9. The linear voltage regulator circuit of claim 8, wherein, The power switch tube and the driving control circuit are integrated in the same chip.

10. The linear voltage regulator circuit of claim 9, wherein, The power supply unit comprises: a second voltage stabilizing diode, an anode of which receives the input voltage, and a cathode of which is connected with a first node through a second resistor; a first capacitor connected between the first node and a reference ground; and a third resistor and a second capacitor connected in series between the cathode of the second voltage stabilizing diode and the reference ground, wherein the power supply unit outputs the power supply voltage at the first node.

11. The linear voltage regulator circuit of claim 9, wherein, The power supply unit comprises: a fourth resistor, a first end of which receives the input voltage; A fifth resistor, having a first end connected to the second end of the fourth resistor; A third diode, having an anode connected to the second end of the fifth resistor and a cathode connected to the second node; A third capacitor, connected in parallel to the fourth resistor, The power supply unit outputs the power supply voltage at the second node.

12. The linear voltage regulator circuit of claim 10, wherein, The chip comprises: A first pin, receiving the power supply voltage; A second pin, connected to the collector of the bipolar transistor; A third pin, connected to the inductor; A fourth pin, connected to the sampling resistor; A fifth pin, a chip reference ground pin, connected to the fourth pin.

13. The linear voltage regulator circuit of claim 11, wherein, The chip comprises: A sixth pin, receiving the power supply voltage and connected to the collector of the bipolar transistor; A seventh pin, connected to the drain of the power switch tube and connected to the inductor; An eighth pin, connected to the sampling resistor; A ninth pin, connected to the source of the power switch tube and connected to the high potential node of the voltage output circuit.

14. The linear voltage regulator circuit of claim 12, wherein, The linear voltage regulator circuit further comprises: A sixth resistor, connected between the second pin and the third pin.

15. The linear voltage regulator circuit of claim 13, wherein, The linear voltage regulator circuit further comprises: A ninth resistor, connected between the ninth pin and the reference ground.

16. The linear voltage regulator circuit of claim 1, wherein, The resistance of the sampling resistor is less than a preset value.

17. The linear voltage regulator circuit of claim 1, wherein, The inductor is connected between the output of the linear voltage regulator circuit and the drain of the power switch tube, or the inductor is connected between the input of the linear voltage regulator circuit and the drain of the power switch tube.

18. A switched mode power supply wherein, Comprise: A three-phase conversion circuit, receiving a grid voltage and outputting a first voltage signal; The linear voltage regulator circuit according to any one of claims 1-17, connected to the three-phase conversion circuit, receiving the first voltage signal and outputting a preset second voltage signal.

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