A soft start circuit and a power supply circuit

Abstract

The present invention discloses a soft start circuit and a power supply circuit. The soft start circuit is arranged between the negative electrode of the DC bus capacitor and the negative electrode of the DC source; after the start-up, the DC source and the DC bus capacitor are connected according to the current input by the DC bus capacitor in the constant current module; one end of the soft start circuit is also connected to the filter protection module, and is used to control the conduction between the DC source and the DC bus capacitor according to the voltage output by the filter protection module at the start of the start-up. Through the present invention, when the input current of the DC bus capacitor is too large, the DC source and the DC bus capacitor can be disconnected, and the soft start can be realized only by the soft start circuit, the circuit structure is simple, no complicated control program is required, and the control efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of electronic power technology, and in particular to a soft start circuit and a power supply circuit. Background Art

[0002] In the prior art, the load is generally powered by a power supply circuit. As the requirements for integration and miniaturization of load circuits (such as LED lamps) become increasingly higher, the technical solutions of the existing power supply use a relay charging circuit or a thermistor to suppress the size of the starting current, and the circuit is complex and large in size. After the thermistor is started, there is always loss and it is sensitive to temperature. When the lamp is turned on and off at high temperatures, the current suppression effect of the thermistor is weakened and the circuit components cannot be effectively protected. Using a chip to control the switching device can achieve soft start, but it requires the chip control circuit and control program, which makes the design of the load power supply circuit complicated.

[0003] With regard to the problem that the power supply circuit required for the soft start function in the prior art is complex in design and difficult to implement, no effective solution has been proposed so far. Summary of the invention

[0004] The embodiments of the present invention provide a soft start circuit and a power supply circuit to solve the problem that the power supply circuit required for the soft start function in the prior art is complex in design and difficult to implement.

[0005] In order to solve the above technical problems, the present invention provides a soft start circuit, which is applied to a power supply circuit, wherein the power supply circuit includes a filter protection module and a constant current module, wherein the filter protection module is connected to a DC source, wherein the constant current module includes a DC bus capacitor, and wherein the soft start circuit is arranged between the negative electrode of the DC bus capacitor and the negative terminal of the DC source; and is used for controlling whether the DC source and the DC bus capacitor are connected after the start-up according to the current input by the DC bus capacitor in the constant current module;

[0006] One end of the soft start circuit is also connected to the filter protection module, and is used to control the conduction between the DC source and the DC bus capacitor according to the voltage output by the filter protection module at the start of startup.

[0007] Furthermore, the soft start circuit includes a soft start chip, which includes:

[0008] The first pin is connected to the positive terminal of the DC source through the filter capacitor and the charging resistor in the filter protection module, and is used to input a voltage signal at the start time to control the conduction between the fourth pin and the fifth pin; wherein the fourth pin is connected to the first end of the sampling resistor, and the second end of the sampling resistor is connected to the negative terminal of the DC source; the fifth pin is connected to the negative electrode of the DC bus capacitor;

[0009] The second pin and the third pin are respectively connected to the two ends of the sampling resistor, and are used to detect the voltage across the two ends of the sampling resistor; wherein the voltage across the two ends of the sampling resistor is proportional to the current input by the DC bus capacitor;

[0010] The soft start chip is used to control the on / off between the fourth pin and the fifth pin according to the voltage across the sampling resistor after the start of startup, thereby controlling whether the DC source and the DC bus capacitor are connected.

[0011] Furthermore, the soft start chip also includes:

[0012] A first switch, arranged between the fourth pin and the fifth pin, with a control end connected to the first pin; and used for controlling the on-off between the fourth pin and the fifth pin by turning on and off itself;

[0013] A detection unit, arranged between the second pin and the third pin, for detecting the voltage across the sampling resistor;

[0014] A second switch is arranged between the second pin and the first pin, and is used for turning on when the voltage across the sampling resistor is greater than a first preset value, thereby controlling the first switch to be turned off; and turning off when the voltage across the sampling resistor is less than a second preset value, thereby controlling the first switch to be turned on; wherein the second preset value is less than the first preset value.

[0015] Furthermore, the soft start chip also includes:

[0016] The first unidirectional element is connected between the second pin and the first pin and is connected in series with the second switch to control the current to flow from the first pin to the second pin.

[0017] Furthermore, the soft start chip also includes:

[0018] The voltage stabilizing unit is arranged between the gate and the source of the first switch and is used to stabilize the voltage between the gate and the source of the first switch.

[0019] Furthermore, the soft start circuit further includes: an inductor, a first end of which is connected to the negative electrode of the DC bus capacitor, and a second end of which is connected to the fifth pin;

[0020] The soft start chip further includes: a sixth pin, a first end of which is connected to the fifth pin, and a second end of which is connected between the positive terminal of the DC source and the positive electrode of the DC bus capacitor;

[0021] The inductor, the fifth pin, the sixth pin and the DC bus capacitor form a closed loop, which is used to maintain the voltage across the DC bus capacitor when the DC source stops supplying power to the DC bus capacitor.

[0022] Furthermore, the soft start chip also includes:

[0023] The second unidirectional element has an anode connected to the fifth pin and a cathode connected to the sixth pin; and is used to control the current to flow from the fifth pin to the sixth pin.

[0024] Furthermore, the soft start chip also includes:

[0025] The seventh pin is connected between the positive terminal of the DC source and the positive electrode of the DC bus capacitor, and is used to input a voltage signal to control the first switch to maintain an on state after startup is completed.

[0026] Furthermore, the soft start circuit further includes:

[0027] A voltage limiting resistor is arranged between the line extending between the positive terminal of the DC source and the positive electrode of the DC bus capacitor and the seventh pin, and is used to limit the voltage input to the seventh pin.

[0028] The present invention also provides a power supply circuit, comprising a filter protection module and a constant current module, and is characterized in that it also comprises the above-mentioned soft start circuit.

[0029] By applying the technical solution of the present invention, a soft start circuit is arranged between the negative electrode of the DC bus capacitor and the negative electrode terminal of the DC source; after the start-up, whether the DC source and the DC bus capacitor are connected is controlled according to the current input by the DC bus capacitor in the constant current module; one end of the soft start circuit is also connected to the filter protection module, which is used to control the conduction between the DC source and the DC bus capacitor according to the voltage output by the filter protection module at the start of the start-up, and can control the DC source and the DC bus capacitor to be disconnected when the current input by the DC bus capacitor is too large, and the soft start is realized only by the soft start circuit, the circuit structure is simple, no complicated control program is required, and the control efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a structural diagram of a power supply circuit and a soft start circuit according to an embodiment of the present invention;

[0031] Figure 2 is a structural diagram of a soft start circuit according to another embodiment of the present invention;

[0032] Figure 3 is a structural diagram of a soft start chip according to an embodiment of the present invention;

[0033] Figure 4 is a structural diagram of a power supply circuit according to an embodiment of the present invention;

[0034] Figure 5 1 is a comparison diagram of a starting current waveform of an existing starting circuit and a starting current waveform of a soft starting circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings, and "multiple" generally includes at least two.

[0037] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0038] It should be understood that although the terms first, second, etc. may be used to describe switches in the embodiments of the present invention, the switches should not be limited to these terms. These terms are only used to distinguish different switches. For example, without departing from the scope of the embodiments of the present invention, the first switch may also be referred to as the second switch, and similarly, the second switch may also be referred to as the first switch.

[0039] As used herein, the words "if" and "if" may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)", depending on the context.

[0040] It should also be noted that the term "includes", "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, so that a commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the commodity or device including the elements.

[0041] The optional embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0042] Example 1

[0043] This embodiment provides a soft start circuit, which is applied to a power supply circuit. Figure 1 is a structural diagram of a power supply circuit and a soft start circuit according to an embodiment of the present invention, Figure 1 2 is a structural diagram of a soft start circuit and a power supply circuit according to an embodiment of the present invention. Figure 1 As shown, the power supply circuit includes a filter protection module 10 and a constant current module 30, the filter protection module 10 includes a charging resistor R1, a filter capacitor C1 and a fuse FUSE1, the filter capacitor C1 is connected to the DC source through the charging resistor R1 and the fuse FUSE1, the constant current module 30 includes a DC bus capacitor C2, the positive electrode of the DC bus capacitor C2 is connected to the positive terminal of the DC source through the fuse FUSE1, and the negative electrode is connected to the negative terminal of the DC source, and the constant current module 30 also includes a half-bridge resonant circuit composed of a switch tube Q2, a switch tube Q3, a second inductor L2, a transformer T1, and a third capacitor C3 to achieve efficient isolation conversion. The output is composed of a rectifier circuit composed of diodes D3, D4, and a fourth capacitor C4, and the output voltage is sent to the LED light source module 40 through the positive terminal V0+. The LED light source module 40 includes two parallel LED lamp beads, and can also include a resistor R4, which is connected in parallel at both ends of the LED lamp beads.

[0044] like Figure 1 As shown, the soft start circuit 20 is arranged between the negative electrode of the DC bus capacitor C2 in the constant current module 30 and the negative terminal of the DC source; it is used to control whether the DC source and the DC bus capacitor are connected according to the current input by the DC bus capacitor in the constant current module after the start-up;

[0045] One end of the soft start circuit 20 is also connected to the filter protection module 10, and is used to control the conduction between the DC source and the DC bus capacitor according to the voltage output by the filter protection module at the start of startup.

[0046] Through the soft start circuit of this embodiment, a soft start circuit is set between the negative electrode of the DC bus capacitor and the negative terminal of the DC source; after the start of starting, whether the DC source and the DC bus capacitor are connected is controlled according to the current input by the DC bus capacitor in the constant current module; one end of the soft start circuit is also connected to the filter protection module, which is used to control the conduction between the DC source and the DC bus capacitor according to the voltage output by the filter protection module at the start of starting, and can control the DC source and the DC bus capacitor to be disconnected when the current input to the DC bus capacitor is too large, and soft starting is achieved only through the soft start circuit, the circuit structure is simple, no complicated control program is required, and the control efficiency is improved.

[0047] Example 2

[0048] This embodiment provides another soft start circuit. Figure 2 is a structural diagram of a soft start circuit according to another embodiment of the present invention. In order to specifically implement the soft start function, as shown in FIG. Figure 2 As shown, the soft start circuit includes a soft start chip IC, which includes: a first pin IN1, connected to the positive terminal of the DC source through the filter capacitor C1 and the charging resistor R1 in the filter protection module, and used to input a voltage signal at the start of startup to control the conduction between the fourth pin DC2- and the fifth pin DC1-; wherein the fourth pin DC2- is connected to the first end of the sampling resistor R2, and the second end of the sampling resistor R2 is connected to the negative terminal of the DC source; the fifth pin DC1- is connected to the negative electrode of the DC bus capacitor C2; the second pin ISEN1 and the third pin ISEN2 are respectively connected to the two ends of the sampling resistor R2, and are used to detect the voltage across the two ends of the sampling resistor R2; wherein the voltage across the two ends of the sampling resistor R2 is proportional to the current input to the DC bus capacitor; the soft start chip IC is used to control the on-off between the fourth pin DC2- and the fifth pin DC1- according to the voltage across the two ends of the sampling resistor R2 after the startup starts, thereby controlling whether the DC source and the DC bus capacitor are conductive.

[0049] Figure 3 : is a structural diagram of a soft start chip according to an embodiment of the present invention, in order to realize the on-off control between the fourth pin DC2- and the fifth pin DC1- according to the voltage across the sampling resistor R2, as shown in FIG. Figure 3 As shown, the soft start chip IC also includes:

[0050] The first switch Q1 is arranged between the fourth pin DC2- and the fifth pin DC1-, and its control end is connected to the first pin IN1; and is used to control the on-off between the fourth pin DC2- and the fifth pin DC1- by turning on and off itself;

[0051] The detection unit 201 is provided between the second pin ISEN1 and the third pin ISEN2 and is used to detect the voltage across the sampling resistor R2;

[0052] The second switch K is arranged between the second pin ISEN1 and the first pin IN1, and is used to turn on when the voltage across the sampling resistor R2 is greater than the first preset value, thereby controlling the first switch Q1 to turn off; and to turn off when the voltage across the sampling resistor R2 is less than the second preset value, thereby controlling the first switch Q1 to turn on; wherein the second preset value is less than the first preset value, and the specific values ​​of the second preset value and the first preset value need to be determined according to the maximum current allowed to pass through the DC bus capacitor and the resistance value of the sampling resistor R2. By repeatedly turning on and off the second switch K, the first switch Q1 is controlled to be repeatedly turned on and off, thereby controlling the current flowing into the DC bus capacitor, that is, controlling the starting current.

[0053] In order to prevent the current from flowing from the second pin ISEN1 to the first pin IN1, Figure 2 The soft start chip IC further includes: a first unidirectional element D1 connected between the second pin ISEN1 and the first pin IN1 and connected in series with the second switch K for controlling the current to flow from the first pin IN1 to the second pin ISEN1.

[0054] If the driving voltage of the first switch Q1 is too large, it may cause the first switch Q1 to fail. In order to avoid this situation, the above-mentioned soft start chip IC also includes: a voltage stabilizing unit ZD1, which is arranged between the gate and the source of the first switch Q, and is used to stabilize the voltage between the gate and the source of the first switch, that is, to limit the driving voltage of the first switch Q1.

[0055] According to the above, when the current of the DC bus capacitor C2 is greater than the first preset value, the DC source and the DC bus capacitor C2 are disconnected. At this time, the DC bus capacitor C2 loses the power supply. In order to maintain the voltage across the DC bus capacitor C2 when the DC source and the DC bus capacitor C2 are disconnected, as shown in FIG. Figure 3 The soft start chip IC shown also includes: a sixth pin DC+, a first end of which is connected to the fifth pin DC1-, such as Figure 2 As shown, the soft start circuit further includes: an inductor L1, a first end of which is connected to the negative electrode of the DC bus capacitor C2, a second end of which is connected to the fifth pin DC1-, and a second end of the sixth pin DC+ is connected between the positive terminal of the DC source and the positive electrode of the DC bus capacitor C2.

[0056] The inductor L1, the fifth pin DC1-, the sixth pin DC+ and the DC bus capacitor C2 form a closed loop for maintaining the voltage across the DC bus capacitor C2 when the DC source stops supplying power to the DC bus capacitor C2.

[0057] In order to prevent the current from flowing from the sixth pin DC+ to the fifth pin DC1-, Figure 3As shown, the soft start chip IC further includes: a second unidirectional element D2, whose anode is connected to the fifth pin DC1-, and whose cathode is connected to the sixth pin DC+; and is used to control the current to flow from the fifth pin DC1- to the sixth pin DC+.

[0058] Since the first pin IN1 is connected to the filter capacitor C1, after the startup is completed, the bus capacitor inputs DC power, and the filter capacitor C1 has the function of blocking DC power. Therefore, the first pin IN1 no longer inputs a voltage signal. In order to control the first switch Q1 to continue to conduct, and then control the load to conduct with the DC source, as shown in FIG. Figure 2 As shown, the above-mentioned soft start chip IC also includes:

[0059] The seventh pin IN2 is connected between the positive terminal of the DC source and the positive electrode of the DC bus capacitor C2, and is used to input a voltage signal to control the first switch to be turned on after the startup is completed.

[0060] Since the chip pin cannot input too high voltage, in order to limit the voltage input to the seventh pin IN2, such as Figure 2 As shown, the soft start circuit further includes: a voltage limiting resistor R3, which is arranged between the line extending between the positive terminal of the DC source and the positive electrode of the DC bus capacitor C2 and the seventh pin IN2, and is used to limit the voltage input to the seventh pin IN2. In the above chip IC, a reserved pin NC may also be included.

[0061] Example 3

[0062] This embodiment provides a power supply circuit. Figure 4 is a structural diagram of a power supply circuit according to an embodiment of the present invention, Figure 4 As shown, the power supply circuit includes a filter protection module 10 and a constant current module 30, the constant current module 30 is connected to the LED light source module 40, and also includes a soft start circuit 20 for controlling the starting current through the soft start circuit 30 to avoid excessive starting current.

[0063] Example 4

[0064] This embodiment provides another soft start circuit, which is applied to a power supply circuit, as mentioned above. Figure 1 As shown in , the power supply circuit includes: a filter protection module 10, the soft start circuit 20, a DC / DC constant current module 30 (and the constant current module 30 in the above embodiment), and an LED light source module 40. The DC output current passes through the DC bus and is input to the filter protection module 10. The soft start circuit 20 controls the high-frequency opening and closing of the built-in switch tube by collecting voltage and current signals, charges the DC bus capacitor C2, and then passes through the rear-stage DC / DC constant current module 30 to output a driving current to control the LED light source module to light up, completing the startup process.

[0065] The filter protection module 10 is composed of a charging resistor R1, a filter capacitor C1, and a fuse FUSE1, and is used to cut off the fault when a serious short circuit fault occurs in the subsequent circuit to avoid affecting the power supply of the DC source bus.

[0066] The DC / DC constant current module 30 includes a half-bridge resonant circuit composed of a switch tube Q2, a switch tube Q3, an inductor L2, a transformer T1, and a third capacitor C3 to achieve efficient isolation conversion. The output is composed of a rectifier circuit composed of a diode D3, a diode D4, and a fourth capacitor C4, and the output voltage is sent to the LED light source module 40 through the positive terminal V0+. The LED light source module 40 includes two parallel LED lamp beads, and may also include a resistor R4, which is connected in parallel at both ends of the LED lamp beads.

[0067] The soft start circuit includes a soft start chip IC, as mentioned above Figure 3 As described in the embodiment, the first to seventh pins, the detection unit 201, the second switch K (i.e., the second switch K in the above embodiment), the diode D1 (i.e., the first unidirectional conductive element D1 in the above embodiment), the diode D2 (i.e., the second unidirectional conductive element D2 in the above embodiment), the voltage regulator ZD1 (and the voltage regulator unit ZD1 in the above embodiment), and the switch tube Q1 (i.e., the first switch Q1 in the above embodiment).

[0068] The working principle of the soft start chip IC is:

[0069] The first pin IN1 of the soft start chip IC is connected to the filter capacitor C1 and the charging resistor R1 externally. When the DC source is turned on, the DC source charges C1 through the charging resistor R1, generates a rising edge voltage signal, controls the switch tube Q1 to be turned on, and the voltage regulator ZD1 limits the driving voltage value of the switch tube Q1 to protect the switch tube Q1; when the driving voltage value Vgs reaches the turn-on threshold of the switch tube Q1, the switch tube Q1 is turned on, and the DC bus capacitor C2, the inductor L1, and the sampling resistor R2 form a loop, and the DC source charges the DC bus capacitor C2. Since the capacitor voltage cannot change suddenly, the charging current of the DC bus capacitor C2 increases at the moment of power-on. The current peak can be suppressed by using the principle that the current of the inductor L1 cannot change suddenly. The current passes through the fifth pin DC1- of the soft start chip IC, passes through the switch tube Q1, is output from the fourth pin DC2-, passes through the current sampling resistor R2, and returns to the negative pole of the DC source.

[0070] A voltage signal (U=R*I) is generated across the sampling resistor R2. The second pin ISEN1 and the third pin ISEN2 of the soft start chip IC collect the voltage signal U across the sampling resistor R2 and transmit it to the detection module 201. When the voltage U is higher than the first reference value Von_ref (i.e., the first preset value in the above embodiment), the second pin ISEN1 and the negative electrode of the DC source are connected, and the drive voltage Vgs of the switch tube Q1 is pulled down and then turned off. After the switch tube Q1 is turned off, the DC bus C2 continues to flow through the inductor L1 and the diode D1 to maintain the voltage across the two ends. When the voltage U across the sampling resistor R2 is less than the second reference value Voff ref (i.e., the second preset value in the above embodiment), the detection module 201 controls the second pin ISEN1 to be disconnected from the negative electrode of the DC source. At this time, the DC source charges C1 through the charging resistor R1, generates a rising edge voltage signal, causes the switch tube drive voltage Vgs to rise, and then controls the switch tube Q1, and so on.

[0071] By calculating and changing the resistance value of the sampling resistor R2, the soft start peak current can be changed to meet the needs of different products, and it can also be used as an overcurrent protection function for the circuit input.

[0072] As the voltage across the DC bus capacitor C2 gradually approaches the bus voltage value, each charging current value will gradually decrease. When the voltage U across the sampling resistor R2 is always less than the Voff ref value, the detection module 201 controls the second pin ISEN1 to remain disconnected from the negative electrode of the DC source, and keeps the drive voltage Vgs at a high level through the seventh pin IN2, controls the switch tube Q1 to be turned on, and completes the soft start process.

[0073] Figure 5 : is a comparison diagram of the starting current waveform of the existing starting circuit and the starting current waveform of the soft starting circuit according to the embodiment of the present invention, wherein: Figure 5 (a) is the starting current waveform of the existing starting circuit. Figure 5 (b) is the starting current waveform of the soft start circuit according to the embodiment of the present invention, and to is the starting time. By comparison, it can be seen that, compared with the prior art, after adopting the soft start circuit of the present invention, the peak current Imax value is greatly reduced, and the maximum current overshoot value can be calculated and set.

[0074] After the soft start is completed, the DC bus capacitor C2 reaches the bus voltage setting value, the subsequent DC / DC constant current module starts, and drives the load to work. In this embodiment, the load is an LED light source module. After the soft start is completed, the LED light source module is lit.

[0075] The circuit embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place, or may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0076] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A soft start circuit, applied to a power supply circuit, the power supply circuit comprising a filter protection module and a constant current module, the filter protection module is connected to a DC source, the constant current module comprises a DC bus capacitor, characterized in that: The soft start circuit is arranged between the negative electrode of the DC bus capacitor and the negative electrode terminal of the DC source; and is used to control whether the DC source and the DC bus capacitor are connected according to the current input by the DC bus capacitor in the constant current module after the start of the startup; One end of the soft start circuit is also connected to the filter protection module, and is used to control the conduction between the DC source and the DC bus capacitor according to the voltage output by the filter protection module at the start of startup.

2. The soft start circuit according to claim 1, characterized in that: The soft start circuit includes a soft start chip, including: The first pin is connected to the positive terminal of the DC source through the filter capacitor and the charging resistor in the filter protection module, and is used to input a voltage signal at the start time to control the conduction between the fourth pin and the fifth pin; wherein the fourth pin is connected to the first end of the sampling resistor, and the second end of the sampling resistor is connected to the negative terminal of the DC source; the fifth pin is connected to the negative electrode of the DC bus capacitor; The second pin and the third pin are respectively connected to the two ends of the sampling resistor, and are used to detect the voltage across the two ends of the sampling resistor; wherein the voltage across the two ends of the sampling resistor is proportional to the current input by the DC bus capacitor; The soft start chip is used to control the on / off between the fourth pin and the fifth pin according to the voltage across the sampling resistor after the start of startup, thereby controlling whether the DC source and the DC bus capacitor are connected.

3. The soft start circuit according to claim 2, characterized in that: The soft start chip also includes: A first switch, arranged between the fourth pin and the fifth pin, with a control end connected to the first pin; and used for controlling the on-off between the fourth pin and the fifth pin by turning on and off itself; A detection unit, arranged between the second pin and the third pin, for detecting the voltage across the sampling resistor; A second switch is arranged between the second pin and the first pin, and is used for turning on when the voltage across the sampling resistor is greater than a first preset value, thereby controlling the first switch to be turned off; and turning off when the voltage across the sampling resistor is less than a second preset value, thereby controlling the first switch to be turned on; wherein the second preset value is less than the first preset value.

4. The soft start circuit according to claim 3, characterized in that: The soft start chip also includes: The first unidirectional element is connected between the second pin and the first pin and is connected in series with the second switch to control the current to flow from the first pin to the second pin.

5. The soft start circuit according to claim 3, characterized in that: The soft start chip also includes: The voltage stabilizing unit is arranged between the gate and the source of the first switch and is used to stabilize the voltage between the gate and the source of the first switch.

6. The soft start circuit according to claim 2, characterized in that: The soft start circuit further includes: an inductor, a first end of which is connected to the negative electrode of the DC bus capacitor, and a second end of which is connected to the fifth pin; The soft start chip further includes: a sixth pin, a first end of which is connected to the fifth pin, and a second end of which is connected between the positive terminal of the DC source and the positive electrode of the DC bus capacitor; The inductor, the fifth pin, the sixth pin and the DC bus capacitor form a closed loop, which is used to maintain the voltage across the DC bus capacitor when the DC source stops supplying power to the DC bus capacitor.

7. The soft start circuit according to claim 6, characterized in that: The soft start chip also includes: The second unidirectional element has an anode connected to the fifth pin and a cathode connected to the sixth pin; and is used to control the current to flow from the fifth pin to the sixth pin.

8. The soft start circuit according to claim 3, characterized in that: The soft start chip also includes: The seventh pin is connected between the positive terminal of the DC source and the positive electrode of the DC bus capacitor, and is used to input a voltage signal to control the first switch to maintain an on state after startup is completed.

9. The soft start circuit according to claim 8, characterized in that: The soft start circuit also includes: A voltage limiting resistor is arranged between the line extending between the positive terminal of the DC source and the positive electrode of the DC bus capacitor and the seventh pin, and is used to limit the voltage input to the seventh pin.

10. A power supply circuit, comprising a filter protection module and a constant current module, characterized in that: It also includes the soft start circuit according to any one of claims 1 to 9.

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