Power supply soft start circuit suitable for new energy and power products and switching power supply

Abstract

The invention relates to the technical field of circuits, and discloses a power supply soft start circuit and a switching power supply suitable for new energy and electric power products, which are suitable for flow batteries, photovoltaic inverters, intelligent direct current metering and control equipment, light stacking controllers and the like, and control chip output and realize soft start by controlling a feedback pin of a chip. Parameters can be set by adjusting external resistors and capacitors, surge can be suppressed, output capacitor charging current is prevented from reaching a limit at the starting moment of a power supply, current stress and input voltage drop to the circuit and the rear end are reduced, and a power-on time sequence can be controlled. The method does not need to pay for the unused soft start function in the chip, only needs to replace the unit elements when damaged, is low in cost, and is suitable for low-power or cost-sensitive scenes. And high-temperature-resistant and high-pressure-resistant discrete components can be used for improving the reliability, and low-cost discrete components can also be used. The circuit is wide in applicability, can adjust the delay time, and is adaptive to each chip. The structure is simple, external devices are few, and cost is low.

Description

Technical Field

[0001] The present invention relates to the field of circuit technology, and in particular to a power soft-start circuit and a switching power supply suitable for new energy and power products. Background Art

[0002] In power supply applications for products such as flow batteries, photovoltaic inverters, intelligent DC metering and control equipment, and stacked photovoltaic controllers, the output capacitor's initial voltage is zero. Directly charging at full power can generate a significant inrush current, potentially damaging the chip or causing input power anomalies. A soft-start circuit is required to reduce stress on power supply components, avoid current surges when the power is turned on, and minimize the impact of overshoot on downstream devices caused by the instantaneous start-up of the switching power supply. Traditional soft-start circuits are often integrated within the chip, achieving soft start through digital logic or low-current charging. While this circuit has a high level of integration, it presents the following issues:

[0003] 1. Products such as flow batteries, photovoltaic inverters, intelligent DC metering and control equipment, and stacked solar controllers often need to operate in extreme environments (such as high and low temperatures, high voltage, and strong electromagnetic interference). In such cases, they may fail due to insufficient design redundancy, and the entire chip must be replaced after a failure, which is costly.

[0004] 2. When the soft-start time is short and a high transient load appears on the back end, the soft-start time may reach its limit, but the chip may not detect the predetermined voltage, resulting in repeated restarts.

[0005] 3. The internally integrated soft-start circuit increases the chip design complexity and manufacturing cost, especially in low-power or cost-sensitive scenarios, and is not as economical as an external solution.

[0006] 4. Unable to meet certain special requirements, such as quickly responding to load changes or handling extremely large surge currents, and its dynamic adjustment capability may be weaker than that of external adjustable circuits. Summary of the Invention

[0007] In view of the deficiencies and defects in the prior art, the present invention provides an external power soft start circuit and a switching power supply, which can adjust the soft start time according to actual conditions.

[0008] In a first aspect, the present invention provides a power soft start circuit, comprising a capacitor, a first diode, a second diode, a first resistor, and a second resistor.

[0009] One end of the capacitor is connected to the output voltage, and the other end is connected to one end of the first resistor; the other end of the first resistor is respectively connected to one end of the second resistor, the positive electrode of the first diode and the negative electrode of the second diode; the other end of the second resistor is connected to the ground; the negative electrode of the first diode is connected to the feedback voltage input terminal; and the positive electrode of the second diode is connected to the ground.

[0010] Preferably, the power soft start circuit is applicable to liquid flow batteries, photovoltaic inverters, intelligent DC metering and control equipment, and stacked light controllers.

[0011] Preferably, when the power supply is started, the output voltage begins to rise, the power supply soft start circuit starts to work, the capacitor starts to charge and feeds back the charging current to the feedback voltage input terminal through the first diode, raising the feedback voltage, thereby slowing down the output voltage rising speed. After the capacitor is fully charged, the soft start is completed and the first diode is cut off; after the power supply is abnormal or shuts down automatically, the capacitor is discharged through the second diode.

[0012] In a second aspect, the present invention further provides a switching power supply, comprising the power soft start circuit as described above.

[0013] Compared with the prior art, the advantages of the present invention are:

[0014] An external soft-start circuit is composed of capacitors, resistors, and diodes. The current of the chip feedback pin is controlled, thereby controlling the chip output waveform to achieve the soft-start purpose.

[0015] Key parameters such as startup time and current limit can be freely set by adjusting external resistors and capacitors. This can effectively suppress inrush current and prevent the current charging the output capacitor from reaching the current limit of the switching power supply at the moment the power supply starts. It can also reduce the current stress and input voltage drop on the switching power supply circuit itself and the downstream load, while also completing the power-on timing control.

[0016] There is no need to pay extra for the unused soft-start function inside the chip. When damaged, only a single component needs to be replaced, which costs much less than replacing the entire chip. This is more economical and more suitable for low-power or cost-sensitive application scenarios (such as consumer electronics).

[0017] The solution is flexible and controllable, and high-temperature and high-voltage resistant discrete components can be selected to improve the reliability of the system in harsh environments (such as industrial control and automotive electronics). Low-cost discrete components can also be selected to control economic costs.

[0018] It has wide applicability and can easily adjust the delay time through external devices, and is compatible with various voltage feedback chips.

[0019] The external soft start circuit has a simple structure, fewer external components and lower cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 FIG. 1 is an electrical block diagram of the first embodiment of the present invention.

[0021] Figure 2 FIG. 4 is an overall electrical schematic diagram of the first embodiment of the present invention.

[0022] Figure 3 This is an electrical schematic diagram showing the connection relationship of the soft start circuit in the first embodiment of the present invention.

[0023] Figure 4 This is an electrical schematic diagram showing the connection relationship of the soft start circuit in the second embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] A power supply soft start circuit includes a capacitor for soft start, a first diode for soft start feedback charging, a second diode for capacitor discharge, a first resistor for limiting soft start charging current, and a second resistor for capacitor discharge.

[0026] First embodiment: Figure 1 As shown, the present invention provides a switching power supply, including a voltage input circuit, a soft-start circuit, a power chip, and an output circuit. The voltage input circuit is connected to the power chip to supply power to the entire circuit. The soft-start circuit is connected to the output circuit and the power chip. Current is fed back to the power chip through the output terminal of the soft-start circuit. The power chip outputs waveforms with different duty cycles, thereby controlling the output voltage rise time and achieving the soft-start purpose.

[0027] like Figure 2As shown, VIN provides power to the entire circuit; C3 and C4 are input filter capacitors connected in parallel between VIN and GND; R3 and R8 are enable resistors, R3 is connected in series with R8 and then connected in parallel between VIN and GND, providing enable voltage to the power chip through voltage division; C7 is a decoupling capacitor, connected in parallel to both sides of R8 and closer to the power chip; D1 is a conventional power chip (pin 1 is VIN; pin 2 is EN; pin 3 is GND; pin 4 is FB; pin 5 is SW; pin 6 is BOOT); C2 is a bootstrap capacitor, connected in series with resistor R4 and then connected in parallel between pins 6 and 5 of D1; capacitor C1, first resistor R1, second resistor R2, first diode VD1, second diode VD2 forms a soft-start circuit; one end of C1 is connected to the output voltage, and the other end is connected to one end of R1; the other end of R1 is connected to one end of R2, the positive terminal of VD1, and the negative terminal of VD2 respectively; the other end of R2 is grounded; the negative terminal of VD1 is connected to the feedback voltage input terminal; the positive terminal of VD2 is grounded; R7 and R6 are output feedback resistors, R7 is connected in series with R6 and connected between VOUT and GND, and the connection between R7 and R6 is connected to pin 4 of D1, providing the feedback voltage for normal output through the voltage divider of R7 and R6; C5 and C6 are output filter capacitors, C5 and C6 are connected in parallel and then connected in series between VOUT and GND; R5 is the load; L1 is the output inductor, connected in series between pin 5 of D1 and VOUT.

[0028] When VIN is powered on, chip D1 starts working, and the output terminals R7 and R6 provide feedback. Pin 5 of D1 outputs a waveform with a large duty cycle. After the output terminal establishes a voltage, C1 is charged. The current flows through C1, R1, and VD1 to pin 4 of D1. The current at pin 4 increases and the voltage rises. At this time, the feedback is dominated by the soft-start circuit, and the output duty cycle of pin 5 of D1 decreases. The voltage rises slowly, and the rise time is linearly related to the charging time of the C1 capacitor, achieving the soft-start purpose. When the capacitor is fully charged, C1 is in a high-impedance state, and the soft-start circuit is disconnected. At this time, the feedback voltage is dominated by R7 and R6. When the circuit is powered off or the back-end is abnormal, the C1 capacitor discharges first, and the current flows to the other end of C1 in the direction of R5-VD2-R1, completing the rapid discharge of the capacitor to ensure that the circuit still has the soft-start function when it is restarted.

[0029] like Figure 3As shown in Figure 1, the soft-start circuit is connected to a feedback circuit consisting of two operational amplifiers, N1A and N2A. Vref is the output of a reference voltage source, typically 0.6V or 2.5V. Pin 8 of N1A is a high-level input, pin 4 is a low-level input, pin 2 is connected to pin 1 of N1A, pin 3 is connected to the reference voltage source, the output of pin 1 is connected to the negative terminal of operational amplifier N2A, and the positive terminal of N2A is connected to current sampling resistor R9. When the system starts, capacitor C1 is charged. The charging current flows through R1 and VD1 into pin 2 of N1A, raising the voltage at the negative terminal of N1A and reducing the output of N1A. At this point, the soft-start circuit establishes voltage feedback logic with N1A, controlling the system output voltage. The output of N1A is fed to the negative terminal of N2A, while the positive terminal of N2A is connected to R9. As the current flowing through R9 changes, the voltage on R9 changes accordingly, interacting with the output of N1A. The output signal enters the chip's PWM control circuit to control the output voltage.

[0030] Second embodiment: Figure 4 As shown, the present invention provides a switching power supply, wherein a capacitor C8, a first resistor R10, a second resistor R11, a first diode VD3, and a second diode VD4 form a soft start circuit. One end of C8 is connected to the output voltage, and the other end is connected to one end of R10; the other end of R10 is connected to one end of R11, the positive terminal of VD3, and the negative terminal of VD4; the other end of R11 is connected to ground; the negative terminal of VD3 is connected to the reference terminal of an adjustable shunt regulator TS1; the positive terminal of VD4 is connected to ground and the anode of TS1. The cathode of TS1 is connected to the negative terminal of an operational amplifier N3A. This soft start circuit is connected in series with the reference terminal of TS1 to form a differential amplifier circuit. This circuit performs an extremely precise comparison between the input voltage signal and the 2.5V reference voltage generated by a bandgap reference voltage source. Once a slight difference is detected between the two, the differential amplifier circuit reacts quickly and amplifies the voltage difference. When the device starts up, the input voltage charges C8. Current flows through C8, R10, and VD3, raising the voltage at the TS1 reference terminal and slowing the output of the differential amplifier, thus achieving soft start. Once the capacitor is fully charged, C8 enters a high-impedance state, disconnecting the soft-start circuit and enabling normal back-end operation. The regulated power supply in this embodiment utilizes a bandgap reference voltage source, which exhibits extremely low temperature drift in various operating environments. The soft-start circuit in this embodiment utilizes temperature-insensitive resistors and capacitors that are compatible with the reference voltage source, ensuring that the conditions are met under all operating conditions.

[0031] In the field of switching power supplies, especially isolated switching power supplies, the reference voltage source plays an indispensable role. The isolated feedback system composed of the reference voltage source and the optocoupler is the key to ensuring the stable output of the switching power supply. High-precision isolated power supplies all adopt the secondary feedback mode. At this time, the difficulty of soft starting increases, and the primary soft start circuit can no longer meet the conditions very stably. Therefore, the applicant adds a soft start circuit to the isolated feedback system composed of the reference voltage source and the optocoupler. The principle is as described above, which realizes stable and accurate soft start and greatly improves the performance of the switching power supply.

[0032] In summary, the present invention utilizes operational amplifier chips for buck, boost, flyback, and forward power supplies, enabling circuit designs that meet the soft-start time requirements of various circuits simply by changing the corresponding parameters. For example, by adjusting the precision of the capacitor and the first resistor, the charge and discharge waveforms and speed can be precisely controlled, thereby achieving the desired soft-start time and waveform. The withstand voltage and temperature coefficient of the capacitor and the first resistor can also be adjusted to meet the requirements of high-voltage, high-current applications.

[0033] The above embodiments are illustrations of specific implementation methods of this patent, rather than limitations of the present invention. Technicians in the relevant technical field may make various transformations and changes to obtain corresponding equivalent technical solutions without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should be included in the patent protection scope of the present invention.

Claims

1. A power soft start circuit suitable for new energy and power products, characterized by: including a capacitor, a first diode, a second diode, a first resistor, and a second resistor; One end of the capacitor is connected to the output voltage, and the other end is connected to one end of the first resistor; the other end of the first resistor is respectively connected to one end of the second resistor, the positive electrode of the first diode and the negative electrode of the second diode; the other end of the second resistor is connected to the ground; the negative electrode of the first diode is connected to the feedback voltage input terminal; and the positive electrode of the second diode is connected to the ground.

2. A power soft start circuit suitable for new energy and power products according to claim 1, characterized in that: The power soft start circuit is suitable for liquid flow batteries, photovoltaic inverters, intelligent DC metering and control equipment, and stacked light controllers.

3. A power soft start circuit suitable for new energy and power products according to any one of claims 1-2, characterized in that: When the power supply starts, the output voltage begins to rise, the power supply soft-start circuit starts to work, the capacitor starts to charge and feeds back the charging current to the feedback voltage input terminal through the first diode, raising the feedback voltage and thereby slowing down the output voltage rise speed. After the capacitor is fully charged, the soft start is completed and the first diode is cut off; if the power supply is abnormal or shuts down automatically, the capacitor is discharged through the second diode.

4. A switching power supply suitable for new energy and power products, characterized by: The switching power supply includes the power soft start circuit according to any one of claims 1 to 4.

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