Soft start circuit for DC-DC switching power supply chip and control method thereof

Abstract

The invention discloses a soft start circuit for a DC-DC switching power supply chip and a control method thereof, the soft start circuit comprises a soft start control circuit, a drive circuit, a power full bridge, an isolation transformer and a rectification circuit which are electrically connected in sequence, the soft start control circuit generates N groups of output signals, the N groups of output signals are sequentially jumped into effective signals according to a preset time interval; the power full bridge comprises N groups of full bridge units which are connected in parallel; the rectifying circuit is connected with a secondary side inductor of the isolation transformer, receives energy of the isolation transformer and converts the energy into a direct-current power supply for output; the feedback circuit is used for detecting whether the output voltage of the rectifying circuit reaches a feedback signal of a rated value or not and feeding back the feedback signal to the soft start control circuit; an output signal of the soft start control circuit and a feedback signal are subjected to logical operation to generate an enable control signal, the drive circuit is controlled through the enable control signal to drive the corresponding full-bridge units, and the magnitude of the start current is controlled through the number of the driven full-bridge units.

Description

Technical Field

[0001] This invention belongs to the field of power supply technology, specifically relating to a soft-start circuit and its control method for a DC-DC switching power supply chip. Background Technology

[0002] In modern industry and communications, various switching power supplies are increasingly widely used. Currently, the development trend of switching power supply chips is towards smaller size, higher efficiency, and higher reliability. Reliability issues in switching power supply chips typically occur during the startup process; therefore, establishing a stable and secure startup process is crucial for improving the reliability of switching power supply chips.

[0003] Traditional DC-DC switching power supply chips typically have a storage capacitor connected in parallel at the output port to provide the load current source. During the initial startup phase, the voltage across the storage capacitor is zero, significantly different from the rated output voltage of the power supply chip. The internal power circuitry then supplies a large current to the storage capacitor, causing the output voltage to rise rapidly and resulting in a high surge overshoot voltage across the capacitor. Excessive overshoot voltage can reduce the lifespan of internal components and, in severe cases, directly damage devices connected to the output port, while also damaging or degrading the performance of the storage capacitor. Summary of the Invention

[0004] The first objective of this invention is to provide a soft-start circuit for DC-DC switching power supply chips, solving the problem of output overshoot in DC-DC switching power supply chips and improving product reliability. The second objective is to provide a control method for the soft-start circuit of DC-DC switching power supply chips.

[0005] The technical solution adopted for the first objective of this invention is as follows: A soft-start circuit for a DC-DC switching power supply chip includes a soft-start control circuit, a drive circuit, a power full-bridge circuit, an isolation transformer, and a rectifier circuit, which are connected in sequence. The soft-start control circuit generates N sets of output signals, where N is a positive integer and N≥2. The N sets of output signals sequentially change into valid signals at preset time intervals. The power full bridge includes N groups of full bridge units connected in parallel. The input terminal of each group of full bridge units is connected to a DC input power supply, and the output terminal is connected to the primary inductance of the isolation transformer. The rectifier circuit is connected to the secondary inductor of the isolation transformer, receives the energy transmitted by the isolation transformer, and converts it into DC power output; It also includes a feedback circuit for detecting the output voltage of the rectifier circuit and generating a feedback signal to indicate whether the output voltage has reached the rated value, and then feeding the feedback signal back to the soft-start control circuit. The output signal of the soft-start control circuit and the feedback signal of the feedback circuit are logically operated to generate an enable control signal. The soft-start control circuit controls the drive circuit to drive the corresponding full-bridge unit through the enable control signal, and controls the magnitude of the starting current by the number of full-bridge units driven.

[0006] The soft-start circuit for a DC-DC switching power supply chip provided by this invention enables the drive circuit sequentially after the primary side of the chip is powered on. This drive circuit drives the corresponding power full-bridge circuit, and energy is transferred to the secondary side of the switching power supply chip through the isolation transformer. When the secondary side output voltage reaches the rated value, a feedback signal is sent to the soft-start control circuit on the primary side through the feedback circuit to interrupt the soft-start process. In the initial stage of startup, the starting current is limited by restricting the number of power full-bridge units connected to the circuit. In subsequent stages, the number of full-bridge units connected to the circuit is gradually increased, increasing the starting current and achieving a slow and steady increase in output voltage, thus solving the problem of output overshoot in DC-DC switching power supply chips.

[0007] The present invention also has the following preferred designs: The driving circuit of the present invention includes N driving units. The N sets of enable control signals generated by the soft-start control circuit correspond one-to-one with the N driving units of the driving circuit. The N driving units correspond one-to-one with the N sets of full-bridge units of the power full-bridge, making the control path clear and simplifying the control logic.

[0008] In the power full-bridge of the present invention, the conductivity of the switching transistors in the first to Nth groups of full-bridge units increases exponentially. The first advantage of this preferred design is that the device size of the first few groups of full-bridge units in the power full-bridge can be very small, allowing for better limitation of the startup current during the initial startup phase. The second advantage is that, to achieve the same energy transfer capability, the power full-bridge requires fewer groups of full-bridge units, resulting in a simpler design.

[0009] The feedback circuit of the present invention includes a pulse generation circuit, a modulation circuit, an isolation capacitor, and a demodulation circuit connected in sequence. The pulse generation circuit is connected to the output terminal of the rectifier circuit, detects the output voltage of the rectifier circuit, and generates a pulse signal as the feedback signal when the output voltage reaches the rated value. The pulse signal is fed back to the soft-start control circuit after passing through the modulation circuit, the isolation capacitor, and the demodulation circuit.

[0010] The soft-start control circuit of the present invention includes a soft-start control signal generation circuit and a logic operation circuit. The soft-start control signal generation circuit has N output ports. The logic operation circuit is an AND gate circuit. The input of the AND gate circuit is the output signal of the soft-start control signal generation circuit and the inverted signal of the pulse signal. The output is the enable control signal.

[0011] The feedback circuit of this invention uses a pulse generation circuit, which, in conjunction with an AND gate circuit, simplifies the logic operation of the soft-start control circuit and makes control more convenient.

[0012] The second objective of this invention is to provide a control method for the soft-start circuit of the aforementioned DC-DC switching power supply chip, comprising the following steps: After the primary side of the isolation transformer of the DC-DC switching power supply chip is powered on, the soft-start control circuit generates N sets of output signals. The N sets of output signals are sequentially changed into valid signals at preset time intervals. The output signals and the feedback signals of the feedback circuit are logically operated to generate an enable control signal. After receiving the corresponding enable control signal, the drive circuit drives the corresponding full-bridge unit on the subsequent power full-bridge to enter the working state in sequence, and transmits energy to the secondary side of the isolation transformer. The rectifier circuit converts the energy on the secondary side of the isolation transformer into DC power output. The feedback circuit detects the output voltage of the rectifier circuit and outputs a feedback signal to the soft-start control circuit. After receiving the feedback signal that the output voltage has reached the rated value, the soft-start control circuit ends the soft-start process.

[0013] After receiving a feedback signal indicating that the output voltage of the rectifier circuit has reached its rated value, the soft-start control circuit of this invention converts all N sets of output signals generated by the soft-start control circuit into valid signals. These signals then drive all N sets of full-bridge units of the power full-bridge to enter the working state via the driving circuit. That is, after the soft-start process is completed, connecting all full-bridge units of the power full-bridge to the circuit enhances the load-carrying capacity of the switching power supply chip and improves energy transfer efficiency.

[0014] The preset time interval for the transition of the N sets of output signals generated by the soft-start control circuit of the present invention to valid signals is 1ms. This preset time interval can be flexibly set according to actual application requirements.

[0015] The present invention has the following beneficial effects: 1. The soft-start circuit of the DC-DC switching power supply chip of the present invention: In the initial stage of startup, the startup current can be limited by restricting the number of power full-bridge units connected to the circuit; in subsequent stages, the number of full-bridge units connected to the circuit is gradually increased to increase the startup current. This invention precisely controls the amount of energy transferred to the secondary side of the isolation transformer by controlling the number of power full-bridge units connected to the circuit, achieving a slow and steady increase in output voltage, thus solving the problem of output overshoot in DC-DC switching power supply chips.

[0016] 2. The closed-loop control circuit of the present invention, consisting of a soft-start control circuit, a drive circuit, a power full-bridge circuit, an isolation transformer, a rectifier circuit, and a feedback circuit, has a simple and clear control path, is not easily affected by external environmental interference, and has strong stability.

[0017] 3. After the soft start is completed, the present invention connects the entire power bridge into the circuit, which can enhance the load capacity of the switching power supply chip and improve the energy transmission efficiency. Attached Figure Description

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 This is a schematic diagram of the soft-start circuit of the DC-DC switching power supply chip of the present invention. Figure 2 This is a schematic diagram of the soft-start control circuit of the DC-DC switching power supply chip in the embodiment. Figure 3 This is a schematic diagram of the driving circuit of the DC-DC switching power supply chip in the embodiment. Figure 4 This is a circuit topology diagram of the full-bridge driver for the DC-DC switching power supply chip in the embodiment; Figure 5 This is a schematic diagram illustrating the change in the output signal of the soft-start control circuit during the soft-start process of the DC-DC switching power supply chip in the embodiment. Figure 6 This is a schematic diagram illustrating the change in the secondary output voltage of the DC-DC switching power supply chip during the soft-start process in the embodiment.

[0019] Explanation of reference numerals in the attached figures: 1. Soft-start control circuit; 2. Drive circuit; 3. Power full-bridge; 4. Isolation transformer; 5. Rectifier circuit; 6. Pulse generation circuit; 7. Modulation circuit; 8. Isolation capacitor; 9. Demodulation circuit; 11. Soft start control signal generation circuit; 12. Logic operation circuit. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention more apparent, exemplary embodiments according to the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely a part of the embodiments of the present invention, and not all of the embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein. Based on the embodiments of the present invention described herein, all other embodiments obtained by those skilled in the art without inventive effort should fall within the protection scope of the present invention.

[0021] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0022] Example: like Figures 1 to 4 As shown, a soft-start circuit for a DC-DC switching power supply chip includes a soft-start control circuit 1, a drive circuit 2, a power full-bridge circuit 3, an isolation transformer 4, and a rectifier circuit 5, which are connected in sequence. The soft-start control circuit 1 generates N sets of output signals, where N is a positive integer and N≥2. The N sets of output signals sequentially change to valid signals at preset time intervals. The N sets of output signals are sequentially denoted as C1, C2, ..., CN. The power full-bridge 3 comprises N groups of full-bridge units connected in parallel. The input of each group is connected to the DC power supply input Vin, and the output is connected to the primary inductance of the isolation transformer 4. Each group of full-bridge units includes four switching transistors, such as... Figure 4 As shown, the N groups of full-bridge units are denoted as 1M, 2M, ..., NM, where the switching transistors of full-bridge unit 1M are G11, G12, G11', G12', the switching transistors of full-bridge unit 2M are G21, G22, G21', G22', and so on, and the switching transistors of full-bridge unit NM are GN1, GN2, GN1', GN2'; The rectifier circuit 5 is connected to the secondary inductor of the isolation transformer 4, receives the energy transmitted by the isolation transformer 4 and converts it into DC power output; It also includes a feedback circuit, which is used to detect the output voltage VOUT of the rectifier circuit 5 and generate a feedback signal FB to indicate whether the output voltage has reached the rated value, and then feeds the feedback signal FB back to the soft start control circuit 1. The output signals C1 to CN of the soft-start control circuit 1 are logically operated with the feedback signal of the feedback circuit to generate enable control signals CT1 to CTN. The soft-start control circuit 1 controls the drive circuit 2 to drive the corresponding full-bridge unit through the enable control signals CT1 to CTN, and controls the magnitude of the starting current by the number of driven full-bridge units.

[0023] In a preferred embodiment, the drive circuit 2 includes N drive units, denoted as drive 1# to drive N#. The N sets of enable control signals CT1 to CTN generated by the soft start control circuit 1 correspond one-to-one with the N drive units of the drive circuit 2. The N drive units correspond one-to-one with the N sets of full-bridge units of the power full-bridge 3, making the control path clear and simplifying the control logic.

[0024] In a preferred embodiment, the conductivity of the switching transistors in the first to Nth groups of the power full-bridge circuit increases exponentially, allowing the output voltage to rise steadily as the number of full-bridge units connected to the circuit increases sequentially. In other embodiments, switching transistors with the same conductivity can also be used.

[0025] In a preferred embodiment, the feedback circuit includes a pulse generation circuit 6, a modulation circuit 7, an isolation capacitor 8, and a demodulation circuit 9 connected in sequence. The pulse generation circuit 6 is connected to the output terminal of the rectifier circuit 5 and detects the output voltage VOUT of the rectifier circuit 5. When the output voltage VOUT reaches the rated value, a pulse signal is generated as a feedback signal FB. The pulse signal is fed back to the soft-start control circuit 1 after passing through the modulation circuit 7, the isolation capacitor 8, and the demodulation circuit 9.

[0026] In a preferred embodiment, the soft-start control circuit 1 includes a soft-start control signal generation circuit 11 and a logic operation circuit 12. The soft-start control signal generation circuit 11 has N output ports and output signals C1 to CN. The logic operation circuit 12 is an AND gate circuit. The input of the AND gate circuit is the output signals C1 to CN of the soft-start control signal generation circuit 11 and the inverted signal FB' of the pulse signal. The output is the enable control signals CT1 to CTN.

[0027] The control method for the soft-start circuit of the DC-DC switching power supply chip described above includes the following steps: After the primary side of the isolation transformer 4 of the DC-DC switching power supply chip is powered on, the soft-start control circuit 1 generates N sets of output signals C1 to CN. (See [link]). Figure 5 The N groups of output signals sequentially change into valid signals at preset time intervals. The output signals and the feedback signal FB of the feedback circuit are logically operated to generate enable control signals CT1 to CTN. After receiving the corresponding enable control signals CT1~CTN, the drive circuit 2 drives the corresponding full-bridge units on the subsequent power full-bridge 3 to enter the working state in sequence, and transmits energy to the secondary side of the isolation transformer 4. The rectifier circuit 5 converts the energy of the secondary side of the isolation transformer 4 into DC power output. The feedback circuit detects the output voltage VOUT of the rectifier circuit 5 and outputs a feedback signal to the soft-start control circuit 1. After receiving the feedback signal that the output voltage VOUT has reached the rated value, the soft-start control circuit 1 ends the soft-start process.

[0028] The specific working process of this embodiment is as follows: After the primary side of the DC-DC switching power supply chip is powered on, an output port of the soft-start control signal generation circuit 11 in the soft-start control circuit 1 outputs a valid signal C1. After performing an AND logic operation with the inverse signal FB' of the feedback signal FB, an enable control signal CT1 is output to the drive circuit 2, which drives the 1# circuit to start working and drives the full-bridge unit 1M. Other full-bridge units are in the off state. Energy is transferred to the secondary side through the isolation transformer 4. The output voltage VOUT of the secondary side after passing through the rectifier circuit 5 rises slowly.

[0029] In this embodiment, the preset time interval for the N sets of output signals generated by the soft-start control circuit 1 to transition to valid signals is 1ms.

[0030] If the secondary-side output voltage VOUT does not reach the rated value within 1ms, the feedback circuit will not feed back a pulse signal. The output port of the soft-start control signal generation circuit outputs a valid signal C2, which is ANDed with the inverse signal FB' of the feedback signal FB. After the AND operation, the enable control signal CT2 is output to the drive circuit 2, and the drive circuit #2 starts to work, driving the full-bridge unit 2M, driving full-bridge 1M and driving full-bridge 2M to work. Other full-bridge units are in the off state, increasing the energy transferred to the secondary side. The secondary-side output voltage VOUT continues to rise, and the speed increases.

[0031] If the secondary-side output voltage VOUT does not reach the rated value within 2ms, the feedback circuit will not feed back a pulse signal. The output port of the soft-start control signal generation circuit outputs a valid signal C3, which is ANDed with the inverse signal FB' of the feedback signal FB. After the AND operation, the enable control signal CT3 is output to the drive circuit 2, driving the 3# circuit to start working. This drives the full-bridge unit 3M, full-bridge unit 1M, full-bridge unit 2M, and full-bridge unit 3M to work, while other full-bridge units remain in the off state. This continues to increase the energy transferred to the secondary side, and the secondary-side output voltage VOUT continues to rise at a faster rate.

[0032] Similarly, if the secondary-side output voltage VOUT does not reach its rated value within Nms, the feedback circuit will not provide a pulse signal. The output port of the soft-start control signal generation circuit 11 outputs a valid signal CN, which is ANDed with the inverse signal FB' of the feedback signal FB. This results in an enable control signal CTN being output to the drive circuit 2, starting the N# circuit and driving the full-bridge unit NM to continue increasing the energy transferred to the secondary side. The secondary-side output voltage VOUT continues to rise, and the speed increases. At this point, all power full-bridge circuits are connected to the circuit, the transferred energy reaches its maximum value, and the secondary-side output voltage VOUT steadily rises until it reaches a stable voltage. The change in the secondary-side output voltage during this soft-start process is as follows: Figure 6 As shown.

[0033] If the secondary output voltage VOUT reaches the rated voltage value during the soft start process, the pulse generation circuit 6 outputs a pulse signal, which is fed back to the primary side through the feedback circuit. After the soft start control signal generation circuit 11 detects the pulse signal, it ends the soft start process.

[0034] In this embodiment, after the soft-start control circuit 1 receives the feedback signal that the output voltage VOUT of the rectifier circuit 5 has reached the rated value, all N sets of output signals generated by the soft-start control circuit 1 become valid signals, driving all N sets of full-bridge units of the power full-bridge 3 to enter the working state through the drive circuit 2. That is, after the soft start is completed, connecting all full-bridge units of the power full-bridge 3 into the circuit can enhance the load-carrying capacity of the switching power supply chip and improve the energy transfer efficiency.

[0035] All the terms "electrical connection" and "connection" mentioned in this patent application do not refer to direct connection of components, but rather to the ability to form a better connection structure by adding or removing connecting accessories according to the specific implementation. The use of "electrical connection" in this invention is only to emphasize this meaning, but it does not exclude the use of "connection" and the like to have the same meaning.

[0036] The above embodiments of the present invention are not intended to limit the scope of protection of the present invention. The implementation of the present invention is not limited thereto. All other modifications, substitutions or alterations made to the above structure of the present invention based on the above content of the present invention, in accordance with ordinary technical knowledge and common practice in the field, without departing from the basic technical idea of ​​the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A soft-start circuit for a DC-DC switching power supply chip, characterized in that: It includes a soft-start control circuit, a drive circuit, a power bridge, an isolation transformer, and a rectifier circuit, which are connected in sequence. The soft-start control circuit generates N sets of output signals, where N is a positive integer and N≥2. The N sets of output signals sequentially change into valid signals at preset time intervals. The power full bridge includes N groups of full bridge units connected in parallel. The input terminal of each group of full bridge units is connected to a DC input power supply, and the output terminal is connected to the primary inductance of the isolation transformer. The rectifier circuit is connected to the secondary inductor of the isolation transformer, receives the energy transmitted by the isolation transformer, and converts it into DC power output; It also includes a feedback circuit for detecting the output voltage of the rectifier circuit and generating a feedback signal to indicate whether the output voltage has reached the rated value, and then feeding the feedback signal back to the soft-start control circuit. The output signal of the soft-start control circuit and the feedback signal of the feedback circuit are logically operated to generate an enable control signal. The soft-start control circuit controls the drive circuit to drive the corresponding full-bridge unit through the enable control signal, and controls the magnitude of the starting current by the number of full-bridge units driven.

2. The soft-start circuit for a DC-DC switching power supply chip according to claim 1, characterized in that: The drive circuit includes N drive units. The N sets of enable control signals generated by the soft-start control circuit correspond one-to-one with the N drive units of the drive circuit, and the N drive units correspond one-to-one with the N sets of full-bridge units of the power full-bridge.

3. The soft-start circuit for a DC-DC switching power supply chip according to claim 1, characterized in that: The conductivity of the switching transistors in the first to Nth groups of the full-bridge power bridge increases exponentially.

4. The soft-start circuit for a DC-DC switching power supply chip according to claim 1, characterized in that: The feedback circuit includes a pulse generation circuit, a modulation circuit, an isolation capacitor, and a demodulation circuit connected in sequence. The pulse generation circuit is connected to the output terminal of the rectifier circuit, detects the output voltage of the rectifier circuit, and generates a pulse signal as the feedback signal when the output voltage reaches the rated value. The pulse signal is fed back to the soft-start control circuit after passing through the modulation circuit, the isolation capacitor, and the demodulation circuit.

5. The soft-start circuit for a DC-DC switching power supply chip according to claim 4, characterized in that: The soft-start control circuit includes a soft-start control signal generation circuit and a logic operation circuit. The soft-start control signal generation circuit has N signal output ports. The logic operation circuit is an AND gate circuit. The input of the AND gate circuit is the output signal of the soft-start control signal generation circuit and the inverted signal of the pulse signal. The output is the enable control signal.

6. A control method for a soft-start circuit of a DC-DC switching power supply chip as described in any one of claims 1 to 5, characterized in that, Includes the following steps: After the primary side of the isolation transformer of the DC-DC switching power supply chip is powered on, the soft-start control circuit generates N sets of output signals. The N sets of output signals are sequentially changed into valid signals at preset time intervals. The output signals and the feedback signals of the feedback circuit are logically operated to generate an enable control signal. After receiving the corresponding enable control signal, the drive circuit drives the corresponding full-bridge unit on the subsequent power full-bridge to enter the working state in sequence, and transmits energy to the secondary side of the isolation transformer. The rectifier circuit converts the energy on the secondary side of the isolation transformer into DC power output. The feedback circuit detects the output voltage of the rectifier circuit and outputs a feedback signal to the soft-start control circuit. After receiving the feedback signal that the output voltage has reached the rated value, the soft-start control circuit ends the soft-start process.

7. The control method according to claim 6, characterized in that: After receiving a feedback signal that the output voltage of the rectifier circuit has reached the rated value, the soft-start control circuit generates N sets of output signals that all become valid signals, and drives all N sets of full-bridge units of the power full-bridge to enter the working state through the drive circuit.

8. The control method according to claim 6, characterized in that, The preset time interval for the N sets of output signals generated by the soft-start control circuit to transition to valid signals is 1ms.

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