Double-end soft start circuit structure and application method thereof

Abstract

The invention discloses a double-end soft start circuit structure and an application method thereof, and relates to the technical field of switching power supplies, and the structure comprises an external time adjustable soft start circuit module which comprises an N-type field effect transistor NM1, the drain electrode of which is electrically connected with an external power supply, the grid electrode of which is electrically connected with the output end of an amplifier, and the source electrode of which is grounded and connected with the first input end of an EA; the off-chip capacitor is electrically connected with the first input end of the EA; the positive input end of the amplifier receives reference voltage, and the negative input end of the amplifier is connected between the first input end of the EA and the source electrode of the NM1; the internal fixed soft start circuit module comprises an oscillator OSC module, a frequency divider DIV module and an R2R module which are connected in sequence, and a resistor R1 is connected between the output end of the R2R module and the second input end of the EA; by combining the two circuits, overcharge voltage and surge current are prevented from being generated in the starting process of the DCAC converter chip.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and in particular to a double-end soft start circuit structure and an application method thereof. Background Art

[0002] For DCDC converter chips, during the chip power-on process, due to loop response problems, it takes a certain amount of time for the output voltage to rise to the target voltage. The feedback voltage during the output voltage rising stage is less than the set reference voltage, resulting in the error amplifier not working in a balanced state. The error amplifier output signal is too high, causing the loop to work at 100% duty cycle. The output capacitor will be quickly charged to generate surge current, which is much larger than the steady-state current under normal loop operation. This will seriously affect the normal output of the chip and even cause components to burn out.

[0003] Therefore, it is usually necessary to set up a soft-start circuit to provide a soft-start signal to replace the reference voltage at the input of the error amplifier. By comparing the slowly and smoothly rising signal of the soft start with the feedback voltage signal, the chip's working duty cycle is limited to avoid the problem of excessive surge current in the output capacitor causing overcharging of the output voltage.

[0004] The soft start signal currently used is generated by charging a fixed capacitor with an internal fixed current. The implementation method of this soft start is to continuously charge the capacitor so that the capacitance increases slowly. However, the size of the capacitor has a great influence on the area of ​​the chip. At the same time, the soft start time is relatively fixed and cannot meet diverse needs. Summary of the invention

[0005] In view of the shortcomings of the prior art that the size of the capacitor has a great influence on the area of ​​the chip and the soft-start time is relatively fixed, the present invention proposes a double-terminal soft-start circuit structure and an application method thereof, wherein an internal fixed soft-start circuit signal and an externally adjustable soft-start signal generated by an externally adjustable soft-start circuit structure and an internally fixed soft-start circuit structure are input into the positive input terminal of EA, so that during the slow startup of the chip, the feedback voltage slowly rises and finally stabilizes to a reference voltage, thereby solving the problems existing in the prior art.

[0006] A double-terminal soft-start circuit structure, comprising: The external time adjustable soft start circuit module includes an N-type field effect transistor NM1, an amplifier A1 and an off-chip capacitor The drain of NM1 is electrically connected to the external power supply, the gate is electrically connected to the output terminal of A1, the source is grounded and electrically connected to the first input terminal of the error amplifier EA of the DCAC converter; The positive input terminal of A1 receives the reference voltage, and the negative input terminal is connected between the first input terminal of EA and the source of NM1; An internal fixed soft start circuit module comprises an oscillator OSC module, a frequency divider DIV module and an R2R module connected in sequence; the output end of the R2R module is electrically connected to the second input end of the EA; one end of a resistor R1 is connected between the output end of the R2R module and the second input end of the EA, and the other end of the resistor R1 is connected to an external power supply.

[0007] Furthermore, a soft starter SOFTSTART1 is connected between the source of NM1 and the negative input terminal of A1.

[0008] Furthermore, a soft starter SOFTSTART2 is connected between the output end of the R2R module and R1.

[0009] Furthermore, the working mode of the external time adjustable soft start circuit module is: when the external power supply is turned on, the voltage at the first input terminal of EA is lower than the reference voltage After passing through amplifier A1, a high-level signal is output to turn on NM1, and the current flowing from the off-chip capacitor to the drain of NM1 through the external power supply and the current flowing from the source of NM1 to the ground The current difference is charged to generate a soft start signal .

[0010] Furthermore, the off-chip capacitor The current flowing to the drain of NM1 through the external power supply and the current flowing to the source of NM1 The current difference is used for charging, and the charging time for: .

[0011] Furthermore, the working mode of the internal fixed soft start circuit module is: when the external power supply is turned on, the oscillator OSC module generates a clock signal of fixed duration, and the clock signal is input into the frequency divider DIV module. The DIV module divides the clock signal, and the divided signal enters the R2R module. The internal switch of R2R is controlled by the frequency division signal to control the voltage division ratio of the resistor R1, so that the resistance of R2R increases, generating a rising soft-start voltage signal .

[0012] Furthermore, the soft start voltage signal for: .

[0013] The present invention also includes a method for applying a double-ended soft start circuit structure to a DC-AC converter, comprising the following steps: Generate an internal fixed soft start circuit signal through an external adjustable soft start circuit module and an internal fixed soft start circuit module and an externally adjustable soft-start signal ; Will and are input to the first input terminal and the second input terminal of the error amplifier EA respectively; during the power-on startup process of the DCAC converter, the feedback voltage of the DCAC converter Through the output voltage As the DCAC converter is powered on, the feedback voltage increases with or When the setting Startup time exceeds When the startup time is long, the feedback voltage follows rise; when Startup time is less than When the startup time is long, the feedback voltage follows rise.

[0014] The present invention also proposes a DCAC converter, including a DCAC converter module and the double-end soft start circuit structure; the first input end of the error amplifier EA in the DCAC converter module is connected to the output end of the external time-adjustable soft start circuit module, and the second input end of the error amplifier EA in the DCAC converter module is connected to the output end of the internal fixed soft start circuit module.

[0015] The present invention provides a double-end soft start circuit structure and an application method thereof, which have the following beneficial effects: The present invention inputs an internal fixed soft start circuit signal and an external adjustable soft start signal generated by two circuits, an external adjustable soft start circuit structure and an internal fixed soft start circuit structure, into two positive input terminals of an error amplifier EA, so that during the slow start process of a DCDC converter chip, a feedback voltage slowly rises and is finally stabilized as a reference voltage, and the output voltage of the DCDC converter slowly rises following the soft start voltage, so that overcharge voltage and surge current are avoided during the start process, a soft start function is realized, and the circuit is better protected. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a structural diagram of an externally adjustable soft start circuit in an embodiment of the present invention; Figure 2 This is a structural diagram of an internal fixed soft start circuit in an embodiment of the present invention; Figure 3These are two schematic diagrams of soft start effects in the embodiments of the present invention; Figure 3 a is a schematic diagram of the soft start effect of the external adjustable soft start circuit. Figure 3 b is a schematic diagram of the soft start effect of the internal fixed soft start circuit; Figure 4 Schematic diagram of the soft start function of the system in the embodiment of the present invention. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0018] The invention provides a double-end soft start circuit structure, which comprises an external adjustable soft start circuit structure and an internal fixed soft start circuit structure.

[0019] The external adjustable soft start circuit structure is as follows Figure 1 As shown, it specifically includes a power supply, an N-type field effect transistor NM1, an amplifier A1 and an off-chip capacitor ; Current Connect to the output current of the power supply Flows to the drain of NM1, the off-chip capacitor is connected between the soft starter SOFTSTART1 terminal and the ground, the gate of NM1 is connected to the output of amplifier A1, and the output current of the source of NM1 flows to ground, the source is connected to SOFTSTART1; the positive input of operational amplifier A1 is connected to , the negative input is connected to SOFTSTART1 and the output is connected to the gate of NM1.

[0020] The working principle is: when the chip is powered on by external power, The terminal voltage is low, lower than the reference voltage , amplifier A1 will Voltage and After amplification, the high-level signal is output to turn on NM1, and the off-chip capacitor is and Current difference charging, charging time is:

[0021] It can be seen from the above formula that the external adjustable soft start time can be set by setting the size of the external capacitor to set the soft start time.

[0022] The internal fixed soft start circuit structure is as follows Figure 2 As shown, including power supply V CC, oscillator OSC module, divider DIV module and R2R module; resistor R1 is connected to the power supply V CC and The OSC module is connected to the divider DIV module and provides a fixed clock signal CLK with a duty cycle of 50%; the DIV module is connected between the OSC module and the R2R module, and divides the clock signal input from the oscillator OSC module to generate clock control signals with different multiples and input them into the R2R module; R2R is connected to the DIV module, 2 and ground, used to receive the divided clock control signal generated by the DIV module, and generate a slowly increasing soft start voltage signal through the resistor R1 voltage divider .

[0023] The working principle is: the oscillator OSC module generates a fixed-duration clock signal and inputs it into the divider module. The divider divides the fixed clock signal, and the divided signal enters the R2R module. The divided signal controls the internal switch of R2R to control the internal resistance voltage division ratio of R2R, so that the overall resistance of R2R gradually increases, thereby generating a slowly rising soft start voltage signal. .That The voltage formula is:

[0024] An internal fixed soft start circuit signal is generated by using two circuits: an external adjustable soft start circuit structure and an internal fixed soft start circuit structure and an externally adjustable soft-start signal , two soft start signals are input to the positive input terminal of the error amplifier EA, such as Figure 3 As shown. During the chip power-on startup process, the feedback voltage By output voltage The feedback voltage is divided by the external adjustable soft start voltage. Or internal fixed soft start voltage When the external soft-start voltage is set The startup time exceeds the internal fixed soft start voltage When the startup time is longer, the feedback voltage follows the external soft-start voltage gradually increases, and when the external soft-start voltage The duration is set too short, less than the internal fixed soft start voltage. When the feedback voltage follows the internal fixed-duration soft-start voltage signal Voltage rises.

[0025] The two soft start effect diagrams are as follows: Figure 3 As shown, when the external capacitor is set to make the soft-start voltage The rising speed is compared with the internal fixed soft start voltage When the rising speed is fast, the feedback voltage Follow the internal fixed soft start voltage Slowly rising, output voltage When the external capacitor is set to make the off-chip adjustable soft-start voltage The rising speed is compared with the internal fixed soft start voltage When the rising speed is slow, the feedback voltage Follow-up external adjustable soft-start voltage Slowly rising, output voltage Also rose accordingly.

[0026] The two soft starts play the same role, making the feedback voltage rise slowly and finally stabilize to the reference voltage during the chip slow startup process, and making the DCDC converter output voltage rise slowly following the soft start voltage, avoiding overcharge voltage and surge current during the startup process, realizing the soft start function, and better protecting the circuit.

[0027] Based on the above inventive concept, the present invention proposes a DCAC converter, including a DCAC converter module and a double-end soft start circuit structure; the first input end of the error amplifier EA in the DCAC converter module is connected to the output end of the external time-adjustable soft start circuit module, and the second input end of the error amplifier EA in the DCAC converter module is connected to the output end of the internal fixed soft start circuit module.

[0028] The present invention proposes a flexible and variable double-end soft-start circuit structure to meet flexible and diverse needs. At the same time, in order to avoid the soft-start time being set too short, the internal soft-start signal provides further protection to prevent the startup time from being too short and generating excessive surge current to damage the chip.

[0029] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A double-ended soft start circuit structure, characterized in that: include: The external time adjustable soft start circuit module includes an N-type field effect transistor NM1, an amplifier A1 and an off-chip capacitor The drain of NM1 is electrically connected to the external power supply, the gate is electrically connected to the output terminal of A1, the source is grounded and electrically connected to the first input terminal of the error amplifier EA of the DCAC converter; The positive input terminal of A1 receives the reference voltage, and the negative input terminal is connected between the first input terminal of EA and the source of NM1; An internal fixed soft start circuit module comprises an oscillator OSC module, a frequency divider DIV module and an R2R module connected in sequence; the output end of the R2R module is electrically connected to the second input end of the EA; one end of a resistor R1 is connected between the output end of the R2R module and the second input end of the EA, and the other end of the resistor R1 is connected to an external power supply.

2. A double-ended soft start circuit structure according to claim 1, characterized in that: A soft starter SOFTSTART1 is connected between the source of NM1 and the negative input terminal of A1.

3. A double-ended soft start circuit structure according to claim 1, characterized in that: A soft starter SOFTSTART2 is connected between the output end of the R2R module and R1.

4. A double-ended soft start circuit structure according to claim 1, characterized in that: The working mode of the external time adjustable soft start circuit module is: when the external power supply is turned on, the voltage at the first input terminal of EA is lower than the reference voltage After passing through amplifier A1, a high-level signal is output to turn on NM1, and the current flowing from the off-chip capacitor to the drain of NM1 through the external power supply and the current flowing from the source of NM1 to the ground The current difference is charged to generate a soft start signal .

5. A double-ended soft start circuit structure according to claim 4, characterized in that: The off-chip capacitor The current flowing to the drain of NM1 through the external power supply and the current flowing to the source of NM1 The current difference is charged, and the charging time for: 。 6. A double-terminal soft start circuit structure according to claim 5, characterized in that: The working mode of the internal fixed soft start circuit module is: when the external power supply is turned on, the oscillator OSC module generates a clock signal of fixed duration, and the clock signal is input into the frequency divider DIV module. The DIV module divides the clock signal, and the divided signal enters the R2R module. The internal switch of R2R is controlled by the frequency division signal to control the voltage division ratio of the resistor R1, so that the resistance of R2R increases, generating a rising soft-start voltage signal .

7. A double-end soft start circuit structure according to claim 6, characterized in that: The soft start voltage signal for: 。 8. A method for applying the double-ended soft start circuit structure according to claim 7 to a DCAC converter, characterized in that: The following steps are involved: Generate an internal fixed soft start circuit signal through an external adjustable soft start circuit module and an internal fixed soft start circuit module and an externally adjustable soft-start signal ; Will and are input to the first input terminal and the second input terminal of the error amplifier EA respectively; during the power-on startup process of the DCAC converter, the feedback voltage of the DCAC converter Through the output voltage As the DCAC converter is powered on, the feedback voltage increases with or When the setting Startup time exceeds When the startup time is long, the feedback voltage follows rise; when Startup time is less than When the startup time is long, the feedback voltage follows rise.

9. A DCAC converter, characterized in that: It comprises a DCAC converter module and a double-end soft start circuit structure according to any one of claims 1 to 7; the first input end of the error amplifier EA in the DCAC converter module is connected to the output end of the external time-adjustable soft start circuit module, and the second input end of the error amplifier EA in the DCAC converter module is connected to the output end of the internal fixed soft start circuit module.

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