Soft start control circuit based on output voltage feedback

Abstract

The invention discloses a soft start control circuit based on output voltage feedback, the soft start control circuit comprises a buffer circuit and a control circuit, the buffer circuit comprises an operational amplifier; the buffer circuit is used for preventing the output voltage from generating an overshoot phenomenon, so that the curve change of the output voltage is smooth; the control circuit comprises a capacitor, a control tube, a voltage dividing assembly and a discharge tube, the capacitor is connected with a drain electrode of the discharge tube and the operational amplifier, and the voltage dividing assembly is connected with the capacitor and the control tube; the control circuit is used for controlling soft start time. According to the invention, the response speed of the soft start control circuit can be improved, and the output voltage overshoot phenomenon is avoided; moreover, the soft start time can be accurately controlled, and the surge current in the power-on process can be effectively and controllably limited.

Description

Technical Field

[0001] The invention belongs to the technical field of integrated circuits and relates to a soft start control circuit based on output voltage feedback. Background Art

[0002] A soft-start circuit is a circuit design used to limit the inrush current impact when electronic equipment or motors start up. It limits the current by controlling the voltage rise rate, thereby reducing damage to the power supply and load devices and improving the reliability and life of the system.

[0003] Traditional soft-start circuits often use a constant current source to charge or discharge a capacitor, causing the output voltage to rise slowly, thus achieving soft-start. However, during the voltage ramp-up process, traditional soft-start circuits can still cause problems such as output overshoot due to the system loop's slow response speed, especially when the input voltage rises faster than the system loop's response speed. Furthermore, due to the lack of a feedback mechanism, the soft-start system cannot monitor output voltage changes in real time, making it impossible to precisely control the charging process and the soft-start time uncontrollable. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a soft-start control circuit based on output voltage feedback. The circuit has a high open-loop gain, can improve the response speed of the system, and avoid output voltage overshoot; and can accurately control the soft-start time, achieve precise control of the charging process, and effectively and controllably limit the inrush current during the power-on process.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions: A soft start control circuit based on output voltage feedback, the soft start control circuit comprising: A buffer circuit, the buffer circuit including an operational amplifier; the buffer circuit is used to prevent the output voltage from overshooting and make the output voltage curve change smoothly; A control circuit includes a capacitor, a control tube, a voltage divider component, and a discharge tube. The capacitor is connected to the drain of the discharge tube and the operational amplifier, and the voltage divider component is connected to the capacitor and the control tube respectively. The control circuit is used to control the soft start time, and the voltage divider component is used to feed back the output voltage to the capacitor to form a feedback loop.

[0006] Optionally, the operational amplifier includes a rail-to-rail operational amplifier, and the capacitor is respectively connected to the drain of the discharge tube and the non-inverting input terminal of the rail-to-rail operational amplifier.

[0007] Optionally, the soft start control circuit further includes a power tube, the gate of which is respectively connected to the inverting input terminal and the output terminal of the rail-to-rail operational amplifier; the power tube is used to regulate the output voltage according to its conduction degree.

[0008] Optionally, the voltage divider component includes a passive element or an active element, the passive element includes a resistor, the resistor includes a first resistor and a second resistor, the capacitor is connected to the first resistor and the second resistor respectively, the drain of the control tube is connected to the second resistor, and the first resistor is connected to the drain of the power tube.

[0009] Optionally, the resistance ratio of the first resistor to the second resistor is adjusted according to the soft start time; the resistance ratio of the first resistor to the second resistor is 1:(1-3).

[0010] Optionally, the soft start control circuit also includes a driving voltage detection circuit, which includes a first inverter and a second inverter, the output end of the first inverter is connected to the input end of the second inverter, the input end of the first inverter is connected to the gate of the power tube, the output end of the second inverter is connected to the gate of the control tube, and the drain of the power tube is connected to the first resistor; the driving voltage detection circuit is used to monitor the gate voltage of the power tube, and when the gate voltage of the power tube is lower than a preset threshold voltage, the driving voltage detection circuit cuts off the soft start control circuit.

[0011] Optionally, the first inverter includes a first transistor, a second transistor, and a third transistor, the gate of the power transistor is connected to the gates of the first transistor, the second transistor, and the third transistor, respectively, the drain of the first transistor is connected to the source of the second transistor, and the drain of the second transistor is connected to the drain of the third transistor; The second inverter includes a fourth transistor, a fifth transistor and a sixth transistor, the drain of the second transistor is connected to the gates of the fourth transistor, the fifth transistor and the sixth transistor respectively, the gate of the control tube is connected to the drain of the fourth transistor and the drain of the fifth transistor respectively, and the source of the fifth transistor is connected to the drain of the sixth transistor.

[0012] Optionally, the rail-to-rail operational amplifier includes a complementary differential input circuit, which includes a first input tube, a second input tube, a third input tube and a fourth input tube, the source of the first input tube is connected to the source of the fourth input tube, the source of the second input tube is connected to the source of the third input tube, the drain of the discharge tube is connected to the gates of the first input tube and the second input tube respectively, and the gate of the power tube is connected to the gates of the third input tube and the fourth input tube respectively; the first input tube and the fourth input tube are respectively N-type transistors, and the second input tube and the third input tube are respectively P-type transistors.

[0013] Optionally, the soft start control circuit also includes an enable control circuit, which includes a first enable tube, a second enable tube, a third enable tube and an inverter, wherein the gate of the first enable tube is respectively connected to the output end of the inverter and the gate of the third enable tube, the drain of the first enable tube is respectively connected to the gate of the discharge tube and the drain of the third enable tube, the input end of the inverter and the gate of the second enable tube are respectively connected to a power supply power-on reset signal, the drain of the second enable tube is respectively connected to the operational amplifier, the capacitor and the drain of the discharge tube, and the source of the third enable tube and the source of the discharge tube are respectively connected to the power ground; the enable control circuit is used to control the initial state of the soft start control circuit before the power is powered on.

[0014] Optionally, the soft start control circuit also includes a current bias circuit, which includes a reference current source and a current mirror tube, the output end of the reference current source is connected to the source of the first enabling tube, the drain of the current mirror tube is connected to the drain of the first enabling tube, the gate of the current mirror tube is connected to the gate of the discharge tube, and the source of the current mirror tube is connected to the power ground; the current bias circuit is used to discharge the capacitor.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a soft-start control circuit based on output voltage feedback. The buffer uses a high-precision operational amplifier with a high open-loop gain, which can improve the response speed of the soft-start control circuit, support power rail swing, and ensure that the gate voltage can still be accurately controlled under low voltage difference. The output stage uses a Class AB output circuit to increase the output swing, ensure that the voltage output device is fully turned on or off, make the output voltage curve change smoothly, and avoid output voltage overshoot. After the control circuit is powered on, the current source discharges one end of the capacitor, causing the voltage output end of the soft start control circuit to slowly open; the voltage divider component feeds the output voltage back to the capacitor, forming a feedback loop, and controls the change in the two ends of the capacitor by driving the voltage detection circuit, thereby facilitating the control of the soft start time. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of a soft start control circuit based on output voltage feedback according to an embodiment of the present invention; Figure 2 A schematic diagram of a buffer circuit of a soft start control circuit based on output voltage feedback according to an embodiment of the present invention; Figure 3 The figure is a schematic diagram of a soft start control circuit driving a voltage detection circuit based on output voltage feedback according to an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0018] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0019] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances. Example

[0020] like Figures 1 to 3As shown, a soft start control circuit based on output voltage feedback includes an enable control circuit, a current bias circuit, a buffer circuit, a control circuit, a drive voltage detection circuit and a power tube PowerMOS, wherein the power tube PowerMOS can also be a sampling power tube, and the power tube PowerMOS is used to regulate the output voltage according to its conduction degree.

[0021] The buffer circuit Buffer includes an operational amplifier, which is a rail-to-rail operational amplifier. The non-inverting input terminal of the rail-to-rail operational amplifier is connected to the control circuit, and the gate of the power transistor Power MOS is respectively connected to the inverting input terminal and output terminal of the rail-to-rail operational amplifier. The power transistor Power MOS outputs a voltage VOUT through the drain. The buffer circuit is used to prevent the output voltage from overshooting and make the output voltage curve change smoothly.

[0022] The control circuit includes a capacitor, a control tube MN4, a voltage divider component, and a discharge tube MN3. The positive electrode VA of the capacitor is connected to the drain of the discharge tube MN3 and the non-inverting input terminal of the rail-to-rail operational amplifier. The source of the control tube MN4 is connected to the power ground, and the gate of the control tube MN4 is connected to the drive voltage detection circuit. The control circuit facilitates controlling the soft start time.

[0023] The voltage divider component includes passive components or active components. Active components include but are not limited to transistors. Passive components include but are not limited to resistors. The resistors include a first resistor R1 and a second resistor R2. The soft start time is set to 95 microseconds. The resistance ratio of the first resistor R1 and the second resistor R2 is 1:1. The negative electrode of the capacitor is connected to one end of the first resistor R1 and one end of the second resistor R2, respectively. The drain of the control transistor MN4 is connected to the other end of the second resistor R2. The other end of the first resistor R1 is connected to the drain of the power transistor Power MOS. Due to the limitation of the minimum operating voltage, the resistance value of the second resistor R2 accounts for a minimum proportion of 50% of the total resistance value of the voltage divider component. The voltage divider component is used to feed back the output voltage VOUT to the capacitor to form a feedback loop. The feedback voltage value is equal to 1 / 2*VOUT to achieve fast startup.

[0024] The drive voltage detection circuit includes a first inverter and a second inverter. The output of the first inverter is connected to the input of the second inverter, the input of the first inverter is connected to the gate of the power transistor Power MOS, the output of the second inverter is connected to the gate of the control transistor MN4, and the drain of the power transistor Power MOS is connected to the first resistor R1. The drive voltage detection circuit is used to monitor the gate voltage of the power transistor Power MOS. When the gate voltage of the power transistor Power MOS is lower than 890mV, the drive voltage detection circuit cuts off the soft start control circuit. The first inverter includes a first transistor MP3, a second transistor MP4, and a third transistor MN5. The gate of the power transistor PowerMOS is connected to the gates of the first transistor MP3, the second transistor MP4, and the third transistor MN5, respectively. The drain of the first transistor MP3 is connected to the source of the second transistor MP4, the drain of the second transistor MP4 is connected to the drain of the third transistor MN5, and the source of the third transistor MN5 is grounded. The second inverter includes a fourth transistor MP5, a fifth transistor MN6, and a sixth transistor MN7. The drain of the second transistor MP4 is connected to the gates of the fourth transistor MP5, the fifth transistor MN6, and the sixth transistor MN7, respectively. The gate of the control transistor MN4 is connected to the drain of the fourth transistor MP5 and the drain of the fifth transistor MN6, respectively. The source of the fifth transistor MN6 is connected to the drain of the sixth transistor MN7. The source of the sixth transistor MN7 is grounded.

[0025] The rail-to-rail operational amplifier includes a complementary differential input circuit, which includes a first input transistor MN8, a second input transistor MP6, a third input transistor MP7, and a fourth input transistor MN9. The source of the first input transistor MN8 is connected to the source of the fourth input transistor MN9, the source of the second input transistor MP6 is connected to the source of the third input transistor MP7, the drain of the discharge transistor MN3 is connected to the gates of the first input transistor MN8 and the second input transistor MP6, respectively, and the gate of the power transistor Power MOS is connected to the gates of the third input transistor MP7 and the fourth input transistor MN9, respectively. The first input transistor MN8 and the fourth input transistor MN9 are N-type transistors, and the second input transistor MP6 and the third input transistor MP7 are P-type transistors. The N-type transistors and the P-type transistors are connected in parallel to extend the input common mode range. When the input voltage (VA terminal) is close to the power supply, the P-type transistor differential pair is turned off and the N-type transistor differential pair is turned on. When the input voltage (VA terminal) is close to zero, the N-type transistor differential pair is turned off and the P-type transistor differential pair is turned on. Rail supports power rail swing, ensuring that the gate voltage of the power MOS tube can still be accurately controlled at low voltage difference, ensuring that the power tube is fully turned on or off, making the voltage change curve smoother.

[0026] The soft start control circuit also includes an enable control circuit, which includes a first enable transistor MP1, a second enable transistor MP2, a third enable transistor MN1, and an inverter INV. The gate of the first enable transistor MP1 is respectively connected to the output terminal of the inverter INV and the gate of the third enable transistor MN1. The drain of the first enable transistor MP1 is respectively connected to the gate of the discharge transistor MN3 and the drain of the third enable transistor MN1. The input terminal of the inverter INV and the gate of the second enable transistor MP2 are respectively connected to a power-on reset signal. The drain of the second enable transistor MP2 is respectively connected to the non-inverting input terminal of the rail-to-rail operational amplifier, the positive terminal VA of the capacitor, and the drain of the discharge transistor MN3. The source of the third enable transistor MN1 and the source of the discharge transistor MN3 are respectively connected to the power ground. The enable control circuit is used to control the initial state of the soft start control circuit before the power is powered on.

[0027] The soft start control circuit also includes a current bias circuit, which includes a reference current source and a current mirror tube MN2. The output terminal IPTAT of the reference current source is connected to the source of the first enabling tube MP1, the drain of the current mirror tube MN2 is connected to the drain of the first enabling tube MP1, the gate of the current mirror tube MN2 is connected to the gate of the discharge tube MN3, and the source of the current mirror tube MN2 and the source of the discharge tube MN3 are respectively connected to the power ground. The current bias circuit is used to control the magnitude of the capacitor discharge current. Example

[0028] like Figures 1 to 3 As shown, a soft start control circuit based on output voltage feedback includes an enable control circuit, a current bias circuit, a buffer circuit, a control circuit, a drive voltage detection circuit and a power tube PowerMOS, wherein the power tube PowerMOS can also be a sampling power tube, and the power tube PowerMOS is used to regulate the output voltage according to its conduction degree.

[0029] The buffer circuit Buffer includes an operational amplifier, which is a rail-to-rail operational amplifier. The non-inverting input terminal of the rail-to-rail operational amplifier is connected to the control circuit, and the gate of the power transistor Power MOS is respectively connected to the inverting input terminal and output terminal of the rail-to-rail operational amplifier. The power transistor Power MOS outputs a voltage VOUT through the drain. The buffer circuit is used to prevent the output voltage from overshooting and make the output voltage curve change smoothly.

[0030] The control circuit includes a capacitor, a control tube MN4, a voltage divider component, and a discharge tube MN3. The positive electrode VA of the capacitor is connected to the drain of the discharge tube MN3 and the non-inverting input terminal of the rail-to-rail operational amplifier. The source of the control tube MN4 is connected to the power ground, and the gate of the control tube MN4 is connected to the drive voltage detection circuit. The control circuit facilitates controlling the soft start time.

[0031] The voltage divider component includes passive or active components. Active components include, but are not limited to, transistors. Passive components include, but are not limited to, resistors. The resistors include a first resistor R1 and a second resistor R2. The soft-start time is set to 145 microseconds. The resistance ratio of the first resistor R1 to the second resistor R2 is 1:3. The negative electrode of the capacitor is connected to one end of the first resistor R1 and one end of the second resistor R2, respectively. The drain of the control transistor MN4 is connected to the other end of the second resistor R2. The other end of the first resistor R1 is connected to the drain of the power transistor Power MOS. Due to the operating range limitations of the rail-to-rail operational amplifier amplification region, the maximum ratio of the resistance value of the second resistor R2 to the total resistance value of the voltage divider component is 75%. If the ratio of the resistance value of the second resistor R2 to the total resistance value of the voltage divider component exceeds 75%, the accuracy of the soft-start time will be affected. The voltage divider component is used to feed back the output voltage VOUT to the capacitor to form a feedback loop. The feedback voltage is equal to 3 / 4*VOUT, thereby achieving slow startup.

[0032] The drive voltage detection circuit includes a first inverter and a second inverter. The output of the first inverter is connected to the input of the second inverter, the input of the first inverter is connected to the gate of the power transistor Power MOS, the output of the second inverter is connected to the gate of the control transistor MN4, and the drain of the power transistor Power MOS is connected to the first resistor R1. The drive voltage detection circuit is used to monitor the gate voltage of the power transistor Power MOS. When the gate voltage of the power transistor Power MOS is lower than 890mV, the drive voltage detection circuit cuts off the soft start control circuit. The first inverter includes a first transistor MP3, a second transistor MP4, and a third transistor MN5. The gate of the power transistor PowerMOS is connected to the gates of the first transistor MP3, the second transistor MP4, and the third transistor MN5, respectively. The drain of the first transistor MP3 is connected to the source of the second transistor MP4, the drain of the second transistor MP4 is connected to the drain of the third transistor MN5, and the source of the third transistor MN5 is grounded. The second inverter includes a fourth transistor MP5, a fifth transistor MN6, and a sixth transistor MN7. The drain of the second transistor MP4 is connected to the gates of the fourth transistor MP5, the fifth transistor MN6, and the sixth transistor MN7, respectively. The gate of the control transistor MN4 is connected to the drain of the fourth transistor MP5 and the drain of the fifth transistor MN6, respectively. The source of the fifth transistor MN6 is connected to the drain of the sixth transistor MN7. The source of the sixth transistor MN7 is grounded.

[0033] The rail-to-rail operational amplifier includes a complementary differential input circuit, which includes a first input transistor MN8, a second input transistor MP6, a third input transistor MP7, and a fourth input transistor MN9. The source of the first input transistor MN8 is connected to the source of the fourth input transistor MN9, the source of the second input transistor MP6 is connected to the source of the third input transistor MP7, the drain of the discharge transistor MN3 is connected to the gates of the first input transistor MN8 and the second input transistor MP6, respectively, and the gate of the power transistor Power MOS is connected to the gates of the third input transistor MP7 and the fourth input transistor MN9, respectively. The first input transistor MN8 and the fourth input transistor MN9 are N-type transistors, and the second input transistor MP6 and the third input transistor MP7 are P-type transistors. The N-type transistors and the P-type transistors are connected in parallel to extend the input common mode range. When the input voltage (VA terminal) is close to the power supply, the P-type transistor differential pair is turned off and the N-type transistor differential pair is turned on. When the input voltage (VA terminal) is close to zero, the N-type transistor differential pair is turned off and the P-type transistor differential pair is turned on. Rail supports power rail swing, ensuring that the gate voltage of the power MOS tube can still be accurately controlled at low voltage difference, ensuring that the power tube is fully turned on or off, making the voltage change curve smoother.

[0034] The soft start control circuit also includes an enable control circuit, which includes a first enable transistor MP1, a second enable transistor MP2, a third enable transistor MN1, and an inverter INV. The gate of the first enable transistor MP1 is respectively connected to the output terminal of the inverter INV and the gate of the third enable transistor MN1. The drain of the first enable transistor MP1 is respectively connected to the gate of the discharge transistor MN3 and the drain of the third enable transistor MN1. The input terminal of the inverter INV and the gate of the second enable transistor MP2 are respectively connected to a power-on reset signal. The drain of the second enable transistor MP2 is respectively connected to the non-inverting input terminal of the rail-to-rail operational amplifier, the positive terminal VA of the capacitor, and the drain of the discharge transistor MN3. The source of the third enable transistor MN1 and the source of the discharge transistor MN3 are respectively connected to the power ground. The enable control circuit is used to control the initial state of the soft start control circuit before the power is powered on.

[0035] The soft start control circuit also includes a current bias circuit, which includes a reference current source and a current mirror tube MN2. The output terminal IPTAT of the reference current source is connected to the source of the first enabling tube MP1, the drain of the current mirror tube MN2 is connected to the drain of the first enabling tube MP1, the gate of the current mirror tube MN2 is connected to the gate of the discharge tube MN3, and the source of the current mirror tube MN2 and the source of the discharge tube MN3 are respectively connected to the power ground. The current bias circuit is used to control the magnitude of the capacitor discharge current. Example

[0036] like Figures 1 to 3 As shown, a soft start control circuit based on output voltage feedback includes an enable control circuit, a current bias circuit, a buffer circuit, a control circuit, a drive voltage detection circuit and a power tube PowerMOS, wherein the power tube PowerMOS can also be a sampling power tube, and the power tube PowerMOS is used to regulate the output voltage according to its conduction degree.

[0037] The buffer circuit Buffer includes an operational amplifier, which is a rail-to-rail operational amplifier. The non-inverting input terminal of the rail-to-rail operational amplifier is connected to the control circuit, and the gate of the power transistor Power MOS is respectively connected to the inverting input terminal and output terminal of the rail-to-rail operational amplifier. The power transistor Power MOS outputs a voltage VOUT through the drain. The buffer circuit is used to prevent the output voltage from overshooting and make the output voltage curve change smoothly.

[0038] The control circuit includes a capacitor, a control tube MN4, a voltage divider component, and a discharge tube MN3. The positive electrode VA of the capacitor is connected to the drain of the discharge tube MN3 and the non-inverting input terminal of the rail-to-rail operational amplifier. The source of the control tube MN4 is connected to the power ground, and the gate of the control tube MN4 is connected to the drive voltage detection circuit. The control circuit facilitates controlling the soft start time.

[0039] The voltage divider component includes passive components or active components. Active components include but are not limited to transistors. Passive components include but are not limited to resistors. The resistors include a first resistor R1 and a second resistor R2. The soft start time is set to 130 microseconds. The resistance ratio of the first resistor R1 and the second resistor R2 is 1:2. The negative electrode of the capacitor is connected to one end of the first resistor R1 and one end of the second resistor R2, respectively. The drain of the control tube MN4 is connected to the other end of the second resistor R2, and the other end of the first resistor R1 is connected to the drain of the power tube Power MOS. The voltage divider component is used to feed back the output voltage VOUT to the capacitor to form a feedback loop. The feedback voltage is equal to 2 / 3*VOUT to achieve medium-speed startup.

[0040] The drive voltage detection circuit includes a first inverter and a second inverter. The output of the first inverter is connected to the input of the second inverter, the input of the first inverter is connected to the gate of the power transistor Power MOS, the output of the second inverter is connected to the gate of the control transistor MN4, and the drain of the power transistor Power MOS is connected to the first resistor R1. The drive voltage detection circuit is used to monitor the gate voltage of the power transistor Power MOS. When the gate voltage of the power transistor Power MOS is lower than 890mV, the drive voltage detection circuit cuts off the soft start control circuit. The first inverter includes a first transistor MP3, a second transistor MP4, and a third transistor MN5. The gate of the power transistor PowerMOS is connected to the gates of the first transistor MP3, the second transistor MP4, and the third transistor MN5, respectively. The drain of the first transistor MP3 is connected to the source of the second transistor MP4, the drain of the second transistor MP4 is connected to the drain of the third transistor MN5, and the source of the third transistor MN5 is grounded. The second inverter includes a fourth transistor MP5, a fifth transistor MN6, and a sixth transistor MN7. The drain of the second transistor MP4 is connected to the gates of the fourth transistor MP5, the fifth transistor MN6, and the sixth transistor MN7, respectively. The gate of the control transistor MN4 is connected to the drain of the fourth transistor MP5 and the drain of the fifth transistor MN6, respectively. The source of the fifth transistor MN6 is connected to the drain of the sixth transistor MN7. The source of the sixth transistor MN7 is grounded.

[0041] The rail-to-rail operational amplifier includes a complementary differential input circuit, which includes a first input transistor MN8, a second input transistor MP6, a third input transistor MP7, and a fourth input transistor MN9. The source of the first input transistor MN8 is connected to the source of the fourth input transistor MN9, the source of the second input transistor MP6 is connected to the source of the third input transistor MP7, the drain of the discharge transistor MN3 is connected to the gates of the first input transistor MN8 and the second input transistor MP6, respectively, and the gate of the power transistor Power MOS is connected to the gates of the third input transistor MP7 and the fourth input transistor MN9, respectively. The first input transistor MN8 and the fourth input transistor MN9 are N-type transistors, and the second input transistor MP6 and the third input transistor MP7 are P-type transistors. The N-type transistors and the P-type transistors are connected in parallel to extend the input common mode range. When the input voltage (VA terminal) is close to the power supply, the P-type transistor differential pair is turned off and the N-type transistor differential pair is turned on. When the input voltage (VA terminal) is close to zero, the N-type transistor differential pair is turned off and the P-type transistor differential pair is turned on. Rail supports power rail swing, ensuring that the gate voltage of the power MOS tube can still be accurately controlled at low voltage difference, ensuring that the power tube is fully turned on or off, making the voltage change curve smoother.

[0042] The soft start control circuit also includes an enable control circuit, which includes a first enable transistor MP1, a second enable transistor MP2, a third enable transistor MN1, and an inverter INV. The gate of the first enable transistor MP1 is respectively connected to the output terminal of the inverter INV and the gate of the third enable transistor MN1. The drain of the first enable transistor MP1 is respectively connected to the gate of the discharge transistor MN3 and the drain of the third enable transistor MN1. The input terminal of the inverter INV and the gate of the second enable transistor MP2 are respectively connected to a power-on reset signal. The drain of the second enable transistor MP2 is respectively connected to the non-inverting input terminal of the rail-to-rail operational amplifier, the positive terminal VA of the capacitor, and the drain of the discharge transistor MN3. The source of the third enable transistor MN1 and the source of the discharge transistor MN3 are respectively connected to the power ground. The enable control circuit is used to control the initial state of the soft start control circuit before the power is powered on.

[0043] The soft start control circuit also includes a current bias circuit, which includes a reference current source and a current mirror tube MN2. The output terminal IPTAT of the reference current source is connected to the source of the first enabling tube MP1, the drain of the current mirror tube MN2 is connected to the drain of the first enabling tube MP1, the gate of the current mirror tube MN2 is connected to the gate of the discharge tube MN3, and the source of the current mirror tube MN2 and the source of the discharge tube MN3 are respectively connected to the power ground. The current bias circuit is used to control the magnitude of the capacitor discharge current.

[0044] The working method of this embodiment is as follows: the power-on reset signal POR controls the gates of the first enable transistor, the second enable transistor, and the third enable transistor. Before power is applied, the power-on reset signal POR is at a low level, the first enable transistor MP1 is turned off, the third enable transistor MN1 is turned on, and the gate of the current mirror transistor MN2 is pulled to a low level, turning off the current mirror transistor MN2, thereby preventing the reference current IPTAT from being mirrored to the discharge transistor MN3. Because the power-on reset signal POR is at a low level, the second enable transistor MP2 is turned on, and the positive electrode VA of the capacitor is initially pulled to a high level by the second enable transistor MP2. Due to the rail-to-rail operation of the operational amplifier, the gate voltage DRV (the inverting input port of the operational amplifier) ​​of the power transistor POWER MOS follows the change of VA (the non-inverting input port of the operational amplifier), and the power transistor POWER MOS is in an off state.

[0045] After the power is turned on, the power-on reset signal POR turns on the first enable transistor MP1, the current mirror transistor MN2 stops pulling down, the second enable transistor MP2 and the third enable transistor MN1 are turned off, and the reference current IPTAT flows through the first enable transistor MP1 to the drain of the current mirror transistor MN2, thereby mirroring the reference current IPTAT to the discharge transistor MN3. The second enable transistor MP2 stops pulling up the node of the capacitor positive electrode VA, and the current of the discharge transistor MN3 discharges the node of the capacitor positive electrode VA. The voltage level of the capacitor positive electrode VA is pulled down, and the gate voltage level of the power transistor POWER MOS is also pulled down, so that the power transistor POWER MOS slowly turns on. The output voltage Vout of the power MOS tube is fed back to the negative electrode of the capacitor to form a closed-loop control. Since the resistance ratio of the first resistor R1 to the second resistor R2 is 1:2, the feedback voltage fed back to the capacitor is 2 / 3*VOUT. Since the voltage across the capacitor cannot change suddenly, the capacitor discharges slowly, and the voltage at the positive terminal VA of the capacitor slowly decreases. When the drive voltage detection circuit detects that the gate voltage DRV of the power tube POWER MOS drops to 890mV, the drive voltage detection circuit pulls down the gate voltage SSC of the control tube MN4, thereby shutting down the soft-start control loop. The negative electrode of the capacitor will be directly coupled to the drain of the power tube POWER MOS, and the output voltage VOUT will hardly change. At this time, the positive electrode VA of the capacitor will accelerate the discharge speed, and the power tube POWER MOS will be fully turned on, completing the soft-start process.

[0046] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A soft start control circuit based on output voltage feedback, characterized in that: The soft start control circuit includes: A buffer circuit, the buffer circuit including an operational amplifier; the buffer circuit is used to prevent the output voltage from overshooting and make the output voltage curve change smoothly; A control circuit includes a capacitor, a control tube, a voltage divider component, and a discharge tube. The capacitor is connected to the drain of the discharge tube and the operational amplifier, and the voltage divider component is connected to the capacitor and the control tube respectively. The control circuit is used to control the soft start time, and the voltage divider component is used to feed back the output voltage to the capacitor to form a feedback loop.

2. The soft-start control circuit based on output voltage feedback according to claim 1, wherein: The operational amplifier includes a rail-to-rail operational amplifier, and the capacitor is connected to the drain of the discharge tube and the non-inverting input terminal of the rail-to-rail operational amplifier respectively.

3. The soft-start control circuit based on output voltage feedback according to claim 2, wherein: The soft start control circuit further includes a power tube, the gate of which is respectively connected to the inverting input terminal and the output terminal of the rail-to-rail operational amplifier; the power tube is used to adjust the output voltage according to its conduction degree.

4. The soft-start control circuit based on output voltage feedback according to claim 3, wherein: The voltage divider component includes a passive element or an active element, the passive element includes a resistor, the resistor includes a first resistor and a second resistor, the capacitor is connected to the first resistor and the second resistor respectively, the drain of the control tube is connected to the second resistor, and the first resistor is connected to the drain of the power tube.

5. The gate voltage driving circuit based on voltage feedback according to claim 4, characterized in that: According to the soft start time, the resistance ratio of the first resistor to the second resistor is adjusted; the resistance ratio of the first resistor to the second resistor is 1:(1-3).

6. The soft-start control circuit based on output voltage feedback according to claim 3, wherein: The soft start control circuit further includes a drive voltage detection circuit, the drive voltage detection circuit including a first inverter and a second inverter, the output end of the first inverter is connected to the input end of the second inverter, the input end of the first inverter is connected to the gate of the power tube, the output end of the second inverter is connected to the gate of the control tube, and the drain of the power tube is connected to the first resistor; The driving voltage detection circuit is used to monitor the gate voltage of the power tube. When the gate voltage of the power tube is lower than a preset threshold voltage, the driving voltage detection circuit disconnects the soft start control circuit.

7. The soft-start control circuit based on output voltage feedback according to claim 6, wherein: The first inverter includes a first transistor, a second transistor, and a third transistor, the gate of the power transistor is connected to the gates of the first transistor, the second transistor, and the third transistor respectively, the drain of the first transistor is connected to the source of the second transistor, and the drain of the second transistor is connected to the drain of the third transistor; The second inverter includes a fourth transistor, a fifth transistor and a sixth transistor, the drain of the second transistor is connected to the gates of the fourth transistor, the fifth transistor and the sixth transistor respectively, the gate of the control tube is connected to the drain of the fourth transistor and the drain of the fifth transistor respectively, and the source of the fifth transistor is connected to the drain of the sixth transistor.

8. The soft-start control circuit based on output voltage feedback according to claim 3, wherein: The rail-to-rail operational amplifier includes a complementary differential input circuit, which includes a first input tube, a second input tube, a third input tube, and a fourth input tube. The source of the first input tube is connected to the source of the fourth input tube, the source of the second input tube is connected to the source of the third input tube, the drain of the discharge tube is connected to the gates of the first and second input tubes, respectively, and the gate of the power tube is connected to the gates of the third and fourth input tubes, respectively. The first and fourth input tubes are both N-type transistors, and the second and third input tubes are both P-type transistors.

9. The soft-start control circuit based on output voltage feedback according to claim 1, wherein: The soft start control circuit also includes an enable control circuit, which includes a first enable transistor, a second enable transistor, a third enable transistor, and an inverter. The gate of the first enable transistor is respectively connected to the output terminal of the inverter and the gate of the third enable transistor, the drain of the first enable transistor is respectively connected to the gate of the discharge transistor and the drain of the third enable transistor, the input terminal of the inverter and the gate of the second enable transistor are respectively connected to a power-on reset signal, the drain of the second enable transistor is respectively connected to the operational amplifier, the capacitor, and the drain of the discharge transistor, and the source of the third enable transistor and the source of the discharge transistor are respectively connected to a power ground. The enable control circuit is used to control the initial state of the soft start control circuit before power is applied.

10. The soft-start control circuit based on output voltage feedback according to claim 9, characterized in that: The soft start control circuit also includes a current bias circuit, which includes a reference current source and a current mirror tube. The output end of the reference current source is connected to the source of the first enabling tube, the drain of the current mirror tube is connected to the drain of the first enabling tube, the gate of the current mirror tube is connected to the gate of the discharge tube, and the source of the current mirror tube is connected to the power ground. The current bias circuit is used to control the magnitude of the capacitor discharge current.

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