A soft start circuit

Abstract

The present invention provides a soft start circuit, which relates to the technical field of integrated circuits, including an on-off control circuit and a voltage ramp-up circuit, wherein the on-off control terminal of the on-off control circuit is connected to the charging control terminal of the voltage ramp-up circuit, and the voltage output terminal of the voltage ramp-up circuit is connected to an external device to be started; the on-off control circuit is used to control the intermittent conduction of the charging control terminal of the voltage ramp-up circuit to perform slow charging, and provide a slowly rising starting voltage to the device to be started to achieve soft start. The beneficial effect is that the current of the constant current power supply in the voltage ramp-up circuit does not need to be very small, and normal operation can be guaranteed under high temperature or other conditions of large interference. In high temperature or large interference situations, the soft start circuit can work normally, thereby improving the reliability of the entire circuit. The circuit has the characteristics of simple structure, small layout area, good scalability, high reliability, etc., and can be widely used in analog integrated circuits that require soft start circuits.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and in particular to a soft start circuit. Background Art

[0002] With the continuous development and progress of semiconductor technology, many integrated circuits are now widely implemented using low-voltage process technology. These circuits are extremely sensitive to input voltage. Once the input voltage exceeds the rated value, these circuits may be damaged. Therefore, the power output or power conversion integrated circuits that power these circuits require a soft-start mechanism during the startup process to ensure that the output voltage can rise slowly and smoothly, thereby effectively preventing the output voltage from exceeding the rated value.

[0003] There are many ways to implement soft start circuits, which can be mainly divided into two categories: analog soft start and digital soft start. The digital soft start circuit uses a digital signal to control the gradual increase of the reference voltage, thereby achieving a gradual increase in the output voltage. This implementation method has many specific forms. For example, the reference voltage can be divided by multiple resistors to achieve a phased increase in the output voltage. However, this method requires the use of more resistors and requires precise matching between resistors, which usually requires complex wiring, or even multi-layer wiring, which occupies a large layout area and is not conducive to achieving high integration.

[0004] On the other hand, analog soft-start circuits mainly use resistors or constant currents to charge capacitors to achieve soft-start. This method is very suitable when the soft-start time is short. However, if a long soft-start is required, a larger resistor or capacitor will be required, which will also occupy a larger layout area and is not conducive to integration. If a smaller capacitor is chosen, a smaller charging current is required, but in high temperature or high interference environments, the capacitor is prone to leakage, which will cause the soft-start to fail and the circuit to not work properly. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a soft start circuit, including an on-off control circuit and a voltage ramp-up circuit, wherein the on-off control end of the on-off control circuit is connected to the charging control end of the voltage ramp-up circuit, and the voltage output end of the voltage ramp-up circuit is connected to an external device to be started; the on-off control circuit is used to control the intermittent conduction of the charging control end of the voltage ramp-up circuit to perform slow charging, thereby providing a slowly rising starting voltage to the device to be started to achieve soft start.

[0006] Preferably, the on-off control circuit includes: a ring oscillation circuit, the signal output end of the ring oscillation circuit is connected to the input end of a signal inverter, and the signal output end of the ring oscillation circuit and the output end of the signal inverter are connected to the charging control end of the voltage ramp-up circuit.

[0007] Preferably, the ring oscillation circuit comprises: three inverters whose input and output ends are connected in series in sequence, a capacitor is connected between the output end of the first inverter and the input end of the second inverter, and the output end of the third inverter is connected to the input end of the signal inverter.

[0008] Preferably, the voltage ramp-up circuit includes: a constant current power supply, wherein the power supply end of the constant current power supply is respectively connected to the source of the first PMOS tube and the source of the second PMOS tube, and the gate of the first PMOS tube and the gate of the second PMOS tube are connected to the on-off control end of the on-off control circuit; a soft start capacitor, wherein the upper plate of the soft start capacitor is connected to the drain of the second PMOS tube, the lower plate of the soft start capacitor is connected to the drain of the first PMOS tube and the drain of the first NMOS tube, the source of the first NMOS tube is grounded, and the drain and gate of the first NMOS tube are short-circuited; a second NMOS tube, wherein the gate of the second NMOS tube is connected to the upper plate of the soft start capacitor, the drain of the second NMOS tube is connected to a voltage source, and the source of the second NMOS tube is connected to an external device to be started.

[0009] Preferably, it also includes a voltage divider circuit, which is connected between the voltage output end of the voltage ramp-up circuit and an external device to be started, and is used to adjust the starting voltage output by the voltage ramp-up circuit to adjust the soft start time.

[0010] Preferably, the voltage divider circuit includes: a first resistor, one end of the first resistor is connected to the voltage output end of the voltage ramp-up circuit and a first filter capacitor, the other end of the first resistor is respectively connected to one end of a second resistor and one end of a third resistor, the other end of the third resistor is connected to a second filter capacitor and an external device to be started.

[0011] Preferably, a third NMOS tube is further included, wherein the drain of the third NMOS tube is connected to the upper plate connected to the soft-start capacitor, the source of the third NMOS tube is grounded, and the gate of the third NMOS tube receives a discharge enable signal.

[0012] The above technical solution has the following advantages or beneficial effects: the on-off control circuit controls the intermittent conduction of the charging control terminal of the voltage ramp circuit to perform slow charging, and provides a slowly rising starting voltage to the starting device to achieve soft starting. Therefore, the current of the constant current power supply in the voltage ramp circuit does not need to be very small, and it can ensure normal operation under high temperature or other conditions of large interference. The soft start circuit can work normally in high temperature or large interference situations, thereby improving the reliability of the entire circuit. The circuit has the characteristics of simple structure, small layout area, good scalability, high reliability, etc., and can be widely used in analog integrated circuits that require soft start circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is an existing conventional soft start circuit;

[0014] Figure 2 A structural schematic diagram of a soft start circuit in a preferred embodiment of the present invention;

[0015] Figure 3 It is a structural schematic diagram of an on-off control circuit in a preferred embodiment of the present invention;

[0016] Figure 4 It is a schematic diagram of the structure of a voltage ramp-up circuit and a voltage divider circuit in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0017] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The present invention is not limited to this embodiment, and other embodiments may also fall within the scope of the present invention as long as they conform to the gist of the present invention.

[0018] In a preferred embodiment of the present invention, based on the above-mentioned problems existing in the prior art, a soft start circuit is provided, including an on-off control circuit 1 and a voltage ramp-up circuit 2, wherein the on-off control end of the on-off control circuit 1 is connected to the charging control end of the voltage ramp-up circuit 2, and the voltage output end of the voltage ramp-up circuit 2 is connected to an external device to be started 3; the on-off control circuit 1 is used to control the intermittent conduction of the charging control end of the voltage ramp-up circuit 2 to perform slow charging, thereby providing a slowly rising starting voltage to the device to be started 3 to achieve soft start.

[0019] like Figure 1As shown, it is a conventional soft start circuit in the prior art, wherein I0 is a constant current source, C0 is a soft start capacitor, Q0 is an enable tube, and Q0 is turned on when the circuit is not working to discharge C0. When the circuit is working, Q0 is turned off, and the constant current source I0 charges the soft start capacitor C0, so that the output voltage Vo rises slowly to achieve the soft start function. Due to the area factor in the integrated circuit, the capacitor C0 cannot be too large, so the constant current source current can only be reduced to achieve a slow increase in Vo, but if the current is too small, it will cause the Q0 leakage current to be greater than the constant current source current under high temperature or large interference, so that the capacitor C0 cannot complete the charging, and the soft start circuit cannot work normally. If the constant current source current is increased, it is necessary to increase the area of ​​the soft start capacitor at the same time to achieve the soft start function.

[0020] In view of the above problems existing in the prior art, the present invention provides a highly reliable soft start circuit. Figure 2 The circuit shown includes an on-off control circuit 1 and a voltage ramp-up circuit 2. The on-off control circuit 1 controls the intermittent conduction of the charging control terminal of the voltage ramp-up circuit 2 to perform slow charging, and provides a slowly rising starting voltage to the starting device 3 to achieve soft starting. Therefore, the current of the constant current power supply in the voltage ramp-up circuit 2 does not need to be very small, and it can ensure normal operation under high temperature or other conditions of large interference. In high temperature or large interference situations, the soft start circuit can work normally, thereby improving the reliability of the entire circuit. The circuit has the characteristics of simple structure, small layout area, good scalability, high reliability, etc., and can be widely used in analog integrated circuits that require soft start circuits.

[0021] In a preferred embodiment of the present invention, the on-off control circuit 1 includes: a ring oscillation circuit 11, the signal output end of the ring oscillation circuit 11 is connected to the input end of a signal inverter I4, and the signal output end of the ring oscillation circuit 11 and the output end of the signal inverter I4 are connected to the charging control end of the voltage ramp-up circuit 2.

[0022] In a preferred embodiment of the present invention, the ring oscillation circuit 11 includes: three inverters I1, I2, and I3 whose input and output ends are connected in series in sequence, a capacitor C1 is connected between the output end of the first inverter I1 and the input end of the second inverter I2, and the output end of the third inverter I3 is connected to the input end of the signal inverter I4.

[0023] Specifically, Figure 3As shown, the on-off control circuit is composed of 4 inverters and a capacitor C1, wherein the inverter I1, the inverter I2, the inverter I3 and the capacitor C1 form a ring oscillation circuit, outputting CLK1, and the signal inverter I4 outputs CLK2, which is opposite in phase to CLK1. The ring oscillation circuit outputs a clock signal CLK1 with a very small high-level duty cycle, and the high-level duty cycle is D. CLK2 is the inverted signal of CLK1, and is a clock signal with a very small low-level duty cycle, so its low-level duty cycle is D. When the signal CLK2 is at a low level, the charging control terminal of the voltage ramp-up circuit is turned on for charging. Through this intermittent conduction mode, the slow charging is controlled to provide a slowly rising starting voltage to the device to be started to achieve soft start.

[0024] In a preferred embodiment of the present invention, the voltage ramp-up circuit 2 includes: a constant current power supply I5, the power supply end of the constant current power supply I5 is respectively connected to the source of the first PMOS tube Q1 and the source of the second PMOS tube Q2, the gate of the first PMOS tube Q1 and the gate of the second PMOS tube Q2 are connected to the on-off control end of the on-off control circuit 1; a soft start capacitor C2, the upper plate of the soft start capacitor C2 is connected to the drain of the second PMOS tube Q2, the lower plate of the soft start capacitor C2 is connected to the drain of the first PMOS tube Q1 and the drain of the first NMOS tube Q3, the source of the first NMOS tube Q3 is grounded, and the drain and gate of the first NMOS tube Q3 are short-circuited; a second NMOS tube Q4, the gate of the second NMOS tube Q4 is connected to the upper plate of the soft start capacitor C2, the drain of the second NMOS tube Q4 is connected to the voltage source VDD, and the source of the second NMOS tube Q4 is connected to the external device 3 to be started.

[0025] Specifically, in this embodiment, Figure 4 As shown, the voltage slow-rise circuit 2 is composed of a constant current power supply I5, a first PMOS transistor Q1, a second PMOS transistor Q2, a first NMOS transistor Q3, a second NMOS transistor Q4, and a soft-start capacitor C2.

[0026] The constant current power supply I5 provides a stable and reliable constant current with a current value of I. The first PMOS tube Q1 is turned on or off by CLK1, and the second PMOS tube Q2 is turned on or off by CLK2.

[0027] The soft start capacitor C2 has a capacitance of C, and its upper plate is used as a voltage output to control the gate of the second NMOS transistor Q4.

[0028] The source of the first NMOS transistor Q3 is grounded, and the gate and drain of the first NMOS transistor Q3 are short-circuited and connected to the lower plate of the soft-start capacitor C2.

[0029] CLK1 and CLK2 are anti-phase signals, so that the first PMOS tube Q1 and the second PMOS tube Q2 are alternately turned on. When the second PMOS tube Q2 is turned on, the soft-start capacitor C2 is charged. Since CLK2 is a low-level signal with a very small duty cycle, the charging current of the soft-start capacitor C2 is very small. Under the action of CLK1 and CLK2, the first PMOS tube Q1 and the second PMOS tube Q2 are alternately turned on, so that the upper plate voltage of the soft-start capacitor C2 gradually increases, and the source voltage of the second NMOS tube Q4 gradually increases, thereby providing a slowly increasing starting voltage to the starting device 3 to achieve soft starting.

[0030] The current for charging the soft-start capacitor C2 is reduced by the conduction time proportion D of the second PMOS tube Q2, so the current I of the constant current power supply I5 does not need to be very small, and normal operation can be guaranteed under high temperature or other large interference conditions.

[0031] In a preferred embodiment of the present invention, a voltage divider circuit 4 is further included, which is connected between the voltage output terminal A of the voltage ramp-up circuit 2 and the external device to be started 3, and is used to adjust the starting voltage output by the voltage ramp-up circuit 2 to adjust the soft start time.

[0032] In a preferred embodiment of the present invention, the voltage divider circuit 4 includes: a first resistor R1, one end of the first resistor R1 is connected to the voltage output end of the voltage ramp-up circuit 2 and the first filter capacitor C3, the other end of the first resistor R1 is respectively connected to one end of the second resistor R2 and one end of the third resistor R3, and the other end V0 of the third resistor R3 is connected to the second filter capacitor C4 and the external device to be started 3.

[0033] Specifically, in this embodiment, Figure 4 As shown, it also includes a voltage divider circuit 4, which is composed of a first filter capacitor C3, a resistor R1, a resistor R2, a resistor R3, and a second filter capacitor C4.

[0034] The source voltage of the second NMOS tube Q4 gradually increases, and after the voltage is divided by the resistor R1 and the resistor R2, it is filtered by the resistor R3 and the second filter capacitor C4 to output a slowly rising voltage, thereby realizing the soft start circuit function. In addition, by adjusting the voltage division ratio of the resistor R1 and the resistor R2, the soft start time can be further adjusted, so the duty cycle of the constant current source or the charging can be increased, thereby further improving the reliability of the soft start circuit.

[0035] In a preferred embodiment of the present invention, a third NMOS transistor Q5 is further included, the drain of the third NMOS transistor Q5 is connected to the upper plate of the soft start capacitor C2, the source of the third NMOS transistor Q5 is grounded, and the gate of the third NMOS transistor Q5 receives the discharge enable signal EN.

[0036] Specifically, in this embodiment, Figure 4 As shown, the third NMOS tube Q5 is also included. The third NMOS tube Q5 is a discharge tube. When the circuit is not working, it is turned on to discharge the soft start capacitor C2.

[0037] It can be seen from all the above embodiments that the soft start circuit of the present invention uses fewer electronic components, has the characteristics of simple structure, small footprint, good scalability, high reliability, etc., and can be widely used in analog integrated circuits that require soft start circuits.

[0038] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of this specification and illustrations should be included in the protection scope of the present invention.

Claims

1. A soft start circuit, characterized in that: It includes an on-off control circuit and a voltage ramp-up circuit, wherein the on-off control terminal of the on-off control circuit is connected to the charging control terminal of the voltage ramp-up circuit, and the voltage output terminal of the voltage ramp-up circuit is connected to an external device to be started; The voltage ramp-up circuit comprises: A constant current power supply, wherein the power supply end of the constant current power supply is respectively connected to the source of the first PMOS tube and the source of the second PMOS tube, the on-off control end of the on-off control circuit includes a first control end and a second control end, the gate of the first PMOS tube is connected to the first control end, the gate of the second PMOS tube is connected to the second control end, and the signals output by the first control end and the second control end are inverted; A soft-start capacitor, wherein the upper plate of the soft-start capacitor is connected to the drain of the second PMOS tube, the lower plate of the soft-start capacitor is connected to the drain of the first PMOS tube and the drain of the first NMOS tube, the source of the first NMOS tube is grounded, and the drain and gate of the first NMOS tube are short-circuited; a second NMOS tube, wherein the gate of the second NMOS tube is connected to the upper plate of the soft-start capacitor, the drain of the second NMOS tube is connected to a voltage source, and the source of the second NMOS tube is connected to an external device to be started; The on-off control circuit is used to control the intermittent conduction of the charging control terminal of the voltage slow-rise circuit to perform slow charging, and provide a slowly rising starting voltage to the device to be started to achieve soft starting.

2. The soft start circuit according to claim 1, characterized in that: The on-off control circuit comprises: A ring oscillation circuit, wherein the signal output end of the ring oscillation circuit is connected to the input end of a signal inverter, and the signal output end of the ring oscillation circuit and the output end of the signal inverter are connected to the charging control end of the voltage ramp-up circuit.

3. The soft start circuit according to claim 2, characterized in that: The ring oscillator circuit comprises: Three inverters with input terminals and output terminals connected in series in sequence, a capacitor is connected between the output terminal of the first inverter and the input terminal of the second inverter, and the output terminal of the third inverter is connected to the input terminal of the signal inverter.

4. The soft start circuit according to claim 1, characterized in that: It also includes a voltage divider circuit, which is connected between the voltage output end of the voltage ramp-up circuit and an external device to be started, and is used to adjust the starting voltage output by the voltage ramp-up circuit to adjust the soft start time.

5. The soft start circuit according to claim 4, characterized in that: The voltage divider circuit comprises: A first resistor, one end of the first resistor is connected to the voltage output end of the voltage ramp-up circuit and the first filter capacitor, the other end of the first resistor is respectively connected to one end of the second resistor and one end of the third resistor, the other end of the third resistor is connected to the second filter capacitor and an external device to be started.

6. The soft start circuit according to claim 1, characterized in that: It also includes a third NMOS tube, the drain of the third NMOS tube is connected to the upper plate of the soft start capacitor, the source of the third NMOS tube is grounded, and the gate of the third NMOS tube receives a discharge enable signal.

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