CN110018707B - Low dropout linear regulator circuit with overcurrent protection - Google Patents

Abstract

The invention discloses a low dropout regulator circuit with an overcurrent protection function. The invention comprises a voltage stabilizer part, a current detection part and a current control part, and has the technical effects of high sampling precision and good circuit stability. The invention adopts the current-voltage conversion type sampling circuit instead of the sampling resistor, thereby avoiding the problems that the sampling resistor is easily influenced by temperature and process and the like. The sampling stability is good. The sampling structure of the source follower adopted by the invention can inhibit the change of the sampling over-current threshold value caused by the change of the output voltage, and can ensure that the input voltage range of the LDO is wider. The circuit structure is simple. And the foldback type working mode is adopted, so that the overcurrent protection capability can be effectively enhanced.

Description

Low dropout linear regulator circuit with overcurrent protection

technical field

The invention relates to a low-dropout linear voltage regulator circuit with overcurrent protection function.

Background technique

Nowadays, all kinds of portable electronic devices represented by smart phones are developing rapidly, and they play an important role in the economy and society. Power management chips with excellent performance are the foundation of advanced portable electronic devices and the basic requirements to ensure the normal operation of electronic systems. External power supplies inevitably contain high-frequency noise or ripple voltages. These high frequency noise voltages usually propagate through the electronic system through coupling capacitors, DC paths. When the amplitude of the noise signal is comparable to the normal signal, the electronic system cannot function properly. The main function of the power management chip is to reduce the high-frequency noise in the power supply of the electronic system, improve the power supply rejection ratio, and suppress the influence of the output load current change on the power supply voltage.

Common power management chips include switching power supply DC-DC and low dropout linear regulators (LDOs). Although the switching power supply has the advantages of high efficiency, due to the need for an external inductor or transformer, it has problems such as large switching noise and bulky circuit. LDO linear regulators have been more and more widely used because of their advantages of high integration, low noise, low quiescent current and simple structure.

The protection measures of the power supply are very important to the whole electronic system, such as overvoltage, overcurrent, overheating protection, etc. When an electronic product fails, such as a short circuit on the input side or an open circuit on the output side, the power supply must disconnect its output voltage to avoid the burnout of the power and output side equipment. However, it is not suitable to directly turn off the power supply, and the circuit must be able to resume operation after the overcurrent event is removed. Therefore, designing an overcurrent protection structure that does not affect the normal operation of the LDO is very important for the design of the power circuit of the portable electronic device.

SUMMARY OF THE INVENTION

The main technical problem solved by the present invention is to provide a low-dropout linear voltage stabilizer circuit with overcurrent protection function suitable for LDO voltage stabilizer, the function of which is to detect the overcurrent state of the LDO and adaptively reduce the power tube to avoid damage to the power tube due to long-term high current in the overcurrent protection stage.

In order to realize the above-mentioned technical purpose, the technical scheme of the present invention is:

A low-dropout linear voltage stabilizer circuit with overcurrent protection function includes a voltage stabilizer part and an overcurrent protection part, the voltage stabilizer part includes a voltage reference source, an error amplifier, a power tube and a feedback resistor, the The voltage reference source is connected to the error amplifier and the overcurrent protection part to provide the reference voltage, the error amplifier, the feedback resistor, the power tube and the overcurrent protection part are connected to each other, and the power tube provides the power supply for driving the load, The feedback resistor collects the output voltage of the power tube and feeds it back to the error amplifier, and the error amplifier adjusts the conduction current of the power tube by obtaining the feedback information from the feedback resistor; the overcurrent protection part includes a current detection unit and a current control unit , the current detection unit is connected to the power tube to monitor the current of the power tube and send the monitored information to the current control unit, the current control unit clamps the power tube when overcurrent occurs and the current of the power tube is greater than the first threshold The voltage is kept stable so that the current does not increase, and when the power tube current is greater than the second threshold value, the power tube voltage is pulled up to decrease the current, wherein the second threshold value is greater than the first threshold value.

The described low-dropout linear voltage regulator circuit with overcurrent protection function, the current control unit includes a "folded" protection circuit for clamping the voltage of the power tube to keep stable, and a protection circuit for pulling up the voltage of the power tube. "Back-type" protection circuit, the "fold-type" protection circuit is connected to the power tube and the current detection unit, and is activated by the current detection unit when the current of the power tube is greater than the first threshold, forming a relationship between the power tube and the current detection unit The negative feedback loop is used to clamp the voltage of the power tube to keep the voltage stable. The "return" protection circuit is connected to the "folded" protection circuit and the power tube, and is started by the power tube when the current of the power tube is greater than the second threshold, and the power tube is pulled up. voltage to reduce the current.

The described low-dropout linear voltage regulator circuit with overcurrent protection function, the current detection unit includes a second transistor M2, a third transistor M3 and an overcurrent detection voltage comparator AP, the second transistor The gate and drain of M2 are coupled to the input voltage source VCC, and the source is coupled to the fourth node n4; the gate of the third transistor M3 is coupled to the second reference voltage source V _ref2 , and the drain is coupled to the fourth node n4, the source is coupled to the ground level GND; the positive phase input terminal of the overcurrent detection voltage comparator AP is coupled to the fourth node n2, the negative phase input terminal is coupled to the fourth node n4, and the output terminal is coupled to the fifth node n4 node n5;

The described low-dropout linear voltage regulator circuit with overcurrent protection function, the "folded" protection circuit includes a fourth transistor M4, and the gate of the fourth transistor M4 is coupled to the fifth node n5 , the source is coupled to the input voltage source VCC, and the drain is coupled to the second node n2.

The described low-dropout linear voltage regulator circuit with overcurrent protection function, the "return type" protection circuit includes a fifth transistor M5, a sixth transistor M6 and a third resistor R3, the fifth transistor The gate of M5 is coupled to the sixth node n6, the source is coupled to the input voltage source VCC, the drain is coupled to the second node n2, the gate of the sixth transistor M6 is coupled to the third reference voltage source _Vref3 , the source The pole is coupled to the input voltage source VCC, the drain is coupled to the third node n3, and the third resistor R3 is coupled between the sixth node n6 and the input voltage source VCC.

The described low-dropout linear voltage regulator circuit with overcurrent protection function, the fifth transistor M5, the sixth transistor M6, the seventh transistor M7, the eighth transistor M8, the ninth transistor M5, the sixth transistor M6, the seventh transistor M7, the eighth transistor M8, the ninth transistor M9, a third resistor R3 and a fourth resistor R4; the gate of the fifth transistor M5 is coupled to the sixth node n6, the source is coupled to the input voltage source VCC, and the drain is coupled to the second node n2; the The gate of the sixth transistor M6 is coupled to the gate of the ninth transistor M9, the source is coupled to the third node n3, and the drain is coupled to the sixth node n6; the gate of the seventh transistor M7 is coupled to the second Node n2, the source is coupled to the input voltage source VCC, and the drain is coupled to the source of the eighth transistor M8; the gate of the eighth transistor M8 is coupled to the third node n3, and the drain is coupled to the ninth transistor M9. drain; the drain and gate of the ninth transistor M9 are also coupled to the gate of the sixth transistor M6, and the source is coupled to the ground level GND after being connected in series with the fourth resistor R4; the third resistor R3 is coupled between the sixth node n6 and the input voltage source VCC.

The described low-dropout linear voltage regulator circuit with overcurrent protection function, the voltage regulator part includes a voltage reference source, an error amplifier EA, a first transistor M1 as a power tube, and a first transistor as a feedback resistor. Resistor R1 and second resistor R2, the voltage reference source is set between the input voltage source VCC and the ground level GND, and is connected to the overcurrent protection part, the non-inverting input terminal of the error amplifier EA is coupled to the first A node n1, the negative input terminal is coupled to the first reference voltage source V _ref1 , and the output terminal is coupled to the second node n2; the gate of the first transistor M1 is coupled to the second node n2, and the source is coupled to the input voltage source VCC, the drain is coupled to the third node n3, the first resistor R1 and the second resistor R2 are respectively coupled between the third node n3 and the first node n1 and between the first node n1 and the ground level GND.

The technical effect of the invention is that the sampling precision is high and the circuit stability is good. The present invention adopts the sampling circuit of current-voltage conversion type instead of sampling resistance, which avoids the problem that the sampling resistance is easily affected by temperature and process. Sampling stability is good. The sampling structure of the source follower adopted in the present invention can suppress the change of the sampling overcurrent threshold value caused by the change of the output voltage, and can make the input voltage range of the LDO wider. The circuit structure is simple. And the "foldback" working mode can effectively enhance the protection capability of overcurrent.

Description of drawings

Fig. 1 is a block diagram of the present invention;

2 is a schematic diagram of the circuit structure of the present invention;

3 is a circuit diagram of Embodiment 1 of an overcurrent protection circuit of a low-dropout linear regulator;

4 is a schematic diagram of the internal structure of the overcurrent detection voltage comparator AP;

5 is a circuit diagram of Embodiment 2 of an overcurrent protection circuit of a low-dropout linear regulator;

Fig. 6 is a scheme diagram for testing the static response of the overcurrent protection circuit;

FIG. 7 is a schematic diagram of the static response effect of the overcurrent protection circuit;

Fig. 8 is a scheme diagram of testing the transient response of the overcurrent protection circuit;

FIG. 9 is a schematic diagram of the transient response effect of the overcurrent protection circuit.

Detailed ways

The present invention will be further described below with reference to the embodiments shown in the accompanying drawings.

The design of the LDO overcurrent protection circuit of the present invention is composed of the following parts:

The voltage regulator part, whose function is to provide a stable step-down circuit in a given power module;

The current detection part, whose function is to detect the current inside the power tube in real time, and transmit the detected result to the current control part;

The function of the current control part is to accept and respond to the output inversion brought by the current detection part, and to protect against the overcurrent fact brought by the output inversion, so as to achieve the effect of protecting the power tube from damage;

Figure 2 is a system block diagram of a low dropout linear regulator. The system consists of a voltage reference source, an error amplifier, an overcurrent protection circuit, a power tube, a feedback resistor and peripheral devices. The voltage reference source provides a stable reference for the error amplifier and the overcurrent protection circuit. The error amplifier adjusts the conduction current of the power tube through the negative feedback loop, so that the output voltage is maintained at a relatively constant value. The gain and bandwidth of the error amplifier determine the stability and accuracy of the LDO. The over-current protection circuit is to detect the over-current state and provide protection for the system when it is overloaded. The large current of the load is mainly provided by the power tube. The feedback resistor is to feed back the collected output voltage to the error amplifier, so as to precisely control the output voltage. The output voltage and output current can be expressed by the following formulas:

Where μ, C, W ₁ , L ₁ , V _GS1 and V _TH1 are the carrier mobility, gate oxide thickness, gate width, gate length, gate-source voltage and threshold voltage of the power transistor M1, respectively.

In the present invention, the idea of power tube overcurrent protection is: for a certain power tube, its μ, C, W ₁ , L ₁ , and V _TH1 are all certain values; therefore, it is only necessary to reduce the gate-source voltage V of M1 _GS1 can reduce the output current I1. Therefore, the core module of the overcurrent protection circuit is to detect the overload state and reduce the value of the gate-source voltage V _GS1 of M1. Correspondingly, the interior of the overcurrent protection circuit must contain two sub-modules: a current detection module and a current control module. The purpose of designing the current detection module is to monitor the current of the power tube M1 in real time and feed back the detected information to the current control module in real time; while the purpose of designing the current control module is to respond quickly and pull the load after the current detection module detects an overload. The gate-source voltage of the high-power transistor M1. The "foldback" mode of operation can enhance the protection capability of overcurrent. From the output voltage-output current relationship curve of the LDO, the "foldback" working mode should be divided into (1) "foldback" section and (2) "foldback" section. In the (1) "folded" section, the output current is clamped but still slightly increased, and the power device originally controlled by the error amplifier will be controlled by a first-stage pull-up transistor, so the original negative feedback loop is destroyed. , the linear regulator does not work properly, and the output voltage decreases; in the (2) "return" section, the output current will decrease with the decrease of the output voltage. The purpose of setting the "folded" section here is actually to realize the "return" section, because the realization of the "return" section requires the assistance of the output voltage drop, that is, the negative feedback loop under normal operation needs to be Only the "folded" section can destroy the original feedback loop, so that the voltage regulator cannot be regulated, the output voltage drops, and the "folded" section is opened to achieve the effect of reducing the current. The protection circuit of the present invention can realize the "folded" section and the "returned" section respectively, which greatly enhances the robustness of the overcurrent protection.

Embodiment 1: see Figure 3

FIG. 3 is a schematic diagram of Embodiment 1 of the overcurrent protection circuit of the low dropout linear voltage regulator of the present invention. The current detection module composed of M2, M3 and AP and the current control module composed of M4, M5, M6 and R3 involved in this embodiment are proposed based on the above-mentioned principle of overcurrent protection. The specific working principle of the first embodiment is as follows:

The current detection module is composed of M2, M3 and AP. M2 and M3 adopt the current-voltage conversion sampling structure of the source follower, and AP is an overcurrent detection voltage comparator. The specific structure of AP is shown in Figure 4. The voltage comparator circuit designed in this paper has a simple structure and adopts a two-stage amplification structure. Among them, the pre-amplifier adopts a differential amplifier circuit composed of M10-M14, and the differential circuit is used to suppress the interference of the common mode signal, which improves the common mode rejection ratio and reduces the interference of noise in the signal. The second-stage amplification adopts a cascode circuit composed of M15 and M16. The method of realizing sampling is to convert the output current _{I 1} into the sampling voltage VA , and the method of realizing the conversion is as follows:

Equation 2 is the current expression of the power transistor working in the saturation region, which shows that the drain current I ₁ is only related to the gate-source voltage V _GS1 of the power transistor when the power transistor works in the saturation region under a given condition. (that is, when μ, C, W, L, and V _TH are all determined), and the gate-source voltage of the power transistor is determined by the difference between the input voltage (the second power supply voltage V _CC ) and the error amplifier. Therefore, the detection of the current of the power tube can be realized by detecting the gate-source voltage of the power tube. But this sampling method of current-to-voltage conversion may have some problems in regulators. Since the input voltage in the regulator is not fixed, when the value of the input voltage changes, the current value sampled through the current-voltage conversion will change. However, the overcurrent protection value is predetermined. Here, the process of determining the overcurrent protection value is generally as follows: a protection current threshold value I _lim is given in advance, and this value can be converted into a protection voltage threshold value V _lim by formula 2. Therefore, it is necessary to design a circuit with constant protection current and voltage threshold to avoid problems such as false triggering and non-protection of the LDO system. In this embodiment, the above problem is solved by a source follower structure. The source follower is composed of M2 and M3, and its working principle is as follows: M2 is a diode-connected transistor, so M2 always works in the saturation region. Add a reference voltage source slightly larger than its threshold voltage to the gate of M3, at this time, M3 can be used as a stable current source. When V _CC changes, the n5 point can change with the V _CC change, and this relationship can be expressed as Equation 3:

V _CC -V _n5 =C (3)

where C is a constant. According to this formula, n1 can be used as an overcurrent voltage threshold that can always be stable in response to changes in V _CC . Therefore, a voltage comparator AP can be used to detect the overcurrent condition of the LDO system. This can be achieved by connecting n1 and n5 to the positive phase and negative phase input terminals of the voltage comparator respectively. If the voltage regulator system works below the safe current (I _D <I _lim ), at this time, the voltage at point n1 is greater than the voltage at point n5, and the output of the comparator is a high level. High level represents normal state. If the voltage regulator system finds an overload phenomenon (I _D >I _lim ), at this time, the potential of point n1 is less than the potential of point n5, the output of the voltage comparator changes from high level to low level, the output is reversed, and the change It will be sent to the current control module behind, and then the voltage regulator system will be over-current protected.

According to FIG. 3 , the current control module in this embodiment is composed of a "folded" protection circuit and a "returned" protection circuit. Among them, M4 and M5 are the pull-up tube of the "folded" protection circuit and the pull-up tube of the "back-type" protection circuit, respectively, and M6 is the switch tube of the "back-type" protection circuit, and its source reference is provided by the reference circuit. The normal input voltage is the same as the reference voltage, and R3 is a sampling resistor. The current control module receives changes from the overcurrent detection module to reduce the current of the LDO. According to Equation 2, the idea of reducing the power tube current is to increase the gate-source voltage. The solution adopted in this embodiment is to use the "folded" protection circuit pull-up transistor M4 and the "back-type" protection circuit pull-up transistor M5 to pull up the gate voltage of the power transistor, and the "folded" protection circuit pull-up transistor M4 makes the A negative feedback loop is formed between the power tube and the overcurrent detection voltage comparator, so the grid voltage of the power tube is clamped and no longer drops. The purpose of the "back-type" protection circuit to pull up the transistor M5 is to further increase the gate voltage after the establishment of the above negative feedback loop, so as to achieve the purpose of reducing the large current of the power transistor. The working principle of the current control module is as follows: when the voltage regulator is in a normal working state (I ₁ <I _lim ), the output of the comparator AP is high, the first-level pull-up transistor M4 is turned off, and the current control module does not work. Once the load current reaches the protection current threshold, the output of the comparator AP is reversed, at this time, the M4 tube is turned on, and the negative feedback loop is turned on. Then the output voltage Vout drops sharply, and when it drops to a certain voltage (V _REF4 -Vout>V _TH6 ), the switch M6 is turned on. Due to the continuous decrease of Vout, the current I ₂ flowing through the switch M6 will continue to increase until:

V _TH5 = I ₂ R ₃ -V _CC (4)

At this time, I2 makes the voltage drop flowing through R3 become larger, the potential of the n7 node becomes lower, and the secondary pull-up transistor M5 is turned on. Then the gate potential previously clamped by M4 is pulled high, so the clamped current is greatly reduced. When the overcurrent state ends, the current control module stops working and the system returns to normal.

Embodiment 2: refer to accompanying drawing 5

FIG. 5 is a schematic diagram of Embodiment 2 of the overcurrent protection circuit of the low dropout linear voltage regulator of the present invention. The current detection module composed of M2, M3 and AP and the current control module composed of M4, M5, M6, M7, M8, M9, R3 and R4 involved in this embodiment are proposed based on the above-mentioned overcurrent protection principle of. The specific working principle of the second embodiment is as follows:

Since the second embodiment and the first embodiment use the same current detection module, only the working principle of the current control part will be described. In this embodiment, the pull-up transistors M4 and M5 of the "foldback" protection circuit are still used to pull up the gate-source voltage V _GS1 of M1 after the overload occurs. Here, it is only a way to trigger the "foldback" protection circuit to turn on the pull-up transistors of M5. There are differences, the specific circuit implementation principle is as follows:

When the system works normally, the comparator AP outputs a high level, and the current control module does not work. When the overload condition is reached, the pull-up transistor M4 of the "folded" protection circuit is turned on, and the output voltage Vout begins to drop sharply. In the process of Vout dropping sharply, when V _S6 -Vout<V _TH6 is satisfied, the switch M6 is turned on. Since the M6 is turned on, Vout will still drop. According to Equation 1, it can be obtained that when V _GS9 =V _S9 -Vout becomes larger, the current flowing through the M6 branch I ₂ will continue to increase, and the current will continue to increase until the current reaches Equation 4. At this time, the pull-up tube M5 of the "back-type" protection circuit is turned on, V _GS1 is pulled high, and the current in the power tube is reduced. When the overcurrent state ends, the current control module stops working and the system returns to normal.

FIG. 6 is a circuit diagram of a test scheme for the response of the overcurrent protection circuit in the example of the present invention. The test method of the present invention is to add a variable load resistance to the load end in the LDO system. The load resistance range is 0.1Ω to 20Ω. By adjusting the variable load circuit, the output voltage and output current are measured. relationship to observe the effect of overcurrent protection.

FIG. 7 is a schematic diagram of the static response effect of the overcurrent protection circuit in the example of the present invention. In the present invention, the output voltage is set to 1.8V, and the overcurrent protection threshold is set to 200mA. It can be seen from Figure 7 that the voltage is always maintained at 1.8V before the load current reaches 200mA, which indicates that the voltage regulator system is always working normally. Once the current reaches 200mA (the first inflection point in the figure), the pull-up transistor of the "folded" protection circuit is turned on, the output voltage begins to drop, and the current still has a small increase at this time. When the output voltage drops to the point where the pull-up tube of the "return" protection circuit can be turned on (the second inflection point in the figure), the current will be reduced from 210mA to 35mA. At this time, the large current will be reduced, reducing the overload of the power tube. and heat build-up so that the regulator system is protected. As can be seen from Figure 7, the output voltage-output current relationship of (1) section is the "folded" protection section, and the output voltage-output current relationship of (2) section is the "folded" protection section.

FIG. 8 is a circuit diagram of a scheme for testing the transient response of an overcurrent protection circuit in an example of the present invention. Since the test in Figure 6 can only reflect the static overcurrent protection curve, and the actual overcurrent state often occurs instantaneously, it is necessary to test the transient response of the overcurrent protection. The method to test the transient response of the overcurrent protection circuit in this example is: add an NMOS transistor MP controlled by a signal generator to the output end of the voltage stabilizer, and the signal generator generates a square wave signal V _PLUSE , when the square wave When the wave signal is at a low level, the NMOS tube is turned off. Due to the large size of the NMOS transistor MP, when the square wave signal jumps to a high level, a large current will be generated in the entire circuit instantaneously. Therefore, the overcurrent protection circuit can be detected through the entire instantaneous large current.

Fig. 9 is the transient response timing diagram of the overcurrent protection circuit in this embodiment. The pulse signal gives a square wave signal V _PLUSE of 3 cycles. The result shows that when V _PLUSE is at a low level, there is almost no current flow in the entire branch. However, the output of the LDO is normal. When the result jumps to a high level, the MP tube instantly generates a current greater than 200mA, and then the current will be instantly reduced to below 35mA within 35μS. Under the control of the square wave for three consecutive cycles, it can be found that the circuit can still resume normal operation after the overcurrent state is removed.

The first, fourth, and fifth transistors are NMOS devices, and the second, third, and sixth transistors are PMOS devices. The first reference voltage source is the reference voltage source of the error amplifier, the input voltage source is the high-level voltage source given by the power supply of the whole circuit, and the second reference voltage source is the reference voltage source of the voltage comparator. The third reference power source is a reference voltage source for the sixth transistor. The reference voltage source is generated by the voltage reference source, that is, the bandgap reference circuit. The voltage reference source is usually a stable voltage, and they will not change with the power supply voltage and temperature. The purpose of setting the voltage reference source is to provide the error amplifier and overcurrent protection. Part of the bias voltage is provided so that they can work in the expected state. For example, the value of the first reference voltage source V _REF1 connected to the power tube is calculated under the output voltage of the linear regulator that has been set. .

The above-mentioned embodiments are only examples of the present invention. Although the best embodiments of the present invention and the accompanying drawings are disclosed for the purpose of illustration, those skilled in the art will understand that: without departing from the spirit and scope of the present invention and the appended claims Within, various substitutions, changes and modifications are possible. Therefore, the present invention should not be limited to what is disclosed in the preferred embodiments and drawings.

Claims (6)

1. A low-dropout linear regulator circuit with an overcurrent protection function is characterized by comprising a regulator part and an overcurrent protection part, wherein the regulator part comprises a voltage reference source, an error amplifier, a power tube and a feedback resistor, the voltage reference source is connected with the error amplifier and the overcurrent protection part to provide reference voltage, the error amplifier, the feedback resistor, the power tube and the overcurrent protection part are connected with each other, the power tube provides a power supply for driving a load to work, the feedback resistor acquires the output voltage of the power tube and feeds the output voltage back to the error amplifier, and the error amplifier adjusts the conduction current of the power tube by obtaining feedback information from the feedback resistor; the overcurrent protection part comprises a current detection unit and a current control unit, wherein the current detection unit is connected to the power tube to monitor the current of the power tube and send monitored information to the current control unit, the current control unit clamps the voltage of the power tube to keep stable when overcurrent occurs and the current of the power tube is greater than a first threshold value so that the current is not increased any more, and pulls up the voltage of the power tube to reduce the current when the current of the power tube is greater than a second threshold value, wherein the second threshold value is greater than the first threshold value;

the current control unit comprises a folded protection circuit used for clamping the voltage of the power tube and keeping the voltage stable and a return protection circuit used for pulling up the voltage of the power tube, the folded protection circuit is connected with the power tube and the current detection unit and is started by the current detection unit when the current of the power tube is larger than a first threshold value, a negative feedback loop is formed between the folded protection circuit and the power tube and the current detection unit to clamp the voltage of the power tube and keep the voltage stable, the return protection circuit is connected with the folded protection circuit and the power tube and is started by the power tube when the current of the power tube is larger than a second threshold value, and the voltage of the power tube is pulled up to reduce the current.

2. The low dropout regulator circuit with overcurrent protection function of claim 1, wherein the current detection unit comprises a second transistor M2, a third transistor M3 and an overcurrent detection voltage comparator AP, the gate and drain of the second transistor M2 are coupled to the input voltage source VCC, and the source is coupled to a fourth node n 4; the gate of the third transistor M3 is coupled to a second reference voltage source V_ref2Drain coupled to the fourth node n4, source coupled to ground level GND; the positive phase input terminal of the over-current detection voltage comparator AP is coupled to the fourth node n2, the negative phase input terminal thereof is coupled to the fourth node n4, and the output terminal thereof is coupled to the fifth node n 5.

3. The low dropout regulator circuit with overcurrent protection as recited in claim 1, wherein the folded protection circuit comprises a fourth transistor M4, the gate of the fourth transistor M4 is coupled to a fifth node n5, the source is coupled to the input voltage source VCC, and the drain is coupled to a second node n 2.

4. The low dropout regulator circuit of claim 1 wherein the flyback protection circuit comprises a fifth transistor M5, a sixth transistor M6 and a third resistor R3, wherein the gate of the fifth transistor M5 is coupled to a sixth node n6, the source is coupled to the input voltage source VCC, the drain is coupled to a second node n2, and the gate of the sixth transistor M6 is coupled to a third reference voltage source V2_ref3And the drain is coupled to an input voltage source VCC, the source is coupled to a third node n3, and the third resistor R3 is coupled between a sixth node n6 and the input voltage source VCC.

5. The low dropout regulator circuit with the overcurrent protection function of claim 1, wherein the "flyback" protection circuit comprises a fifth transistor M5, a sixth transistor M6, a seventh transistor M7, an eighth transistor M8, a ninth transistor M9, a third resistor R3 and a fourth resistor R4; the gate of the fifth transistor M5 is coupled to the sixth node n6, the source is coupled to the input voltage source VCC, and the drain is coupled to the second node n 2; the gate of the sixth transistor M6 is coupled to the gate of the ninth transistor M9, the source is coupled to the third node n3, and the drain is coupled to the sixth node n 6; the gate of the seventh transistor M7 is coupled to the second node n2, the source is coupled to the input voltage source VCC, and the drain is coupled to the source of the eighth transistor M8; the gate of the eighth transistor M8 is coupled to the third node n3, and the drain is coupled to the drain of the ninth transistor M9; the drain and the gate of the ninth transistor M9 are also coupled to the gate of the sixth transistor M6, and the source is coupled to the ground level GND after being connected in series with the fourth resistor R4; the third resistor R3 is coupled between the sixth node n6 and the input voltage source VCC.

6. A low dropout regulator circuit having an overcurrent protection function as claimed in any one of claims 2 to 5, wherein the regulator part comprises a voltage reference source, an error amplifier EA, a first transistor M1 as a power transistor, a first resistor R1 and a second resistor R2 as a feedback resistor, the voltage reference source is disposed between an input voltage source VCC and a ground level GND and connected to the overcurrent protection part, a positive input terminal of the error amplifier EA is coupled to the first node n1, and a negative input terminal is coupled to the first reference voltage source V_ref1An output terminal coupled to a second node n 2; the first transistor M1 has a gate coupled to the second node n2, a source coupled to the input voltage source VCC, a drain coupled to the third node n3, and the first resistor R1 and the second resistor R2 are respectively coupled between the third node n3 and the first node n1 and between the first node n1 and the ground level GND.

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