MCU power supply low-voltage detection circuit structure

Abstract

The invention provides an MCU power supply low-voltage detection circuit structure, which comprises a current sampling branch, a reference current branch, a current comparison branch, a first current mirror structure, a second current mirror structure and a constant current source structure, and is characterized in that the current sampling branch samples and converts MCU power supply voltage into sampling current through a sampling resistor and a plurality of unidirectional conductive tubes; the sampling current is mirrored to a current comparison branch through a first current mirror structure to obtain a first mirrored current; the reference current branch generates a reference current which does not change along with the MCU power supply voltage through a constant current source structure, and the reference current is mirrored to the current comparison branch through a second current mirror structure to obtain a second mirrored current; and the current comparison branch circuit compares the first mirror current with the second mirror current, performs high-potential or low-potential flip output according to a comparison result, shapes the flip output through two phase inverters, and outputs a corresponding high level or low level.

Description

Technical Field

[0001] The present invention relates to the technical field of voltage detection, and in particular to a circuit structure for detecting low voltage of an MCU power supply. Background Art

[0002] MCU (Microcontroller Unit) is a microcomputer chip that integrates a processor, memory, and input / output interface. The MCU power supply voltage must be controlled within a certain range to ensure that the chip can maintain a stable operating state. If the power supply voltage is too high, the transistor will be damaged. If the power supply voltage is too low, the system will have various execution errors.

[0003] The MCU low-voltage detection circuit can detect transient changes in the power supply voltage. When the power supply voltage is higher than a certain threshold voltage, the MCU starts to work normally. When the power supply voltage is lower than the threshold voltage, part of the MCU circuit is shut down. This can effectively prevent the harm caused by the MCU power supply voltage being too low.

[0004] Traditional low voltage detection circuits such as Figure 1 As shown, it includes a voltage sampling circuit, a bandgap reference circuit and a voltage comparator. The bandgap reference circuit generates a reference voltage that does not drift with temperature. The voltage sampling circuit uses multiple resistors R10, R20, and R30 to form a resistor voltage divider network to sample the power supply voltage. The sampled voltage and the reference voltage are compared by a voltage comparator to determine whether the power supply voltage is in a low voltage state. The low voltage detection circuit requires an independent bandgap reference circuit, resulting in a complex circuit structure and high power consumption. The temperature drift of the low voltage detection circuit depends entirely on the temperature drift coefficient of the reference voltage, and the temperature drift characteristics are poor. In addition, in order to reduce power consumption, the resistor voltage divider often has a large resistance value, resulting in a large resistor volume and thus occupying a large area.

[0005] Patent document CN110501548A discloses a micro-power low-voltage detection circuit for MCU. Compared with the traditional low-voltage detection circuit, it removes the bandgap reference circuit, does not require resistor voltage division, has a simple structure, consumes very little power, and is very small in size, so it occupies a small area. In order to ensure zero temperature drift of the detection point, the detection circuit needs to reasonably select the resistance value and type of the ballast resistor so that all MOS tubes in the entire circuit work in a subthreshold state. However, due to the large deviation of the resistance with the process, the sampling voltage of the circuit changes greatly with PVT (process voltage temperature), and the temperature drift characteristic is poor, resulting in a large change in the flip threshold of the detection voltage. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a low voltage detection circuit with low power consumption, small occupied area and small change of flip threshold with PVT.

[0007] In order to solve the above technical problems, the present invention provides an MCU power supply low voltage detection circuit structure, including a current sampling branch, a reference current branch, a current comparison branch, a first current mirror structure, a second current mirror structure and a constant current source structure, wherein:

[0008] The current sampling branch includes a sampling resistor and a plurality of unidirectional conductive tubes connected in series, wherein the series input end is connected to the MCU power supply, and the series output end is connected to the current comparison branch via a first current mirror structure; the current sampling branch converts the MCU power supply voltage sampling into a sampling current through the sampling resistor and the plurality of unidirectional conductive tubes, and then mirrors the sampling current to the current comparison branch through the first current mirror structure to obtain a first mirror current;

[0009] The input end of the reference current branch is connected to the current sampling branch via a constant current source structure, and the output end is connected to the current comparison branch via a second current mirror structure; the reference current branch generates a reference current that does not change with the MCU power supply voltage through the constant current source structure, and then the reference current is mirrored to the current comparison branch through the second current mirror structure to obtain a second mirror current;

[0010] The current comparison branch includes two inverters. After the two inverters are connected in series, the series input end is connected between the output end of the first current mirror structure and the output end of the second current mirror structure; the current comparison branch compares the first mirror current with the second mirror current, performs a high potential or low potential flip output according to the comparison result, and shapes the flip output through two inverters to output a corresponding high level or low level.

[0011] Furthermore, the unidirectional conductive tube is a triode whose base and collector are short-circuited.

[0012] Furthermore, the first current mirror structure includes an input stage device and an output stage device, the input stage device is connected in series in a current sampling branch, and the output stage device is connected in series in a current comparison branch.

[0013] Furthermore, the input-stage device and the output-stage device of the first current mirror structure are both NPN-type triodes; the collector of the input-stage device is connected to the series output end of the sampling resistor and multiple unidirectional conductive tubes, the emitter is grounded, the base is short-circuited with the collector and connected to the base of the output-stage device; the base of the output-stage device is connected to the base of the input-stage device, the collector is connected to the current comparison branch, and the emitter is grounded.

[0014] Furthermore, the constant current source structure includes an input stage device and an output stage device, the input stage device is connected in series in a current sampling branch, and the output stage device is connected in series in a reference current branch.

[0015] Furthermore, the input-stage device and the output-stage device of the constant current source structure are both NPN-type triodes; the collector of the input-stage device is connected to the series output end of the sampling resistor and multiple unidirectional conductive tubes, the emitter is grounded, the base is short-circuited with the collector and connected to the base of the output-stage device; the base of the output-stage device is connected to the base of the input-stage device, the emitter is grounded via a ballast resistor, and the collector is connected to a second current mirror structure.

[0016] Furthermore, the constant current source structure and the first current mirror structure share the same input stage device.

[0017] Furthermore, the second current mirror structure includes an input stage device and an output stage device, the input stage device is connected in series in the reference current branch, and the output stage device is connected in series in the current comparison branch.

[0018] Furthermore, the input-stage device and the output-stage device of the second current mirror structure are both P-type MOS tubes; the drain of the input-stage device is connected to the constant current source structure, the source is connected to the MCU power supply, the gate short-circuit the drain and is connected to the gate of the output-stage device; the gate of the output-stage device is connected to the gate of the input-stage device, the drain is connected to the current comparison branch, and the source is connected to the MCU power supply.

[0019] Furthermore, the current comparison branch also includes two P-type MOS tubes for generating voltage reversal hysteresis, the source of the first MOS tube is connected to the MCU power supply, the gate is connected to the output stage device of the second current mirror structure, the drain is connected to the source of the second MOS tube, the gate of the second MOS tube is connected to the contact between the two inverters, and the drain is connected to the series input terminals of the two inverters.

[0020] The present invention has the following beneficial effects: in the current sampling branch, since the unidirectional conductive tube has a forward voltage drop, multiple unidirectional conductive tubes are connected in series to reduce the sampling current, so that the sampling resistor can select a smaller value, which has low power consumption and small occupied area. According to the principle of the constant current source structure, the VBE (base and emitter) voltage difference between the input stage device and the output stage device has a positive temperature coefficient, and the VBE voltage of transistors such as the input stage device, the output stage device and the unidirectional conductive tube of the current mirror has a negative temperature coefficient. Therefore, the positive temperature coefficient can be changed by changing the amplification ratio of the current mirror structure and the negative temperature coefficient can be adjusted by changing the number of accesses of the unidirectional conductive tube, so that the negative temperature coefficient and the positive temperature coefficient can offset each other to obtain a zero temperature coefficient, thereby ensuring that the low-voltage detection circuit structure has a very low temperature drift coefficient within the entire operating temperature range of the MCU, so that the flip threshold changes little with PVT, and an accurate flip output threshold can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the circuit schematic diagram of the traditional low voltage detection circuit.

[0022] Figure 2 It is a circuit schematic diagram of the MCU power supply low voltage detection circuit structure of the first embodiment of the present invention.

[0023] Figure 3 It is a circuit schematic diagram of the MCU power supply low voltage detection circuit structure of the second embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with specific implementation methods.

[0025] Embodiment 1

[0026] This embodiment provides a MCU power supply low voltage detection circuit structure, such as Figure 2 As shown, the MCU power supply low voltage detection circuit structure includes a current sampling branch (current I IN0 Where the branch), the reference current branch (current I ref branch), current comparison branch (current I IN1 and current I ref1 The branch where it is located), a first current mirror structure, a second current mirror structure and a constant current source structure.

[0027] The first current mirror structure includes a transistor Q1 and a transistor Q2, wherein the transistor Q1 is an input stage device of the first current mirror structure, the transistor Q2 is an output stage device of the first current mirror structure, and the transistor Q1 and the transistor Q2 are specifically NPN transistors. The second current mirror structure includes a MOS transistor MP2 and a MOS transistor MP1, wherein the MOS transistor MP2 is an input stage device of the second current mirror structure, the MOS transistor MP1 is an output stage device of the second current mirror structure, and the MOS transistor MP2 and the MOS transistor MP1 are specifically P-type MOS transistors. The constant current source structure is specifically a Widlar constant current source structure, which includes a transistor Q1, a transistor Q3 and a ballast resistor R1, wherein the transistor Q1 is an input stage device of the constant current source structure, then the constant current source structure and the first current mirror structure share the same input stage device, the transistor Q3 is an output stage device of the constant current source structure, and the transistor Q3 is specifically an NPN transistor.

[0028] The current sampling branch includes a sampling resistor R2, multiple unidirectional conductive tubes Q d1 , Q d2 ,…,Q dN And transistor Q1, among which the unidirectional conductive tube Q d1 , Q d2 ,…,Q dN The number of unidirectional conductive tubes is N, and each unidirectional conductive tube is specifically an NPN transistor with its base and collector short-circuited. After the base and collector of the transistor are short-circuited, it exhibits the characteristics of a unidirectional conductive tube.d1 , Q d2 ,…,Q dN The first current mirror structure is connected in series, with the series input end serving as the input end of the current sampling branch, connected to the MCU power supply VIN, and the series output end connected to the collector of the transistor Q1. In the first current mirror structure, the transistor Q1 is an input-level device, which is connected in series in the current sampling branch. Specifically, the collector of the transistor Q1 is connected to the sampling resistor R2 and a plurality of unidirectional conductive tubes Q d1 , Q d2 ,…,Q dN The series output end of the transistor Q2 has an emitter connected to the ground, a base short-circuited to the collector and connected to the base of the transistor Q2, and the transistor Q2 is an output stage device, which is connected in series in the current comparison branch. Specifically, the base of the transistor Q2 is connected to the base of the transistor Q1, the collector is connected to the current comparison branch, and the emitter is grounded. It can be seen that the input end of the current sampling branch is connected to the MCU power supply VIN, and the output end is connected to the current comparison branch through the first current mirror structure. Therefore, the current sampling branch can be connected through the sampling resistor R2 and multiple unidirectional conductive tubes Q d1 , Q d2 ,…,Q dN Convert the voltage sampling of MCU power supply VIN into sampling current I IN0 , and then the sampling current I IN0 Mirrored to the current comparison branch, the first mirror current I is obtained IN1 .

[0029] The reference current branch includes transistor Q3, ballast resistor R1 and MOS tube MP2. In the constant current source structure, transistor Q1 is an input stage device, which is connected in series in the current sampling branch. Specifically, the collector of transistor Q1 is connected to the sampling resistor R2 and multiple unidirectional conductive tubes Q d1 , Q d2 ,…,Q dNThe series output end of the transistor Q3 has an emitter connected to ground, a base short-circuited to the collector and connected to the base of the transistor Q3, and the transistor Q3 is an output-stage device, which is connected in series in the reference current sampling branch. Specifically, the base of the transistor Q3 is connected to the base of the transistor Q1, the emitter is grounded through the ballast resistor R1, the collector is connected to the drain of the MOS tube MP2, and the source of the MOS tube MP2 is connected to the MCU power supply VIN, so that the branch where the transistor Q1 is located and the branch where the transistor Q3 is located form a constant current source structure. In the second current mirror structure, the MOS tube MP2 is an input-stage device, which is connected in series in the reference current branch. Specifically, the drain of the MOS tube MP2 is connected to the collector of the transistor Q3, the source is connected to the MCU power supply VIN, the gate is short-circuited to the drain and connected to the gate of the MOS tube MP1, and the MOS tube MP1 is an output-stage device, which is connected in series in the current comparison branch. Specifically, the gate of the MOS tube MP1 is connected to the gate of the MOS tube MP2, the drain is connected to the current comparison branch, and the source is connected to the MCU power supply VIN. It can be seen that the reference current branch is connected to the current sampling branch through the constant current source structure and connected to the current comparison branch through the second current mirror structure. Therefore, the reference current branch can generate a reference current I that does not change with the MCU power supply voltage through the constant current source structure. ref , and then the reference current I ref Mirrored to the current comparison branch, the second mirror current I ref1 .

[0030] The current comparison branch includes a transistor Q2, a MOS tube MP1 and two inverters INV1 and INV2. The collector of the transistor Q2 is connected to the drain of the MOS tube MP1. After the inverter INV1 and the inverter INV2 are connected in series, the series input terminal is connected to the junction between the collector of the transistor Q2 and the drain of the MOS tube MP1, that is, the junction between the output terminal of the first current mirror structure and the output terminal of the second current mirror structure. The series output terminal VOUT is a level output terminal. The current comparison branch also includes a MOS tube MP3 and a MOS tube MP4 for generating a voltage reversal hysteresis. The MOS tube MP3 and the MOS tube MP4 are specifically P-type MOS tubes. The source of the MOS tube MP3 is connected to the MCU power supply VIN, the gate is connected to the gate of the MOS tube MP2, and the drain is connected to the source of the MOS tube MP4; the source of the MOS tube MP4 is connected to the drain of the MOS tube MP3, the gate is connected to the contact between the inverter INV1 and the inverter INV2, and the drain is connected to the series input end of the inverter INV1 and the inverter INV2, then the MOS tube MP4 is a switch tube, which controls the opening and closing of the branch current where the MOS tube MP3 and the triode Q2 are located.

[0031] The current comparison branch converts the first mirror current I IN1 The second mirror current I ref1Compare, and perform high potential or low potential flip output according to the comparison result, and shape the flip output through two inverters to output the corresponding high level or low level. Specifically: when the voltage of the MCU power supply VIN is large, the first mirror current I IN1 >Second mirror current I ref1 At this time, the pull-down capability of transistor Q2 is stronger than the pull-up capability of MOS tube MP1, so the collector voltage of transistor Q2 is too low, causing transistor Q2 to enter the linear region and fail to mirror the load current I IN0 , and MOS tube MP1 successfully mirrors the reference current I ref Get the second mirror current I ref1 At this time, the collector of transistor Q2 is pulled down to a low potential, and then shaped by two inverters INV1 and INV2 to output a low level. When the voltage of the MCU power supply VIN is small, the first mirror current I IN1 <Second mirror current I ref1 At this time, the pull-up capability of MOS tube MP1 is stronger than the pull-down capability of transistor Q2, so the drain voltage of MOS tube MP1 is too high, causing MOS tube MP1 to enter the linear region and fail to mirror the reference current I ref , and transistor Q2 successfully mirrors the load current I IN0 Get the first mirror current I IN1 At this time, the drain of MOS tube MP1 is pulled up to a high potential, and then shaped by two inverters INV1 and INV2 to output a high level. It can be seen that there is a critical point that makes the first mirror current I IN1 = Second mirror current I ref1 , the input VIN obtained at the critical point is the output flip threshold.

[0032] In this embodiment, the magnification ratio of transistors Q1, Q2 and Q3 is K:1:1, and the width-to-length ratio of MOS transistors MP3, MP1 and MP2 is M1:M2:1, where K, M1 and M2 are constants independent of temperature. d1 , Q d2 ,…,Q dN The number of them is N, and each unidirectional conductive tube is the same.

[0033] When the voltage of the MCU power supply VIN input changes from large to small, the voltage outputted by the output terminal VOUT of the low voltage detection circuit structure changes from low to high. Before the change, the output voltage VOUT is low, and the gate voltage of the MOS tube MP4 is high before passing through the inverter INV2. The voltage from the gate to the source V GS is a positive voltage. At this time, the MOS tube MP4 is turned off, so that the current in the branch where the MOS tube MP3 is located is closed. Then the sampling current I IN0 for:

[0034]

[0035] Among them, V INL The voltage of the MCU power supply VIN input changes from large to small. BEQ1 is the voltage difference between the base and emitter of transistor Q1, V BEQd1 Q is a unidirectional conductive tube d1 The voltage difference between the base and the emitter is due to multiple unidirectional conductive tubes Q d1 , Q d2 ,…,Q dN Same, then NV BEQd1 For multiple unidirectional conductive tubes Q d1 , Q d2 ,…,Q dN The sum of the pressure differences.

[0036] The first mirror current I IN1 for:

[0037]

[0038] The reference current I is obtained based on the principle of Widlar constant current source structure. ref for:

[0039]

[0040] Among them, V BEQ1 is the voltage difference between the base and emitter of transistor Q1, V BEQ3 is the voltage difference between the base and emitter of transistor Q3.

[0041] The second mirror current I ref1 for:

[0042] I ref1 =M2I ref #(4).

[0043] At the critical point, the first mirror current I IN1 = Second mirror current I ref1 , combining formulas (1), (2), (3), and (4), we have:

[0044]

[0045] Solving for V INL get:

[0046]

[0047] When the voltage input by the MCU power supply VIN changes from low to high, the voltage output by the output terminal VOUT of the low voltage detection circuit structure changes from high to low. Before the change, the output voltage VOUT is high, and the gate voltage of the MOS tube MP4 is low before passing through the inverter INV2. The voltage from the gate to the source V GS is a negative voltage. At this time, the MOS tube MP4 is turned on, so that the branch current where the MOS tube MP3 is located is turned on. Then the second mirror current I ref1 Changes to:

[0048] I ref1 =(M1+M2)I ref #(6);

[0049] At this time, the sampling current I IN0 for:

[0050]

[0051] Among them, V INH The power supply voltage when the voltage of the MCU power supply VIN input changes from small to large, V BEQ1 is the voltage difference between the base and emitter of transistor Q1, V BEQd1 Q is a unidirectional conductive tube d1 The voltage difference between the base and the emitter is due to multiple unidirectional conductive tubes Q d1 , Q d2 ,…,Q dN Same, then NV BEQd1 For multiple unidirectional conductive tubes Q d1 , Q d2 ,…,Q dN The sum of the pressure differences.

[0052] At the critical point, the first mirror current I IN1 = Second mirror current I ref1 , combining formulas (2), (3), (6), and (7), we have:

[0053]

[0054] Solving for V INH get:

[0055]

[0056] From formula (1) and formula (7), we can see that in the current sampling branch, since the unidirectional conductive tube has a forward voltage drop, connecting multiple unidirectional conductive tubes in series can reduce the sampling current I IN0 , the more the number of unidirectional conductive tubes, the greater the sampling current I IN0 The smaller the sampling current I IN0By connecting N unidirectional conductive tubes in series, the sampling resistor R2 can be selected to have a smaller value, which reduces power consumption and reduces the size of the resistor. Since the resistor on the MCU chip is much larger than that of the triode, the small size of the resistor can effectively reduce the occupied area.

[0057] From formula (5) and formula (8), it can be seen that when the sampling resistor R2 and the ballast resistor R1 are selected from the same type of resistors with the same temperature coefficient, the resistance ratio is a quantity independent of temperature, and the constants K, M1, and M2 are constants independent of temperature. From the principle of the constant current source structure, it can be seen that the voltage difference V between the input stage device and the output stage device is BEQ1 -V BEQ3 It has a positive temperature coefficient, and for the triode, the voltage difference VBE between its base and emitter decreases with the increase of temperature, then the VBE voltage of the input stage device, output stage device and unidirectional conductive tube of the current mirror structure has a negative temperature coefficient. Therefore, the positive temperature coefficient can be adjusted by changing the amplification ratio K, M1, M2 of the current mirror structure, and the negative temperature coefficient can be adjusted by changing the number of connections N of the unidirectional conductive tube, so that the negative temperature coefficient and the positive temperature coefficient can offset each other to obtain a zero temperature coefficient, thereby ensuring that the low-voltage detection circuit structure has a very low temperature drift coefficient within the entire operating temperature range of the MCU, so that the flip threshold changes little with PVT (process voltage temperature), and an accurate flip output threshold can be obtained.

[0058] It should be noted that in reality, the voltage of the MCU power supply VIN will fluctuate up and down, and may reach the low voltage alarm threshold in a very short time, and fluctuate around the threshold. At this time, the low voltage alarm will be continuously triggered and cleared. To avoid this phenomenon, a voltage reversal hysteresis needs to be designed. When the voltage of the MCU power supply VIN reaches the low voltage alarm threshold, if the voltage of the MCU power supply VIN recovers, the voltage reversal hysteresis needs to be restored before the low voltage alarm can be cleared. Specifically, the voltage reversal hysteresis V hys for:

[0059] V hys =|V INH -V INL |#(9);

[0060] Substituting formula (5) and (8) into the above equation, we obtain:

[0061]

[0062] From formula (10), we can know that in order to prevent the voltage from constantly flipping and constantly triggering the low voltage alarm and releasing the alarm, the second mirror current I can be changed by adjusting the ratio M1 of MOS tube MP3 and MOS tube MP2. ref1 To accurately generate the voltage reversal hysteresis V hysWhen the voltage of the MCU power supply VIN reaches the low voltage alarm threshold, the voltage of the MCU power supply VIN needs to recover the voltage reversal hysteresis V hys The low pressure alarm can be released only after that.

[0063] Embodiment 2

[0064] This embodiment provides Figure 3 The MCU power supply low voltage detection circuit structure shown in the figure has the same overall structure as the MCU power supply low voltage detection circuit structure provided in the first embodiment, except that: the MCU power supply low voltage detection circuit structure of the present embodiment replaces the triode Q1, triode Q2, and triode Q3 of the first embodiment with N-type MOS tubes MN1, MOS tube MN2, and MOS tube MN3, and multiple unidirectional conductive tubes Q d1 , Q d2 ,…,Q dN Replaced with multiple N-type MOS tubes MN d1 MN d2 、…、MN dN .

[0065] The above is only an implementation method of the invention, and does not limit the scope of patent protection. Those skilled in the art can make non-substantial changes or substitutions based on the invention, which still fall within the scope of patent protection.

Claims

1. A MCU power supply low voltage detection circuit structure, characterized in that: It includes a current sampling branch, a reference current branch, a current comparison branch, a first current mirror structure, a second current mirror structure and a constant current source structure, wherein: The current sampling branch includes a sampling resistor and a plurality of unidirectional conductive tubes connected in series, wherein the series input end is connected to the MCU power supply, and the series output end is connected to the current comparison branch via a first current mirror structure; the current sampling branch converts the MCU power supply voltage sampling into a sampling current through the sampling resistor and the plurality of unidirectional conductive tubes, and then mirrors the sampling current to the current comparison branch through the first current mirror structure to obtain a first mirror current; The input end of the reference current branch is connected to the current sampling branch via a constant current source structure, and the output end is connected to the current comparison branch via a second current mirror structure; the reference current branch generates a reference current that does not change with the MCU power supply voltage through the constant current source structure, and then the reference current is mirrored to the current comparison branch through the second current mirror structure to obtain a second mirror current; The current comparison branch includes two inverters. After the two inverters are connected in series, the series input end is connected between the output end of the first current mirror structure and the output end of the second current mirror structure; the current comparison branch compares the first mirror current with the second mirror current, performs a high potential or low potential flip output according to the comparison result, and shapes the flip output through two inverters to output a corresponding high level or low level.

2. The MCU power supply low voltage detection circuit structure according to claim 1 is characterized in that: The unidirectional conductive tube is a triode whose base and collector are short-circuited.

3. The MCU power supply low voltage detection circuit structure according to claim 1 is characterized in that: The first current mirror structure includes an input stage device and an output stage device. The input stage device is connected in series in a current sampling branch, and the output stage device is connected in series in a current comparison branch.

4. The MCU power supply low voltage detection circuit structure according to claim 3 is characterized in that: The input-stage device and the output-stage device of the first current mirror structure are both NPN-type triodes; the collector of the input-stage device is connected to the series output end of the sampling resistor and multiple unidirectional conductive tubes, the emitter is grounded, the base is short-circuited with the collector and connected to the base of the output-stage device; the base of the output-stage device is connected to the base of the input-stage device, the collector is connected to the current comparison branch, and the emitter is grounded.

5. The MCU power supply low voltage detection circuit structure according to claim 1 is characterized in that: The constant current source structure comprises an input stage device and an output stage device, wherein the input stage device is connected in series in a current sampling branch, and the output stage device is connected in series in a reference current branch.

6. The MCU power supply low voltage detection circuit structure according to claim 5 is characterized in that: The input-stage device and the output-stage device of the constant current source structure are both NPN-type triodes; the collector of the input-stage device is connected to the series output end of the sampling resistor and multiple unidirectional conductive tubes, the emitter is grounded, the base is short-circuited with the collector and connected to the base of the output-stage device; the base of the output-stage device is connected to the base of the input-stage device, the emitter is grounded via a ballast resistor, and the collector is connected to the second current mirror structure.

7. The MCU power supply low voltage detection circuit structure according to claim 4 or 6, characterized in that: The constant current source structure and the first current mirror structure share the same input stage device.

8. The MCU power supply low voltage detection circuit structure according to claim 1 is characterized in that: The second current mirror structure includes an input stage device and an output stage device, wherein the input stage device is connected in series in a reference current branch, and the output stage device is connected in series in a current comparison branch.

9. The MCU power supply low voltage detection circuit structure according to claim 8 is characterized in that: The input stage device and the output stage device of the second current mirror structure are both P-type MOS tubes; the drain of the input stage device is connected to the constant current source structure, the source is connected to the MCU power supply, the gate short-circuit the drain and is connected to the gate of the output stage device; the gate of the output stage device is connected to the gate of the input stage device, the drain is connected to the current comparison branch, and the source is connected to the MCU power supply.

10. The MCU power supply low voltage detection circuit structure according to claim 1 is characterized in that the current The comparison branch also includes two P-type MOS tubes for generating voltage reversal hysteresis. The source of the first MOS tube is connected to the MCU power supply, the gate is connected to the output stage device of the second current mirror structure, the drain is connected to the source of the second MOS tube, the gate of the second MOS tube is connected to the junction between the two inverters, and the drain is connected to the series input terminals of the two inverters.

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