WO2021253704A1

WO2021253704A1 - Under-voltage protection circuit

Info

Publication number: WO2021253704A1
Application number: PCT/CN2020/124664
Authority: WO
Inventors: 龚晓寒; 盛云
Original assignee: 苏州纳芯微电子股份有限公司
Priority date: 2020-06-17
Filing date: 2020-10-29
Publication date: 2021-12-23
Also published as: CN111682503A

Abstract

An under-voltage protection circuit, comprising a power supply voltage, a threshold module (1) connected to the power supply voltage, and a switch module (2) connected to the threshold module (1); the threshold module (1) outputs threshold voltage, the switch module (2) receives the threshold voltage and outputs a switching signal, the switching signal comprising an opening signal and a closing signal; and the threshold module (1) receives the switching signal so as to adjust the threshold voltage. When the power supply voltage is greater than the threshold voltage, the switch module (2) outputs the closing signal, and the threshold voltage is lowered. When the power supply voltage is less than the threshold voltage, the switch module (2) outputs the opening signal, and the threshold voltage is raised. The threshold voltage can be generated directly by the power supply voltage by means of the threshold module (1), and a fast response can be achieved without additionally configuring a setup circuit having a reference voltage. Moreover, there is also no need for an additional comparator circuit, which simplifies the circuit while also achieving the function of the circuit, and the under-voltage protection circuit also has the requirement of precision.

Description

Undervoltage protection circuit

This application claims the priority of a Chinese patent application whose application date is June 17, 2020, the application number is 202010555850.3, and the invention title is "Undervoltage Protection Circuit", the entire content of which is incorporated into this application by reference.

Technical field

The invention relates to the field of analog circuits, in particular to a high-speed and high-precision undervoltage protection circuit.

Background technique

The undervoltage protection circuit in the prior art needs to compare the voltage division value of the power supply voltage VDD with the reference voltage Vref, and directly set a comparator to output the comparison result, and control the start and stop of the subsequent circuit. Therefore, when the voltage division value of the power supply voltage VDD is greater than the reference voltage Vref, the subsequent circuit is activated; and when the voltage division value of the power supply voltage VDD is less than the reference voltage Vref, the subsequent circuit is closed, thereby implementing undervoltage protection. In addition, the comparison result can be used to adjust the voltage division value of the power supply voltage VDD, so as to realize the hysteresis of the voltage division value of the power supply voltage VDD and prevent jitter.

However, in the prior art to compare voltages, the reference voltage Vref needs to be established first, which depends on the establishment accuracy and establishment speed of the reference voltage Vref. The general reference voltage Vref is the output of the bandgap reference, which usually requires a settling time of 10-100 μs, which limits the judgment speed of the power supply voltage VDD. If a simple reference voltage is established in order to increase the speed, the accuracy is difficult to be guaranteed.

Therefore, a new high-speed and high-precision undervoltage protection circuit must be designed.

Summary of the invention

In order to solve one of the above-mentioned problems, the present invention provides an undervoltage protection circuit. The undervoltage protection circuit includes a power supply voltage, a threshold module connected with the power supply voltage, and a switch module connected with the threshold module; the threshold module outputs a threshold Voltage, the switch module receives a threshold voltage and outputs a switch signal, the switch signal includes an open signal and a close signal, and the threshold module receives the switch signal to adjust the threshold voltage;

When the threshold voltage is greater than the power supply voltage, the switch module outputs an off signal, and the threshold voltage increases;

When the threshold voltage is less than the power supply voltage, the switch module outputs a closing signal, and the threshold voltage is reduced.

As a further improvement of the present invention, the threshold module includes a first triode and a second triode, the bases of the first triode and the second triode are connected to each other, and the emitters are both grounded. The base and collector of the first triode are connected to each other; the threshold module also includes a first adjustable resistance module and a second adjustable resistance module, the collector of the first triode is connected through the first adjustable resistance module Into the power supply voltage, the collector of the second triode is connected to the power supply voltage through the second adjustable resistance module.

As a further improvement of the present invention, the first adjustable resistance module includes a first resistor and a third resistor connected in series, and a first switch connected in parallel to the first resistor, and the second adjustable resistance module includes a second resistor connected in series. The resistor and the fourth resistor and the second switch connected in parallel to the second resistor; when the switch module outputs an open signal, the first switch and the second switch are opened, and when the switch module outputs a close signal, the first switch and the second switch The second switch is closed.

As a further improvement of the present invention, the resistance values of the first resistor and the second resistor are equal, and the resistance values of the third resistor and the fourth resistor are equal.

As a further improvement of the present invention, the threshold module further includes a fifth resistor, and the emitter of the second triode is grounded through the fifth resistor.

As a further improvement of the present invention, the threshold module further includes a sixth resistor and a seventh resistor, the base of the first triode is grounded through the sixth resistor, and the collector of the second triode is grounded through the seventh resistor. The resistance is grounded; the resistance values of the sixth resistance and the seventh resistance are equal.

As a further improvement of the present invention, when the switch module outputs a disconnect signal, the threshold voltage UVLO+ is:

When the switch module outputs a closing signal, the threshold voltage UVLO- is:

Among them, VT refers to the thermal voltage, and n is the multiple difference between the area of the first triode and the second triode.

As a further improvement of the present invention, the area of the second triode is n times that of the first triode, and n>1.

As a further improvement of the present invention, the switch module includes a comparator, the output terminal of the comparator outputs a switching signal, the negative input terminal is connected with the collector of the first triode, and the positive input terminal is connected with the second triode. The collectors are connected.

As a further improvement of the present invention, the switch module includes a third triode and an eighth resistor, the base of the third triode is connected to the collector of the second triode, the emitter is grounded, and the collector passes through The eighth resistor is connected to the power supply voltage; the switch module also includes a PMOS tube and an NMOS tube, the gate of the PMOS tube and the gate of the NMOS tube are both connected to the collector of the third triode, and the source of the PMOS tube Connect the power supply voltage, the source of the NMOS tube is grounded, and the drains of the PMOS tube and the NMOS tube are connected to each other and output switching signals.

Compared with the prior art, in the present invention, the threshold voltage can be directly generated by the power supply voltage through the threshold module, so there is no need to additionally set a reference voltage establishing circuit, and thus a quick response can be achieved. Moreover, the switch module can directly output the switch signal through the threshold voltage, which is equivalent to a built-in comparator. It also does not require an additional comparator circuit. While simplifying the circuit, it can also realize the function of the circuit and meet the requirements of accuracy. . In addition, the switch module of the present invention can output an off signal and an on signal to adjust the threshold voltage, thereby providing a hysteresis interval for the threshold voltage, allowing the threshold voltage to swing between UVLO+ and UVLO- to prevent frequent jitter.

Description of the drawings

Fig. 1 is a circuit diagram of the first implementation of the undervoltage protection circuit of the present invention;

Fig. 2 is a circuit diagram of a second embodiment of the undervoltage protection circuit of the present invention.

detailed description

In order to enable those skilled in the art to better understand the technical solutions of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described The embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

As shown in Figs. 1 to 2, an undervoltage protection circuit is provided. The undervoltage protection circuit includes a power supply voltage VDD, a threshold module 1 connected to the power supply voltage VDD, and a switch module 2 connected to the threshold module 1; The threshold module 1 outputs the threshold voltage UVLO, the switch module 2 receives the threshold voltage UVLO and outputs a switching signal, the switching signal includes an open signal and a close signal, and the threshold module 1 receives the switching signal to perform the threshold voltage UVLO adjust;

When the threshold voltage UVLO is greater than the power supply voltage VDD, the switch module 2 outputs an off signal, and the threshold voltage UVLO increases;

When the threshold voltage UVLO is less than the power supply voltage VDD, the switch module 2 outputs a closing signal, and the threshold voltage UVLO decreases.

Therefore, in the present invention, the power supply voltage VDD can directly generate the threshold voltage UVLO through the threshold module 1, so there is no need to set up a circuit for establishing a reference voltage separately, and thus a fast response can be achieved. Moreover, the switch module 2 can directly output the switch signal through the threshold voltage UVLO, which is equivalent to a built-in comparator, and no additional comparator circuit is also required, which simplifies the circuit while also realizing the function of the circuit with precision. Requirements. In addition, the switch module 2 in the present invention can output an off signal and an on signal to adjust the threshold voltage UVLO, thereby providing a hysteresis interval for the threshold voltage UVLO, allowing the threshold voltage to swing between UVLO+ and UVLO- to prevent frequent occurrences. Of jitter.

Further, the threshold module 1 includes a first triode Q1 and a second triode Q2, the bases of the first triode Q1 and the second triode Q2 are connected to each other, and the emitters are both grounded, so The base and collector of the first transistor Q1 are connected to each other; the threshold module 1 also includes a first adjustable resistance module and a second adjustable resistance module, and the collector of the first transistor Q1 passes through the first adjustable resistance module. The resistance adjustment module is connected to the power supply voltage VDD, and the collector of the second transistor Q2 is connected to the power supply voltage VDD through the second adjustable resistance module.

In the present invention, the threshold module 1 includes a first triode Q1 and a second triode Q2. It is known that the voltage Vbe between the base and the emitter of the triode has a temperature coefficient, and as the temperature increases And reduce. The difference between the Vbe of the two transistors connected to the base, that is, delta_Vbe, also has a temperature coefficient, and is a positive temperature coefficient, which increases with the increase in temperature. Therefore, in order to further improve the accuracy and reduce the influence of temperature on the threshold voltage UVLO, therefore, in the present invention, the first transistor Q1 and the second transistor Q2 are used, and the double-sided transistor circuit is used to form delta_Vbe, thereby adding and cooperating with Vbe In order to obtain the zero temperature coefficient, the accuracy and stability of the threshold voltage UVLO can be improved. specific,

delta_V _be =VT*ln(n);

Among them, VT refers to the thermal voltage (thermal voltage), that is, the potential difference caused by temperature changes, and is positively correlated with temperature.

In addition, in the present invention, the first adjustable resistance module and the second adjustable resistance module are controlled by the switch signal, and the resistance values can be adjusted separately, so that the threshold voltage UVLO is changed by the resistance value change to form the threshold voltage UVLO The hysteresis to prevent jitter.

Specifically, the first adjustable resistance module includes a first resistor R1 and a third resistor R3 connected in series, and a first switch k1 connected in parallel to the first resistor R1, and the second adjustable resistor module includes a second resistor R1 connected in series. The resistor R2 and the fourth resistor R4 and the second switch k2 connected in parallel to the second resistor R2; when the switch module 2 outputs a disconnect signal, the first switch k1 and the second switch k2 are disconnected, and the switch module 2 outputs When the signal is closed, the first switch k1 and the second switch k2 are closed.

Therefore, when the switch module 2 outputs a disconnection signal, the first switch k1 and the second switch k2 are disconnected, and the first resistor R1 and the second resistor R2 are connected to the circuit, so that the first transistor Q1 and the second transistor Q1 are connected to the circuit. The partial voltage at the collector of the transistor Q2 is reduced; when the switch module 2 outputs the closing signal, the first switch k1 and the second switch k2 are closed, and the first resistor R1 and the second resistor R2 are short-circuited, so that the first resistor R1 and the second resistor R2 are short-circuited. The partial voltages at the collectors of the transistor Q1 and the second transistor Q2 increase. Thus, the value of the threshold voltage UVLO is changed, and an adjustment interval is given to the threshold voltage UVLO to prevent fluctuations in the comparison process.

Moreover, in the present invention, the resistance values of the first resistor R1 and the second resistor R2 are equal, and the resistance values of the third resistor R3 and the fourth resistor R4 are equal. This ensures that the voltages at the collectors of the first transistor Q1 and the second transistor Q2 are equal.

In addition, the threshold module 1 further includes a fifth resistor R5, and the emitter of the second transistor Q2 is grounded through the fifth resistor R5. Therefore, the fifth resistor R5 can also provide a voltage division.

The threshold module 1 further includes a sixth resistor R6 and a seventh resistor R7, the base of the first transistor Q1 is grounded through the sixth resistor R6, and the collector of the second transistor Q2 is through the seventh resistor. R7 is grounded; the resistance values of the sixth resistor R6 and the seventh resistor R7 are equal. Since, as described above, the base and collector of the first triode Q1 are connected, the collector corresponding to the first triode Q1 is also grounded through the sixth resistor R6. The resistance values of the sixth resistor R6 and the seventh resistor R7 are also equal, so as to further ensure that the voltages at the collectors of the first transistor Q1 and the second transistor Q2 are the same.

Therefore, when the switch module 2 outputs a disconnect signal, the threshold voltage UVLO+ is:

When the switch module 2 outputs the closing signal, the threshold voltage UVLO- is:

Among them, as mentioned above, VT refers to the thermal voltage, and n is the multiple difference between the areas of the first transistor Q1 and the second transistor Q2.

Therefore, VT is a positive temperature coefficient and Vbe is a negative temperature coefficient. Therefore, the threshold voltage UVLO, which is close to zero temperature coefficient, can be obtained by adjusting the resistance of the resistors R2/R4/R5/R7 and the value of ln(n). Improve the accuracy of the threshold voltage UVLO. In addition, the above components can also be adjusted to arbitrarily adjust the absolute values of UVLO+ and UVLO-, which expands the application scenarios and is more flexible and practical.

In addition, the area of the second transistor Q2 is n times that of the first transistor Q1, and n>1, so that the temperature coefficient can be adjusted. At the same time, in the present invention, the area of the second transistor Q2 is relatively larger to apply the above formula.

The switch module 2 is used to compare the magnitude between the threshold voltage UVLO and the power supply voltage VDD, and output the comparison result to the subsequent circuit, and output a switch signal to adjust the magnitude of the threshold voltage UVLO. Specifically, in the present invention, two embodiments of the switch module 2 are provided.

In the first embodiment, as shown in FIG. 1, the switch module 2 includes a comparator C1, the output terminal of the comparator C1 outputs a switching signal, and the negative input terminal is connected to the collector of the first transistor Q1 , The positive input terminal is connected to the collector of the second transistor Q2. Therefore, the positive and negative ends of the comparator C1 are respectively connected to the collectors of the second triode Q2 and the first triode Q1 to compare the collectors of the first triode Q1 and the second triode Q2. The voltage. However, since the collector of the second transistor Q2 is grounded through the seventh resistor R7, the voltage at the positive input terminal of the comparator C1 is proportionally calculated and is equivalent to the power supply voltage VDD, while the voltage at the negative input terminal of the comparator C1 is proportionally calculated Calculated, it is equivalent to the threshold voltage UVLO. Then, when VDD>UVLO, the output terminal of the comparator C1 outputs a high level to start the subsequent circuit, and the first switch k1 and the second switch k2 are closed, thereby reducing the value of the threshold voltage UVLO, so that UVLO+ becomes UVLO -; When VDD<UVLO, the output terminal of the comparator C1 outputs a low level, the subsequent circuit is closed, and the first switch k1 and the second switch k2 are disconnected, thereby increasing the value of the threshold voltage UVLO, making UVLO- change It is UVLO+.

In the second embodiment, as shown in FIG. 2, the switch module 2 includes a third transistor Q3 and an eighth resistor R8, and the base of the third transistor Q3 is connected to the second transistor Q2. The collector and emitter are grounded, and the collector is connected to the power supply voltage VDD through the eighth resistor R8; the switch module 2 also includes a PMOS tube M1 and an NMOS tube M2, the gate of the PMOS tube M1 and the gate of the NMOS tube M2 The poles are all connected to the collector of the third transistor Q3, the source of the PMOS tube M1 is connected to the power supply voltage VDD, the source of the NMOS tube M2 is grounded, and the drains of the PMOS tube M1 and the NMOS tube M2 are connected to each other and output switching signals.

In this embodiment, the third transistor Q3, the eighth resistor R8, the PMOS tube M1, and the NMOS tube M2 constitute the switch module 2, and output switching signals to the first switch k1 and the second switch k2, and simultaneously output power The comparison result of the voltage VDD and the threshold voltage UVLO is given to the subsequent circuit.

Therefore, when VDD>UVLO, the base voltage at the third transistor Q3 is further increased, the third transistor Q3 is connected, and the voltage at the collector of the third transistor Q3 becomes zero. The PMOS tube M1 is turned on at a low level, so the voltage at the drain of the PMOS tube M1 becomes a high level; the subsequent circuit is started, and the first switch k1 and the second switch k2 are closed, thereby reducing the threshold voltage UVLO The value of UVLO+ becomes UVLO-. When VDD<UVLO, the result is opposite, so I won't repeat it here.

In summary, in the present invention, the threshold voltage UVLO is equivalent to directly generated by the power supply voltage VDD, so there is no need to additionally set the threshold voltage UVLO circuit; thus, it can be directly compared in the undervoltage protection circuit of the present invention, Therefore, quick response can be achieved.

In addition, in the threshold voltage UVLO of the present invention, by setting the first transistor Q1 and the second transistor Q2 circuit, the positive temperature coefficient and the negative temperature coefficient are added separately and adjusted to zero temperature coefficient, thereby The threshold voltage UVLO is closer to zero temperature coefficient, and the accuracy of the threshold voltage UVLO is improved.

In addition, the value of the threshold voltage UVLO can also be adjusted arbitrarily, which is more flexible and practical, and expands the application scenarios.

In addition, it should be understood that although this specification is described in accordance with the implementation manners, not each implementation manner only includes an independent technical solution. This narration in the specification is only for clarity, and those skilled in the art should regard the specification as a whole The technical solutions in the various embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

The series of detailed descriptions listed above are only specific descriptions of feasible implementations of the present invention, and are not intended to limit the scope of protection of the present invention. Any equivalent implementations or changes made without departing from the technical spirit of the present invention All should be included in the protection scope of the present invention.

Claims

An undervoltage protection circuit, characterized in that the undervoltage protection circuit includes a power supply voltage, a threshold module connected to the power supply voltage, and a switch module connected to the threshold module; the threshold module outputs a threshold voltage, and the switch The module receives the threshold voltage and outputs a switching signal, the switching signal includes an open signal and a close signal, and the threshold module receives the switching signal to adjust the threshold voltage;

When the threshold voltage is greater than the power supply voltage, the switch module outputs an off signal, and the threshold voltage increases;

When the threshold voltage is less than the power supply voltage, the switch module outputs a closing signal, and the threshold voltage is reduced.
The undervoltage protection circuit according to claim 1, wherein the threshold module comprises a first triode and a second triode, and the bases of the first triode and the second triode are mutually connected. Both the connection and the emitter are grounded, and the base and collector of the first triode are connected to each other; the threshold module further includes a first adjustable resistance module and a second adjustable resistance module, the collector of the first triode The electrode is connected to the power supply voltage through the first adjustable resistance module, and the collector of the second triode is connected to the power supply voltage through the second adjustable resistance module.
The undervoltage protection circuit according to claim 2, wherein the first adjustable resistance module includes a first resistor and a third resistor connected in series, and a first switch connected in parallel to the first resistor, and the second The adjustable resistance module includes a second resistor and a fourth resistor connected in series and a second switch connected in parallel to the second resistor; when the switch module outputs a disconnect signal, the first switch and the second switch are disconnected, and the switch module outputs When the signal is closed, the first switch and the second switch are closed.
The undervoltage protection circuit according to claim 3, wherein the resistance values of the first resistor and the second resistor are equal, and the resistance values of the third resistor and the fourth resistor are equal.
The undervoltage protection circuit according to claim 3, wherein the threshold module further comprises a fifth resistor, and the emitter of the second triode is grounded through the fifth resistor.
The undervoltage protection circuit according to claim 5, wherein the threshold module further comprises a sixth resistor and a seventh resistor, the base of the first triode is grounded through the sixth resistor, and the second The collector of the triode is grounded through the seventh resistor; the resistance of the sixth resistor and the seventh resistor are equal.
The under-voltage protection circuit according to claim 6, wherein when the switch module outputs a disconnection signal, the threshold voltage UVLO+ is:

When the switch module outputs a closing signal, the threshold voltage UVLO- is:

Among them, VT refers to the thermal voltage, and n is the multiple difference between the area of the first triode and the second triode.
The undervoltage protection circuit according to claim 7, wherein the area of the second triode is n times that of the first triode, and n>1.
The undervoltage protection circuit according to claim 6, wherein the switch module comprises a comparator, the output terminal of the comparator outputs a switching signal, and the negative input terminal is connected to the collector of the first triode, The positive input terminal is connected to the collector of the second triode.
The undervoltage protection circuit according to claim 6, wherein the switch module includes a third triode and an eighth resistor, and the base of the third triode is connected to the collector of the second triode. The electrode, the emitter are grounded, and the collector is connected to the power supply voltage through the eighth resistor; the switch module also includes a PMOS tube and an NMOS tube, and the gate of the PMOS tube and the gate of the NMOS tube are both connected to the third triode The source of the PMOS tube is connected to the power supply voltage, the source of the NMOS tube is grounded, and the drains of the PMOS tube and the NMOS tube are connected to each other and output switching signals.