Linear regulator circuit having input under-voltage detection function

Abstract

The present invention provides a linear regulator circuit having an input under-voltage detection function. The linear regulator circuit comprises a power supply control unit, a reference voltage generation unit, and a voltage stabilizing unit, the reference voltage generation unit is separately connected to the power supply control unit and the voltage stabilizing unit, the voltage stabilizing unit is connected to an output end, and the power supply control unit is connected between an input end and the output end; the reference voltage generation unit is configured to generate a stable reference voltage, and a bias current for the power supply control unit to work normally; the voltage stabilizing unit is configured to output a feedback voltage when an output voltage of the output end is higher than a preset threshold; and the power supply control unit is configured to modulate a control signal on the basis of the feedback voltage of the output voltage and the reference voltage, so that the voltage of the output end is regulated. The present invention improves the flexibility of the circuit system by means of the unique input under-voltage detection function and voltage stabilization feedback function. The present invention has a simple circuit design, low cost, and high reliability and sustainable development performance.

Description

Linear regulator circuit with input under-voltage detection function

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 2024106993609, filed May 31, 2024. The contents of the aforementioned application are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application relates to the field of power electronics and switching power supply applications, and in particular to a linear regulator circuit with input under-voltage detection function. BACKGROUND

[0004] In circuit design, linear regulators with input under-voltage detection function (LDO) are widely used to power controllers. In complex systems, strict timing control is often required among multiple controllers. For example, in power synchronous rectification control, the secondary side drive power supply usually needs to be powered on after the output voltage stabilizes to a certain value to ensure smooth transition of synchronous rectification. Currently, there are mainly two traditional methods to handle this problem:

[0005] First, use an RC delay network to achieve power-on delay: this method generates a fixed delay through a simple resistor-capacitor network. Although it is simple to deploy, its main disadvantage is that it cannot accurately control the power-on timing. In addition, the RC delay circuit will also have a delay when powering off, which may cause the circuit to fail to work as expected in the case of power failure restart, thereby affecting the stability and reliability of the system.

[0006] Second, build a complex timing judgment circuit: this solution usually involves using a timing control circuit composed of comparators, operational amplifiers, and other active chips. Although this can improve the accuracy of timing control, it also increases the complexity and cost of the circuit, especially in applications that require high power density design, this approach is not suitable.

[0007] These two traditional methods have their own advantages and disadvantages, but neither can perfectly solve the problem of timing control, especially in applications that require high precision and high reliability. Therefore, exploring a new method that can accurately and flexibly control timing while meeting the requirements of high power density has become an important research direction in this field.

[0008] SUMMARY

[0009] The present application aims to provide a linear regulator circuit with input under-voltage detection function that can accurately control timing and improve the stability of the power supply system.

[0010] Technical solution: The linear voltage regulator circuit with input under-voltage detection function comprises a power supply control unit, a reference voltage generation unit and a voltage stabilizing unit,

[0011] The reference voltage generation unit is connected with the power supply control unit and the voltage stabilizing unit respectively, the voltage stabilizing unit is connected to the output end, and the power supply control unit is connected between the input end and the output end.

[0012] The reference voltage generation unit is configured to generate a stable reference voltage and a bias current for normal operation of the power supply control unit.

[0013] The voltage stabilizing unit is configured to output a feedback voltage when the output voltage of the output end is higher than a preset threshold.

[0014] The power supply control unit is configured to modulate the control signal based on the feedback voltage and the reference voltage of the output voltage, so that the voltage of the output end is adjusted.

[0015] Further, a voltage dividing unit is further included, the voltage dividing unit is connected with the reference end of the power supply control unit and the reference voltage generation unit respectively, and the voltage dividing unit is configured to divide the input voltage to generate a voltage proportional to the input voltage, so that the power supply control unit is turned on.

[0016] Further, the reference voltage generation unit comprises a reference chip TL431 and a first resistor, one anode end of the reference chip TL431 is connected with the voltage stabilizing unit, and the other anode end is connected to the ground through the first resistor, and the cathode end of the reference chip TL431 is connected with the power supply control unit.

[0017] Further, the voltage stabilizing unit is a voltage stabilizing tube, one end of the voltage stabilizing tube is connected with the output end, and the other end is connected with the reference voltage generation unit.

[0018] Further, the power supply control unit comprises a PNP triode and a second resistor, the second resistor is connected with the base and the emitter of the PNP triode.

[0019] The base of the PNP triode is connected with the reference voltage generation unit, the collector of the PNP triode is connected with the output end, and the emitter of the PNP triode is connected with the input end.

[0020] Further, the voltage dividing unit comprises a third resistor and a fourth resistor,

[0021] The connection end of the third resistor and the fourth resistor is connected with the reference voltage generation unit, the other end of the fourth resistor is grounded, and the other end of the third resistor is connected with the input end.

[0022] Further, the PNP triode input voltage is less than the reference voltage multiplied by the ratio of the third resistor to the sum of the third resistor and the fourth resistor, and the PNP triode is not conductive.

[0023] Further, the PNP triode input voltage is greater than the reference voltage multiplied by the ratio of the third resistor to the sum of the third resistor and the fourth resistor, and the PNP triode is conductive.

[0024] Further, the voltage of the voltage stabilizing tube is greater than the output voltage, and the voltage stabilizing tube is broken down and conductive.

[0025] Further, the voltage of the voltage stabilizing tube is less than or equal to the preset threshold voltage.

[0026] Beneficial effects: the application has strict timing control, which ensures that the voltage stabilizing tube can be quickly turned on when the output voltage exceeds the set value, thereby protecting the circuit from overvoltage damage.

[0027] The reference voltage generation unit of the application generates a stable reference voltage for the power control unit through the voltage dividing resistors third resistor and fourth resistor and the reference voltage generation function of the reference chip TL431, and uses the reference voltage to control the on and off timing of the power control unit, not only increasing the application flexibility of the circuit, but also enabling it to play a special role in occasions requiring voltage compensation, ensuring that the system can still run continuously and stably when the power supply condition is unstable.

[0028] The application improves the flexibility and stability of the circuit system through its unique input under-voltage detection and voltage stabilizing feedback function.

[0029] The circuit of the application is simple in design, low in cost, and has high reliability and sustainable development. BRIEF DESCRIPTION OF DRAWINGS

[0030] Fig. 1 is a schematic diagram of a linear voltage regulator circuit structure with input under-voltage detection function. DETAILED DESCRIPTION

[0031] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of the present application. Unless otherwise defined, the technical terms or scientific terms used herein should be understood as the common meanings thereof by those skilled in the art. The similar words such as "comprise" used herein mean that the elements or objects before the words cover the elements or objects listed after the words and their equivalents, and do not exclude other elements or objects.

[0032] As shown in FIG. 1, an embodiment of the present application provides a linear voltage regulator circuit with input under-voltage detection function, which comprises a power control unit 1, a reference voltage generating unit 2, a voltage stabilizing unit 3 and a voltage dividing unit 4. The reference voltage generating unit 2 is connected with the power control unit 1 and the voltage stabilizing unit 3 respectively, the voltage stabilizing unit 3 is connected to an output end, and the power control unit 1 is connected between an input end and the output end.

[0033] The reference voltage generating unit 2 comprises a reference chip TL431 U1 and a first resistor R1. One anode end of the reference chip TL431 U1 is connected with the voltage stabilizing unit 3, and the other anode end is connected to the ground through the first resistor R1. A cathode end of the reference chip TL431 U1 is connected with the power control unit 1. The reference voltage generating unit 2 is configured to generate a stable reference voltage and a bias current for normal operation of the power control unit 1. The first resistor R1 is connected with a reference voltage source inside the reference chip TL431 U1 to form a reference current source. The first resistor R1 provides a stable reference current or voltage for the reference chip TL431 U1, ensures correct and stable operation of the reference chip TL431 U1, and can also limit the current flowing through the internal reference source to protect the circuit from overcurrent damage. There is a feedback loop between the output voltage of the reference chip TL431 U1 and the output voltage of the output end. When the output voltage of the output end changes, the internal circuit of the linear voltage regulator circuit can be automatically adjusted through the feedback loop of the reference chip TL431 U1 to restore the output voltage to the set value. The voltage dividing network composed of the third resistor R3 and the fourth resistor R4 realizes the input under-voltage detection function in the linear voltage regulator circuit together with the reference voltage generating unit of the reference chip TL431 U1.

[0034] The voltage stabilizing unit 3 is a voltage stabilizing tube Z1, one end of the voltage stabilizing tube Z1 is connected to the output end, and the other end is connected to the reference voltage generating unit 2. The voltage stabilizing unit 3 is configured to output a feedback voltage when the output voltage of the output end is higher than a preset threshold voltage. The above-mentioned preset threshold voltage is greater than or equal to the rated breakdown voltage of the voltage stabilizing tube Z1. In the reverse breakdown state, even if the current flowing through the voltage stabilizing tube Z1 changes, the voltage across the voltage stabilizing tube Z1 can remain substantially constant. When the voltage in the circuit exceeds the Zener voltage of the voltage stabilizing tube Z1, the voltage stabilizing tube Z1 is turned on, and the excess voltage is shunted through the first resistor R1, preventing the voltage from rising further, thereby protecting other elements in the circuit.

[0035] The power supply control unit 1 includes a PNP transistor Q1 and a second resistor R2 connected to the base and emitter of the PNP transistor Q1; the base of the PNP transistor Q1 is connected to the reference voltage generating unit 2, the collector of the PNP transistor Q1 is connected to the output end, and the emitter of the PNP transistor Q1 is connected to the input end. When the input voltage of the PNP transistor Q1 is less than the reference voltage multiplied by the ratio of the third resistor R3 to the sum of the third resistor R3 and the fourth resistor R4, the PNP transistor Q1 is not turned on. When the input voltage of the PNP transistor Q1 is greater than the reference voltage multiplied by the ratio of the third resistor R3 to the sum of the third resistor R3 and the fourth resistor R4, the PNP transistor Q1 is turned on. The power supply control unit 1 is configured to modulate the control signal based on the feedback voltage of the output voltage and the reference voltage, so that the voltage of the output end is adjusted.

[0036] The voltage dividing unit 4 is connected to the reference end of the power supply control unit 1 and the reference voltage generating unit 2, respectively, and is configured to divide the input voltage to generate a voltage proportional to the input voltage to turn on the power supply control unit 1. The voltage dividing unit 4 includes a third resistor R3 and a fourth resistor R4, the connection end of the third resistor R3 and the fourth resistor R4 is connected to the reference voltage generating unit 2, the other end of the fourth resistor R4 is grounded, and the other end of the third resistor R3 is connected to the input end. By adjusting the values of the third resistor R3 and the fourth resistor R4, the output voltage of the TL431 U1 can be changed, which in turn affects the conduction or cutoff of the PNP transistor Q1. According to the design requirements of the circuit, it is determined when the input voltage is lower than which threshold value the undervoltage detection needs to be triggered. According to the required detection voltage range and the characteristics of TL431, appropriate values of the third resistor R3 and the fourth resistor R4 are selected to ensure that the output voltage of TL431 can accurately reflect the state of the input voltage. Through actual testing and adjustment of the values of the third resistor R3 and the fourth resistor R4, it is ensured that the output voltage of TL431 can accurately trigger the conduction of the PNP transistor when the input voltage is lower than the set threshold value, thereby realizing the undervoltage detection.

[0037] The on and off state of the PNP transistor Q1 depends on the output voltage of the reference chip TL431 U1. When the input voltage is less than the ratio of the fourth resistor R4 to the third resistor R3 and the fourth resistor R4 and the reference voltage (V in <N*V ref ), the reference end voltage of the reference chip TL431 U1 is lower than the reference voltage, the reference chip TL431 U1 enters the saturation state, the cathode end voltage approaches the input voltage, the output voltage of the reference chip TL431 U1 is lower than its internal reference voltage, causing the switch tube to be cut off, the output voltage cannot be established, and the circuit is in the open state. When the input voltage is greater than the ratio of the fourth resistor R4 to the third resistor R3 and the fourth resistor R4 and the reference voltage (V in >N*V ref ), the reference end voltage of the reference chip TL431 U1 is higher than the reference voltage, the cathode end voltage begins to decrease, the output voltage of the reference chip TL431 U1 is higher than its internal reference voltage, causing the switch tube to be turned on, the output voltage begins to be established, and the circuit is in the closed state. The ratio of the fourth resistor R4 to the third resistor R3 and the fourth resistor R4 determines the ratio of the output voltage at the output end to the input voltage. By selecting appropriate values of the third resistor R3 and the fourth resistor R4, the minimum turn-on voltage of the linear voltage regulator can be set. The larger this ratio, the smaller the turn-on voltage. At the same time, through the voltage division network and the reference voltage generation unit of the reference chip TL431 U1, the stability of the output voltage when the input voltage changes can be realized, ensuring that the circuit can work normally under different conditions.

[0038] When the output voltage exceeds the voltage across the zener diode Z1, the zener diode Z1 will break down and conduct, and the breakdown current will flow through the first resistor R1. This current will cause the voltage across the first resistor R1 to rise. The rise in voltage across the first resistor R1 will cause the anode potential of the reference chip TL431 U1 to rise, as the anode of the reference chip TL431 U1 is connected to the two ends of the zener diode Z1. The reference chip TL431 U1 is a circuit with feedback function, and the voltage between its reference end and anode will be adjusted through internal circuit to restore to the value of the reference voltage. The reference voltage is a preset voltage value, which represents the desired stable output voltage of the circuit. When the voltage between the reference end and the anode of the reference chip TL431 U1 decreases to the reference voltage, the circuit enters a stable closed-loop state. This means that the output voltage is maintained near the reference voltage, and even if the input voltage or load changes, the circuit will automatically adjust to maintain the stability of the output voltage.

[0039] When the circuit enters a stable state, the output voltage value is equal to the sum of the voltage across the zener diode Z1 and the voltage obtained by the fourth resistor R4, minus the reference voltage value. Specifically:

[0040] wherein V in is the input voltage of the input terminal, V o is the output voltage of the output terminal, V ref is the reference voltage, is the voltage across the zener Z1;

[0041] It can be seen that the output of V O is equal to plus a component V', that is, when N is large, it can be considered that The component V' is usually used as a control signal or reference voltage in the circuit, for adjusting other parameters of the circuit, such as the on-off state of the switching tube. In this way, the circuit can automatically adjust the output voltage according to the change of the input voltage, in order to maintain the stability and accuracy of the circuit.

[0042] Specifically, when the input voltage V in = 0-15V, the required output voltage V O = 10V, the reference voltage V ref = 2.5V of the reference chip TL431 U1, the third resistor R3 = 3kΩ, the fourth resistor R4 = 1kΩ, and is the zener Z1, at this time, when the input voltage V in is less than 10V, the output voltage V O = 0; when the input voltage V in is greater than 10V, the output voltage V O > 0.

[0043] The present application has strict timing control, which ensures that when the output voltage exceeds the set value, the zener can be quickly turned on, thereby protecting the circuit from overvoltage damage.

[0044] The reference voltage generation unit of the present application generates a stable reference voltage for the power control unit through the voltage dividing resistors third resistor and fourth resistor and the reference voltage generation function of the reference chip TL431, and uses the reference voltage to control the on-off timing of the power control unit, which not only increases the application flexibility of the circuit, but also enables it to play a special role in occasions requiring voltage compensation, ensuring that the system can still run continuously and stably when the power supply condition is unstable.

[0045] The present application improves the flexibility and stability of the circuit system through its unique input under-voltage detection and voltage stabilization feedback function.

[0046] The circuit of the present application is simple in design, low in cost, and has high reliability and sustainable development.

[0047] While the embodiments of the application have been illustrated and described in detail, it will be readily apparent to those skilled in the art that various modifications and changes can be made to the embodiments without departing from the scope of the application as described in the claims. It is therefore intended that the application not be limited to the exact embodiments described herein, but that the application can also include all such modifications and changes as fall within the scope of the claimed application. Moreover, the application illustratively described herein suitably can be practiced in the absence of any element or step which is not specifically disclosed herein.

Claims

1. A linear voltage regulator circuit with input undervoltage detection function, characterized in that, It includes a power control unit, a reference voltage generation unit, and a voltage regulation unit. The reference voltage generation unit is connected to the power control unit and the voltage regulation unit respectively. The voltage regulation unit is connected to the output terminal, and the power control unit is connected between the input terminal and the output terminal. The reference voltage generation unit is configured to generate a stable reference voltage and a bias current for the normal operation of the power control unit. The voltage regulator unit is configured to output a feedback voltage when the output voltage at the output terminal is higher than a preset threshold voltage; The power control unit is configured to modulate the control signal based on the feedback voltage and reference voltage of the output voltage, so that the voltage at the output terminal is regulated.

2. The circuit according to claim 1, characterized in that, It also includes a voltage divider unit, which is connected to the reference terminals of the power control unit and the reference voltage generation unit, respectively. The voltage divider unit is configured to divide the input voltage to generate a voltage proportional to the input voltage so as to turn on the power control unit.

3. The circuit according to claim 2, characterized in that, The reference voltage generation unit includes a reference chip TL431 and a first resistor. One anode of the reference chip TL431 is connected to the voltage regulation unit, and the other anode is connected to ground through the first resistor. The cathode of the reference chip TL431 is connected to the power control unit.

4. The circuit according to claim 3, characterized in that, The voltage regulation unit is a Zener diode, with one end of the Zener diode connected to the output terminal and the other end connected to the reference voltage generation unit.

5. The circuit according to claim 4, characterized in that, The power control unit includes a PNP transistor and a second resistor, the second resistor being connected to the base and emitter of the PNP transistor; The base of the PNP transistor is connected to the reference voltage generation unit, the collector of the PNP transistor is connected to the output terminal, and the emitter of the PNP transistor is connected to the input terminal.

6. The circuit according to claim 5, characterized in that, The voltage divider unit includes a third resistor and a fourth resistor. The connection terminals of the third resistor and the fourth resistor are connected to the reference voltage generation unit, the other end of the fourth resistor is grounded, and the other end of the third resistor is connected to the input terminal.

7. The circuit according to claim 6, characterized in that, When the input voltage of the PNP transistor is less than the reference voltage multiplied by the ratio of the third resistor to the sum of the third and fourth resistors, the PNP transistor is not conducting.

8. The circuit according to claim 7, characterized in that, When the input voltage of the PNP transistor is greater than the reference voltage multiplied by the ratio of the third resistor to the sum of the third and fourth resistors, the PNP transistor is turned on.

9. The circuit according to claim 8, characterized in that, When the voltage of the Zener diode is greater than the output voltage, the Zener diode breaks down and becomes conductive.

10. The circuit according to claim 9, characterized in that, The voltage of the Zener diode is less than or equal to the preset threshold voltage.

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