CN215154253U

CN215154253U - Low-side output circuit with current limiting function

Info

Publication number: CN215154253U
Application number: CN202121438254.3U
Authority: CN
Inventors: 王文榜; 陈岚; 王小杰; 冯杰
Original assignee: Wuhan Jimu Intelligent Technology Co ltd
Current assignee: Wuhan Jimu Intelligent Technology Co ltd
Priority date: 2021-06-25
Filing date: 2021-06-25
Publication date: 2021-12-14
Anticipated expiration: 2031-06-25

Abstract

The application provides a low side output circuit with current-limiting function belongs to automotive electronics circuit technical field, specifically includes MOS pipe Q1, triode Q2, load resistance R1 and feedback resistance R4, MOS pipe Q1's drain electrode passes through load resistance R1 and is connected with power V1's positive pole, power V1's negative pole ground connection, MOS pipe Q1's gate is passed through resistance R2 and is connected with control signal source, MOS pipe Q1's gate still with triode Q2's collecting electrode is connected, MOS pipe Q1's source with triode Q2's base is connected, MOS pipe Q1's source still pass through feedback resistance R4 with triode Q2's emitter is connected, triode Q2's emitter still pass through resistance R3 with resistance R2's output is connected, triode Q2's emitter still grounds. Through the scheme of this application, can avoid MOS pipe because of the problem that load current is big and burn out, and circuit structure is simple, reduces manufacturing cost.

Description

Low-side output circuit with current limiting function

Technical Field

The application relates to the technical field of automotive electronic circuits, in particular to a low-side output circuit with a current limiting function.

Background

With the increasing automobile sales volume along with the automobile family, people have higher and higher requirements on various aspects of automobiles, such as safety performance, operating performance, comfort level and the like. The higher the requirement, the more severe the requirements are put on the related parts of automobile sensors, electronic appliances and the like. The electronic control units of the automobile body are increased from the past 2-3 to 10 or more, and the diversity of functions of single parts and components necessarily increases the complexity of an electronic circuit system, including hardware, low-level driving, algorithms and the like, wherein the hardware design is a basic carrier for realizing the functions of the whole parts and components.

The load devices (such as an actuating motor and an LED lamp) on the vehicle are driven by the power MOS tube. Some loads need to be driven at a low side, large current surge can occur due to the fact that the electricity utilization environment on an automobile is complex, when the current of the loads becomes large instantly, if the current change exceeds the maximum current of a driving circuit, an NMOS tube is easy to burn out. If some intelligent driving chips are adopted, the internal parts of the intelligent driving chips have the function of overcurrent protection, but the price of the chips is more expensive, and the cost is greatly increased.

SUMMERY OF THE UTILITY MODEL

Embodiments of the present invention provide a low-side output circuit with a current limiting function, which at least partially solves the problems in the prior art.

In a first aspect, an embodiment of the present application provides a low-side output circuit with a current limiting function, where the circuit includes: the power supply comprises a MOS tube Q1, a triode Q2, a load resistor R1 and a feedback resistor R4, wherein the drain electrode of the MOS tube Q1 is connected with the positive electrode of a power supply V1 through a load resistor R1, the negative electrode of the power supply V1 is grounded, the grid electrode of the MOS tube Q1 is connected with a control signal source through a resistor R2, the grid electrode of the MOS tube Q1 is further connected with the collector electrode of the triode Q2, the source electrode of the MOS tube Q1 is connected with the base electrode of the triode Q2, the source electrode of the MOS tube Q1 is further connected with the emitter electrode of the triode Q2 through a feedback resistor R4, the emitter electrode of the triode Q2 is further connected with the output end of the resistor R2 through a resistor R3, and the emitter electrode of the triode Q2 is also grounded.

According to a specific implementation manner of the embodiment of the present application, the transistor Q2 is an NPN transistor, and the MOS transistor Q1 is an NMOS transistor.

According to a specific implementation manner of the embodiment of the application, the low-side output circuit is further provided with a filter capacitor C1, and the drain of the MOS transistor Q1 is further grounded through the filter capacitor C1.

According to a specific implementation manner of the embodiment of the application, the maximum output current I of the circuit_max≤110％I_dWherein, I_dIs the rated current of the load resistor R1.

According to a specific implementation manner of the embodiment of the application, the power P of the feedback resistor R4>2×I2_maxXr, where R is the resistance value of the feedback resistor R4.

According to a specific implementation manner of the embodiment of the present application, the MOS transistor Q1 is of a BSP130 model.

According to a specific implementation manner of the embodiment of the present application, the type of the transistor Q2 is BC 817.

In a second aspect, an embodiment of the present application further provides a low-side output circuit with a current limiting function, where the circuit includes: the MOS tube Q1, triode Q2, load resistance R1 and feedback component constantan wire, the drain electrode of MOS tube Q1 passes through load resistance R1 and is connected with the positive pole of power V1, the negative pole ground connection of power V1, the grid of MOS tube Q1 passes through resistance R2 and is connected with the control signal source, the grid of MOS tube Q1 still with triode Q2's collecting electrode is connected, the source of MOS tube Q1 with triode Q2's base is connected, the source of MOS tube Q1 still passes through the constantan wire and is connected with triode Q2's projecting pole, triode Q2's projecting pole still passes through resistance R3 and is connected with resistance R2's output, triode Q2's projecting pole still ground connection.

According to a specific implementation manner of the embodiment of the present application, the drain of the MOS transistor Q1 is further grounded through a filter capacitor C1.

Advantageous effects

The low-side output circuit with the current limiting function in the embodiment of the application realizes the current limiting function through the negative feedback function of the triode by adding the triode and the feedback resistor, thereby protecting an MOS (metal oxide semiconductor) tube in the circuit and avoiding the situation that the MOS tube is burnt out due to the instant increase of load current or the fact that an input error is connected to a higher-voltage power supply; and the circuit structure is simple, and the manufacturing cost is low.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a prior art low side output circuit diagram;

fig. 2 is a diagram of a low-side output circuit with current limiting function according to an embodiment of the present invention;

fig. 3 is a diagram of a low-side output circuit with current limiting according to another embodiment of the present invention;

fig. 4 is a voltage-current variation flow chart of a low-side output circuit diagram with a current limiting function according to an embodiment of the present invention.

Detailed Description

The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

The following description of the embodiments of the present application is provided by way of specific examples, and other advantages and effects of the present application will be readily apparent to those skilled in the art from the disclosure herein. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments. The present application is capable of other and different embodiments and its several details are capable of modifications and/or changes in various respects, all without departing from the spirit of the present application. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It is noted that various aspects of the embodiments are described below within the scope of the appended claims. It should be apparent that the aspects described herein may be embodied in a wide variety of forms and that any specific structure and/or function described herein is merely illustrative. Based on the present application, one skilled in the art should appreciate that one aspect described herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented and/or a method practiced using any number of the aspects set forth herein. Additionally, such an apparatus may be implemented and/or such a method may be practiced using other structure and/or functionality in addition to one or more of the aspects set forth herein.

It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present application, and the drawings only show the components related to the present application rather than the number, shape and size of the components in actual implementation, and the type, amount and ratio of the components in actual implementation may be changed arbitrarily, and the layout of the components may be more complicated.

In addition, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, it will be understood by those skilled in the art that the aspects may be practiced without these specific details.

In the field of automotive electronics, load devices on a vehicle are all driven by power MOS tubes. Some loads require low-side driving, as shown in fig. 1, in which the load current is about 100mA and the maximum current of the NMOS transistor is 350 mA. Because the electricity environment on the automobile is relatively complex, large-current surge can occur. When the load current becomes large instantly, if the current variation exceeds the maximum current 350mA of the driving circuit, the NMOS tube is easy to burn out.

To solve the above problem, a common method is to increase the driving current margin, for example, the actual rated current is 100mA, and an NMOS transistor with a driving capability of more than 3 times (350 mA in this example) is selected to increase the driving capability. When the load current exceeds the rated current 100mA and does not exceed 350mA, the driving circuit can still work under the condition that the load is not burnt out, and the driving circuit is not burnt out. But when the load current exceeds 350mA, the driving NMOS transistor is also burnt. This solution can only solve some of the situations, and the problem is not solved completely.

In view of the above problem, an embodiment of the present application provides a low-side output circuit with a current limiting function, and as shown in fig. 2, the circuit includes: the power supply comprises a MOS tube Q1, a triode Q2, a load resistor R1 and a feedback resistor R4, wherein the drain electrode of the MOS tube Q1 is connected with the positive electrode of a power supply V1 through a load resistor R1, the negative electrode of the power supply V1 is grounded, the grid electrode of the MOS tube Q1 is connected with a control signal source through a resistor R2, the grid electrode of the MOS tube Q1 is further connected with the collector electrode of the triode Q2, the source electrode of the MOS tube Q1 is connected with the base electrode of the triode Q2, the source electrode of the MOS tube Q1 is further connected with the emitter electrode of the triode Q2 through a feedback resistor R4, the emitter electrode of the triode Q2 is further connected with the output end of the resistor R2 through a resistor R3, and the emitter electrode of the triode Q2 is also grounded. Specifically, the triode Q2 is an NPN triode, and the MOS transistor Q1 is an NMOS transistor. The control signal source may be a pin of the CPU or the MCU, and is used to output a control signal.

Furthermore, the drain of the MOS transistor Q1 is grounded through a filter capacitor C1, the MOS transistor may have voltage fluctuation when operating at high frequency, and the filter capacitor C1 is used for filtering high-frequency noise to perform a voltage stabilizing function.

In one embodiment, the MOS transistor Q1 is of the type BSP 130.

In one embodiment, the transistor Q2 has a model number BC 817.

It should be noted that the types of the MOS transistor Q1 and the transistor Q2 can be selected according to actual circuit conditions, and are not limited to those listed in the above embodiments.

For convenience of describing the operation principle of the low-side output circuit with current limiting function in the embodiment of the present application, a detailed description is provided below with reference to fig. 3, specific parameters of each component are labeled in the figure, a maximum current limiting 110mA is implemented in the embodiment, and a flow chart of dynamic changes of voltage and current in the circuit is referred to fig. 4.

In this embodiment, the voltage of the power source V1 is 12V, the resistance of the load resistor R1 is 120 Ω, the resistance of the feedback resistor R4 is 6 Ω, the resistance of the resistor R2 is 1k Ω, the resistance of the resistor R3 is 10k Ω, and the capacitance of the filter capacitor C1 is 47 nF. It should be noted that the specific values of the components in the present embodiment are merely for reference, and can be adjusted according to the actual situation in the automotive electronic circuit, and are not limited to those listed in the present embodiment.

When the circuit is working normally, the current value I flowing through the load R1_dAnd about 96mA, the MOS transistor Q1 is in a saturated conducting state at this time, and the transistor Q2 is in a cut-off state.

When the resistance of the load R1 becomes large, the load current I_dThe value becomes smaller, and the use of the MOS transistor Q1 is not affected, and is not analyzed here.

When the resistance of the load R1 becomes smaller, the load current I_dThe larger the value, the larger the current flowing through the resistor R4. As known from ohm's law, the voltage value Vbe across the resistor R4 also becomes large. When the Vbe voltage is greater than the base turn-on voltage of transistor Q2 (0.66V in this example), transistor Q2 starts to turn on, and transistor Q2 enters the amplifying state from the off state. As the current into the base of transistor Q2 continues to increase, the current into the collector of transistor Q2 from point a also increases, thereby causing the voltage at a to become progressively smaller. When the voltage value of VA is less than the saturation conduction voltage threshold voltage of MOS transistor Q1At the value Vth, the MOS transistor Q1 is put into an amplified state, and the conduction channel between the gate and the source of the MOS transistor Q1 is narrowed, so that the value of the current flowing from the drain to the source of the MOS transistor Q1, that is, the load current Id value is reduced. Namely, the current limiting function is realized by using the negative feedback function of the triode Q2, so that the MOS transistor Q1 is protected.

As the load current Id continues to decrease, the value of the current flowing across the feedback resistor R4 also decreases accordingly. As is known from ohm's law, the voltage value Vbe across the resistor R4 also decreases. When the voltage Vbe is smaller than the typical value of the base electrode opening voltage of the triode Q2 and is 0.66V, the triode Q2 enters a cut-off state again, the voltage value of VA rises again, and when the voltage value of VA is larger than the threshold voltage value Vth of the saturation conducting voltage of the MOS transistor Q1, the MOS transistor Q1 enters a saturation state again, so that the original normal state of the whole circuit is recovered.

When the load resistor is used specifically, the rated current I of the load resistor R1 needs to be determined firstly_d。

According to I_dDetermining the maximum output current I_max. Due to the action of negative feedback, according to need I_maxIs slightly larger than I_dNamely, the maximum output current I of the circuit is generally not required to be reserved with large margin_max≤110％I_dPreferably, the balance is left between 5% and 10%. If the maximum output current I_maxAnd in order to accurately control the current within 5%, a triode with a base starting voltage Vth with a smaller fluctuation range influenced by temperature is selected, so that the consistency is convenient to control. In other cases, a triode with a smaller base starting voltage range can be selected, so that the consistency is convenient to control.

For the selection of the feedback resistor R4, the resistance value R of the feedback resistor R4 is Vth/I_maxSince the load current is generally larger, a feedback resistor with larger power P must be selected and a margin is reserved. The margin of more than 2 times is common in automobile electronics, and the power of the feedback resistor R4

It should be noted that, if the control accuracy is required to be relatively high, the accuracy of the feedback resistor also needs to be selected with high accuracy.

In one embodiment, the package for the feedback resistor is typically relatively large, considering that the power of the resistor is a large concern with the package. Current I_dIn the case of a relatively large value, the feedback resistance R4 needs to be replaced by a high-precision constantan wire.

The utility model provides an embodiment, to the problem that MOS pipe easily burns out among the current on-vehicle load low side drive circuit, invented a low side output circuit based on triode negative feedback effect realizes current-limiting function, mainly was applicable to the scene of the external interface low side output of automotive electronics product, the drive of common LED lamp or relay solenoid that is used for driving. By selecting the feedback resistors with different resistance values, the maximum output current can be accurately set. When the output current exceeds the set maximum current, the self current regulation function of the circuit can be realized through negative feedback action, so that the output is limited below the set maximum current value, and the circuit can avoid the condition that a drive NMOS tube is damaged due to load short circuit or output misconnection to a higher-voltage power supply; and has the advantages of simple circuit structure and low manufacturing cost.

The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A low-side output circuit having a current limiting function, the circuit comprising: the power supply comprises a MOS tube Q1, a triode Q2, a load resistor R1 and a feedback resistor R4, wherein the drain electrode of the MOS tube Q1 is connected with the positive electrode of a power supply V1 through a load resistor R1, the negative electrode of the power supply V1 is grounded, the grid electrode of the MOS tube Q1 is connected with a control signal source through a resistor R2, the grid electrode of the MOS tube Q1 is further connected with the collector electrode of the triode Q2, the source electrode of the MOS tube Q1 is connected with the base electrode of the triode Q2, the source electrode of the MOS tube Q1 is further connected with the emitter electrode of the triode Q2 through a feedback resistor R4, the emitter electrode of the triode Q2 is further connected with the output end of the resistor R2 through a resistor R3, and the emitter electrode of the triode Q2 is also grounded.

2. The low-side output circuit with current-limiting function of claim 1, wherein said transistor Q2 is an NPN transistor, and said MOS transistor Q1 is an NMOS transistor.

3. The low-side output circuit with current limiting function according to claim 1, wherein said low-side output circuit further comprises a filter capacitor C1, and the drain of said MOS transistor Q1 is further grounded through said filter capacitor C1.

4. The low-side output circuit with current limiting function according to claim 2, wherein the maximum output current I of the low-side output circuit_max≤110％I_dWherein, I_dIs the rated current of the load resistor R1.

5. The low-side output circuit with current limiting function of claim 4, wherein the power of the feedback resistor R4

Where R is the resistance of the feedback resistor R4.

6. The low-side output circuit with the current limiting function according to any one of claims 1 to 5, wherein the MOS transistor Q1 is of a type BSP 130.

7. The low-side output circuit with the current limiting function according to any one of claims 1 to 5, wherein the type of the transistor Q2 is BC 817.

8. A low-side output circuit having a current limiting function, the circuit comprising: the MOS tube Q1, triode Q2, load resistance R1 and feedback component constantan wire, the drain electrode of MOS tube Q1 passes through load resistance R1 and is connected with the positive pole of power V1, the negative pole ground connection of power V1, the grid of MOS tube Q1 passes through resistance R2 and is connected with the control signal source, the grid of MOS tube Q1 still with triode Q2's collecting electrode is connected, the source of MOS tube Q1 with triode Q2's base is connected, the source of MOS tube Q1 still passes through the constantan wire and is connected with triode Q2's projecting pole, triode Q2's projecting pole still passes through resistance R3 and is connected with resistance R2's output, triode Q2's projecting pole still ground connection.

9. The low-side output circuit with current-limiting function of claim 8, wherein said transistor Q2 is an NPN transistor, and said MOS transistor Q1 is an NMOS transistor.

10. The low-side output circuit with the current limiting function of claim 8, wherein the drain of the MOS transistor Q1 is further grounded through a filter capacitor C1.