CN216851291U

CN216851291U - Constant current source with short-circuit protection function

Info

Publication number: CN216851291U
Application number: CN202220063907.2U
Authority: CN
Inventors: 张翔; 张一禾; 李青; 夏青云
Original assignee: Shenzhen Bohai Digital Intelligence Technology Co ltd
Current assignee: Shenzhen Bohai Digital Intelligence Technology Co ltd
Priority date: 2022-01-11
Filing date: 2022-01-11
Publication date: 2022-06-28
Anticipated expiration: 2032-01-11

Abstract

The application relates to a take short-circuit protection function's constant current source, this constant current source includes: the constant current circuit is connected with the thermistor and is used for being connected with a load through the thermistor; the constant current circuit is in contact with the thermistor to conduct heat to the thermistor to raise the resistance of the thermistor when the constant current circuit is short-circuited. The constant current source with the short-circuit protection function transfers the heat of the constant current circuit to the serially connected thermistor in the short-circuit state, so that the resistance value of the thermistor is increased to a high-resistance state, the output current and the voltage difference of the constant current circuit can be reduced, the constant current circuit can maintain a low-power consumption state in the short-circuit state, the effect of protecting the circuit in a low-cost mode can be realized, the circuit power consumption of the constant current source in the short-circuit state is also reduced, and the operation and maintenance cost of the constant current source is reduced.

Description

Constant current source with short circuit protection function

Technical Field

The disclosure relates to the field of power supply circuits, in particular to a constant current source with a short-circuit protection function.

Background

The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

For the constant current output, a short circuit phenomenon may occur due to various reasons, and at this time, the original load power is all added to the constant current main output circuit, resulting in the heating of the constant current source device.

The existing constant current source can reduce power consumption through a feedback circuit and a Schmitt circuit to finish protection, and then enters an initial state after a short circuit phenomenon disappears (even a load is dropped once and is electrified again). However, for many meters with 4-20 mA (1 or more) constant current sources, the occurrence of short circuit accidents is rare, and the additional protection (circuit) may generate heat to be space and cost-limited, thereby increasing the use cost.

SUMMERY OF THE UTILITY MODEL

In view of the above, it is necessary to provide a constant current source with a short-circuit protection function for reducing power consumption of the constant current source in a short-circuit state.

The utility model provides a take short-circuit protection function's constant current source includes: the constant current circuit is connected with the thermistor and is used for being connected with a load through the thermistor; the constant current circuit is in contact with the thermistor to conduct heat to the thermistor to raise the resistance of the thermistor when the constant current circuit is short-circuited.

Preferably, the thermistor is a PTC thermistor.

Preferably, when the temperature of the thermistor is lower than the curie point, the resistance value of the thermistor is in a first range, and when the temperature of the thermistor is greater than or equal to the curie point, the resistance value of the thermistor is in a second range.

Preferably, the first range is 1-2 ohms, and the second range is 500 ohms.

Preferably, the constant current circuit includes a first resistor and a first triode, one end of the first resistor is connected to a power supply, the other end of the first resistor is connected to the first triode, an output end of the first triode is connected to one end of the thermistor, and the other end of the thermistor is connected to the load.

Preferably, the constant current circuit further includes a second resistor and a second triode, the power supply is connected to one end of the second resistor through the second triode, the other end of the second resistor is grounded, and the first triode is connected to the second triode to control the current flowing through the first triode.

Preferably, the first transistor and the second transistor are NPN transistors, wherein,

the end E of the first triode is connected to the ends B of the first resistor and the second triode, the end B of the first triode is connected to the ends C of the second resistor and the second triode, and the end C of the first triode is connected to the thermistor;

the end E of the second triode is connected to the first resistor and the power supply, the end B of the second triode is connected to the end E of the first triode and the first resistor, and the end C of the second triode is connected to the end C of the second resistor and the first triode.

Preferably, the device further comprises a diode, and the thermistor is connected with the load through the diode.

Preferably, the power supply further comprises an overvoltage protection circuit, one end of the overvoltage protection circuit is connected to the diode, and the other end of the overvoltage protection circuit is grounded.

Preferably, the overvoltage protection circuit comprises one or more of a voltage stabilizing diode, a capacitor and a resistor.

Compared with the prior art, the constant current source with the short-circuit protection function transfers the heat of the constant current circuit to the serially connected thermistor in the short-circuit state, so that the resistance value of the thermistor is increased to the high-resistance state, and the output current and the voltage difference of the constant current circuit can be reduced.

Drawings

In order to illustrate the embodiments more clearly, the drawings that will be needed in the description of the embodiments will be briefly described below, it being apparent that the drawings in the following description are some examples of the disclosure, and that other drawings may be derived from those drawings by a person skilled in the art without inventive effort.

Fig. 1 is a schematic circuit diagram of a constant current source with a short-circuit protection function.

Fig. 2 is a schematic diagram of the thermistor and constant current circuit.

Description of the main elements

The following detailed description will further illustrate the disclosure in conjunction with the above-described figures.

Detailed Description

In order that the above objects, features and advantages of the present disclosure can be more clearly understood, a detailed description of the present disclosure will be given below with reference to the accompanying drawings and detailed description. In addition, the embodiments and features of the embodiments of the present application may be combined with each other without conflict. In the following description, numerous specific details are set forth to provide a thorough understanding of the present disclosure, and the described embodiments are merely a subset of the embodiments of the present disclosure, rather than a complete embodiment. All other embodiments, which can be derived by one of ordinary skill in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present disclosure.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure.

In various embodiments, for convenience in description and not limitation of the disclosure, the term "coupled" as used in the specification and claims of the present disclosure is not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships are changed accordingly.

Fig. 1 is a schematic circuit diagram of a constant current source with a short-circuit protection function. As shown in fig. 1, the constant current source with short-circuit protection function includes a constant current circuit 10, a thermistor PTC, an overvoltage protection circuit 20, and a plug 30. The constant current circuit 10 is used for generating a constant current output, the thermistor PTC can rapidly raise the tissue to protect the constant current circuit 10 when receiving the heat of the constant current circuit 10, the overvoltage protection circuit 20 is used for protecting the output from overvoltage, and the plug 30 is used for connecting a load circuit (not shown in the figure).

As shown in fig. 1, the constant current circuit 10 includes a first transistor Q1, a second transistor Q2, a first resistor R1, and a second resistor R2. One end of the first resistor R1 is connected to a power supply, the other end of the first resistor R1 is connected to the first triode Q1, the output end of the first triode Q1 is connected to one end of the thermistor PTC, and the other end of the thermistor PTC is connected to the load. The power supply is connected to one end of the second resistor R2 through the second transistor Q2, the other end of the second resistor R2 is grounded, and the first transistor Q1 is connected to the second transistor Q2, so as to control the current flowing through the first transistor Q1. In this way, the voltage of the first resistor R1 is monitored by the second transistor Q2, so that the base current control of the first transistor Q1 is completed, and the constant current control of the constant current circuit 10 can be realized. As an example, the first and second transistors Q2 may be NPN transistors, wherein the terminal E of the first transistor Q1 is connected to the terminals B of the first resistor R1 and the second transistor Q2, the terminal B is connected to the terminals C of the second resistor R2 and the second transistor Q2, and the terminal C is connected to the thermistor PTC. The end E of the second triode Q2 is connected to the first resistor R1 and the power supply, the end B is connected to the end E of the first triode Q1 and the first resistor R1, and the end C is connected to the second resistor R2 and the end C of the first triode Q1. As an example, the voltage of the power supply may be 24V normal, the output current of the constant current source is 5mA to 160mA, 250mA is taken as an example for the entry protection, and the parameters of each device of the constant current circuit 10 are designed as follows.

As shown in fig. 1, since the second resistor R2 provides a base current for the first transistor Q1, in the case that the effective output current of the constant current circuit 10 is less than 200mA, and in the case that the collector current of the first transistor Q1 is less than or equal to 200mA and the amplification factor is greater than or equal to 100 times, the second resistor R2 is about 24V (voltage)/2A (base current of the first transistor Q1), and is 12K ohm. Considering the maximum voltage drop of 0.6V of the first resistor R1, a resistor of 10K ohms may be practically used. The resistance value of the first resistor R1 determines the magnitude of the output current of the constant current circuit 10. When the operating voltage of the second transistor Q2 is 0.65V and the current is 0.2A, the resistance of the first resistor R1 is 0.65/0.2 — 3.25 ohms, so that a resistor of 3.3 ohms can be selected.

Through test, under the condition of no heat dissipation, the output of the constant current circuit 10 is 220mA transient state (constant current source current limiting) and 120mA (thermistor PTC self-heating) steady state. The transient state of 220mA is actually measured on a circuit board (with nearly 1 square centimeter heat dissipation), and the normal state is realized after the protection of 160mA, so that the design requirement is met.

The constant current circuit 10 is connected to the thermistor PTC, and is connected to a load through the thermistor PTC. In this embodiment, the constant current source further includes a diode D1, and the thermistor PTC is connected to the load through the diode D1. For the convenience of connection, the thermistor PTC of the constant current source is connected to the plug 30, and is electrically connected to the load through the plug 30. In the present embodiment, the connector 30 is a three-terminal connector 30, and the polarities of both sides are the same, for example, the polarities of both sides may be ground connection, so as to play a role of "fool-proof".

The overvoltage protection circuit 20 has one end connected to the diode D1 and the other end grounded, and thus, it functions as an overvoltage protection. In some embodiments, the overvoltage protection circuit 20 includes one or more of a zener diode TVS, a capacitor C1, and a resistor. In this embodiment, the overvoltage protection circuit 20 includes a voltage regulator diode TVS, a capacitor C1, and a third resistor R3. The voltage regulator diode TVS may be a transient suppression diode, which is connected in parallel with the capacitor C1 and the third resistor R3, and has one end connected to the N-terminal of the diode D1 and the other end grounded, so as to perform an overvoltage protection function.

Fig. 2 is a schematic diagram of the thermistor PTC and constant current circuit 10. As shown in fig. 1 and 2, the constant current circuit 10 is in contact with the thermistor PTC to conduct heat to the thermistor PTC to raise the resistance of the thermistor PTC when the constant current circuit 10 is short-circuited. In this embodiment, the thermistor PTC is a PTC thermistor PTC, and when the temperature of the thermistor PTC is lower than the curie point, the resistance of the thermistor PTC is in a first range, and when the temperature of the thermistor PTC is higher than or equal to the curie point, the resistance of the thermistor PTC is in a second range. In some preferred embodiments, the first range is 1 to 2 ohms and the second range is 500 ohms.

In some embodiments, the thermistor PTC may be in direct contact with the first triode of the constant current circuit 10 for heat conduction, and in other embodiments, heat conduction may also be achieved through a heat conductor (e.g., metal, thermally conductive graphite, etc.). When the constant current circuit 10 enters a short-circuit state, the first triode Q1 generates a large amount of heat, after the heat is conducted to the thermistor PTC, the thermistor PTC enters a curie point, and the resistance value thereof increases to enter a second range, resulting in a decrease in the output current of the constant current source and a reduction in the first output current and the voltage difference, thereby playing a role of protecting the circuit and generating no large amount of power consumption. The actual measurement of the circuit shows that after the temperature of the thermistor PTC exceeds the Curie point and the resistance value enters a second range, the passing current is only 50 mA. After the short circuit phenomenon disappears, the PTC of the thermistor exits the working state, and after the resistance value enters a first range, the circuit is recovered and continues to output according to the normal setting.

When the constant current circuit works, a load is connected with a constant current source through the plug connector 30, and a first triode Q1, a second triode Q2, a first resistor R1 and a second resistor R2 of the constant current circuit 10 output constant current to the load through the thermistor PTC and the diode D1.

After the short circuit occurs, the first transistor Q1 heats up to limit the current, and the voltage drop across it is approximately equal to the heating of the supply voltage. The heat generated by the first triode Q1 is conducted to the thermistor PTC, so that the thermistor PTC enters a high resistance state, and the resistance value of the thermistor PTC is suddenly changed from the first range to the second range, thereby reducing the current and the voltage difference of the first triode Q1, and enabling the constant current circuit 10 to enter a low power consumption state. Meanwhile, the working margin of the constant current source can still be basically unchanged according to normal work, the extra expense caused by accidents is reduced, and the circuit protection action is completed without exceeding the rated power.

The constant current source with the short-circuit protection function transfers the heat of the constant current circuit 10 to the thermistor PTC connected in series in a short-circuit state, so that the resistance value of the thermistor PTC is increased to a high-resistance state, and the output current and the voltage difference of the constant current circuit 10 can be reduced, therefore, the constant current circuit 10 can maintain a low-power consumption state in the short-circuit state, not only can play a role of protecting the circuit in a low-cost mode, but also can reduce the circuit power consumption of the constant current source in the short-circuit state, and reduce the operation and maintenance cost of the constant current source.

In several embodiments provided in the present disclosure, it will be apparent to those skilled in the art that the present disclosure is not limited to the details of the above-described exemplary embodiments, and can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the disclosure being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Furthermore, it is obvious that the word "comprising" does not exclude other elements or steps, and the singular does not exclude the plural. The terms first, second, etc. are used to denote names, but not any particular order.

Although the present disclosure has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the present disclosure.

Claims

1. A constant current source with a short-circuit protection function is characterized by comprising: the constant current circuit is connected with the thermistor and is used for being connected with a load through the thermistor; the constant current circuit is in contact with the thermistor to conduct heat to the thermistor to raise the resistance of the thermistor when the constant current circuit is short-circuited.

2. The constant current source with the short-circuit protection function according to claim 1, wherein the thermistor is a PTC thermistor.

3. The constant current source with a short-circuit protection function according to claim 1, wherein the resistance value of the thermistor is in a first range when the temperature of the thermistor is lower than the curie point, and the resistance value of the thermistor is in a second range when the temperature of the thermistor is greater than or equal to the curie point.

4. The constant current source with short-circuit protection function according to claim 3, wherein the first range is 1 to 2 ohms, and the second range is 500 ohms.

5. The constant current source with the short-circuit protection function according to claim 1, wherein the constant current circuit includes a first resistor and a first transistor, one end of the first resistor is connected to a power supply, the other end of the first resistor is connected to the first transistor, an output end of the first transistor is connected to one end of the thermistor, and the other end of the thermistor is connected to the load.

6. The constant current source with the short-circuit protection function according to claim 5, wherein the constant current circuit further comprises a second resistor and a second transistor, the power supply is connected to one end of the second resistor through the second transistor, the other end of the second resistor is grounded, and the first transistor is connected to the second transistor to control the current flowing through the first transistor.

7. The constant current source with short-circuit protection of claim 6, wherein said first and second transistors are NPN transistors, wherein,

8. The constant current source with the short-circuit protection function according to claim 7, further comprising a diode, wherein the thermistor is connected to the load through the diode.

9. The constant current source with the short-circuit protection function according to claim 8, further comprising an overvoltage protection circuit, one end of which is connected to the diode and the other end of which is grounded.

10. The constant current source with short-circuit protection function according to claim 9, wherein the overvoltage protection circuit comprises one or more of a zener diode, a capacitor and a resistor.