Constant current output protection circuit
By introducing PTC and TVS protection circuits into the constant current output circuit, the problem of overheating damage caused by short circuits is solved, achieving the effect of reducing maintenance costs without increasing circuit size.
Patent Information
- Application Number
- CN202520413010.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-11
- Publication Date
- 2026-02-10
- Estimated Expiration
- 2035-03-11
AI Technical Summary
Existing constant current output circuits are prone to overheating damage under short-circuit conditions, and short circuits occur frequently in unattended equipment, resulting in high maintenance costs.
The protection circuit consists of a positive temperature coefficient thermistor (PTC) and a transient voltage suppressor diode (TVS). Under short-circuit conditions, the PTC heats up rapidly and enters a high-resistance state to achieve current limiting protection, and the circuit recovers after the short circuit disappears.
Without increasing the circuit size, it effectively prevents overheating damage caused by short circuits, reduces operating and maintenance costs, and ensures that the circuit returns to normal operation after a short circuit.
Smart Images
Figure CN223898968U_ABST
Abstract
Description
[Technical Field]
[0001] This utility model relates to the field of current output protection technology, and in particular to a constant current output protection circuit. [Background Technology]
[0002] For constant current output, a short circuit may occur for various reasons. At this time, the original load power is all applied to the constant current main output circuit, resulting in heat generation.
[0003] For many instruments with 4-20mA (one or more) constant current source outputs, short circuit accidents are rare. Therefore, the additional protection (circuit) design may be limited by space and cost.
[0004] However, in practical applications, especially in unattended power plants, oil wells, and pipeline inspections, short circuits during product operation always occur with a probability of 1 in 1000 to 5. In reality, online monitoring instruments cannot be fully wireless, as product purchase costs, installation levels, and maintenance requirements vary. In a 400-square-kilometer uninhabited area covered by tens of thousands of instruments, a short circuit occurring almost every few days, causing a source of damage, significantly increases operating costs. [Utility Model Content]
[0005] To overcome the above problems, this utility model proposes a constant current output protection circuit that can effectively solve the above problems.
[0006] The present invention provides a technical solution to the above-mentioned technical problems by providing a constant current output protection circuit, including a constant current source, a short-circuit protection device, an overvoltage protection device, a current guiding device, and a plug-in device. The short-circuit protection device and the overvoltage protection device are respectively connected to the constant current source. The current guiding device is connected to the short-circuit protection device. The overvoltage protection device and the current guiding device are connected together to the plug-in device. The short-circuit protection device is a positive temperature coefficient thermistor PTC1. The overvoltage protection device includes a transient voltage suppressor diode TVS1, a capacitor C1, and a resistor R3. One end of the resistor R3 is connected to the constant current source. One end of the capacitor C1 is connected to one end of the resistor R3. The other end of the capacitor C1 is connected to the other end of the resistor R3. Pin 1 of the transient voltage suppressor diode TVS1 is connected to one end of the capacitor C1 and then grounded together. Pin 2 of the transient voltage suppressor diode TVS1 is connected to the other end of the capacitor C1 and then connected together to the current guiding device.
[0007] Preferably, the constant current source includes transistors Q1 and Q2, resistors R1 and R2. Pin 2 of transistor Q2 is connected to one end of resistor R1. Pin 1 of transistor Q2 and pin 3 of transistor Q1 are connected together to the other end of resistor R1. Pin 1 of transistor Q1 and pin 3 of transistor Q2 are connected together to resistor R2. Pin 2 of transistor Q1 is connected to one end of a positive temperature coefficient thermistor PTC1.
[0008] Preferably, the current guiding device is a current guiding diode D1, one end of which is connected to one end of a positive temperature coefficient thermistor PTC1.
[0009] Preferably, the plug-in device is a three-terminal connector J1 with one polarity on each side.
[0010] Compared with existing technologies, the constant current output protection circuit of this invention utilizes the rapid heating of the constant current tube under short-circuit conditions, causing the integrated PTC to enter its Curie point (high resistance), thereby limiting the current and reducing the constant current output current (equivalent to its storage condition, no longer a hot spot), thus providing protection. Without increasing the source size (heat dissipation), it very simply solves the problem of source overheating damage caused by short circuits, reducing operating and maintenance costs. When the short circuit disappears, the PTC exits its working state, the circuit recovers, and continues to operate according to normal settings. [Attached Image Description]
[0011] Figure 1 This is a block diagram of the constant current output protection circuit of this utility model;
[0012] Figure 2 This is a schematic diagram of the constant current output protection circuit of this utility model.
Detailed Implementation Methods
[0013] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this utility model.
[0014] It should be noted that in this embodiment of the invention, all directional indications (such as up, down, left, right, front, back, etc.) are limited to relative positions on the specified view, rather than absolute positions.
[0015] Furthermore, in this utility model, the use of terms such as "first," "second," etc., is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this utility model, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.
[0016] Please see Figure 1 and Figure 2 The constant current output protection circuit of this utility model includes a constant current source, a short circuit protection device, an overvoltage protection device, a current guiding device, and a plug-in device. The short circuit protection device and the overvoltage protection device are respectively connected to the constant current source. The current guiding device is connected to the short circuit protection device. The overvoltage protection device and the current guiding device are connected together to the plug-in device.
[0017] The short-circuit protection device is a positive temperature coefficient thermistor PTC1.
[0018] The overvoltage protection device includes a transient voltage suppressor diode (TVS1), a capacitor C1, and a resistor R3. One end of the resistor R3 is connected to a constant current source. One end of the capacitor C1 is connected to one end of the resistor R3, and the other end of the capacitor C1 is connected to the other end of the resistor R3. Pin 1 of the transient voltage suppressor diode TVS1 is connected to one end of the capacitor C1 and then grounded together. Pin 2 of the transient voltage suppressor diode TVS1 is connected to the other end of the capacitor C1 and then connected together to a current-directing device. This overvoltage protection device is for protecting the output from unexpected overvoltage and is unrelated to short-circuit protection.
[0019] The constant current source includes transistors Q1 and Q2, resistors R1 and R2. Pin 2 of transistor Q2 is connected to one end of resistor R1. Pin 1 of transistor Q2 and pin 3 of transistor Q1 are connected together to the other end of resistor R1. Pin 1 of transistor Q1 and pin 3 of transistor Q2 are connected together to resistor R2. Pin 2 of transistor Q1 is connected to one end of a positive temperature coefficient thermistor PTC1. The physical thermal resistance between PTC1 and Q1 is minimal.
[0020] The current guiding device is a current guiding diode D1, one end of which is connected to one end of a positive temperature coefficient thermistor PTC1.
[0021] The connector is a three-terminal connector J1, with one polarity on each side to prevent "foolproofing".
[0022] Principle Explanation: Q2 monitors the voltage across R1 to control the base current of Q1, thus achieving constant current control during output short circuit. At this time, the voltage across EC of Q1 is above 20V, the current is 0.22A, and the power dissipation of Q1 is above 4W. However, considering only non-short circuit heat dissipation: 0.2V (EC voltage) x 0.2 (A) = 0.04 (W), resulting in an effective heat dissipation of 0.4W. PTC1 and Q1 have the lowest thermal resistance in the PCB design, facilitating PTC1's entry into operating mode: the hot spot shifts from Q1 to PTC1, with a measured current of approximately 5mA (1.2W).
[0023] Design (calculation) based on a normal 24V output of 5 to 160mA and protection activation at 250mA:
[0024] See Figure 2 R2 provides the base current for Q1. When the effective output is less than 200mA, and the amplification factor of Q1 is greater than or equal to 100 when the collector current is less than or equal to 200mA, then R2 is approximately 24 (voltage) / 2 (Q1 base current), which is 12KΩ. Considering the maximum voltage drop of R1 is 0.6V, 10KΩ is actually used. The resistance value of R1 determines the output current: Assuming the operating voltage of Q2 is 0.65V and the current is 0.2A, then R1 = 0.65 / 0.2 = 3.25Ω, and 3.3Ω is selected. Actual test results (without heat dissipation) show a transient of 220mA (constant current source current limiting) and a steady-state of 120mA (PTC self-heating). On the product's circuit board (with nearly 1 square centimeter of heat dissipation), the measured transient is 220mA, and the normal state after protection is 160mA (meets requirements).
[0025] Compared with existing technologies, the constant current output protection circuit of this invention utilizes the rapid heating of the constant current tube under short-circuit conditions, causing the integrated PTC to enter its Curie point (high resistance), thereby limiting the current and reducing the constant current output current (equivalent to its storage condition, no longer a hot spot), thus providing protection. Without increasing the source size (heat dissipation), it very simply solves the problem of source overheating damage caused by short circuits, reducing operating and maintenance costs. When the short circuit disappears, the PTC exits its working state, the circuit recovers, and continues to operate according to normal settings.
[0026] The above description is only a preferred embodiment of the present utility model and does not limit the patent scope of the present utility model. Any modifications, equivalent substitutions and improvements made within the concept of the present utility model should be included within the patent protection scope of the present utility model.
Claims
1. A constant current output protection circuit, characterized in that, It includes a constant current source, a short-circuit protection device, an overvoltage protection device, a current guiding device, and a plug-in device. The short-circuit protection device and the overvoltage protection device are respectively connected to the constant current source. The current guiding device is connected to the short-circuit protection device. The overvoltage protection device and the current guiding device are connected together to the plug-in device. The short-circuit protection device is a positive temperature coefficient thermistor PTC1; The overvoltage protection device includes a transient voltage suppressor diode (TVS1), a capacitor (C1), and a resistor (R3). One end of the resistor (R3) is connected to a constant current source. One end of the capacitor (C1) is connected to one end of the resistor (R3), and the other end of the capacitor (C1) is connected to the other end of the resistor (R3). Pin 1 of the transient voltage suppressor diode (TVS1) is connected to one end of the capacitor (C1) and then grounded together. Pin 2 of the transient voltage suppressor diode (TVS1) is connected to the other end of the capacitor (C1) and then connected together to a current guiding device.
2. The constant current output protection circuit as described in claim 1, characterized in that, The constant current source includes transistors Q1 and Q2, resistors R1 and R2. Pin 2 of transistor Q2 is connected to one end of resistor R1. Pin 1 of transistor Q2 and pin 3 of transistor Q1 are connected together to the other end of resistor R1. Pin 1 of transistor Q1 and pin 3 of transistor Q2 are connected together to resistor R2. Pin 2 of transistor Q1 is connected to one end of a positive temperature coefficient thermistor PTC1.
3. The constant current output protection circuit as described in claim 1, characterized in that, The current guiding device is a current guiding diode D1, one end of which is connected to one end of a positive temperature coefficient thermistor PTC1.
4. The constant current output protection circuit as described in claim 1, characterized in that, The connector is a three-terminal connector J1 with one polarity on each side.