PLC power-up soft start protection device
By combining EMI filtering circuits and soft-start circuits, the problem of surge current at the moment of PLC controller power-on is solved, achieving smooth current transition and interference suppression, thereby improving the stability and reliability of the PLC system.
Patent Information
- Application Number
- CN202522463450.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-20
- Publication Date
- 2026-11-03
- Estimated Expiration
- 2035-11-20
AI Technical Summary
Existing PLC controllers are prone to generating large surge currents at the moment of power-on, which can lead to overload of power supply components, contact burning or system reset. Furthermore, existing soft-start circuits are limited in application or are costly in industrial environments.
An EMI filter circuit and a soft-start circuit are adopted, combined with a power current-limiting resistor and a MOSFET controllable conduction method. The EMI filter circuit suppresses high-frequency noise and transient interference, while the soft-start circuit limits the input current at the moment of power-on and achieves smooth conduction through a delay module to prevent surge impact caused by the charging of the large bus capacitor.
It effectively suppresses surge current at power-on, avoids damage to the power module, improves the operational stability and anti-interference performance of the PLC device, and also has data storage capabilities, enhancing system reliability and electromagnetic compatibility.
Smart Images
Figure CN224935577U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of industrial automation and power protection circuits, specifically to a PLC power-on soft start protection device. Background Technology
[0002] A Programmable Logic Controller (PLC) is a microprocessor-based digital control system capable of automatically controlling external expansion components. Therefore, it has wide and important applications in control systems of various devices. In a PLC system, the power supply is the core of the entire device's stable operation. It not only needs to provide stable voltage to the processor, memory, and input / output modules, but also needs to cope with frequent power switching and surge interference in industrial environments. Especially at the moment of power-on, the PLC power supply often generates a large inrush current, which can easily lead to overload of power supply components, contact burning, or even system reset. To reduce such inrushes, a soft-start circuit is usually designed into the power supply to effectively protect the PLC and its peripheral circuits by controlling the current changes during power-on.
[0003] To achieve data storage after power failure, large-capacity capacitors are typically connected in parallel on the power bus of small PLC systems, which further increases the inrush current at power-on. Common soft-start circuits in existing technologies mainly include: connecting a current-limiting resistor in series at the input and short-circuiting the resistor via a relay after voltage stabilization; this circuit is simple, but the relay is bulky and has a limited lifespan, making it unsuitable for small PLC applications; gradually turning on a MOSFET with PWM modulation provides good soft-start performance, but its application is limited in industrial environments with high interference; some dedicated chips integrate soft-start functionality, but these rely on specific components and are costly; traditional MOSFET plus RC delay schemes present a dilemma in soft-start time selection: too short a time results in insufficient suppression, while too long a time can cause the MOSFET to overheat excessively in the linear region, potentially burning out the device.
[0004] Therefore, the design of a power-on soft-start scheme for small PLCs, which must not only cope with the surge current brought by large-capacity loads, but also adapt to complex and harsh industrial environments, remains an important technical problem that urgently needs to be solved. Summary of the Invention
[0005] The purpose of this invention is to overcome the defect in the prior art that PLC controllers are prone to generating large surge currents at the moment of power-on, and to provide a PLC power-on soft-start protection device. This device can effectively control the input current in the initial stage of power connection, reduce the surge current caused by the charging of the large capacitor on the power bus, avoid impact on the power module and related components, and improve the operating stability and anti-interference performance of the PLC device.
[0006] To achieve the above objectives, this utility model discloses a PLC power-on soft start protection device, which includes an EMI filter circuit and a soft start circuit. The EMI filter circuit adopts an LCR filter network structure. The soft start circuit adopts a combination of a power current-limiting resistor and a MOSFET with controllable conduction. After the PLC power supply is filtered by the EMI filter circuit to remove conducted interference, it is then current-limited by the soft start circuit.
[0007] This invention employs an EMI filter network to suppress high-frequency noise and transient interference from the input power supply, including differential-mode interference and common-mode interference, while reducing interference conducted outward from the power line. It also uses a combination of power current limiting and controllable conduction of MOSFETs to effectively limit the input current at the moment the PLC is powered on, preventing surge impacts caused by the charging of large-capacity capacitors on the bus.
[0008] Furthermore, the soft-start circuit includes a power resistor module, a controller protection module, a delay module, and a control switching switch; the power resistor module uses a coated wire-wound resistor R4 to limit the input current; the controller protection module consists of a Zener diode VD2 and a bidirectional transient voltage suppressor diode VD1 to control the voltage level; the control switching switch module consists of parallel resistors R1, R2, and R3 and a PMOS transistor Q1; the delay module consists of resistor R2 and capacitors C7, C8, C9, and C10 to control the PMOS transistor Q1 to turn on with a delay.
[0009] This invention's soft-start circuit limits current at power-on instantaneously via a power resistor module. After a set time, a control switch gradually short-circuits the power resistor using a delay module, thus completing a smooth power-on process. Furthermore, the control device protection module limits the amplitude of the gate control level, ensuring that the field-effect transistor (PMOS transistor Q1) is not damaged.
[0010] Furthermore, the aforementioned PLC power-on soft-start protection device also includes a reverse connection protection circuit; the reverse connection protection circuit uses diode D1, which is connected to PMOS transistor Q1 in the soft-start circuit. The reverse connection protection circuit automatically blocks the current when the positive and negative terminals of the power supply are reversed, preventing damage caused by incorrect wiring.
[0011] Furthermore, the PLC power-on soft-start protection device of this utility model also includes a power-down retention circuit; the power-down retention circuit includes multiple electrolytic capacitors connected in parallel, with the positive terminal connected to the controller protection module and the negative terminal connected to the control switching module. By utilizing the power-down retention circuit to release energy at the moment of power failure, the PLC controller can complete the necessary data saving or status maintenance operations in a very short time, thereby improving the system's reliability and fault tolerance.
[0012] Furthermore, the aforementioned EMI filter circuit comprises an LCR filter network consisting of a common-mode inductor CM1, film capacitors C1 and C6, and safety capacitors C2, C3, C4, and C5. Safety capacitors C2, C3, C4, and C5 are Y capacitors, connected in parallel between the power input line and protective ground (PE). The common-mode inductor forms an impedance barrier for high-frequency common-mode signals, while the capacitors provide a high-frequency bypass path, achieving dual suppression of input power supply noise and effectively improving the electromagnetic compatibility of the power supply system.
[0013] More specifically, the circuit connection of the PLC power-on soft-start protection device of this utility model is as follows: A bidirectional transient voltage suppression diode VD1 and a film capacitor C1 are connected in parallel and then connected to the power input ports 24V_IN and 0V_IN respectively; one end of the safety capacitor C2 is connected to the power input port 24V_IN, and the other end is connected to the power protection ground PE; one end of the safety capacitor C3 is connected to the power input port 0V_IN, and the other end is connected to the power protection ground PE; pin 1 of the common mode inductor CM1 is connected to one end of both the safety capacitor C2 and the film capacitor C1; pin 2 of the common mode inductor CM1 is connected to one end of both the safety capacitor C4 and the film capacitor C6; pin 3 of the common mode inductor CM1 is connected to the other end of both the safety capacitor C3 and the film capacitor C1; pin 4 of the common mode inductor CM1 is connected to the other end of both the safety capacitor C5 and the film capacitor C6; one end of the resistor R1 is connected to the film capacitor C5; one end of the resistor R1 is connected to the film capacitor C6; one end of the resistor R1 is connected to the film capacitor C4; one end of the common mode inductor CM1 is connected to the film capacitor C6; one end of the common mode inductor CM1 is connected to the film capacitor C5; one end of the common mode inductor CM1 is connected to the film capacitor C6; one end of the common mode inductor CM ... One end of capacitor C6 is connected to the resistor; the other end of resistor R1 is connected to one end of resistor R2; the other end of resistor R2 is connected to the other end of film capacitor C6; the two ends of capacitors C7, C8, C9, C10 and Zener diode VD2 are respectively connected to the two ends of resistor R1; one end of resistor R3 is connected to one end of capacitors C7, C8, C9, C10 and Zener diode VD2; the other end of resistor R3 is connected to the gate of PMOS transistor Q1; the source of PMOS transistor Q1 is connected to one end of Zener diode VD2; the drain of PMOS transistor Q1 is connected to one end of diode D1; and the coated wire-wound resistor R4 is connected in parallel between the source and drain of PMOS transistor Q1; the other end of Zener diode VD2 is connected to the positive terminal of electrolytic capacitors CE1, CE2, CE3, and CE4; the negative terminal of electrolytic capacitors CE1, CE2, CE3, and CE4 is connected to resistor R2.
[0014] This invention has the following advantages over the prior art: This invention provides a PLC power-on soft-start protection device. This device, through the coordinated operation of a power resistor and a MOSFET, limits the input current at power-on and achieves smooth conduction via a delay module, effectively reducing surge impact from bus capacitor charging and exhibiting excellent soft-start performance. The EMI filter circuit employs an LCR filter network structure, simultaneously suppressing common-mode and differential-mode interference, reducing conducted and radiated interference on power lines, and improving the system's electromagnetic compatibility. Voltage limiting and surge suppression components in the control and protection module effectively prevent damage to the circuit from voltage surges and electrostatic interference; the reverse connection protection circuit automatically blocks current in case of incorrect wiring polarity, preventing component burnout. The power-down retention circuit, composed of multiple parallel electrolytic capacitors, provides short-term energy support to the PLC during power failure, ensuring data preservation and status maintenance, and improving the system's power-down resilience and operational reliability.
[0015] This device features a compact structure and high integration, employing a MOSFET and power resistor scheme. It boasts a long lifespan and easy maintenance, making it suitable for power input protection in various PLC control systems. In summary, this utility model's PLC power-on soft-start protection device achieves smooth power-on and surge suppression while also providing filtering, protection, and energy storage functions. It offers advantages such as simple structure, high reliability, and excellent electromagnetic compatibility.
[0016] It should be understood that all combinations of the foregoing concepts and the additional concepts described in more detail below can be considered part of the inventive subject matter of this disclosure, provided that such concepts do not contradict each other.
[0017] The foregoing and other aspects, embodiments, and features of the present invention will be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as features and / or beneficial effects of exemplary embodiments, will become apparent from the following description or may be learned through practice of specific embodiments according to the teachings of the present invention. Attached Figure Description
[0018] Figure 1 This is a structural block diagram of the PLC power-on soft start device of this utility model; Figure 2 This is a circuit diagram of the PLC power-on soft start device of this utility model. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. All other embodiments obtained by those skilled in the art based on the described embodiments of this utility model without creative effort are within the scope of protection of this utility model. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this utility model pertains.
[0020] The terms "first," "second," and similar words used in this utility model application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular forms of "an," "a," or "the," etc., do not indicate a quantity limitation, but rather indicate the presence of at least one. Terms such as "comprising" or "including" indicate that the element or object preceding "comprising" encompasses the features, integrals, steps, operations, elements, and / or components listed following "comprising" or "including," and do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or sets thereof. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.
[0021] This invention provides a PLC power-on soft-start protection device: This PLC power-on soft-start protection circuit effectively suppresses surge current at the moment of power-on, preventing damage to the power module or malfunction of fuses due to excessive inrush current, thereby improving the reliability and service life of the PLC system. The device enables a smooth transition of voltage and current during the initial power-on phase, reducing power supply stress while ensuring a stable start-up process for downstream loads.
[0022] The PLC power-on soft-start protection circuit device disclosed in this utility model will be further described in detail below with reference to the embodiments shown in the accompanying drawings.
[0023] like Figure 1 As shown, a PLC power-on soft start protection device includes a power EMI filter circuit, a soft start circuit, a reverse connection protection circuit, and a power-off retention circuit; wherein, the soft start circuit includes a power resistor module, a controller protection module, a delay module, and a control switching module.
[0024] The EMI filter circuit is used to filter out conducted interference at the input of the PLC power supply (i.e., the 24V power supply shown in the diagram). It can suppress both differential-mode and common-mode interference, thereby improving the electromagnetic compatibility of the system. The soft-start circuit limits the current through the power resistor module and MOSFET at the moment of power-on. After the set time is reached, the delay module gradually shorts the power resistor by the control switching module, thereby completing the smooth power-on process. The controller protection module can limit the amplitude of the gate control level to ensure that the MOSFET is not damaged. The reverse connection protection circuit can automatically block the current when the positive and negative terminals of the power supply are reversed, avoiding damage caused by wiring errors. The power-down retention circuit releases energy at the moment of power failure, enabling the PLC controller to complete the necessary data saving or status maintenance operations in a very short time, thereby improving the reliability and fault tolerance of the system.
[0025] like Figure 2 As shown, the power supply EMI filter circuit consists of a common-mode inductor CM1, film capacitors C1 and C6, and safety capacitors C2, C3, C4, and C5, forming an LCR filter network. The common-mode inductor CM1 provides high impedance to common-mode interference current flowing through the two lines while maintaining normal power frequency signal transmission, effectively attenuating common-mode noise. Film capacitors C1 and C6 suppress differential-mode interference signals, reducing high-frequency interference between power lines caused by switching device operation, rectification, and load changes. Safety capacitors C2 to C5 are Y capacitors, connected in parallel between the power input line and protective ground (PE), used to discharge common-mode interference current generated by electromagnetic coupling, reducing external radiated interference and its impact on internal control circuits.
[0026] The soft-start circuit consists of resistors R1, R2, and R3, a Zener diode VD2, a bidirectional transient suppression diode VD1, a PMOS transistor Q1, capacitors C7-C10, and a coated wire-wound resistor R4. The power resistor module uses the coated wire-wound resistor R4 to limit the input current during the initial power connection, preventing surge current generated during the charging of the bus capacitor from impacting the power module and related components. The delay module, composed of resistor R2 and capacitors C7-C10, generates a delay control signal during the RC charging and discharging process to achieve slow turn-on of the PMOS transistor. The delay duration can be configured by the capacitance values of C7-C10. The control device protection module consists of a Zener diode VD2 and a bidirectional transient suppression diode VD1. VD2 stabilizes the control signal voltage to prevent damage to the PMOS transistor due to excessive gate drive voltage; VD1 absorbs external surge and electrostatic discharge energy.
[0027] The control switching module consists of resistors R1-R3 and a PMOS transistor Q1, used to automatically switch between the current-limiting phase and the normal operation phase. During the initial power-on phase, PMOS transistor Q1 is off, and current is limited by the coated wire-wound resistor R4 to charge the bus capacitor. When the output voltage of the RC delay module rises to the gate threshold, PMOS transistor Q1 gradually turns on, bypassing the current-limiting resistor R4 and switching the power supply to a low-resistance state. This process achieves a smooth current transition and effectively prevents surge impacts.
[0028] Through the synergistic effect of the above modules, the soft-start circuit realizes the soft-start control strategy of "current-limited charging - delayed conduction - automatic bypass", which not only ensures the safe charging of the bus capacitor, but also ensures that the MOSFET operates in the safe operating area (SOA), thereby significantly improving the reliability and stability of the PLC power input terminal.
[0029] like Figure 2 As shown, the reverse connection protection circuit is composed of diode D1, which is used to prevent damage to the circuit when the positive and negative terminals of the power supply are reversed.
[0030] The power-down retention circuit consists of electrolytic capacitors CE1, CE2, CE3, and CE4, which are used to release energy when the power is lost, ensuring the continuous operation of the PLC controller or data retention for a short period of time.
[0031] The specific connection relationships of each component are as follows: A bidirectional transient voltage suppressor diode VD1 is connected in parallel with a film capacitor C1, and then connected to the power input ports 24V_IN and 0V_IN respectively. One end of the safety capacitor C2 is connected to the power input port 24V_IN, and the other end is connected to the protective earth PE. One end of the safety capacitor C3 is connected to the power input port 0V_IN, and the other end is connected to the protective earth PE. Pin 1 of the common mode inductor CM1 is connected to one end of both the safety capacitor C2 and the film capacitor C1. Pin 2 of the common mode inductor CM1 is connected to one end of both the safety capacitor C4 and the film capacitor C6. Pin 3 of the common mode inductor CM1 is connected to the other end of both the safety capacitor C3 and the film capacitor C1. Pin 4 of the common mode inductor CM1 is connected to the other end of both the safety capacitor C5 and the film capacitor C6. One end of the resistor R1 is connected to one end of the film capacitor C6. The other end is connected to one end of resistor R2, and the other end of resistor R2 is connected to the other end of film capacitor C6; the two ends of capacitors C7, C8, C9, C10 and Zener diode VD2 are respectively connected to the two ends of resistor R1; one end of resistor R3 is connected to one end of capacitors C7, C8, C9, C10 and Zener diode VD2, and the other end of resistor R3 is connected to the gate of PMOS transistor Q1; the source of PMOS transistor Q1 is connected to one end of Zener diode VD2, and the drain of PMOS transistor Q1 is connected to one end of diode D1. At the same time, a coated wire-wound resistor R4 is connected in parallel between the source and drain of PMOS transistor Q1; the other end of Zener diode VD2 is connected to the positive terminal of electrolytic capacitors CE1, CE2, CE3, and CE4, and the negative terminal of electrolytic capacitors CE1, CE2, CE3, and CE4 is connected to resistor R2.
[0032] This utility model PLC power-on soft start device achieves multi-level protection and control of the input power supply by setting an EMI filter circuit, a soft start circuit, a reverse connection protection circuit, and a power-off retention circuit at the input terminal.
[0033] The following is in conjunction with the appendix Figure 1 and attached Figure 2 The following is a further description of a specific example of the PLC power-on soft-start protection circuit device disclosed in this utility model: When the external 24V power supply is connected, the input voltage first passes through the power EMI filter circuit. This circuit uses an LCR filter network structure to suppress high-frequency noise and transient interference signals in the input power supply, effectively filtering out common-mode and differential-mode interference. The filtered voltage then enters the soft-start phase. In the initial power-up stage, the soft-start circuit, through the coordinated operation of the power current-limiting resistor and the PMOS transistor, limits the input current, allowing the bus capacitor to charge at a controlled rate, thus avoiding surge impacts caused by excessive initial capacitor charging current. This invention introduces a current-limiting charging process in the initial power-up stage, causing the current to gradually rise from zero, forming a smooth power-up curve. As the charging voltage of the delay module gradually increases, the gate potential change of the PMOS transistor guides its slow conduction, ultimately bypassing the current-limiting resistor and allowing the system to smoothly switch from current-limiting mode to a low-resistance normal power supply state. This process suppresses power-up surge impacts, ensuring the safe and stable operation of the power module and load.
[0034] To prevent damage caused by incorrect wiring polarity, this device is equipped with a reverse connection protection circuit. When the positive and negative terminals of the power supply are reversed, the reverse connection protection circuit automatically blocks the input current, preventing reverse current from entering the subsequent circuits, thereby avoiding damage or burnout of power devices and control modules due to reverse voltage. In the event of a power outage or momentary power failure, the power-off retention circuit comes into play. This circuit consists of multiple large-capacity electrolytic capacitors connected in parallel. Normally in a charged state, these capacitors release stored energy the instant the power is cut off, providing short-term power support to the PLC controller and storage module. This allows the system to complete critical data saving, output status maintenance, or safe shutdown operations within hundreds of milliseconds of power failure, thereby improving system reliability and data security.
[0035] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Those skilled in the art to which this invention pertains can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of this invention shall be determined by the claims.
Claims
1. A PLC power-on soft-start protection device, wherein the PLC power-on soft-start protection device is located at the PLC power input terminal, characterized in that, The PLC power-on soft start protection device includes an EMI filter circuit and a soft start circuit; the EMI filter circuit adopts an LCR filter network structure; the soft start circuit adopts a combination of a power current-limiting resistor and a MOSFET with controllable conduction; after the PLC power supply is filtered by the EMI filter circuit to remove conducted interference, it is then current-limited by the soft start circuit.
2. The PLC power-on soft-start protection device according to claim 1, characterized in that, The soft-start circuit includes a power resistor module, a controller protection module, a delay module, and a control switch. The power resistor module uses a coated wire-wound resistor R4 to limit the input current. The controller protection module consists of a Zener diode VD2 and a bidirectional transient voltage suppressor diode VD1 to control the voltage level. The control switch module consists of parallel resistors R1, R2, and R3, and a PMOS transistor Q1. The delay module consists of resistor R2 and capacitors C7, C8, C9, and C10 to control the PMOS transistor Q1 to turn on after a delay.
3. The PLC power-on soft-start protection device according to claim 2, characterized in that, The PLC power-on soft start protection device also includes a reverse connection protection circuit; the reverse connection protection circuit includes a diode D1; the reverse connection protection circuit is connected to the PMOS transistor Q1 in the soft start circuit.
4. The PLC power-on soft-start protection device according to claim 3, characterized in that, The PLC power-on soft start protection device also includes a power-off retention circuit; the power-off retention circuit includes multiple electrolytic capacitors connected in parallel, with the positive terminal connected to the controller protection module and the negative terminal connected to the control switching module.
5. The PLC power-on soft-start protection device according to claim 4, characterized in that, The EMI filter circuit consists of a common-mode inductor CM1, thin-film capacitors C1 and C6, and safety capacitors C2, C3, C4, and C5, which together form an LCR filter network. The safety capacitors C2, C3, C4, and C5 are Y capacitors, which are connected in parallel between the power input line and the protective ground PE.
6. The PLC power-on soft-start protection device according to claim 5, characterized in that, The bidirectional transient voltage suppressor diode VD1 and the film capacitor C1 are connected in parallel and then connected to the power input ports 24V_IN and 0V_IN respectively; one end of the safety capacitor C2 is connected to the power input port 24V_IN, and the other end is connected to the power protection ground PE; one end of the safety capacitor C3 is connected to the power input port 0V_IN, and the other end is connected to the power protection ground PE; pin 1 of the common mode inductor CM1 is connected to one end of the safety capacitor C2 and the film capacitor C1 respectively; pin 2 of the common mode inductor CM1 is connected to one end of the safety capacitor C4 and the film capacitor C6 respectively; pin 3 of the common mode inductor CM1 is connected to the other end of the safety capacitor C3 and the film capacitor C1 respectively; pin 4 of the common mode inductor CM1 is connected to the other end of the safety capacitor C5 and the film capacitor C6 respectively; one end of the resistor R1 is connected to one end of the film capacitor C6, and the resistor R1... The other end is connected to one end of resistor R2, and the other end of resistor R2 is connected to the other end of film capacitor C6; the two ends of capacitors C7, C8, C9, C10 and Zener diode VD2 are respectively connected to the two ends of resistor R1; one end of resistor R3 is connected to one end of capacitors C7, C8, C9, C10 and Zener diode VD2, and the other end of resistor R3 is connected to the gate of PMOS transistor Q1; the source of PMOS transistor Q1 is connected to one end of Zener diode VD2, and the drain of PMOS transistor Q1 is connected to one end of diode D1. At the same time, the coated wire-wound resistor R4 is connected in parallel between the source and drain of PMOS transistor Q1; the other end of Zener diode VD2 is connected to the positive terminal of electrolytic capacitors CE1, CE2, CE3, and CE4, and the negative terminal of electrolytic capacitors CE1, CE2, CE3, and CE4 is connected to resistor R2.