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Selection and Description of Circuit Protection

Author: Tanssion Date: 2023-07-21 Hits: 0

Ⅰ. The way of circuit protection
Ⅱ. Steps to avoid malfunction or failure of circuit protection devices
Ⅲ. Factors to be considered in the selection and application of circuit protection devices
Ⅳ. Procedures for testing and verifying the performance and reliability of circuit protection devices
Ⅴ.What is a circuit protection device called?

As the number of electronic devices used in all industries continues to increase and the processing capabilities of costly FPGAs and processors continue to expand, these devices operate in harsh environments. The type and energy contained in a surge event will vary depending on the region in which the electronic device is used; circuits can be subjected to conditions such as overvoltage, overcurrent, reverse voltage, and reverse current. Therefore, all input conditions must be considered and mechanisms must be implemented to protect the circuit from voltage and current surges.

Many traditional reliable protection solutions such as diodes, fuses and TVS devices are able to remain protected, but they are often inefficient, bulky and require maintenance. In order to solve these deficiencies, active intelligent protection ICs have emerged, they can meet the protection requirements of traditional methods, and from some aspects, they are more reliable.

Overvoltage, overcurrent, surge, electromagnetic interference, electrostatic discharge, etc. have always been the focus of circuit protection. Therefore, the mainstream circuit protection devices in the market are mainly lightning protection/overvoltage/overcurrent/anti-static.

Ⅰ. The way of circuit protection

1. Traditional circuit protection

Traditional circuit protection approaches are based on multiple devices rather than one, such as transient voltage suppressors (TVS) for overvoltage protection, line fuses for overcurrent protection, series diodes for reverse battery/source protection, and a mix of capacitors and inductors to filter lower power spikes. Although the discrete configuration can meet the established specification requirements (to protect the downstream circuit), it needs to go through many screenings to select the appropriate filter specification.

2. Line fuse

It is a common circuit protection device used to provide overcurrent protection in the circuit. It is a safety wire, usually made of metal or alloy wire, installed in the fuse holder in the circuit.

Overcurrent protection can be implemented using common line fuses with higher than nominal fusing ratings. The biggest problem with fuses is that they have to be replaced once they blow. The design of the fuse is quite simple, but the maintenance is relatively complicated, especially in difficult-to-reach locations, so it will still be time-consuming and costly in the later stage. Maintenance requirements can be reduced by using a backup fuse, such as a resettable fuse, which uses a positive temperature coefficient to open the circuit when higher than nominal current flows through the device.

The choice of line fuse depends on the rated current and rated voltage of the circuit. When designing the circuit, the appropriate rated current value of the fuse should be selected according to the circuit load and the rated current of the electrical equipment. Too much current will cause the fuse to blow prematurely, while too little current will not provide effective overload protection. Aside from maintenance issues, one of the biggest problems with fuses is their reaction time, which can vary greatly depending on the type of fuse chosen.

3. TVS (Transient Voltage Suppressor)

A relatively simple device that protects downstream circuitry from high voltage spikes on the power supply. Also known as TVS diodes or TVS protection diodes. It is a device used to protect electronic equipment and circuits from transient overvoltage. Transient voltages are high voltage pulses that appear instantaneously, usually caused by lightning strikes, power switches, momentary changes in inductance and capacitance, etc.

A TVS transient voltage suppressor is usually a diode structure and works on the basis that it has a high resistance at normal operating voltage, but it quickly switches to a low resistance state when the voltage exceeds its rated transient voltage. When an instantaneous overvoltage occurs in the circuit, the TVS diode will quickly conduct, absorb the energy of the overvoltage, and divert the overvoltage to the ground or other conductors, thereby protecting subsequent circuits and equipment.

While TVS devices are effective at suppressing extremely high voltage excursions, they are not immune to damage when subjected to sustained overvoltage and therefore require periodic monitoring or replacement. Another concern is that the TVS might short out, disconnecting the input power. Also, depending on the amount of power involved, their size may need to be large to meet the margin requirements, resulting in a corresponding increase in solution size. Even if the TVS is correctly sized, the downstream circuitry must be able to handle the clamping voltage, increasing the downstream voltage rating requirements.

4. Inductive and capacitive filters

Inductive and capacitive filters are commonly used types of electronic filters, which are used to remove stray noise, waveform distortion and frequency interference in circuits to achieve signal filtering and waveform shaping.

Inductive and capacitive filters pass amplitude limiting, but usually only capture larger amplitudes, letting go of smaller spikes. These smaller transients can still cause damage to downstream circuitry, so additional passive filters are required to smooth out the spikes. This can be achieved by using discrete inductors and capacitors, sized so that they attenuate voltages beyond the frequency range.

Filters are usually used in power supply and signal processing circuits. By adjusting the cutoff frequency of the filter, signals in a specific frequency range can be selectively filtered out or passed.

Inductive and capacitive filters are divided into high-pass filters and low-pass filters.

High-pass filter: Allows signals above the cutoff frequency to pass while rejecting signals below the cutoff frequency. In a high-pass filter, capacitors are connected in series and inductors are connected in parallel, and the cutoff frequency determines the passband of the filter. High-pass filters are often used to remove low-frequency noise and DC offsets.

Low-pass filter: Allows signals below the cutoff frequency to pass while rejecting signals above the cutoff frequency. In a low-pass filter, inductors are connected in series and capacitors are connected in parallel, and the cutoff frequency determines the passband of the filter. Low-pass filters are commonly used to remove high-frequency noise and shape waveforms.

5. Surge suppressors provide active protection

Surge suppressors usually use passive components such as diodes, Gas Discharge Tube, GDT, Metal Oxide Varistor, and MOV to absorb or disperse overvoltage and protect equipment and components in the circuit.

The surge stopper uses an easy-to-use controller IC and series N-channel MOSFETs, eliminating the need for complex shunt circuits (TVS devices, fuses, inductors, and capacitors). Surge stopper controllers can greatly simplify system design because only a few components need to be dimensioned and qualified.

The surge suppressor continuously monitors the input voltage and current. Under rated operating conditions, the controller drives the gate of the N-channel MOSFET pass device fully on, providing a low-impedance path from input to output. In the event of an overvoltage or surge (the threshold is given by a feedback network at the output), the IC regulates the gate of the N-channel MOSFET, clamping the MOSFET's output voltage to the level set by the resistor divider.

Surge stoppers are divided into output disconnect protection controllers, linear surge stoppers, switching surge stoppers, and gate clamps.

Output disconnection protection controller: It is a protection device used in power systems or electronic equipment. Its main function is to automatically cut off the output circuit when a fault or abnormal situation is detected to protect the circuit and equipment from damage. A protection controller is not a true surge suppressor, but it does stop surges. Like a surge stopper, a protection controller monitors for overvoltage and overcurrent conditions, but instead of clamping or regulating the output, it protects downstream electronics by immediately disconnecting the output. When the current in the circuit exceeds the set rated current value, the output disconnection protection controller will automatically cut off the output circuit to avoid damage to the equipment due to overload. When the voltage in the circuit exceeds the set rated voltage value, the output disconnection protection controller will automatically disconnect the circuit to prevent the equipment from being affected by excessive voltage.

Linear surge suppressor: It is a surge protection device used in power system or electronic equipment to suppress surge voltage or overvoltage in the circuit. It uses the principle of linear circuits to consume or disperse overvoltage energy through linear components such as resistors, capacitors, and inductors, and protect circuits and equipment from overvoltage damage. Linear surge suppressors work like resistors and capacitors. When a surge voltage or overvoltage occurs in a circuit, a linear surge suppressor guides the overvoltage to its internal linear element, dissipating the energy to eliminate the overvoltage. They are typically used to dissipate low energy, low frequency overvoltages, but for high energy and high frequency overvoltages, linear surge suppressors have limited effectiveness. A linear surge suppressor drives a series MOSFET in a similar way to a linear regulator, limiting the output voltage to a preset safe value and dissipating excess energy in the MOSFET. To protect the MOSFETs, the device limits the time spent in high dissipation regions by employing a capacitor fault timer.

Switching surge suppressor: It is used to suppress the surge voltage or overvoltage generated by the switching operation, and protect the circuit and equipment from the damage of the surge voltage.

Gate Clamp: The gate clamp surge suppressor uses an internal or external clamp to limit the voltage at the gate pin to this voltage value, and then the threshold voltage of the MOSFET determines the output voltage limit.

Ⅱ. Steps to avoid malfunction or failure of circuit protection devices

1. Select the appropriate protection device: When designing and selecting the circuit protection device, the appropriate protection device that meets the actual needs should be selected according to the load characteristics, rated current and voltage of the circuit, and the working environment of the equipment. Ensure that the rated parameters of the protection device match the circuit and equipment to avoid malfunction or failure due to improper selection.

2. Prevent environmental interference: When installing the circuit protection device, avoid it being disturbed by the external environment, such as avoid exposing the protection device to harsh environments such as high temperature, humidity, corrosive gas or vibration.

3. Use reliable protection devices: choose protection devices with well-known brands and reliable quality, and avoid using devices with low quality or unknown sources to reduce the probability of device failure or malfunction.

4. Arrange the circuit reasonably: Arrange the circuit reasonably, avoid circuit wiring confusion and interference, reduce electromagnetic interference and electrical interference, so as to ensure that the protection device can accurately respond to fault signals.

5. Equipment overload protection: In addition to the circuit protection device, the equipment itself should also consider overload protection measures. Reasonably set the rated working range of the equipment to avoid working above the rated load for a long time.

6. Regular testing and maintenance: regular testing and maintenance of circuit protection devices to ensure their normal operation. Including checking whether the connection of the protective device is firm, observing whether the indicator light and display are normal, testing the response time of the device, etc. If a problem is found, repair or replace the protective device in time.

Ⅲ. Factors to be considered in the selection and application of circuit protection devices

1. Circuit load characteristics: Understand the nature of the circuit load, including parameters such as current, voltage, power, frequency, etc., to select the appropriate rated parameters of the protective device.

2. Protection type: Select the corresponding protection device according to the fault type of the circuit. Common protection types include overload protection, short circuit protection, overvoltage protection, undervoltage protection, overtemperature protection, etc.

3. Response time: Consider the response time of protection devices, especially for key equipment and systems, as fast as possible protection response is required to prevent damage or accident expansion.

4. Rated current and voltage: Make sure that the rated current and voltage of the protective device match the circuit load, and avoid choosing too small or too large a protective device.

5. Environmental conditions: Consider the working environment of the protection device, including temperature, humidity, corrosive gas, etc., and select a suitable device with good environmental adaptability.

6. Circuit complexity: Considering the complexity and level of the circuit, for complex circuit systems, it may be necessary to set up multi-level protection devices to ensure comprehensive protection.

7. Reliability: Choose protective devices with well-known brands and reliable quality, and avoid using devices with low quality or unknown sources to improve the reliability of the device.

8. Economy: When choosing a protective device, it is necessary to consider the balance between cost and performance to meet budget and performance requirements.

Ⅳ. Procedures for testing and verifying the performance and reliability of circuit protection devices

1. Rated parameter test: First, verify whether the rated parameters of the protection device, including rated current, rated voltage, and rated power, match the circuit load.

2. Response time test: Test the response time of the protection device, that is, how quickly the protection device can trigger and cut off the circuit when a circuit fault occurs. Use professional testing equipment or instruments to test to ensure that the response time meets the requirements.

3. Environmental adaptability test: Test the adaptability of the protective device under various environmental conditions, including temperature, humidity, vibration, etc., to ensure that it can work normally in different environments.

4. Fault simulation test: By simulating circuit faults, such as overload, short circuit, overvoltage, etc., the protection device is triggered to verify whether it can accurately cut off the circuit and prevent further expansion of the fault.

5. Coordination test with other protection devices: For multi-level protection systems, test the coordination between the protection device and other protection devices to ensure that the circuits can be effectively responded and cut off at different levels.

6. Repeated testing: Conduct repeated testing, including multiple triggers of the protection device and multiple resets, to ensure that it can work reliably and return to normal.

Ⅴ.What is a circuit protection device called?

A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by overcurrent. Its basic function is to interrupt current flow to protect equipment and to prevent the risk of fire.


Frequently Asked Questions

1、What is the judgment of the protection type of circuit protection?
First of all, we must understand the types of faults that may occur in the circuit, such as overload, short circuit, overvoltage, undervoltage, overtemperature, etc. Select the corresponding protection device according to the type of circuit fault. Understand the load characteristics of the circuit, including current, voltage, power and other parameters, as well as the rated value and working conditions of the load. Choose the appropriate protection device according to the load characteristics.
2、What are the common faults of circuit protection devices?
A protective device falsely triggers when there is no actual fault, causing the circuit to open unexpectedly. It may be caused by equipment failure, environmental interference, wiring problems, etc. The protection device does not trigger properly when the actual fault occurs, leaving the circuit unprotected. It may be caused by device aging, component damage, wrong settings, etc. The protective device may alarm to indicate a fault, but there is no fault, possibly due to a fault indicator light or a problem with the signal circuit.

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