What methods do PCBA engineers often use to protect circuits?

Protection devices are used to protect circuits and equipment from power failures or other damage. Here are several common types of protection devices and their descriptions:

1. Diode

A diode is an electronic device used to control the direction of current flow. In circuits, diodes are often used to prevent reverse current from flowing in or to protect other devices from overvoltage.

A voltage regulator diode, also known as a voltage regulator or Zener diode, is a specially designed diode used to provide a stable voltage output.

The characteristic of a voltage regulator diode is its reverse breakdown voltage (Zener voltage). When the reverse voltage exceeds its specific breakdown voltage, the voltage regulator diode enters a reverse breakdown state and conducts current. Compared to ordinary diodes, voltage regulator diodes are carefully designed to maintain a stable voltage in the reverse breakdown region.

The working principle of a voltage regulator diode is based on the voltage breakdown effect. When the voltage is below its reverse breakdown voltage, the diode maintains a stable voltage across its two ends, allowing reverse current to flow through. This characteristic enables the voltage regulator diode to provide a stable reference voltage in a circuit or stabilize the input voltage at a specific value.

Zener diodes are commonly used in the following applications:

1. Voltage regulation: Zener diodes can be used as voltage regulators in circuits to stabilize the input voltage at a specific output voltage. This is very important for electronic devices and circuits that require stable voltage.

2. Reference voltage: Zener diodes can be used as reference voltage sources in circuits. By selecting the appropriate Zener diode, a fixed reference voltage can be provided for calibration and comparison of other signals.

3. Voltage regulation: Zener diodes can also be used for voltage regulation functions in circuits. By controlling the current flow of the Zener diode, the voltage value in the circuit can be adjusted to achieve the desired voltage regulation function.

The selection of Zener diodes depends on the required stable voltage and operating current. They have different breakdown voltages and power characteristics, so they need to be evaluated based on specific applications and requirements when selecting Zener diodes.

Zener diodes are specially designed diodes that can provide stable voltage outputs. They are widely used in electronic circuits for functions such as voltage regulation, reference voltage, and voltage regulation.

2. Metal Oxide Varistor (MOV)

MOV is a device used for overvoltage protection. It is composed of metal oxide particles evenly distributed in a ceramic matrix, which can become conductive when the voltage exceeds its rated value, thereby absorbing the energy of the overvoltage and protecting other devices in the circuit.

The characteristic of MOV is its nonlinear resistance characteristics. Within the normal operating voltage range, MOV exhibits a high resistance state and has almost no effect on the circuit. However, when the voltage suddenly increases to exceed its rated voltage, MOV quickly changes to a low resistance state to absorb the energy of the overvoltage and direct it to the ground or other low impedance paths.

The working principle of MOV is based on the varistor effect. When the voltage exceeds its rated voltage, the electric field strength between the oxide particles becomes larger, so that the resistance between the particles decreases. This enables MOV to provide very high current capacity and effectively protect other circuits and equipment from overvoltage damage.

Metal oxide varistors are commonly used in the following applications:

1. Overvoltage protection: MOV is mainly used for overvoltage protection to prevent the voltage from exceeding the rated value that the device or circuit can withstand. When an overvoltage condition occurs, MOV responds quickly and turns on, directing the overvoltage to the ground or other low impedance paths to protect other sensitive components.

2. Surge protection: MOVs are commonly used in power lines and communication lines to protect equipment from power surges (voltage mutations). They are able to absorb and suppress transient voltage peaks, preventing equipment from potential damage.

3. Surge protection: MOVs are also widely used in surge protectors to prevent damage to electronic equipment and circuits caused by lightning strikes, power surges, and other electromagnetic interference. They are able to absorb and disperse surge energy, protecting equipment from transient overvoltages.

Selecting the appropriate MOV depends on the required rated voltage, maximum current capacity, and response time. The rated voltage of the MOV should be slightly higher than the maximum operating voltage of the circuit to be protected, while the maximum current capacity should meet the requirements of the system. The response time should be fast enough to ensure a quick response to overvoltage.

Metal oxide varistors are components used for overvoltage protection that absorb overvoltage energy and protect other circuits and equipment from damage. They play an important role in areas such as overvoltage protection, surge protection, and surge protection.

3. Transient Voltage Suppressor (TVS)

Transient Voltage Suppressor (TVS) is an electronic device used to suppress transient overvoltage. It can respond quickly and absorb the energy of overvoltage, and can provide effective protection when voltage changes suddenly or transient voltage occurs, preventing the voltage from exceeding the set threshold.

The working principle of TVS devices is based on the breakdown voltage effect. When a transient overvoltage occurs in the circuit, the TVS device will quickly change to a low impedance state, directing the energy of the overvoltage to the ground or other low impedance paths. By absorbing and dispersing the energy of the overvoltage, the TVS device can limit the voltage rise rate and protect other sensitive components.

TVS devices are usually composed of gas discharge tubes (Gas Discharge Tube, GDT) or silicon carbide diodes (Silicon Carbide Diode, SiC Diode). Gas discharge tubes form a discharge path based on gas when the voltage is too high, while silicon carbide diodes use the special properties of silicon carbide materials to form a conductive path under the breakdown voltage.

Transient voltage suppressors are commonly used in the following applications:

1. Surge protection: TVS devices are mainly used for surge protection to prevent overvoltage caused by lightning strikes, power surges, power searches and other electromagnetic interference. They can absorb and suppress transient voltage peaks to protect circuits and equipment from damage.

2. Communication line protection: TVS devices are widely used in communication lines to protect equipment from power searches and electromagnetic interference. They can quickly respond and absorb transient overvoltages to protect the stable operation of communication equipment.

3. Power line protection: TVS devices are also used for power line protection to prevent power searches and other overvoltage events from damaging power supply equipment. They can absorb and disperse overvoltage energy to protect the normal operation of power supply equipment.

Selecting the appropriate TVS device depends on the required rated voltage, maximum current capacity and response time. The rated voltage of the TVS device should be slightly higher than the maximum operating voltage of the circuit to be protected, and the maximum current capacity should meet the requirements of the system. The response time should be fast enough to ensure timely suppression of transient overvoltages.

Transient voltage suppressors play an important role in the fields of surge protection, communication line protection and power line protection.

4. Fuse

A fuse is a common electronic component used to protect circuits and devices from damage caused by overcurrent. It is a passive protection device that prevents excessive current from flowing by disconnecting the circuit.

A fuse is usually made of a thin wire or wire with a low breaking current. When the current in the circuit exceeds the rated current of the fuse, the filament inside the fuse will heat up and melt, cutting off the flow of current.

The main features and working principles of fuses are as follows:

1. Rated Current: The rated current of a fuse refers to the maximum current value it can safely withstand. When the current exceeds the rated current, the fuse will melt to stop the current from flowing.

2. Blow Time: The blow time of a fuse refers to the time from when the current exceeds the rated current to when it blows. The blow time depends on the design and characteristics of the fuse, usually between a few milliseconds and a few seconds.

3. Breaking Capacity: Breaking capacity refers to the maximum current or energy that a fuse can safely break. The fuse's breaking capacity needs to match the circuit's load and short-circuit current to ensure that the current can be effectively cut off under fault conditions.

4. Type: There are many types of fuses, including fast-acting, time-delay, high voltage, etc. Different types of fuses are suitable for different application scenarios and requirements.

The main function of a fuse is to provide overload protection in a circuit. When the current in a circuit increases abnormally, which may cause a circuit failure or equipment damage, the fuse will quickly blow and cut off the current flow, thereby protecting the circuit and equipment from damage.

When selecting an appropriate fuse, factors such as the circuit's rated current, short-circuit current, rated voltage, and environmental conditions need to be considered. Correctly selecting a fuse can ensure the safety and reliability of the circuit and provide effective overload protection.

5. Negative Temperature Coefficient Thermistor (NTC Thermistor)

Negative temperature coefficient thermistor is an electronic component whose resistance value decreases as the temperature increases.

NTC thermistors are usually made of metal oxides or semiconductor materials. In the lattice structure of the material, certain impurities are doped, which interfere with the movement of electrons in the lattice. As the temperature increases, the energy of the electrons in the temperature-sensitive material increases, and the interaction between the electrons and the impurities weakens, resulting in an increase in the migration speed and conductivity of the electrons and a decrease in the resistance value.

The characteristics and applications of NTC thermistors include:

1. Temperature sensor: Since the resistance value of NTC thermistors is inversely proportional to the temperature, they are widely used as temperature sensors. By measuring the resistance value, the change in ambient temperature can be determined.

2. Temperature compensation: NTC thermistors can be used in temperature compensation circuits. Due to the characteristic that its resistance value changes with temperature, it can be connected in series or in parallel with other components (such as thermistors and resistors) to achieve stable operation of the circuit at different temperatures.

3. Temperature control: NTC thermistors can play an important role in temperature control circuits. By monitoring the change in resistance value, the operation of the heating element or cooling element can be controlled to maintain a stable state within a specific temperature range.

4. Power supply protection: NTC thermistors can also be used for power supply protection. In power supply circuits, they can be used as overcurrent protectors. When the current exceeds a certain threshold, due to the drop in resistance value, they can limit the flow of current and protect the power supply and other circuits from damage caused by excessive current.

In summary, NTC thermistors are thermally sensitive components with a negative temperature coefficient, whose resistance value decreases as the temperature increases. They are widely used in temperature sensing, temperature compensation, temperature control, and power supply protection.

6. Polymeric Positive Temperature Coefficient (PPTC)

PPTC electronic fuses are also an overcurrent protection device. They have low resistance, but when the current exceeds the rated value, a thermal effect occurs, causing the resistance to increase, limiting the flow of current. They are usually used as resettable fuses or overcurrent protection devices. PPTC components are made of special polymer materials and have a resistance characteristic of a positive temperature coefficient.

The resistance of PPTC components is usually low at room temperature, allowing current to flow in the component without a significant voltage drop. However, when an overcurrent condition occurs, the PPTC component heats up due to the increased current passing through it. As the temperature increases, the resistance of the polymer material increases significantly.

The key characteristic of the PPTC component is its ability to limit the flow of current under fault conditions. When the current exceeds the rated threshold, the PPTC component heats up and its resistance increases rapidly. This high resistance state acts as a resettable fuse, effectively limiting the current to protect the circuit and connected components.

Once the fault condition is removed and the current drops below a certain threshold, the PPTC component cools and its resistance returns to a lower value. This resettable characteristic makes PPTC components different from traditional fuses, and they do not need to be replaced after tripping.

PPTC components are used in a variety of electronic circuits and systems that require overcurrent protection. They are commonly used in power supplies, battery packs, motors, communication equipment, and automotive electronics. PPTC components have advantages such as small size, resettable operation, and fast response to overcurrent events.

When selecting a PPTC component, important parameters need to be considered, including rated voltage, current, and holding current. The rated voltage should be higher than the operating voltage of the circuit, while the current rating should match the maximum expected current. The holding current specifies the current level at which the element trips and increases resistance.

PPTC elements provide reliable, resettable overcurrent protection for electronic circuits, helping to improve safety and reliability.