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Circuit Protection for Power Supply: A Guide

Circuit protection for power supply involves various mechanisms and components to prevent damage to electronic circuits and devices from faults, overloads, or abnormal conditions. These protections help maintain the reliability and safety of electronic systems.

Circuit Protection for Power Supply Mechanisms

Some common circuit protection for power supply mechanisms are:

Uninterruptible power supply unit used to ensure critical equipment remains operational.

There’s a variety of aspects that go into automotive PCB design, from thermal to layout to safety considerations.

  • Overload Protection: Overload protection prevents a circuit or device from operating at a current level higher than it was designed to handle. Protecting equipment from prolonged or sustained currents that exceed its rated capacity is typically part of this process. In overload situations, components, insulation, and wiring can be damaged due to overheating. Often, this protection is used in motors, transformers, and appliances.
  • Short-Circuit Protection (SCP): The SCP prevents circuit damage caused by short circuits, where a low-resistance path is formed between two points. As a result of a short circuit, the normal resistance of a circuit is bypassed, causing a rapid surge in current that can be dangerous. The result could be overheating, fires, equipment damage, and severe safety risks. An SCP usually involves quickly shutting down the power supply output to prevent excessive current flow.
  • Overvoltage Protection (OVP): OVP protects the circuit from voltage spikes or surges that could damage the components. Voltage clamping circuits, transient voltage suppressors (TVS), or specialized OVP integrated circuits (ICs) can accomplish this.
  • Overtemperature Protection (OTP): The OTP prevents the circuit from operating above its safe temperature. A thermal sensor monitors the temperature of critical components and triggers a shutdown or reduction of power output if temperatures rise too high.
  • Brownout Protection: When the input voltage falls below a certain threshold, this protection prevents the power supply from operating, helping to avoid erratic behavior or damage.
  • Reverse Polarity Protection: This protection prevents damage when the power supply is connected with reverse polarity. Current flowing in the wrong direction can be blocked by diodes or metal-oxide-semiconductor field-effect transistors (MOSFETs).
  • Soft-Start Circuits: When the power supply is turned on, these circuits gradually ramp up the output voltage, reducing the initial inrush current. It prevents sudden spikes in current that could damage components.
  • Electromagnetic Interference (EMI) Filters: By reducing electromagnetic interference, these filters ensure that the power supply's operation does not interfere with nearby electronics.
  • Remote Sensing: Using remote sensing, some power supplies compensate for voltage drops along the connecting cables and deliver the correct voltage at the load.
With these protection mechanisms, power supplies can handle various operating conditions while minimizing the risk of damage to connected devices. Depending on the power supply type and application, different protection features may be required.
Electronic thermistor used to monitor the temperature of critical components in power supply

Electronic thermistor used to monitor the temperature of critical components in power supply

Circuit Protection for Power Supply: Monitoring Devices

Circuit protection for power supply relies on monitoring devices that continuously monitor various parameters and situations to make them operate reliably and safely. Some standard monitoring devices include:

  • Voltage Supervisors: The voltage supervisor, also known as the voltage detector or voltage monitor, tracks the power supply's output voltage and triggers protective measures if the voltage falls below or exceeds predefined thresholds. The voltage supervisor is used to implement overvoltage and undervoltage protection.
  • Thermal Sensors: Thermistors and temperature sensors monitor the temperature of critical components in the power supply. When temperatures rise above a safe level, they trigger shutdown mechanisms to protect against overheating.
  • Current Sensing Devices: The current sensors, also known as current monitors, measure the current flowing through a circuit and provide feedback. They are used to implement overload protection and current limiting.
  • Isolation Barriers and Monitors: Power supply isolation monitors ensure the integrity of isolation barriers, especially in systems where electrical isolation between inputs and outputs is essential for safety. Any breakdown in isolation triggers protective measures.
  • Ground Fault Detectors: These devices can detect ground faults by monitoring the current flow between the circuit and ground. They are critical in applications such as medical equipment, where ground isolation is crucial.
  • Digital Controllers: Using microcontrollers or digital signal processors (DSPs), digital controllers can implement advanced protection algorithms and real-time monitoring, making their protection ability more flexible and programmable.
  • Power Monitoring ICs: Voltage, current, power, and energy consumption can all be monitored with power monitoring integrated circuits. They can be used for power sequencing and tracking and implementing various protection mechanisms.
  • Remote Monitoring and Control Systems: Power supplies can be integrated into broader monitoring and control systems in industrial or critical applications, enabling centralized management and diagnostics.
  • Communication Interfaces: Communication interfaces, such as inter-integrated circuit (I2C), serial peripheral interface (SPI), or universal asynchronous receiver/transmitter (UART) protocols, allow external monitoring and control of power supply parameters. They are especially useful for remote monitoring and control.
  • Event Logging and Alarms: Technicians can analyze the historical performance of the power supply and identify potential problems by logging critical events, faults, and protection triggers.
A monitoring device is selected because of the specific protection requirements of the power supply and the circuitry connected to it. Based on their criticality and safety considerations, different industries and applications may prioritize different monitoring aspects, such as voltage, current, temperature, or isolation.

Circuit Protection for Power Supply: By Industry

Representation of an automotive fuse designed to protect circuits from overload conditions

Representation of an automotive fuse designed to protect circuits from overload conditions

Circuit Protection for Power Supply by Industry
Automotive Aerospace Medical Communication Electricity
Transient voltage suppressors Redundancy and fault tolerance Isolation barriers and monitors Uninterruptible power supply Overload and overvoltage protection
Reverse polarity protection Overvoltage and overload protection Ground fault detectors Surge protection Short-circuit protection
Fuse and circuit breaker protection EMI shielding and filtering Redundancy and reliability protection Overload and overvoltage protection Ground fault protection
EMI filters Thermal management EMC compliance Remote monitoring Thermal protection
The automotive, aerospace, medical, communications, and electricity industries have stringent requirements for circuit protection for power supplies due to the critical nature of their applications. The following is how each of these industries typically approaches circuit protection for power supply:

Automotive Industry

  • Transient voltage suppressors (TVS): When load dumps or electrostatic discharges occur, TVS diodes can prevent voltage spikes and transients. Their purpose is to protect sensitive electronic components on the vehicle from damage.
  • Reverse polarity protection: Automotive power supply often incorporates diodes or MOSFETs to protect against reverse polarity since incorrect polarity connections can damage components.
  • Fuse and circuit breaker protection: Circuit breakers and fuses are widely used in vehicles to protect circuits from overload conditions. They are critical in automotive systems to prevent short circuits and fires.
  • EMI filters: EMI filters reduce the risk of electrical system disruptions caused by electromagnetic interference generated by automotive electronics.

Aerospace Industry

  • Redundancy and fault tolerance — To ensure continuous operation regardless of component failure, aerospace systems often incorporate redundant power supply and protection circuits.
  • Overvoltage and overload protection — Aerospace power supplies have advanced protection mechanisms to prevent overvoltages and overloads. These mechanisms include precision voltage regulators and current-limiting circuits.
  • EMI filtering — Aerospace systems require effective EMI filtering to ensure that electromagnetic interference doesn't compromise the integrity of critical systems.
  • Thermal management — Temperature sensors and thermal management systems are crucial for preventing overheating of components in confined aerospace environments.

Medical Industry

  • Ground fault detection — Medical equipment must monitor and detect ground faults to prevent electrical hazards to patients and operators.
  • Redundancy and reliability — Many medical devices, especially life-critical equipment, incorporate redundant power supplies and protection circuits to guarantee continuous operation in case of failures.
  • Isolation barriers and monitoring — Isolation monitors ensure that isolation barriers are intact, crucial for preventing leakage currents and electrical hazards in medical settings.
  • EMC Compliance — Medical equipment must meet electromagnetic compatibility (EMC) requirements to prevent interference with other medical devices and ensure proper functioning.

Communications Industry

  • Uninterruptible power supply (UPS) — Communications facilities often use UPS systems to provide backup power during outages or fluctuations. UPS systems ensure that critical equipment remains operational and data integrity is maintained.
  • Surge protection — Communications equipment is vulnerable to voltage spikes caused by lightning, switching, or other transient events. Surge protectors are used to divert excessive voltage away from sensitive components.
  • Overload and overvoltage protection — Protection mechanisms like fuses, circuit breakers, and voltage clamping circuits safeguard against overload and overvoltage conditions that could damage equipment.
  • Remote monitoring — Telecommunications sites often incorporate remote monitoring and management systems that allow operators to monitor power supply performance, receive alerts, and perform diagnostics remotely.

Electricity Industry

  • Overload and overvoltage protection — Overload protection devices such as fuses and circuit breakers prevent excessive current from flowing through a circuit. If the current exceeds a predetermined threshold, these devices will open the circuit, interrupting the flow of electricity and preventing damage to the power supply and connected equipment. Overvoltage protection safeguards against voltage spikes or surges due to lightning strikes, equipment failures, or other factors. Surge protectors and voltage clamping devices are commonly used to divert excess voltage away from sensitive components, preventing damage.
  • Short-circuit protection — Short circuits occur when a low-resistance path is unintentionally created between two circuit points. This can cause a massive surge in current, potentially damaging the power supply and other components. Circuit breakers and fuses with short-circuit protection are designed to detect and respond to such faults quickly.
  • Ground fault protection — Ground faults occur when a current-carrying conductor unintentionally comes into contact with a conductive surface or ground. Ground fault circuit interrupters (GFCIs) are designed to detect these imbalances and quickly interrupt the circuit to prevent shocks and electrocution.
  • Thermal protection — Power supplies can generate heat during operation. Overheating can lead to malfunctions or even fires. Thermal protection mechanisms, such as temperature sensors and thermal fuses, are used to shut down the power supply if temperatures exceed safe levels.

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