This article will outline some essential circuit protection considerations in consumer electronics and some relevant protection standards.
The Need for Circuit Protection in Consumer Electronics
Circuit protection is critical in consumer electronics for the following reasons:
Linear and switched-mode power supplies (SMPS) are prone to overvoltage events due to poor power quality that can damage components in electronic products.
Increasingly, electronic products have smaller manufacturing geometries and inadequate grounding due to advances in IC design. Consequently, lower voltage and current levels are causing more failures in the PCBs.
Portable electronics like smartwatches, digital cameras, and other hand-held devices used in dry environments are susceptible to overvoltage events (e.g., ESD) at the USB ports or I/O connector pins, due to human contact or frequent plugging/unplugging.
Personal electronic devices at a workstation.
Overcurrent is a prevalent problem in consumer electronics that increase the risk of electric shock, fires, and explosions. Overcurrent occurs when the supply current exceeds the current-carrying capacity of the device, usually due to overloading, arcing, short-circuits, and grounding faults.
Overcurrent protection devices for consumer electronics limit the amount of current flowing through circuits, allowing products to "fail gracefully." The following are some examples:
These non-reusable devices interrupt excessive current flow through a circuit by melting a thin conductor film. Fuse ratings in consumer electronics are up to 300 volts.
There are several fuse types, including standard ferrule-type fuses (commonly utilised for overcurrent protection in mains plugs of electronic appliances), ultra-rapid fuses that help to safeguard sensitive semiconductors, such as diodes, transistors and thyristors, and fast-acting fuses capable of protecting cables from melting during overload conditions.
Positive Temperature Coefficient (PTC) Devices
PTC devices consist of a doped polymer material with a temperature-sensitive resistance. When overcurrent flows through the circuit, the polymer material heats up and enters into a high resistive state, limiting current flow. When the fault current stops flowing or the device cools, the resistance drops, and the device re-enters a high conductive state.
Overvoltage events or power surges can cause electric shock or damage sensitive components such as ICs. Overvoltage protection devices for consumer electronics automatically shut off the supply voltage whenever it exceeds the rated voltage of the product.
Zener diodes are ideal for protecting circuits against ESD and voltage transients. They consist of a highly-doped p-n junction that exhibits reverse-breakdown characteristics to shut off the supply voltage when it exceeds a preset level. The breakdown voltage threshold for Zener diodes can be anywhere from 1.2 to 200 V.
Transient Voltage Suppression (TVS) Diodes
TVS diodes are semiconductor-based devices capable of clamping voltage transients such as those created by lightning, ESD events, and inductive loads such as generators, electric motors, relays, and transformers. TVS diodes are useful in applications such as DC supply protection, operational amplifier protection, DC load protection, LED driver protection, Power over Ethernet (PoE) equipment protection, and more.
Metal Oxide Varistors (MOVs)
MOVs are protective components having a resistance that varies with the applied voltage, making them suitable for surge protection in consumer electronics. Under standard voltage, a MOV remains in a non-conductive state as a shunt-mode device. However, when a voltage surge occurs (e.g., from a lightning strike), it enters into failure mode by melting or vaporising to open the circuit.
Electrostatic Discharge (ESD) Protection
ESD is a significant problem in consumer electronics that results from friction between different materials coming in contact with each other. This friction causes electric charges to build upon the surfaces, which can go unnoticed until a person touches it (usually felt as a zap or jolt of electricity coursing through the body) or damages a sensitive internal component.
ESD events can generate as much as 15 KV of energy. Without adequate protection, ESD events cause soft failures (e.g., signal disruption in communication devices), latent failures (degraded functioning), and catastrophic failures (e.g., damaged circuit traces or blown components on a PCB).
Mobile phone charging ports are susceptible to ESD events. TVS diodes can can provide ESD suppression to protect sensitive components.
ESD Protection Standards and Requirements for Consumer Electronics
IEC 61000-4-2 is a standard by the International Electrotechnical Commission (IEC), providing guidelines for engineers and technicians to ensure ESD immunity in electronic products. The equivalent standard in Europe is EN 61000-4-2. IEC 61000-4-2 covers test methods, levels, and requirements for electronic products to be certified as immune against ESD effects.
For the testing requirement, ESD simulators (aka ESD guns) can test the immunity of electronic components. ESD simulators apply high-voltage, high-current, and high-frequency pulses to the equipment under test (EUT) for a specified period while an observer analyses the failure modes and mechanisms on the PCB, e.g., ground failure, short circuits due to inadequate creepage distances, power decoupling issues, and more.
Component failures may also result from design defects, such as poor shielding for EMI transients. Where an electronic product passes the ESD test, it receives a "CE" marking indicating compliance with health, safety, and environmental standards for the European Economic Area (EEA).
Assuring the Reliability and Safety of Consumer Products
The test levels utilised for IEC 61000-4-2 qualification are based on direct contact or air discharge applied to the EUT in vertical or horizontal planes. Both discharge methods have four or more levels, ranging from ±2 kV to ±8 kV in direct contact discharge and ±2 kV to ±15 kV in air discharge.
Circuit protection is an essential requirement in the electronic products people use every day. Primarily, it assures the reliability of devices and the safety of consumers. Moreover, circuit protection standards such as IEC 61000-4-2 and EN 61000-4-2 help protect customers by providing electronic product manufacturing guidelines.
Protective devices such as the ones discussed above limit current and voltage levels in electronic products to safe levels to minimise fire, electric shock, and component damage.