Surge Suppression in LED Lights|
Article - February 9, 2016 By LarsonElectronics.com
Surge Suppression in LED Lights
LEDs rely on a steady-state current to function optimally. Such luminaries utilize small components that actively monitors incoming currents to ensure the circuit does not get fried by an electrical surge.
Defining Inrush Current
When a current-sensitive fixture, such as LEDs, is turned on, the unit draws input current instantaneously. Inrush current is the maximum rate of the incoming current, as it makes it way to charge the capacitors located in the input section of the device. The current usually reaches its peak at the beginning of exposure, eventually decreasing to a normalized current with help from other electrical components- such as surge suppressors. The problem with this activity is that it can damage the equipment, greatly reducing its lifespan. In most cases, the abrupt current surge contains greater amplitude, compared to the operating current.
In LEDs, the incoming current may display different behaviors. For example, it may peak early then dip down to a steady-state current; or decrease then peak before normalizing. Because of this, it is crucial not to overlook the possibility of encountering the “worst case” inrush current. This typically occurs when the voltage starting angle is at 90 degrees (voltage starting angles may vary from 0 degrees to 170 degrees).
A Negative Temperature Coefficient (NTC) thermistor is an electrical component that detects temperature shifts in the applicable device. During an increase in temperature-related conditions, the unit is able to lower its electrical resistance. In application, the inrush current limiter is designed to protect circuits. Composed of metallic oxides, the thermistor can manage a broad range of temperatures, allowing it to be used in damp conditions or environments.
When an LED light is turned on, the NTC component increases its resistance due to the presence of an inrush current. As electrical exposure increases, the unit heats up, resistance decreases and power is eventually allowed to safely pass through the circuit. Inrush current limiters can be found in the following two locations on a circuit: after the bridge rectifier or at the mains inputs.
Inrush current limiters must be cooled down after power is removed, due to the amount of heat they suppress during usage. This cool-down period may last between 20 seconds to one minute, depending on the specifications of the component, its surrounding temperature and mounting method. During this time, the resistance of the part increases significantly. When identifying the piece based on its print mark, the first digit displays the resistance of the component in normal conditions, while the letter and the next digit indicates the size (in diameter) of the part. According to a report from Data and Strategies Group, Inc., NTC thermistors are the most popular type of surge suppression components, with a whopping 90 percent of the electronics industry using the unit for electrical protection.
Metal Oxide Varistors (MOVs) are parts that are used to suppress electrical surges in LEDs. Commonly applied in overvoltage conditions, the component works by diverting extra voltage away from the fixture. The durable units can handle peak current ranges between 20-70,000A and peak energy ratings between 0.01-10,000J. MOVs are composed of zinc oxide (over 90 percent), combined with a ceramic-like material. The mixture allows the part to absorb abrupt voltage spikes and handle unpredictable currents. During its lifespan, the component degrades slowly due to continuous use. Failure can occur when the unit is exposed to a large, unmanageable current surge or over time, through the exposure of numerous small surges. As the MOV degrades, its functionality diminishes, which causes current leakages in the device (raising its temperature). To prevent smoke or fire, a thermal disconnect is applied that disengages the circuit before such occurrences can fully materialize.
Multilayer Varistors (MLVs) are special varistors that focus on mitigating currents in circuit boards. The component is composed of several layers of fine grain ceramic, and is designed to handle electrostatic discharge (ESD). Each layer is positioning with alternating connections between two electrodes, while every other layer is connected to the same electrode. This configuration allows the unit to handle higher resistance levels at lower voltages. It also has faster response times, compared to MOVs. In application, they are used to support data-line and power-supply transient suppression. MLVs support DC voltage ratings ranging between three and 120V.
Fixed and Variable Resistors
Resistors are applicable to limiting inrush currents. Commonly used to protect low power circuitry, such components are generally more cost effective than thermistors. There are two basic types of resistors: fixed resistor and variable resistor. A fixed resistor is used when restricting a current within a specific range, and can also be applied when dividing voltage. Its constant resistance is determined by the manufacturer. Variable resistors are typically used when varying the amount of current being supplied to a section of a circuit. The level of resistance can be adjusted from zero ohms to a maximum resistance value set by the manufacturer. Such components are found in light dimmer switches, sensors and consumer electronics.