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Keeping The Lights On: ESD And warm Protection For LED Lighting Systems

There are many factors which could affect solid state lighting in electronic design from stress issues, to packaging-related issues to component-related issues. Design engineers will need to pass these 4 elements in mind. You will find three key threats that affect the reliability of LED lighting systems in electronic designs:

  • Electrostatic discharge (ESD) events, including lightning Transient overcurrent events and surges
  • Current and voltage spikes during hot swapping Reverse voltage effects
  • Overtemperature protection

For LED lighting systems for being reliable, all the components and subsystems should be protected effectively against these dangers, which have been encountered during assembly, maintenance and operation. High-performance ESD and overtemperature protection can safeguard against these dangers, becoming a longer lifetime, lower maintenance costs and increased longevity of the LED lighting system. Using high-quality protection ESD and overtemperature components provide effective and cost-efficient protection for LED arrays, their power supplies and control circuits.

LED system overview

An LED bulb – or over technically, a luminaire – is composed of three basic subsystems: an LED power supply, a power-input connection to the grid, as well as an LED engine. The LED engine is usually further converted into LED arrays, LED drivers and control units.

Over days gone by a number of years, smart LED luminaires have become popular resulting from features including push-button control and maintenance. As a result, a fourth subsystem – communication power supplies and interfaces – is likewise often utilized in the luminaires. This will give smart networked lighting systems to become deployed that boost efficiency superiority lighting, and enables facility managers be aware of status for each luminaire for maintenance.

As the LED lighting system technologies have matured, engineers realized they needed the right way to prevent ESD events and high energy surges from affecting the luminaire also to ensure system reliability. These surges can result in both immediate failures (often for a junction) along with an increased rate of degradation brought on by latent damage. Each of the four subsystems is often in contact with events that can cause this sort of damage. As engineers read the vitality of possible events, they might determine what suitable protection products are needed.

A basic LED lighting system architecture that showcasing overvoltage and overtemperature protection devices

High-energy surges

Voltage-dependent resistors, also known as varistors, have always been a solution preferred by overvoltage protection. The reason being the electrical resistance varies with the applied voltage. Engineers should select varistors that can support the conditions from the end application.

Take for example the protection of power supplies. Metal oxide varistors are particularly well-suited to shield the strength supplies of LED lighting systems from larger energetic surges. The look may specify varistors which include a tight design, or that give protection against big ESD events just like lightning strikes. And, as a consequence of harsh nature of the elements and expense of maintenance, LED lighting systems suitable for streetlights should meet both ANSI/IEEE C62.41.2 along with the DOE MSSLC Model Specification for LED roadway luminaires. When this happens, surge arresters along with varistors supply a space-saving integrated solution with ideal performance.

In the power input connection, a single package which includes a disk varistor connected in series which has a thermally coupled fuse is most effective to produce the safety required. In such a case, in case the varistor overheats, the thermal fuse – which can be encapsulated in a plastic housing – disconnects the varistor from your power circuit preventing fire, safely closing the device.

Low-energy and ESD discharges

Transient-voltage-suppression (TVS) diodes have already been for quite a few years to guard circuits from low-voltage ESD events below 25 Joules. However, multilayer varistors offer important advantages over traditional TVS diodes. Examples include more miniature sizes and insertion heights, more dependable performance, faster response times, and better overall operation across wide temperatures. Additionally, TVS diodes can effectively be utilized to satisfy the absorption requirements in terms of component size.

LED engines integrate numerous LEDS that happen to be normally series-connected strings, parallel-connected strings or perhaps a combined both. For more LED fails in a series-connected string, the full series will fail. It is because LEDs in a series-connected string could potentially cause an antenna effect making the array more responsive to ESD events. Multilayer varistors provide protection against such events.

Networks are frequently reconfigured, moved, replaced and taken offline for maintenance. Consequently, hot swapping the type of practice, and hot swapping might cause ESD events and low-voltage spikes. Multilayer varistors or TVS diodes that have already extremely low parasitic capacitance are preferred to your ESD protection of knowledge lines for your management of luminaires. Such diodes will assure which the devices would remain completely functional for specified lifetimes.

Diodes vs. Varistors

Diodes and varistors are made to meet unique design challenges for many applications. These solutions will often be ruggedized, have a smaller footprint, or are supposed to prevent certain kinds of surge currents.

For example, the EPCOS CeraDiode from TDK was created to absorb high energy in the better rate than TVS diodes and has a lesser footprint. Eighty percent with the component level of this program can be used to absorb the power ESD events, which can be preferable over the 30 % of ordinary TVS diodes – and possesses the same performance. Due to this, non-standard parts might be of interest when they help minimize space requirements and provide the same or improved performance. Many of the crucial in applications that want miniaturization, reliable protection, and high performance.

An demonstration of a specialized or non-standard component use to protect against ESD events

Another example is bidirectional protection against ESD and transient disturbances supplied by multilayer varistors. A regular TVS diode is inherently unidirectional, which makes it recommended to design by 50 percent diodes. However, varistors provide bidirectional protection as being a single component with the same protection. In such a case, varistors will supply a size and expense benefit to the structure.

Other varistors provide reliable performance at higher temperatures. A typical TVS diode starts derating at 70 degrees, that’s cheaper than many applications require, rendering it essential to purchase a varistor which can operate reliably on the very large temperature spectrum, thereby limiting failures a result of temperature fluctuation.

Temperature protection

In most all cases, sudden failures in LED lighting systems are due to thermal stresses. Because LEDs demand a constant current to supply an uninterrupted luminance, their temperature have to be controlled precisely within narrow limits. Thermistors, or thermally sensitive resistors, are a precise and cost-effective sensor for measuring temperature.

A thermistor is a device whose electrical resistance is controlled by temperature. There are two varieties of thermistors: NTC thermistors and PTC thermistors. In NTC thermistors, or negative temperature coefficient thermistors, resistance decreases as temperature increases. In PTC thermistors, or positive temperature coefficient thermistors, resistance increases as temperature increases.

NTC thermistors are available surface mounted design (SMD) packages, and protect the LED arrays against overheating and help control their temperature profile at peak lumen efficiency. This really is accomplished by automatically adjusting the actual towards the LEDs. As well as intelligent circuits, they enable an effective control system.

Temperature-compensated LED driver with no IC

In temperature-compensated LED driver designs without integrated circuits, PTC thermistors can help to eliminate the high temperatures of your forward current by placing them in series towards the LED. In such a design, a lot of the LED current flows from the PTC thermistors.

Keeping the lights on

As LED technology is constantly mature, design engineers can increasingly pun intended, the high- and low-energy surges and ESD events that affect LED reliability just by determining the best option protection devices which can be necessary for application. On top of that, they can also arrange for the best temperature protection necessary for their applications, thereby keeping the lights on in an literal way.

Courtesy: Epcos