Plugs Improve Flexible LED Strips

By Contributed Article | April 25, 2016

A new direct-plug solution makes connecting LED strips almost as easy as screwing in a light bulb.



Flexible strips for LED lighting

Figure 1. Flexible LED strips are as easy to connect as light bulbs when the plug-and-socket principle is transferred to flexible LED strips.

Electronics designers and developers are always looking for suitable connection solutions for flexible LED strips. Reliability, functionality, size, and electrical requirements are important considerations in connection systems for electronic assemblies involving LEDs. A new direct-plug solution makes connecting LED strips almost as easy as screwing in a light bulb (Figure 1).

The newest flexible LED strips have a high level of system efficiency with a luminous efficacy of 160 lumens per watt (lm/W). Just two years ago, similar strips were rated at only 100 lm/W. This comparison shows how quickly LED technology is progressing, but connection technology for LED strips is not developing quite as fast.

Easy Replacement

The first light bulbs in the late 19th century were unreliable and had a service life of less than 1,000 hours, but they were suitable for a broad range of applications. The connection technology used in light bulbs is so simple and well conceived that anyone can replace them quickly – which compensates for the disadvantage of short service life.

The example of light bulbs shows how important the right connection methods are for new lighting technologies. Flexible LED strips are now being used in a wide variety of lighting solutions, such as accent lighting for building facades or indirect ceiling lighting. LED manufacturers have improved the technology behind LED strips, and they are now replacing conventional lighting in many applications. Today’s flexible LED strips offer consistent color and a unified and clear color impression. In addition to boasting high luminous efficacy and balanced light emission, the LED strips are rugged and long lasting.

Flexible LED Strips in Action

Conventional lighting techniques allow developers and designers to use established sockets and plugs, such as G1 mount base types for T8 fluorescent lamps or E27 sockets for incandescent lamps with E27 sockets. Solutions like these make it easy to form a mechanical and electrical connection. Unfortunately, comparable sockets and plugs have yet to be established for flexible LED strips. The delicate, flexible LED strips are generally transported on reels in lengths of five to 10 meters. Quality-conscious manufacturers also provide ESD-compliant packaging. The strips are fitted on the underside with a self-adhesive film and are divided into multiple segments. The space between two segments is marked so that the LED strips can be divided using a simple cutting tool (Figure 2).

Flexible LED in segments

Figure 2. Flexible LED strips in segments: Strips can only be divided at the marked positions between segments, and they are easy to connect at the sectioning points using plug-in connectors from Phoenix Contact’s PTF series.

The required length is unwound from the reel and cut in the marked areas prior to installation and then glued to a lamp as a light source. The adhesive layer creates a permanent, mechanical connection between the strip and the lighting solution. However, the user cannot refer to any standard connection procedures and systems when establishing an electrical connection; an improved connection technology is on the wish list of many lighting manufacturers.

Connection Technology Requirements

Traditional light bulbs have little in common with today’s flexible LED strips. Since LEDs have a service life of at least 50,000 hours, the focus is no longer on making lights rapidly replaceable but on ensuring that connections are secure and convenient when mounting lights.

Traditionally, LED strips are connected to a power supply by soldering conductors to solder pads located at the sectioning points (Figure 2). However, this process can cause problems when used in serial manufacturing. ESD directives play an important role in this context because ESDs are one of the most frequent causes of breakdowns in integrated circuits based on semiconductors – and an LED strip involves just such a circuit. LEDs that only tolerate reverse voltages of 5V to 30V are especially vulnerable. The term “reverse voltage” refers to the maximum voltage that an LED can tolerate in the event of voltage reversal or electrostatic discharge. Because of this, ESD protection should be a consideration when soldering conductors to solder pads. The soldering duration and temperature must be precisely maintained throughout the soldering process to prevent damage to the circuits. Also, a high degree of manual dexterity is required to connect RGB strips using small soldering tips because the solder pads are often just one millimeter wide and positioned side by side (Figure 3). When soldering manually, extreme care has to be taken to ensure a solid connection that will last at least 50,000 hours.

Figure 3. Connection dimensions for the direct-plug system from Phoenix Contact: Flexible LED strips for 10mm (left) and 8mm wide strips. The PCB thickness (t) should measure between 0.15mm and 0.3mm in the connection area.

Figure 3. Connection dimensions for the direct-plug system from Phoenix Contact: Flexible LED strips for 10mm (left) and 8mm wide strips. The PCB thickness (t) should measure between 0.15mm and 0.3mm in the connection area.

Socket and Plug for LED Strips

It would be a great help to lighting manufacturers if a type of socket and plug comparable to that used in conventional lighting were available for flexible LED strips. Such a system would be long lasting, safe, and easy to operate, while requiring only a low design envelope for soldering. It would also take applicable standards into consideration, as conventional lighting does. But the flexible nature of LED strips places high demands on such a system. It would be ideal if there were a connection solution at every sectioning point. However, this requirement would make the strips much more expensive. An alternative is a system that creates a connection directly where the strip is divided.

To meet this requirement, a newly designed direct plug system relies as much as possible on a socket/plug system. The area on the PCB reserved for solder pads serves as a socket or connection surface for LED strips (Figure 3).

The strip manufacturer then defines the dimensions of the solder pads in this area; in practice, the dimensions and the number of connections vary greatly depending on the type of strip. For example, two connection pads for one plus/minus connection are usually enough for white light. RGB LED strips, which can produce every color by mixing red, green, and blue, require four connection pads (RGB+). The width of the lighting strip also varies depending on design; 8mm or 10mm widths are frequently used, and four possible contact pads are provided for these strips (Figure 3).

Direct-Plug System as a Socket

Once a socket site has been identified, the direct-plug system serves as a socket (to stick with the light bulb analogy). The plug system, which is hardly wider than the strip itself, allows flexible LED strips to be connected on their socket or terminal sides. The strips are simply plugged into the open plugs. When the plug is inserted, the built-in contacts connect to the contact pads, and the LED strip is connected. There are two or four color-coded switching cables connected to the plug, and these are then connected directly to the power supply.

This system allows safe and reliable connections. Manufacturers of flexible LED strips who want to offer their customers high-quality connections take care to ensure that contact surfaces in their latest developments and designs are suitable for plug-in connectors. This solution will accelerate the already rapid spread of flexible LED strips.

This article was authored by Lukas Muth, Combicon product marketing, Phoenix Contact GmbH & Co. KG; and James Dunbar, product marketing manager, PCC, Phoenix Contact USA.

 Visit Phoenix Contact online.

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