LED Technology Is More Widely Understood

LED lighting is becoming mainstream and luminaire-­makers are jumping on the bandwagon with viable products now that the technology is more widely understood. In the early days few lighting firms could get their heads around semiconductor heatsinking and precision optical alignment, and few LED-makers realised that no one wants to install a reflow oven, or even lift a soldering iron, to make light fittings. Now the luminaire companies are learning to be a bit more high-tech, the LED-makers are getting a bit more practical, and connector firms are continuing to bridge the remaining gap with easy-to-handle products that deliver electronic industry precision to the LEDs. Right at the start of power LEDs, Lumileds was selling LEDs mounted on 20mm hexagonal ‘star’ boards alongside its un-mounted products. The star board allowed anyone with a screwdriver to attach the LED to a piece of aluminium and power it up to try it. The star was probably the first example of the LED ‘light engine’ – a genre that has become another popular span in the LED-maker to luminaire-maker bridge. Unfortunately, the star board still requires soldering, making it a no-no for most light fitting manufactures. Seeing this, German lighting parts maker BJB was early on the scene with a connector that mounted over the star board on the same two screws as the star. The BJB connector has sprung contacts that press onto the star’s contact pads – removing the need for solder – and includes poke-in wire terminals. The lighting industry loves ‘poke-in’ terminals because they offer fast assembly. A spring mechanism inside will grip a stripped single-strand (solid core) or tinned multi-core wire as soon as it is poked in. Insulation-displacement Insulation-displacement connectors are another fast-termination industry favourite – removing the need for stripping, but requiring a custom insertion tool. The BJB connector system includes an optional second moulding that holds a lens, from UK optical firm Carclo, in the correct position to focus the light into a beam. TE Connectivity (Tyco Electronics until March this year) now has something similar to the BJB system which is branded Nevalo LED Socket (formerly called Solder-less LED Socket). The Type CM Nevalo socket, for example, provides solder-less quick termination to Cree’s MP-L power LEDs. The MP-L is one of the new breed of LED that are in some ways the successor to the star concept – rectangular ceramic tiles carrying multiple die – in this case 1,500lm-worth of die on a 11x12mm tile. Contacts are generally on top, rather than underneath with single-die ceramic packages. Bridgelux beat Cree to market with these larger multi-die lighting LEDs, and all of Bridgelux’ LEDs have a couple of holes in them for screws so they can be attached as easily as stars – Cree has some bolt-down ones in the pipeline too. An MP-L LED does not have screw holes, so CM connector holds it down to the heatsink or metal-clad PCB (MCPCB) with pressure supplied through its mounting holes by standard M3 or No.4 screws. CM versions are available that have lugs to retain one of Ledil’s Tyra reflectors, and with electrical ports for a TE MiniCT crimp-style connector for wires (LED-to-wire), or contacts to take connections down to PCB tracks alongside the LED (LED-to-board). The other connection option is ‘LED-to-inverted wire’, which points the MiniCT socket through (or over the edge of) the PCB to enable the customer to connect from behind. The firm is expecting use in custom single-source spot lighting fixtures, fixtures with multiple distributed high-intensity sources, and in integrated retrofit PAR30, PAR38 and MR-16 spotlights. Connector firm Molex and LED-maker Bridgelux took this concept a little further and together developed a two-part system called Helieon (pictured), which takes LED lighting to somewhere much nearer incandescent light bulbs ease-of-use. One part of the connector – equivalent to a bulb-holder – is screwed to aluminium metal work and has a bayonet-style mechanical receptacle above a large hole all the way down to the metalwork. This part also has receptacles for wires which are connected to contacts around the bayonet. The second part of the connector is analogous to the bayonet or screw base of a light bulb and is a bayonet integrated into the base of an LED-reflector assembly. Once pushed into the chassis-mounted part, the electrical connections are made and a heat path is established between LED and chassis. Consumers can twist out the LED assembly themselves to change a defective part or replace it with one of a different beam width or colour temperature. Philips has subsequently brought out a similar system called Fortimo Twistable, as has GE through its acquisition of Journee Lighting. Critically, all three systems allow simple mechanical assembly at the luminaire plant without soldering. For independent light engine companies there are several connector ranges for taking wires onto PCBs and light engines inside light fittings. JST makes a 3A 300Vac/dc system called LEB particularly for board-to-board and wire-to-board use around light engines. The parts are surface-mount and height has been kept to 2.7mm, which is comparable to the height of the power LEDs alongside. One- and two-circuit versions are available, and a fork-style contact in the receptacle allows a small amount of misalignment side-to-side for board-to-board use where there is more than one connector between the boards. “The contact has a high contact pressure and enough mating stroke to provide stable contact performance even if the PCB expands and contracts due to heat,” claimed the firm. Flying lead plugs have a solder-free crimp attachment for the wires from 22AWG to 26AWG, and the connectors are polarised to block reversed connection. In keeping with the hot working environment, operating range is -55°C to 105°C. Contact resistance is 20m initially, rising to 40m after environmental testing. This brings the maximum voltage drop across an LED’s connectors up to 240mV – something that designers have to keep an eye on as long series strings of separate LEDs have a lot of connections. The firm’s LEA range has similar electrical characteristics, but offers a different physical style and locking. TE Connectivity is in the LED wire-to-board market too, this time with a 3.9mm high 4A 240Vac poke-in design for 18AWG to 22AWG wires. Operation is -40°C to +105°C and there are black or white surface-mount variants with one or two circuits, plus a through-hole version. A smaller version (2.5mm high) takes solid wires from 24AWG to 26AWG and handles up to 3A. For under-cupboard and alcove lighting, strips of LEDs mounted on long thin PCBs are starting to occupy niches previously filled by fluorescent striplights, and there are even replacements made for larger fluorescent tubes that use long strips of LEDs inside. For these LED strips there is a host of wire-to-board connectors and board-to-board connectors that allow end-to-end butting – something that was impossible with fluorescents. AVX offers LED strip connectors in its 9175, 9176 and 9177 wire-to-board series, and its 9159 and 9159 board-to-board series. For example, 9175 is an insulation displacement low-profile (3.45mm) connector series with two- or three-wire positions: 26AWG or 28AWG solid or stranded wires are inserted into the contact slot using a custom tool without needing to remove the insulation. Contact material is of phosphor bronze and the parts can cope with 1A continuous through all contacts at 25°C, 125V. Maximum termination resistance is 20m and operation is from -40°C to +125°C. Some of the series have a optional clip-over wire retainer for high-vibration environments, and 9159 is a series of female-to-female couplers that mate two LED strip PCBs with track-type edge-connectors on their ends. Larger versions offer up to 15A/contact through 14AWG to 20AWG wires, and some variants will work down to -55°C. With a few exceptions, however much the LED makers and luminaire manufactures try to meet one another’s requirements, a connector company still has to bridge the gap. Source: www.ledinside.com