AC-Direct Driving LED Strings

With each passing year, LED lights (light-emitting diodes) are continuing to offer better performance at a lower cost. Because of this, the main expense now associated with LEDs is the infrastructure in the conventional lighting fixture - the housing, connectors, PCB, optics, and perhaps most critically of all, the power supply. This has driven attempts to design and create more inexpensive architecture, specifically looking to reduce the cost of the power supply. Below, we’ll discuss the development of AC-direct LED systems and how it has helped to eliminate the need for a conventional and expensive AC-DC switch-mode power supply.

Eliminating the SMPS

Designing out the switch-mode power supply (SMPS) was essential to reducing costs in modern LEDs. However, the logistics behind making that a reality was much more complex than initially thought. The primary function of the SMPS in conventional high-brightness LEDs was to step the AC mains voltage down to the DC forward voltage of an LED or string of LEDs. As an alternative, designers opted for a simpler approach of having no stepping down. Therefore, the AC-direct regulation scheme achieves this by switching LEDs on in sequence following the mains sinusoidal voltage. Compared to the SMPS equivalent, the AC-direct design is much simpler, easier to assemble, and smaller as it only requires a single PCB. However, even with this innovation, there are some drawbacks. 

The Drawbacks

One of the major drawbacks of the AC-direct LED with a centralized control design is heat. Because current regulation and power dissipation are concentrated in a single IC, the IC becomes an extreme hot spot. This requires special counter measures to negate the risk of overheating damage. Additionally, the centralized form of AC-direct regulation lacks flexibility in terms of functionality and performance optimization. These short-comings have led to an additional upgrade to a more flexible AC-direct LED regulation scheme.

The Upgrade - Distributed Control Scheme

The upgraded AC-direct LED employs a distributed control scheme as opposed to a centralized scheme. The distributed scheme offers benefits that the centralized scheme can not, chiefly its flexibility. The flexibility of the circuit topology allows the system designer to accommodate a wide array of LED arrangements in order to achieve the perfect balance between functionality, performance, and cost. Furthermore, the distributed approach gives the user the ability to select any LEDs, whether classic low-voltage types or multi-junction high-voltage LEDs. These upgrades to the AC-direct LED lights, not only help reduce costs normally associated with LEDs, but also contribute toward the conservation of additional energy.

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