Wednesday, August 10, 2016

Re-exploring direct AC LED lighting and does LED lighting use DC or AC?

We'd described the pros and cons of direct AC ('Alternating Current') 2 years ago. Today we re-examined the following;
1. How does the AC LED lighting actually work?
2. Re-examined the pros and cons of direct AC Led lighting / luminaire.

The summary........

- In summary, LED lighting is still using the DC (Direct Current) principle to operate.
- We make use of electrical components (some people call it IC driver) to alter the input AC power.
- First, one must understand that AC wave form is a sine curve with both positive and negative crests / trough. (Look at the pictures below)
- The IC Driver will flip all the negative curve upwards. So one get a series of positive crests only. (It will then look like a ridge mountain in Nepal or the French Alps)
- Next the driver will slice only the top part of all the crest from left to right. It is like taking a ruler to link all top part of the mountain together with a tangential line.
- We surely cannot have a perfect straight flat line (Direct Current) depending how close you examine the curve.
- But, this would achieve an effect that is as close to a straight flat unbroken line which might just be good enough for the LED lighting to work well.

The story......................

Creating DC power from AC
• Alternating Current or AC is a voltage that varies over time as it is delivered by the power company. To be used in LED Lighting/luminaire you need to convert the AC into DC using a bridge rectifier (turning AC in to pulsed DC) and then filtering (smoothing the pulsed DC into a continuous DC).

Fig.1 Rectification

Filtering - Passive components are used to smooth the rectified signal to a constant DC voltage. Without control, the output voltage will fluctuate with input voltage
Fig.2 Filtering

Picture courtesy from Seoul Semiconductor on their ACRich3 LED module

Further to the above, our personal opinion on a strong advantage for AC LED lighting comes on the back of the recent breakthrough in thermal control for the IC driver. With this heat issue under control, AC lighting should start proliferating the LED lighting industry soon.

Article contributed by Leong Weisheng.


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