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Led Full Wave Vs Half Wave?


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I am new to this hobby and am looking to setup an LED display just because of the power requirements are so much less.

I see a lot of talk about Full Wave and Half Wave LED strings.

From what I understand is that the LED strings will turn on at a certain voltage that seems to be different from Manufacture to Manufacture. 75V seems to be tossed out a lot.

What this implies is that the LED is only on for a short time in the complete 60Hz cycle. Something like 5mSec out of 16mSec.

I was guessing that a Full Wave LED string would simple take half the LEDs and turn them around so they use the other half cycle? But maybe these strings actually have a rectifier circuit in them?

With that being said, I assumed the LOR did a simple PWM on the wave forms going out to the strings to control the Intensity. For LEDS, for this to work they would have to know the turn on Voltage and then the phase of the AC line.

Is this in fact how the LOR works or am I missing something.


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Half wave strings usually have one half of the LED's conducting on one half cycle, and the rest on the other. Many LEDs do put out some light well below their rated voltage, but it is a tiny fraction.. So you probably get a tiny bit of light nearly half the time, but full light for about 1/4 of the cycle.

I will say that different half wave strings seem to have narrower lit times than others. Some seem pretty stable, unless I am seeing them in my peripheral vision, with relative motion, and others seem like strobe lights just looking at them head on and still.

The full wave strings are rectified, so you get twice as many pulses of light of the same width. They are not constant on like some seem to think, unless you put in a filter cap, and that leads to stings burning up when dimmed, like one manufacturer had issues with a couple of years ago.. (but they were actually voltage doubling, not just filtering) But nearly everybody agrees that 120 pulses per second is is going to appear visually solid and stable for a much larger portion of the population than 60 pulses per second.

The last controller design I saw that did PWM rectified the power, so as to only use one IGBT per channel. This has the issue that most half wave strings only lit one half or the other, and did not work with strobe lights, because they need AC for the voltage doubler. It looks like the DIY community is not actively promoting that design any more. High frequency PWM with full AC cycle support would probably provide the most linear and best result.

What LOR does is phase angle dimming, like any residential light dimmer. It uses triacs, so switching off only occurs at the zero current events, that in linear loads are at the voltage zero crossings. So dimming is accomplished by how far through the half cycle you delay triggering the triac. This has the result of compressing most of the dimming range for LED lights into the range between about 25% and 75%.

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