Go on, please expand your statement and explain exactly how it is that using a bridge rectifier would be more efficient than using and inductor. Humiliate us with your profound genius.
We are on the edge of our seats awaiting your explanation, Mr. Jasen.
Impatiently waiting.... Bob
I assume he meant it is more efficient to run the LEDs from a full wave rectified supply rather than half wave which for a given LED maximum rated current requires twice as many LEDs for the same light output.
it nearly doubles the power factor of the LEDs that's got to help.
Bye. Jasen
LEDS
You need to think this through. The LEDs can only handle so much power, whether it is half wave, two half wave, or DC. The diodes need to be protected from reverse voltage, so series stings of anti parallel diodes does this, and lights the diodes of each pair on alternate half cycles.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
You need to understand LEDs. LEDs are specified with an allowable maximum current and that is a DC specification.
If they bother to specify anything more than a DC maximum you will likely find it is a pulse rating for 10us or a few 10's of us width with very low duty cycle. LEDS have a low thermal mass and can't take much more than their rated current for much more than a fraction of a millisecond.
A typical power IR LED (which is specified for pulse operation) has a 100us pulse current specification of twice the DC maximum but only for duty cycles of less than 2%. At 50% duty cycle the current rating is about 15% more than the DC rating.
Running LEDS on unsmoothed full wave rectified 50/60Hz ac already reduces the maximum available light output, using half wave rectification halves that output again.
I've been designing them into equipment for 30 years. For a one off like this, its the simplest way to do the job. Yes, there are a lot of ways to do it, but simply adding a full wave bridge offers no real advantage unless the output is filtered and something is done to protect the LEDs from spikes on the AC line. Have you noticed the number of LED traffic lights with one or more group of dead LEDs? I see them all over the place.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
Full wave lets you use half the number of LEDs. That is almost a 50% saving on cost, assembly time and finished unit size. Those advantages seem pretty real to me.
Tim
efficiency
The OP wanted to use 200, so where is the savings?
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
[snip]
LOL!
I suspect 200 LEDs might have been selected over 100 because they wanted the output of ~200 LEDs. To get that with half-wave they'd need ~400 LEDs.
But if the OP really does want to use 200 LEDs to get the output of 100 I suggest full-wave rectification and only soldering in ~100 of the LEDs (just over 100, to cover bridge losses). The rest could be used in the base as ballast (mass) to help stop the lamp falling over. That would be around half the effort and half the solder (there's your savings!) and all 200 would still have been used. They'd get over 90 spares in the base too - you only get one in the bottom of a Maglite.
Tim
Tim Auton wrote: [snip]
Oops. Of course you don't need more than 100 LEDs to get the output of
100 LEDs. I had written a bit about efficiency and I cut it out and... well, you get the idea.Tim
no, you need to think it through.
two parallel strings of 20 LED s min series each running at half the current twice as often will have a lower voltage drop but still produce the same output. the voltage will probably be reduced by enough that you could add another LED and get more output.
Bye. Jasen
With the 200 LEDS in a cluster they will run quite hot. Do whatever the hell you want, but it won't hold up if you push the LEDs to their full ratings without some type of cooling. I've seen a lot of LEDs dim, and die from running too hot.
Some genius got the idea to use them to show that the power was on to the radios in the burnin cabinets at Cincinnati, Electronics. They didn't last a year.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
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