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Redundant LED driving solutions.

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(@copperthiever)
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Since I got interested in building my own LEDs, I started by dissecting standard mains powered LED bulbs and fixtures only to get confused from all the different arrangements of leds and power delivery circuits.

Browsing the internet for various specialty LED emitters, I had no clue what to use to power them.

I finally learned about constant current led drivers. But looking at anything that is made and sold specifically for LED, looks like a lot of cost cutting measures have been taken. And I would not trust them to power the LED without some kind drawbacks in efficency, power output tolerances, flicker.

I also don't understand how cob led are also driven with CC drivers, since they have multiple series of led in parallel. Like if one series of LED fails, would it not then overcurrent the rest of the series?

I just hate being at the mercy of the compromises the LED industry has made to cut costs.

So if I am avoiding any purpose made LED CC dri ers.

How would I design my led circuits to have most redundancy? What kind of constant voltage power supplies/converters would be best for driving led? 

Are there any constant voltage power supplies where voltage could be easily adjusted in a limited range for dimming?

I really don't like the concept of pwm dimming. 

 
Posted : 29/12/2024 1:27 pm
(@copperthiever)
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I am mostly concerned with low power led 10w and under

And relatively small drivers/power supplies to potentially fit into existing led fixtures.

 
Posted : 29/12/2024 1:45 pm
marcdraco
(@marcdraco)
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LEDs are current driven. Voltage is a secondary concern really - provided the voltage is within range of the device. The more voltage you apply, the more current flows (once you pass the turn on threshold).

Each LED has an needs to pass a certain voltage to turn on but the brightness can be controlled by current or a PWM. You can do both actually.

The whole point of of constant current is that it's... well ... constant. Within the compliance range of the current source (or sink) the circuit will maintain the same amount of current. If an LED blows then the current will be applied to the remaining devices causing them to overload but the chances of that are pretty slim unless they are driven hard and/or  allowed to overheat.

A current "mirror" is a pretty simple circuit. You set the operating current and then one or more "mirrors" apply that current to each device along the chain. In this way you can make the programming current variable (with a potentiometer or a digipot). Operational amplifiers often have a very wide range of supply voltages because they use mirrors to set everything up internally.

A basic mirror requires two transistors but you only need a single programming resistor a whole bunch of devices. You could drive each LED with one transistor or multiple LEDs in series per transistor - but watch out for the SOA of the transistors so you don't fry them.

You can also run several LEDs on each mirror (to save costs and complexity).


Take everything I say with a pinch of salt, I might be wrong and it's a very *expensive* way to learn!

 
Posted : 29/12/2024 9:49 pm
marcdraco
(@marcdraco)
Posts: 701
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I'm assuming here that you're talking about a DC supply. A lot of LED bulbs use capacitive droppers, a low-cost technique that always makes me feel a little uneasy (even though I know how it works). Big Clive (YouTube) frequently discusses these a lot.

This "X-ray" (cough) of a filament lamp from China is classic Clive. He's a top notch chap, very clever and really funny too.


Take everything I say with a pinch of salt, I might be wrong and it's a very *expensive* way to learn!

 
Posted : 29/12/2024 10:04 pm
(@copperthiever)
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@marcdraco

I was thinking more along the lines dc-dc converters.

I think I am liking the redundancy and flexibility of combining common 5v, 12-24v power supplies and dc-dc boost/buck converters. 

I was looking at dc/dc converters for battery power led projects. But it only dawned on me now I could just use a common ac/dc power supply together with the same dc/dc converters.

This post was modified 1 month ago 2 times by CopperThiever
 
Posted : 30/12/2024 5:46 pm
marcdraco
(@marcdraco)
Posts: 701
Moderator at Large
 

Boost converters come at some cost - power drain. They're reasonably efficient now but if you're looking to drive something meaty, it's going to need a meatier something to drive that.

A lot depends the application - I can't be any more help without details -- some of the specialist optics lads might be a better bet.


Take everything I say with a pinch of salt, I might be wrong and it's a very *expensive* way to learn!

 
Posted : 30/12/2024 10:58 pm