# Delay in power to LED from adapter



## REP (Sep 16, 2014)

I have LED undercabinet lighting. I use to have a 12v 2A power supply which worked great until it burned out. I purchased a replacement adapter with a bit more power 12v 3.8A to hopefully ensure that the power supply remains cool and does not burn out inside a year. The problem is that the adapter has a 2-3 second delay before turning the lights on.

My setup is that I have a motion sensor that delivers the power to an electrical outlet which the power supply is connected to. So, when I walk in the kitchen, the sensor is triggered, power goes to the outlet/power supply and the undercabinet lights come on. The new power supply, for some reason, when triggered, does not deliver power to the lights until a brief delay. Now 2-3 seconds does not sound like a lot but, I can pretty much walk across the entire kitchen before the lights are triggered, and it's a bit frustrating when I'm use to the satisfaction of instant light.

I'll likely look to replace this power supply, but was wondering if there is something in the power supply specs that I need to be aware of that may help me determine if there is a delayed output of power or not.

Thanks
Bill


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## WhiteRabbit (Sep 18, 2014)

I'm observing a similar effect on my motion activated overhead LED light in our laundry room. It's a Lutron occupancy switch circa 2010, before LED's were popular. I just recently upgraded from a fluorescent bulb there to an LED bulb (it came with its own LED ballast that replaced the fluorescent ballast). The Lutron had no delay when switching on a fluorescent light. Could it be we need a sensor designed specifically to switch on/off LED's? It seems wrong that a fluorescent light would switch on faster than an LED light. In the end, it's got to be either the ballast or the electronic switch (or possibly some kind of interaction between them) that's causing the delay. AFAIK, the LED's themselves should turn on instantaneously the moment they are driven by a sufficient current. Indeed, before installing the new LED bulb (a roughly $100 circline), I tested it using a $125 CC CV bench power supply typically used for electronics prototyping, and I didn't notice any delay at all. So, at least in my case, the problem is definitely not the LED's or the bulb.

Removing the occupancy sensor from the equation would determine if it's a possible culprit or not. If it isn't, then I have the same question as you regarding LED power supply specs. I know that for fluorescent, an "instant" power supply is just that, whereas a "rapid" power supply comes with an annoying, noticeable delay. Does the same nomenclature apply for LED's, or are there different specs/nomenclature needed to get an LED power supply that's truly instantaneous?


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## evilc66 (Sep 18, 2014)

It's to do with the way the power supply is created. The delay in on time is due to the capacitors on the front end of the power supply needing to charge before it can output a stable voltage. There are other options for the power supplies and LED drivers the two of you are talking about that will offer much faster turn on times, but will come at a cost.


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## REP (Sep 18, 2014)

Interesting. My situation is that the old power adapter worked very quickly. perhaps a .5 second delay. I recall the first adapter they sent me was a 12V 1A and it had a similar delay. The LED company replaced that with a 12v 2A and everything was great.

Fast forward, I just assumed that as long as I had more than sufficient power, the delay should not be an issue so I went with a 12v 3.8A, however, the results were disappointing.

I guess what I'm asking - is there something about an adapter that I can identify in the specs that would speak to the speed the power would output, once plugged in.


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## WhiteRabbit (Sep 18, 2014)

evilc66 said:


> It's to do with the way the power supply is created. The delay in on time is due to the capacitors on the front end of the power supply needing to charge before it can output a stable voltage. There are other options for the power supplies and LED drivers the two of you are talking about that will offer much faster turn on times, but will come at a cost.



Thanks for your post. So what are the additional specs/nomenclature for an LED power supply that's instant?

Your comment ended on the cliff-hanger "but will come at a cost." IIRC, rapid power supplies extend fluorescent bulb life as compared to instant power supplies. Is there a similar effect regarding LED life? i.e. Is that part of the "cost" you're referring to, or by "cost" were you referring just to dollar cost of the power supply itself?


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## DIWdiver (Sep 18, 2014)

As an engineer who often designs power supply circuits, I can confidently say that 2-3 seconds is quite a long turn-on delay for a supply like that. Unfortunately, such things are rarely specified in the data available before you buy it and try it. If you get a name brand like Meanwell, you might be able to find that information, but they won't be as cheap as the no-names you can readily find in so many of the bargain sites and outlets. If you find the specification, it may go by any of a number of names, including turn-on delay, power-on time, softstart time, etc.

The old-style supplies with iron-core transformers (relatively heavy for the power level) came on almost instantly (less than 0.1 seconds). These are fine products, and not at all hard on the LEDs provided they have a decent voltage regulator. LEDs can be switched from full off to full on thousands of times per second for their entire lives with no ill effects. The newer ferrite-core designs (much smaller and lighter for the power level), are often more efficient and less expensive, especially at power levels above a few watts. That's why you rarely see iron-core transformers in new products any more.

Unfortunately the flexibility offered by the new designs also allows more variability in performance characteristics like turn-on time, hold-up time, overshoot, ripple frequency, noise, etc. Since a few seconds makes no difference in a lot of applications, it's not something that every designer will care much about. If it can be traded for something else, like lower cost, it often will be.

Supplies specifically designed for lighting will often be designed to come on rapidly, for exactly the reason you mention. But buying one you know in advance you will like could well be more expensive.

So evilc66 may be right that the supply you want will be more expensive, but it ain't necessarily so. You could try another model of low-cost supply and find it much more suitable. Or you could try several and not find a better one. Or you could really luck out and find one that someone you trust can tell you is both cheap and good. Or you can pay your money and move on.


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## REP (Sep 19, 2014)

Thanks DIWdiver,

Unless someone here can suggest a power supply that they use and works well .... <pauses for immediate response> .... I may have to go with your suggested trial and error. I dug through a lot of my old power supplies hoping I would have one that met my criteria without any success.

Your explanation has been very helpful.


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## WhiteRabbit (Sep 19, 2014)

If on the trial and error path, it would help if there's a way to test a power supply on the bench to better avoid the hassle of a full install and testing it in-situ. Also, if it fails to pass muster, it may be easier to pack and return it if it doesn't look blatantly "used." So, for bench testing, what sort of dummy load should be used, and what sort of measurements taken?


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## alpg88 (Sep 19, 2014)

my led bathroom light does same thing, about a second. i use meanwell driver that i got from led supply, great driver, and it was not cheap.


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## DIWdiver (Sep 19, 2014)

I would say it's unlikely it will matter what kind of load you use for testing. I'd look at maybe a 100 ohm, 2W resistor. The only measurement that's relevant to this particular discussion is how fast it turns on. I would use a small LED with a series resistor in parallel with the load resistor, just to see when it comes on.

If using really cheap supplies, it might be good to measure the voltage too.

It's certainly possible for one to turn on very fast. Cree managed to pack a 9W driver and a handful of LEDs in the $7 bulbs I bought at the home center a few months ago, and they come on faster than you can blink.


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## WhiteRabbit (Sep 19, 2014)

alpg88 said:


> my led bathroom light does same thing, about a second. i use meanwell driver that i got from led supply, great driver, and it was not cheap.



I started to look at a Meanwell Power Supply (http://www.meanwell.com/search/APC-35/APC-35-spec.pdf), and I notice that the "setup" is 1500ms, and the rise time is 40ms. I'm not sure the technical definition of "setup", but perhaps it's related to the observed problem? The 1500ms is in the ballpark of what we are experiencing.


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## WhiteRabbit (Sep 19, 2014)

Yup, looks like setup time (ton) is the culprit:






http://nz.wellforces.com/resources/what-is-set-up-rise-hold-time/322/#.VBzI1PldUwB

So, what we each need to find find is one of those "faster than you can blink" LED drivers like DIWdiver's referring to. Who makes those, I wonder? I suggest we start by looking at power supplies that have detailed datasheets. At least MeanwWell seems honest about the issue, even though it's buried in the datasheet and not highlighted with a big red "WARNING! 1.5 Second turn-on Delay!" on the case of the LED driver itself.


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## DIWdiver (Sep 19, 2014)

"Our sales would plummet!"

Quote from Monty Python's Crunchy Frog skit.

Oh, sorry. Apparently the sketch is called "Trade Description Act". I couldn't resist having a listen.


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## WhiteRabbit (Sep 19, 2014)

I barely started looking, and I've already found (an equivalent?) MeanWell whose turn-on time is 500ms: http://www.ledsupply.com/content/pdf/led-driver-meanwell-lpc-35-700_documentation.pdf That already would be a lot less annoying.

Can anyone here do better and maybe find one that's faster still? From what DIWdiver said, 100ms (or less if possible) seems like it would be a good target.


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## eebowler (Sep 20, 2014)

I've always assumed the delay wasn intentionally built into the power supply to prevent damage to your device (laptop for e.g.) from an inrush of current when you apply power or from overvoltage spikes when current returns after a blackout.


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## WhiteRabbit (Sep 20, 2014)

eebowler said:


> I've always assumed the delay wasn intentionally built into the power supply to prevent damage to your device (laptop for e.g.) from an inrush of current when you apply power or from overvoltage spikes when current returns after a blackout.



Is that relevant for LED's? Or, if so, are there other ways to achieve the benefits without suffering the delay? I was hoping that there was a CREE-like "blink of an eye" type driver (cf DIWdiver above) that could be purchased to power our respective LED bulbs.

In looking at just a very few meanwell datasheets, the range covered 500ms up to 3000ms. The cheaper ones seem to take longer. Therefore, my suggestion based on that unscientific sample set: maybe start by looking at the most expensive AC-to-DC constant current LED drivers to see what can be achieved, and then if necessary back-off from there. In my case the specs on what I'm looking for is 700ma constant current, which probably requires around 26v DC or thereabouts. Regardless, if any one of us finds a good driver with a fast turn-on, I'm wagering the odds are good that a driver in the same product family as what's discovered will fit our individual needs. In short, we should all gain by pooling our info.

Anyhow, surely we can't be the first ones on CPF to have a need like this? There should already be some collective knowledge about where to look for a quality driver.


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## SemiMan (Sep 20, 2014)

WhiteRabbit said:


> Yup, looks like setup time (ton) is the culprit:
> 
> 
> 
> ...



That's because Meanwell does not care a rats butt about joe blow on the street buying their supplies, and anyone that they do care about, knows enough to ask about the turn on time if it is important to the product.

500msec turn-on would be noticeable, but not distracting. Issue is most constant voltage supplies are not designed for lighting (at least in volume). Constant current supplies for lighting will tend to perform better. Simple cheaper LED drivers often turn on quicker as there is less "going on" in the supply that needs to be charged.


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## SemiMan (Sep 20, 2014)

WhiteRabbit said:


> Is that relevant for LED's? Or, if so, are there other ways to achieve the benefits without suffering the delay? I was hoping that there was a CREE-like "blink of an eye" type driver (cf DIWdiver above) that could be purchased to power our respective LED bulbs.
> 
> In looking at just a very few meanwell datasheets, the range covered 500ms up to 3000ms. The cheaper ones seem to take longer. Therefore, my suggestion based on that unscientific sample set: maybe start by looking at the most expensive AC-to-DC constant current LED drivers to see what can be achieved, and then if necessary back-off from there. In my case the specs on what I'm looking for is 700ma constant current, which probably requires around 26v DC or thereabouts. Regardless, if any one of us finds a good driver with a fast turn-on, I'm wagering the odds are good that a driver in the same product family as what's discovered will fit our individual needs. In short, we should all gain by pooling our info.
> 
> Anyhow, surely we can't be the first ones on CPF to have a need like this? There should already be some collective knowledge about where to look for a quality driver.



Cost and turn on time will not be related. More complex supplies take longer to turn on. A fast turn on costs more for the same architecture, but I can build a fast turn on simple supply for less money than a complex slow turn on supply.


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## WhiteRabbit (Sep 21, 2014)

This morning I spent several hours looking, and I can't find anything with a datasheet that shows less than 500ms turn-on time. Most datasheets don't even characterize it. I'm throwing in the towel.

I hope someone else has better luck....


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## REP (Sep 27, 2014)

WhiteRabbit said:


> This morning I spent several hours looking, and I can't find anything with a datasheet that shows less than 500ms turn-on time. Most datasheets don't even characterize it. I'm throwing in the towel.
> 
> I hope someone else has better luck....




I appreciate everyone's effort on this. I did quite a bit of internet searching, but to no avail. I figured I'd just ask the question, and for the most part, what I got out of this is that I need to be prepared for a bit of trial and error. I may look at power supplies used by the security industry for a fast power supply, however, I would think the LED market would be much larger now. I'll post back if I find anything.

Thanks!


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## WhiteRabbit (Sep 27, 2014)

I have a hypothesis that LED drivers whose buck converters operate at a higher frequency are more likely to have a shorter turn-on time. For those here who are experienced at designing power supplies, does that sound correct?


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## SemiMan (Sep 27, 2014)

No it is not correct and since we are talking isolated AC supplies there is likely no buck involved but still switching frequency has little impact.


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## eebowler (Sep 28, 2014)

REP. I have a 1A, 12V 'adapter' from an old NiMH charger powering three XML LEDs in series at the moment. Current to the LEDs is about 1.75A. No start up time. It in the kitchen and has been going for almost a year now. One LED died twice but, I wouldn't automatically attribute it to the adapter since I used old, used, undesirable LEDs. Time on per day is close to three hrs. (cell phone chargers don't have a start up delay either but their output voltages are obviously too low for your use.)


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## DIWdiver (Sep 28, 2014)

Putting a load that draws 1.75A at about 10v on a supply rated at 1A, 12v is clearly way out of spec. The behavior of that particular setup is not very informative to a general case, except to confirm that 12V, 1A supplies can have very low turn-on time.

Glad to hear you are happy with your setup!

BTW, if a particular LED is consistently blowing, I would look at whether that one is hotter than the others for some reason.


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