Output of Aurora 'constant voltage LED driver' (SMPSU)

[JohnW2]

Ignoring any/all terminological/semantic arguments, I've been looking at the output of an Aurora AU-LED1012CV 12 V ('eff') 800 mA 'constant voltage LED driver' (which I had on my shelf) with a view to using it for something else.

Despite being "12 V eff", if I look at its output when unloaded, I see what is essentially 'clean 12V) with superimposed pulses of about 0.3V amplitude at a frequency of 1-2 Hz, which took me rather by surprise.

If I apply a small load, then those 1-2 Hz pulses go away and all I then see superimposed on the 12V DC are pulses of about 25 mV at a frequency of about 40 kHz, which is roughly what I had expected.

That very small 40 kHz component is easy enough to essentially 'get rid of' - so, provided I ensure that there is enough minimum load to prevent the 1-2 Hz stuff to go away, it seems to be quite usable as a pretty clean 12V source.

However, I wonder if anyone has any idea as to what the 1-2 Hz pulses, when the device is unloaded, are all about - and if anyone has any other comments?

Kind Regards, John

 

[DetlefSchmitz]

John. I am totally not an expert. But since 2013 the EU Ecodesign Directive has required very low power consumption by a power supply under low load. There is a similar initiative in the USA called Energy Star. So it would seem that modern supplies detect the low load and switch to a special mode which guarantees low power from the mains in these circumstances. This would likely explain the different behaviours. More than this would be just guesswork on my part.

 

[JohnW2]

John. I am totally not an expert. But since 2013 the EU Ecodesign Directive has required very low power consumption by a power supply under low load. There is a similar initiative in the USA called Energy Star. So it would seem that modern supplies detect the low load and switch to a special mode which guarantees low power from the mains in these circumstances. This would likely explain the different behaviours. More than this would be just guesswork on my part.

Thanks. I suppose it could be related to something like that - I've certainly currently got no other ideas.

Maybe, with no load, it's only 'enabling' any input current at all for very brief periods every 1-2 secs, with the 12V I'm seeing in between being due to a charged capacitor. I suppose that would be analogous to the games that cellphones play to minimise battery usage when not actually being 'used'.

Mind you, this particular device only consumes (well, delivers, so a bit more for heat!) 9.6W at 'full load', so I would imagine that, even if one took no special measures, it consumption with no load would be 'very small' by most standards.

Kind Regards, John

 

[JohnW2]

Maybe, with no load, it's only 'enabling' any input current at all for very brief periods every 1-2 secs, with the 12V I'm seeing in between being due to a charged capacitor. I suppose that would be analogous to the games that cellphones play to minimise battery usage when not actually being 'used'.

The more I think about it, the more I come to think that something like that might well be the explanation.

By experiment, is seems that something like a 50mA (600mW) load is need to get rid of the 1-2 Hz phenomenon (which suddenly disappears when one passes the threshold). Aurora say nothing about a minimum load but I suppose that, for the intended purpose (supplying LED lamps/bulbs), the load would never be that low.

What does somewhat surprise me is that they seem to be being rather 'pessimistic' (or 'over-honest'?) in describing the output as "DC 12V eff". As bernard often reminds us "12V eff" usually refers to a situation in which the instantaneous voltage is never anywhere near 12V - but, rather, it consists of pulses of a much higher voltage (maybe ~30V) which average over time to about 12V.

In contrast, once one is over what appears to be the 'minimum load' this PSU seems to produce pretty clean 12V DC, with just a small very amount (about 0.2%) of high frequency ripple (less than the amount of 50Hz ripple one would see with many a 'traditional' PSU).

That high frequency 'ripple' is, as one might expect, quite complex (which makes it difficult to get my aged 'scope to synch on anything). The primary 'pulses' come at a rate corresponding to roughly 70 kHz (not 40 kHz as I mistakenly typed in my OP), but those 'pulses' contain components at around 2.5 MHz, seemingly with very small 'microbursts' of an even higher frequencies between the 'primary pulses' ....

Kind Regards, John

 

[JohnW2]

Further to the above, and as one might expect, when one increases the load (this is about 360 mA, i.e. about 4.3 W), things get somewhat 'cleaner' - that 'pulse' is around 30mV at its peak.

What I don't fully understand is that, although I don't think it's a problem as it is, I am not having much success in significantly 'suppressing' that pulse with RC filtering ....

Kind Regards, John

 

[DetlefSchmitz]

To get an idea of the size of the issue, leave the scope earth where it is and put the probe on the earth point as well.

 

[akist]

Just to say, and sorry for speaking out of turn, be careful with "12V LED drivers" as thousands sold on ebay and elsewhere. They are very, very badly made, with live traces precariously close to output traces and with a Y1 cap to smother spikes but which inadvertently pushes main voltages down the output. And 50% of them get very hot and break at 50% amps drawn or go into oscillations. There was a huge thread when I was investigating those there: http://www.eevblog.com/forum/testge...esent-in-the-output-pins/msg592438/#msg592438

 

[ban-all-sheds]

Ignoring any/all terminological/semantic arguments,

So far, so good....

 

[JohnW2]

Just to say, and sorry for speaking out of turn, be careful with "12V LED drivers" as thousands sold on ebay and elsewhere. They are very, very badly made, with live traces precariously close to output traces and with a Y1 cap to smother spikes but which inadvertently pushes main voltages down the output. And 50% of them get very hot and break at 50% amps drawn or go into oscillations.

All very true - but Aurora are, to the best of my knowledge, one of the most reputable manufacturers of such things - so if even theirs are not 'safe', we probably have a problem!

Kind Regards, John

 

[JohnW2]

To get an idea of the size of the issue, leave the scope earth where it is and put the probe on the earth point as well.

Very interesting! Qualitatively similar (but now pretty symmetrical around 'zero'), but with a much higher frequency component (~ 30 Mhz) superimposed on the ~70 Hz 'pulses'. If I touch either or both sides of the PSU output, or even put my hand on its case, the amplitude drops by about 25-30% (all that with an ~360 mA load). It's certainly all coming from the PSU (rather than the BBC or whatever!), since the 'line becomes totally flat' on the scope if I remove its 230V input. In both of the following, the peak-to-peak voltage is around 40 mV; in the first, the x-axis is 0.5 μs/division (you can just about see the 'divisions') and in the second it's about 0.17 μs/division (a third of the first one) - with apologies for the not-too-clear photos! ...

Kind Regards, John

 

[DetlefSchmitz]

Not sure what you're using this for but anything less than 5% of excursions on a supply is generally perfectly acceptable. If you really need better then filtering is an option. Just don't expect to be able to examine the results of the filtering with basic scope techniques. There are ways round the scope measurements, but probably not worth the effort. Best ways to check the filter attenuation is with spice.

 

[JohnW2]

Not sure what you're using this for but anything less than 5% of excursions on a supply is generally perfectly acceptable.

Sure, I indicated that it was 'fit for my purpose' in my OP ..

.... That very small 40 kHz [should say 70 kHz] component is easy enough to essentially 'get rid of' - so, provided I ensure that there is enough minimum load to prevent the 1-2 Hz stuff to go away, it seems to be quite usable as a pretty clean 12V source....

... and, subsquently ...

In contrast, once one is over what appears to be the 'minimum load' this PSU seems to produce pretty clean 12V DC, with just a small very amount (about 0.2%) of high frequency ripple (less than the amount of 50Hz ripple one would see with many a 'traditional' PSU).

My subsequent experiments and writing have really just been a matter of curiosity.

If you really need better then filtering is an option. Just don't expect to be able to examine the results of the filtering with basic scope techniques.

Given what I see when the scope probes are 'shorted', that's clearly the case!

There are ways round the scope measurements, but probably not worth the effort. Best ways to check the filter attenuation is with spice.

What's "spice"?

Kind Regards, John

 

[DetlefSchmitz]

https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html

I often use this. It has saved me endless design mistakes.

(It's free!)

 

[JohnW2]

https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html
I often use this. It has saved me endless design mistakes. (It's free!)

Many thanks - I'll have a look at it!

Kind Regards, John

 

[JohnW2]

https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html

Many thanks again. It's great fun, and seemingly pretty clever, although I think it's going to take a while for me to get to grips with it. I'm not sure that it's necessarily relevant to what I'm currently doing and what we've been discussing, but I can see it being very useful in the future! I'm surprised that it's free.

Returning to where I started this thread, I think that one lesson to be learned is that one does not have to be too negative or 'frightened' of "12V eff" (or similar), without looking to see what one has actually got. A PSU which produced, say, 36V pulses with a 1:2 mark:space ratio (which is roughly what some "12 V eff" LED 'drivers' appear to do, at least conceptually) would have been useless for what I currently want - but what I actually have seems to be a perfectly satisfactory source of surprisingly clean (and constant!) 12V DC, give or take the 'minimum load' issue.

Kind Regards, John