LED transformers

[ericmark]

It is unlikely humans can see any flicker caused by 50 Hz or more, birds may see it, but not humans. However the whole process is controlled by what is know as switch mode or pulse width modulated output, and there is a minimum and maximum size of pulse and gap between pulses, once the gap is at a minimum next is to switch off, so in essence you start to pulse the pulses as the whole unit switches on and off. This may be seen as flickering but would only happen if under loaded.

 

[ericmark]

SFk, thanks.

How about this one from s/fix?
http://www.screwfix.com/p/aurora-co...5w/4338t#product_additional_details_container

That would seem at first glance OK, however some odd things stated on the advert says non dimmable, leading edge, maximum dimmable wattage 1W and voltage in 12 ~ 240 V that does seem odd!

 

[DIWhat]

It is unlikely humans can see any flicker caused by 50 Hz or more, birds may see it, but not humans. However the whole process is controlled by what is know as switch mode or pulse width modulated output, and there is a minimum and maximum size of pulse and gap between pulses, once the gap is at a minimum next is to switch off, so in essence you start to pulse the pulses as the whole unit switches on and off. This may be seen as flickering but would only happen if under loaded.

Hmm I don't think my driver is underloaded, it's a 60w dimmable driver, the max load from the led strip is about 43W. At the moment I just have a normal switch attached to it, not a dimmer.

 

[ericmark]

It could be down to cable length or type, there is a report on another page on radio interference until a twisted pair was used. Twisting cables together allows us to match a feeder, it is a little complex, with AC and the supply is really AC in that the current alternated between zero and maximum even if the polarity does not alternate, the cable has both a capacitance and inductance and if the distance between wires in the cable and the twist of the wires is carefully matched then the two will cancel themselves out.

If they are not cancelled you can get over heating of the supply, we really notice this with radio, you will hear the CB guy talking about SWR or standing wave ratio, what happens if not unity some of the power is reflected back into the radio set.

However at 50 Hz this is really not a problem, at 47 kHz used by some switch mode power supplies it could start causing a problem.

 

[JohnW2]

If they are not cancelled you can get over heating of the supply, we really notice this with radio, you will hear the CB guy talking about SWR or standing wave ratio, what happens if not unity some of the power is reflected back into the radio set. ... However at 50 Hz this is really not a problem, at 47 kHz used by some switch mode power supplies it could start causing a problem.

I seriously doubt it. At 47kHz, the wavelength (hence length of standing wave) is over 6 km.

As bernard has illustrated, using a twisted pair will reduce radiated energy from a short length of cable carrying, say, 47kHz, but that is die to simple 'cancellation' within the cable, nothing to do with standing waves or matching the 'characteristic impedance' of the cable to the impedance of the load (to reduce standing waves).

Kind Regards, John