MR16 LEDS and their drivers

[boy01zone]

We all know that MR16 LEDs need a dc supply drivers, but why? We know that if we use AC transformer we get main flicker.

The bulb connector is NOT polarised, can be fitted either way.

 

[EFLImpudence]

It could be because the terms are misused.

MR16 240V ones do not.

 

[boy01zone]

MR16 are only 12 volt not 240V

 

[stillp]

MR16 refers to the reflector size, not the voltage.

 

[EFLImpudence]

We all know that 12V LEDs need a dc supply drivers, but why?

Because that's what they need to work.

We know that if we use AC transformer we get main flicker.

Because that's not what they need to work.

The bulb connector is NOT polarised, can be fitted either way.

Yes.

240V LED lamps have the driver in the lamp.



I suppose LED lamps are not MR at all because they don't have a Multifacited Reflector.

 

[winston1]

All the 12 V MR16 size LEDs I have come across can run on AC or DC. I assume they have a bridge rectifier inside.
If you try to run them off a SMPS designed for halogens with a minimum load higher than the LED yes you will have problems.

 

[ban-all-sheds]

We all know that MR16 LEDs need a dc supply drivers

All?

This one doesn't:

 

[ban-all-sheds]

MR16 are only 12 volt not 240V

This one's 240V:

 

[EFLImpudence]

Ah. That one has an MR.


Edit - another one has appeared which is not.

 

[winston1]

DELETED.

 

[ericmark]

Yes all LED's need drivers as the LED is a current device not a voltage device. In the main MR16 packages have the drivers built into the package to make the package voltage rather than current dependent. Be it 12 volt or 230 volt AC or DC very few if any MR16 devices need external drivers.

The 230 volt type are designed to work on A.C.

The 12 volt types could clearly work AC or DC the question is if 12 volt peak or 12 volt RMS and if 12 volt peak very few AC power supplies will be within the voltage required.

Even with 12 volt RMS the sin wave wave form with 16 volt peak may be well exceeded when using a switch mode regulated power supply and I would think that is the main problem.

Switch mode supplies may produce a squared off wave form with 24 volt peak rather than 16 volt and unless there is something to smooth out these peaks likely it will damage the diodes.

I fitted some 0.58W 12 volt LED lamps to my torsional transformer and to start with they all worked but the life was rather short and I have no idea if the short life is due to poor build or higher than 12 volt peak voltage.

With units costing £1 each OK worth trying but with larger types even at just £4 each since you need to run them for a year before you will know if they will last a year there is a clear problem.

230 volt versions publish the spec and often voltage listed as 150 ~ 250 volt ac but the 12 volt versions have no spec published that I could find so no idea if they will work 11.8 ~ 12.2 volt or 9 ~ 15 volt or 6 ~ 24 volt there is just nothing published. I am sure at 8.5 volt a.c. RMS which will give a 12 volt peak would work OK.

But I for one would not buy a replacement power supply at 8.5 vac rather than 12 vdc if I want a replacement may as well be DC.

I think really GU5.3 bulbs rated 12 volt should work either AC or DC but the lighting industry seems very poor at giving descriptions they call 12 vdc power supplies drivers when clearly they are not and seem to go out of their way to confuse anyone trying to buy parts.

 

[winston1]

With a sine wave peak is 1.414 times the RMS, so 12 V RMS is around 17 V peak. With a square wave RMS and peak are the same i.e. 12 V in the cases we are considering. Do not confuse it with peak to peak as the lamps have bridge rectifiers in them.
The diodes will never see peak voltage, remember they are current driven.

 

[bernardgreen]

With a square wave RMS and peak are the same

Are you sure about that ? Would the mark space ratio if the square wave not be important. ?

 

[winston1]

With a square wave RMS and peak are the same

Are you sure about that ? Would the mark space ratio if the square wave not be important. ?

Er yes, but surely a "square" wave has a 1:1 mark space ratio equally balanced around 0v. Any other ratio would be a rectangular wave.

 

[ericmark]

may produce a squared off wave form with 24 volt peak

I did not say square wave but was thinking about the mark/space ratio at 25% mark and 75% space then 24 volt is possible. Only way to know is with an oscilloscope.

I remember as a kid trying to make a DC power supply for my train set. And being surprised at getting 12 VDC with rectifier but add a capacitor it jumped to 16 volt. A TV repair man explained it to me and I never forgot.

Of course the load will affect the voltage with a diode and capacitor and so it is had to ensure it does not climb above 12 without adding a voltage regulator.

With 230 vac likely most LED lamps use a built in switch mode controller to limit the current. But with 12 volt it could have electronics or it could have a simple resistor. We see many LED spot lights with three LED's and at 3 volt each that's 9 volt so a simple resistor is all that is required.

With most coming from China we really have no idea what is in the lamps. The the pineapple type it has been found there are live wires exposed never mind no proper regulation.

I always buy from UK high street and one hopes any dangerous lamps will be identified and even if after I buy there will be a recall. But who knows?