Turning on and off AC MR16 LEDs with logic level DC

[eccerr0r]

I have a few MR16 bulbs (including that SORAA) LED, they are all low voltage AC input. I want to be able to turn them on and off with a logic level signal.

While I can drive with DC and simply use an open collector/drain transistor, I do wonder about the long term reliability of them with DC...

... but what would people prefer to do? Assume 12VAC (60Hz) and 12VDC are both readily available.

option 1: as above, drive with an open collector/drain DC with DC control.
option 2: use a TRIAC to gate 12VAC with a DC control
option 3: Use a relay to gate 12VAC.
option 4: use an H-bridge and drive with DC control
option 5: Take the MR16 LEDs apart, rid the rectifiers, use DC direct.


The higher number options are getting less and less desirable due to cost...

And is there another option that would be even better?

[stj]

Re: Turning on and off AC MR16 LEDs with logic level DC

AC with an opto-isolated triac.

[eccerr0r]

Re: Turning on and off AC MR16 LEDs with logic level DC

I'd imagine running a triac in region I,IV with a DC input should be sufficient, no isolation needed (12VAC is isolated of course, transformer off of mains but then the DC segment needs to be isolated from AC.) The pass triac would need to pass nearly an amp, so either I need a solid state relay, or triac + optoisolator combination.

I was also worried about the voltage drop across the triac would be fairly significant compared to a transistor, but maybe it's not nearly as bad as I think, don't know. I rarely see triacs used on 12VAC for some reason or another, usually it's on mains voltage so that the drop is less significant compared to the total drop.

[sam_sam_sam]

Re: Turning on and off AC MR16 LEDs with logic level DC

You could use one of these if you decide to go DC voltage

https://www.ebay.com/itm/2pcs-ANET-A...IAAOSwpe1bLG5Q

You might want to look at this triac

LJ series triac

https://www.automation.com/automatio...eries-of-triac

I might get some or something similar that can be used down to 24 volts

[budm]

Re: Turning on and off AC MR16 LEDs with logic level DC

Do you know how much AC current you will be drawing?
If you take the lamp apart, I would like to see the inside of it.

[eccerr0r]

Re: Turning on and off AC MR16 LEDs with logic level DC

Yes, about an amp. So no (direct drive) DIP8 or DIP4 optoisolators.

I wish I could just run DC to these things ... technically it should work, except half of the rectifier diodes get double the duty cycle...

Also I think most triacs would go down to 12VAC no problem, but just like anything else in an efficient design, voltage drop as a percentage of total voltage drop is something to consider.

[sam_sam_sam]

Re: Turning on and off AC MR16 LEDs with logic level DC

Do you know how much AC current you will be drawing?
If you take the lamp apart, I would like to see the inside of it.

I have taken this type apart before most have a rectifiers in them and are not polarized
I would not be surprised if there is this type out but have not seen them in a MR16

What I can tell you is that at lower voltage from 10 volts to 12 volts the amperage is a little higher than 13 to 15 volts now know this is a little weird but at the lower voltage the light runs cooler and not as bright

One note the MR16 that I have used before the housing gets very warm almost to point that you can not touch it this is after running for hours —> they are very hard to take apart with out damaging the LED board so be careful when taking them apart


The quality of the LEDs have lot to be desired in the MR16 that I have used before
You will be lucky if they last a year running them 8 hours a night

I hope this helps

[redwire]

Re: Turning on and off AC MR16 LEDs with logic level DC

I did this once for a 50W halogen MR16 light. This was for a rat tail-flick meter a PhD had me design and build. I used DC as he wanted a dimmer also. Lamp on, start a stopwatch and heating up the rat tail until it flicks away. Something to do with how much anesthetic the rat was under.

Most solid-state switches like triacs or BJT have losses and make heat.
Rule of thumb for triacs/SSR is 1W of heat generated per amp.
Zero-cross triac drive optocouplers such as MOC3041 are no good as most need >20V at least to go out of zero-cross inhibit.

Most efficient is to use two Nch power mosfets and a photo-voltaic optocoupler to turn them on.
This makes an AC SSR using mosfets. Vishay VOM1271 or Toshiba TLP series as examples. This gives 8.4V drive for two back-back Nch mosfets.

[eccerr0r]

Re: Turning on and off AC MR16 LEDs with logic level DC

Hmm... thanks, may have to look into mosfet AC switching too, haven't considered that due to the weird drive requirements needed, even if I just make a transfer gate with an N and P-ch. The photovoltaic optocouplers are interesting solution...

I suppose at this point, RFI is not a huge deal though good idea to keep that in mind. Using a mechanical relay is sure to cause RFI, though the duty cycle of the switching will be so low that the occasional switching events won't be a big deal, even if the di/dt is high for the lamp...

[stj]

Re: Turning on and off AC MR16 LEDs with logic level DC

can we clarify the load - is it halogen or some led conversion??

if it's halogen, you just need to duplicate the circuit used in soldering stations to drive 24vac from the mcu.

[eccerr0r]

Re: Turning on and off AC MR16 LEDs with logic level DC

These are LEDs that were meant to be halogen replacements - so were meant to take AC.

Actually if they were tungsten halogen lamps, I could run straight DC with them. The main concern is that the LEDs have a bridge rectifier of which only half would be used if I ran straight DC.

[stj]

Re: Turning on and off AC MR16 LEDs with logic level DC

if you run a halogen from dc it will overheat,
if you try to use led lamps on a triac they wont work, the triacs will splutter because there is not enough current flowng to keep them on - been there myself.

[eccerr0r]

Re: Turning on and off AC MR16 LEDs with logic level DC

Halogens will run fine off of DC, car headlamps have been running them for years; you just need to make sure the RMS power is the same as AC.

It also depends on the TRIAC, likely their minimum holding current isn't being honored due to the switching nature, and shutting down. A resistor ballast load will remedy that.

[stj]

Re: Turning on and off AC MR16 LEDs with logic level DC

yes, car headlamps are intended for dc, AC lamps on dc will get 1.44 x the intended power.

[eccerr0r]

Re: Turning on and off AC MR16 LEDs with logic level DC

Incidentally, of the LED MR16's I've played with, if the voltage is below a certain point, it will draw full current and NOT LIGHT UP!!! Ugh... I wonder what kind of damage it will take if it's left like this for an extended period of time....

[sam_sam_sam]

Re: Turning on and off AC MR16 LEDs with logic level DC

Incidentally, of the LED MR16's I've played with, if the voltage is below a certain point, it will draw full current and NOT LIGHT UP!!! Ugh... I wonder what kind of damage it will take if it's left like this for an extended period of time....

I have seen this myself before and asked the same question
( depends on who makes the LED module )
I did not understand this either

[stj]

Re: Turning on and off AC MR16 LEDs with logic level DC

probably the chip is latched and is driving an inductor as the load.

btw, if the sora uses a bridge rectifier then dc is fine.
if it has a single diode the it should still be fine but you need to get the polarity right.

[eccerr0r]

Re: Turning on and off AC MR16 LEDs with logic level DC

The two types I've seen so far both use bridge rectifiers, however it's just like PSUs where if you use DC, two of the diodes dissipate all of the drop and the other two never share dissipation like if it were run under AC.

[budm]

Re: Turning on and off AC MR16 LEDs with logic level DC

yes, car headlamps are intended for dc, AC lamps on dc will get 1.44 x the intended power.

Can you please provide the link to that info?
Resistive load (non inductive resistor, lamp (PTC)): An RMS voltage produces the same heating effect as a the same DC voltage.

[redwire]

Re: Turning on and off AC MR16 LEDs with logic level DC

Tore apart a Philips MR16 LED bulb. I busted it up a bit because of the glass housing and silicone glue.

The main board has a bridge rectifier and 270uF 30V filter cap with AL8821 boost-converter for MR16 LED's.

The bulb has a 20V COB LED with current control SOIC-8 PLD1B/H1A01A and 0.75R current-set, on the heatsink. I'm not sure what that is for. It's a two-pin connector between the boost and LED board.