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Solid State240V dimmers and LED lights pulsating

Ok, I know this is caused by interference between the switch-mode converters in these wizz-bang new 240V lighting units, but what's the simplest way to stop it?

Also, it is likely to be frequency-dependent impedance variations, or leaking of the actual switching frequency onto the wiring between the units? In other words, is a ferrite clamp or power-line filter likely to help?

The dimmers are Lumex LoadSmart LED Dimmer, LT1D459LS series. The LEDS are Atom AT9039. The circuit most affected has four LEDS. The circuit with 2 doesn't seem to do it (not readily anyhow), and the five-LED one seems less susceptible.

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Clifford Heath.
Reply to
Clifford Heath
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How do you know it's interference?

Cheers

Klaus

Reply to
Klaus Kragelund

The dimmer doesn't pulsate with a halogen load. The LED doesn't pulsate on full power. Both use SMPS technology inside, and they don't work with each other.

What do you suggest it is?

FWIW, the pulsation is from about 0.3Hz to 2Hz, depth perhaps 25% brightness variation around the set point. The depth and frequency varies with the set point. Sometimes it stays stable for a while, then suddenly starts pulsing and perhaps stabilizes again, perhaps not. It will pulsate at a variety of set points, anything short of about 70% brightness it seems.

Reply to
Clifford Heath

On Jul 24, 2017, Clifford Heath wrote (in article ):

Be aware that constant-power switching power supplies present a negative impedance to their supply, which is another switcher in this case. A series resistor in the line between may help.

Joe Gwinn

Reply to
Joseph Gwinn

Have you tried adding a low wattage (15-25W) incandescant bulb to the circuit? The holding current requirement of the SCRs used in the dimmers is likely not being met so they pulse. BTDT. Art

Reply to
Artemus

An IOT worm exfiltrating your private keys.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

Probably MOSFETs, not SCRs. These dimmers are designed for LEDs, but the manufacturer only guarantees correct operation with their own LEDs.

Clifford Heath.

Reply to
Clifford Heath

Ouch - I was hoping it would be a higher (beat) frequency effect so an inductor or other RFI filter would help.

The pulsation is quite slow (

Reply to
Clifford Heath

On Jul 24, 2017, Clifford Heath wrote (in article ):

I have no idea - it will depend on the design of the various power supplies, in particular the control laws built into the regulators of the respective power supplies.

I would just try a few resistors and see. All that?s needed is enough positive resistance to reduce the loop gain a bit by swamping most of the negative resistance.

If it really is a beat of some kind, the series resistor will have no effect.

They probably did, for their products only. It?s done by analyzing the total circuit (covering both products when connected together) using Spice, usually LT Spice. I?m not a Power guy, but I?ve watched them work.

Joe Gwinn

Reply to
Joseph Gwinn

If the pulsation frequency is high, it would not be detected ny the human eye - after all, a 60 Hz lamp is switching on

-off 60 times a second, and the human eye does not detect any pulsations. OTOH, typical SMPS frequencies are in the KHz (ones we manufacture run between 50KHz -

75KHz). So what could be causing these low frequency signals ?
Reply to
dakupoto

Many dimmers have an absolute minimum load before they will perform according to specification. If your LED lamp doesn't draw that minimum load then the dimmer control loop can become unstable/chaotic.

To eliminate this possibility find a low powered incandescent night pygmy light type and see if that also pulsates on the dimmer.

On a 60Hz supply the lamp flicker frequency is 120Hz.

Instability as a light dimmer controller fights another control circuit in the LED doing its best to supply a constant current to the LED.

--
Regards, 
Martin Brown
Reply to
Martin Brown

control loop instability

NT

Reply to
tabbypurr

You're off by a factor of two. Lights flicker at 120Hz. 60Hz flicker makes me sick (old displays).

Reply to
krw

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