I bought a bunch of very cheap 18W LED lamps. I love them; they look great and the light is excellent, however the drivers throw out a lot of RFI and is interfering with my radio (quite bad at 50MHz, but also significant from 25MHz-150MHz). The interference is being caused by the driver (I can outline how this was diagnosed if helpful; the radiation all seems to be coming from the transformer though it decreases a little when I add common mode chokes to the AC input and DC output wires). This has to get fixed.

I have been reading many of the related questions regarding LED drivers and have learned a lot. Am experimenting with capacitors and ferrite to reduce the RFI. Ultimately, I suspect I will end up replacing the driver. How do I know the new driver will be any better than the current one? What should I look for? Are there any certifications that matter? There are plenty to select from at the usual electronics component stores.

In case it helps, I think this is the driver with the RFI condition: https://www.dhgate.com/store/product/led-driver-input-ac85v-265v-output-36-63v/259582128.html The resemblance is uncanny; the specifications are the same, but my driver's PCB has the DC output wires slightly closer together.

enter image description here

  • \$\begingroup\$ I think some of the IC manufacturers provide reference designs for LED lamps which deal much better with these problems. I've opened up countless LED lamps and NOT ONCE have I seen anything close to the number of parts and complexity of the reference designs from the IC manufacturers. You might find a good reference design, build it, see if that helps. Otherwise, clad home within a mu-metal can and an added, full Faraday shield. Use LED lamps freely within the home. Place HAM gear in separate structure some distance away on your acreage. Use only incandescent lighting there. ;) \$\endgroup\$
    – jonk
    Oct 19, 2018 at 2:13
  • \$\begingroup\$ @jonk. Must be a cheap import that bypassed FCC regulations for EMI noise. The better ones have a copper or tin shield over and around the electronics, even if in a plastic enclosure. \$\endgroup\$
    – user105652
    Oct 19, 2018 at 2:23
  • \$\begingroup\$ @Sparky256 this is absolutely a cheap import and has no UL stamp, though it does have a CE stamp. Also, I crumpled aluminum foil around the plastic housing and it made no difference. \$\endgroup\$ Oct 19, 2018 at 2:37
  • 2
    \$\begingroup\$ Take the output leads, and run them around the core of a large toroid. Do the same for the input 117VAC leads. \$\endgroup\$ Oct 19, 2018 at 3:04
  • \$\begingroup\$ I did this; added apprx 5000 ohms in the frequency ranges of interest. Made a small difference, not nearly enough. A small loop antenna was used to pick up the signal while listening to the radio; max noise was heard when the loop was right next to the transformer. I will enjoy debugging and perhaps even fixing this, but I probably will end up buying a new driver anyhow since it is for a house and I am not an electronics expert. \$\endgroup\$ Oct 19, 2018 at 10:34

1 Answer 1


EMI is a major problem with LED drivers, especially in automobiles.
And there are many methods to minimize.

It's very likely a combination of things.
The electrical design, the PCB layout, and no enclosure.

Discontinuous currents are the most likely to generate EMI. I do not see an inductor on the output so it can't be pretty.

The constant current (CC) circuit monitors the output current and adjusts the amount of current by turning the output off and on very quickly (switching) which is typically at a frequency between 100 Khz and 1 Mhz. How long the output is on and how long it is off (duty cycle) is how the amount of current is regulated.

A CC driver should then smooth out the on of off pulses which is typically done with a inductor with an inductance tuned to the switching frequency. High frequency switching allows the use of smaller less expensive inductors, and vise versa.

This image shows the on and off pulses (LX) that are regulating the current.
The ILED shows the pulses after they go through the inductor and output capacitors.

This is an example of continuous conduction.
Meaning the current through the LEDs never goes to zero.

enter image description here

This is an example of ILED in discontinuous conduction mode.

enter image description here
Source: Understanding Buck Power Stages in Switchmode Power Supplies

In the schematic below you can see the LX pin on the regulator and the inductor highlighted in blue (the part yours does not have).
It's the LX pin the turns the current off and on and the inductor that smooths it out.

The parts highlighted in yellow are not part of the constant current stage. They are added to minimize conductive EMI output to the power source.

The upper right hand is the "input EMI" filter to minimize conductive EMI back to the power source (input).

A 1µF cap was put across the output to the string of LEDs. This cap and a ferrite bead was added to minimize the radiated EMI.

This was added to meet EN 55022:2010 Infor­ma­tion tech­nol­ogy equip­ment– Radio dis­tur­bance char­ac­ter­is­tics– Lim­its and meth­ods of mea­sure­ment

enter image description here

You need to use a battery powered radio and an electric powered radio to determine if the source is conductive EMI from the power wires and or from radiated EMI (airwaves).

The PCB design is very important for minimizing radiated EMI.
The tracks on the PCB are antennas.

For example from the above schematic D1 and L1 should be near the LX pin, and CVCC should be near the VCC pin, and the connecting copper traces should be short and thick.

I always have two PCB layers for ground and power. Even if the PCB lay could be done on two layers, I use a four layer board with the two power and ground. If I can do a single sided layout and do not expect huge EMI issues I will use the one layer for ground.

The enclosure

When I design a product I enclose it in an aluminum box where the bottom and top overlap and leaves no gaps (almost air tight).

Any connectors are EMI shielded. If AC mains is used for power a EMI filter is added to the power line.


If you want it done right, the driver used by the high end LED fixtures is the Mean Well HLG line.

Notice the hermetically sealed aluminum enclosure.
Has powerline EMI filter.
Has power factor correction.
Is priced between 25¢ and 75¢ per watt. 185W-240W=>25¢, 40W=>75¢, 60-100W=>50¢
Up to 94% wall watt efficiency
7 year warranty
Does not interfere with your radio.

Mean Well is the only vendor I use for CC or CV power supplies.

enter image description here

enter image description here

  • \$\begingroup\$ believe there are counterfeit MeanWell clones (logo, FCC markings and all) so one must still be a bit careful with the integrity of the distribution channel. \$\endgroup\$ Oct 19, 2018 at 5:19
  • 1
    \$\begingroup\$ @SpehroPefhany I buy mine from Arrow because they have free shipping. Shipping power supplies gets expensive these days. \$\endgroup\$ Oct 19, 2018 at 5:35
  • \$\begingroup\$ @SpehroPefhany You are correct. I am very picky about who I buy from. meanwellaustralia.com.au/news/… \$\endgroup\$ Oct 19, 2018 at 5:46
  • 1
    \$\begingroup\$ Yes, I figured you were well aware, it's just a gentle reminder for those who may naively think they can go through gray market channels and necessarily get genuine product. \$\endgroup\$ Oct 19, 2018 at 9:49
  • 1
    \$\begingroup\$ As a follow-up, Mean Well HLG is not available in an appropriate size (or perhaps I mis-read their specs) so I replaced the unit with Mean Well APC-25-350. RFI is gone now. Thank you for pointing me in the correct direction. \$\endgroup\$ Oct 27, 2018 at 0:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.