LED drivers on Boeing and Airbus passenger aircraft? - Page 1
Forum section: electronics / projects

author: ocset
author_rank: Super Contributor
timestamp: January 02, 2020, 07:12:28 pm
content: Is it likely to be true that on Boeing and Airbus passenger aircraft, the actual LED drivers are in the form of linear regulators because switch mode types are too noisy?...ie for the led lighting in the cabin, the passenger section, the luggage racks and the toilets and cooking areas etc.

author: Yansi
author_rank: Super Contributor
timestamp: January 02, 2020, 07:19:34 pm
content: No.

author: rrinker
author_rank: Super Contributor
timestamp: January 02, 2020, 08:05:29 pm
content: Friend of mine works for a company that designs and produces many of those voltage converters, and also space-rated ones for satellites. They are some of the most amazingly compact switch-mode converters you ever saw. Extremely high efficiency, as well.

author: jmelson
author_rank: Super Contributor
timestamp: January 02, 2020, 08:05:59 pm
content: Quote from: treez on January 02, 2020, 07:12:28 pmAlmost certainly, the cabin lighting runs off 120 V 400 Hz AC power, so not likely. Note the cabin lights blink VERY noticeably when the engines are started and the alternators come on lineand synch to the bus.Jon

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 02, 2020, 08:40:31 pm
content: Contact those guys:https://utcaerospacesystems.com/product_gallery/lighting-systems/

author: Zero999
author_rank: Super Contributor
timestamp: January 02, 2020, 08:44:21 pm
content: Linear power supplies are far too bulky and use too much power. Noise can be minimised by good design and EMI filtering.

author: ocset
author_rank: Super Contributor
timestamp: January 03, 2020, 01:42:20 pm
content: QuoteThanks, someone told me that there is indeed an SMPS PFC and switcher connected to the 120V, 400Hz....but they just provide a downstream voltage rail which linear led current regulators use.

author: eugenenine
author_rank: Frequent Contributor
timestamp: January 03, 2020, 07:30:18 pm
content: I would think they also would have one regulator for a long string of lights rather than one regulator per light like consumer replaceable lights.I know some automotive lights work that way. There is one PWM output from the body computer that all dimmable lights are connected to.

author: Zero999
author_rank: Super Contributor
timestamp: January 03, 2020, 08:55:51 pm
content: Using one regulator for a string would certainly save space and probably energy.I wouldn't be surprised if the also use capacitive or inductive droppers, as the capacitor/inductor can be relatively small at 400Hz, but the poor power factor might be an issue. I suppose using a mixture of inductive and capacitive ballasts would improve the overall power factor of the system.

author: Red Squirrel
author_rank: Super Contributor
timestamp: January 04, 2020, 02:03:53 am
content: I imagine decent thought is put into noise, but I think most effort would go towards making the critical stuff not susceptible in first place. Easier to protect 1 device than to control 100's of devices, some of which you may have no control over (ex: stuff passengers may have).

author: tooki
author_rank: Super Contributor
timestamp: January 04, 2020, 08:57:44 am
content: Quote from: treez on January 03, 2020, 01:42:20 pmMy hunch is that the downstream regulators are still switch-mode DC-DC converters, and that by “linear”, they mean that there is no PWM or other pulsing on the output to the LEDs.

author: tom66
author_rank: Super Contributor
timestamp: January 04, 2020, 09:48:29 am
content: Quote from: Yansi on January 02, 2020, 07:19:34 pmI almost ended up working for a company that created LED lighting for trains. While the power supplies to convert from the DC vehicle bus were switchmode, to the string voltage plus a few volts, the LED strips themselves used linear current regulation (usually a transistor or opamp circuit) to balance current between strips. The outputs were PWM'd.On the most recent Airbus flight I was on, the PWM of the interior lights was uncomfortably visible at times.

author: Kilrah
author_rank: Unknown
timestamp: January 04, 2020, 11:36:44 am
content: Quote from: tooki on January 04, 2020, 08:57:44 amOn the RGB LED-lit aircraft I've been on there definitely is PWM, and it tends to be an annoying frequency that's low enough to notice.

author: Simon
author_rank: Unknown
timestamp: January 04, 2020, 12:03:45 pm
content: switch mode does not have to mean noisy, but it's a lot of work which is why the military/aero space rated regulators are more expensive.

author: tooki
author_rank: Super Contributor
timestamp: January 04, 2020, 09:12:31 pm
content: Quote from: Kilrah on January 04, 2020, 11:36:44 amAirbus?The only aircraft with RGB lighting I’ve been on are Boeing 787s. I’m super sensitive to PWM flicker, and though I was curious and actively tried to identify whether it was PWM dimmed, I detected no flicker, so it’s either linear, fully smoothed, or at a very, very high PWM frequency (upwards of 3KHz).

author: mc172
author_rank: Frequent Contributor
timestamp: January 04, 2020, 09:34:43 pm
content: Quote from: Simon on January 04, 2020, 12:03:45 pmI don't think that's true. From my experience in aerospace, the expense is usually to do with reliability (including meeting and proving MTBF requirements), meeting safety cases, number of points of failure and having to deal with a massive working temperature range.

author: Simon
author_rank: Unknown
timestamp: January 04, 2020, 09:58:53 pm
content: Quote from: mc172 on January 04, 2020, 09:34:43 pmYes AND the fact that you have to filter the crap out of the thing so where you had one power inductor and a capacitor now you have several, you don't use aluminium caps you use polymer caps, board space goes up and the tests are expensive. You could fail the test and so repeat again the whole design process. You can buy a thing half the size of a match box for £5 but it will pass virtually nothing, to get it to pass aerospace it will probably end up 4 times bigger along with all the testing and as you say the reliability considerations are also a factor but just getting it through EMC will make it an order of magnitude more expensive.