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Isolated power supplies in LED lightbulbs


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My question is why are they isolated? For the first 20 years of my life, lightbulbs were filament ones only. They had a thin glass bulb, which could easily break, exposing the filaments. Although the filaments would then burn out, the filament supports would be live.

Now we have LED lightbulbs, and I can't see why they are isolated. The casing is plastic, really hard to break, and it takes a load of effort to touch the LEDs. Some bulbs are transformerless, often using capacitive droppers, while others have a full switch-mode power supply, and all of those seem to be isolated. One that I have just looked at has a Y capacitor, with milled isolation gap in the PCB, from the HT to the LT side of the transformer, when you could just have a link.

Even if a flyback power supply is used, that can be used as a non-isolated transformer with a single inductor. I've seen that done in a WiFi power switch, where there is a relay output and the electronics can't be touched.

I can see the point in isolation if someone can touch the LT side, but not in a lightbulb. There seems to be a lot of effort going into making it isolated for no reason.

I know that there are some bulb shapes, particularly GU10, where the LEDs can be very close to the front of the bulb, and some of those have been made with no isolation and nothing to protect the circuit from being touched, which is dangerous. However, for most bulb shapes, the LEDs are a long way from what can be touched.

Any thoughts?


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Most Helpful Member
Old light bulbs and sockets do not match today's safety requirements. We all have put a finger in a socket.

Safety requirements are clear. You must have isolation between power lines and people. If the LED is on the powerline you can not touch the LED even after using a hammer.

But if the LED is isolated then no glass/plastic is required.

Isolation inside a transformer does not have a break test. Isolation by a plastic cover must be strong.

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