LED light bulb - is it safe?

[senderj]

LED light bulb

I bought a LED light bulb, unfamous brand because of the low price. But I found that there is no transformer in it. The 220VAC direct connect to a full bridge, then to some RC filter and then direct to the LEDs. I don't know if this is a safe design. However, I found that even some famous brand such as Philips or Panasonic, their LED light bulbs are of the same size as mine, which I think is too small to house a transformer. Should I continue to use it?

 

[betwixt]

Re: LED light bulb

I have one like that here too. There is a long string of LEDs in series so they need a high voltage to operate them but there isn't a series resistor or regulator. They certainly work but I would guess the first voltage spike to hit them would cause damage. In fact, it's likely that if one or more LEDs go short circuit, there would be a cascade failure of all the rest as their current rocketed upward.

Brian.

 

[eclectica]

Re: LED light bulb

Difficult to say if it is 'safe' to use. Hopefully it is, but you never know for certain.

If the capacitor is being used in series with the circuit as a limiter, then it could fail if they are cheap ones (especially if your electricity supply has many spikes). Then the LEDs will go out (either 'quietly', or more dramatically after a brief emission of smoke) depending on capacitor failure mode. :|

You could fit a 385V (or similar) metal oxide varistor across the incoming supply in order to try and clamp the spikes before they hit the LED circuit. (However, if the supply is really noisy and there are many spikes, then MOVs can overheat and burn too!) I tend to use them in many of my circuits and also use a 100C temperature dependant fuse placed close to the MOV and inline with the supply too just in case, so the whole circuit cuts out if the MOV has an overdissipation problem. We have lots of 5kw motors switching in and out, so there are many spikes.

Hopefully this is helpful and may give you some leads (no pun intended) to follow up.

Regards
E.

 

[senderj]

LED light bulb

Thanks for the replies. I'll give it a try and see what happen.

 

[ark5230]

LED light bulb

It is based on simple technique of obtaining lower working voltages with minimal component. Many chargable batteries use to employ similar circuit. A multimeter could be used to check voltages. So far as safety is concerned unless it is exposed to become hazardous there should not be a problem.

 

[betwixt]

Re: LED light bulb

ark5230, I believe you are thinking of the trick of using a capacitor as the current limiter. Using the capacitive reactance as though it was a resistor.

In these lights there is no capacitor in series with the LEDs, there is just a bridge rectifier, a filter capacitor and a lot of series connected LEDs. The current is limited only by the combined internal resistance of the LEDs. They work of course but without any limiting or regulation, the current is highly dependent on the voltage applied to them. Higher than normal mains voltage or spikes can easily cause over-current and burn them out.

Brian.