IKEA lamp transformer failed

Why do you think the rectifier EXISTS? The lamp doesn't care whether it's ac or dc. At least the first order effects don't care. It should be a tiny bit happier with AC.

I assumed that a 12V halogen bulb would take DC voltage. Am I wrong? The lamp stopped working, the bulb is OK (continuity fine, at least).

Probably.

Something's odd, though. If you've got 12V from the transformer, but the light won't light, you need to do more troubleshooting.

My apologies. Turns out the output socket on the transformer was cooked and I'll have to bypass it.

Probably to reduce the total power to the bulb, to make it less bright. A cheap way of implementing off/low/high.

Geoff.

OK, but the diode would get shorted on high, so don't think that's the issue. AC is present and should light the light.

Somebody should know how the redeposition of tungsten from the halogen interacts with the different notching patterns created by DC and AC currents.

If you run a lamp on DC the almost molten tungsten gradually migrates to one end of the filament leaving weak spots at the other end where it becomes thinner - this shortens lamp life compared to running on AC.

Nope. The first overvoltage power glitch will blow the bulb.

The blown module is *NOT* a transformer and rectifier. You probably have a module with a 12V output switching power supply inside. They like to fail. The problem is that something got lost in the translation from Chinese to English, resulting in these switchers being labeled as "transformers". For example:

is labeled an "electronic transformer". It's not. It's a switching power supply. However, since it does transform 117vAC to 12vDC, I guess it could be considered a type of transformer.

You should be able to read the label on the switcher to find a replacement. If not, obtain the power rating of the halogen bulb in watts, and search for a "XX watt halogen lamp transformer".

They intentionally run on DC. This article explains some of it:

Quoting: The "electronic" transformer represents an alternative means of power conversion to the more standard iron core, 50 Hz transformer technique. The advantages of the electronic transformer compared with the classical solution are: - The output power from the electronic transformer to the lamp can be varied, thus dimming control can be added; - It is possible to include protection against short circuit of the lamp filament; - Weight can be reduced and the construction made more compact; - Acoustic noise (mains hum) is eliminated.

In addition, if you've ever watched an AC driven light bulb filament on a high speed camera, the filament vibrates slightly at 60Hz. This is not a problem when the filament is fairly thin, flexible, and cool. However, doing the same at the higher temperatures of a halogen bulb will vibrate the stiff filament until it breaks.

DC rules. Edison was right and Tesla was wrong.

Oops. I goofed. The halogen bulbs run on AC. Looks like it will work with just a transformer with no diode required.

Sorry(tm).

Which was my experience with various utility lamps running halogen bulbs. The slightest power glitch blew the bulb. In my case, it was a glitchy emergency generator.

However, I was wrong. The electronic transformer really is an AC to AC transformer, not AC to DC. Sorry for the mistake.

Many thanks for the info. As posted earlier, it turned out the transformer output socket was cooked. And, when this was fixed (or rather bypassed), it turned out the toggle switch on the bulb holder was also cooked :-)

Flip the lamp in the socket monthly, maybe?

The migration is extremely lumpy so you still get weakened spots on the relatively thicker sections of the filament, and I vagely remember the book I read years ago explaining why reversing the DC doesn't help as much as you'd expect - unfortunately I can't remember what that explanation was.

"Ian Field" wrote in news:vvV_p.155577$ snipped-for-privacy@newsfe27.ams:

if the lamp has a transformer,why is the bulb running on DC? transformers output AC. you would have to add an extra component(diode) at more cost,and for lesser performance.

Or is the "transformer" actually a AC-DC switching converter? I have a LED gooseneck desk lamp that has an AC-DC switching converter,in the line plug.

All the electronic 'transformers' I've looked inside had a circuit remarkably similar to a CFL - except no ballast coil and the primary of a toroidal transformer is half bridge style between the O/P & divider capacitors.

AFAICR I've never seen one with a secondary side rectifier.

It just happened that someone suggested DC operation and I'm one of those pointing out that it wouldn't provide optimum lamp life.

Flip it 50 or 60 times per second, that will do.