Electronics > Beginners

can an energy saving bulb be run off DC ?

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Simon:
As above. Could i run a standard energy saving bulb on 240V DC ? I'm guessing they use switch mode voltage converters in them so must be DC/DC so they must rectify the mains at the input ?

mikeselectricstuff:
Probably, but remember that 240VAC rectified does not make 240VDC - it's around 330V.
YMMV with different makes, but all the ones I've seen rectify the mains and so should work on DC.
Note however that any internal fuse may suffer arcing problems at DC in the case of an internal fault.

Zero999:
Yes, a CFL will work off DC.

I'm not sure if it'll work at full brightness on 240VDC. After the rectifier, there's a smoothing capacitor with just below the peak mains voltage on so you may need 325V to get full brightness.


Plenty of information can be found on CFL circuits in the Internet:
http://www.nxp.com/documents/application_note/AN00048.pdf
http://www.pavouk.org/hw/lamp/en_index.html
http://www.google.co.uk/search?client=opera&rls=en&q=CFL+circuit&sourceid=opera&ie=utf-8&oe=utf-8&channel=suggest

Ed.Kloonk:
 ;D

johnwa:
As others have said, it is possible to run CFLs from DC. However, be aware that there are a few different designs of the driver circuits for them. The older ones used a bridge rectifer straight into a filter cap on the input. These will work fine on 340VDC. However, the power factor of this design is pretty terrible, so in recent years a new design has been showing up. These isolate the filter cap from the rectifer with another diode, and the tube is run from the unfiltered DC - the filter cap only supplies the control circuit. Since the tube supply in this design is only 240VRMS, the tube will be overdriven  if run from 340VDC.

I once built an inverter for driving these that supplied 340VDC, pulse width modulated to provide an appropriate RMS value. It may be possible to find a suitable DC value between 240V and 340V that provides acceptable operation. (The driver circuit is underdriven at 240VDC, and the transistors may not saturate). It would probably be best to measure the power consumption, and get it to equal the value when the bulb is driven from 240VAC.

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