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Old 31st March 2009, 09:25 PM   #1
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Default Halogen transformers

I've just found some halogen transformers for 6 that give 12Vrms they are described as "Independent IP20 transformers". I know some halogen lights are powered from 30KHz supplies, but not sure about these.

Can i use them to power a 20W/6Ohm class A amp?

Would 30KHz be rectifiable?
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Old 31st March 2009, 11:07 PM   #2
Eva is offline Eva  Spain
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These transformers provide ~30Khz chopped AC following the mains waveform envelope. The purpose of this is to achieve good power factor. They are not easy to modify for producing DC. The switching stage is usually self oscillating with bipolar transistors. Input capacitor for mains rectification is of very low value.
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Old 1st April 2009, 02:52 AM   #3
star882 is offline star882  United States
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If they're heavy, they might just be normal transformers.
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Old 1st April 2009, 12:28 PM   #4
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Quote:
Originally posted by Eva
These transformers provide ~30Khz chopped AC following the mains waveform envelope. The purpose of this is to achieve good power factor. They are not easy to modify for producing DC. The switching stage is usually self oscillating with bipolar transistors. Input capacitor for mains rectification is of very low value.
This may explain the plurarlity of noises is see on the scope since i have both halogen lamps and electronic fluorescent lights at my lab.

I knew it was silly to think that one could feed a class A amp from a 12 psu but i wanted to be sure.

Thanks!

Quote:
Originally posted by star882
If they're heavy, they might just be normal transformers.
A long time ago i had an halogen lamp that was feed from a normal tranformer, too bad i didn't keep it.
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Old 13th April 2009, 10:09 AM   #5
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Quote:
Originally posted by Eva
These transformers [...] are not easy to modify for producing DC.
It has been done: http://www.qrp4u.de/docs/en/tube_smps/index.htm

Of course, there's no PFC, and you will almost definitely need additional filtering. BTW, the pics on the site above serve to illustrate just about everything you can do wrong wrt. electrical safety!
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