# How can I get 3.7V 100mA from the 220V phase line? [duplicate]

Possible Duplicate:
Transformless power supply without ground

If I have access only to the 220V phase line, and I would like to charge a 3.7V battery, is it possible, without null line?

For example:

220V
------------------ 3.7 charger --------------
Source                                      |
light
|
Null line


## marked as duplicate by stevenvh, Kevin VermeerJun 11 '12 at 14:48

• Ah yes this is almost the same, and there is an example. Do I have to delete this post? – OHLÁLÁ Jun 11 '12 at 14:05
• You can't since the answer has votes. Don't worry, a moderator will close it, then there can't be any new answers. End of story. – stevenvh Jun 11 '12 at 14:07
• @ungibungi, no worries. Glad we could be of help. The site has a large wealth of existing questions, if we have one we will get it cleaned up for you. – Kortuk Jun 11 '12 at 14:55

So 4 of diodes in both directions in series with the load will give you a voltage drop of $\pm$ 3V as a square wave. You can rectify this with Schottky diodes and still have more than 2V left. There are switchers (SMPS, Switched Mode Power Supply) which can boost 1.2V to whatever your charger needs.