Transformer Less 5v Power Suplly

[neuralc]

Hi all,

I have seen some circuits using varistors, diodes, capacitors and voltage regulator to get 5V directly from 220v Power Line.
Some one have experienced to use such kind of solution with uC? In industrial applications? The varistor should "catch" high voltages, but its still safe?


ThX

NeuralC

 

[flatulent]

Off line supplies that do not have transformers are very unsafe. EC safety rules require having two independent insulating shells totally surrounding both the supply and the load it powers. For low power supplies this costs more than a transformer.

 

[Frosty]

If you pick yourself up a SCH for a domestic heating contoller/timer or digital stat like from Honeywell/Sunvic/Danfoss you will have a good example of how it is done.

It seems like yo want to control something that is mains powered and have space confinement.

But as flatulent says, it is not easy to meet safety criterea for such a circuit, but it is possible.

Layout is also a serious pain if space is limited (like in a heating contoller ) so you generally have to make a lot of cut outs to make sure you have meet the correct flashover/isolation requirements between live rails at required humidity levels.

But most of these I have seen drop the DC after recification via large power resistors and create a lot of heat/energy loss which usually means higher MTBF for the product. Higher the current you want, more you will generate in heat because of the huge voltage drop across the R's.

Its not nice way to do it at all.

:R

 

[sokrat]

Hi all

dear i use this circuit in some application it work good
see this link

**broken link removed**


THANKS

S 8O KRAT

 

[czpir]

Try the following links for some help but remember to use proper isolation using a small transformer and DO TAKE CARE as you would have high voltages on the circuit.

http://www.aaroncake.net/circuits/supply5.htm
**broken link removed**

Alternatively you could try to study the lightweight power supplies that come with equipment like computer network switches, routers etc.

These PSUs do not use heavy transormers but have smaller transformers and inductors within them. They are good and can even support large current draws (I have used upto 5amps).

You could obtain one of these PSUs, remove the plastic casing and use the PCB and sockets with your application, best results and is well isolated from the mains.

I also remember someone telling me that you could build a transformerless PSU using IGBTs, but I have no ideas on this :?

Hope this helps.

 

[GrandAlf]

If you do not need much current, you can use a hi voltage cap in series with the mains, then rectify it. Some small nicad battery chargers use this tecnique.

 

[neuralc]

Hi flatulent,

Do you have some material about EC safety rules?
My product is DIN rail control system...

ThX

NeuralC

 

[nikhilele]

sokrat:

h**p://www.elektroda.pl/eboard/searchtopic59105-transformer.html

this topic cannot be found

 

[Nimer]

hi didnt quite understand the prblem here . but if youdont have a transformer then you control circuit would be unprotected

regards

 

[nikhilele]

transformer is may be undesirable because it takes lot of space and for small products or gadaget one has to think for transformerless power supply as X10 boards are using