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transformerless power supply

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yaghoubi

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Dear
I need a supply that could provide 12VDC/350ma and it should be small and cost effectiveness as well.
I have done many searches and found several circuits but I don't know how it works and how I could get optimum it.
I was wondering if you'd mind helping me understand how I can design a good one.
Thanks
Ehsan
 

Hi,
yaghoubi,what is ur power source?i don't think circuit can produce power just by it own.

lizardno1
 
The link to the circuit has been removed by moderators- it is highly dangerous and should not be used.

Keith
 

Dear friends!
Hi
You can use a ceramic capacitor(series with diode and parallel with resistor) .
Or you can use a fly back converters or forward converters with a little ferrite transformer.for example you can use uc3844 or uc3845 for this purpose.its safety is very high. because is isolated.
Best lucks!
Goldsmith
 
Thanks friends
is it possible to use diode bridge and then use dc-dc converter ICs?
Could u please introduce several ICs that could 240v to 12v?
 

yaghoubi said:
Dear
I need a supply that could provide 12VDC/350ma and it should be small and cost effectiveness as well.
I have done many searches and found several circuits but I don't know how it works and how I could get optimum it.
I was wondering if you'd mind helping me understand how I can design a good one.
Thanks
Ehsan
Click to expand...

I am afraid I do not get exactly your question . What is your input voltage and how small you need it to be? ?

There are a lot of small new brand transformer today that you can buy one and use with a bridge .
But, If you want to make it really small it must be a switching power supply .
Designing efficient switching Power supply is not very easy that anyone do.
But to show all a perspective :
In any switching design the input frequency must be changed to a higher level .
Choosing appropriate Core is the hardest part of a switching power supply design .
After choosing appropriate core you should wrap The Primary and Secondary on it .
( These are not really easy for every one ) The thickness of wire in primary and secondary must be calculated and the number of turns also.

Regards,
 
Last edited:
Dear Ehsan
Hi
I can send to you a simple circuit for your aim if you want.
Regards
Goldsmith
 

Dear yaghoubi,
Check the following design by ST:
**broken link removed**
Hope it'll be useful for you.
 

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design power supply 240vac to 12vdc (uper 350ma)

I intend to design micro-controller power supply.
Is it possible to use diode bridge and then use dc-dc converter ICs?
Is there any IC that can withstand 240v and reduce the voltage to 12v?

Don't start new threads with the same content.Threads merged [alexan_e]
Click to expand...
 

Obviously, the above linked ST design would work with a bridge rectifier as well, if you prefer it for some reason.

As with all transformerless power supplies, the DC output voltage is galvanically connected to the mains and must be carefully protected against being touched. This restricts the usability of transformerless supplies to a very few applications, e.g. LED lamps with protective case, embedded processors controlling mains powered home appliances like washing machines. The technique isn't applicable for any circuits with exposed terminals or other conducting parts at risk to be touched by a person.
 
Few words of warning, when using power source circuits without isolation transformer.

If the supply plug rotates oppositely, all zero connected (grounded) parts become energized to 240Vac
including all components and devices connected to power source.

If the power supply zero connection wire getting loose from circuit all parts are connected to 240Vac
including all components and devices connected to power source.

Tranformerless PS_.jpg
 
Few words of warning
Click to expand...
The simple rule applied by all safety regulations is to consider circuit parts without sufficient insulation related to the mains voltage as hazardous contact voltage. You don't need to think about live or neutral connection in this regard.
 
Even if a plug cannot rotate you should NEVER rely on Live/Neutral being the correct way round.

Keith
 

example of isolated transformless power supply...
max current 100mA
hope this helps

alim sans transfo 100mA max.jpg
 

Kripton2035 said:
example of isolated transformless power supply...
max current 100mA
hope this helps

View attachment 60475
Click to expand...
DANGER
That is NOT an isolated power supply and thinking it as such is dangerous.
The resistors can break down and high voltage arc over. Or the capacitors break down and arc internally.
In both cases the insulation layer is measured in fraction of micrometers. Distance between plates in the capacitor.
Er and possibly no insulating distance in the resistors.

Only a transformer (or optical eg lamp => solar cell) is isolated. The primary and secondary are insulated from each other by
insulated additional material eg tape.
 
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Re: design power supply 240vac to 12vdc (uper 350ma)

To convert 240Vac to 12Vdc,definitely u will need a transformer.When we design a power supply system,we should and must take safety(to power source,cascades after the power supply,even human body) into consideration.
 

I think you can build it by fly-back power supply.
It is very smart and safe. dimension of it's board is just 1.5*2*2 cubic centimeter
You can find it in many market's for example LED power supply mounted in lamp socket.
 

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