230Vac to 12 Vdc???

[bubulindo]

I need to convert 230Vac to 12 Vdc using the minimum material possible, which means no transformer.
The rectification of the 230V wave doesn't have to be perfect because i will need the 12V to connect a relay and a CD4013 flip flop.

Best regards, Carlos Cardoso

 

[ScottyUK]

You could use a Class Y capacitive dropper, but this will not provide galvanic isolation and should be used with appropriate caution.

 

[m3]

Hi Carlos,

Try this:

_____| |_______|\|_______________
| | | |/| | +
C2 | D2 |
230VCA _|_ |+
D1 /_\ ----- 12VDC
| ----- C2
___________|___________|_________-


C2= 1,5uF 275Vca (polipropileno)
D1= 1N5349 (diodo zener )
D2= 1N4007
C2= 470uF 25V (eletrolitico)

Regards,

M3

 

[m3]

____| |_______|\|_______________
| | | |/| | +
C2 | D2 |
230VCA _|_ |+
D1 /_\ ----- 12VDC
| ----- C2
________|___________|_________-

 

[blcpro]

Why not try rectifying the AC, then dropping the voltage using some Zener diodes, as appropriate for your power needs?

 

[ScottyUK]

blcpro,

This method works but is very inefficient: compare power in to circuit compared with power delivered to the load. Capacitors are cheap and don't dissipate real heat (just imaginary heat ), but still drop voltage across them. Feed a rectifier through the dropping capacitor, then smooth as required for your circuit.

 

[peebee]

Use an SCR to chop the wave to about 14V peak and feed that into a capacitor to smooth it out a little. Use a resistance voltage divider to trigger the SCR turn-on. Total part count: 5 (2 resistors, an SCR, a cap, and a fuse).

BEWARE: Any no-transformer solution you attempt here will obviously not be isolated from the power source. Translation: DANGER WILL ROBINSON! DANGER! You should SERIOUSLY consider a transformer if for no other reason than power line isolation. I'd strongly suggest you reconsider your requirement to eliminate the transformer.

Have you considered using a plain-old wall-wart transformer? Those things are practically free, plus you get the very desireable POWER LINE ISOLATION as previously mentioned.

 

[peebee]

DANGER DANGER DANGER

Oh yeah -- A better SCR circuit might use an RC voltage divider as the trigger -- this is really more of a phase angle controller, gotta bust out the vector calcs for this one.

DANGER DANGER DANGER

For real down and dirty, just use a resistance voltage divider fed into a diode, use that to charge a cap. You'd only want to use this for very very low power levels.

DANGER DANGER DANGER

 

[RAMConsult]

The only proper response to this question is "DON'T EVEN THINK ABOUT IT!!!" The failure of any single component in any 'simple' circuit will place full line voltage, 230VAC, where only 12VDC is expected! This will fry your relay, your CD4013 IC and anything (and anybody) that is attached to this circuitry. Go into an electronics catalog and order a commercial power supply or follow peebee's suggestion of using a wall transformer as the cheapest appropriate solution. Be safe, please.

 

[jbartos]

Suggestion: If there is no danger to personnel, then 230VAC can be rectified and then chopped and filtered. Also, a sensitive protection will be needed.

 

[ScottyUK]

RAMconsult,

I agree this kind of thing goes against everything your instinct tells you, but these circuits are frequently used: the lighting dimmer on a wall being a prime example, as are some of the electronic ballasts used with fluorescent tubes.

When used in a carefully considered design, they are a useful means of providing small amounts of power cheaply when the application does not require isolation, or where isolation is provided by some other means. The safety aspect depends heavily on the application, and on specification of components designed for service on the mains.

As RAMconsult says, unless you are very sure what you are doing when designing a supply for direct connection to the line, let someone else do it and buy it from them.

 

[buzzp]

A PCB mount xformer is less than a dollar for a 2.5VA rating in small quantities.
I agree that isolation should be provided but on many occasions it is not. Whether or not it is safe is another story and can only depend on the whole design and what function it plays. Trying to use a voltage divider for 230VAC is difficult due to heat. I have done it but the device was only rated for 40C and I was not proud of it, heat kills.

 

[peebee]

See thread240-66929

 

[peebee]

Gopi -- your question has absolutely nothing to do with the posted question, which related to 12vdc power supplies. I suggest you start a new thread.

But before you even do that, search this site for VOLTAGE DROP. This question has come up MANY times lately within the last few weeks, and several replies have been posted with links to free voltage drop calculators.

Please check out faq731-376 for additional information.