looking for something instead of transformer

[Fahime]

I always use a transformer and a diod bridge to convert 220Vac to 10-15Vdc. Now I was wondering if I could replace an Ic that is cheap, small size and light?
It's ok if you tell me an Ic instead of just transformer too.

 

[Optikon]

I always use a transformer and a diod bridge to convert 220Vac to 10-15Vdc. Now I was wondering if I could replace an Ic that is cheap, small size and light?
It's ok if you tell me an Ic instead of just transformer too.

The way many mains power converters do it is to directlty rectify off of line and then chop (switch) HV DC in a switch-mode fashion. There are control IC's available that can control the switching duty cycle. These are usually followed by a much smaller transformer (because of higher switching frequency) to get the voltage levels to something near the desired output.

HOWEVER,

Without a tranformer at all you will lose electrical isolation from mains and this is NOT recommended for both the sake of your circuits and your safety. You need to have a high voltage rated transformer in place for isolation or else you are asking for trouble.

 

[Ayne]

SAFETY First

**broken link removed**

 

[mvs sarma]

You did not indicate load requirement,as at higher currents smps woul be costworthy. you may perhaps try

TNY246 from M/s Power Integration Inc,
KA5LO380 from M/s Fairchild semi or even
Viper50 from M/s ST Micro

sometimes you could get these devices from scrapped Cellphone chargers(if the device is good ofcourse)

 

[Hero999]

The warning on the web page is wrong, it doesn't float 12V above earth, it uses a bridge rectifier so there will be huge 330V pulses (with respect to earth) on both the positive and negitive lines.

 

[Nigel Goodwin]

The warning on the web page is wrong, it doesn't float 12V above earth, it uses a bridge rectifier so there will be huge 330V pulses (with respect to earth) on both the positive and negitive lines.

Sorry, but the website is correct!. The bridge is fed from a 16V odd p-p with respect to neutral (clamoed by two zeners), NOT with mains voltage.

However, if you have to ask, you shouldn't be even considering something like this!.

 

[Hero999]

That's true, I didn't notice those zenners.

 

[Tarsil]

Nice link!

 

[Sceadwian]

How unsafe is not decoupling from mains really? If say a transformer's primary and secondary insulation fails and they suddenly become de-issolated, what kind of current limiting is really there? The whole thing would become a mass of molten metal and plasma relativly quickly, and considering the relativly high energy available this is easy for even relativly extended periods of time (a few 10's of ms's with circuit breakers) 5 volt circuits only go 'bad' with a puff of smoke and a bad smell. 120 volt circuits go bad with a ball of flame and a corpse. There has to be a solid logical boundry between what is a safe 'alternative' method of coupling to mains besides a pair of coupled inductors, which is like dark ages tech nowdays and between modern semi conductor methods of voltage regulation. Even just a high valued current limit resistor on the mains side with feedback to an internal shutoff I think is more effective than a basic transformer setup. If you acount for maximum theoretical voltage and current pulses. At least on supplies less than 500ma's or so.

 

[Nigel Goodwin]

Transformers provide isolation, it's EXCEEDINGLY rare for the isolation to break down. As for them being 'dark ages technology' they are as important now as they have always been, perhaps even more so?.

Any other methods are only trying to do a crude imitation of a transformer, and generally doing a poor job of it! - and far more dangerous besides.

 

[Hero999]

All isolated power supplies of any considerable power output use a transformers. Even switch mode power supplies which often have two (the feedback from the DC is often sent via an pulse transformer).

 

[grim]

How unsafe is not decoupling from mains really? If say a transformer's primary and secondary insulation fails and they suddenly become de-issolated, what kind of current limiting is really there? The whole thing would become a mass of molten metal and plasma relativly quickly, and considering the relativly high energy available this is easy for even relativly extended periods of time (a few 10's of ms's with circuit breakers) 5 volt circuits only go 'bad' with a puff of smoke and a bad smell. 120 volt circuits go bad with a ball of flame and a corpse. There has to be a solid logical boundry between what is a safe 'alternative' method of coupling to mains besides a pair of coupled inductors, which is like dark ages tech nowdays and between modern semi conductor methods of voltage regulation. Even just a high valued current limit resistor on the mains side with feedback to an internal shutoff I think is more effective than a basic transformer setup. If you acount for maximum theoretical voltage and current pulses. At least on supplies less than 500ma's or so.

you would prefer to rely on some electronics detecting a leakage current to protect you than an isolating transformer?

ok, I challange you. 240v input. 12v output. our delicate dangly parts connected to the 12v line.

i will use a transformer. you can use whatever.

they may be dark age technology, but that just means they work really well, and nothing has been found that is better.