help

[ice311087]

hi guys,i would like to know if any of u can help me with a cellphone charger circuit using a flyback converter...(12V input-required output 5v)...its for my project

 

[Krumlink]

Why not use a 5V regulator???

 

[Roff]

hi guys,i would like to know if any of u can help me with a cellphone charger circuit using a flyback converter...(12V input-required output 5v)...its for my project

You don't need a flyback circuit. They are for getting high voltage from low voltage. You need a buck converter, or, if the current is low, a linear regulator, as Krumlink suggested.
Whether this is what you actually need for a cellphone charger, I don't know.

 

[ice311087]

no...the thing is i have been asked to specifically do this as a project...
a charger using flyback converter or any simple circuit that uses a flyback converter...

 

[ice311087]

thanks for that piece of info Ron...then is there some circuit that steps up a lower voltage to 5V...maybe from the ordinary 1.5v battery..

 

[Roff]

thanks for that piece of info Ron...then is there some circuit that steps up a lower voltage to 5V...maybe from the ordinary 1.5v battery..

You can use a flyback converter for that.

 

[blueroomelectronics]

You can buy AA cell phone chargers for less than you could build one for.

 

[Roff]

You can buy AA cell phone chargers for less than you could build one for.

But if it's a school project, he might not get a very good grade if he buys one and submits it as his project.
Of course, it might not be a school project. What a surprise that would be!

 

[RadioRon]

Isn't the classic Joule Thief circuit a flyback topology?

 

[Roff]

Isn't the classic Joule Thief circuit a flyback topology?

I looked up a few definitions of flyback converter, and they seem to be pretty consistent in saying that the output is isolated by a transformer winding from the source. Otherwise, the circuitry is like a boost converter, which I guess the joule thief is. I'm sure you could modify the joule thief to have a transformer-coupled output, but why???

 

[RadioRon]

Well, I was really just curious.

 

[Roff]

Well, I was really just curious.

No, I didn't mean why were you asking. I was just asking a rhetorical question - why would anyone want to implement the joule thief with transformer isolation.