3A adaptor for driving LCD

chris_ivan wrote:
> thanks for the recommendation. To be honest, I usually build power
> supply module for microcontroller system whose current need around 1A.
> So far I don't find any difficulties with linear regulator. This is the
> first time I build 3A adaptor. I'm gonna start learning the alternative
> using switching regulator. Ah, also in the city where I live in,
> electronic shops typically sells adaptor around 1A, if I need more
> current, I ought to build it by my own. I also looked for switching
> transformer to reduce the size of the stuff, but I hardly found it.

Learning is great.

http://webench.national.com/appinfo/power/webench/index.cgi

Kelly

"chris_ivan" <chris.ivan@gmail.com> wrote in message 
news:1139906299.586337.132050@g44g2000cwa.googlegroups.com...
>
> This may seems a stupid question, but I would be if I don't ask. I just
> wonder whether it is possible to build 3A adaptor using 1A linear
> regulators connected in parallel. In theory it's possible, isn't it?

It is possible in theory, but in practice you'll have problems with current 
sharing - i.e. it will almost certainly prove tricky to get the parallel 
regulators to share nicely. It can be done rather better with a single 
regulator reference/feedback/comparison circuit and a number of series-pass 
MOSFETs in parallel and bolted onto the same heatsink... but a switcher is a 
far better approach. A linear regulator providing 3A is, no matter which way 
you do it, going to waste an awful lot of energy as excess heat which will 
need dumping somehow.

Steve
http://www.fivetrees.com 

chris_ivan wrote:
> Steve at fivetrees wrote:
> > To be blunt, I think you're going about this the wrong way. For that kind of
> > application, I would strongly recommend you use a switching regulator.
> > However, with respect, if you're struggling with a linear regulator, you'll
> > be in all kinds of trouble with a switcher. Why not just buy a switching
> > module?
> >
> > Steve
> > http://www.fivetrees.com
>
> Hi Steve,
>
> thanks for the recommendation. To be honest, I usually build power
> supply module for microcontroller system whose current need around 1A.
> So far I don't find any difficulties with linear regulator. This is the
> first time I build 3A adaptor. I'm gonna start learning the alternative
> using switching regulator. Ah, also in the city where I live in,
> electronic shops typically sells adaptor around 1A, if I need more
> current, I ought to build it by my own. I also looked for switching
> transformer to reduce the size of the stuff, but I hardly found it.

You can easily build one for a few bucks.   A 30V 7A MOSFET
costs around $1.   Unfortunately, most controllers are very small and
difficult to build without a PCB.  Everything else can be hand wired,
includind the MOSFET.  We are thinking about build an adaptor just
for the controller (lm3485), expanding from MSOP-8 to DIP-8.

>
> This may seems a stupid question, but I would be if I don't ask. I just
> wonder whether it is possible to build 3A adaptor using 1A linear
> regulators connected in parallel. In theory it's possible, isn't it?

No, it's not.  They all see overloading conditions and shut down
itself.
You can use by-pass MOSFET or IGBT.  But why not using switchers
with 80% to 90% efficiency?

> 
> Thank you for the suggestion, it really helps.
> 
> Ivan