SMPS - Switching Mode Power Supplies - Any example ?

[flotulopex]

Hello,

I need to power a circuit I made with the main's AC. This because I use it's frequency (50Hz in Europe) to clock my PIC. My circuit draws around 50mA (mainly due to the 7-Seg 4-Digit LED display).

Using a transformer is very easy but extremeley unefficient regarding space and power dissipation.

I've heard quite a lot about SMPS (Switching Mode Power Supplies).

There are lots of theoretical documents about this subject but, unfortunately, I couldn't find at least one electronic shema example about this.

Does anyone know where I could find this kind of information?

[HenrikOlsson]

Hi,
Perhaps you should take a look at Microchip AN954. May or may not work with that much current. Be careful!

/Henrik Olsson.

[mister_e]

depending your current requirement, you may find some already built one fore few bucks. i don't think they even need to be design in most case.

Most company have some SMPS controller IC as well. worth to have a look there.

[flotulopex]

Hello Mister_E,

Would you have one or more links to these components please? I must not search the right way (correct words) since I can't find anything.

By the way, what do you use (what would you use) in this case?

Thank you HenrikOlsson, I read this application note already. Unfortunately, this kind of power supply allows only extremeley narrow min/max power ranges.

[mister_e]

How much current do you need?

[flotulopex]

I need around 0,05mA.

Input voltage is 230VAC 50Hz (Europe).

[mister_e]

eeuuuhh 0.05 mA or 0.05 A

[flotulopex]

... had a translation problem.

It is 0,05A or 50mA.

[mister_e]

same thing to me, but it make much sense...

for ONLY 50mA, i don't think it really worth to build something really complicated and over price the whole thing. Maybe the Melanie's Transformerless Power Supply example could be enough with few mods.

My english is really bad.... :-)

mine too, but... who cares

EDIT: maybe something around those one
http://www.discovercircuits.com/DJ-C.../offline5v.htm
http://www.st.com/stonline/products/...re/an/8313.pdf

be really careful with that kind of stuff..

[keithdoxey]

EEEEKKKK!!!!!!

OK, so it does say that the circuit is NON ISOLATED and DANGEROUS VOLTAGES EXIST EVERYWHERE but I would suggest that by having the dropper resistor in the neutral leg rather than the HOT leg, it is making it more dangerous than it need be.

If the resistor fails then the circuit stops working but EVERYTHING WILL STILL BE LIVE whereas if the resistor was in the live leg and failed then it would still stop working but the majority of the circuit would only be connected to neutral. Still wouldnt want to touch any part of it though!

Obviously using a 2 pin mains connector would mean that there is no guarantee of polarity anyway so the above point would be irrelevant.

[mister_e]

i agree, it's ALWAYS dangerous if not properly insulated from the user.

You could be surprise to look at some TV schematic... no coincidence why the user button are as this far of the front plate and have those plastic shaft in between.

If you know what you do, if you install enough protection, if you screen the user from any potential risk, life is good.

You don't want to reverse engineer most programmable thermostat, cofee maker, etc etc...

Advanced components industries, do some nice small transformer.
http://www.advancedcomponents.com/go...FQy8QAodBl8-OA