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Understanding power supplies and building one

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xmen_xwk

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I need to build a good power supply for 1A load or lower. I have few laying around and some phone chargers.
After I opened almost all of them, the phone chargers looks quite simple while the SMPS do look quite complicated, of course SMPS do.

Here are pictures of some.
first.JPG

The marked color green is resistor, what does it need here ?
The marked color yellow seems like some kind of capacitor. Maybe it helps suppressing the AC EMI ?
The marked color red, seems like double inductor. What does it do here ?

These things are common in SMPS at input side.

One more question why do they use many other components, why not just use Switch mode or linear regulator after transformer and rectifier ?
 

xmen_xwk said:
The marked color green is resistor, what does it need here ?
The marked color yellow seems like some kind of capacitor. Maybe it helps suppressing the AC EMI ?
The marked color red, seems like double inductor. What does it do here ?
Click to expand...

The green object is probably a varistor; if the applied voltage goes too high, it pulls the voltage down and blows the fuse. Sometimes you will find that the beast is alive but the rest of the circuit is gone.

The yellow capacitor does control EMI. It also blocks, exactly in the same way, high frequency, high voltage spikes to enter the circuit.

The red object is a double inductor- it is clearly visible. This too acts as EMI blocker. This also blocks input rush current when the power supply is first turned on (the rush current is used to charge the input side power capacitors).

The "one more question" is fit for an interview or an exam. Too long for me to type.
 

Hi,

Safety first: You are working with dangerous high voltage. And it seems you are not that experienced with safety rules.
Don't hurt yourself and don't hurt others.
Even when powered off some capacitors may carry dangerous voltages.

******

Please read some tutorials about power supplies.

There are so many topologies and different circuits around...and so much theory about the operation modes..it can not be explained in a couple of sentences.

Additionally i think it's not the best way to learn about power supplies with reverse engineering.
I rather think going to some application notes where the function and calculation for every single device is explained is the better way.

Klaus
 

I have read some tutorials, all they do is use transformer, rectifier and linear voltage regulator. While that seems very simple, no tutorial explain any of this, about the power supplies I have.
 

xmen_xwk said:
I have read some tutorials, all they do is use transformer, rectifier and linear voltage regulator. While that seems very simple, no tutorial explain any of this, about the power supplies I have.
Click to expand...

Whatever people may say, devices you have shown are real complex beasts. They are tough to design and complex to understand. There are several different topologies (different permutations and combinations of the same components) and they are still evolving (that is why you will not find details about them in regular text books).

As KlausST (#3 post above) has rightly pointed out, the best way to learn about new technologies is to study the application notes- well I think that is the only way.

Then if you have difficulty, please come back here and ask questions. But there is no short cut to study.
 

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