Why cell phone chargers are so light ??

[purifier]

Cell phone charger

An AC -> DC conversion is achieved using a rectifier.. And the step down is achieved by a transformer... So, suppose i stepdown 230V to 20V and that 20V I rectify to around 9-12V, I get my required output. But, this would definately make my ciruit look bigger.

Nowadays, the Nokia chargers(adapter) weigh as low as 80gms... What do they contain... Can anyone post the schematic please? I was wondering how that DC(which is required for the charging purpose) is being achieved by that small adapter...

 

[DarkJedi]

Re: Cell phone charger

Here is a thought... why dont you open one?

 

[dr_em]

Cell phone charger

It's the same technology that makes your computer's power supply lighter and more efficient, or recharges the battery in your electric shaver: switching technology. Switching circuits do away with bulky transformers but have a high pitch (frequency) whine that's very annoying, if you have good hearing.

Sorry, I don't have a schematic, but if you browse around on the web I'm sure you'll find a few.

Good luck!

 

[purifier]

Re: Cell phone charger

I only have one charger with me and so i don't think i can break it open... in that case i'll have to my cellphone aside too... And Switching Circuits? How are they useful here and in what way can they replace the bulky transformers?

 

[electronrancher]

Cell phone charger

i broke one open to answer the same question. it used a diode bridge to convert 120vAC to 240VDC then a HV step-down to buck 240v to 5v.

it's light because there is no transformer, but it is not simple to implement 240v buck converter.
one - it's lethal if you screw up
two - 300v chips are hard to find
three - 300v caps, etc are expensive


purifier - a buck converter switches on and off at a few hundred kHz - the width of each pulse can vary from 0% to 100%, giving an output voltage of 0-VIN. For this 240v-5v application, the converter is running at about 2% duty cycle. and it's not that there are NO magnetics, there is just no transformer ,so no heavy iron core.
all DC-DC converter switch into an inductor, but they switch so fast (kHz-MHz) the inductor can be tiny, so they are small and light -> giving a total system weight made up mostly of the plastic shell for the AC wall wart.

 

[rkdrkd]

Cell phone charger

Open it and check..

 

[purifier]

Re: Cell phone charger

Hmm...opened one...and found some devices...small ones....and it includes a bridge rectifier... Now, is there any way i can design such a circuit myself? Can anyone post a schematic?

 

[nicleo]

Re: Cell phone charger

Nowadays, the Nokia chargers(adapter) weigh as low as 80gms... What do they contain... Can anyone post the schematic please? I was wondering how that DC(which is required for the charging purpose) is being achieved by that small adapter...

The charger uses Offline SMPS topology. You can find such schematic in On Semiconductor website.
I have captured some clear photos of the circuit insides the Nokia Charger. I have uploaded the photos to this board. You can find them at

 

[purifier]

Re: Cell phone charger

Thanks nic....I'm downloading the file now...I'll get back to this post...