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[SOLVED] How to understand SMPS mobile charger schematics.

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avinash.kashyap

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Hi,
Here posted is a cheap mobile charger schematics based on power transistor 13001 (NPN), and output is 6.4V 0.350A which gives 2.24Watts output. I'm planning to modify this circuit to get 24v 0.250A which comes to be 6Watts output while the limit of this power transistor is 7Watts. Obviously to achieve this the transformer + snubber + feedback circuit has to be modified to use the same transistor.
But the circuit formed by the transformer coil (t1 + t2), (which is providing some kind of feedback) + R3 + C3 which goes to the base of the transistor; and a signal diode 1N4148 links to this circuit from the Z2 (6v2 Zener); is not clear to me.
Fairchild Semiconductor's Application Note 4137 helped a lot to understand the basics of SMPS design but still the abovementioned part is not clear to me.Please help me to understand that.

Here is the circuit of the charger:
MCSMPS.JPG

========================================================================
This seems to be an oscillator circuit to "switch" the transistor, but still need to understand the operation. Need help :)

Here is the Fairchild's application note:
 

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  • AN-4137.pdf
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Last edited:

Re: Help needed: To understand SMPS mobile charger schematics.

...destiny wanted me to find the solution for this... ;) ...so somewhat i did...
...the following link says that how this MJE13003 and the feedback winding forms a switching circuit the frequency of which is determined by their respective values...

A simple inverter for flourescent lamps

...i would still request someone more knowledgeable to throw more light on this...

...but i was able to convert this charger to give 15V+ output @ 350mA, and for this i had to change two components one was the output capacitor and second was the high frequency transformer...the details of the changes are as follows...

1. output capacitor changed from 470uF/ 10v to 470uF/ 35v.
2. transformer was rewould as: (i) primary: #40 SWG 400turns start from pin 3 and end on pin 4 (ii) secondary: #32 SWG 20turns start from pin 6 and end on pin 5 (iii) feedback winding: #40 SWG 20turns start from pin 1 and end on pin 2

...remember to rewind this transformer in the order given e.g. first the primary, then secondary and feedback in the last...i will soon post this whole exercise as a complete project so that anyone can have a "switch mode" bench top power supply with a variable voltage setting... :) ...wait till then...

...NOTE OF CAUTION: the centre leg area of the EE core of the transformer was ~17mm square so on the basis of the information i got from the internet i considered this core to be able to handle upto 10Watts of power...but i really did not dare to push it to the limits and kept it [ 15V @ .350A = 5.25Watts ]...there are a lot of things to keep in mind while modifying a given smps e.g. like this cheap one, and for that i would really recommond the application note attahed and internet...and the best security is to use a 500mA fuse between the AC power outlet and your project supply...
 
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Re: Help needed: To understand SMPS mobile charger schematics.

Hi,
Many thanks for your post.
We are a bunch of college students doing our miniproject on making a mobile charger. Your diagram is a very good aid in our project.
Hope you can easily finish your work 'n post the whole project here.

Thanks again!
 
Re: Help needed: To understand SMPS mobile charger schematics.

... :) happy to hear that you found this "reverse engineering" kind of project useful...
...though i've completed the project, but still experimenting with the transformer to understand the basics...because i'm just an enthusiast and don't have any academic knowledge...
...if you need some specific output with this charger you just need to change the zener accordingly and would be great if you can experiment with a resistance (start from the value 10 ohm and move upto 75 ohm, better to use a 100 ohm pot)between Emitter and Ground, which reduces load on the transistor...and you can leave a query here anytime... :) ...wish you luck...
...and one more thing you can keep the number of turns as, (i) primary: 180 turns (ii) secondary: 15 turns (iii) feedback: 15 turns...
 
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Re: Help needed: To understand SMPS mobile charger schematics.

Hi, I just simulated the ckt from your first post in multisim: 'n I'm getting zero output!!
But I made the following changes:
(i) Instead of 1n5819 I used 1n5822
(ii)I took the transistor as 2sc4341

Why do you think I got 0V across C1?

'n one more thing, I would like to know the internal wiring of a certain transistor; I found it in the mobile charger, so I think it is like the one in your ckt. I have attached several photos of the PCB housing it (since I haven't got a good cam :(.. ) pls let me know what u think..
 

Attachments

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    Photo0153[1].jpg
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  • Photo0151[1].jpg
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  • Photo0149[1].jpg
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Re: Help needed: To understand SMPS mobile charger schematics.

vishnu.mthss said:
Hi, I just simulated the ckt from your first post in multisim: 'n I'm getting zero output!!
But I made the following changes:
(i) Instead of 1n5819 I used 1n5822
(ii)I took the transistor as 2sc4341

Why do you think I got 0V across C1?

'n one more thing, I would like to know the internal wiring of a certain transistor; I found it in the mobile charger, so I think it is like the one in your ckt. I have attached several photos of the PCB housing it (since I haven't got a good cam :(.. ) pls let me know what u think..
Click to expand...

(i) ...according to datasheet that seems ok...
(ii) ...couldn't find it's datasheet, So can't say anything...but if it's high voltage switching NPN transistor then it should be ok...

...And about the 0V...
...well i have never used multisim, i use LTSpice IV...i generally get 0V when i miss to connect the ground planes properly...you might have missed on the ground planes, which have to be connected to both sides (different grounds) of the transformer...try this out...

...and for the internal working of the transistor you can try to find the appropriate datasheet and/ or application notes...yes...the pictures which you have posted are not clear enough, but you should try to find out the markings on the transistor e.g. KSE13001, MJE13001 etc. and search these terms on internet...you'll get some useful information...because i did the same for my this project to find out the datasheet of this transistor...
 
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Re: Help needed: To understand SMPS mobile charger schematics.

k. thanks.. :)
will let u know if i get this done.!
 

Re: Help needed: To understand SMPS mobile charger schematics.

thanks avinash.kashyap
your posted cheap mobile charger schematics based on power transistor 13001 (NPN) has pulled me here while searching on net for the circuit diagram of a nokia charger model AC-3 ( approximately same as your attachment)

What I am doing from this chrager is I am trying to drive three high brightness white LED's.
Making sort of mains LED bulb for darky pathway trying to save some bucks on everyday use of regular CFLs.

After searching lot of circuits on net for mains LED driving, I came out with an idea to use my mobile charger from junk.
there are many other circutis as simple as lowering voltages using capacitor, resistor and a bridge rectifire and then a reverse biasd zener parallel to LED array. But that did'nt satisfied me since no good regulation of current through LEDs.

still searching for optimum solution ( better LED driving on less watts) but at the moment trying this mobile charger circuit's output (5v).

when jsut trying to reverse engineer my charger's schematic, found your attachment.

now I want to tweak for my application,

after repair it was giving approx 5v dc output ( unloaded)
1- I used three LED's in parallel with a little current limiting resistor.

2- Also I changed the zener on the base of 13001 to 12v zener. now charger output is 11.48v unloaded and I connected all three LED's in series without any current limiting resistor. output drops to 9.7v and LEDs are drawing 165 mA. Then tried with two LED's in series , voltage out now is approx 7V and current drawing is 280mA . I noticed that voltage is adopted automatically when i use one, two or three LEDs in series but current passing through LED's vary with largest current 450 mA when using one LED ( current is exceeding LED current limit) ( voltage on output terminal is approx 3.64v ). Two in series and current downs to 260 mA. ( voltage on output terminal is approx 7.07v now). Three in series and current downs to ( voltage on output terminal is approx 9.76v now).
Another trial : i used all three in parallel with ( charger with zener 12v output unload 11.48v ) voltage on terminal with LEDs connected now is voltage on output terminal is approx 3.2v now and current passing through parallel string is 470mA .



How to optimize the situation,
among several options are:

use 12v zener and use three LED in series.
use 12v zener and three LED in parallel with a current limit resistor.
jump down the charger out to approx 3v or 4v and drive LED's in parallel directly. ( not experimented yet)

My goal is to get brightest LED's on this circuit while saving some Mains watts.
I have no specs for LEDs' but I guess these are cree LEDs ( or similar) because these are also from my junk.
I guess 300mA is tha max limit for this LED

plesae suggest everybody any help is welcome

using mobile charger SMPS has benefit in my opnion :
operating voltage approx 100 to 240v
some sort of regulation is found built in ( zener on base )
such chargers are readily available.

Also I am working on building a torch using similar LED's but can't find a satisfactory battery effecient and brightness effecient solution.

-tried joule thief ( boost convertor, or blocking oscillator) not good current regulation on output side so not LED effeciency and most circuits are 1.5v AA batery based. I am planning on 4.5V rechargeable battery

-tried buck converters ( mostly need IC's not readily available at my side )

-tried circuits with current regulation in series with battery from LM317 or Mosfets etc. regulation is good but they unneccessary drain battery in order to achieve current regulation.so not battery effecient.

please also suggest for this.

thanks
 
Last edited:
Re: Help needed: To understand SMPS mobile charger schematics.

I think thread is closed since it is already SOLVED.

I will post my matter in a new thread
 

Re: Help needed: To understand SMPS mobile charger schematics.

Thanks avinash.kashyap
I was looking information about this.
I have a old cellphone charger and the schematics is quite similar than yours

:grin:
 

Re: Help needed: To understand SMPS mobile charger schematics.

sunnyimran said:
thanks avinash.kashyap
your posted cheap mobile charger schematics based on power transistor 13001 (NPN) has pulled me here while searching on net for the circuit diagram of a nokia charger model AC-3 ( approximately same as your attachment)

What I am doing from this chrager is I am trying to drive three high brightness white LED's.
Making sort of mains LED bulb for darky pathway trying to save some bucks on everyday use of regular CFLs.

After searching lot of circuits on net for mains LED driving, I came out with an idea to use my mobile charger from junk.
there are many other circutis as simple as lowering voltages using capacitor, resistor and a bridge rectifire and then a reverse biasd zener parallel to LED array. But that did'nt satisfied me since no good regulation of current through LEDs.

still searching for optimum solution ( better LED driving on less watts) but at the moment trying this mobile charger circuit's output (5v).

when jsut trying to reverse engineer my charger's schematic, found your attachment.

now I want to tweak for my application,

after repair it was giving approx 5v dc output ( unloaded)
1- I used three LED's in parallel with a little current limiting resistor.

2- Also I changed the zener on the base of 13001 to 12v zener. now charger output is 11.48v unloaded and I connected all three LED's in series without any current limiting resistor. output drops to 9.7v and LEDs are drawing 165 mA. Then tried with two LED's in series , voltage out now is approx 7V and current drawing is 280mA . I noticed that voltage is adopted automatically when i use one, two or three LEDs in series but current passing through LED's vary with largest current 450 mA when using one LED ( current is exceeding LED current limit) ( voltage on output terminal is approx 3.64v ). Two in series and current downs to 260 mA. ( voltage on output terminal is approx 7.07v now). Three in series and current downs to ( voltage on output terminal is approx 9.76v now).
Another trial : i used all three in parallel with ( charger with zener 12v output unload 11.48v ) voltage on terminal with LEDs connected now is voltage on output terminal is approx 3.2v now and current passing through parallel string is 470mA .



How to optimize the situation,
among several options are:

use 12v zener and use three LED in series.
use 12v zener and three LED in parallel with a current limit resistor.
jump down the charger out to approx 3v or 4v and drive LED's in parallel directly. ( not experimented yet)

My goal is to get brightest LED's on this circuit while saving some Mains watts.
I have no specs for LEDs' but I guess these are cree LEDs ( or similar) because these are also from my junk.
I guess 300mA is tha max limit for this LED

plesae suggest everybody any help is welcome

using mobile charger SMPS has benefit in my opnion :
operating voltage approx 100 to 240v
some sort of regulation is found built in ( zener on base )
such chargers are readily available.

Also I am working on building a torch using similar LED's but can't find a satisfactory battery effecient and brightness effecient solution.

-tried joule thief ( boost convertor, or blocking oscillator) not good current regulation on output side so not LED effeciency and most circuits are 1.5v AA batery based. I am planning on 4.5V rechargeable battery

-tried buck converters ( mostly need IC's not readily available at my side )

-tried circuits with current regulation in series with battery from LM317 or Mosfets etc. regulation is good but they unneccessary drain battery in order to achieve current regulation.so not battery effecient.

please also suggest for this.

thanks
Click to expand...

It was a good attempt. However, a nokia charger is designed to limit the current delivery to about 650-700 ma and its open ckt voltage is about 6.5V however at full current it is about 3.8Volts. a 1 watt LED takes about 350MA and about the same voltage 3.8. Therefore you can use two LEDs in parallel to get full output from them or use three and they will run for the rest of your life. you can also a single 3W LED that can replace about 8 Watt of CFL. If you directly connect a single 1W LED it might fail.
I wish to know how I can increase the output current from the charger so that I can get more output from the same equipment. If you have idea pl let me know. I know very little electronics!
Good luck!
 

Re: Help needed: To understand SMPS mobile charger schematics.

I have assamble the first given circuit with modified transformer -primary 200 turn; secondary 30 turn; f/b 30 turn and get output upto 35 volt but voltage gets varying continue and after some time it reduce upto half. After sometime switch off and again on will give 35 v again with same characteristics. Can any one help?
 

Re: Help needed: To understand SMPS mobile charger schematics.

avinash.kashyap said:
Hi,
Here posted is a cheap mobile charger schematics based on power transistor 13001 (NPN), and output is 6.4V 0.350A which gives 2.24Watts output. I'm planning to modify this circuit to get 24v 0.250A which comes to be 6Watts output while the limit of this power transistor is 7Watts. Obviously to achieve this the transformer + snubber + feedback circuit has to be modified to use the same transistor.
But the circuit formed by the transformer coil (t1 + t2), (which is providing some kind of feedback) + R3 + C3 which goes to the base of the transistor; and a signal diode 1N4148 links to this circuit from the Z2 (6v2 Zener); is not clear to me.
Fairchild Semiconductor's Application Note 4137 helped a lot to understand the basics of SMPS design but still the abovementioned part is not clear to me.Please help me to understand that.

Here is the circuit of the charger:
View attachment 64415

========================================================================
This seems to be an oscillator circuit to "switch" the transistor, but still need to understand the operation. Need help :)

Here is the Fairchild's application note:
Click to expand...


provide
transformer details

- - - Updated - - -

pls provide transformer details
 

Re: Help needed: To understand SMPS mobile charger schematics.

Transformer -primary 200 turn-40SWG; secondary 30 turn-32SWG; f/b 30 turn-40SWG with E19.
 

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