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..
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
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
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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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