avinash.kashyap
Junior Member level 3
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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 MCSMPS.JPG](https://www.edaboard.com/data/attachments/12/12838-63a375aa910888949665d9250f279838.jpg)
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This seems to be an oscillator circuit to "switch" the transistor, but still need to understand the operation. Need help![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Here is the Fairchild's application note:
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 MCSMPS.JPG](https://www.edaboard.com/data/attachments/12/12838-63a375aa910888949665d9250f279838.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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