making usb mobile charger help

Thread Starter

Asad ahmed1

Joined Feb 10, 2016
68
your mains transformer must be low current, or the regulator is using a lot of current and pulling the supply down.
It gave me 5.7 V I would apply bridge rectification but it makes my output to 3 volts because of rectifiers Iam going to get a new transformer old charger transformer is not coming handy ...
i want to ask that why our modern charger dont use the bridge rectification at the end
i saw the inside circuit they first bridge rectify the input ac to dc then they pass it to MOSFET to get high frequency Square wave after that they pass it to transformer and step the voltage down and after that there was only one rectifier and capacity what would happen if there was a bridge rectifier ...I get the idea that in order to make the size of capacitor short we increase the frequency ..why they dont just put the bridge rectifier ...
 

turbo1600

Joined Jan 12, 2016
7
First I put the step down transformer to get 5.7 volts then I put a diode and bunch of capacitors after that I put 7805 ic to get constant 5 volts but my out is 4.95 ...will it works ..is my circuit is correct for charging and giving constant supply..
I made bridge rectifier but it reduces my output ....
hi, you say you got 5.7 v , then u put a diode in which will bring voltage to about 5.3 v, then your using a regulator , but the 7805 will need a input of 2-3 volts more than output voltage..
 
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