making usb mobile charger help

Thread Starter

Asad ahmed1

Joined Feb 10, 2016
68
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 ....
 

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bushrat

Joined Nov 29, 2014
209
Post a schematic of what you have completed so far, it will help everyone see what you are doing.

Using one diode, you are only getting half of sine wave, capacitor will discharge lower, and you will see ripples on your 7805, see this link
Using full bridge rectifier, capacitor will remain charged (close to full charge) and it will have less ripples on your 7805, see this link
 

Thread Starter

Asad ahmed1

Joined Feb 10, 2016
68
Post a schematic of what you have completed so far, it will help everyone see what you are doing.

Using one diode, you are only getting half of sine wave, capacitor will discharge lower, and you will see ripples on your 7805, see this link
Using full bridge rectifier, capacitor will remain charged (close to full charge) and it will have less ripples on your 7805, see this link
my circuit is same as this the difference is that I stepped the ac voltage down to 5.7 V and in place of 3300nf I placed 3 4 capcitors .after that i placed the 7805 ic and placed 0.1 uf there ...the output came 4.95
 

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bushrat

Joined Nov 29, 2014
209
..so are you using AC to convert into DC or are you using a battery of higher voltage and a transformer to step it down to lower voltage?..
 

bushrat

Joined Nov 29, 2014
209
Be careful when working with high voltage AC, it hurts.
Stepping voltage down to 5.7 v can cause problems on your voltage regulator. Can you set it at somewhere between 9-24 V?

 

bertus

Joined Apr 5, 2008
20,326
Hello,

With 5.7 volts from the transformer and a bridge rectifier with e decent capacitor, you will get about 6.66 Volts at the input of the regulator.
As the regulator needs at least 2 Volts higher input voltage as the output voltage, you will have troubles with the regulation.
Either use a transformer with a higher output voltage or use a Low Drop Out regulator.

Bertus
 

bushrat

Joined Nov 29, 2014
209
For 7805 to work properly, it needs minimum 7 V to operate. If you look on the datasheet, it says that 7805 has 2V dropout, and maximum input voltage is 35V.
5.7V will not work properly for you. If may work if you hvae no load, but once you connect something, the voltage will drop even lower, below 5 V.
 

Thread Starter

Asad ahmed1

Joined Feb 10, 2016
68
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