What's wrong with this circuit? 12-0-12 1 Ampere Transformer Mobile Phone Charger?

Thread Starter

amit1972

Joined Sep 15, 2013
1
I have already build up a circuit with 12-0-12 1 Amp. Step Down Transformer against AC 220-240~. Connected bridge rectifier with 4 pcs. of IN4007
Diode 470 micro farad 50 volt electrolytic capacitor supplying 15.49 DC going to breadboard having 7805 Power Regulator IC with 470 micro farad in the output with 5.1volt Zener Diode. After that connecting USB jack to my Android phone. My phone is taking charges but as the time goes, voltage drops up to 4.42 Dc & taking long time for the ampere to fluctuate continuously e.g. .32mA max to 00 mA lowest?

Where is the fault actually ? Why it doesn't give constant output of 5 /5.01 volt dc with a constant Ampere during charging of my Android Phone ?

Awaiting for your valuable suggestion ?

Regards,

amit
 

#12

Joined Nov 30, 2010
18,186
I'm thinking the power dissipated by the 7805 chip might be overheating it so it goes into safety mode. How hot is it?
Did you install the capacitors required to avoid the chip going into oscillation?

You can not expect that regulator chip to be accurate to 5.01 volts (2/10 of a %) but you can expect it to be stable at whatever voltage it actually produces. Also, the voltage supply is not in charge of forcing a constant current into your battery, the phone is in charge of that.

Annnd..he logged out in 2 minutes. Nothing to see here. Move along.
 
Last edited:

hp1729

Joined Nov 23, 2015
2,304
I have already build up a circuit with 12-0-12 1 Amp. Step Down Transformer against AC 220-240~. Connected bridge rectifier with 4 pcs. of IN4007
Diode 470 micro farad 50 volt electrolytic capacitor supplying 15.49 DC going to breadboard having 7805 Power Regulator IC with 470 micro farad in the output with 5.1volt Zener Diode. After that connecting USB jack to my Android phone. My phone is taking charges but as the time goes, voltage drops up to 4.42 Dc & taking long time for the ampere to fluctuate continuously e.g. .32mA max to 00 mA lowest?

Where is the fault actually ? Why it doesn't give constant output of 5 /5.01 volt dc with a constant Ampere during charging of my Android Phone ?

Awaiting for your valuable suggestion ?

Regards,

amit
Hmmm ... 15 V in, 5 V out means 10 v dropped across the regulator, at how much current? Gives a total of how much power? From your description I agree, getting too hot. Heat sink time.
 
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