transformerless power supply 5A

[antoine magdi]

I read everywhere that the disadvantages of a transformerless power supply;
it only supplies small curent....
can anyone help me in the uploaded schematic to tell me if there is a problem in such a cuircuit to supply 5A....

 

[ericgibbs]

I read everywhere that the disadvantages of a transformerless power supply;
it only supplies small curent....
can anyone help me in the uploaded schematic to tell me if there is a problem in such a cuircuit to supply 5A....

hi,
Work out the capacitive reactance of a 0.55uF cap at 50Hz...post what you get.

Formula: Xc= 1/[2*pi*50*0.55*10^-6]

 

[antoine magdi]

Irms=Vrms/Xc
Irms=311*[2*pi*50*0.55*10^-6]=5A
is that you mean?!

 

[ericgibbs]

Irms=Vrms/Xc
Irms=311*[2*pi*50*0.55*10^-6]=5A
is that you mean?!

hi,
Xc= 1/[2*pi*50*.55*10^-6] = 5.79K

So Current = 220/5790 = 0.038A.!

To get 5A from 220Vac the Xc would have to 44R. thats about 70uF.

EDIT: where did you get the circuit.?

 

[antoine magdi]

it's a circuit of an power supply with a transformer and i edited it....

ok, if i put C1 equals to 70uF, it will work without any damage as a transformerless power supply which supplies 5A

THANX FOR HELPING ME!

 

[blueroomelectronics]

Have you priced out high voltage bipolar 70uF caps? Can you even buy them?

 

[ericgibbs]

it's a circuit of an power supply with a transformer and i edited it....

ok, if i put C1 equals to 70uF, it will work without any damage as a transformerless power supply which supplies 5A

THANX FOR HELPING ME!

hi,
The cost of buying caps to make up 70uF is very expensive and very bulky.!

You would need about five 16uF 250Vac motor start caps, thats about £100ish.
Also the zener diode would have to conduct 5A when the load is disconnected, thats approx 5V *5A = 25Watt! zener,

Its a very bad idea.

Buy a 9V 5A mains transformer. say 50VA for about £10 and make a safe power supply.

 

[antoine magdi]

thanks everyone for help...

 

[blueroomelectronics]

You can buy small light 5V @ 2A switchmode wall adapters pretty cheap. I can get them from Sayal here in Toronto for about $2.50