Transformer less power supply??

[ambi]

Hii genius.. :smile:

I am designing the x-rated capacitor power supply for my project ..
i need 5v 300mA output from 230v input
Pl suggest me that what range of x-rated capacitor must be added at input to get desired output of 300mA?

Thank you

 

[KlausST]

Hi,

no schematic, no frequency. so we need to guess..

the lowest possible capacitor value for 230V and 300mA is.

xc = 230V / 300mA = 767 Ohms

c = 1/(2 * Pi * f * xc) = 4.2 uF (for 50Hz)

But must probably you need much more.

is it available as X2?

Klaus

 

[ambi]

Here is the example diagram

Frequency is 50Hz
and no X2 :|

 

[KlausST]

Hi,

the problem with your circuit is, that even if your circuit draws no load, then at least 5V x 300mA = 1.5W is dissipated in the zener.

My estimation: about 10uF.
Mind the power dissipation of the zener, mind to adjust R2.

a transformer may be lower power, smaller, cheaper...

Klaus

 

[Vbase]

Hii genius.. :smile:

I am designing the x-rated capacitor power supply for my project ..
i need 5v 300mA output from 230v input
Pl suggest me that what range of x-rated capacitor must be added at input to get desired output of 300mA?

Thank you

You will get high ripple on the 5V because the 470uF charges to 5V and when the 230VAC is 0 the voltage on the cap will drop. If you add a resistor of 22R between the zener and the 470uF and add another 470uF across the zener the ripple will be much smaller.

 

[schmitt trigger]

View attachment 116594

Here is the example diagram

Frequency is 50Hz
and no X2 :|

What you would have to do, is then to parallel enough X2 capacitors to obtain the required capacitance.

Since X2 caps are not cheap, you may find out when you actually take the costs of all the components, that a small 2VA rated transformer could actually be similar or lower in price.
In the past, I've done that same analysis, and found out that transformerless supplies ara cost-effective for currents below 150 ma.