i have to get the output voltage of 20v from 230v Ac. without using the step down transformer. i Have a idea of connecting the higer watt resistor to get the required output. But i m not aware of how much watts should be connected to get the required output. Is there any calculation to get the accurate watts resistor to get the required output.
simple law...
P = I*V or
P = I*I*R
where P, is the power going to be disspated across the R and I,the current you r drawing through the resistor(from 230VAC) and R,of course the resistor value and V,210V(for ur application)
First, you must make sure what is your output load. Then from there you can calculte the value of current flows. Resistor watt required: (Output voltage of transformer - desired output voltege)x current.
It's a capacitive divider, like a resistive divider. You could built a divider with any component. Z1/(Z1+Z2)
It divide only the AC signal, and it works great only if the load is constant ( the voltage depend on the load...)
Without a transformer you cannot isolate from the mains, so be VERY careful. Don't count on the outlet being wired properly either. Tranformers are an important safety issue.