The Resistive Power Supply
When designing a resistive power supply, the value of the “dropper resistor” is obtained by taking 12v from 240v = 230v. This is the voltage across the dropper resistor.
Let us allow 20mA current through the dropper resistor.
The value of the dropper resistor is: 230/0.02 = 11,500 ohms = 11k5.
The wattage of the resistor = 4.6watts The resistor can be made up of a number of resistors placed at different locations on the board to improve heat dissipation.
You can see the advantage of a capacitor-fed power supply.
