A capacitive dropper is one simple method used in some transformerless power supply circuits. In this method a capacitor is connected in series with the AC supply to limit the current going into the circuit.
This calculator helps us to find the theoretical capacitor value according to the input AC voltage and required current.
Capacitive Dropper Calculator
Enter the AC supply voltage and required current to calculate the theoretical dropper capacitor value.
This type of supply is not electrically isolated from the mains. The calculated capacitor value is only an ideal estimate. Actual DC output current depends on the rectifier, filter capacitor, load and circuit design. Use a certified isolated AC-to-DC power supply for touch-accessible equipment.
Enter the values and click Calculate.
Formula used: C = I / (2 × π × f × V). Current is entered in amperes and capacitance is converted to microfarads.
This formula estimates the capacitance for an ideal AC current. It does not guarantee the same DC output current from a rectifier-based power supply.
How it Works
First enter the input AC voltage in volts. For example if the supply is 230V AC then enter 230.
Next select the AC frequency. This will normally be 50Hz or 60Hz depending on the mains supply.
Now enter the required current in milliamps. For example if you want to calculate the capacitor value for an ideal AC current of 50mA then enter 50 in the current box.
After entering these values click the Calculate Capacitor button. The calculator will show the theoretical capacitance value in microfarads.
The working is quite simple. When the AC frequency or supply voltage is increased the same capacitor can pass more current. Similarly if we want more current from the capacitor then a higher capacitance will generally be required.
But note this...the current entered in this calculator is an ideal AC current estimate. It does not mean that we will get exactly the same current at the DC output after connecting a bridge rectifier and filter capacitor.
The actual DC output current depends on the complete circuit and the type of load connected to it. So the calculated capacitor value should not be treated as the final value for building a practical power supply.
Also remember that a transformerless capacitive dropper does not provide electrical isolation from the mains. Its DC output can be at a dangerous mains potential even when the output voltage looks low. For any equipment which can be touched by a person it is much safer to use a properly rated isolated AC to DC power supply.
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