- on Miscellaneous Electronics
- Published in issue 3/2002 on page 0
Capacitor as AC Voltage Dropper
transformerless power supply
Some designs, because of lack of space or for some other reason, do not use a power supply transformer. Instead, an ‘AC voltage dropper’ in the shape of a capacitor is fitted. On more than one occasion readers have asked us the details of how this works and how the value should be calculated.If the power supply for (part of) a circuit requires only a few milliamps from the mains the well-known ‘transformerless’ solution is frequently used. Here, a capacitor is used as an ‘AC voltage dropper’. This method is not actually used all that often, because the advantage of the smaller size is offset by the disadvantage of reduced electrical safety. Observe that the power supply is coupled directly to the mains and this is not really that elegant a solution, of course.