This is the schematic diagram of LED indicator for 220V AC Mains which can be used to indicate that the cable lines is connected to 220v electrical installations.
The current through the LED is not limited to the resistor, but the capacitance of the capacitor. The capacitance can be selected so that the current passing through it could regulate directly after power LED. Since the current leads the voltage by 90?, does not arise (ideally) no power loss of the capacitor and the capacitor is not heated. Reactance capacitor can be easily calculated with the following formula:
where Xc is capacitive reactance in Ohm, pi (3.14), f frequency in Hertz and C the capacitance in Farad.
A capacitor with a capacity of 100nF will have for grid frequency reactance:
1 / (2x3.14x50x10-7) = 31831 Ohm
If you connect this capacitor voltage network, it will be the power flow 230/31831 = 0.0072 A. If we connect in series with the capacitor bridge rectifier with LED, the current has substantially altered.
Resistor R1 has only one task – during off indicator light capacitor discharge and prevent unpleasant “kick” while handling the device off.
Warning: The entire circuit is connected to the high voltage electrical network. Therefore, it is necessary to work at maintaining the necessary caution.
source:http://www.belza.cz/ac-led/kontrol.htm
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Pleasde note that:
1. R1 must be rated for over 320V to survive peak mains voltage - thus usually needs a half watt resisitor or above.
2. R2 limits the inrush current at switch-on so that the rectifier diode bridge is not over loaded. It must also be rated for full peak mains pulse but does not need to be of a high wattage
3. C1 must be of the "X2" type so that it fails gracefully i.e.open circuits when overstressed.
4. The bridge rectifier diode can be quite small e.g. 1N4148 as ther only pass the LED current except at switch-on.
I want to use this circuit on a 12v system
Am impressed with those cct diagrams.I"ll start building some of them.