as_CIRCUIT_LED_POWER_INDICATOR

Published:2009/7/9 5:21:00 Author:May | From:SeekIC

Many electronic circuits need an indication that they are under power; for most ac circuits, a neon lamp is the device of choice. A bidirectional tricolor LED can be used if a capacitor is connected in series with the LED to limit the current through the LED. A1-μF, 250-WVdc capacitor, which has a reactance of 2650 ohms at 60 Hz, is used in series with an LED to limit the current through the unit to 43 mA. The impedance of the LED is low compared to the reactance of the capacitor, so nearly al the impedance will be caused by the capacitor with the added advantage of no energy loss caused by the capacitor. The power of the LED is 1.175Vx0.043 A=50 mW compared to an NE-2H at 250 mW. For 230V, use a 0.47-μF, 400-WVdc capacitor.



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