AC MAINS LED indicator schematic

Posted on Mar 9, 2013

Often the need to control light switch on the instrument. If napájíme LED source of low DC voltage sufficient to classify a series of LED-resistor of appropriate resistance. Another situation occurs, if a small supply available, or to indicate when the voltage needed before the safety equipment supplied. In such cases, has been used for many years with the glow resistor ballasts, see Figure 1 . This solution is not very elegant, but it is reliable and relatively inexpensive. Network lights, we can produce LED. Use a resistor, however, precipitation in this case is not appropriate. While neon is an operating voltage of 70-150 V and current of only a fraction of mA, standard LED current requires about 10 mA at a voltage of about 2 V. Involvement with LED lights is the figure 2.

AC MAINS LED indicator schematic
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AC MAINS LED indicator schematic - image 1
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AC MAINS LED indicator schematic - image 2
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AC MAINS LED indicator schematic - image 3
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Consider, however, this involvement in more detail. The joke is that the current through the LEDs is limited by the resistor, but the capacitor capacitance. Capacitance can be chosen so that the current through it can directly regulate the power LED. Since the current leads voltage by 90 degrees, does not arise in the (ideal) capacitor is no capacitor power loss and does not heat. Reactance of the capacitor can be easily calculated where Xc is capacitive reactance in ohms, pi pi (3.14 ..), f frequency in Hz and C capacitance in farad. Capacitor with a capacity of 100 nF will have the network frequency reactance 1 / (2.3, 14.50.10 -7) = 31,831 ohms. If you connect this capacitor to the voltage, current will flow through it 230/31831 = 0.0072 A. If you connect a capacitor in series with the LED bridge rectifier according to Figure 2 , the stream has been substantially altered. In terms of functionality is more important often overlooked resistor R2. In practice, it is only rarely will switch on the device when the voltage is currently close to zero. Reflective nature can be calculated that half the time the phase conductor to zero even more effective than the reported 230 V. When your pilot light, it must be possible to charge capacitor C1. At this moment pass capacitor (and thus the LED) current pulse, which can be several orders of magnitude larger than the steady alternating current. The current pulse there will...

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