Turning on the light bulb with two switches. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting
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This circuit is designed to turn off the lighting using two switches remote from each other. The light is on when only one of the switches is closed. If both switches are closed or open, then the light is off. Schemes based on the EXCLUSIVE OR logical element work according to the same algorithm.
The circuit assembled on two electromagnetic relays (Fig. 1) is self-explanatory. Figure 2 shows a diagram without a relay. If only one switch is closed in it, for example, SA1, then a voltage close to the mains voltage appears on the capacitor C1. In this case, the capacitor C2 plays the role of reactance, through which the current is supplied to the diode bridge VD1 ... VD4, and then to the LED of the optocoupler VU1, the diode bridge VD8 ... VD11 and the control electrode of the triac VS1. The triac opens and the light is on.
Rice. 1. Scheme on two electromagnetic relays
Rice. 2. Circuit without relay
If both switches are closed, then equal voltages applied to C1 and C2 are subtracted from each other, and the LED in the VU1 optocoupler does not work. It also does not work if both switches are open. In these cases, the light is off.
At the moment of switching, the resistance switches R1 and R2 limit the current flowing through the capacitors C1 and C2, and the diodes VD5 ... VD7 and the resistor R5 limit the current through the LED of the optocoupler VU1. With a load of not more than 100 W, the VS1 triac is used without a heatsink. To calculate the current flowing through the capacitors C1 and C2 when one of the switches is on, you can neglect the resistances R1 and R2, the voltage drop across the diode bridge VD1 ... VD4 and use the equivalent circuit shown in Fig. 3.
Fig. 3
In this circuit, the effective value of the current flowing through each capacitor is:
where Ueff - effective voltage value (Ueff = 220 V); R=R1=R2=510 OM; f = 50 Hz; C \u1d C2 \u0,22d CXNUMX \uXNUMXd XNUMX uF.
Author: D.Novotorov, N.Novgorod; Publication: radioradar.net
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