Twilight switch on lighting. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Twilight switch on lighting. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Lighting

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The main function of the proposed system is to turn on the lighting (or other electrical load) at the moment the illumination level drops below a certain threshold. This is a typical twilight switch with one exception: systems of this type usually turn off the lights at dawn, and the proposed system is equipped with a built-in timer control that turns off the device after a certain period of time.

A typical application of the proposed device may be garden lighting or lighting of outbuildings. After dark, the lighting turns on and off, depending on the programming option of the device, after 2, 4,6, 8 or 12 hours. The device has a built-in protection system against short-term operation of lighting before premature reactivation.

Regardless of the function of the twilight switch, the device can also work as a normal timer, triggered by an impulse or a logic level, turn on the lighting or connect another load.

In addition, the timer has an additional very interesting function - detecting the moment the voltage passes through zero and turning on the triac at that moment. This eliminates the need for a variety of filters to suppress interference.

The figure shows a diagram of a twilight switch.

(click to enlarge)

Technical specifications

Load power, W......1000
Supply voltage NT1315, V......3...5
Current consumption NT1315, uA......25-50
Maximum triac control current, mA......7

The device is built according to a typical circuit based on the IC NT1315, which is powered from the mains voltage of 220 V through the diode D1. The voltage level is set using a divider on resistors R6 and R7, the zener diode D2 maintains a stable voltage.

Triac Q1 is controlled by short pulses from the output of TRIAC IC1. Synchronization with the network and detection of zero crossing is provided by the resistor R5, which is connected to the ZC (Zero Crossing) input.

The timer can be started in three ways.

1. When the voltage at the CDS pin drops below half the supply voltage. This situation is possible when the resistance of the photoresistor, with a decrease in illumination, increases to 220 kOhm. This state should last for about 1 minute, which eliminates possible interference and prevents the timer from starting in case of short-term changes in the light level. It should be noted that the value of the resistor R3 must be selected depending on the type of photoresistor used in the device.

2. When a negative pulse is applied to the ONESHOT input with a duration of more than 60 ms.

3. When submitting a low log. input LEVEL

The timer on time is set using jumper JP1.

The permissible load power depends on the type of triac used and the availability of good cooling.

Author: A.Yarug

See other articles Section Lighting.

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