Line-voltage-automatic-night-light

Description: This circuit exhibits stable threshold characteristics based on the photo-diode current in the Ll4Cl, which generates a base-emitter voltage drop across the sensitivity setting resistor. The double phase shift network that supplies voltage to the ST-4 trigger ensures triac triggering at line voltage phase angles small enough to minimize radio frequency interference (RFI) issues with a lamp load. This design eliminates the necessity for a large, expensive inductor, incorporates the dV/dt snubber network, and utilizes lower voltage capacitors compared to the snubber of the RFI suppression network typically employed. The addition of a programmable unijunction timer can modify this circuit to turn the lamp on for a fixed time interval whenever its environment becomes dark. Only the modifications to the previous circuit are presented for simplicity. When power is applied to the lamp, the 2N6028 timer initiates. Upon the completion of the time interval, the HllC3 is triggered, turning off the lamp by preventing the ST-4 from triggering the triac. The SCR of the HllC3 remains on until the Ll4Cl is illuminated, allowing the 2N6076 to commutate it off. Due to capacitor leakage currents, temperature variations, and component tolerances, the time delay may vary significantly from nominal values.

This circuit design effectively combines photo-sensing elements with a triac control mechanism, resulting in a reliable lighting solution that responds to ambient light conditions. The use of a photo-diode in conjunction with a sensitivity setting resistor allows for precise control of the base-emitter voltage, ensuring consistent operation across varying environmental conditions. The double phase shift network is critical in managing the timing of the triac's activation, providing a means to trigger the lamp efficiently while minimizing interference that could disrupt nearby electronic devices.

The programmable unijunction timer (2N6028) adds a layer of functionality, enabling the circuit to automatically turn on the lamp when ambient light levels drop below a certain threshold. This feature is particularly useful in applications such as outdoor lighting or automated indoor lighting systems, where energy efficiency and convenience are paramount. The timing mechanism is designed to be straightforward, with the timer initiating upon power application and triggering the HllC3 to deactivate the lamp after a predetermined interval.

The HllC3 SCR plays a vital role in the circuit's operation by ensuring that the lamp remains off until the Ll4Cl photo-diode detects sufficient light to allow the 2N6076 to turn off the SCR. This mechanism not only maintains the lamp's operational integrity but also enhances safety by preventing unintended activation.

It is important to note that variations in component characteristics, such as leakage currents in capacitors and temperature fluctuations, can lead to discrepancies in the timing intervals. Therefore, careful selection of components and consideration of their tolerances is essential for achieving the desired performance and reliability in real-world applications. This circuit represents a sophisticated blend of analog and digital techniques, providing an effective solution for automated lighting control.This circuit has stable threshold characteristics from its dependence on the-photo diode current in the Ll4Cl to generate a base emitter voltage drop across the sensitivity setting resistor. The double phase shift network supplying voltage to the ST-4 trigger insures triac triggering at line voltage phase angles small enough to minimize RFI problems with a lamp load.

This eliminates the need for a large, expensive inductor, contains the dV/dt snubber network, and utilizes lower voltage capacitors than the snubber of rfi suppression network normally used. The addition of a programmable unijunction timer can modify this circuit to tum the lamp on for a fixed time interval each time its environment gets dark. Only the additions to the previous circuit are shown in the interest of simplicity. When power is applied to the lamp, the 2N6028 timer starts. Upon completion of the time interval, the HllC3 is triggered and turns off the lamp by preventing the ST-4 from triggering the triac.

The SCR of the HllC3 will stay on until the Ll4Cl is illuminated and allows the 2N6076 to commutate it off. Because of capacitor leakage currents. temperature variations and component tolerances, the time delay may vary considerably from nominal values.