Low Voltage CircuitPower Supplies

Solid-State Light-Sensitive Switch Schematic Circuit Diagram

Direct Mains Connection for Efficient Electronic Switching

Solid-state light-sensitive switch: This electronic switch is specifically engineered for direct mains connection, eliminating the need for a low-voltage supply and thereby minimizing both cost and space requirements. The circuit’s primary function is to activate a lamp in low-light conditions and deactivate it when the ambient light increases. Notably, the switching process occurs without the use of a relay, mitigating issues related to sparks and mains pollution arising from contacts and coil inductance.

Mains-Powered Switch Operation through Integrated Components

The switch derives power directly from the mains through components R10, C4, D3, D2, and C3. A voltage reference, D1, provides a constant 8.2 V to a light measuring network comprising R2-P1. As the light intensity diminishes, the light-dependent resistor (LDR) R2 experiences an increase in resistance. Consequently, the voltage across P1 decreases, leading to a reduction in the gate-source voltage of FL’T’T1. When switch S1 is closed, the combination of R3 and C2 establishes a time constant that ensures the gate voltage of T1 changes more gradually than the resistance of R2. This deliberate design choice prevents the circuit from reacting to rapid fluctuations in ambient light intensity.

Solid-state light-sensitive switch Schematic diagram

Schmitt Trigger Formation with Components T1, T2, R4, R5, Re, and R8

A Schmitt trigger is configured by combining components T1, T2, R4, R5, Re, and R8. Under normal conditions, T1 is in a conducting state, keeping T2 turned off. When the gate voltage of the VET falls below a specific threshold, T2 is activated. As a result, T3 begins conducting, providing the necessary gate current to trigger Tri1. This action leads to the activation of the load, Lamp Lai. Conversely, when the light intensity surpasses the level set by P1, T1 is activated, causing the load to be deactivated.

Inclusion of Switch S1 and Resistor R9 for Circuit Control

Switch S1 is incorporated to temporarily disable the time constant during adjustments. Additionally, resistor R9 plays a crucial role in discharging capacitor C4 after the circuit has been disconnected from the mains.

Safety Warning: High-Voltage Precautions and Electrical Insulation

Due to the presence of dangerous voltages at various points in the circuit, it is imperative to ensure proper electrical insulation. Work on the circuit should never be undertaken when connected to the mains. It is essential to verify that no part of the circuit is accessible during setup, adjustment, or operation.

 

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