SCR LIGHT DIMMER

Provides full range of brightness control for up to 500 watts of lamps. The UJT Q1 generates turn-on pulses for SCR-L. Stern, "Thyristors Provide New Opportunities for Electronic Applications in the Home," Motorola Application Note AN-141, Dec. 1965.

The described circuit is a dimmer switch designed to control the brightness of incandescent lamps, with a maximum load capacity of 500 watts. The key component in this circuit is the Unijunction Transistor (UJT), labeled as Q1, which functions as a pulse generator. This UJT is responsible for creating the necessary turn-on pulses that trigger the Silicon Controlled Rectifier (SCR), referred to as SCR-L in the description.

The operation of the circuit begins when an input voltage is applied. The UJT Q1 is configured to operate in its negative resistance region, allowing it to generate a series of pulses. These pulses are fed into the gate of the SCR, which, once triggered, allows current to flow through the load (the lamps). By adjusting the resistance in the timing circuit associated with the UJT, the frequency and width of the pulses can be controlled, thereby regulating the amount of power delivered to the lamps and effectively dimming their brightness.

The SCR's ability to remain on once triggered makes it suitable for this application, as it continues to conduct until the current flowing through it drops below a certain threshold, at which point it turns off. This characteristic allows for smooth dimming without flickering, making it ideal for residential lighting applications.

The circuit design also includes safety features to prevent overheating and to ensure stable operation under varying load conditions. Proper heat sinking for the SCR is essential to manage thermal performance, especially when operating at higher power levels. Additionally, the circuit may incorporate filtering components to reduce electrical noise and improve performance.

Overall, this brightness control circuit exemplifies the application of thyristor technology in home electronics, providing users with enhanced control over their lighting environments.Provides full range of brightness control for up to 500w of lamps. Ujt Q1 provides turn. on pulses for scr-L. Stern, "Thyristors Provide New Opportunities for Electronic Applications in the Home, " Motorola Application Note AN-141, Dec. 1965. 🔗 External reference