Posted by Circuits Arena on Saturday, 17 January 2015
Automatic On and Off Lamp is the artlcle explaining Automatic On and Off Lamp : The circuit uses a transformer-less power provide to get low-volt DC. As capacitors C1 and C2 ar connected in...
Automatic On and Off Lamp :
The circuit uses a transformer-less power provide to get low-volt DC. As capacitors C1 and C2 ar connected in AC lines, these ought to be X-rated capacitors. This minimises area and makes the unit light-weight. in contrast to a standard electrical phenomenon power provide, a additional economical power provide style is employed for spike-free operation. part (L) and neutral (N) lines have identical circuits thus reversal in polarity whereas plugging won't have an effect on the circuit. 105K (1µF) 400V AC capacitors ar used which will drop 230V AC to low-level AC. Resistors R1 and R2 shield the facility provide from instant inpour current. sufferer resistors R3 and R4, parallel to C1 and C2, take away the keep current from the capacitors at power off to forestall shock from keep energy within the capacitors.
A rectifier bridge comprising D1 through D4 (1N4007) rectifies low-volt AC to DC and smoothing condenser C3 offers ripple-free DC for the circuit. The output voltage from the facility provide is enough to work the circuit as well as the relay. inexperienced LED1 indicates power-on standing. electrical device R5 limits diode current.
Fig.Circuit diagram of an automatic on and off lamp.
The circuit could be a easy bi-stable arrangement victimisation standard timer IC 555 (IC1). Linking its threshold (pin 6) and trigger (pin 2) controls its flip-flop operation. once the edge input is high, it resets the flip-flop and keeps the output low. once the trigger input is low, flip-flop triggers and output turns high. that the combined action of threshold and trigger inputs provides the bi-stable change action to regulate relay driver junction transistor T1. The bi-stable action of IC1 is controlled by LDR1 and resistance R6 (470k). the worth of 5mm LDR are often up to one mega-ohm, looking on the close lightweight conditions. A 1MΩ resistance in situ of R6 will create the sensitivity adjustment straightforward.
During day time, LDR1 has low resistance, that makes threshold pin half-dozen of IC1 high. This resets the timer and also the output of IC1 remains low. It takes junction transistor T1 to cut-off state. The relay is de-energised, that the lamp remains off throughout day time.
