<H3 class="post-title entry-title" align=left>Simple Emergency Light Circuit
This is a design for simple emergency light. This circuit is work automatically. The circuit is work based on power failure. This is the figure of the circuit.
[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]
Operation of the circuit is the circuit remains OFF when the mains power is available and switches ON when there is a power failure. When mains power is available, it is stepped down by transformer T1, rectified by diodes D1&D2, filtered by the capacitor C2 and regulated by the 9V regulator IC 7809 to produce 9V DC. The transformer T1 can be a 230V AC primary, 12 – 0 - 12V secondary, 500mA transformer. This 9V DC is used for charging the battery. While the battery is charging the diode D3 is forward biased and this makes the emitter potential of transistor Q1 lower than the base potential and this makes the transistor OFF. The lamp will not glow.
When AC mains is not available, the diode D3 will be reverse biased and this makes the emitter potential of transistor Q1 higher than base potential and Q1 becomes ON. The lamp glows and continues to glow as long as there is no mains supply. The capacitors C1 and C3 act as decoupling capacitors. Battery B1 can be a 6V lead acid battery or five 1.2V Ni-Cd cells in series. The fuse F1 can be a 0.5A one.