Night lamp using scrap CFL

An unserviceable CFL, the filament has reached the end of its life but
there is every possibility that the electronic ballast circuit inside
the bottom of the CFL is in working condition. The night lamp circuit
described here uses the serviceable electronic circuit fitted in the
base of an 11-watt CFL

 For constructing this night lamp, remove the CFL glass tube and replace it
with four white LEDs as described below. You should be careful not to
break the tube as it contains hazardous materials such as mercury.
Carefully open the base of CFL holder using an appropriate tool. You can
 see the electronic ballast circuit on a circular PCB

Use the components from the ballast circuit and a series combination of
four bright white LEDs as shown in Fig. 1. Remove all other components
from the original ballast circuit. As per the requirement of light
intensity in your room, you can increase the number of white LEDs up to
eight. As shown in Figure, the full-wave bridge rectifier
comprising diodes D1 through D4 converts AC voltage into DC voltage.
Snubber capacitor C1 at the input reduces the line input voltage of 230V
 to a very low-level AC voltage. Series current-limiting resistor R2 and
 series inductor coil L1 avoid voltage spikes. Fit the circular 

PCB in the waste CFL holder and your night lamp is ready for use.

Photo Timer Circuit

Time is set by potentiometer R2 which provides a range or 1 sec. To 100 seconds with timing capacitor C1 of 100uF. The output at pin 3 is normally low and the relay is held off. A momentary push on switch S1 energies the relay which is held closed for a time 1.1 X (R1+R2). C1 and then released. The exact length of the timing interval will depend on the actual capacitance of C1. Most electrolytic capacitors are rated on the basis of minimum guaranteed value and the actual value may be higher. The circuit should be calibrated for various positions of the control knob of R2 after the timing capacitor has had a chance to age. Once the capacitor has reached its stable value, the timings provided should be well within the photographic requirements.

Parts List


C1-100uF,25Velectrolytic
C2-0.01uF,discceramic
D1,D2-DR50or1N4001
R!,R2-10Kohms,¼watts
R3-1Mohms,potentiometer
RLY1-12V, DC relay, operating current less than 200mA
S1-Push-to-onswitch
U1-NE555timerIC


P1 & P2 are for exposure lamp ckt.