Brightness Control for small Lamps by IC 555

Switch-mode driven 1.5V bulbs
Portable unit – 3V battery supply
This device was designed on request, to control the light intensity of four filament lamps (i.e. a ring illuminator) powered by two AA or AAA batteries, for close-up pictures with a digital camera. Obviously it can be used in other ways, at anyone’s will.
IC1 generates a 150Hz square wave having a variable duty-cycle. When the cursor of P1 is fully rotated towards D1, the output positive pulses appearing at pin 3 of IC1 are very narrow. Bulb LP1, driven by Q1, is off as the voltage across its leads is too low. When the cursor of P1 is rotated towards R2, the output pulses increase in width, reaching their maximum amplitude when the potentiometer is rotated fully clockwise. In this way the bulb reaches its full brightness.

Parts:
P1________________470K Linear Potentiometer
R1_________________10K 1/4W Resistor
R2_________________47K 1/4W Resistor (See Notes)
R3__________________1K5 1/4W Resistor
C1_________________22nF 63V Polyester Capacitor
C2________________100µF 25V Electrolytic Capacitor
D1,D2___________1N4148 75V 150mA Diodes
IC1_______________7555 or TS555CN CMos Timer IC
Q1_______________BD681 100V 4A NPN Darlington Transistor
LP1_______________1.5V 200mA Bulb (See Notes)
SW1_______________SPST Switch
B1__________________3V (Two 1.5V AA or AAA cells in series, etc.)

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Thank you.

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