Brightness Controller Circuit For Small Lamps and Leds

Switch-mode driven 1.5V bulb, 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.




Circuit diagram:



Brightness Controller Circuit For Small Lamps and Leds



Parts:

P1 = 470K
R1 = 10K
R2 = 47K
R3 = 1.5K
C1 = 22nF-63V
C2 = 100uF-25V
D1 = 1N4148
D2 = 1N4148
Q1 = BD681
B1 = 2xAA cells in series
IC1 = 7555 or TS555CN
LP1 = 1.5V 200mA Bulb
SW1 = SPST Switch



Notes:


Source: Red Free Circuit Design