Control013

                                          

Brightness Control for Small Lamps
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Schematic design of Brightness control for small lamps
Part List :
Capacitors	Resistors
C1        =   22 nF / 63V Polyester C2        = 100 μF / 25V Electrolytic Diodes D1,D2= 1N4148 Semiconductors IC1       = 7555 or TS555CN Q1        = BD681	P1     =   470K Ω Linear potentiometer R1     =     10K Ω ¼W R2     =     47K Ω ¼W R3     =     1K5 Ω ¼W Others SW      = SPST Switch LP1      = 1.5V 200mA Bulb B1        = 3V (2x1.5V AA/AAA cells in series,etc)
Notes
Switching operated 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) for close-up pictures with a digital camera, powered by two AA or AAA batteries. Obviously it can be used in other ways, at anyone's will. IC1 generates a 150Hz squarewave 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. Lamp 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 lamp reaches its full brightness. LP1 could be one or more 1.5V bulbs wired in parallel. Maximum total output current allowed is about 1A.     R2 limits the output voltage, measured across LP1 leads, to 1.5V. Its actual value is dependent on the total current drawn by the bulb(s) and should be set at full load in order to obtain about 1.5V across the bulb(s) leads when P1 is rotated fully clockwise.

Source : Electronics Lab