Friday, July 4, 2014

Variable LED Intensity Controller Circuit

The post presents a couple of simple LED intensity controller circuit which may be appropriately configured for specific related applications. The idea was requested by Mr. Chand.

The Request

Hello Swagatam

I would like to have a circuit designed by you which is very simple and straightforward. This will be incorporated as a stand alone feature in a device which I am working on. What my requirements are -

1. A row of 12 displays (1 seven segment type x 12)

2. A potentiometer with knob to control each display illumination individually ( so in all 12 pot knobs). Each knob increases or decreases the intensity value from 0 to 9 for its individual display.

3. A separate row of 3 displays (1 seven segment type x 3). Function remains the same as point number 2 above.

Please let me know the cost for this circuit along with the schematics.


Chand Sharma

The Design

The proposed LED intensity controller circuit may be learned as shown in the diagram.

Two diagrams can be seen, the left hand side may be used for controlling common anode type displays while the right hand side for common cathode types.

The design is basically a common collector BJT circuit where the base potential of the relevant transistors get proportionately delivered across their emitter base terminals.

Thus by varying the potential at their bases the emitter potential is also proportionately varied with a range right from 0V to the maximum supply voltage level (-0.7V).

Each of the following LED intensity controller modules could be used for the proposed 7 segment LED display control application. The preset may be replaced with a pot and its dial appropriately calibrated for getting the intended varying illumination through a range of 0 to 9.

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