Saturday, 30 June 2012
VERSATILE VACTROL LED DRIVER:
HOW IT WORKS:
The operational amplifier is configured as a voltage adder / summer, meaning that it adds the input voltages toghether and this becomes the output voltage. It is also an inverting amplifier, that is that its output voltage falls as the inputs become more positive. In order that the LED current moves in the same sense as the inputs, the LED and its resistor are connected the other way round and returned to the +ve supply rail.
By cascading two of the simple vca's an improved vca can be made, this of course requires two vactrols. The right hand opamp acts as a buffer, to the output of the second stage but also provides some amplification to overcome the losses in the resistor networks.
COMPLETE VACTROL BASED VCA