Techniques used for isolation amplifiers

The increasing use today of switch mode techniques for power control and conversion have increased the requirements such that both voltage and current from DC to high frequency need to be measured. A commonly encountered problem is the direct on line power supply. The incoming mains supply is bridge rectified, smoothed by a large capacitor and the resulting DC used to power the switching circuitry. This is all elegantly simple except that the negative rail is superimposed on a 350 V half sine wave and all the control signals which are only a few volts in amplitude are swamped. Enter the isolation amplifier. Modern isolation amplifiers have become quite sophisticated devices mainly because of the difficulties of transferring the DC component of the signal across the isolation barrier. Several methods to overcome this problem are in use, the most common of which is described