Abstract: This application note describes the use of a current-sense amplifier along with an optocoupler to extend the operating voltage range up to 1,000 volts for high-voltage applications. The circuit relies on the optocoupler's isolation barrier to separate the high-side and grounded side of the 1,000V system. Op amps are used to eliminate photodiode non-linearity and drift and provide an accurate output voltage proportional to the load on the 1kV supply.