Isolated Voltage Sensor Saved

This circuit measures an isolated voltage. First is a difference amplifier that scales the voltage to a low range. The difference amp. also includes a single-pole, low-pass filter. The signal then goes to an optical isolation circuit based on Broadcom's HCNR201 integrated circuit. The isolation circuit provides closed loop linear isolation and low pass filtering. The current controlled current source is a LED and photo-diode pair.