AP4300
DC Input, Isolating Signal Conditioner

The AP4300 is useful in eliminating ground loop problems in existing systems, and is a preventive measure in the design of new systems. The DC input/output isolation allows a difference in potential of up to 600V between the input and output ground. This allows the benefits of grounded inputs to be realized, without creating ground loops.

The DC input is amplified and filtered before being fed to a comparator. The comparator, in conjunction with a precision-ramp generator, outputs  duty-cycle which in turn drives an optical isolator. The photo-isolator accurately reproduces the duty-cycle and provides an isolated signal. The isolated duty-cycle is then converted back to a DC level proportional to the input. The DC signal is then buffered by an output stage which allows zero and span adjustments. In units having a current output (e.g. 0-10V) the output is taken directly from the discrete driver transistor of the buffer stage. The internal power supplies for the input and output circuitry use independent transformer secondary's to maintain isolation.