Using a comparator (one section of a LM3900) I connect the (+) input to a
source voltage via a 1K resitor.
The source is obtained from a series load resistor, so that as the load
varies so does the source voltage to the (+) input.

The (-) input is connected to the wiper of a 5K pot. The comarators open
collector output via 2K2 to pos supply.

The idea is to compare the two inputs so that a signal can be detected at
the output of the comparator depending on the level applied to the (+)
input comared to the setting on the (-) input. Normal comaparator operation.

All unused terminals grounded, the chip supply is decoupled.

The problem I am experiencing is that the voltage on the (-) input is also
varying slightly in sympathy to the varying voltage on the (+) source input,
enough so as to prevent the comparator from operating when set to small
values, ie: 0.8 volts.

Example:
The (-) input is set to 0.8 volts.
With the equipment output circuit running at normal load the applied source
voltage on the comarators (+) input is 0.5 volts.
When the output load is increased the source voltage at (+) input increases
accordingly, but so to does the voltage at the (-) input. The result is that
the comparator does not "compare" at the expected point( 0.8volts) - if at
all. Sometimes the preset voltage on (-) keeps lifting to a level above the
source with the result that the comarator does not trigger.
Does anyone know how to overcome this "voltage creep"? What should I do to
prevent it?

I hope I have explained the problem adequately.

Any assistance appreciated.

**********************************************
Time is a great teacher, but unfortunately it kills all its pupils
-- Hector Berlioz