I have a minor problem !
I am using the power supply transformer on a circuit which dosent have a
constant load to measure the mains supply voltage on a '73.
Problem, transformer is only 6 VA load regulation is less than brillant
consequently measurements are not consistant depandant on the state of the
load.
I can provide an external voltage ref (TL431) and if a current sensing
resistor is placed in the -ve supply after the DC cap a current value can be
sensed if the TL431 ref is taken to the supply side then a load proportinal
voltage ref can be generated for the A-D
I need to measure a 3% supply window in the renge 207 to 277 v AC and a load
current varation of 100mA to 500mA at 12v this provides about a 12% secondary
voltage varation which needs corecting before measurements are taken.
Any body had this problem before ?.... Got a better idea ?........

Cheers Steve.......