part in the isolated feedback design and they must be accommodated in the part
value calculations. Optoisolators, for instance the C
trr
, can vary over a range of
300 percent, which may necessitate a potentiometer to be added to the circuit.
Some optoisolators are sorted by their manufacturers to a narrower C
trr
range,
but it is rare and not liked by them. The voltage reference should also be a
temperature-compensated variety, such as provided in the TL431.
The issue of output accuracy from unit to unit usually requires that the ref-
erence used be trimmed to two percent variation or less, and the resistors within
the resistor voltage divider be one ...