[GreenKeys] Loop driver question

[Jeffrey D Angus]

A series resistor and a high voltage approximates a current source.

A current source by definition has to have a "infinitely high" voltage
to be able to source a given current through a "infinitely high"
resistance.

The limit of the maximum voltage is called "compliance." In a typical
DC loop supply, that limit is 120 VDC.

The rise time of the current in an inductor (such as a selector magnet)
is limited by the maximum voltage available to overcome the
initial impedance of the selector magnet.

Using a current source instead of a fixed resistor allows the effective
series resistance to drop to zero if need be to force the current to
the set value as quickly as possible then rise to the value needed to
maintain the set current.

A 120 VDC supply with an approximately 2000 ohm resistor is the
epitome of simplicity.

Jeff-1.0
wa6fwi