Specifications

Driving Inductive Loads
Question: How can I drive an inductive load or a large electro-magnet with a power supply?
Answer: One of the popular uses of Agilent power supplies is driving large magnets. Magnets are commonly used in
several industries including nuclear fusion research and magnetic resonance imaging. However, there are a couple of
problems that can arise in these applications.
Power supply oscillation can occur when driving an inductive load or magnet.
It may be difficult to ramp the current through the magnet fast enough (especially withcryogenic magnets).
Since a magnet is basically a large inductor, the power supply must be stable when driving a large inductive load.
Inductive loads present no stability problems in the CV mode, however, in the CC mode a parallel resonant network
is formed by the inductance of the load and the output capacitance of the power supply. This can cause ringing, or
even oscillation at a frequency given by the formula:
Frequency of oscillation = 1 / [(2)(3.1416)(LC)^.5]
Also, the rate of current flow through a magnet is determined by the formula: di/dt = L/V
The larger the magnet, the higher the voltage must be to drive it at a given ramp rate. The power supplies maximum
voltage ratings may be insufficient for these applications. In other cases, a higher current may be needed than one
power supply can provide. Paralleling power supplies to get more current for driving magnets increases the
possibility of oscillation problems, which can destroy the DUT (Device Under Test).
The solution to these problems is to use a power supply that has stability for inductive loads either built-in, or
provided as a special option. Here are some examples:
6680A and 6681A (5 kW): have internal stabilization for loads up to 7 Henrys
6010A*, 6011A, 6012B*, 6030A, 6031A, 6632A and 6038A* have special options available:
Option J01 - stabilization for loads up to 10 Henrys
Option J02 - stabilization for loads of 10 to 25 Henrys ( * = J02 not available for these supplies)
For driving inductive loads when using the 664x, 665x, 667x and 668x supplies, refer to their Operating Manuals to
understand power supply stability. Contact your local Sales Office for information about specials for these and/or
other Agilent power supplies.