Inductance - ILX Lightwave LDX-36000 Series User Manual

Inductance

An electric current i flowing around a circuit produces a magnetic field and hence
a magnetic flux  through the circuit. The ratio of the magnetic flux to the current
is called the inductance. The voltage developed across an inductance L (in
Henries), when the current is changing at a rate given by dl
V = Ldl / dt
The inductance of a circular conductive loop made of a circular conductor can be
determined using:
Where:
• 
• r is the radius of the loop
• a is the radius of the conductor
• Y is a constant. Y=0 when the current flows in the surface of the wire (skin effect), Y=1/4
From Equation 2, it is easy to see that the inductance of a conductor is directly
proportional to the radius of the conductor loop. A loop area is formed with wire
conductors from the source (anode) through the laser and returning (cathode) to
the source when they are physically separated.
Part of the 36000's laser diode protection strategy includes an adjustable voltage
limit where the instrument monitors the voltage across the load and compares it
against the programmable limit. In the event of an over-voltage condition, the
instrument will automatically disable the current source output. When the current
source output is enabled, depending on the setpoint, there is a large dl/dt. By
Equation 1, any additional inductance in addition to the inductance of the cable
may cause a voltage spike exceeding the programmed voltage limit and possibly
the maximum compliance voltage of the instrument causing an E-503 error. The
instrument control will disable the output in this event.
The output terminals are left floating relative to earth ground to suppress AC
power-on/power-off transients that may occur through an earth-ground path as
well as accommodate different laser packages and grounding schemes. If the
03_10
Note: With high currents, connections to the cable end or the laser should be secure and
tight. Avoid point contracts, maximizing surface area for connections is advisable.
Increased resistance due to poor connections will cause high voltage drops and I
heating which could be dangerous or damaging to improperly sized conductors and/or the
conductor insulation.
Equation 1
and 
are the permeability of free space and wire respectively
o r
when the current is homogeneous across the wire.
O P E R A T I O N
Connections for General Operation
Equation 2
C H A P T E R
2
R
/dt (in A/s) is:
Load
LDX-36000 Series
3
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