Instrumentation and Test Expert

Example Saturable Reactor Design for ATE (page 5)

IV. EXAMPLE SATURABLE REACTOR DESIGN Based on a toroidal core with the following dimensions: Outside Diameter .0235 meters, Inside Diameter .0075 meters, Cross Section Area .0002 meters squared

The number of turns required to achieve a given inductance can be determined using the peak permeability of the material, geometry of the material, and the desired inductance; the designer can calculate the required number of turns of wire.

A control winding is needed to apply a magnetic field to adjust the coil inductance. Since a DC electrical signal is going to be used to adjust the value of the primary winding inductance, the number of turns for the secondary winding is best determined through numerical solution or experimentation. The value of the H field applied by the control coil is determined by the number of turns and the current through the control winding.
From the above equation the magnetic field, and therefore the permeability can be controlled independent of inductor core geometry. Plotting the inductance of the primary winding against the current through the control winding creates the following chart.

Figure 3. Calculated inductance vs. control coil current for a sample inductor design. In this example the inductance of the primary winding varies from 22mH to 18mH with a current variation of 2.6A to 3.8A. For 800 discrete steps in this range and by assuming a simple first order approximation of the curve above, the current source must control its current in 1.5mA steps over the entire current range.

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