Internal Name: Three Wire Controller

What’s New: The two windings of a traditional system are wired in series and a center tap brought out from the common connection, so the windings are driven with three power drivers instead of four.

Status: Issued U.S. Nov 3, 2009.  PDF version to be available soon.

Why: Unlike the Single-Winding Solenoid approach, there are no performance compromises. This topology eliminates between 25% and 40% of the power driver electronics (depending on the configuration) while retaining 100% of the functionality obtained with the traditional four-wire and four-driver topology, thus reducing costs.

How: The operation of a dual-latching solenoid normally calls for only one of the two windings to be energized at any given time.  If the four wires coming from the two windings are interconnected to provide two end leads plus a center tap common to both windings, then these three leads can be driven with just three electronic driver circuits instead of four.  If, for example, a left-hand winding is to be driven, then the appropriate voltage differential is applied between the left-hand and center drive outputs, while the right-hand drive output is driven to match the voltage of the center output.  Thus, the voltage differential driving the right-hand winding is zero and the winding remains un-energized.  When the left-hand winding has been energized, done its work, and has been shut down, then the right-hand winding can be energized with the needed voltage differential while the differential on the left side is maintained at zero.  If there is overlap in operation of the windings, but such that one winding is being shut down as the other winding is simultaneously energized, then there is still no performance compromise in going from four drivers to three.  We see no reason not to employ this topology and eliminate at least 25% of the power driver electronics, with no performance compromises.  A simplified center-tap driver, using diode clamping instead of active pull-up, increases the cost savings to about 40% on power electronics while retaining full capability except, possibly, in a sensorless configuration, which is now described.
A variation on our patented “Sensorless Position Measurement” invention is described in this patent, providing for sensorless measurement and control in the three wire context.

Download: Three Wire Drive/Sense for Dual Solenoid, U.S. 7,612,978

Magnesense LLC Gorham,ME (207) 839-8637

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