A radio-controlled model car that normally operates off a series of alkaline batteries is to be converted to operate contactlessly using inductive power instead of batteries. The car will be raced on tracks. These race tracks have six wires buried in the surface that are supplied constant three phase current at 38.4kHz to produce a moving magnetic field above the roadway surface. Inductive pick-ups will be placed under each car to capture this field and provide power. This power will need to be processed appropriately for the on-board DC motor controller.

Two regulators are needed to replace the function of the battery. The first is a pick-up regulator. The second is a DC-DC converter.

The IPT pick-up regulator
The pick-up will require a single winding with a number of turns on a ferrite bar placed in close proximity to an IPT track to couple power from the IPT track. Under short circuit conditions and when placed at a defined distance from the track.The winding should be parallel tuned with suitable capacitors. The output voltage of the pick-up must be regulated, using a hysteretic op-amp regulator. Actual power delivery is also dependent on how well the pick-up coil is positioned over the three phase IPT track, the tuning of the pick-up circuit, and the control. A suitable op-amp/comparator will be required for voltage regulation.

The DC-DC Converter
A Buck converter is to be built to properly interface the IPT pick-up regulation board with the drive electronics of the car. This should be designed with fast acceleration and high speed. Protection for accidental over-voltage must be provided in the design. The controller chip for this converter will be a Unitrode UC3843 current mode controller. The inductor must be wound on an EFD20 core to ensure that your design will fit in the space available. Feedback & grounding issues will need to be considered.