A charging station that charges torque tools without charging contacts

The task

A battery-powered torque tool is put down between two jobs, and that holder is the natural place to charge it. Charging contacts on the housing are the usual way, but in a workshop, contacts are also where dirt and wear take hold. Contactless charging removes that spot: the tool is put down and charges.

The client wanted a charging station of its own for this, based on the Qi standard and matched to its tool family. Unlike a smartphone on a charging mat, a tool with metal parts and its own housing shape lies on the coil, and the station may only transfer power when a matching receiver is present, and must limit or shut down with metallic foreign objects.

The solution

The charging station is split into two circuit boards: a transmitter board with the Qi transmitter IC, the inverter, the voltage regulation and the measurement of the coil current, and a coil board with the transmitter coil and the indicator lights, which can be positioned independently to suit the housing geometry. Power comes over USB; the cable shield is connected to the station's reference potential.

The way there began with a proof of concept on evaluation hardware, checking whether coupling and power were achievable with the tool at all. Concept, requirements, schematic and layout of both boards and commissioning followed. The configuration of the transmitter IC, in particular foreign object detection and tuning to the coil, was set in several iterations on the actual mechanical assembly and verified with tested metallic foreign objects.

EMC pre-testing ran early, on the first hardware, so that changes to coil and layout could still flow into the second round rather than surfacing in the approval lab. The results are the concept, schematics and layouts of both boards, the tuned configuration of the charging IC and the results of commissioning and pre-testing.