Receiver Design
Today I've completed the design of my Qi Receiver -> 6cell NiMH charger. I'ts been quite a lot of work, and what has struck me both in this design and in my preliminary Qi power BeagleBone Cape is that power management / power routing in Qi designs is not that simple when you include charge controllers / external charge sources etcetera. Nevertheless, I'm quite positive about my design using the Qi receiver. Attached you will find the schematic and PCB. I do have to warn about the schematic; I'm still busy getting the right order codes to the components, I'll updat the files when I'm ready doing that.
This is a screenshot of the schematic, I'll highlight some of the contents, from left to right.
- Far left: terminals for the pickup coil, and a lot of capacitors for resonance / capacitive communication
- Qi ReceiverQi Receiver bq51013 IC
- Middle, under: BQ2002-TBQ2002-T NiMH charge controller, supplied by the output of the receiver IC. This IC monitors the cells for a temperature change.
- Middle, upper: TPS61165TPS61165 boost converter. This is actually a white LED driver! Why take a white led driver as a boost converter? The bq2002 regulates its output based on the assumption that the battery will be charged with a constant current source. The TPS61165EVM-283TPS61165EVM-283 is designed as a constant current source (low Vref for feedback pin, so a low value sense resistor can be used-> less power dissipation) and is able to deliver 0.5A @ ~9V output. A zener is used in the feedback path to limit the output voltage (zener starts conducting at ~9V, and runs current into a higher rsense resistor, thus raising the FB pin voltage). The bq2002 controls the output switch (far right) to enable / disable power to the battery pack. The double P-FET prevents conduction in either direction when truned off.
Layout
I decided to give OSHpark a try as PCB manufacturer, so I'll get purple PCB's as well 
The complete receiver and charger are placed on 25x45mm.
Rails
What was I doing this for? For driving and charging a LEGO train on the track! In a previous post I showed a proof of principal, but I wanted to get a better energy transfer, and maybe even use the Qi power detection stop the train exactly above the transmitter. I used theWuerth Qi transmitter coilWuerth Qi transmitter coil in the prototest, and will put that inside the railroad tracks. See result of Dremeling below!
