Hi，
I'm using an LTC4125 as a TX unit and half-wave diodes rectifier with a common DC-DC chip as RX unit, to manage a wireless power system on a robot arm's end, and support about 5V output voltage and 200mA load.
Here are the schematic and the diagram.
(sorry that I can't show the complete parameters due to company strategy)
Worth mentioning that I pull CTD pin to PGND to end searching after the first search and avoid output's hiccup, as it's a continuously supplying system not a charging system. Now it can work well functionally.
The problem is, when the load reaches 200mA, my design's maximum, the input current is 500mA and the efficiency is 40% (it's acceptable); but when I reduce the load till 0, VTANK and input current increase at the same time, making the efficiency very bad. The input current will finally be around Ith, and this performance blurs the line between light load and RX coil absence, making VFB fault condition hard to work right. It's also not as described in the datasheet 'Transmit Power Automatically Adjusts to Receiver Load'.
In another post it is suggested that if using some other type of receiver, set LTC4125 to switch with fixed duty cycle. I wonder if there's any method to still adjust receiver load when using my type of receiver, or are there any other suggetions to optimize my receiver design and fit my need. Thank you very much!
Simon