Other Parts Discussed in Thread: LM5105, , BQ51025
I'm working on a wireless power transmitter for 25-30W wireless power transfer. Because the coil geometry (and electrical specs) are not WPC standard, I've pursued a custom full-bridge resonant driver using LM5105 and CSD88537 FETs. WPC/Qi compliance is not relevant, or required.
I understand that WPC has a rather complicated system of modulating the TX power per RX request by changing the:
- Bridge supply voltage
- Drive frequency
- Duty cycle
Clearly there's a rationale for this complexity. But what happens if the TX power is not reduced for low RX load?
Driving a full-bridge at 100% duty cycle into an open-circuit RX won't raise the RX voltage infinitely high, nor will it dissipate 20W into thin air. There is some relationship with reflected impedance and turns ratio, but I want to confirm my understanding. Could you please help to explain the downside of not reducing TX power for low load?
Fsw is 130kHz. Supply voltage is 12V.
Lpri (in-situ, with secondary in proximity) is 15.7uH, requiring Cpri=97nF series capacitance
Lsec (in-situ, with primary in proximity) is 30.3uH, requiring Csec=47nF series capacitance
