The power output of provides a guaranteed 6VAC/20mA/50kHz minimum output into a resistive load with fluctations possible up to 12VAC. Other loads are not specified. The output impedance is not specified, but I think we could model the source as 12VAC/50kHz/300\${\Omega}\$ output impedance.
I want to power a DC circuit from it that may have "instantaneous" peak consumptions higher than 20mA.
I wonder how to maximize DC power @3V3. Without losses, 0.12W max would be available. A big enough capacitor would help cope with peak currents.
One method I think of is to add an up transformer to multiply the source voltage by 4 or 5 times to stay within safe limits at all times. So 6V/300\${\Omega}\$ source would become a 30VAC/50kHz/1k5\${\Omega}\$ (max 60V) source that could be used by a switched mode rectifier.
EDIT:
I found an interesting search term: "Synchronous rectification", used in secondaries of SMPS.
I found chips that do not need (direct) control concerning the primary side.
- Diodes/APR347 operates from 4.5V up.
- OnSemi/NCP43080 specified for up to 1MHz.
- Diodes/APR34330 incorporates the mosfet.
- Active bridge controller: NXP/TEA2208T
- TI/UCC24612 - sensing up to 230V.
Most of those seem to do only "half-wave" rectification.
EDIT2: I search for the term "Resonant rectification" while thinking of the principle used in a class D RF power amplifier with an LC-tank. This gave some other interesting results - I am not sure it's fundamentally different from "Synchronous rectification".
Resources:
- ST/SRK2001 - Dual gate driver for use with a transformer with center tap.
- onsemi/NCP4390 - Dual gate, requires primary current sensor.
- Patent US5701243A
Other thoughts?