AN842 Datasheet, PDF (3/4 Pages) Silicon Laboratories – Use a Self-Powered Op Amp to Create a Low-Leakage Rectifier

AN842
Figure 3.
The op amp’s bandwidth limits the circuit to lower-frequency signals. At bandwidths higher than 500 Hz, the
amplifier’s gain begins to decline. As the signal frequency increases, the MOSFET remains off, and the body diode
of the MOSFET takes over the rectification function. An input with a fast fall time could potentially drag the output
with reverse current through the MOSFET. However, for small currents, the MOSFET operates in its sub-threshold
range. The amplifier quickly turns off due to the exponential relationship of the gate-to-source voltage to the drain-
to-source current in the sub-threshold range. The limiting factor is the amplifier’s slew rate of 1.5V/msec. As long
as you don’t load the circuit so heavily that you drive the MOSFET into its linear range, reverse currents won’t
exceed forward currents.
You can use the circuit in a micropower solar-harvesting application (Figure 3). Depending on the light, the BPW34
cells generate 10 to 30 µA at 0.8 to 1.5 V. The active-diode circuit rectifies the peak harvested voltage in conditions
of rapidly changing light and minimizes reverse leakage to the cells.
Please see the documentation for the TS1001 Op Amp. For additional information, contact Silicon Labs.
Rev. 1.0
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