AN842 Datasheet, PDF (1/4 Pages) Silicon Laboratories – Use a Self-Powered Op Amp to Create a Low-Leakage Rectifier

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Use a Self-Powered Op Amp to Create a Low-Leakage Rectifier
An Amplifier that Works at 0.8 V is Key
1. Introduction
Figure 1.
You can combine a carefully chosen op amp, a low-threshold P-channel MOSFET, and two feedback resistors to
make a rectifier circuit with less forward drop than a diode (Figure 1). The rectified output voltage powers the active
circuitry, so no additional power supply is necessary. The circuit’s quiescent current is lower than most Schottky
diodes’ reverse-leakage current. This circuit provides active rectification at voltage drops as low as 0.8V. At lower
voltages, the MOSFET’s body diode takes over as an ordinary diode.
The op-amp circuit turns on the MOSFET as a forward voltage develops between the input and the output voltages,
according to the following equation:
where VGATE is the MOSFET’s gate drive, VIN is the input voltage, and VOUT is the output voltage. You can
relate the input and the output voltages to the MOSFET’s drain-to-source and gate-to-source voltages, according
to the following equations:
Rev. 1.0 1/15
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