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Shockley equation is non-linear but without any linearisation effort such as in BJT small signal biasing, half wave rectifier passes almost an undistorted half sine wave.

In amplifier we bring the bias to a linear region for a small signal.

What confuses me in rectification theres no such thing as linearization and we use the diode in non linear way but how come the current wave form is not distorted? Imagine a half wave or full wave rectifier with pure resistive load. The current looks not distorted. We have a non linear component yet the current is not effected from this nonlinearity it looks like. ?

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    \$\begingroup\$ um, who says the current isn't distorted? That seems like a wrong claim. \$\endgroup\$ – Marcus Müller May 26 '19 at 20:10
  • \$\begingroup\$ The current looks not distorted You cannot conclude that a (halve) sinewave isn't distorted by just looking at it (on an oscilloscope for example). A 1% harmonic distortion isn't visible to human eyes like that. Use a spectrum analyzer to look at the spectrum (harmonic content) to draw proper conclusions. Biasing an amplifier doesn't mean it becomes linear, it means it behaves linear enough. There is always signal distortion, the trick is to keep the distortion low enough. \$\endgroup\$ – Bimpelrekkie May 26 '19 at 20:30
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The current and voltage waveforms ARE distorted by the diodes, but you seem to have unrealistic expectations about the expected magnitude of the distortion.

The forward voltage of the diode varies in a nonlinear way based on the current through it, but it's limited to a volt or two at most, depending on the current. Also, the diode blocks current almost entirely until the forward voltage exceeds about 0.6 V. Together, these effects create a kind of crossover distortion near the zero-crossings of the line voltage. Unless you're looking for it specifically, you might not notice it.

Otherwise, the waveform seen on an oscilloscope looks very much like a half-sine curve.

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The current thru a silicon diode will increase 2X for a tiny 0.018 volt change across the diode. And 0.058 volts causes 10:1, and 2*0.058 volts = 0.116 volts causes 100:1 change in current.

Thus with 160 volt peak power line voltages (using a 1:1 transformer for safety), the 0.116 voltage is less than 1/1,000 distortion.

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