Rectifying Diodes

This simple yet ingenious circuit (not my design, lest you think I’m conceited) serves the purpose of illustrating diode rectification behavior, and provides a potential project for students to build and test.

There is a lot to discuss in this question. Not only does the concept of “curve tracing” merit attention, but the specific operation of this circuit is worthy of investigation as well. The reason I asked students to determine the “curve” for a resistor was to introduce them to the idea of graphing component current/voltage functions, and also to allow them to analyze the circuit with a more linear component under test than a semiconductor.

An important question to ask here is why channel Y of the oscilloscope must be inverted to obtain the graphs shown. What would the graphs look like if the channel were not inverted?

The challenge question may be rephrased as, ïs the excitation voltage waveshape critical to obtaining a precise curve?” One way to demonstrate this is to use a function generator as the excitation voltage source (a transformer may be necessary to isolate the function generator ground from the oscilloscope ground!), and to try different waveshapes, watching the responses on the oscilloscope screen.

This question provides a good opportunity to review the direction of current through a battery when charging, versus when discharging. It also shows a way we can prevent the generator from “motoring” without having to use a reverse-current relay.