Diodes, one-way current conductors, are used for voltage regulation, AC/DC conversion, and circuit protection. Forward-biased at 0.6V, conduct current, reverse bias blocks it.

There will be an odd-looking circuit that seems to make no sense at all, an amplifier formed from just a forward-biased diode and a couple of resistors.

For example, improving the switching efficiency (the fraction of contacted molecules at forward bias) would potentially lead to orders-of-magnitude gain in the rectification ratio.

There will be an odd-looking circuit that seems to make no sense at all, an amplifier formed from just a forward-biased diode and a couple of resistors.

In forward mode, approximately 150 µA flows through the diode, causing D4 to be reverse-biased and holding comparator U1’s inverting input low. This turns off the red LED.