1. A diode that is used in a circuit to allow signals to pass in one direction but to block those in the other direction and therefore prevent damage from surges in the reverse direction.

2. The diodes formed by the collector-substrate junctions in bipolar integrated circuits. In order to maintain isolation between parts of the integrated circuits these junctions must always be reverse biased. This is achieved by maintaining the potential of the substrate so that none of the diodes becomes forward biased. Similar diodes are formed in MOS integrated circuits by the source-substrate junctions, drain-substrate junctions, and, once formed, the channel-substrate junctions. The substrate material must be held at a suitable potential to maintain the isolation between parts of the circuit, as with bipolar circuits.