Understanding the key parameters of diodes and other components used in reference voltage circuits can help avoid issues in different application circuits across many disciplines.
Voltage regulators and voltage references are essential to most electronic circuits, whether analog, digital, or a combination of the two. Although these circuits can appear deceivingly simple, much experience in worst-case analysis has shown them to also be the source of a large percentage of problems or issues as part of larger circuit designs. Often, these issues are due in part to a lack of understanding of the actual complexities of these seemingly simple circuits. Another major contributor is a general lack of data from integrated-circuit (IC) manufacturers—data that is critical to completing a successful and robust design.
First, there is some confusion about the types and descriptions of different devices commonly used to provide a stable voltage source. A reference diode is a two-port element that does not provide a voltage by itself. The reference diode is either a Zener diode or bandgap shunt regulator, requiring an external current source. There is no significant difference between a reference diode and a Zener diode, other than the fact that a reference diode is generally a temperaturecompensated device and is often available with tighter initial tolerances than Zener diodes. A Zener diode allows current flow not only in the normal forward direction but also in the reverse direction when the applied voltage is larger than the breakdown voltage (or Zener knee voltage). A conventional diode will not allow significant current flow if it is reverse biased below its reverse breakdown voltage.