Negative regulator instability (by Gerard Larooy)

Component: 79 series

Category: Linear voltage regulator

79 series, i.e. 7905, 7012, 7915 etc. These are negative voltage regulators marketed as a complement to the popular positive 78 series. The snag is that the negative regulators have a totally different internal schematic probably due to NPN vs PNP chip transistor manufacturing issues. An upside of this is slightly lower dropout voltage but the snag is more critical pin bypassing for stability. In other words 79 regulators from some manufacturers have a tendency for instability when using standard bypassing that works all the time for the 78xx series. If output voltage doesn't need to be accurate, discrete components will win hands down.

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