This application note describes a device originally designed to solve the specific problem of needing a negative supply when only a positive supply is available. This is very common, and occurs, for example, in systems using
dynamic RAMs where the three-supply devices require a low current body bias supply of around -5V. Negative supply voltage is also desired in systems with a lot of digital logic (at+5V) but containing a small analog section using A/O
converters, such as the ICL7107 or ICL7109 and/or op amps and comparators, operating on ground referenced signals. In all these cases, the current requirement and regulation are not very demanding, but nevertheless, generating such a-5V supply is usually expensive and inefficient. Typically, a large number of discrete and integrated-circuit components are needed to convert the common +5V line into a negative one, or to add an extra output to the main supply, the backplane wiring, etc.