Simple Circuit Provides +5V Gate Bias from -48V Input

Published:2012/11/8 1:28:00 Author:muriel | Keyword: Simple Circuit, +5V Gate Bias, -48V Input | From:SeekIC

A similar version of this article appeared in the September 19, 2002 issue of EDN magazine.A small and simple circuit (Figure 1) derives +5V from the -48V rail widely used in telecom applications. Useful for gate bias and other purposes, the 5V supply delivers up to 5mA. A shunt reference (U1) defines -5V as ground reference for a charge pump (U2), and the charge pump doubles this 5V difference (between system ground and charge pump ground) to produce +5V with respect to the system ground.The shunt reference maintains 5V across its terminals by regulating its own current (IS), which in turn is determined by the value of R. Current through R (IR) is fairly constant, and varies only with the input voltage. IR, the sum of the charge-pump and shunt-reference currents (IR = ICP + IS), has maximum and minimum values set by the shunt reference.



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