WidlarBandgap - 2 I?3EE.TOURNAL OF SOLID-STATE CIRCUITS,VOL...

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2 I?3EE.TOURNALOF SOLID-STATECIRCUITS,VOL. SC-6, NO 1, FIN+RU.iRY1971 New Developments in IC Voltage Regulators ROBERT J. WIDLAR Abstract—A temperature-compensated voltage reference that provides numerous advantages over zener diodes is described along with the implementation of thermal overload protection for monolithic circuits. The application of these and other advanced design techniques to IC voltage regulators is covered, and an ex- ample of a practical design is given. INTRODUCTION M ONOLITHIC regulators have been receiving considerable attention during the last year or two. With the exception of operational am- plifiers and voltage comparators, regulators Ieacl other categories of linear devices in sales. Hence, considerable effort has gone into improving their performance and gen- eral utility. Increasing the output-current capability, reducing the number of external components, and minimizing external trimming are obvious areas for improvement of older designs. Higher reliability under actual field conditions is less obvious, but probably more essential. Lfinimum input voltages less than the present 7–9 V would also increase the usefulness of these circuits. Some techniques for realizing these objectives will be described. Further, a practical design for an on-card regulator that provicles 5 V for logic circuits will be given. This circuit has three active leads, so it can be supplied in standard transistor power packages. It re- quires no external components and can reliably deliver output currents in excess of 1 A. DESIGN CONCEPTS A ~imp]ified schematic of a typical wlt.age regulator is shown in Fig. 1. An operational amplifier compares a reference voltage with a fraction of the output voltage and controls a series-pass transistor to regulate the out- put. Some form of overload protection is usually pro- vided. Here, the output current is limited by Q1 and RI. The low cost of IC regulators has created a consider- able interest in on-card regulation, that is, to provide local regulation for each printed-circuit card in a sys- tem. Rough preregulation is used in the main power source, and the power is distributed without excessvie concern for line drops. The local regulators then smooth out the voltage variatiom caused by line drops and elim- inate the transients on the main power bus. A useful on-card regulator must include everything within one package, including the series-pass transistor. The author has previously advancecl arguments against Manuscript received March 23, 1970; revised July 10, 1970. The author is with National Semiconductor, Santa Clara, Calif. REFERENCE UNREGULATED INPUT SERIES PASS TRANSISTOR REGULATED OUTPUT & UR2 Fig. 1. Bmic series regulator circuit. inducting the pass transistor in an integrated-circuit regulator [1], First, there are no stanclard multilead power packages. Second, integrated circuits necessarily have a lower maximum operating temperature because they contain low-level circuitry. This means that an IC regulator needs a more massive heat sink. Third, the gross
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WidlarBandgap - 2 I?3EE.TOURNAL OF SOLID-STATE CIRCUITS,VOL...

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