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Saturating Regulator for Lightly Loaded Voltage Supply

IP.com Disclosure Number: IPCOM000051824D
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Homan, LC: AUTHOR [+2]

Abstract

The power supply of Fig. 1 produces a positive DC voltage +V1 at relatively heavy loading, such as +5 V at 5 A, and a negative bias voltage at much lighter loading, e.g., -5 V at 0.2 A. Because of the loading mismatch, the lower-value filter capacitor C2 as compared with C1, the coupling characteristics of transformer X, and the turn-on times of diodes D1 and D2, the -V2 transformer winding will typically exhibit a voltage waveform 10 having an overshoot 11, as illustrated in Fig. 2.

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Saturating Regulator for Lightly Loaded Voltage Supply

The power supply of Fig. 1 produces a positive DC voltage +V1 at relatively heavy loading, such as +5 V at 5 A, and a negative bias voltage at much lighter loading, e.g., -5 V at 0.2 A. Because of the loading mismatch, the lower-value filter capacitor C2 as compared with C1, the coupling characteristics of transformer X, and the turn-on times of diodes D1 and D2, the -V2 transformer winding will typically exhibit a voltage waveform 10 having an overshoot 11, as illustrated in Fig. 2.

Without the saturating regulator, the overshoot would cause the -V2 DC voltage to exceed regulation limits at light loads. This DC voltage is clipped off, as shown at 13, by a transistor Q driven by an operational amplifier A from a resistive divider R1, R2. Whenever the midpoint of the output voltages drops below true ground, amplifier A cuts off transistor Q; at heavier loads Q is saturated, with only a very small collector-to-emitter voltage drop. This eliminates the need for an expensive and inefficient linear regulator on the -V2 supply, or for overly tight specifications on D2, C2 and X. Moreover, no overvoltage protection against pass-element shorting is required; Q drops only a small voltage at low power so failure is less likely, and a failure which might occur is less destructive to load components.

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