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Increased Efficiency Vhf Rectifier/Filter

IP.com Disclosure Number: IPCOM000047799D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 67K

Publishing Venue

IBM

Related People

Dobberstein, EA: AUTHOR

Abstract

Low output voltage power supplies, based upon switching conversion of a high bulk input voltage, use Schottky diodes in their output rectifier/filter stages for obtaining low voltage drop and fast switching characteristics, as suggested in Fig. 1. A circuit of this type is illustrated in Fig. 2. However, with the present trend towards lower voltages for computer power supplies there is a corresponding trend towards operating such low forward drop circuits with decreasing efficiency since, at lower output voltages, the rectifier/filter circuit has a fixed loss at a given current which becomes the dominant factor in determining the efficiency of high frequency switching. For example, a Schottky rectifier operating into an L-C filter (in a circuit configuration such as that shown in Fig.

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Increased Efficiency Vhf Rectifier/Filter

Low output voltage power supplies, based upon switching conversion of a high bulk input voltage, use Schottky diodes in their output rectifier/filter stages for obtaining low voltage drop and fast switching characteristics, as suggested in Fig. 1. A circuit of this type is illustrated in Fig. 2. However, with the present trend towards lower voltages for computer power supplies there is a corresponding trend towards operating such low forward drop circuits with decreasing efficiency since, at lower output voltages, the rectifier/filter circuit has a fixed loss at a given current which becomes the dominant factor in determining the efficiency of high frequency switching. For example, a Schottky rectifier operating into an L-C filter (in a circuit configuration such as that shown in Fig. 2) will produce the following power loss as a percentage of output delivered, assuming a 30 A constant current drawn from the filter output:

(Image Omitted)

In the energy-conscious environment of the foreseeable future this declining efficiency becomes a substantial concern. It also tends to increase the cost of the power switching stage since it must deliver both useful and wasted output power. This tendency can be overcome in the following manner. From Fig. 1 it is apparent that the rectifier voltage drop can be almost halved by operating the rectifier at current well below its rating, which amounts to choosing a rectifier rated at several times the required current. Unfortunately, Schottky rectifiers which could be used in this manner are produced in rather expensive TO-3 or stud-mount metallic packages, whereas inexpensive Schottky rectifiers available in TO-220 plastic packages present a more restricted current-delivering capability. The expense of the metallic packages is compounded by their lower production volumes. An alternative presently contemplated is to combine the inexpensive plastic units in parallel packages to achieve the desired operating current effects. Since there is statistical variation in the forward characteristics from one device to another substantial current imbalance ca...