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Cross-Field Current Sense Inductor

IP.com Disclosure Number: IPCOM000043064D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Homan, LC: AUTHOR [+2]

Abstract

Overcurrents in a power supply caused by high resistance shorts or medium overcurrent loads can be sensed using resistors, but there are problems which make their use unattractive. Current sense resistors placed in series with the power supply output degrade output regulation. If sense resistors are made small, then the voltage which must be measured is small and is hard to measure, and extra circuitry is required because of reference circuits, level shifts, etc. Also, tight tolerance current sense resistors tend to be expensive. A cross-field inductor can be used to detect an overcurrent of a DC power. The current, IOC (Fig. 1), of the output of interest is circulated through the screw hole of a standard pot core. This IOC current creates an orthogonal field to the field of the winding B (Fig. 2).

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Cross-Field Current Sense Inductor

Overcurrents in a power supply caused by high resistance shorts or medium overcurrent loads can be sensed using resistors, but there are problems which make their use unattractive. Current sense resistors placed in series with the power supply output degrade output regulation. If sense resistors are made small, then the voltage which must be measured is small and is hard to measure, and extra circuitry is required because of reference circuits, level shifts, etc.

Also, tight tolerance current sense resistors tend to be expensive. A cross-field inductor can be used to detect an overcurrent of a DC power. The current, IOC (Fig. 1), of the output of interest is circulated through the screw hole of a standard pot core. This IOC current creates an orthogonal field to the field of the winding B (Fig. 2). Thus, no signal is coupled from the "A" to the "B" windings. IOC current in winding A does affect the permeability of the core and affects the inductance L of winding B, as seen in Fig. 3. When the inductance is sensed, the appropriate current detect point can be chosen. The appropriate overcurrent point can be adjusted by adjusting the position of the core halves 10 and 20 (Fig.
1). The cross-field inductor can be placed in either the positive or negative leg of the supply output without inserting a voltage drop similar to a resistor. The voltage sensed across resistor R is on the order of volts instead of millivolts. The cross-field inductor can be placed in series with the output and not degrade regulation. Also, tight tolerance resistors are not needed. Another advantage is that the winding "A" with capacitor CF2 creates a high-frequency filter (L-section filter). The inductance of winding "A" varies with IOC from 1 to 10 microhenries; therefore,...