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An Apparatus for Lossless Current Sensing

IP.com Disclosure Number: IPCOM000099065D
Publication Date: 2005-Mar-10
Document File: 4 page(s) / 56K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that maintains thermally-stable, highly-accurate current and power monitoring with virtually no power loss associated with current sensing. Benefits include improving efficiency and reducing power dissipation.

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An Apparatus for Lossless Current Sensing

Disclosed is a method that maintains thermally-stable, highly-accurate current and power monitoring with virtually no power loss associated with current sensing. Benefits include improving efficiency and reducing power dissipation.

Background

For power monitoring and power profiling, voltage regulator modules (VRM) and current share current sensors are widely used. These devices are often employed in multi-processor base board and multi-phase VRM environments (e.g. desktops, servers, laptops, and a variety of other electronic systems). The current sensors provide and support CPU power monitoring, control, over-current protection, load sharing functions, and VRM automatic voltage positioning.

Accurate monitoring provides precise information of power consumption, which allows for optimal server system control, resulting in the best data center performance. The more accurate the current sensing circuit is, the more precisely output power is shared between DC-DC converter phases, or converters connected in parallel. This in turn provides higher reliability and reduces each phase power rating and overall VRM cost.

Since conventional methods of current monitoring do not provide the required accuracy and are very temperature sensitive, low-tolerance, low-impedance current sense resistors are still the best choice and are widely used for these purposes. However, the minimum impedance of a high current sense resistor with 1% tolerance available on the market is 1 mohm. Using this resistor in high load current applications may noticeably affect the efficiency of the VRM. Using sense resistors in the power distribution circuits may result in efficiency losses or affect voltage regulation.

General Description

The disclosed method maintains thermally-stable, highly-accurate current and power monitoring with virtually no power loss associated with current sensing. Figure 1 shows a block-diagram for current sensing. The method is based on monitoring voltage drop across existing copper “sensors” (e.g. PCB trace, inductor winding), and using a reference (i.e. compensation) sensor with the same thermal coefficient exposed to the same temperature. Dividing down the first signal by the second one generates a temperature independent signal directly proportional to the load current, without introducing any losses in the power distribution network.

  

A detailed schematic diagram with an existing VRM inductor is shown in Figure 2. It employs an existing VRM inductor winding W1 equivalent series resistance (ESR) as a current sensor. It also incorporates AC content compensating winding W2. The winding W2 is connected in series with the main “primary” windingW1, so that their identical leads (either beginnings or ends) are tied together. The identical winding leads are shown in Figure 2 by dots positioned at one of the leads. The AC voltage generated across the two remaining leads equal zero, because AC contents acro...