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Line Voltage Threshold Detector

IP.com Disclosure Number: IPCOM000082672D
Original Publication Date: 1975-Jan-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 61K

Publishing Venue

IBM

Related People

Stammely, TE: AUTHOR

Abstract

Sensing line voltage conditions quickly and accurately is extremely important. In many situations, a loss of power may result in the loss of volatile memory. If the power loss can be detected in the early stages, volatile memory may be stored on permanent memory such as disk files before the power loss results in the destruction of the volatile data.

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Line Voltage Threshold Detector

Sensing line voltage conditions quickly and accurately is extremely important. In many situations, a loss of power may result in the loss of volatile memory. If the power loss can be detected in the early stages, volatile memory may be stored on permanent memory such as disk files before the power loss results in the destruction of the volatile data.

The line voltage threshold detector and signalling unit described provides a logical signal to initiate whatever function is necessary, before the power supplies drop out of regulation upon the detection of a drop in line voltage. The drop must be detected sufficiently early to provide the necessary time for movement of data from volatile memory to the disk, and provide sufficient time so that the disk drive motor speed is not reduced below minimum allowable limits. The predictable accuracy of the sense point is within + or - 3% to prevent false trips, since the sense point selected is close to the bottom AC line tolerance. Typical response time is equal to or less than one-half cycle of the line voltage.

Various configurations of line interrogation devices are available. Some use a zero-crossing detector to establish a reference measuring point. Using such an approach is desirable, since instant response to line changes is achieved. Unfortunately, however, circuit requirements are necessarily complex. The circuit described uses a technique of continuous voltage analog sampling, which results in a considerable reduction in cost and complexity.

In Fig. 1, two operational amplifiers (OP-AMP) 1 and 2 are used as threshold detectors. The output of operational amplifier 1 may be represented by two current sources and two switches, as indicated in the drawing. A capacitor C1 is connected between the output of operational amplifier 1 and ground to form an integrator. Io illustrated within OP-AMP 1 is constant, because the OP-AMP output current is internally limited to Io when the output is shorted or required to supply a current greater than Io. By selecting capacitor C1 large enough, the driving current is constant...