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# DC Current Sense Circuit for AC To DC Converters

IP.com Disclosure Number: IPCOM000083921D
Original Publication Date: 1975-Aug-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 53K

IBM

## Related People

Johari, GC: AUTHOR

## Abstract

It is frequently desired to sense the DC current provided by an AC/DC converter. Such converters may draw their energy from a three-phase AC power line and convert it to DC by full or half-wave bridge rectifier circuits.

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DC Current Sense Circuit for AC To DC Converters

It is frequently desired to sense the DC current provided by an AC/DC converter. Such converters may draw their energy from a three-phase AC power line and convert it to DC by full or half-wave bridge rectifier circuits.

In order to provide overcurrent sense and other control functions, it is often desirable to have a metering system which measures the value of the DC current thus produced, but is isolated from both the AC source and the DC derived therefrom.

Fig. 1 shows a sense circuit for this purpose which includes current transformers CT1, CT2 and CT3 on the A, R and C phase lines of a three-phase supply. At any one moment the algebraic sum of the three phase currents IL1, IL2, IL3 is zero but, arithmetically, these currents are a measure of the DC current drawn by the main power circuit.

This arithmetic function is derived by summing the DC components of currents ICT1, ICT2, ICT3 from the current transformers in a full-wave bridge rectifier circuit CR1--CR6 having an instrument load R. The output voltage VO1 is a measure of the current through R, which is a direct analog of the unfiltered DC current at the output of the rectifier in the "main power circuit". Usually the main power circuit will contain a filter to smooth its DC output.

To convert VO1 to a direct analog of such a smoothed main output, VO1 can be converted to a steady-state value, at VO2-REF, by a high-input impedance averaging filter connected...