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Combined Overvoltage/Overcurrent Detector

IP.com Disclosure Number: IPCOM000034485D
Original Publication Date: 1989-Mar-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 32K

IBM

Related People

Petrowsky, WJ: AUTHOR

Abstract

Both overvoltage and overcurrent faults are detected by a single detector circuit. A DC load current IL passes through a current sense resistor 1 (Fig. 1) to a load 2. The resistance of the resistor 1 is less than 1 ohm, for example, but this creates a potential difference VS-VO . VS is sampled by a divider, which is composed of resistors 3 and 4, with a threshold voltage, VTH, between the resistors 3 and 4 being supplied to a comparator 5 at its inverting input. VO is connected to the comparator 5 at its non-inverting input through a resistor 6. Each of the resistors 3 and 6 is substantially the same resistance, about 1K ohm, for example. When there is an overcurrent condition so that IL increases beyond its threshold, VO drops so that VTH exceeds VO .

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Combined Overvoltage/Overcurrent Detector

Both overvoltage and overcurrent faults are detected by a single detector circuit. A DC load current IL passes through a current sense resistor 1 (Fig. 1) to a load
2. The resistance of the resistor 1 is less than 1 ohm, for example, but this creates a potential difference VS-VO . VS is sampled by a divider, which is composed of resistors 3 and 4, with a threshold voltage, VTH, between the resistors 3 and 4 being supplied to a comparator 5 at its inverting input. VO is connected to the comparator 5 at its non-inverting input through a resistor 6. Each of the resistors 3 and 6 is substantially the same resistance, about 1K ohm, for example. When there is an overcurrent condition so that IL increases beyond its threshold, VO drops so that VTH exceeds VO . When this occurs, the comparator 5 changes its output state from a logic one to a logic zero. This indicates an overcurrent condition only when VS is within its normal operating range.

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If IL is within its normal operating limits so that it is not in an overcurrent condition and VS is beyond its normal limits so that an overvoltage fault exists, VO exceeds the breakdown voltage of a Zener diode 7. This clamps a breakdown voltage VP at the non-inverting input of the comparator 5. This results in VTH exceeding VP to cause the comparator 5 to change its output logic from a logic one to a logic zero. This indicates an overvoltage condition when IL is within its...