Browse Prior Art Database

Power Line AC Voltage Presence Sensor

IP.com Disclosure Number: IPCOM000040151D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 65K

Publishing Venue

IBM

Related People

Ahladas, SJ: AUTHOR

Abstract

This circuit arrangement provides a single zener diode to simultaneously monitor proper voltage on a poly-phase AC power supply to a system. The zener is on the high voltage side of the supply and is biased to provide a stable reference. A threshold detector operates by switching the zener bias current through an optical isolator. The optical isolator output is coupled to a circuit designed to be consistent even with variations in the optical isolator. AC Voltage Presence (ACVP) sensors are used to detect if the AC voltage at a given point is below a predetermined value. Such sensors are invaluable for isolating faults in power systems. When placed inside a power supply for example, this sensor can be used to tell if the power supply has enough voltage to operate or not.

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Power Line AC Voltage Presence Sensor

This circuit arrangement provides a single zener diode to simultaneously monitor proper voltage on a poly-phase AC power supply to a system. The zener is on the high voltage side of the supply and is biased to provide a stable reference. A threshold detector operates by switching the zener bias current through an optical isolator. The optical isolator output is coupled to a circuit designed to be consistent even with variations in the optical isolator. AC Voltage Presence (ACVP) sensors are used to detect if the AC voltage at a given point is below a predetermined value. Such sensors are invaluable for isolating faults in power systems. When placed inside a power supply for example, this sensor can be used to tell if the power supply has enough voltage to operate or not. This allows the fault to be narrowed down to a defective power supply, or something upstream (where additional ACVPs may be located for further isolation). The sensed voltage Vsense is converted into high voltage DC in the AC-to-DC converter 10 shown in Fig. 1. The high voltage DC (HVDC) is used to provide bias to a reference circuit 12. The reference circuit 12 is then compared with the HVDC in the threshold detector 14. The AC-to-DC converter has no filter (for polyphase inputs), and as a result, the HVDC contains the peaks of the AC input waveforms. If one or more of the input waveforms drops low enough to cause a piece of the HVDC waveform to fall below the reference voltage, the threshold detector switches during this time. The threshold detector is isolated
(16) from the pulse hold circuit 18 for safety reasons. The pulse hold and reset block 18 takes the isolated threshold detector output and

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holds any fault comparisons for a period of time long enough to sense if the faults are periodic (i.e., one phase low or missing in a polyphase application). If the faults are periodic, the pulse hold output is a steady level. If they are not periodic, this block automatically resets. The AC-to-DC converter 20 of Fig. 2 is simply a full-wave bridge. Resistor 22 biases the zener 24 to generate th...