Transformerless power monitor circuit having means for electronically latching DC alarms

• US 5,079,688 A
• Filed: 12/13/1990
• Issued: 01/07/1992
• Est. Priority Date: 12/13/1989
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Kido, Toru
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): Voeltz, Emanuel T.
• Application Number:
  US07/627,141
• Time in Patent Office: 390 Days
• Field of Search: 363/52, 363/125, 323/299, 361/90, 361/91, 361/111, 364/480, 364/481, 364/483, 364/492, 340/635, 340/641, 340/645, 340/650, 340/660-664
• US Class Current: 363/125
• CPC Class Codes: G06F 1/30 Means for acting in the event of power-supply failure or interruption, e.g. power-supply fluctuations for resetting only G06F1/24

Abstract

In a power monitor circuit, AC power-line voltage is converted by a DC power supply to a regulated DC voltage. The DC power supply shuts down itself in the event of a failure therein. The output of DC supply rises from zero to a specified value in slow response to power-on state and drops to zero in slow response to a significant drop in the AC voltage. A rectifier-filter converts the AC voltage to a nonregulated DC voltage. The output of the rectifier-filter rises in quick response to the power-on state and drops in quick response to the significant AC voltage drop. If the output of DC power supply drops below a specified theshold due to AC power-line failure or due to its own failure, a DC low-voltage signal is generated. If the output of rectifier-filter rises above a specified low level a first AC transitory signal is generated and if it drops below a specified high level a second AC transitory signal is generated. A latch circuit is energized with the nonregulated DC voltage to latch the DC low-voltage signal if it occurs during the interval between the first and second AC transitory signals and supplies a DC alarm signal to computer circuitry. A power controller is energized with the regulated DC voltage to supply control signals to the computer circuitry in response to the first and second AC transistory signals.

Claims

1. A power monitor circuit comprising:

DC power supply means for converting an AC power-line voltage to a first DC voltage for energizing a utilization circuit and shutting itself down if an overvoltage or overcurrent occurs therein;

rectifier-filter means for converting said AC power-line voltage to a second DC voltage;

DC low-voltage detector means for monitoring the level of voltage at the output of said DC power supply means and generating a DC low-voltage indicating signal in response to a significant drop in the monitored voltage level below a specified value;

AC low-voltage detector means for monitoring the level of voltage at the output of said rectifier-filter means and generating a normal-state signal when the monitored voltage level is higher than a specified value and an AC alarm signal when the monitored voltage level is lower than a specified value; and

latch means energized with the second DC voltage for latching said DC low-voltage indicating signal during the presence of said normal-state signal and deriving a DC alarm signal from the latched signal.

2. A power monitor circuit as claimed in claim 1, wherein said DC low-voltage detector means includes a photodiode circuit for generating an optical pulse as said DC low-voltage indicating signal, and wherein said latch means includes a photothyristor circuit responsive to said optical pulse during said interval to derive said DC alarm signal.

3. A power monitor circuit comprising:

DC power supply means for converting an AC power-line voltage to a first, regulated DC voltage, said power supply means shutting itself down if an overvoltage or overcurrent occurs therein and having operating characteristics such that the level of voltage at the output thereof rises from zero to a regulated value in slow response to application of said power-line voltage thereto and drops to zero in slow response to a significant drop in said AC power-line voltage;

rectifier-filter means for converting said AC power-line voltage to a second, nonregulated DC voltage, said rectifier-filter means having operating characteristics such that the level of voltage at the output thereof rises from zero to an operating value in quick response to application of said power-line voltage thereto and drops to zero in quick response to said significant drop in said AC power-line voltage;

DC low-voltage detector means for monitoring the level of voltage at the output of said DC power supply means and generating a DC low-voltage indicating signal in response to a significant drop in the monitored voltage level below a specified value;

AC low-voltage detector means for monitoring the level of voltage at the output of said rectifier-filter means and generating a first AC transitory signal in response to a rise in the monitored voltage level to said operating value and a second AC transitory signal in response to a drop of the monitored voltage level to a value at or near zero voltage;

latch means energized with the second DC voltage for latching said DC low-voltage indicating signal during an interval beginning with the occurrence of said first AC transitory signal and terminating with the occurrence of said second AC transitory signal and deriving a DC alarm signal from the latched signal; and

power control means energized with said regulated DC voltage for controlling a utilization circuit in response to said first and second AC transitory signals.

4. A power monitor circuit as claimed in claim 3, wherein said DC low-voltage detector means includes a photodiode circuit for generating an optical pulse as said DC low-voltage indicating signal, and wherein said latch means includes a photothyristor circuit responsive to said optical pulse during said interval to derive said DC alarm signal.

5. A power monitor circuit as claimed in claim 3, wherein said power control means is insensitive to said first AC transitory signal which is generated when said AC power-line voltage is initially applied to said power monitor circuit.