Browse Prior Art Database

Phase Loss Monitor for Three Phase Power Circuits

IP.com Disclosure Number: IPCOM000045846D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Beck, HJ: AUTHOR

Abstract

Power supplies for printers often use three-phase power circuits with three constant-voltage transformers to stabilize the AC voltage before rectification. If one of the three phases drops out, operation of the printer continues because rectification of the other two phases ensures a sufficiently smooth DC voltage. However, short-term high loads may lead to sporadic errors.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 66% of the total text.

Page 1 of 2

Phase Loss Monitor for Three Phase Power Circuits

Power supplies for printers often use three-phase power circuits with three constant-voltage transformers to stabilize the AC voltage before rectification. If one of the three phases drops out, operation of the printer continues because rectification of the other two phases ensures a sufficiently smooth DC voltage. However, short-term high loads may lead to sporadic errors.

The circuit shown in Fig. 1 detects whether one or two phases are missing by counting missing positive half cycles of one or two power phases. If only a limited number of cycles, say, twenty, are missing, no drop is indicated. If one or two phases are continuously missing, this is indicated by a light-emitting diode (LED) blinking at a rate of 2.5 Hz. Line cycle disturbances, occurring at a low rate, cause the LED to be switched off during the first twenty missing line cycles and to be continuously switched on during the subsequent twenty line cycles, and so on.

Output voltages of the three transformer output windings A, B and C for the three phases are fed to a voltage divider, consisting of resistors R1 and R2, through diodes DA, DB and DC. The voltage across resistor R2 is clipped at a level of 4.6 volts by a zener diode (ZD) and applied to a Schmitt trigger (STR). Output pulses from the STR are applied to a cascade of two counters CTR 1 and CTR 2 dividing the pulse input sequence by 10:1 and 2:1, respectively. The output potential of CTR 2...