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UNDERVOLTAGE SUPERVISION CIRCUIT

IP.com Disclosure Number: IPCOM000249815D
Publication Date: 2017-Apr-10
Document File: 6 page(s) / 137K

Publishing Venue

The IP.com Prior Art Database

Related People

Sjöroos Jukka-Pekka: AUTHOR [+2]

Abstract

This document presents a solution for undervoltage supervision used in offline power supplies. The proposed configuration is used to achieve voltage line monitoring with low cost and part count. The configuration that is proposed in this document uses a supervision circuit that changes the operation mode of the power supply when a line dip occurs.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 40% of the total text.

Page 1 of 6  FI-1617901

© Copyright [2017] ABB. All rights reserved.

UNDERVOLTAGE SUPERVISION CIRCUIT

Summary

This document presents a solution for undervoltage supervision used in offline power supplies.

The proposed configuration is used to achieve voltage line monitoring with low cost and part

count.

Background

A conventional offline power supply uses a full-wave rectifier bridge and a bulk capacitor to supply

DC-voltage to the downstream converter stage. Usually a NTC-resistor is used to limit inrush

current when the power supply is switched on. Because of negative temperature coefficient of the

resistor, at the beginning the resistance value is high and charging current is limited. When the

bulk capacitor is fully charged the resistance decreases and power loss is minimized.

However if a short line dip occurs, the resistance of the NTC will not have time to increase and

when the line resumes, the inrush charging current of the bulk capacitor will not be limited. This

could cause damage of components.

A more reliable solution is to add Power line under voltage supervision. This can be done by using

microcontrollers, which however are increasing the cost and complexity of the converter.

Invention

The configuration that is proposed in this document solves all problems mentioned above by using

a supervision circuit that changes the operation mode of the power supply when a line dip occurs.

The proposed solution uses a low cost solution which has low part count and better reliability.

An undervoltage supervision circuit

The proposed system for undervoltage supervision is shown in Fig. 1. The proposed system

include a “Bridge rectifier”, a bulk capacitor “C1”, a charging resistor “R1” and a switch “S1”. The

invention also includes a “converter stage” and an “undervoltage supervision circuit” which is used

to monitor the line voltage and change the operation mode of the converter if any kind of failure

at the line voltage is detected.

Page 2 of 6  FI-1617901

© Copyright [2017] ABB. All rights reserved.

AC- source

Converter stage

Undervoltage supervision circuit

uin

Power-enable

Power-enable

S1

R1

C1

Bridge rectifier

uac

uref

+

-

uin

Fig. 1. A proposed system for undervoltage supervision.

The AC-source provides voltage uac which is rectified to DC-voltage uin by the bridge rectifier. The

DC-voltage uin is fed to the converter stage and the undervoltage supervision circuit. The

converter stage feeds a voltage uref to the undervoltage supervision circuit. The undervoltage

supervision circuit generates an output signal “Power-enable”. The resistor R1 and the switch S1

are connected in parallel and are enabled or disabled according to the voltage uin. The converter

operates at two different operation modes: A “Charge mode” and a “Normal operation”. During

the “charge mode” switch S1 is disabled and capacitor C1 is charged via R1. When C1 is fully

charged S1 is enabled and the operation mode is changed to the “normal operation”.

A simplified un...