Browse Prior Art Database

Overcurrent Protector With Automatic Reset

IP.com Disclosure Number: IPCOM000084765D
Original Publication Date: 1976-Jan-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Maddox, RA: AUTHOR

Abstract

Current is interrupted by a transient short and is automatically restored when the short is removed.

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Overcurrent Protector With Automatic Reset

Current is interrupted by a transient short and is automatically restored when the short is removed.

Current I from a power supply normally passes through Q1 and a load R(L), C(L). In this state, transistor Q1 is conductive because the voltage E' is greater than the zener diode voltage drop V(Z). This applies a turn-off bias to transistor 03 to hold off transistor Q2 which, in turn, allows transistor Q1 to be on.

When a short across R(L), C(L) or other condition, such as charging of a large capacitive load C(L), causes an excessive current to be drawn from the power supply, the potential E' will drop. Transistor Q3 will turn on when potential E' becomes less than the zener diode Z voltage drop V(Z). This turns on transistor Q2, which turns transistor Q1 off and interrupts current flow through the load R(L), C(L).

As long as the original cause of the high current remains, current through transistor Q2 and R2 holds transistor Q1 off (and current through R3, Q3, D1 and R5 holds transistor Q2 on) to keep the load substantially disconnected from the power supply, even though the supply potential E is normal. When the load condition changes sufficiently, transistor Q1 will conduct again because the current flowing through Q2 and R2 will raise E' sufficiently to turn Q3 off. Transistor Q2 is then held off by transistor Q3 as before as long as the voltage E' is greater than the zener diode Z voltage drop V(Z).

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