Browse Prior Art Database

Overload Protection Device

IP.com Disclosure Number: IPCOM000097277D
Original Publication Date: 1962-Aug-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Ruehli, A: AUTHOR

Abstract

This device prevents transistor circuitry from being destroyed by heating caused by avalanche or Zener effects.

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Overload Protection Device

This device prevents transistor circuitry from being destroyed by heating caused by avalanche or Zener effects.

Transistors 2 and 3 are a flip flop in which transistor 3 normally is nonconducting and transistor 2 conducts. With no output from transistor 3, switching transistor 4 is nonconducting and no current is passed through load L. The setting of the flip flop is effected by closing contact SET. Negative voltage is thus applied to the base of transistor 3, rendering it conductive. Its positive output drives transistor 4 into saturation and current is passed through load L.

If the current exceeds a predetermined value, i. e., if the power supplied to the load becomes too great, the voltage drop across resistors R becomes great, causing transistor 1 to become more conductive. Its negative output is applied to the base of transistor 2 which becomes conductive. The positive output of 2 drives transistor 3 nonconductive, causing transistor 4 to switch the current through load L off. When excess current is removed, the flip flop is set again.

If the SET contact is closed while the excess current is not yet removed, a balance is created. Now, the current is slightly higher than the predetermined maximum, but the voltage is considerably reduced. Thus, because of the reduced power, the circuitry is sufficiently protected.

The time constant of the device is adjusted by capacitor C. It is possible to secure switching times of about ten nano se...