TWO TERMINAL CURRENT LIMITER

• US 3,769,572 A
• Filed: 01/18/1971
• Issued: 10/30/1973
• Est. Priority Date: 01/18/1971
• Status: Expired due to Term

• Current Assignee: Leon S. Doubt
• Original Assignee: Leon S. Doubt
• Inventors: Doubt, Leon S.
• Primary Examiner(s): Goldberg, Gerald
• Application Number:
  US05/106,965
• Time in Patent Office: 1,016 Days
• Field of Search: 323/4,9,22T,1 307/296,297 317/33VR,22
• US Class Current: 323/315
• CPC Class Codes: G05F 1/573 with overcurrent detector
• CPC Class Codes: G05F 3/04 wherein the variable is ac
• CPC Class Codes: G05F 3/22 wherein the transistors are of the bipolar type only G05F3/26, G05F3/30 take precedence
• CPC Class Codes: H02H 9/02 responsive to excess current current limitation for voltage regulators G05F1/573; disconnection after limiting H02H3/025

Abstract

A two terminal current limiter is disclosed. The current limiter includes two (first and second) transistors and two resistors, one of which, acting as a sensing resistor, is connected in series with the collector-emitter path of the first transistor between the said two terminals. When sufficient voltage drop occurs across the sensing resistor, the second transistor is biased into conduction, which together with the second resistor, controls the biasing of the first transistor, thereby controlling the current flow therethrough.

Claims

1. A two terminal current limiting device consisting of:

first and second terminals;

a first transistor with a base, an emitter and a collector;

a first resistor;

means connecting said first transistor collector to said first terminal, said first transistor emitter to one end of said first resistor and the other end of said first resistor to said second terminal;

a second Transistor with a base, an emitter and a collector;

means directly connecting the second transistor base and emitter to opposite ends of said first resistor and the second transistor collector to said first transistor base;

a second resistor; and

means connecting said second resistor between the base-collector junction of said first transistor, whereby when the voltage drop across said first resistor reaches a predetermined value said second transistor is forward biased to vary the bias of said first transistor, provided by said second resistor to limit the current flowing through said first transistor not to exceed a preselected amplitude with the voltage drop across said first resistor not exceeding an amplitude for forward biasing said second transistor.

2. A two terminal current limiting device as in claim 1 including a diode having an anode electrode and a cathode electrode, and means for coupling one of the diode'"'"''"'"'s electrodes to one of said terminals to limit the direction of the flow of current between said first and second terminals to a single direction.

3. A two terminal current limiting device, for limiting the amplitude of current from a source of alternating current to a load between which the device is connected in series comprising:

first and second units each unit including first and second terminals, a first transistor with a base, an emitter and a collector, a first resistor, means connecting said first transistor collector to said first terminal, said first transistor emitter to one end of said first resistor and the other end of said first resistor to said second terminal, a second transistor, means connecting the second transistor collector to said first transistor base, the second transistor base to the first emitter and the second transistor emitter to said first resistor, whereby only the latter is connected directly across the base-emitter junction of said second transistor, a second resistor, means for connecting said second resistor between the base-collector junction of said first transistor, whereby when the voltage drop across said first resistor reaches a predetermined value said second transistor is forward biased to vary the bias of said first transistor, provided by said second resistor to limit the current flowing through said first transistor not to exceed a preselected amplitude, said predetermined voltage value not exceeding the value necessary to forward bias said second transistor, and a diode for limiting the direction of current flow between said first and second terminals to a single direction; and

means for connecting the first terminal of said first unit to the second terminal of said second unit at a first junction point and the second terminal of the first unit to the first terminal of said second unit at a second junction point.

4. A current limiting device for limiting the amplitude of alternating current between a source of alternating current and a load not to exceed a preselected amplitude, the device being connectable in series between said source and said load, comprising:

first and second units, each unit including, first and second terminals, a first transistor having emitter, collector and base electrodes, a first resistor and a diode connected in series with the emitter collector path of said first transistor between said first and second terminals, and control means including a second transistor with its base to emitter junction directly connected across said first resistor and its collector connected to the base electrode of said first transistor for controlling the current flow across the collector emitter path of said first transistor as a function of the voltage drop across said first resistor, said voltage drop not exceeding the value for forward biasing said second transistor; and

connecting means for connecting the first terminal of said first unit and the second terminal of the second unit to a first junction point adapted to be connected to said sourcE, and for connecting the second terminal of said first unit and the first terminal of said second unit to a second junction point, adapted to be connected to said load, whereby said device is connected only between said source and load at said first and second junction points.

5. A two-terminal device to be connected between a source of direct or alternating current and a load for limiting the amplitude of the current passing to the load, the device comprising:

first and second terminals connectable between the source of current and the load, respectively;

a diode bridge consisting of four diodes, each having a collector and an emitter with two of said four diodes having their respective collectors connected to said first and second terminals and their emitters connected together at one of a pair of junctions, and the other two of said four diodes having their respective emitters connected to said first and second terminals and their collectors connected together to the other of said pair of junctions;

a first transistor having a base, an emitter and a collector, said collector being connected to one of said pair of junctions;

a first resistor being connected directly between said emitter of said first transistor and the other of said pair of junctions;

a second resistor being connected directly between said base of said first transistor and said one of said pair of junctions, said first transistor being thereby conductive of current passing between said pair of junctions;

a second transistor having a base, an emitter and a collector, said collector of said second transistor being connected to the base of said first transistor, said base of said second transistor being connected to the emitter of said first transistor and the emitter of said second transistor being connected to said other of said pair of junctions, said second transistor being normally non-conductive until a sufficient current amplitude through said first resistor produces a voltage drop thereacross which exceeds the base-emitter junction potential of said second transistor, whereupon said second transistor becomes conductive to limit the current flowing through said first transistor between said pair of junctions to an amplitude which is determined by the resistance value of said first resistor.