US3327127A

US3327127A - Current control circuit

Info

Publication number: US3327127A
Authority: US
Inventors: Robert E Pechacek
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-01-28
Filing date: 1964-01-28
Publication date: 1967-06-20
Anticipated expiration: 1984-06-20

Description

June 1967 R. E. PECZHACZEK CURRENT CONTROL CIRCUIT Filed Jan. 28,

INVENTOR. R0851? T E. P H 5 ATTORNEY United States Patent 3,327,127 CURRENT CONTROL CIRCUIT Robert E. Pechacek, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Jan. 28, 1964. Ser. No. 340,838 4 Claims. (Cl. 307-60) The present invention relates in general to current control circuits. More particularly, this invention relates to a, current control circuit providing both current limitingregulating and non-limiting modes of operation.

Current control circuits are generally used as protective devices to prevent undesirable load current changes. One of the primary uses of such current control circuits is to protect a source of power and its load impedance from load current changes due to load impedance variations. Conventional current control circuits are classified as either non-linear or degenerative. In both cases, current control circuits make use of an element serially connected to the load impedance to effect either a high im- .pedance to the load or an impedance fluctuation that varies directly as the current fluctuation. Such a series connected element will consume power under all modes of operation with the proportion of power consumed from the load current source depending upon the internal impedance of the current control circuit as compared to the impedance of the load. Hence, under conditions where load current'vari-ations are the result of load impedance variations the greater the reduction of load impedance, the-more power is-consumed by the control circuit.

Additionally, it is often desirable to provide a current control circuit which allows the load current to vary over a preselected range while preventing the load current from exceeding such range. For example, in the field of quantitative analysis of ions, electrophoresis is a method utilized to separate the various ions of a solution. Generally, this technique requires a current limiting and regulating circuit which will protect both a strip of paper upon which the ion separation takes place and the power supply used to establish a potential difference between the ends of the stripof paper from current overload. In the application of the electrophoresis technique, it is of considerable importance to establish a constant potential difference between the ends of the strip of paper. Hence, it is desirable to provide a current control circuit which allows load current fluctuations only over a preselected range and whose internal impedance in the non-limiting mode is low enough so that the regulation of the voltage across the strip of paper is notimpaired as the impedance of the strip of paper varies.

- The present invention is a non-linear current control circuit designed to limit delivered to a load impedance. The invention comprises a diode serially connected with a power supply and a load impedance in a manner to normally oppose current flow from the power supply generator, whose output is variable, is electrically connected in parallel With the diode in a manner to provide a predetermined forward bias current to the diode. When the load current is less than the forward bias current the diode is in the on state and hence, the current control circuit is operating in the non-limiting -mode. When the load current is equal to or greater than the forward bias current, the diode is in the off state and the only possible path for the 'load current is through the constant current generator. In this mode of operation, the current control circuit is functioning in the limiting-regulating mode.

Accordingly, the present invention provides two distinct advantages over existing current control circuits. First, the dual operating mode of the present current conand regulate the current being.

to the-load. A constant current.

3,327,127 Patented June 20, 1967 trol circuit allows a variation in the load current over a preselected range which is unaffected by the current con trol circuit. Second, since the impedance of the diode in the on state is negligible in comparison to the load impedance, the diode Will consume only a negligible amount of power during the non-limiting operating mode. Furthermore, as a result of this negligible impedance of the diode in the non-limiting operating mode, the regulation of the voltage across the load impedance is not affected by variations in load current.

It is therefore an object of this invention IIO provide a current control circuit having non-limiting and limitingregulating modes of operation.

More particularly, it is an object of this invention to provide a current control circuit which will prevent the load current from exceeding a preset level which level can be varied over a considerable range.

It is a further object of this invention to provide such a current control circuit which will allow the load current to vary in the range below the preset current limit level.

It is another object of this invention to provide a current control circuit in which during non-limiting operating conditions, the impedance of the current control circuit stability.

The manner of achieving these and other objects and advantages will become more apparent from the following detailed description taken in connection with the accompanying drawings in which;

FIGURE 1 is an equivalent circuit diagram embodying the principles set forth by the present invention;

FIGURE 2 is an equivalent circuit diagram illustrating the non-limiting mode of operation of the current control circuit;

FIGURE 3 is an equivalent circuit diagram illustrating the limiting-regulating mode of operation of the current control circuit;

FIGURE 4 illustrates a preferred circuit embodiment of the present invention.

- With reference to FIGURE 1, a non-linear current con trol circuit 11 is electrically connected in series relationship with a power supply 12 and a load impedance 13. Control circuit 11 comprises a diode 14 electrically connected in series relationship with supply 12 and load impedance 13. Diode 14 is poled, i.e., current flow oriented, to oppose the fiow of load current 16 form supply 12 to the load impedance 13. A constant current generator 17 is electrically connected in parallel with diode 14 and a current generator 17 is arranged to provide a forward bias current 18 to the diode 14.

depicted by the closed position of a switch 19. Under these conditions the current control circuit 11 is functioning in the non-limiting mode of operation. In this mode of operation the impedance of the current control circuit 11 is that of the forward biased diode 14 which is negligible.

As a result of the essentially zero impedance of the current control circuit 11 during the non-limiting mode of operation, the potential difference existing between

terminals

21 and 22 of supply 12 is transferred directly .to load impedance 13. Thus, in the non-limiting mode 3 the potential of supply 12 is established at load 13 regardless of load current variations resulting from load impedance fluctuations.

When the load impedance or source variations cause load current 16 to become at least equal to the forward bias current 18 diode 14 is biased to be off state. Referring to FIGURE 3 the off state of diode 14 is depicted by the open position of switch 19. Under these conditions the control circuit 11 is functioning in the current limiting-regulating mode of operation.

When in the off state diode 14 appears as an open circuit to supply 12 and current generator 17. This effectuates an open circuit path which prevents current from flowing therethrough. Consequently, the current path to load impedance 13 is now from positive terminal 21 of supply 12 through the path including current generator 17 through load impedance 13 and back to the negative terminal 22 of supply 12. Since constant current generators have an infinite impedance with respect to their load impedance, when control circuit 11 is functioning in the limiting-regulating mode of operation, load current 16 will be limited to the current output of constant current generator 17 independently of variations in supply 12 and the impedance of load 13. Consequently, the current control circuit 11 provides excellent constant current stability in the limiting-regulating mode of operation.

A preferred embodiment of a circuit embodying the principles of the invention is shown in FIGURE 4. Constant current generator 17 is a pentode circuit energized by supply 23. The pentode circuit comprises a pentode vacuum tube 24, cathode resistor 26, screen grid voltage supply 27, and a variable grid bias supply including a voltage supply 28 and potentiometer 29.

A load current supply 31 is electrically connected in series relationship with a load impedance 32 through a first and second series connected and oppositely poled diodes 33 and 34 respectively. The cathodes of diodes 33 and 34 are electrically connected to a common junction 36. The serially connected diodes 33 and 34 are electrically interposed load 32 and the negative terminal of supply 31. Diode 33 functions as the current comparison element as noted hereinbefore and diode 34 functions to provide a threshold voltage drop which is equal and opposite to that of diode 33. Hence, during the nonlimiting mode of operation, the threshold voltages cancel effectuating a zero impedance path from supply 31 to load 32.

The anode 37 of tube 24 is electrically connected to the common junction 36 of diodes 33 and 34. The positive terminal of supply 23 is electrically connected to the negative terminal of supply 31. The negative terminal of supply 23 is electrically connected through the cathode resistor 26 to the cathode '38 of tube 24. The control grid electrode 39 is electrically connected to the wiper arm 41 of potentiometer 29. In operation wiper arm 41 of potentiometer 29 is adjusted to provide a bias voltage to grid 39 of tube 24 which allows a predetermined current 42 to flow through tube 24. Current 42 is utilized as the forward bias current for diode 33 and, as noted supra, when the load current 43 is equal to or greater than the biasing current 42, the diode will be in the off state and hence, the current control circuit will be functioning in the limiting-regulating mode of operation. Additionally, as noted supra, when the load current 43 is less than the biasing current 42, diode 33 will be in the on state and hence, the current control circuit will be functioning in the non-limiting mode of operation.

In the limiting-regulating mode of operation, load cur- 43 is limited to the current output of the constant current generator 17. Load current 43 will flow from the positive terminal of supply 31 through load 32, through diode 34, through tube 24 from the anode 37 to the cathode 38, through cathode resistor 26 and through supply 23 to the negative side of supply 31.

Circuit parameters for advantageous operation of the current control circuit of the present invention as illustrated heretofore are as follows:

(1) Diodes 33 and 34 IN2484 (2) Power supply 23 volts 75 (3) Power supply 27 do 75 (4) Vacuum tube 24 6CB5 (5) Cathode resistor 26 ohms (6) Power supply 28 volts 10 (7) Potentiometer 29 kilohms 0-10 (8) Forward biasing current ma 25-1 The current control circuit of the present invention constructed in accordance with the above-note parameters exhibited less than 5% variation in load current in the limiting regulating mode over the current limiting range of l to 25 milliarnps.

While the present invention has been hereinbefore described with respect to a single preferred embodiment, numerous modifications and variations are possible within the scope of the invention. For example, in place of the single pentode tube 24, two parallel operated pentode tubes may be used. Such a configuration provides a greater stability with respect to the control circuit constant current characteristics. Furthermore, in place of the single diodes 33 and 34, a plurality of light diodes serially con nected can be used. This enables the diode current path to withstand higher inverse voltages. Hence, the description of the present invention in terms of a single preferred embodiment is not intended to limit the invention except by the terms of the following claims.

What I claim is:

1. In a non-linear current control circuit for limiting and regulating the current delivered to a load impedance from a unidirectional source of power, the combination comprising,

(a) a diode serially interposed said load impedance and said source, said diode poled to oppose current flow between said source and said load impedance,

and

(b) a constant current generator electrically connected in parallel relationship with said diode, said current generator connected to introduce a current flow directed toward the junction of said diode and said load, whereby said current, together with said source of power, controls, the biasing mode of said diode.

2. A current control circuit as recited in claim 1 further defined by said constant current generator being a pentode tube circuit adapted with a separate D.C. power supply wherein said pentode tube circuit generates a constant current independent of said source of power.

3. A current control circuit as recited in claim 1 furthere defined by a second diode serially interposed said load impedance and parallel connected diode and constant current generator, said second diode pole to allow current flow from said source to said load impedance.

4. In a current control circuit for limiting and regulate ing the current delivered to a load impedance from a unidirectional source of power, the combination compris- (a) at least a first semiconductor diode serially interposed said load impedance and said source, said diode poled to oppose current flow between said source and said load impedance,

(b) at least a second semiconductor diode serially interposed said first diode and said load impedance, said diode poled to allow current flow from said source to said load impedance,

(c) a pentode vacuum tube, the anode of said tube electrically connected to the cathode of said first diode, the cathode of said tube serially electrically connected with a resistor and suitable tube D.C. power source to the anode of said first diode,

(d) a screen grid DC. bias supply electrically connected to the screen grid of said tube to introduce a positive voltage thereto with respect to said cathode, and

(e) a variable DC. control grid bias supply electrically connected to the control grid of said tube, said control grid bias supply adjusted to generate a selected current flow through said pentode tube whereby said generated current flows through said load, creating a voltage thereacross, which voltage, in conjunction with said source of power, controls the the biasing mode of said first diode.

References Cited UNITED STATES PATENTS ORIS L. RADER, Primary Examiner.

0 T. J. MADDEN, Assistant Examiner.

Claims

1. IN A NON-LINEAR CURRENT CONTROL CIRCUIT FOR LIMITING AND REGULATING THE CURRENT DELIVERED TO A LOAD IMPEDANCE FROM A UNDIRECTIONAL SOURCE OF POWER, THE COMBINATION COMPRISING, (A) A DIODE SERIALLY INTERPOSED SAID LOAD IMPEDANCE AND SAID SOURCE, SAID DIODE POLED TO OPPOSE CURRENT FLOW BETWEEN SAID SOURCE AND SAID LOAD IMPEDANCE, AND (B) A CONSTANT GENERATOR ELECTRICALLY CONNECTED IN PARALLEL RELATIONSHIP WITH SAID DIODE, SAID CURRENT GENERATOR CONNECTED TO INTRODUCE A CURRENT FLOW DIRECTED TOWARD THE JUNCTION OF SAID DIODE AND SAID LOAD, WHEREBY SAID CURRENT, TOGETHER WITH SAID SOURCE OF POWER, CONTROLS, THE BIASING MODE OF SAID DIODE.