US2972715A

US2972715A - Current reference circuit

Info

Publication number: US2972715A
Application number: US677184A
Authority: US
Inventors: John F Ringelman
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1957-08-05
Filing date: 1957-08-05
Publication date: 1961-02-21
Anticipated expiration: 1978-02-21

Description

Feb. 21, 1961 J. F. RINGELMAN CURRENT REFERENCE CIRCUIT Filed Aug. 5, 1957 J.- (ff 5 5 0 6 r N L 0 4 2 2 ma 5 5 zgtl b L c m .IL E M m H m A M 0 m 9 5 m J K m m@& g E m CURRENT REFERENCE CIRCUIT John F. Ringelman, Qatonsville, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 5, 1957, Ser. No. 677,184

4 Claims. (Cl. 323-89) This invention relates to current reference circuits in general, and in particular to permanent magnet current reference circuits.

A current reference circuit utilizing a permanent magnet for biasing purposes has as its output a substantially constant current through a load even though the magnitude or frequency of its input voltage varies over a predetermined range. To obtain this substantially constant current output from a current reference circuit in the prior art, direct-current compensating ampere-turn have been added to a saturable core of a magnetic amplifier therein in such a manner as to decrease the average bias ampereturns provided by the permanent magnet. Currents induced in these compensating windings by the load windings of the magnetic amplifier require that the compensating circuit have a higher impedance for proper operation of the current reference circuit. For example, a choke has been employed in the compensating circuit to limit these induced currents.

' *It is an object of this invention to provide an improved current reference circuit.

Another object of this invention is to provide an improved current reference circuit wherein a compensating circuit of efiectively infinite impedance is obtained.

A further object of this invention is to provide a simpler, smaller, and inherently more accurate current reference circuit than prior apparatus performing the same function.

Further objects of this invention will become apparent from the following descriptions when taken in conjunction with the accompanying drawing. In said drawing, 'for illustrative purposes only, is shown a preferred form of the invention.

The single figure is a schematic diagram illustrating a permanent magnet current reference embodying the teachings of this invention.

In the drawing, the manner in which the windings have been wound on the magnetic core member has been denoted by the polarity dot convention. The polarity dot convention denotes direction of saturation. That is, current flowing into the polarity dot end of the winding will drive the inductively associated core toward positive saturation. Current fiowing out of the polarity dot end of a Winding will drive the inductively associated core away from positive saturation.

In general, the apparatus illustrated in the figure comprises a permanent magnet 60, a magnetic amplifier 50, a full-wave rectifier 4%), a saturating transformer 30 and terminal means 91 and 92 for applying an alternating current voltage.

The magnetic amplifier 50 comprises a saturable magnetic core member 5'1 having inductively disposed thereon a pair of

load windings

52 and 53 and a pair of compensating

windings

54 and 55. The permanent magnet 60 is disposed in inductive relationship with the magnetic core member 51 of the magnetic amplifier 50 so that a closed flux path between the north and south poles of the permanent magnet 69 through core member 51 is possible.

fitates Patent C) ICC A source of alternating current voltage, not shown, is connected to the terminals 91 and 92. A primary winding 31 of a saturating transformer 30, a terminal 22, an impedance means shown in a resistor 20, and a terminal 21 are connected in series circuit relationship between the terminals 91 and 92. A secondary winding 32 of the saturating transformer 30 is connected in series circuit relationship with the

load windings

52 and 53 of the magnetic amplifier 50 and a full-wave rectifier 40. A load is connected across the output of the full-wave rectifier 40. A compensating circuit for the permanent magnet current reference includes the

compensating windings

54 and 55 of the magnetic amplifier 50 and an adjustable resistor 10 connected in series circuit relation between the

terminals

21 and 22.

On the first half-cycle of the alternating current voltage source to be connected to the terminals 91 and 92, that is, when the terminal 91 is at a positive polarity with respect to the terminal 92, current will flow from the terminal 91 through the primary winding 31 of the saturating transformer 30 and the resistor 20 to the terminal 92. The alternating current voltage connected to the terminals 91 and 92 must have sufiicient magnitude to saturate the transformer 30.

On the first portion of this half-cycle, when the transformer St) is saturating, a voltage will be induced in the secondary winding 32 of such a polarity as to cause a current flow through the load winding 52 and load winding 53 of the magnetic amplifier St), the full-wave rectifier 4t) and the load 8%. After the transformer 30 is saturated, there will be no further induced voltage in the secondary winding 32. The primary winding 31 will approximate zero impedance and a voltage drop across the resistor 20 will appear for the remainder of the half-cycle. This voltage drop across the resistor 20 will be of such a polarity as to cause a current flow from the terminal 22 through the adjustable resistor 10 and the

compensating windings

54 and 55 of the magnetic amplifier 50 to the terminal 21.

The permanent magnet 60 has been inductively disposed with the magnetic core member 51 of the magnetic amplifier 50 in such a manner as to allow a closed flux path. This has the efiect of biasing the magnetic amplifier 50 to some predetermined flux level. The current flowing in the compensating circuit through the compensating windings S4 and 55 applies to the magnetic core member 51 which cooperates with the permanent magnet 60 to set a final fiux level in the magnetic core member 51.

This final flux level regulates the output of the magnetic amplifier 50, in a manner familiar to those skilled in the art, to the load 80 on the next half-cycles.

On the next half-cycle, that is when the terminal 92 is at a positive polarity with respect to the terminal 91, current will flow through the resistor Ztl and the primary winding 31. of the saturating transformer 30 to the terminal 91. Again, while the transformer 30 is saturating, a voltage will be induced in the secondary winding 32 of such a polarity as to cause a current fiow through the full-wave rectifier 40, the load 80 and the load windings 53 and 520i the magnetic amplifier 50. After the transformer 30 saturates, the primary winding 31 approximates a zero impedance and the entire voltage drop from the alternating current voltage connected to the terminals 91 and 92 will be across the resistor 20 for the remainder of the half-cycle. This voltage drop across the resistor 20 will be of such a polarity as to cause a current flow from the terminal 21, through the

compensating windings

54 and 55 of the magnetic amplifier 50 and the adjustable resistor 10 to the terminal 22. Again, the permanent magnet 60 and the

compensating windings

54 and 55 will cooperate to set a final flux level in the magnetic core member 51 which will determine the output of the magnetic amplifier 50, on the next half-cycle, to the load 80.

An impedance means, shown as the resistor 20, in series with the primary winding 31 of the saturating transformer 30 is an ideal coupling for a source of voltage to supply the compensating circuit as it meets both the requirements of causing an increasing compensating current with an increasing supply voltage and a decreasing compensating current at an increasing supply frequency.

In prior art permanent magnet current reference circuits, difficulties were encountered because of the induced currents in the compensating circuit. In the apparatus illustrated in the figure, the induced current difficulties in the compensating circuit do not exist because the compensating circuits source voltage across the resistor 20 will be of sufiicient magnitude to oppose the in- .duced voltages that will appear cycle by.cycle across the

compensating windings

54 and 55. Therefore, a compensating circuit of effectively infinite circuit impedance ,is obtained without using a bulky choke or some other current limiting device as used in the direct current compensating circuits of the prior art. Also, the bridge of rectifiers or other means of obtaining a direct current for the compensating circuit of the prior art is eliminated along with its inherent inaccuracies and changing characteristics. Thus, the permanent magnet current reference illustrated in Fig. 1 is simpler, smaller and inherently more accurate than the direct current compensating reference circuits of the prior art.

In conclusion, it is pointed out that while the illustrated example constitutes a practical embodiment of my .invention, I do not limit myself to the exact details shown,

,since modification of the same may be varied without departing from the spirit of this invention.

I claim as my invention:

1. In a current reference circuit, in combination, a magnetic amplifier comprising saturable means having inductively disposed thereon load winding means and compensating winding means, permanent magnet means disposed in inductive relationship with said saturable means .of said magnetic amplifier, a saturating transformer having primary and secondary windings, said secondary winding of said saturating transformer being connected to said ..load winding means of said magnetic amplifier, means for applying an alternating current voltage to said primary winding of said saturating transformer, and impedance means associated with said primary winding of said saturating transformer coupling said compensating winding .means of said magnetic amplifier to said means for ap' plying an alternating current voltage to said primary .Winding and providing a voltage across said compensatiing winding means upon saturation of said saturable means on each half cycle of said alternating current voltage.

2. In a current reference circuit, in combination, a magnetic amplifier comprising saturable means having inductively disposed thereon load winding means and compensating Winding means, permanent magnet means disposed in inductive relationship with said saturable means of said magnetic amplifier, a saturating transformer having primary and secondary windings, said secondary winding of said saturating transformer being connected to said load winding means of said magnetic amplifier, means for applying an alternating current volt- (i age to said primary winding of said saturating transformer, and impedance means connected in series circuit relationship with said primary winding of said saturating transtormer coupling said compensating winding means of said magnetic amplifier to said means for applying an alternating current voltage to said primary winding and providing a voltage across said compensating winding means upon saturation of said saturable means on each half cycle of said alternating current voltage.

3. In a current reference circuit, in combination, a magnetic amplifier comprising saturable means having inductively disposed thereon load winding means and compensating Winding means, means for adjusting current flow in said compensating winding means, permanent magnet means disposed in inductive relationship with said saturable means of said magnetic amplifier, a saturating transformer having primary and secondary windings, said secondary winding of said saturating transformer being connected to said load winding means of said magnetic amplifier, means for applying an alter-' nating current voltage to said primary winding of said saturating transformer, and impedance means connected in series circuit relationship with said primary winding .of said saturating transformer coupling said compensating winding means of said magnetic amplifier to said means for applying an alternating current voltage to said primary winding and providing a voltage across said compensating winding means upon saturation of said .saturable means on each half cycle of said alternating .current voltage.

'-4. In a current reference circuit, in combination, a .magnetic amplifier comprising a magnetic core member .having inductively disposed thereon a pair of load windings and a pair of compensating windings, permanent magnet means disposed in inductive relationship with said magnetic core member of said magnetic amplifier, a saturating transformer having a primary and a secondary winding, said secondary winding of said saturating transformer being connected to saic. pair of load windings of said magnetic amplifier, means for applying an alternating current voltage to said primary winding of said saturating transformer, and impedance means connected to said primary winding of said saturating transformer whereby said pair of compensating windings of said magnetic amplifier are coupled to said means .for applying an alternating current voltage to said primary winding and providing a voltage across said compensating winding means upon saturation of said saturable means on each half cycle of said alternating current voltage.

References Cited in the file of this patent UNITED STATES PATENTS (Ramey), Electrical Engineering, September 1953, pp. 793 and 794.

The Amplistat and its Application (H. M. Ogle), G. E. Review (October 1950), page 44, Figure 27 relied on.