US3629674A

US3629674A - Transient resistant transistorized blocking oscillator for switching inductive loads

Info

Publication number: US3629674A
Application number: US47496A
Authority: US
Inventors: Ralph V Brown
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1970-06-18
Filing date: 1970-06-18
Publication date: 1971-12-21
Anticipated expiration: 1988-12-21
Also published as: GB1348849A; JPS52522B1; JPS471516A; DE2130267A1; FR2099202A5; AR193351A1; DE2130267C2

Abstract

An electromagnetic fluid pump has a reciprocating plunger driven in one direction by a solenoid and driven in an opposite direction by a spring. A transistor is connected in series with the solenoid to regulate the current therethrough. The transistor is controlled by a detection coil magnetically linked to the solenoid and connected across the emitter-base junction of the transistor. A resistor network is connected in series with the detection coil to increase initial emitter to base voltage thereby assuring initial transistor conduction and to limit reverse voltages during collapse of the magnetic field of the solenoid. A series-connected diode and resistor are connected across the solenoid and the detection coil to draw current from the solenoid through the detection coil during collapse of the solenoid field, thereby protecting the transistor and providing for a rapid collapse of the field resulting in rapid plunger release and increased pump delivery.

Description

United States Patent [72] Inventor Ralph V. Brown Cayuta, N.Y. [21] Appl. No. 47,496 [22] Filed June 18, 1970 [45] Patented Dec. 21,1971 [73] Assignee The Bendix Corporation [54] TRANSIENT RESISTANT TRANSISTORIZED BLOCKING OSCILLATOR FOR SWITCHING INDUCTIVE LOADS 16 Claims, 6 Drawing Figs.

[52] 0.8. CI. 318/128, 317/DIG.6,331/116,4l7/41$,417l48l [51] Int.Cl. ...li02k 33/02 [50] Field Search ..3l7/DIG. 4, DIG. 6, 155.5, 123, l46;417/415,50, 396, 410, 48l;25l/137, 321; 331/154, 156, 116 R, 116 M; 318/128, 132, 130; 310/30 [56] References Cited UNITED STATES PATENTS 3,381,616 5/1968 Wertheimer et a1. 318/130X 3,100,278 8/1963 Reich 331/116M 318/132 3,117,265 l/l964 Favre Primary Examiner-Gerald Goldberg Assistant Examiner-Harry E. Moose, .lr.

Attorneys-Robert A. Benziger and Flame, Hartz, Smith and Thompson ABSTRACT: An electromagnetic fluid pump has a reciprocating plunger driven in one direction by a solenoid and driven in an opposite direction by a spring. A transistor is connected in series with the solenoid to regulate the current therethrough. The transistor is controlled by a detection coil magnetically linked to the solenoid and connected across the emitter-base junction of the transistor. A resistor network is connected in series with the detection coil to increase initial emitter to base voltage thereby assuring initial transistor conduction and to limit reverse voltages during collapse of the magnetic field of the solenoid. A series-connected diode and resistor are connected across the solenoid and the detection coil to draw current from the solenoid through the detection coil during collapse of the solenoid field, thereby protecting the transistor and providing for a rapid collapse of the field resulting in rapid plunger release and increased pump delivery.

PATENTED HECZI IHTI SHEET 1 OF 2 ifiizzf" WITNESS: I I 5m. 573a.

ATTORNEY PATENTEU UECZI I97! SHEET 2 BF 2 [NVEN TOR.

BY 1 a QKMQ ww h ATTORNEY TRANSIENT RESISTANT TRANSISTORIZED BLOCKING OSCILLATOR FOR SWITCHING INDUCTIVE LOADS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to blocking oscillators adapted for switching inductive loads and more particularly to a blocking oscillator that is transient resistant.

2. Description of the Prior Art I-leretofore, electromagnetic fluid pumps have suffered from a plurality of interrelated deficiencies. In order to obtain maximum fluid delivery, solenoids were wound using a maximum number of turns of high-resistance wire. However, the high resistance of the wire limited current flow and made it difficult to start conduction of a switching transistor during cold weather and low power conditions. The large number of turns increased the energy released by the collapsing magnetic field of the solenoid which had to be dissipated without destroying any components. The energy released by the collapsing magnetic field was limited by use of Zener diodes; however, these devices are expensive and thus added excessive costs to the pump.

In order to overcome the problem associated with cold starts and the excessive energy released by the collapsing magnetic field, the solenoid was wound with fewer turns of a lower resistance wire. Use of the low resistance wire necessitated the inclusion of a fuse to prevent excessive current demands in the case of a shorted transistor, the inclusion of a reverse current diode to protect the device in case it was connected to a reverse polarity source and the use of transistors having highcurrent-handling capability. The fuse, diode and transistor added to the cost of the device. Use of fewer turns of low-resistance wire also made the device susceptible to transient voltage conditions resulting in the need for protecting the transistor from these transient conditions.

SUMMARY OF THE INVENTION The present invention contemplates an electromagnetic fluid pump having a solenoid wound with an intermediate number of turns of relatively high resistance wire. A transistor is connected in series with the solenoid control the current therethrough. A detection coil is magnetically linked to the solenoid and functions to control the transistor. The coil is so arranged to provide a transistortum on bias when the current in the solenoid is increasing and a transistor turn off bias when the current is decreasing. As a result, the transistor alternately drives to saturation and then turns off.

The use of a solenoid having a relatively high-resistance wire eliminates the need for a fuse, reverse current diodes and high current rated transistors. The use of relatively high resistance wire allows for an increased number of turns and thereby improves the ability of the device to endure voltage transients.

A series-connected resistor and diode are provided to allow current from the solenoid to flow through the detection coil and back to the solenoid during collapse of the solenoid magnetic field. The energy from the collapsing solenoid field is dissipated in the resistor and the detection coil without destroying any components of the device. This current path is an essential of the present invention. It provides for slowed or controlled discharge of the stored energy during the initial collapse of the field so that discharge voltage is greatly reduced, but provides for extremely rapid collapse of the field during the final discharge interval so that the pump plunger is quickly released resulting in increased fluid delivery.

A resistor is connected in series with the detection coil to increase the transistor emitter to base voltage and assist in ini' tially turning on the transistor. The resistor in conjunction with another resistor in the base circuit of the transistor functions to control transistor turn off so as to limit reverse voltages induced in the solenoid and coil during collapse of the solenoid field. Because of the reduced reverse voltages, a lower cost transistor having low reverse voltage characteristics can beused thereby reducing the cost of the device.

One object of the invention is to provide a switching circuit for an electromagnetic device that is resistant to transient voltages.

Another object of the invention is to provide a switching circuit for an electromagnetic device that is less expensive than circuits heretofore provided.

Another object of the invention is to provide a switching circuit for an electromagnetic device that will start at cold temperatures and at low voltage conditions.

Another object of the invention is to provide a transistor switching circuit for an electromagnetic device that can withstand reverse voltage application.

Another object of the invention is to provide a switching circuit for an electromagnetic device that has a low short circuit current. I

Another object of the invention is to provide an electromagnetic fluid pump that has increased delivery over the pumps heretofore available.

The foregoing and other objects and advantages of the present invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings wherein three embodiments of he present invention are illustrated.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows an end view of an electromagnetic fluid pump constructed in accordance with the present invention.

FIG. 2 shows a sectional view taken along line 1-1 of FIG. 1.

FIG. 3 is an electrical schematic of a switching circuit used in the present invention.

FIGS. 4, 5 and 6 are schematic diagrams of alternate embodiments of switching circuits for use with the present invention.

DESCRIPTION OF THE INVENTION Referring to FIG. 1, there is shown an end view of an electromagnetic fluid pump having a threaded outlet 1 formed in a hexagonal-shaped member 3 which is threaded into one side of a U-shaped member 5. A mounting bracket and cover member 7 slides over member 5 to form an enclosed housing. Member 7 has flanged portions 9 with holes formed therein for mounting the pump to a surface. A transistor 49 is mounted on member 7 and a terminal assembly 13 is mounted on member 5 but insulated therefrom by an insulation 15 so as to be electrically isolated from

members

5 and 7.

Referring to FIG. 2 the pump is shown in cross section. A threaded inlet 17 is formed in a hexagonal-shaped member 19 which is threaded into another side of U-shaped member 5 so that inlet 17 is in alignment withoutlet l. A hollow cylindrical guide member 21 is supported by a cylindrical extension of member 3 and is maintained in axial alignment with inlet 17 and outlet 1. Disposed between the sides of member 5 and coaxially with member 21 are a solenoid winding 23 and a detection coil winding 25. The solenoid is formed of 435 turns of number 22 A.W.G. wire so tat it has a relatively high resistance and inductance. A thin layer of nonmagnetic material in the form of a spool 27 separates the

windings

23 and 25 from the cylindrical extension of member 3 and the sides of member 5. A movable member in the form of reciprocating plunger 29, made of a magnetic material and having an opening therethrough, is slideably mounted within guide member 21. A resilient ring 22 is disposed in coaxial alignment with member 21 in a recess in member 3 and is retained therein by guide member 21. A check valve 24 is mounted in inlet 17 of member 19 to prevent fluid flow other than a unidirectional fluid flow from the inlet to the outlet through cylindrical guide member 21. A spring member 26 is compressively confined between plunger 29 and check valve 24 to urge plunger 29 toward outlet 1 and against resilient ring 22. A check valve 28 is disposed within the opening through plunger 29 for allowing fluid to flow through plunger 29 only in the direction from inlet 17 to outlet I. A retaining means 30 is mounted within plunger 29 for preventing check valve 28 from being dislodged. Member 19 has a recess formed in coaxial alignment with inlet 17 for receiving a portion of member 21, said recess has a circular groove formed therein for receiving an O- ring which provides a seal between member 19 and member 21. Member 7 has openings 39 in the side thereof for passing leads to transistor 11 from electronic circuitry contained within a space 41.

Referring to FIG. 3 there is shown a schematic diagram of the electronic circuitry for the pump. Terminal 13 is adapted to receive a positive DC voltage from either a battery or a rectified AC source. Solenoid 23 has one end connected to terminal 13 and another end connected to an emitter 49a of transistor 49 which also has a collector 490 connected to ground 47 through member 7. A series connection of

resistors

51, 53 and 55 and a diode 57 is connected between a base 49b of transistor 49 and terminal 43. Diode 57 has a cathode connected to terminal 43 and an anode connected to one end of resistor 55. Coil 25 is connected between emitter 49e and another end of resistor 55. Resistor 51 has one end connected to base 49b and another end to resistor 53. A resistor 59 is connected between terminal 45 and the connection between

resistors

51 and 53.

In operation prior to voltage being applied to terminal 13, transistor 49 is in a nonconducting state and piston 29 is urged against resilient ring 22 by spring 26. When a DC voltage is initially applied to terminal 13, current flows through a first path comprising solenoid 23, coil 25, resistor 53 and resistor 59. Current also flows through a second path parallel to the first path, comprising coil 23, the emitter to base junction of transistor 49, resistor 51 and resistor 59. Since the resistance of coil 25 is not very high, resistor 53 is selected to assure a sufficient current flow through the second path, including the emitter to base junction, to initiate conduction of transistor 49.

Solenoid 23 and coil 25 are magnetically linked through plunger 29 so that the initial current flow through solenoid 23 in the direction from terminal 13 to emitter 49e induces a voltage in coil 25 of such polarity as to increase the emitter to base current of transistor 49. The increased base current of transistor 49 results in increased conduction of the transistor thereby increasing the current flowing through solenoid 23 which in turn increases the induced voltage in coil 25 until transistor 49 is driven to saturation.

The saturation current flowing through solenoid 23 is sufficient to drive plunger 29 against spring 26 to a point where spring 26 is fully compressed. When the current in solenoid 23 reaches the saturation level and is at a steady state, coil 25 no longer has a voltage induced therein and the emitter to base current in transistor 49 is insufficient to support saturation conduction of transistor 49, causing transistor 49 to reduce conduction resulting in a decreasing current flow through solenoid 23.

The reduced current flow through solenoid 23 causes the magnetic field therein to begin to collapse so that solenoid 23 and coil 25 each begin to have a reverse voltage induced therein in accordance with the equation e=L(di/dt).

The reverse voltage induced in coil 25 effectively reduces the DC voltage which occurs between the emitter 49c and base 49b of transistor 49 as a result of the DC tum-on bias current tending to flow via series connected solenoid 23, coil 25 and

resistors

53 and 59 and is applied across the emitter to collector junction of transistor 49. The sum of these voltages must not exceed the allowable emitter to collector voltage of the transistor; therefore, the reverse voltages induced in solenoid 23 and coil 25 are limited by controlling the rate of cur-' rent decrease through solenoid 23. Instantaneous turnoff of transistor 49 is prevented by providing a discharge current path through the emitter to base junction of transistor 49, through

resistors

51, 53 and 55 and diode 57. The current through this path sustains the conduction of transistor 49 for a short period of time and thereby reduces the rate of current decrease through solenoid 23 and the reverse voltage induced therein. Thus, transistor 49 continues to conduct for a short time and shares an important portion of the discharge current from solenoid 23.

By preventing a rapid decrease of solenoid current, the reverse voltage is limited allowing for the use of a low-cost transistor having a low emitter to collector voltage characteristic.

Resistors

51, 53 and 55 are selected to properly control the turnoff of transistor 49 and to limit its emitter to base current.

The reverse voltage induced in coil 25 is useful to reverse bias the emitter to base junction of transistor 49 to assure a complete turnoff of the transistor; however, the reverse voltage must be limited so as not to exceed the allowable reverse emitter to base voltage of the transistor. The reverse voltage is limited by the controlled turnoff transistor 49 as previously mentioned.

If the current path through

resistors

51 and 53 were the only path available for the discharge of solenoid 23 current, the solenoid would discharge much too slowly and the pump delivery rate would be unsatisfactory. in order to achieve a rapid, but controlled, collapse of the magnetic field and quick release of the plunger, a second current path through coil 25, resistor 55 and diode 57 is provided. The current through coil 25 serves a useful function by causing a large IR drop across the coil to reduce the effective reverse voltage induced in the coil thereby limiting the reverse emitter to base voltage to a low level allowing for the use of a transistor having a low reverse emitter to base voltage characteristic.

The major portion of the discharge current from solenoid 23 flows through coil 25 and resistor 55 to provide a rapid and safe dissipation of the energy released by the solenoid; however, the current flowing through

resistors

51 and 53 controls the rate of collapse of the magnetic field in the solenoid. Thus, the circuit allows for the use of a low-cost transistor while providing high operating frequency and greater fluid delivery.

Solenoid 23 is wound with number 22 A.W.G. wire as compared with number 20 A.W.G. wire used heretofore. Number 22 A.W.G. wire has sufficient resistance to lower the short circuit current of the device to a level which can easily be sustained by the DC voltage source without failure, thereby eliminating the need for a fuse. The DC source is, in most cases, a battery which in cold weather is at a reduced voltage and transistor 49 has a lower gain at cold temperatures so that transistor 49 may not turn on when number 22 A.W.G. wire is used in solenoid 23. Resistor 53, in series with coil 25, provides additional emitter to base voltage to assure transistor vtumon during cold weather and reduced voltage conditions.

Protection against an application of reverse voltage is provided by the absence of any low-resistance shunt paths as would be the case if a diode clamp were provided across solenoid 23. Three reverse current paths exist providing for approximately 2 amperes of reverse current at 12 volts. The first path is through

resistors

59, 53, 55 and diode 57, a second path is provided through

resistors

59, 53, coil 25 and solenoid 23 and a third path is provided through

resistors

59, 51, the base to emitter junction and solenoid 23. The reverse current through the base to emitter junction is maintained at an acceptable level by the use of resistor 51 and the high resistance of the wire used in solenoid 23.

By using number 22 A.W.G. wire for solenoid 23, the circuit provides its own transient protection. The smaller wire has higher resistance and allows for more turns resulting in a greater inductance. The large inductance is in series with the transistor and prevents short duration transients from reaching the emitter of the transistor. If the transients are longer than the time constant of the solenoid, the high resistance of the solenoid wire acts to dissipate the transient. The circuit does not provide any direct paths for transients to reach the transistor. If an'exceptionally strong transient is present, the circuit will turn on and the transient will be dissipated in the resistance of solenoid 23.

Referring to FIG. 4, there is shownanother embodiment of the invention for use with a higher level voltage source of about 24 volts. When a higher level voltage source is used, low temperature starting is not a problem; however, it is still necessary to dissipate the current resulting from the collapsing magnetic field. Dissipation of the energy stored in the solenoid becomes an even greater problembecause of the increased voltage and current. In the circuit of FIG. 4 the transistor must be able to withstand emitter to collector voltages of up to 60 volts. Such transistors have emitter to base voltage characteristics of about 30 volts and, therefore,

resistors

51 and 53 of FIG. 3 are not required.

To aid in the dissipation of the energy stored in the solenoid, and additional path is provided for discharge of solenoid 23. A resistor 61 is added in series with diode 57 and is connected between the cathode of diode 57 and cathode of diode 65. A diode 63 has an anode connected to emitter 49c and a cathode connected to the cathode of diode 57. Diode 63 provides an additional path for the discharge current from solenoid 23 and resistor 61 limits the current therethrough to a safe level.

A diode 65 is connected in series with the voltage source and has an anode connected to terminal 13 and a cathode connected to solenoid 23. Because of the higher voltage level, a reverse voltage application would destroy the circuit and diode 65 is used to prevent a reverse current flow through the circuit.

Referring to FIG. 5, there is shown another embodiment similar to the one shown in FIG. 6. In the embodiment the resistor 61 and diode 63 have been interchanged and capacitor 69 has been connected across the emitter 49and collector 490 to suppress radio frequencies. In the embodiment a very low emitter to base voltage is maintained, thereby permitting the use of higher voltage transistors while reducing the operating temperature of the transistor by drawing less solenoid discharge current through base 49b.

In FIG. 6 there is shown a circuit for use with a higher level voltage source similar to that of FIG. 4; however, the circuit is designed to withstand applications of 100 volts for 50 milliseconds for military purposes. The transistor is one having a 300 volt emitter to collector characteristic; however, such transistors have very low reverse emitter to base voltage characteristics. The circuit of FIG. 3 was modified by

eliminationof resistors

51 and 53 because low temperature is not a problem with the higher source voltage. A diode 67 was added having a cathode connected to the emitter 49c and an anode connected to the base 49b. Diode 67 acts to clamp the reverse emitter to base voltage at a safe level of about 1 volt. A capacitor 69 is connected between the emitter and collector of transistor 49 to suppress radio frequencies.

Thus, the present invention reduces pump cost by elimination of expensive components and by allowing the use of an inexpensive transistor. The circuit in conjunction with the pump provides delivery rates essentially higher than those heretofore available, while also providing positive cold temperature starts and transient protection. The circuit can withstand reverse voltage application and has a short circuit current sufficiently low to eliminate the need for a fuse.

While my invention has been illustrated with regard to a selected size wire in solenoid 23 and coil 25, the selected values used are for illustrative purposes only and my invention is not to be limited in scope to circuits employing these specific size elements.

Iclaim:

l. A reciprocating electromagnetic device powered by an electrical source comprising:

a reciprocating means;

a transistor having an emitter, a base and a collector;

a solenoid having first and second terminals connected by its first terminal to the emitter and by its second terminal to the electrical source, and magnetically linked to the reciprocating means, said transistor controlling the current flow from the electrical source through the solenoid;

biasing means, including a detection coil means magnetically linked to the solenoid and connected between the emitter and base circuit means of the transistor, responsive to increasing and decreasing solenoid current for respectively biasing the transistor toward saturation and cutoff; and

means of controllably dissipating energy released by the solenoid during collapse of its magnetic field;

said means comprising a serially connected combination of a resistor and a rectifier interconnecting the base of the transistor with the second terminal of the solenoid, the rectifier biased to pass electrical current from the base of the transistor to the second terminal of the solenoid, said means operative to cause the initial stages of collapse of the solenoid field to generate current which prevents transistor cutoff for a brief interval.

2. A device as described in claim I, additionally comprising control means for limiting the initial transistor cutoff bias thereby controlling transistor cutoff, so that a reverse voltage induced in the solenoid by its collapsing magnetic field is limited by controlling the rate of collapse.

3. A device as described in claim 1, wherein the biasing means comprises:

a coil magnetically linked to the solenoid by the reciprocating means and connected to the emitter and base; and

a first resistor connected to the base and the collector.

4. A device as described in claim 3, wherein the biasing means additionally comprises a resistor in series with the coil.

5. A device as described in claim 2, wherein the control means comprises a resistor connected between the base and the biasing means.

6. A device as described in claim 3, additionally comprising a second resistor interposed between the base and a connection between the coil and the first resistor.

7. A device as described in claim 6, additionally comprising a third resistor interposed between the coil and the first and second resistors.

8. A device as described in claim 7, wherein the energy dissipating means comprises:

a fourth resistor; and

a rectifier connected in series with the fourth resistor, said series connected in shunt relationship with the solenoid and coil so that energy released by the solenoid during collapse of its magnetic field is controllably dissipated.

9. A device as described in claim I, additionally comprising a rectifier having a cathode connected to the emitter and an anode connected to the base to limit reverse base to emitter voltage.

10. A device as described in claim 9, additionally including a capacitor between the emitter and collector.

II. A device as described in claim I, additionally comprisa resistor connected between the energy-dissipating means and the solenoid; and a rectifier having a cathode connected to a connection between that last-mentioned resistor and the energy dissipating means and an anode connected to the emitter.

12. A device as described in claim I, wherein the reciprocating means isa plunger in a fluid pump.

13. A device as described in claim 12, additionally compris= a hollow guide means positioned coaxially within the solenoid and having a fluid inlet and a fluid outlet, the plunger being slideably disposed in said guide member for reciprocal movement; and

a check valve means for allowing fluid flow in one direction only that being from the fluid inlet to the fluid outlet.

14. A device as described in claim 1, additionally comprising:

a rectifier having a cathode connected to the solenoid and an anode connected to the energy-dissipating means; and

a resistor connected between the anode of the last-mentioned diode and the emitter of the transistor.

15. A circuit for actuating a movable member, connectable to a source of energy comprising:

direction means connected in series relationship with said main inductive means and interconnecting said emitter electrode and said first resistive means;

said first resistive means responsive to the current in said main inductive means reaching the saturation level operative to cause said transistor means to become less conductive, whereby current flow through said main inductive means tends to decrease; and

means, including serially connected second resistive means and diode means interconnecting said first resistive means and said second terminal, cooperative with said first resistive means and said detection means to maintain, for a brief period of time, a reduced level of conduction in said transistor means whereby a large portion of the energy stored in said main inductive means is dissipated through said transistor means and to thereafter drive said transistor means to cutoff.

16. The circuit as claimed in claim 15 wherein said diode is arranged, and said main inductive means and detection means are coils and are magnetically linked so that said diode is blocked when current flow through said main inductive means is increased and to be conductive when current flow through said main inductive means is decreasing.

Claims

1. A reciprocating electromagnetic device powered by an electrical source comprising: a reciprocating means; a transistor having an emitter, a base and a collector; a solenoid having first and second terminals connected by its first terminal to the emitter and by its second terminal to the electrical source, and magnetically linked to the reciprocating means, said transistor controlling the current flow from the electrical source through the solenoid; biasing means, including a detection coil means magnetically linked to the solenoid and connected between the emitter and base circuit means of the transistor, responsive to increasing and decreasing solenoid current for respectively biasing the transistor toward saturation and cutoff; and means of controllably dissipating energy released by the solenoid during collapse of its magnetic field; said means comprising a serially connected combination of a resistor and a rectifier interconnecting the base of the transistor with the second terminal of the solenoid, the rectifier biased to pass electrical current from the base of the transistor to the second terminal of the solenoid, said means operative to cause the initial stages of collapse of the solenoid field to generate current which prevents transistor cutoff for a brief interval.

2. A device as described in claim 1, additionally comprising control means for limiting the initial transistor cutoff bias thereby controlling transistor cutoff, so that a reverse voltage induced in the solenoid by its collapsing magnetic field is limited by controlling the rate of collapse.

3. A device as described in claim 1, wherein the biasing means comprises: a coil magnetically linked to the solenoid by the reciprocating means and connected to the emitter and base; and a first resistor connected to the base and the collector.

8. A device as described in claim 7, wherein the energy dissipating means comprises: a fourth resistor; and a rectifier connected in series with the fourth resistor, said series connected in shunt relationship with the solenoid and coil so that energy released by the solenoid during collapse of its magnetic field is controllably dissipated.

9. A device as described in claim 1, additionally comprising a rectifier having a cathode connected to the emitter and an anode connected to the base to limit reverse base to emitter voltage.

11. A device as described in claim 1, additionally comprising: a resistor connected between the energy-dissipating means and the solenoid; and a rectifier having a cathode connected to a connection between that last-mentioned resistor and the energy dissipating means and an anode connected to the emitter.

12. A device as described in claim 1, wherein the reciprocating means is a plunger in a fluid pump.

13. A device as described in claim 12, additionally comprising: a hollow guide means positioned coaxially within the solenoid and having a fluid inlet and a fluid outlet, the plunger being slideably disposed in said guide member for reciprocal movement; and a check valve means for allowing fluid flow in one direction only that being from the fluid inlet to the fluid outlet.

14. A device as described in claim 1, additionally comprising: a rectifier having a cathode connected to the solenoid and an anode connected to the energy-dissipating means; and a resistor connected between the anode of the last-mentioned diode and the emitter of the transistor.

15. A circuit for actuating a movable member, connectable to a source of energy comprising: main inductive means having a first terminal and a second terminal, adapted when energized by the source to cause movement of the movable member; transistor means, having a base electrode, a collector electrode and an emitter electrode, connected by said emitter electrode to said first terminal of said inductive means and adapted to control current flow therethrough; first resistive means interconnecting said base electrode and the source of energy; direction means connected in series relationship with said main inductive means and interconnecting said emitter electrode and said first resistive means; said first resistive means responsive to the current in said main inductive means reaching the saturation level operative to cause said transistor means to become less conductive, whereby current flow through said main inductive means tends to decrease; and means, including serially connected second resistive means and diode means interconnecting said first resistive means and said second terminal, cooperative with said first resistive means and said detection means to maintain, for a brief period of time, a reduced level of conduction in said transistor means whereby a large portion of the energy stored in said main inductive means is dissipated through said transistor means and to thereafter drive said transistor means to cutoff.