US3264519A

US3264519A - Arc suppression means

Info

Publication number: US3264519A
Application number: US334173A
Authority: US
Inventors: Robert W Minck
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1963-12-30
Filing date: 1963-12-30
Publication date: 1966-08-02
Anticipated expiration: 1983-08-02

Description

g- 2, 1966 R. w. MINCK ARC SUPPRESSION MEANS 2 SheetsSheet 1 Filed D60. 30 1963 s K H m Mm mm a A 8 w m m R. WVMINCK 3,264,519

ARC SUPPRESSION MEANS Aug. 2, 1966 2 Sheets-Sheet 2 Filed Dec. $0, 1963 ROBERT W. MIA/CK INVENTORf BY 9on5 re. a!

ATTOR/VAYJ United States Patent 3,264,519 ARC SUPPRESSION MEANS Robert W. Minck, Detroit, Mich, assignor to The Ford Motor (Iornpany, Bearborn, Mich, a corporation of Delaware Filed Dec. 30, 1963, Ser. No. 334,173 '7 Claims. (Cl. 3152G6) This invention relates to means for protecting electrical switching elements in current interrupters and more particularly it relates to such a means placed in circuit with the electrical contact points or other switching element of an ignition system for an internal combustion engine.

A typical way of preventing arcing between contact points of an electrical switch when interrupting a current, particularly in an inductive circuit, is to connect a capacitor across the contact points. Upon opening of the contact points the capacitor provides, temporarily, an alternate current path thereby keeping the voltage across the contact points low during the period when the contact points are separating. This reduces arcing and contact electrode deterioration during the opening of the contact points.

In the conventional automotive ignition system, a capacitor is connected across the ignition contact breaker points. This capacitor is necessary for proper operation of the ignition system and to prevent contact wear at an extremely high rate. If a capacitor is not used, there is consistent arcing between the contact breaker points and the associated energy loss prevents sufficient ignition voltage from building up. With the capacitor currently used in automotive ignition systems, arcing is greatly reduced over the case where no capacitor is used, and the resultant small amount of arcing does not affect significantly the buildup of proper ignition voltages. This arcing is still highly undesirable, however, in that it gives rise to rate of contact wear much higher than that which would result with no arcing.

One proposed solution to this problem is to employ a larger capacitor than the one currently used, and this would definitely reduce arcing during contact opening. With a larger capacitor, however, a serious problem of arcing arises upon the closing of the contacts, since the large amount of charge on this larger capacitor would tend to create an arcing condition as the contacts close.

The present invention is directed toward the solution of contact arcing and to the protection of other switching elements in current interrupters and more particularly to the solution of this problem in an internal combustion engine ignition system. In the present invention a large capacitor may be connected across the ignition breaker points, or a switching transistor, if this is used, in the system. This capacitor will be large enough to prevent any arcing when the breaker points open, or to prevent unduly high voltages from occurring across the transistor when the transistor is being switched from its conducting to its nonconducting state. Discharge of the capacitor through the contacts when the contacts are closing, or through the transistor when the transistor is being switched from its nonconducting to its conduct-ing state, is prevented by connecting a zener diode between the ignition breaker points or transistor and the capacitor. This zener diode is poled so that the capacitor may charge when the ignition breaker contacts are opening, or the transistor is being switched to its nonconducting state. The direction of the charging current in this case is in the forward conduction direction of the zener diode. The zener diode is selected to have a zener or reverse breakdown voltage approximately equal to the terminal voltage of the source of electrical energy or storage battery connected to energize the ignition system.

It is well known that when the ignition breaker points open or the transistor is switched to its nonconducting state, that the system in effect becomes an LC oscillatory circuit in which large voltage or energy oscillations occur. For example, with a twelve volt battery the voltage across the primary winding of the ignition coil may rise to 250 volts in an effort to maintain the current flow through the circuit as the ignition breaker contact points open or the transistor is switched to its nonconducting state. These oscillations have both negative and positive voltage amplitudes with a frequency determined by the inductance and capacitance of the circuit. With the zener diode positioned in the circuit, having a reverse breakdown or zener voltage substantially equal or slightly greater than the terminal voltage of the storage battery, substantially all the large amount of energy stored in the capacitor may be returned to the circuit during the opposite polarity swing of the oscillations. This is true since the zener diode will break down and conduct in the reverse direction when the reverse voltage across it exceeds the zener voltage. Thus for all reverse voltages in excess of the zener voltage the circuit is free to oscillate.

When the oscillations die out the capacitor is charged to the battery voltage. The zener diode eifectively isolates the ignition breaker points or transistor from the capacitor when the breaker points close, or the transistor is switched to its conducting state, so that the capacitor cannot discharge through the ignition breaker points or the transistor to cause destructive arcing or energy dissipation. Means are provided, of course, to allow the charge on the capacitor to drain ofi slowly during the time the ignition points are closed, or the transistor is in its conducting state, so that the capacitor is again discharged when the breaker points open or the transistor is switched to its nonconducting state.

Thus, the use of the zener diode eiiectively isolates the capacitor from the ignition breaker points or transistor when the ignition breaker'points are closing or the transistor is being switched to its nonconducting state. At the same time, however, it permits the oscillations in the ignition system and permits this oscillatory energy to be transferred to the secondary winding of the ignition coil and to the spark plugs of the internal combustion engine.

With the use of the zener diode, a much larger arc suppression capacitor than is currently being used may be employed. This arc suppression may be selected to be of a size to prevent arcing when the ignition breaker points are being opened or if a transistor is used, to prevent destructive energy dissipation in the transistor when the transistor is being switched to its nonconducting state. The ignition system of the present invention will furnish proper oscillatory energy to the spark plugs of the ignition system and destructive arcing or energy dissipation will be prevented in the switching element, contact points or transistor, when the switching element is switched to its conducting state.

It should be noted that although the invention has been developed specificaly for ignition systems, that it can be used equally well in other systems in which protection of con-tact points or of transistors is required. An object of the invention is the provision of means for preventing destructively high voltages from being applied to a switching element during opening and clos ing of the switching element.

Another object of the invention is the provision of a means to reduce arcing in the contact points of an electrical switching circuit.

A further object is the provision of an ignition systern for an internal combustion engine in which sub stantially all of the oscillatory energy in the system is delivered to the spark plugs of the system and the switching element that switches the current in the primary circuit of an ignition coil is adequately protected both upon opening and closing of this switching element.

Another object of the invention is the provision of a means for eliminating arcing in the electricl contact points of the ignition system for an internal combustion engine and for simultaneously delivering substantially all of the oscillatory energy in the primary circuit of the ignition coil to the spark plugs of the system.

Other objects and attendant advantages of the present invention will become fully apparent as the specification is considered in connection with the attached drawings in which:

FIGURE 1 is a circuit diagram of an ignition system for an internal combustion engine employing the present invention; 7

. FIGURE 2 is a modification of the invention as applied to the ignition system of FIGURE 1;

FIGURE 3 is a circuit diagram of a transistorized ignition system for an internal combustion engine employing the present invention, and

FIGURE 4 is a modification of the invention as applied to the ignition system of FIGURE 3.

views thereof, there is shown in FIGURE 1 one embodiment of the present invention as applied to a conventional internal combustion engine ignition system in which a source of electrical energy in the form of storage battery has one electrode 11 connected to ground through a lead 12 and the other electrode 13 connected to ignition switch 14 through a lead 15. The ignition switch 14 is connected through a lead 16 to .the primary winding 17 of an igintion coil 18. The terminal of the ignition coil opposite the lead 16 is connected to a junction 19 through a lead 21. The junction 19 is connected through a lead 22 to one contact or electrode 23 of Va set of. distributor contact breaker points 24. The

other contact or electrode 25 of this set of distributor contact breaker points is mounted on a movable arm 26 and this movable arm is connected to a ground lead or wire 27 through a lead 28.

A zener diode 31 is connected to both the primary winding 17 and the contact 23 of distributor contact breaker points 24 by having its anode 32 connected to the junction 19. The cathode '33 of the zener diode other terminal connected to a rotating arm 45 of distri-butor 46 through a lead 47. The distributor is of conventional construction and includes the usual rotor cap in which spaced electrical contacts 51 through 56 are connected to spark plugs 57 .through 62 by means of leads 63 through 68 respectively. As is conventional in distributor construction, the rotating arm 45 is rotated (in synchronism with a contact breaker point interrupting means, preferably in the form of a cam 71, by the power developed by the internal combustion engine that employs this ignition system.

As is conventional in such an ignition system, the distributor con-tact breaker points 24 are closed when the rotating arm 45 is out of contact with the contacts 51 through '56. At this time, assuming the ignition switch 14 to be closed, current builds up in the primary winding 17 of ignition coil 18 creating a rising magnetic field. When the rotating arm 45 reaches one of the contacts 51 through '56, the breaker points 24 are opened so that the contacts or

electrodes

23 and 25 separate. This interrupts the current flow through the primary winding 17 of the ignition coil 18 and induces an electrical voltage of high magnitude in the secondary winding 43. This voltage is applied through the circuit previously described including the lead 47, the rotating arm 45, electrical contacts 51 through 56, and leads 63 through 68, to sequentially fire the spark plugs 57 through 62. a

When thevdistr-ibutor contact breaker points 24 open,

the voltage across the primary winding of the ignition.

' be readily appreciated that when the distributor contact breaker points open, that the primary circuit is in effect a series LC circuit because of the inductance of the primary winding 17 and the capacitance of the capacitor 35. This circuit will oscillate with an amplitude and frequency determined by the circuit parameters and, as stated, the amplitude may exceed 250 volts. These oscillations will gradually die out as determined by the damping ratio of the circuit.

The zener diode 31 may be selected so that ithas a zener or reverse breakdown voitage approximately equal to the terminal voltage of the storage battery 10, and the zener voltage should be greater, in anycase, than the voltage on the capacitor 35, when distributor contact breaker points 24 commence to close. For example, if the terminal voltage of the storage battery 10 is twelve volts, the zener diode may be selected to have a reverse breakdown or zener voltage of thirteen volts.

The high voltage amplitude oscillations alternately apply a reverse voltage or back voltage and a forward voltage on the zener diode 31. All of the energy of that portion of the oscillations that apply a forward voltage to the zener diode 31 may pass through the zener diode 31. That portion of the energy that is above the zener voltage may pass through the zener diode 31 in the reverse or back direction because the zener diode breaks down at this voltage. Thus only that energy that is below the zener voltage of the diode and of a polarity to apply a reverse voltage to the zener diode 31 is lost from the oscillatory energy of the primary circuit of the ignition system.

The capacitor 35 may be selected to be large enough to delay a high voltage rise across the distributor contact breaker points 24 as the breaker contact points 24 open. The voltage rise is delayed until the contacts or

electrodes

23 and 25 are separated sufliciently so that areing cannot occur at the highest voltages induced in the primary Winding 17 of the ignition coil. At this time, of course, the capacitor is effectively connected across the contacts or

electrodes

23 and 25 since the zener diode a conventional linear capacitor or a saturable capacitor of the type that will return to substantially an uncharged condition when the voltage is removed from it.

After the distributor contact breaker points 24 open,

the oscillations described above and the action of the zener diode 31 described above provides a proper oscillatory ignitionvoltage or energy to the spark plugs 57" through 62.

When these oscillations finally die out it can be un-- derstood that the capacitor 35 is charged to the terminal voltage of the battery 10. When the electrodes 23 and of the distributor contact breaker points 24 commence to close, after being opened, the zener diode 31 prevents the capacitor from discharging through the contacts or

electrodes

23 and 25 since the zener voltage or reverse breakdown voltage of the zener diode 31 is equal to or slightly greater than the terminal voltage of the storage battery 16 or the voltage to which the capacitor 35 is charged. Thus the energy stored in the large capacitor 35 is not discharged through these contact breaker points 24 but is discharged through the resistor 38 and the rate of discharge is determined by the time constant of this circuit. It is necessary, of course, that the capacitor 35 be discharged prior to the time that the ignition contact breaker points 24 again commence to open.

In FIGURE 2 the resistor has been eliminated and in this case the use of the zener diode 31 having a low back resistance is contemplated. It is well known that in ignition systems, the contact breaker points are closed for a much longer period of time than they are open and the low back resistance of the zener diode 31 will permit the capacitor 35 to discharge back through the zener diode and through the

closed contact electrodes

23 and 25 of the contact breaker points 24. The resistance of the diode 31, however, will be sufiiciently high so that the capacitor 35 cannot discharge rapidly through the contact breaker points 24- as they close. Rather, the capacitor can discharge slowly through the zener diode 31 and the contact breaker points 24 when they are closed. Thus the contact breaker points 24 will have very little current flow through them to cause arcing upon closing. The circuit of FIGURE 2 implies that a very inexpensive zener diode can be employed since a zener diode with a reasonably low back resistance is very much less expensive than one with a very high back resistance. The same type of zener diode, of course, may be employed in FIGURE 1, if desired, with the additional resistor 38 being provided for a more rapid discharge of the capacitor 35.

In FIGURE 3, the invention is applied to a transistorized ignition system in which a transistor 81 is employed to control current flow in the primary winding 17 of the ignition coil 18. As shown, the transistor 81 is of the NPN type in which a collector S2 is connected to the junction 19 through a lead 83 and the emitter 84 is connected to ground lead or wire 27 through a lea-d 85. Thus the output circuit of the transistor 81, comprising the collector 82 and the emitter 84, is connecied in circuit or in series with the source of electrical energy or battery 10 and the primary winding 17 of the ignition coil 18.

The base 86 of the transistor 81 is connected to the electrode 13 of the battery 1% through a resistor 87 and a set of contact breaker points 88, the lead 16, ignition switch 14 and lead 15. As is conventional in transistor circuits, a biasing resistor 89 is connected between the base 86 and the emitter 84. This is accomplished by connecting the resistor 8Q to the base and to the ground lead or wire 27.

In operation of this circuit, the cam 71 operates in synchronism with the rotating arm as in the embodiment of the invention shown in FIGURE 1. When the set of contact breaker points 88 is closed, the transistor 81 is in its conducting state since the base 86 is properly biased with respect to the emitter 84 and current may flow through the base circuit. When the contact breaker points 88 open, the transistor 81 is switched from its conducting to its nonconducting state since the base circuit is opened by the opening of the con-tact breaker points 88. At this time, the capacitor 35 charges through the zener diode 31 providing a temporary alternate current path for the current that was previously flowing through the transistor when the transistor was in its conducting state and delaying the onset of the high voltage oscillations previously described. This prevents a high voltage rise across the transistor when it is in its switching state, and this prevents high energy dissipation on the transistor when it is being switched from its conductng to its nonconducting state. The high oscillatory voltages can then occur without damage to the transistor 81 because it is substantially nonconducting and very little energy can be dissipated in it. The zener diode 31 in this circuit would be of the same type and have the same rating as the one employed with the circuit shown in FIGURE 1. That is, the zener or reverse breakdown voltage of the zener diode 31 will be approximately equal to or slightly greater than the terminal voltage of the battery 10 or eqaul to or slightly greater than the voltage on the capacitor 35 when the transistor 81 is switched to its conducting state, and the zener diode will act in the same way to permit oscillations in the circuit including the primary winding 17 of the ignition coil and the capacitor 35, thereby permitting oscillatory energy to be applied to the spark plugs 57 through 62 via the distributor 46. This circuit implies that an inexpensive transistor may be employed in the transistorized ignition system since the large voltages induced in the primary winding 17 are delayed until the transistor is completely switched from its conducting to its nonconducting state and the capacitor 35 cannot discharge through the transistor when the transistor is switched from its nonconducting to its conducting state.

When the contact breaker points 88 again close, the transistor 31 will be switched from its nonconducting to its conducting state and the zener diode 31 will prevent the capacitor 35 from discharging back through the transistor 31 and thus prevent high energy dissipation in the transistor 81 when the transistor 81 is switched from its nonconducting to its conducting state.

The resistor 33 provides a path for discharging the capacitor 35 as was the case in the embodiment of the in vention shown in FIGURE 1. In other respects, the embodiment of the invention shown in FIGURE 3 operates in the same manner as the embodiment of the invention shown in FIGURE '1 with the contact breaker points 83 opening when the rotating arm 45 of the distributor 46 is in contact with one of the electrical contacts 51 through 56.

The embodiment of the invention shown in FIGURE 4 is similar to that shown in FIGURE 2 as applied to the transistorized ignition system shown in FIGURE 3. In FIGURE 4, a low back resistance zener diode 31 maybe employed and it functions in the same manner as the low back resistance zener diode disclosed in FIGURE 2.

It can be appreciated that in the embodiment of the invention shown in FIGURES 3 and 4, the contact breaker points 88 switch only low base current of the transistor 81 and, therefore, are not subject to a large amount of arcing and deterioration. Also, it should be appreciated that any pulse generator for generating pulses to turn the transistor 31 on and off to switch it alternately from its conducting to its nonconducting state may be employed in place of the set of ignition contact breaker points 88.

Thus the present invention provides a means for protecting a switching element in a current interrupting circuit during both the opening and the closing of the switching element. It is particularly useful in an ignition system for an internal combustion engine in which it prevents arcing on both the opening and closing of a set of ignition contact breaker points. It may also be employed in an ignition system for an internal combustion engine employing a transistor and it prevents high voltages from being applied across the transistor and thus prevents high energy dissipation in the transistor when it is being switched from either its conducting to its nonconducting state or from its nonconducting to its conducting state. While providing this protection for the switching element in an ignition system, it also permits highly desirable oscillatory energy to be delivered to the spark plugs of the ignition system. This is brought about by the use of the zener diode in the primary circuit of the ignition system that properly protects the ignition contact breaker points or transistor while at the same time permitting oscillatory transfers of energy in the primary circuit of the ignition system at all voltages above the zener or reverse breakdown voltage of the zener diode.

It is to be understood that this invention is not to be limited to the exact construction shown and described but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. a

I claim:

1. In an ignition system for an internal combustion engine the combination comprising, a plurality of spark plugs, an ignition coil including a primary winding and a secondary winding, a distributor for sequentially connecting said secondary winding with said spark plugs, a source of electrical energy and a set of breaker contacts connected in series with said primary winding, means operated by said distributor for periodically opening said set of breaker points in synchronism with the connection of said secondary winding with said spark plugs, a capacitor and a zener diode connectedin series circuit, said series circuit connected across said set of breaker contacts, said zener diode being poled to permit said capacitor to charge through said zener diode when'said breaker con tacts are opened and to prevent rapid discharge of said capacitor through said breaker contacts when said breaker contacts close, said zener diode having a zener breakdown voltage at least equal to the voltage on said capacitor just prior to the time said breaker contacts commence to close.

2. In an ignition system for. an internal combustion engine the combination comprising, a spark plug, an ignition coil including a primary and a secondary winding, said secondary winding being connectable to said spark plug, a source of electrical energy connected to said primary winding of said ignition coil, a set of contacts connected in circuit with said source of electrical energy and said primary winding of said ignition coil for controlling the energization of said primary winding, means operable by the internal combustion engine for opening and closing said set of contacts and for connecting said spark plug to said secondary winding, a capacitor and a zener diode connected in series circuit, said series circuit connected across said set of contacts, said zener diode being poled to [permit said capacitor to charge through said zener diode when said set of contacts opens and for preventing said capacitor from discharging rapidly through said set of contacts when said set of contacts close, said zener diode having a breakdown voltage at least equal to the terminal voltage of said source of electrical energy whereby a majority of the energy stored in said capacitor is returned to said primary winding and said source of electrical energy after said set of contacts opens.

3. An electrical circuit, a source of electrical energy, an inductive circuit element, a switching element connected in series with said source of electrical energy and said inductive circuit element, means coupled to said switching element for switching said switching element between its conducting and nonconducting states, a series circuit including a capacitor and a zener diode connected across said switching element, said zener diode being poled to permit said capacitor to charge when said switching element is switched to its nonconducting state by forward current flow through said zener diode and to prevent rapid discharge of said capacitor through said switching element whensaid switching element is in its conducting state, said zener diode having a breakdown voltage at least equal to the voltage on said capacitor when said switching element is switched from its nonconducting to its conducting state.

4. In an ignition system [for an internal combustion engine the combination comprising, a spark plug, an ignition coil'including a primary and a secondary winding, said 8 secondary winding being connectable to said spark plu a source of electrical energy, a transistor having an output circuit electrode connected in circuit to control the ener gization of said primary winding of said ignition coil from said source of electrical energy, said transistor having an input circuit, means operable by said internal combustion engine and coupled to said input circuit for switching said transistor alternately between a conducting and a nonconducting state, said last mentioned means including means for alternately connecting and disconnecting said secondary winding of said ignition coil to and from said spark plug in synchronism with the switching of said transistor, a capacitor and a zener diode connected in series circuit, said series circuit connected across the output electrodes of said transistor, said zener diode connected series with said primary winding, said zener diode being poled to permit said capacitor to charge by forward current flow through said zener diode when said transistor is switched from its conducting to its nonconducting state and to prevent said capacitor from dischanging rapidly through said transistor when said transistor is switched rfrom its nonconducting to its conducting state, said zener diode having a zener voltage at least equal to the voltage on said capacitor when said transistor is switched to its conducting state.

5. In an ignition system for an internal combustion engine, a spark plug, an ignition coil including a primary winding and a secondary winding, an electrical storage battery, and a switching element connected in series with said primary winding of said ignition co-il, means operable by said internal combustion engine for switching said switching element periodically between conducting and nonconducting states, a capacitor and a zener diode connected in series circuit, said series circuit connected across said switching element and in series with said primary winding of said ignition coil, said capacitor and said primary winding of said ignition forming an inductive capacitive oscillatory circuit producing oscillating voltages across said primary winding having an initial amplitude at least several times greater than the terminal voltage of said source of electrical energy, said zener diode having a reverse breakdown voltage at least equal to the voltage on said capacitor when said switching element is switched to its conduct-ing state, said zener diode being poled in a direction to permit current flow through said zener diode in a forward direction to charge said capacitor whereby a majority of the oscillatory energy may pass through said zener diode between said primary winding and said capacitor after said switching element is switched from the conducting to the nonconducting state and said zener diode prevents said capacitor from discharging through said switching element when said switching element is switched to its conducting state, and means connected to said capacitor for permitting said capacitor to discharge.

6. In an ignition system for an internal combustion engine, a spark plug, an ignition coil including aprimary winding and a secondary winding, an electrical storage battery, and a set of contacts connected in series with said primary winding of said ignition coil, means operable by said internal combustion engine for periodically opening and closing said set of contacts, a capacitor and a zener diode connected in series circuit, said series circuit connected across said set of contacts and in series with said primary winding of said ignition coil, said capacitor and said primary winding of said ignition coil forming an inductive capacitive oscillatory circuit producing oscillating voltages across said primary winding having an initial amplitude at least several times greater than the terminal voltage of said source of electrical energy when said set of contacts is opened, said capacitor being sufficiently large to prevent arcing across said set of contacts as said set of contacts open, said zener diode having a reverse breakdown voltage substantially equal to the terminal voltage of said electrical storage battery and poled in a direction to permit current flow through said zener diode in a forward direction to charge said capacitor whereby a majority of the oscillatory energy may pass through said zener diode between said primary winding and said capacitor during the period when said set of contacts is opened and said zener diode prevents said capacitor from discharging through said set of contacts when said set of contacts is closed, and means connected to said capacitor for permitting said capacitor to discharge.

7. In an ignition system for an internal combustion engine, a spark plug, an ignition coil including a primary winding and a secondary winding, an electrical storage battery, and a transistor connected in series with said primary winding of said ignition coil, means operable by said internal combustion engine for switching said transistor periodically between conducting and nonconducting states, a capacitor and a zener diode connected in series circuit, said series circuit connected across said switching element and in series with said primary winding of said ignition coil, said capacitor and said primary winding of said ignition forming an inductive-capacitive oscillatory circuit producing oscillating voltages across said primary winding having an initial amplitude at least several times greater than the terminal voltage of said source of electrical energy when said transistor is switched to its nonconducting state, said capacitor being sufficiently large to prevent damage to said transistor as said transistor is being switched from its conducting to its nonconducting state, said zener diode having a reverse breakdown voltage substantially equal to the terminal voltage of said electrical storage battery and poled in a direction to permit current flow through said zener diode in a forward direction to charge said capacitor, whereby a majority of the oscillatory energy may pass through said zener diode between said primary winding and said capacitor when said transistor is switched from the conducting to the nonconducting state and said zener diode prevents said capacitor from discharging through said transistor when said transistor is switched to its conducting state, and means connected to said capacitor for permitting said capacitor to discharge.

References Cited by the Examiner UNITED STATES PATENTS 6/1960 Kerr 315209 7/1962 Martin 315209 OTHER REFERENCES 25 JOHN W. HUCKERT, Primary Examiner.

D, O. KRAFT, Assistant Examiner,

Claims

3. AN ELECTRICAL CIRCUIT, A SOURCE OF ELECTRICAL ENERGY, AN INDUCTIVE CIRCUIT ELEMENT, A SWITCHING ELEMENT CONNECTED IN SERIES WITH SAID SOURCE OF ELECTRICAL ENERGY AND SAID INDUCTIVE CIRCUIT ELEMENT, MEANS COUPLED TO SAID SWITCHING ELEMENT FOR SWITCHING SAID SWITCHING ELEMENT BETWEEN ITS CONDUCTING AND NONCONDUCTING STATES, A SERIES CIRCUIT INCLUDING A CAPACITOR AND A ZENER DIODE CONNECTED ACROSS SAID SWITCHING ELEMENT, SAID ZENER DIODE BEING POLED TO PERMIT SAID CAPACITOR TO CHARGE WHEN SAID SWITCHING ELEMENT IS SWITCHED TO ITS NONCONDUCTING STATE BY FORWARD CURRENT FLOW THROUGH SAID ZENER DIODE AND TO PREVENT RAPID DISCHARGE OF SAID CAPACITOR THROUGH SAID SWITCHING ELEMENT WHEN SAID SWITCHING ELEMENT IS IN ITS CONDUCTING STATE, SAID ZENER DIODE HAVING A BREAKDOWN VOLTAGE AT LEAST EQUAL TO THE VOLTAGE ON SAID CAPACITOR WHEN SAID SWITCHING ELEMENT IS SWITCHED FROM ITS NONCONDUCTING TO ITS CONDUCTING STATE.