US 3808513 A
Electronic DC-to-AC inverter system that employs a transistor oscillator using various types of transistors. It includes means to limit reverse voltages at the base-emitter paths of the transistors. It may be included in a continuous-wave high-frequency ignition system for internal combustion engines.
Description (OCR text may contain errors)
Umted States Patent 1191 1111 3,808,513 Canup 1 Apr. 30, 1974  IGNITION SYSTEM INCLUDING DC-AC 3,660,749 5/1972 Kadri 321/45 R X INVERTER 3,582,733 6/1971 Brubaker 321/45 R X 3,662,249 5/1972 Wijsboom.... 321/45 R X 1 1 lnventorlv Robert Canup, mond. Va. 3,635,202 1/1972 155161 et a1.... 123/148 E 3,164,786 1/1965 Wilson 321/45 R  Assgnee' Texam New York 3,119,972 1/1964 Fischman 321/45 R  Filed: Apr. 21, 1972 21 APP] No; 246 212 Primary ExaminerV Vil1iam M. Shoop. .11. I
Attorney, Agent, or F1rmT. H. Whale C. G. R1es  U.S. Cl. 321/45 R, 123/148 E, 331/113 A 51 Int. c1. 1102111 7/52  ABSTRACT  held of Search 123/148 ggs/ Electronic DC-to-AC inverter system that employs a transistor oscillator using various types of transistors. 5 6 R f Ct d It includes means to limit reverse voltages at the base- 1 e erences I e emitter paths of the transistors. It may be included in UNITED STATES PATENTS a continuous-wave high-frequency ignition system for 3,018,413 1/1962 Neapolitakis 123/148 E X internal combustion engines. 3,536,955 10/1970 Sturdevant et a1 331/113 A X 3,596,646 8/1971 Weiss 123/148 E 9 Claims, 6 Drawing Figures CROSS REFERENCES TO RELATED APPLICATIONS This application relates to the copending applications Ser. No. 100,642, filed Dec. 22, 1970; Ser. No. 193,909, filed Oct. 29, 1971; and Ser. No. 209,060,
filed Dec. 17,1971.
BACKGROUND OF THE INVENTION 1. Field of the Invention This invention concerns DC-to-AC inverters in genera] and, more specifically, relates to an improvement for an electronic circuit employing a transistor oscillator. In addition, the invention pertains to a particular use of the foregoing inverter in an ignition system for internal combustion engines.
2. Description of the Prior Art Heretofore, where DC-to-AC inverters employed transistor oscillator circuits and, particularly, where such inverters were employed in continuous-wave highfrequency ignition systems, there was a problem related to the maximum transistor emitter-to-base voltage which was especially severe with certain types of transistors. For example, such characteristics are inherent in transistors using an alloy-diffused epitaxial construction. Thus, in applications such as where an inverter is used in an ignition system for internal combustion engines, there was difficulty with the use of germaniumtype and, particularly, alloy-diffused-base type transistors because of the low emitter-to-base voltage rating of such transistors. A principal problem related to the fact that the temperature tolerance of germanium-type transistors is relatively low. On the other hand, when silicon-type transistors were employed instead of the germanium type, a limitation was found because of low reverse-voltage tolerance across the base-emitter path of the silicon-type transistor. This was particularly true when epitaxial-base type of silicon transistors were considered.
Consequently, it is an object of this invention to provide an improved oscillator circuit for use as a DC-to- AC inverter. Such inverter makes use of low emitter-tobase breakdown voltage type transistors, with means to. overcome the problem of failure due to a reversevoltage puncture of the base-to-emitter junction.
SUMMARY OF THE INVENTION Briefly, the invention concerns a DC-to-AC inverter for use in an ignition system and the like. It comprises a pair of transistors, and oscillator circuit means for connecting said transistors to conduct alternatively over the base-emitter path of each. It also comprises means for limiting the reverse voltage applied over said paths to protect against breakdown of said transistors.
Again briefly, the invention concerns a combination for use in a single-transformer high-frequency continuous-wave ignition system for internal combustion engines. Such combination comprises a transformer having a high-voltage secondary winding for delivering spark voltages to said internal combustion engine, and a center-tapped primary winding on said transformer. It also comprises a pair of transistors connected to said primary winding, the said transistors each having base,
collector and emitter electrodes. It also comprises at least one oscillator feedback winding on said transformer, and circuit means for connecting said transistors into an oscillator having base-to-emitter voltage paths. The said circuit means comprises means for limiting the amplitude of reverse-polarity voltages on said base-to-emitter voltage paths.
' Once more, briefly, the invention concerns a combination for use in a single-transformer high-frequency continuous-wave ignition system for internal combustion engines. It comprises a transformer having a highvoltage secondary winding for delivering spark voltages to said internal combustion engine, and a centertapped primary winding on said transformer, as well as a pair of transistors. The said transistors each have base, collector and emitter electrodes. The combination also comprises an oscillator feedback winding on said transformer, and first circuit means for connecting a DC voltage to said centertap of said primary winding. It also comprises second circuit means for connecting said collector electrodes to the ends of said primary winding, and third circuit means for connecting said emitter electrodes to ground. It also comprises fourth circuit means including a resistor thereon for connecting the ends of said feedback winding to said base electrodes. The third and fourth circuit means comprise portions of a complete circuit including the baseemitter paths of said transistors. The combination also comprises a pair of diodes, one connected between each of said base electrodes and ground, with the polarity being such that the reverse voltages at said baseemitter paths are limited to the forward voltages of said diodes. The combination also comprises an ignition control winding on said transformer, and anenginecontrolled means for cutting off and applying DC bias current in said control winding.
BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects and benefits of the invention will be more fully set forth below in connection with the best mode contemplated by the inventor of carrying out the invention, and in connection with which there are illustrations provided in the drawings, wherein:
FIG. 1 is a schematic circuit diagram illustrating a preferred modification according to the invention.
FIG. 2 is another schematic circuit diagram illustrating a different modification according to the invention.
FIG. 3 is yet another schematic circuit diagram illustrating a third modification of the invention.
FIG. 4 is a schematic circuit diagram of the same modification as FIG. I, but using a grounded positive and PNP transistors. 9
FIG. 5 is a schematic circuit diagram of the same modification as FIG. 2, but using a grounded positive and PNP transistors.
FIG. 6 is a schematic circuit diagram of the same modification as FIG. 3, but using a grounded positive and PNP transistors.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 of the drawings, it will be observed that the circuit diagram illustrates a DC-to-AC inverter, or oscillator 11. While it will be understood that there may be other and different uses for an inverter of this type, it is here being described as being employed in a high-frequency continuous-wave ignition system. Such system makes use of a transformer 12 that has a high-voltage output, or secondary winding 13. Also, as indicated by an arrow 16 and the caption HIGH VOLTAGE TO DISTRIBUTOR," the highvoltage circuit leads to the usual distributor arrangement (not shown) for an internal combustion engine.
The ignition system also includes a control winding 17 on the transformer 12. This control winding determines the timing for the ignition spark signals by controlling the oscillations of the oscillator 1 1. The oscilla- -tor when oscillating develops input energy in a centertapped primary winding 18 that is located on the transformer 12.-
' The manner of controlling the starting and stopping of the oscillator 11 by control winding 17 is fully described in my above-mentioned copending applications so that no detailed reference thereto is necessary here. It may be observed, however, that there is a source of DC current, as indicated by the plus symbol located adjacent to a circuit connector 21. This DC source will ordinarily be a storage battery (not shown) or the like. It would be carried by the vehicle, or otherwise situated adjacent to the internal combustion engine. Also joined to the circuit connector 21, there is a resistor 22 that is connected between the DC source and the upper end (as illustrated in FIG. 1) of the control winding '17. The lower end of winding 17 is connected via a circuit connector 25 to breaker points, or to alternative breakerless control arrangements, as indicated by the caption.
' lator l1 employs two NPN-type transistors and 31.
These are connected so that the collector electrode of each transistor 30 and 31 is connected via a circuit connector 32 and 33, respectively, to the ends of the center-tapped winding 18 on the transformer 12. The emitter electrodes of transistors 30 and 31 are each connected to ground by a circuit connector 36 and 37, respectively. And the center tap of winding 18 is connected to a DC-voltage source via a connector 40 that joins the connector 21 mentioned earlier. Also, for the purpose of the ignition system, there is a capacitor 41 that is preferably connected with its physical location being close to the center tap of winding 18 and to engine ground.
Also, as part of the oscillator, there is a feedback winding 44 on the transformer-l2 that has the ends thereof connected to the base electrodes of the transistors 30 and 31. These connections are made via circuit connectors 46 and 47, respectively. And, there is a resistor 48 connected in series in this circuit so as to limit the current flow which will develop as the oscillator is oscillating and, thus, limit the current in the highvoltage winding 13 during the ignition event.
Previously, when this type of oscillator was-employed for an ignition system it was not feasible to make use of silicon-type transistors and, particularly, epitaxial and diffused-base types, on account of the low reversevoltage capability at the base-emitter path for such types of transistor. However, in accordance with this invention, there is a pair of diodes 50 and 51 that are each connected in parallel across the respective baseto-emitter path of the transistors 30 and 31. This is accomplished by having circuit connectors 54 and 55 going from one side of each of the diodes 50 and 51 to ground. The other side of each of the diodes 50 and 51 is connected to the circuit connectors 46 and 47, respectively, which (as indicated above) lead to the base electrodes of the transistors 30 and 31.
It will be noted that these diodes 50 and 51 are connected with the polarity of each such that any substantial reverse-voltage generated current flow across the base-emitter path of the transistors 30 and 31 will be bypassed through the diode having a low-resistance path. Thus, as soon as the reverse voltage that is rising across the base-to-emitter path of each transistor exceeds whatever forward-voltage rating the corresponding diode has, it will be limited from any further increase by the shunting effect of the low forward resistance through the diode. In this manner, the reverse voltage which would have been applied to each transistor during one-half of the oscillator cycles, will be limited to a safe value. This avoids the condition which would cause failure of the transistors by exceeding the emitter-to-base breakdown voltage. Of course, during the other half of the oscillator cycles, when forwardvoltage conditions exist at each transistor, desirable current flow through the base-emitter path takes place without shunting because of the polarity of the other diode in each case.
It may'be noted that the foregoing circuit provides a combination such that the transistors 30 and 31, which must pass a large current, do not need to have a large base-to-emitter reverse-voltage breakdown capability. Consequently, use may be made of transistors having low emitter-to-base breakdown voltage but which have excellent collector-to-emitter saturation voltage and switching characteristics.
The operation of the system may be described commencing with the starting of the oscillator 1 1. Thus, the decaying magnetic flux in the core of the transformer 12 which is caused by the engine-controlled circuitopening of the winding 17, will induce voltages in all of the transformer windings. When the lower end of winding 44 is positive with respect to the upper end thereof, current will flow over the connector 46 to the base of transistor 30. Then it will continue over the baseemitter forward path of transistor 30 to ground via connector 36. From there it continues from the circuit ground via connector 55 and through the diode 51 to connector 47, with resistor 48 therein, and back to the upper end of the winding 44. This current flow through the transistor 30 will turn it on, and the reverse voltage applied to the other transistor 31 across the basepositive'than the lower end. Then current will flow via connector 47 and resistor 48 to the base of the other transistor 31. It continues over the forward baseemitter path of transistor 31 to ground via connector 37. Then it goes from ground via the connector 54 and the diode 50 back to the lower end of the winding 44 via the connector 46. This limits the reverse voltage across the base-to-emitter junction, or path of transistor to the voltage drop across the diode which is low.
Referring to FIG. 2, there is illustrated a modified form of inverter which is being used in the same type of ignition system for providing high-frequency continuous-wave spark signals. There is a transformer 59 that has a secondary, or high-voltage winding 60 to supply the spark signals to an engine distributor (not shown) or the like. In addition, there is a center-tapped primary winding 63 and feedback winding 64, as well as an oscillation control winding 65.
The control winding 65 acts in the same manner as was described in connection with FIG. 1 and, similarly, there is a circuit connector 68 at one end of the winding 65 which leads to engine-controlled means such as breaker points, as indicated by the caption. Connected to the other end of the winding 65, there are a resistor 69 and a diode 70, with the resistor 69 connected in series to a DC supply over circuit connection 71.
There are a pair of NPN transistors 74 and 75 that have the oscillator electrodes of each connected to the ends of winding 63, while the emitter electrodes are connected to ground, as illustrated. The base electrodes of the transistors are connected into a series circuit with the winding 64. This circuit may be followed from the base of transistor 74 over a circuit connector 78, and via a diode 79 to a circuit connection point 81 and a connector which leads to the one end of the winding 64. The other end of the winding 64 is connected over a connector 83 to a circuit connection point 84 and then via a diode 85, and on over a circuit connector 86 to the base electrode of transistor 75. It will also be noted that there are two additional diodes 90 and 91 that are connected with one electrode to the common circuit points 81 and 84, while the opposite electrode of each is connected to ground, as illustrated.
In this case, the operation of the oscillator is substantially like that. described above in connection with FIG. 1. It will be sufficient to note that the oscillator starts upon the opening of the circuit for energizing winding 65 which produces a decaying magnetic flux in the transformer 59. Such decaying flux induces a voltage in all of the other windings of the transformer, and when the lower end of the winding 64 is positive with respect to the upper end, current will flow from the lower end through diode 79, the base of transistor 74, and back through diode 91, and then via a resistor 92 to complete a circuit to the upper end of the winding 64. Such current flow turns on the transistor 74 and starts the oscillator into oscillation. As this action takes place, the reverse voltage across the base-emitter junction of transistor 75 will be only the voltage drop across the diode 91 in its forward direction which is approximately 7/10 of a volt. When the oscillator switches and the other transistor 75 conducts, the opposite action takes place so that the reverse voltage across the baseemitter junction of transistor 74 will have only the voltage drop across diode 90 applied.
Referring to FIG. 3, it will" be noted that this modification illustrates a modified oscillator circuit being used in an ignition system of a similar type as those described above in relation to FIGS. 1 and 2. In this case, there is a transformer 95 that has a high-voltage secondary winding 96. In addition, there is a control winding 97 as well as a center-tapped primary winding 98. In this modification, there is an oscillator 99, and the feedback for the oscillator is obtained from two separate windings 100 and 101. These windings have one end of each connected to ground, as illustrated. The other end of each of these feedback windings is connected in each case to the base electrode of each of a pair of transistors 104 and 105, respectively. However, in this case, there are resistors 108 and 109 with diodes 110 and 111 respectively connected in shunt thereof. Also, there is another pair of diodes 114 and 115 that are connected between the base electrodes and ground, i.e., across the base-emitter paths of the transistors 105 and 104, respectively.
The operation of the FIG. 3 system is in substance the same as the two other modifications. It may be noted that the resistors 108 and 109 are provided for limiting the amount of current drawn during the reverse-voltage conditions for each half of the oscillation cycle. Also, as with the other modifications, the entire ignition system includes a source of DC voltage, such as a battery 116. The control of the oscillator for creating the debreakdown voltage ratings, particularly silicon-type transistors. Consequently, the high-temperature characteristics of silicon-type transistors may be taken advantage of while obviating the disadvantages of a type of transistor that has low reverse-voltage capability.
It will be appreciated that the modifications illustrated in FIGS. 4, 5 and 6 are each substantially the same in principle as the corresponding FIGS. 1, 2 and 3, respectively. The differences relate to the fact that the FIGS. 4, 5 and 6 modifications make use of PNP transistors instead of NPN type. The operating principles are the same and need not be described in detail. It will be noted that these modifications result in a reverse polarity, i.e. a positive ground circuit in each case.
While the invention has been described above in considerable detail in accordance with the applicable statutes, this is not to be taken as in any way limiting the invention but merely as being descriptive thereof.
1. In a single-transformer high-frequency continuouswave ignition system for internal combustion engines, the combination comprising a transformer having a high-voltage secondary winding for delivering AC spark voltages directly to said internal combustion engine,
a center-tapped primary winding on said transformer,
a pair of transistors connected to said primary winding,
said transistors each havine base, collector and emitter electrodes,
at least one oscillator feedback winding on said transformer, circuit means for connecting said transistors into an oscillator having base-to-emitter voltage paths, said circuit means comprising a diode in shunt of said base-to-emitter voltage paths, for limiting the amplitude of the reverse-polarity voltages, and the combination further comprises a control winding on said transformer, and engine-controlled means for cutting off and applying a DC bias current in said control winding. 2. The invention according to claim 1, wherein the combination further comprises a pair of oscillator feedback windings on said transformer, a resistor in series with each of said feedback windings, and a diode in shunt of each of said resistors for permitting full current flow in the forward direction over said base-to-emitter path. 3. The invention according to claim 1, wherein said transistors are diffused-base type.
4. The invention according to claim 2, wherein said transistors are diffused-base type.
5. The invention according to claim 1, wherein said transistors are silicon type.
6. The invention according to claim 2, wherein said .a transformer having a high-voltage secondary winding for delivering spark voltages to said internal combustion engine,
a center-tapped primary winding on said transformer,
a pair of transistors,
said transistors each having base, collector and emitter electrodes,
an oscillator feedback winding on said transformer,
first circuit means for connecting a DC voltage to said center tap of said primary winding,
vsecond circuit means for connecting said collector electrodes to the ends of said primary winding,
third circuit means for connecting said emitter electrodes to ground,
fourth circuit means, including a resistor therein, for connecting the ends of said feedback winding to said base electrodes,
a pair of diodes, one connected between each said base electrode and ground with polarity for shunting reverse voltages at base-emitter paths in excess of the forward voltages of said diodes,
an ignition-control winding on said transformer, and
transistors are silicon type.