US3878452A

US3878452A - Transistorized magneto ignition system for internal combustion engines

Info

Publication number: US3878452A
Application number: US384282A
Authority: US
Inventors: Georg Haubner; Walter Hofer; Peter Schmaldienst
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1972-08-29
Filing date: 1973-07-31
Publication date: 1975-04-15
Anticipated expiration: 1992-04-15
Also published as: FR2198547A5; JPS5727310B2; DE2242325A1; ATA677273A; DE2242325C3; SE384249B; CA993036A; BE804115A; GB1402688A; YU208773A; BR7306619D0; DE2242325B2; IT993044B; YU35284B; ES418239A1; JPS4964730A; AU5966973A; JPS5621909B2; JPS56101067A; AT325900B

Abstract

Diodes in series with a switching transistor and conducting in the same direction, interposed between the switching transistor and the primary winding of a magneto armature, are used to establish a steady voltage drop during conduction for application over a resistor to the base of the switching transistor to keep the transistor conducting during positive half waves of the magneto generator, except when the transistor is switched off to interrupt the primary current by a control signal. The high voltage for the spark is produced by a secondary winding on the magneto armature. The control signal may be switched on and off by the output of a magnetic pulse transmitter and powered by a capacitor charged by negative half waves of the magneto generator. The system that produces a spark for every positive half wave utilizes a voltage divider containing a Zener diode to generate the control signal when the Zener voltage is reached, and temperature compensating diodes are also provided in this voltage divider.

Description

United States Patent 1191 Haubner et a1.

[54] TRANSISTORIZED MAGNETO IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES [75] Inventors: Georg IIaubner, Berg; Walter I-Iofer,

Schwabach; Peter Schmaldienst, Nurnberg, all of Germany [73] Assignee: Robert Bosch G.m.b.H., Stuttgart,

Germany [22] Filed: July 31, 1973 [21] App]. No.: 384,282

[30] Foreign Application Priority Data Aug. 29, l972 Germany 2242325 [52] US. Cl 322/17; 123/148 E; 310/70 A; 315/218; 315/209 T [51] Int. Cl. F02p 1/00; F02p 1/08; F02p 9/00 1451 Apr. 15, 1975 3,504,373 3/1970 Strelow 315/218 Primary Examiner-J. D. Miller Assistant ExaminerRobert J. Hickey Attorney, Agent, or FirmF1ynn & Frishauf [57] ABSTRACT Diodes in series with a switching transistor and conducting in the same direction, interposed between the switching transistor and the primary winding of a magneto armature, are used to establish a steady voltage drop during conduction for application over a resistor to the base of the switching transistor to keep the transistor conducting during positive half waves of the magneto generator, except when the transistor is switched off to interrupt the primary current by a control signal. The high voltage for the spark is produced by a secondary winding on the magneto armature. The control signal may be switched on and off by the output of a magnetic pulse transmitter and powered by a capacitor charged by negative half waves of the magneto generator. The system that produces a spark for every positive half wave utilizes a voltage divider containing a Zener diode to generate the control signal when the Zener voltage is reached, and temperature compensating diodes are also provided in this voltage divider.

13 Claims, 3 Drawing Figures [58] Field of Search 310/70 R, 70 A; 322/17, 322/91, 94; 315/209, 218, 209 T; 123/148 E, 148 CD [56] References Cited UNITED STATES PATENTS 3,398,353 8/1968 Noddin et a1. 322/91 X 3,484,677 12/1969 Piteo 310/70 R x 3,496,920 2/1970 Shano et al. 310/70 R x TRANSISTORIZED MAGNETO IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES Cross reference is made to the following application of the same inventors: Ser. No. 384.380. filed July 31. 1973 and Ser. No. 384.381. filed July 31. i973.

This invention relates to transistorized magneto ignition systems for internal combustion engines. and particularly to a system in which. at the desired time of ignition. an ignition transistor interrupts the circuit of a primary winding ofa stationary armature of a magneto generator. The primary winding is associated with a secondary winding so that the two function as an ignition coil and the secondary winding strikes a spark at a spark plug gap when the circuit of the primary \vinding is interrupted. In this type of arrangement current is excited in the primary winding of the stationary armature by the rotation of an array of permanent magnets driven by the engine.

In so-called coil ignition systems generally a previously closed primary circuit of the ignition system is opened. causing the magnetic field of the ignition coil built up by the primary current to collapse and to induce a high voltage pulse in the secondary winding which produces the ignition spark. In transistorized systems of this type the interruption of the primary circuit is produced when a control signal switches the ignition transistor from its conducting to its nonconducting condition.

After a spark has been produced in a system of this type. the circuit of the primary winding must be closed again in order to produce the next spark. In batterypowered ignition systems. the necessary control voltage for switching the ignition transistor on again can be obtained from the battery. In so-caled magneto ignition systems. however. the voltage at the terminals of the magneto armature is too small. when the primary winding circuit is short circuited. to switch the ignition transistor completely into the conducting condition as is necessary to build up a strong magnetic field in the ignition coil or in the magneto armature that is built to serve as an ignition coil (which may be referred to as an ignition armature).

In a known form of transistorized magneto ignition systems. the ignition transistor is connected in series with a resistor in the circuit of the primary winding. In such a system when a positive half wave of the ignition armature appears. the ignition transistor is switched on and held in conducting condition by the voltage drop appearing across this resistor until the moment of ignition. At the moment of ignition. the base-emitter path of the ignition transistor is short circuited and the ignition transistor is thereby blocked. This and similar solutions of the problem have the disadvantage that the resistor undesirably loads down the circuit of the primary winding. because it has a current limiting effect and permits only a limited build up of the magnetic field in the ignition armature during the positive half wave of the magneto generator. In consequence. when the circuit of the primary winding is interrupted by the ignition transistor. the high voltage released in the secondary winding of the ignition armature is greatly reduced.

It is an object of this invention to provide a transistorized magneto ignition system in such a way that the magnitude of the primary winding current which is to be interrupted at the instant of ignition is largely uneffected by the presence of control components for the ignition transistor in the circuit of the primary winding.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly. at least one diode is poled for conduction in the same direction as the switching path of the ignition transistor and is connected in series between that switching path and the primary winding. and the control electrode of the ignition transistor is connected over a resistor to the terminal of the diode or diodes farthest from the connection of the diode or diodes to the ignition transistor switching path.

In a preferred form of the invention a series combination of two diodes is connected to the collector of the ignition transistor. the emitter of which is connected with one end of the primary winding of the ignition armature. while the base of the ignition transistor is connected both with a control assembly and. as aforesaid. over a resistor to the diode terminal farthest from the collector of the ignition transistor. which diode terminal is also connected to the other end of the primary winding of the ignition armature. When a positive half wave of the voltage produced in the ignition armature winding appears. the ignition transistor in this ignition system is held in conducting condition while using as control voltage the constant voltage drop across the diodes that is produced when they are conducting. In this solution of the problem the strength ofthe primary current is limited neither by the diodes nor by the ignition transistor. since the latter is held fully in its conducting condition by the control voltage across the diodes until the instant of ignition.

The invention will be described by way of example with reference to the accompanying drawing. in which:

FIG. I is a circuit diagram of an ignition system according to the invention. in which the ignition transistor is switched off by a pulse generator over a control assembly at the instant of ignition;

FIG. 2 is a timing diagram showing the course of control voltages and control currents for switching of the ignition transistor. and

FIG. 3 is a diagram of a portion of the circuit for the primary winding of the same type of magneto ignition device as shown in FIG. I, in which a voltage divider is provided for switching the ignition transistor.

FIG. 1 shows the circuit diagram of an ignition system for a one-cylinder internal combustion engine that is supplied by a magneto generator 10. The magneto 10 consists of a rotating magnet array 11 composed of a number of alternately poled permanent magnets disposed in the circumferential direction of the rotor of the magneto generator. This rotor may. for example, be cast in the fly wheel of the engine and thus driven by it.

The rotor magnets act on an ignition armature 12. mounted on the engine casing. This armature has a winding 13 in the form of an ignition coil. with a primary winding 13a and a secondary winding 13b. The secondary winding 13b is connected over 'an ignition cable 14 with a spark plug 15 of the internal combustion engine.

The primary winding 13a of the ignition armature 12 supplies a primary circuit in which is included the collector-emitter path of an NPN ignition transistor 16. The collector of the transistor 16 is connected to the cathode side of a series combination of two diodes l7 and 18, while the emitter of the transistor 16 is connected to the end of the primary winding 13a which is grounded to the chassis or the motor casing. A resistor 19 is connected from the base of the ignition transistor 16 to the anode of the diode 17. which is also connected to the other end of the primary winding 13a of the ignition armature 12. The base of the ignition tran' sistor 16 is also connected to a control assembly which comprises a switching device 20 and a capacitor 21. The capacitor 21 has one terminal connected with the grounded end of the primary winding 13a and its other terminal connected over a diode 22 with the other end of the primary winding 13a. The diode 22 is poled. with reference to the circuit of the primary winding. oppositely to the polarity of the

diodes

17 and 18. The switching device 20 is connected with a magnetic pulse transmitter 23 for its control. The switching device 20 is connected to the base of the ignition transistor 16, where a second resistor is also connected. with its other end grounded.

The operation of this ignition system can best be explained by reference to the timing diagram of FIG. 2 where the voltages and currents are shown to which the ignition transistor 16 is subject. Against the axis out are plotted both the primary current 1,, and the primary voltage U,, of the primary winding 13a. with the current I shown by the solid curve and the voltage U,, by the dashed curve. Against the axis wI- are plotted the base current I of the ignition transistor 16 and the voltage U across the capacitor 21. with the base current 1,, shown by the solid curve and the capacitor voltage U by the dashed curve.

When the rotary magnet array 11 is rotated in the direction shown in the arrow in FIG. 1 upon starting the engine. the permanents magnets produce a voltage in the primary winding 13a of the ignition armature 12 having positive and negative half waves in alternate succession. When a first positive half wave of the primary voltage U,, appears. the threshold voltage of the

diodes

17 and 18 is soon reached in the primary circuit. That threshold voltage is applied over the resistor 19 to the base of the ignition transistor 16. Since the transistor 16 has its emitter grounded. this voltage causes a base current 1,, to flow which puts the ignition transistor 16 into its conducting condition. The primary circuit over the

diodes

17 and 18 and the switching path of the transistor 16 is now short circuited and a primary current 1,, flows. which produces merely the voltage drop across the

diodes

17 and 18 and across the switching path of the transistor 16 that is necessary for maintaining the conducting condition of the ignition transistor 16. The primary voltage U,, across the winding 13a quickly collapses and remains at a low value while the current flows. When the succeeding negative half wave of the primary voltage U appears. the

diodes

17 and 18 as well as the switching path of the ignition transistor 16 quickly become and remain nonconducting. Since the diode 22 is poled for conduction during this voltage half wave. the capacitor 21 is charged to a negative voltage U... The switching device 20, which for example can be provided in the form of a bistable flipflop stage. is at this time in its blocking condition. so that the capacitor 21 cannot discharge over the switching device 20 and the resistor 24. When the next positive half wave of the primary voltage U,, appears, the ignition transistor 16 is again made conducting. The primary circuit is accordingly again short circuited and a strong magnetic field is built up in the ignition armature 12 by the strong primary current I,,. At the proper time of ignition 1,- the magnetic pulse generator 23 now transmits a control pulse that switches over the switching device 20, so that the voltage U,. across the capacitor 21 is connected by the switching device 20 to the baseemitter path of the ignition transistor 16. The base thereby becomes negative with respect to the emitter, so that the ignition transistor immediately blocks the primary current I,,. With this interruption of the primary current the magnetic field in the ignition armature 12 suddently collapses and induces a high voltage pulsein the secondary winding 13b. which produces a spark in the gap of the spark plug 15.

Upon collapse of the magnetic field in the armature 12 a voltage peak is also induced in the primary winding 13a. but that has no effect on the base of the ignition transistor 16 when the resistor 19 has a high value of resistance. After the capacitor 21 has discharged over the switching device 20 and the resistor 24, the magnetic pulse generator 23 provides a new control pulse to put the switching device 20 back into its blocking condition. During the next negative half wave of the primary voltage U,, the capacitor 21 can now recharge and the ignition cycle can be repeated with each complete revolution of the magnet array 11 in the manner just described.

FIG. 3 shows another circuit for connection to the primary winding of an ignition magneto of the kind shown in FIG. 1. The same components are here provided with the same reference numerals as in FIG. 1. A series combination of two

diodes

17 and 18 is again shown for putting and maintaining the ignition transistor 16 in its conducting condition. The anode connection of the diode 17 is in this case connected over the resistor 19 to the base of an exciting transistor 30 which is coupled with the ignition transistor 16 in a Darlington circuit. The control circuit of the exciting transistor 30 is provided with a control transistor 31 having its collector-emitter path connected in parallel to the combined base-emitter paths of the

transistors

30 and 31 of the Darlington combination. If the ignition transistor 16 were not provided with an exciting transistor 30 in the Darlington circuit. the switching path of the control transistor 31 would be directly in parallel with the base-emitter path of the ignition transistor 16.

The base of the control transistor 31 is connected with the tap 31a of a voltage divider 32, which is connected across (i.e. in parallel with) the primary winding (not shown) of the ignition magneto armature. The voltage divider 32 consists of a resistor 33, two series connected diodes 34 and 35, a Zener diode 36 and another resistor 37. The tap 32a of the voltage divider is located between the Zener diode 36 and the resistor 37. The Zener diode 36 in the upper portion of the voltage divider 32 is poled so that upon the arrival of a positive voltage half wave in the primary circuit of the ignition system. the control transistor31 will receive the positive potential necessary to switch it over into its conducting condition only when the Zener voltage is reached. In order to limit the negative voltage half waves in the primary circuit of the ignition system. the primary winding 13a of the armature 12 is bridged by another diode 38 which is connected in series with a resistor 39. The diode 38 has a polarity opposite to that of the diodes l7 and 18 with reference to the primary circuit.

The operation of the'system shown in FIG. 3 is such that when a positive half wave of the ignition magneto (FIG. 1) applies a positive potential across the resistor 19 to the base of the exciting transistor 30. both the exciting transistor and the ignition transistor 16 are switched into their conducting condition by current flowing to the grounded emitter of the ignition transistor 16. The primary circuit is thereby short-circuited and the primary current flows through the diodes l7 and 18 and through the switching path of the transistor 16. The constant voltage drop across the

diodes

17 and 18 then maintains the

transistors

30 and 16 in their conducting condition. At the ignition time the Zener diode 36 of the voltage divider 32 reaches its Zener voltage and breaks down. so that a positive potential is now applied from the tap 32a to the base of the control transistor 31 for switching the latter into its conducting condition. When the control transistor 31 conducts. the base of the exciting tranistor 30 is grounded and in consequence both the

transistors

30 and 16 are blocked. The primary current is thereby suddenly interrupted. causing a spark to be produced at the gap of the spark plug (not shown). The positive voltage peak then induced in the primary winding (not shown) of the ignition armature has no effect. because it merely drives the control transistor 31. over the Zener diode 36. more strongly into its conducting condition. simply keeping the base of the exciting transistor 30 effec tively grounded.

Towards the end of the positive half wave in the primary circuit the Zener voltage across the Zener diode 36 disappears as the voltage across the primary winding drops. so that the control transistor 31 goes back to its nonconducting condition. The base of the exciting transistor 30 then again goes back to the anode potential of the diode 17 as applied over the resistor 19. The succeeding negative half wave of the magneto. when it arrives. is sufficiently loaded down by the series combination of the now conducting diode 38 and the resistor 39 to prevent generation of a voltage in the secondary winding 13b of the ignition armature 12 sufficiently high to strike a false spark.

The diodes 34 and connected in series with the Zener diode 36 in the voltage divider 32 are designed to shift the ignition timing in such a way as to compensate for the temperature characteristic of the

transistors

30 and 16. so as to prevent the primary voltage from varying with temperature. This ignition system is particularly suitable for magneto generators with only one rotating permanent magnet. since it produces a spark for each positive voltage half wave in the primary circuit.

Although the invention has been described with respect to particular embodiments. it is not limited to these embodiments and modifications and variations may be made within the inventive concept without departing from the spirit of the invention. For example. the stationary armature of the magneto generator can be provided without a high voltage winding. In this case a separate ignition coil is necessary with its primary winding in circuit with the armature winding. It is also possible to utilize only one diode instead of the two

diodes

17 and 18, so long as the voltage drop across the diode during conduction is sufficient for controlling the ignition transistor. A PNP power transistor may be used as the ignition transistor instead of an NPN transistor. in which case the other polarization-sensitive electrical components must be correspondingly poled. Whether the ignition coil providing a high voltage winding is built into the magneto generator or. is separate. the high voltage winding constitutes in each case a voltage step-up means coupled with the magneto armature.

We claim:

1. In an internal combustion engine ignition system having a magneto armature provided with at least one winding arranged to be excited by a magnetized rotor driven by the engine. and having voltage stepup means coupled with said magneto armature. which means is coupled with a low-voltage winding of said armature and connected by ignition cable to at least one spark plug.

an ignition control circuit for connection to said lowvoltage winding of said armature. comprising:

a controllable semiconductor device (16) having its switching path in circuit with said low-voltage winding;

pulse signal means to derive a timing signal for ignition and to supply said signal to the control electrode of said semiconductor device (16);

at least one diode (17.18) connected in series with said switching path of said semiconductor device (16) and poled for conduction in the same direction as said switching path. and

resistance means (19) for turning on said semiconductor device (16) during positive half waves of the output of said low-voltage winding. except while said signal is supplied by said pulse signal means as aforesaid. said resistance means 19) having only two terminals connected in said ignition control circuit and being connected by said terminals. between the control electrode of said semi conductor device (16) and the terminal of said diode(s) which is farthest from the connection thereof to said switching path.

2. An ignition control circuit as defined in claim 1. in which said diode or diodes are connected to the collector end of said switching path of said semiconductor device.

3. An ignition control circuit as defined in claim 2. in which two diodes (17,18) in series with each other are connected in series between said collector end of said switching path and one end of said primary winding (13). in which. further. the emitter end of said switching path is connected to the other end of said primary winding (13:!) and the control electrode of said semiconductor device is connected both to said trigger signal means and. through said resistance means (19). with the end of said primary winding which is connected to said diodes.

4. An ignition control circuit as defined in claim 1. in which said pulse signal means includes a circuit having a switching device (20) responsive to a source of control signals and in circuit with the control electrode of said semiconductor device (16).

5. In an internal combustion engine ignition system having a magneto armature provided with at least one winding arranged to be excited by a magnetized rotor driven by the engine. and having voltage step-means coupled with a low-voltage winding of said armature and connected by ignition cable to at least one spark plug.

pulse signal means to derive a timing signal for ignition and to supply said signal to the control electrode of said semiconductor device l6 said pulse signal means including a switching device (20) responsive to a source of control signals;

at least one diode (17.18) connected in series with said switching path of said semiconductor device (16) and poled for conduction in the same direction as said switching path;

a capacitor (21) and a charging circuit diode (22) therefor. said capacitor having one terminal connected to the common connection of said semiconductor device (16) and said low-voltage winding (13a) and its other terminal connected to said switching device (20) and to one terminal of said charging circuit diode (22). said charging circuit diode having its other terminal connected to the other end of said low-voltage winding (13a). and being poled in the opposite direction of conduction with respect to said diode(s) (17.18) in circuit with said primary winding (13a) and the switching path of said semiconductor device (16). and

resistance means (19) for turning on said semiconductor device (16) during positive half waves of the output of said low-voltage winding except while said signal is supplied by said pulse signal means as aforesaid. said resistance means being connected between the control electrode of said semiconductor device (16) and the terminal of said diode(s) (17.18) which is farthest from the connection thereof to said switching path.

6. An ignition control circuit as defined in claim 1. in which a second resistance means (24) is connected in parallel with the control path ofsaid semiconductor device (16).

7. An ignition control circuit as defined in claim 1 in which said semiconductor device (16) is a single transistor.

8. An ignition control circuit as defined in claim 1. in which saidsemiconductor device (16) is a plurality of transistors in a Darlington circuit combination.

9. An ignition control circuit as defined in claim 1, in which said pulse signal means includes a control transistor (31) having its collector-emitter path connected in parallel to the control path of said semiconductor dedriven by the engine. and having voltage step-up means coupled with a low-voltage winding of said armature and connected by ignition cable to at least one spark plug.

a Darlington circuit transistor combination (16) having its switching path in circuit with said lowvoltage winding;

pulse signal means to derive a timing signal for ignition and to supply said signal to the control electrode of said Darlington circuit transistor combination (16). said pulse signal means including a con trol transistor (31 having its collector-emitter path connected in parallel with the control path of said Darlington circuit transistor combination (16) and including a voltage divider (32) connected across said low-voltage winding (13a), the base of said control transistor (31) being connected to the tap of said voltage divider;

at least one diode (17,18) connected in series with said switching path of said semiconductor device (16) and poled for conduction in the same direction as said switching path;

resistance means (19) for turning on said Darlington combination (16) during positive half waves of the output of said low-voltage winding except while said signal is supplied by said pulse signal means as aforesaid. said resistance means being connected between the control electrode of said Darlington combination l6) and the terminal of said diode(s) (17.18) which is farthest from the connection thereof to said switching path.

11. An ignition control circuit as defined in claim 10. in which one branch of said voltage divider (32) includes a Zener diode (36) which is so poled that when the Zener voltage is reached. said control transistor (31) receives a potential such as to switch said control transistor (31) into its conductive condition.

12. An ignition control circuit as defined in claim 11, in which said Zener diode (36) is connected in series with at least one additional diode (34,35).

13. An ignition system as defined in claim 1, in which said primary winding (13) is bridged by a series combination of an additional resistor (39) and a reverse wave trimming diode (38), said reverse wave trimming diode being poled with its direction of easy conduction opposite to that .of the diode or diodes (17,18) connected between said primary'winding (13a) and the switching path of said semiconductor device (16).

Claims

1. In an internal combustion engine ignition system having a magneto armature provided with at least one winding arranged to be excited by a magnetized rotor driven by tHe engine, and having voltage step-up means coupled with said magneto armature, which means is coupled with a low-voltage winding of said armature and connected by ignition cable to at least one spark plug, an ignition control circuit for connection to said low-voltage winding of said armature, comprising: a controllable semiconductor device (16) having its switching path in circuit with said low-voltage winding; pulse signal means to derive a timing signal for ignition and to supply said signal to the control electrode of said semiconductor device (16); at least one diode (17,18) connected in series with said switching path of said semiconductor device (16) and poled for conduction in the same direction as said switching path, and resistance means (19) for turning on said semiconductor device (16) during positive half waves of the output of said lowvoltage winding, except while said signal is supplied by said pulse signal means as aforesaid, said resistance means (19) having only two terminals connected in said ignition control circuit and being connected by said terminals, between the control electrode of said semiconductor device (16) and the terminal of said diode(s) which is farthest from the connection thereof to said switching path.

2. An ignition control circuit as defined in claim 1, in which said diode or diodes are connected to the collector end of said switching path of said semiconductor device.

3. An ignition control circuit as defined in claim 2, in which two diodes (17,18) in series with each other are connected in series between said collector end of said switching path and one end of said primary winding (13), in which, further, the emitter end of said switching path is connected to the other end of said primary winding (13a) and the control electrode of said semiconductor device is connected both to said trigger signal means and, through said resistance means (19), with the end of said primary winding (13a) which is connected to said diodes.

4. An ignition control circuit as defined in claim 1, in which said pulse signal means includes a circuit having a switching device (20) responsive to a source of control signals and in circuit with the control electrode of said semiconductor device (16).

5. In an internal combustion engine ignition system having a magneto armature provided with at least one winding arranged to be excited by a magnetized rotor driven by the engine, and having voltage step-means coupled with a low-voltage winding of said armature and connected by ignition cable to at least one spark plug, an ignition control circuit for connection to said low-voltage winding of said armature, comprising: a controllable semiconductor device (16) having its switching path in circuit with said low-voltage winding; pulse signal means to derive a timing signal for ignition and to supply said signal to the control electrode of said semiconductor device (16), said pulse signal means including a switching device (20) responsive to a source of control signals; at least one diode (17,18) connected in series with said switching path of said semiconductor device (16) and poled for conduction in the same direction as said switching path; a capacitor (21) and a charging circuit diode (22) therefor, said capacitor having one terminal connected to the common connection of said semiconductor device (16) and said low-voltage winding (13a) and its other terminal connected to said switching device (20) and to one terminal of said charging circuit diode (22), said charging circuit diode having its other terminal connected to the other end of said low-voltage winding (13a), and being poled in the opposite direction of conduction with respect to said diode(s) (17,18) in circuit with said primary winding (13a) and the switching path of said semiconductor device (16), and resistance means (19) for turning on said semiconductor device (16) during positive half waves of the output of said low-voltage winding except while said signal is supplied by said pulse signal means as aforesaid, said resistance means being connected between the control electrode of said semiconductor device (16) and the terminal of said diode(s) (17,18) which is farthest from the connection thereof to said switching path.

6. An ignition control circuit as defined in claim 1, in which a second resistance means (24) is connected in parallel with the control path of said semiconductor device (16).

8. An ignition control circuit as defined in claim 1, in which said semiconductor device (16) is a plurality of transistors in a Darlington circuit combination.

9. An ignition control circuit as defined in claim 1, in which said pulse signal means includes a control transistor (31) having its collector-emitter path connected in parallel to the control path of said semiconductor device (16).

10. In an internal combustion engine ignition system having a magneto armature provided with at least one winding arranged to be excited by a magnetized rotor driven by the engine, and having voltage step-up means coupled with a low-voltage winding of said armature and connected by ignition cable to at least one spark plug, an ignition control circuit for connection to said low-voltage winding of said armature, comprising: a Darlington circuit transistor combination (16) having its switching path in circuit with said low-voltage winding; pulse signal means to derive a timing signal for ignition and to supply said signal to the control electrode of said Darlington circuit transistor combination (16), said pulse signal means including a control transistor (31) having its collector-emitter path connected in parallel with the control path of said Darlington circuit transistor combination (16) and including a voltage divider (32) connected across said low-voltage winding (13a), the base of said control transistor (31) being connected to the tap of said voltage divider; at least one diode (17,18) connected in series with said switching path of said semiconductor device (16) and poled for conduction in the same direction as said switching path; resistance means (19) for turning on said Darlington combination (16) during positive half waves of the output of said low-voltage winding except while said signal is supplied by said pulse signal means as aforesaid, said resistance means being connected between the control electrode of said Darlington combination (16) and the terminal of said diode(s) (17,18) which is farthest from the connection thereof to said switching path.

11. An ignition control circuit as defined in claim 10, in which one branch of said voltage divider (32) includes a Zener diode (36) which is so poled that when the Zener voltage is reached, said control transistor (31) receives a potential such as to switch said control transistor (31) into its conductive condition.

13. An ignition system as defined in claim 1, in which said primary winding (13) is bridged by a series combination of an additional resistor (39) and a reverse wave trimming diode (38), said reverse wave trimming diode being poled with its direction of easy conduction opposite to that of the diode or diodes (17, 18) connected between said primary winding (13a) and the switching path of said semiconductor device (16).