Circuit configuration for driving an ignition coil

Details Circuit configuration for driving an ignition coil Circuit configuration for driving an ignition coil

2000-08-07

2001-10-30

Paschall, Mark (Department: 3742)

Electric heating

Heating devices

With power supply and voltage or current regulation or...

C219S491000, C219S501000, C219S519000, C307S117000

Reexamination Certificate

active

06310331

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a circuit configuration for driving an ignition coil, which is for example used for generating ignition sparks in spark-ignition engines.
Circuit configurations of this type have a semiconductor switch having a load path connected in series with a primary winding of the ignition coil, and having a control electrode for driving the semiconductor switch in accordance with a drive signal. In this case, the series circuit formed by the semiconductor switch and the primary winding is connected to terminals for a voltage supply.
If, in circuit configurations of this type, the semiconductor switch is closed in dependence of the drive signal, a current which rises over time flows through the primary winding. When the semiconductor switch is subsequently opened, the energy stored in the primary winding is transferred to a secondary winding of the ignition coil, in order to generate an ignition spark at a spark plug connected thereto.
The instant at which the ignition spark is generated or the semiconductor switch is opened is prescribed for the circuit configuration externally, depending on the engine data. Consequently, the period of time between the closing and opening of the first semiconductor switch may vary.
After the closing of the semiconductor switch, and thus the beginning of energy storage in the primary winding, circumstances can occur which should be avoided, such as, for example, an excessive heating of the circuit configuration.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a circuit configuration for driving an ignition coil which overcomes the above-mentioned disadvantages of the heretofore-known circuit configurations of this general type and which, in particular prevents excessive heating of the circuit configuration, and which allows the semiconductor switch to be opened for the purpose of limiting the current through the primary winding, in particular such that, when the semiconductor switch is opened in these cases, the generation of an ignition spark can be prevented.
With the foregoing and other objects in view there is provided, in accordance with the invention, a circuit configuration, in particular in combination with an ignition coil, for driving the ignition coil, the circuit configuration including:
a first semiconductor switch having a first load path to be connected in series with a primary winding of an ignition coil and having a first control electrode for driving the first semiconductor switch in accordance with a first drive signal; and
a second semiconductor switch having a second load path to be connected in parallel with the primary winding and having a second control electrode for driving the second semiconductor switch in accordance with a second drive signal.
In other words, the circuit configuration according to the invention provides an additional, second semiconductor switch having a load path connected in parallel with the primary winding, and having a control electrode for a driving in accordance with a second drive signal.
The second semiconductor switch, which is configured in particular as an insulated gate bipolar transistor or as a field-effect transistor, takes over, as long as it is held in the on state (conducting state) by the second drive signal, the current through the primary coil if the first semiconductor switch is in the off state or the conductivity thereof decreases. The second semiconductor switch is connected in the reverse direction between that terminal of the primary winding which is remote from the first semiconductor switch and the other terminal of the primary winding and, in this case, acts like a controlled freewheeling diode. The second semiconductor switch is conducting only in the direction between a node common to the primary winding and to the first semiconductor switch and the other terminal of the primary winding and is non-conducting (off state) in the other direction. The second semiconductor switch is in the on state, given a positive supply potential, when, if the first semiconductor switch is in the off state, the potential at the node which is common to the primary winding and to the first semiconductor switch rises above the value of a supply potential to which the other terminal of the primary winding is connected. If the second semiconductor switch is in the off state as well as the first semiconductor switch, the energy previously stored in the primary winding is transferred to the secondary coil, and an ignition spark is generated at the ignition coil connected on the secondary side.
One embodiment of the invention provides for the circuit configuration to have a first control circuit connected to a control electrode of the first semiconductor switch, for driving the first semiconductor switch depending on a current through the primary winding and/or the first semiconductor switch. After the closing of the first semiconductor switch, this control circuit detects the current through the primary winding and/or the current through the first semiconductor switch. If this current exceeds a prescribed value, the first semiconductor switch is opened by the first control circuit. The second semiconductor switch then accepts the current from the primary winding until the current has fallen, due to line resistances and the first semiconductor switch switches on again. The current through the primary winding and/or the first semiconductor switch is thus adjusted to a prescribable value by alternately switching on and off or alternately down-regulating and up-regulating of the first semiconductor a switch, and, respectively, the current fluctuates around the prescribable value.
The control electrodes of the first and second semiconductor switches are preferably connected to an input terminal of the circuit configuration to which a drive signal is fed, in accordance with which the ignition spark is generated. As long as no ignition spark is intended to be generated, the first and second semiconductor switches are held in the on state, in which case the first semiconductor switch can occasionally be turned off by the first control circuit for the purpose of regulating the current through the primary winding. In order to avoid the generation of an ignition spark, the current through the primary winding is then taken over by the second semiconductor switch, acting as a freewheeling diode, until the first semiconductor switch is in the on state again. If an ignition spark is intended to be generated, the drive signal causes both semiconductor switches to be turned off, once the primary winding has taken up current.
In accordance with another feature of the invention, the first control circuit has a third semiconductor switch, which is connected between the control electrode of the first semiconductor switch and a reference-ground potential and can be driven in accordance with a current measurement signal dependent on a current through the first semiconductor switch. In order to provide the current measurement signal, a current sensing resistor is preferably provided, which is connected between a load path terminal of the first semiconductor switch and a reference-ground potential, wherein a control electrode of the third semiconductor switch, for feeding in the current measurement signal, is connected to a terminal of the current sensing resistor.
The first and second semiconductor switches are preferably configured as transistors, in particular as insulated gate bipolar transistors or as field-effect transistors.
A further embodiment of the invention provides for a measurement according to the current sensing principle, in order to provide the current measurement signal. In this case, in addition to the first semiconductor switch configured as a transistor, a further transistor is provided, whose control electrode is connected to the control electrode of the first transistor and which is connected by a first load path terminal thereof to a first load path terminal of the first transistor. The

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