Electricity: electrical systems and devices – Igniting systems – For electric spark ignition
Patent
1991-03-08
1992-04-21
Griffin, Donald A.
Electricity: electrical systems and devices
Igniting systems
For electric spark ignition
123623, F23Q 300
Patent
active
051073927
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention relates to a final ignition stage of a transistorized ignition system (TI system) according to the preamble of claim 1.
It is known to control final ignition stages of transistorized ignition systems with a Darlington transistor, in the collector-emitter circuit of which the primary coil current of the ignition coil flows. For necessary limitation of the primary coil current and thus simultaneous limitation of the stored ignition power, the use of an active current regulator is known which is contained in an integrated circuit and installed in hybrid association. Such an integrated active current regulator is relatively costly and expensive.
ADVANTAGES OF THE INVENTION
In a final ignition stage of a transistorized ignition system with the features of claim 1, the integrated active current regulator can be omitted. The function of this current regulator is essentially replaced by the use of a simple control transistor without additional voltage supply. This transistor enters the active range on commencement of the current limitation and partially conducts away to earth the base current flowing into the Darlington transistor. The circuit thus serves to limit the primary coil current and can be used both as a simple current limiter and as a short circuit protection. The subclaims contain advantageous further developments of the subject according to the main claim. In particular, concrete circuits are required with which the driving of the control transistor is improved and the influence of drive voltage tolerances is reduced.
DRAWINGS
Exemplary embodiments of the invention are represented in the drawings and described in greater detail in the subsequent description, wherein:
FIG. 1 shows the circuit of a first exemplary embodiment of the invention,
FIG. 2 is a time-dependency diagram concerning the commencement of the current limitation and showing the characteristic of the primary coil current and the base-emitter voltage,
FIG. 3 shows the circuit of a second exemplary embodiment of the invention,
FIG. 4 is a characteristic line diagram which shows the improvement, in respect of the first exemplary embodiment, which is achieved with the second exemplary embodiment,
FIG. 5 shows a circuit of a third exemplary embodiment.
In the circuit according to FIG. 1, the primary coil current for an ignition coil ZS of a transistorized ignition system 1, which is known per se and not further represented, flows in the collector-emitter circuit of a Darlington transistor DT. The Darlington transistor DT is driven via its base and a base line 1 according to the switching state of a transistor T. The driving occurs with the aid of a drive voltage U.sub.v and a series resistor R.sub.v.
Between the base line 2 to the Darlington transistor DT and earth there is a control transistor T with its collector-emitter circuit. Between the base line 2 and earth there is also a divider circuit consisting of resistors R.sub.1 and R.sub.2. From the centre tap of this divider circuit a line 3 leads to the base of the control transistor T.sub.1, a diode D being arranged in the line 3.
The circuit according to FIG. 1 has the following function: the base voltage present at the Darlington transistor DT is an indirect reproduction of the current flowing in the collector-emitter circuit. Controlling this base voltage by the control transistor T.sub.1 thus permits an indirect control of the collector current or of the primary coil current I.sub.SP.
The base-emitter voltage present at the base of the Darlington transistor in the switched-on state is divided by the divider resistors R.sub.1, R.sub.2 to the level of two diode forward voltages The regulating transistor T.sub.1 is driven with this voltage. The regulating transistor T.sub.1 conducts away to earth a part of the base current for the Darlington transistor. In this way, the Darlington transistor is operated in the active range and the primary coil current I.sub.SP is controlled. The collector current or primary coil current is a function of the base-emi
REFERENCES:
patent: 4084567 (1978-04-01), Hachiga
Bentel Ulrich
Sohner Gerhard
Griffin Donald A.
Robert & Bosch GmbH
Striker Michael J.
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