Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device
Patent
1993-05-25
1995-06-13
Cunningham, Terry D.
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Utilizing three or more electrode solid-state device
327310, 327482, 327488, 327575, H03K 17615
Patent
active
054246717
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a power output stage having a Darlington-pair circuit for switching an inductive load, especially the ignition coil of an internal-combustion engine.
BACKGROUND OF THE INVENTION
When switching inductive loads using power transistors, the requirement often exists to limit the inductive voltage on the power transistor, or that anywhere on the electronic circuit, to a defined value. For this purpose, a protection element can be connected in a known manner in parallel with the emitter-collector junction of the output transistor. Furthermore, European No. 0,174,473 discloses the connection of a zener diode in parallel with the collector-base junction of the output transistor, which zener diode raises the base of the output transistor on reaching an upper limiting voltage of, in general, over 250 volts.
In specific applications, the requirement furthermore exists to be able to carry out voltage limiting at a second, lower voltage level as well, in order, for example, to be able to reduce the stored energy in an ignition coil to this lower voltage level so that no ignition sparks can occur. This so-called spark-free disconnection is fundamentally necessary when the disconnection of the output stage is not intended to be used for producing an ignition spark. In order to create such voltage limiting at a lower voltage level, in the case of the above-mentioned prior art, a voltage divider is connected in parallel with the collector-emitter junction of the output transistor, a pick-off acting via transistor stages on the base of a preliminary-control transistor. Furthermore, an external switching transistor is connected between the base of the preliminary-control transistor and earth in order to predetermine the disconnection mode. Only when this switching transistor is switched off can the base of the preliminary-control transistor be raised to the voltage limit via the voltage divider and the transistor circuit. A large number of components are required for this purpose in the case of the known circuit, which means a cost outlay which is not inconsiderable.
SUMMARY OF THE INVENTION
The power output stage for controlling an inductive load, according to the principles of the present invention, comprises a Darlington circuit including a preliminary-control transistor and an output transistor. A voltage divider including first and second resistors is coupled to the Darlington circuit. In an embodiment of the power output stage according to the present invention, a decoupling diode and an auxiliary transistor are also coupled to the Darlington circuit.
The power output stage according to the present invention, has the advantage that such voltage limiting to a lower voltage level in order to achieve, for example, spark-free disconnection of an ignition coil can also be implemented with a significantly lower component outlay. The layout is in consequence more cost-effective and can more easily be integrated monolithically. A further advantage is that this arrangement can also be used for power output stages which are not fully integrated and have an integrated Darlington-pair circuit, since there is now no longer any need for access between the transistors of the Darlington-pair circuit.
For temperature compensation, the part of the voltage divider located between the pick-off and the collector of the Darlington-pair circuit expediently has a zener diode which is connected in series with one of the resistors.
For many applications, it is expedient or necessary to decouple the divider pick-off from the base of the Darlington-pair circuit. To this end, the pick-off of this voltage divider is connected via at least one decoupling diode to the base of the Darlington-pair circuit.
The raising of the Darlington-pair circuit to the lower limiting voltage can also be carried out, instead of via the input transistor of the Darlington-pair circuit, via an auxiliary transistor whose switching junction bridges the collector-base junction of the output transistor of the Da
REFERENCES:
patent: 4369380 (1983-01-01), Menniti et al.
patent: 4539492 (1985-09-01), Michel et al.
patent: 4564771 (1986-01-01), Flohrs
patent: 4706222 (1987-11-01), Kwiatkowski et al.
patent: 5038054 (1991-08-01), Peyre-Lavigne et al.
Bodig, deceased Bernd
Gademann Lothar
Hohne Gerd
Michel Hartmut
Cunningham Terry D.
Robert & Bosch GmbH
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