Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to opto-electronic ignition systems
such as disclosed in our Canadian Patent Nos. 879,285 and 932,382.
In these prior Patents the transistors which form the bistable
trigger are arranged to switch in inverse relation to one another, so that
if any one transistor is fully saturated, its neighbours are non-conductive.
The purpose of this type of bistable trigger is to ensure that at any
instant of time there is always one transistor fully conductive to act as
a short-circùit path for any transients on the line.
It is an object of the present invention to extend this basic
principle of inverse switching transistors to the use of Darlington pairs.
Due to a rapid advance in lntegrated circuitry over the last few
years, it is advantageous to form as many of the components as possible on
a monolithic chip, together with the photo-detector. This provides an
article which is not only very compact, but which is very cheap to manu-
facture. It is a further object of the invention to achieve a monolithic
construction for a number of the components.
, According to the present invention, there is provided an opto-
, electronic ignition system for controlling switching of the primary winding
`J of an ignition coil of an internal combustion engine, said system compris-
ing a source of radiation; a photo-transistor sensitive to radiation which
will switch on or conduct when exposed to the radiation and switch off when
, the radiation is cut off; means disposed between said source and said photo-
, transistor for intermittently blocking radiation from said source in timed
relation to the engine revolutions so as to control the periods during
which radiation is received by said photo-transistor; and a switching circuit
for controlling switching of the ignition coil responsive to the output of
said photo-transistor; said switching circuit comprising a plurality of
~ pairs of transistors the components of each pair being connected in a
i~ Darlington configuration and means for connecting said pairs of transistors
to each other between said photo-transistor and the ignition coil such
~`, that each Darlington pair switches in inverse relationship to at least one
other Darlington pair and a first Darlington pair
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switches in inverse relationship to said photo-transistor, so as to cause
fast switching of the primary winding of the ignition coil thereby inducing
a spark voltage in the second winding of the coil.
'rhe Darlington pairs, with the possible exception of the last in
the circuit, which may be a power Darlington pair, may be formed on a
monolithic chip, together with the photo-transistor.
A diode may be connected between each junctlon of the Darlington
pairs of the circuit, and the commoned emitter electrodes of all the
second transistors of the Darlington pairs.
Additional features already disclosed in our Canadian Patent
No. 932,382 may include ~:
(a) the provision of a diode across the emitter-collector path of the
photo-transistor;
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(b) at least one zener diode connected between
the commoned collector electrodes of the transistors
fonming the Darlington pair of the~ last stage of the
circuit and the base electrode of the first transistor
of said Darlington pair; and
(c) a zener diode across the radiation source,
which is preferably a gallium arsenide lamp,and the
photo-transistor.
The present invention will now be described in
greater detail, by way of example, with reference to
the accompanying drawing, wherein the sole figure is
a circuit diagram of one preferred form of an opto-
electronic ignition system.
Referring to the drawing, the circuit includes
a solid state gallium arsenide lamp 1, a photo-
- ; transistor 2 and two pairs of D æ lington pairs Q1
and Q2. The lamp 1 and the photo-transistor 2 are
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each in series with respective resistors R1 and R2,
and receive a 7.S volt stabilized supply fxom a zener
~; ~ 20 diode Z1. The zener diode is connected across the 12
volt battery of the vehicle through a resistor R3.
Connected across the emitter-collector electrodes
of the photo-transistor 2 is a diode D1, which serves
not only to ensure clean switching of the photo-
transistor 2, but ensures that any negative transients
on the line during the time that the photo-transistor
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is non-conductive are conducted past the photo-
transistor, and are thus unable to cause any damage
to its structuxe.
The Darlington pairs Q1 and Q2 each consist of
a pair of transistors T1, T2 and T3, T4 respectively,
arranged in conventional Darlington configura~ion.
The base electrode of the transistor T1 is connected
to the collector electrode of the photo-transistor 2.
The commoned collector electrodes of the transistors
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~ 10 T1 and T2 are connected firstly to the base electrode
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of the transistor T3 of the second Darlington pair
Q2 through a diode D3 and, secondly, to the 7.5 volt ~ ,
zenered supply through a resistor R4.
A diode D2 is connected across the commoned
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collector electrodes of the transistors T1 and T2, ~ - -
and the emitter electrode of the transistor T2. The ~
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diode D2 serves to protect the Darlington pairs against ~`
negative going transients, and also against a careless
- mechanic connecting the battery the wTong way around.
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The diode D1 also serves to protect the photo-transistor
2 against reverse battery connection.
The commoned collector electrodes of the transis-
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~ tors T3 and T4 are connected to one end of the primary
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- winding of the ignition coil 4, the other end of which
is connected to the positive terminal of the 12 volt
battery. Between the commoned collector electrodes of
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the transistors T3 and T4, and the base electrode
of the transistor T3, there is connected a series
circuit comprising a pair of zener diodes Z2 and Z3,
and a resistor R5. The purpose of this circuit is,
firstly, to control the rate of switching of the
Darlington pair Q2 and, secondly, to protect ~he
Darlington pair against positive going transients, as
explained in our Canadian Patent No. 932,382.
In one preferred form, the Darlington pair
Q2 is a power Darlington pair, thus ensuring sufficient
current carrying capacity to handle the currents flow-
ing through the primary winding of the coil when the
magnetic field of the coil is being built up.
In the above described embodiment, the photo-
transistor 2, and the Darlington pairs Ql and Q2 all
switch in inverse relation to one another. Thus,
when the photo-transistor 2 receives the infra-red
radiation from the solid-state lamp 1, it will switch
on in the fully saturated condition, which means that
: 20 the Darlington pair Ql is non-conductive whilst the
Darlington pair Q2 is fully on, passing the ignition
coil current through the primary winding of the coil
4. As soon as the infra-red radiation is cut off
from the photo-transistor 2, it is rendered non- -~
conductive, which switches the Darlington pair Ql
: on, and the Darlington pair Q2 off. When the Darlington
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pair Q2 switches off the primary current is inter-
rupted to cause the collapse of the magnetic field
associated with the coil 4, and the induction of a
high voltage in the secondary winding to produce the
spark.
It will be appreciated that where it is desir-
ed to switch in the reverse mode, i.e. the spark is
produced when the photo-transistor 2 is rendered con-
ductive, all that is necessary is to introduce a further
Darlington pair in the chain of Darlington pairs.
The switching on and off of the photo-transistor
; 2 is achieved by means of a bladed disc 3, such as disclosed
in our Canadian Patent No. 932,382, or an apertured disc, `~
such as the type disclosed for the first trigger in our
double trigger Canadian Patent No. 984>935. Preferably,
where the disc is driven fro~ the cam shaft of the engine, ~-
the number of apertures or slots is equal to the number
of cylinders in the engine, but if the disc is not
mounted within the distributor housing, as is conventional,
the number of slots or apertures may be a ~ultiple or
sub-multiple o~ the number of cylinders in the engine.
The Darlington pair Ql, or in the case of the re-
verse de switching trigger, the first two Darlington
psirs in the circuit, ~ay be for-ed on a =onolithic
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chip, together with the photo-transistor 2, the
diode Dl and the resistors R2 and R4, appropriate
interconnections being made by well known integrated
circuit teclmiques. In this construction, the mono- I
lithic chip is mounted within the distributor housing
opposite the gallium arsenide lamp 1, between which
the blades of the chopper disc 3 rotate. The photo- ¦
area of the photo-transistor 2 would occupy between
one quarter and one half the total area of one face
of the monolithic chip, being off-set with respect to
; the centre of the chip, and preferably occupying an
area on one side of the central axis of the chip.
The Darlington pair Ql and associated resistors R2 -
j and R4 together with the diode Dl are formed on the
lS remaining area of the face o the chip and appropriately
connected. The power Darlington pair is mounted on a
separate heat sink outside the distributor housing,
together with the resistors R3 and R5, the zener diodes
Zl to Z3, and the diodes D2 and D3.
` 20 Alternatively, in cases where heat dissipation
is not a serious problem, the power Darlington pair
may also be formed on the monolithic chip.
Although in the above embodiment there are two
series connected zener diodes across the Darlington -
pair Q2, it is possible to provide only a single
zener diode if the voltage rating is high enough
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to effect satisfactory operation of the Darlington
pair in the presence of trsnsients.
It will be appreciated that the chain of
Darlington pairs can have two, four or six pairs for one
mode of switching, or three, five or seven pairs for the
reverse mode of switching. It will be further appreciated
that a diode is inserted between each Darlington pair and
earth.
Whilst the preferred foTm shown in the drawing~
utilizes a bladed or apertured disc, it would be possible
to use any other form of interrupting device, such as a
slotted or apertured drum or cup.
The circuit shown in the drawing may readily be
adapted to be incorporated into the circuits disclosed in -
our Canadian Patent Nos. 984,935 and 1,018,245 and our -
Canadian Patent No. 1,049,609. For example, in Canadian
Patent No. 1,018,245, in the block diagram shown in
Figure 1, the first trigger 11 and the second trigger 12
would each comprise the photo-transistor 2, the Darlington
pair Ql, associated resistors R2 and R4, and the diodes
Dl and D3. A second Darlington pair switching in in~erse
relation to the first pair could be added if necessary.
In each case, the components comprising the first
and second triggers could be formed either on a single
monolithic chip or two separate monolithic chips mounted
side by side.
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