Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device
Reexamination Certificate
2001-08-07
2004-03-02
Nguyen, Minh (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Utilizing three or more electrode solid-state device
C327S205000, C323S282000, C361S078000
Reexamination Certificate
active
06700432
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a two-terminal switch circuit for inclusion in series with a load across the terminals of a voltage supply for periodically energizing the load from the voltage supply. The invention also relates to a road vehicle direction indicator lamp circuit including such a switch circuit -and to a voltage threshold responsive circuit component for use in such a switch circuit.
A two terminal switch circuit of this general kind, for controlling the flashing of the direction-indicating lamps of motor cars or other road vehicles, is shown in
FIG. 2
of FR-A-2344177 and is reproduced as
FIG. 1
of the accompanying diagrammatic drawings. The circuit comprises a controllable switch connected between said terminals, a resistance and a capacitor connected in series in that order between a given one of said terminals and the other one of said terminals, and a voltage threshold responsive arrangement having an output signal/input signal characteristic which exhibits hysteresis. The voltage threshold responsive arrangement couples the common point of the resistance and the capacitor to a control input of the controllable switch for, in operation, closing the switch in the event of the voltage across the capacitor increasing to above a first threshold value and opening the switch in the event of the voltage across the capacitor subsequently decreasing to below a second threshold value which is lower than the first threshold value. The voltage threshold responsive arrangement has a power supply input for receiving an energizing voltage relative to said other one of said terminals.
FIG. 1
of the accompanying drawings, shows this prior art switch circuit
1
of FR-A-2344177. It has two terminals
2
and
3
respectively and comprises a controllable switch
4
which is constructed as a relay having an energizing coil
5
and contacts
6
,
7
which are connected between the terminals
2
and
3
. A resistor
8
and a capacitor
9
are connected in that order between a given one of the terminals
2
and
3
(terminal
2
) and the other one of these terminals (terminal
3
). The switch circuit
1
furthermore includes a voltage threshold responsive arrangement
26
having an output signal/input signal characteristic which exhibits hysteresis. Arrangement
26
has a signal input
27
connected to the common point
12
of the resistor
8
and the capacitor
9
, a signal output
28
connected to a control input
13
of the relay
4
, and a power supply input
29
connected to the terminal
2
for receiving an energizing voltage relative to the terminal
3
. Control input
13
is connected to one end of the energizing coil
5
the other end of which is connected to the terminal
3
.
The voltage threshold responsive arrangement
26
comprises an npn transistor
10
, a pnp transistor
11
, resistors
15
,
16
and
17
, a reservoir (storage) capacitor
18
and a diode
19
. Its signal input
27
is connected to the base of the transistor
10
. The emitter of transistor
10
is connected to the tap
14
of a voltage divider formed by the resistors
15
and
16
, which are connected in series between the power supply input
29
and the terminal
3
. The collector of transistor
10
is connected to the base of the transistor
11
via the resistor
17
. The emitter of transistor
11
is connected to one electrode of the storage capacitor
18
, the other electrode of which is connected to the terminal
3
. The one electrode of the capacitor
18
is also connected to the power supply input
29
via the diode
19
. The collector of transistor
11
is connected to the signal output
28
.
The terminal
3
of switch circuit
1
is connected to ground via a switchable load
20
. Load
20
has first and second terminals
43
and
44
respectively and comprises a pair of left indicator lamps
21
and
22
and a pair of right indicator lamps
23
and
24
of a road vehicle. The load
20
also includes a direction indicator switch
25
which is actuable into first, second and third states in which it connects the pair of lamps
21
,
22
between the terminals
43
and
44
, the pair of lamps
23
,
24
between the terminals
43
and
44
, and is open circuit respectively.
In operation a positive potential relative to ground is applied to terminal
2
by a voltage supply
63
, for example, the battery of the vehicle. When switch
25
is open, i.e. is in its third state, neither of the two pairs of lamps
21
,
22
and
23
,
24
is energized, there is no voltage present between terminal
2
and terminal
3
, and the relay contacts
6
,
7
are open because there is no voltage relative to terminal
3
on the relay control input
13
. If switch
25
is now actuated into its first or second states to connect the pair of lamps
21
,
22
or the pair of lamps
23
,
24
to the terminal
3
, the terminal
3
is then connected to ground through the relevant pair of lamps and therefore becomes negative relative to terminal
2
. Storage capacitor
18
charges through diode
19
to the potential difference which is now present between terminals
2
and
3
, and the emitter of transistor
10
is taken to a potential intermediate those on terminals
2
and
3
by means of the potential divider
15
,
16
. Capacitor
9
starts to charge through resistor
8
. When the voltage across capacitor
9
eventually increases to above a first threshold value equal to the voltage on the emitter of transistor
10
plus the base-emitter threshold voltage of transistor
10
, transistor
10
conducts, turning on transistor
11
so that the collector of transistor
11
applies a positive voltage to the control input
13
of relay
4
. The relay contacts
6
,
7
close, connecting terminal
2
to terminal
3
and thereby energizing the relevant pair of lamps
21
,
22
or
23
,
24
. Although there is no longer any potential difference between terminals
2
and
3
, transistors
10
and
11
continue to be supplied with operating current from the storage capacitor
18
. Closure of the relay contacts
6
,
7
effectively connects the two potential divider resistors
15
and
16
in parallel so that the positive potential on the emitter of transistor
10
relative to terminal
3
is reduced, thereby increasing the forward base-emitter bias of transistor
10
and causing the relay contacts
6
,
7
to be held closed.
Capacitor
9
now starts to discharge through resistor
8
and the closed relay contacts
6
,
7
. When the voltage on capacitor
9
eventually decreases to below a second, lower, threshold value equal to the reduced emitter voltage of transistor
10
plus the base-emitter threshold voltage of transistor
10
transistor
10
turns off, turning off transistor
11
and thereby removing the positive voltage from the control input
13
of relay
4
. The relay contacts
6
,
7
open so that the lamps of the relevant pair
21
,
22
or
23
,
24
are extinguished. The opening of the contacts
6
,
7
also removes the parallel connection of the potential divider resistors
15
and
16
so that the emitter voltage of transistor
10
increases relative to terminal
3
, thereby reducing the base-emitter voltage of transistor
10
still further and causing the ralay contacts
6
,
7
to be held open. Capacitor
9
now starts to change again through resistor
8
and the cycle repeats.
A disadvantage of the known switch circuit is that it is necessary to provide, in addition to a timing capacitor
9
, a storage capacitor
18
to supply operating current to the transistors
10
and
11
at times when the relay contacts
6
,
7
are closed.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a simplification in this respect.
According to a first aspect of the invention there is provided a two-terminal switch circuit for inclusion in series with a load across a voltage supply for periodically energizing the load from the supply comprises a controllable switch connected between said terminals, a resistance and a capacitor connected in series in that order between a given one of said terminals and the other on
Hulshof Jozef J. M.
Misdom Johannes A. C.
Van Rens Frank J. P.
Verhees Johannes L. M.
Nguyen Minh
Waxler Aaron
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