Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~)36671
This invention relates to a voltage drop warning
apparatus for warning that a voltage drop has occurred or
is occurring. More particularly, the invention concerns
a voltage drop indicator that is capable of indicating by
means of a light-emitting diode that a voltage drop has
once occurred or is now occurring.
In electronic digital clocks or other electric
clocks operating with an A.C. power supply synchronized
with the supply frequency, if once the power supply is
' ~ w ~
A 10 in.terrupted or disturbed, the time indication w~th forever
lag behind, even after restoration of the supply. Often
the user is unaware of the lag.
In clocks.operating with a D.C. power source, e.g.,
a dry cell, when the source becomes weak and reduces its
output voltage below a specified threshold level, the time
indication becomes inaccurate. To monitor any such weaken- -
ing of the power source, a known voltage indicating device
such as a light-emitting diode, a miniature incandescent
lamp or an ammeter can be used, but the power consumption
of any such permanently indicating device is a disadvantage.
One device previously proposed comprises a push-button switch -~
that is closed to check the voltage, but this device has the
drawback that an indication of lowered voltage is only
obtained when the button is pressed.
The ob~ect of the present invention is to provide
a voltage drop warning apparatus that automatically warns of
a voltage drop or interruption while avoiding the above
disadvantage~.
To this end the invention consists of a voltage-
drop warning apparatus comprising a series connection includ-
ing a load, indicator means and a semiconductor switching
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element having a control electrode, said series connection
being for connection across positive and negative sides
of a power source, and a negative-resistance device
comprising a complementary connection of an n-channel field-
effect transistor and a p-channel field-effect transistor,
an end of the negative-resistance device being connected
to a ~unction point between said load and the switching
element, and the other end of said device being connected
to said control electrode.
. This invention is applicable for indicating the
occurrence of a voltage interruption in an A.C. power
source.
This invention is also applicable for indicating
the occurrence of a voltage diminution in a D.C. power ,~
source.
This invention is also applicable for warning of -;~
the occurrence of a time lag in an analogue or digital ~ ::
clock or the occurrence of errors in data from a data
processing apparatus.
The preferred forms of the invention have the
advantage that their construction is very simple, dispensing : ,'
with mechanical devices such as a relay or ammeter, and the
circuits consume very small power even for continuous
indication.
Embodiments of the invention are illustrated by way
of example in the accompanying drawings, in which: -
,Figure 1 is a circuit of a negative-resistance
device used in apparatus according to an embodiment of
the present invention;
Figure 2 is a diagram showing a voltage-current
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characteristic of the device shown in Figure l;
Figure 3 is a circuit of a warning apparatus
according to an embodiment of the present invention;
Figures 4 and 4a are voltage-current characteristic
diagrams for Figure 3;
Figure 5 is a circuit diagram of another example -
of the present invention; and
Figure 6 is a circuit diagram of still another ~-
example of the present invention.
A negative-resistance device is explained in
Figure 1 which shows a prior art circuit, see for example
IEEE Transactions on Circuit Theory, March 1963, pages
25-35, article entitled "Synthesis of Electronic Bistable
Circuits" by ~Ø Hill et al, and Proceedings of The IEEE,
April 1965, page 404, article entitled "Negative Resistance ~
Circuit using two Complementary Field Effect Transistors" ~ `
by S. Ostefjeld.
In Figure 1, the gate electrode Gl of an n-channel
type FET 21 is connected to the drain electrode D2 of a
p-channel type FET 22, and the gate electrode G2 of the
p-channel type FET 22 is connected to the drain electrode
Dl of the n-channel type FET 21. The source electrodes Sl
and S2 of FETs 21 and 22 are connected to each other.
When a voltage V is applied across two outer termin-
als 31 and 32, i.e., across the drain electrodes (with positive ;
potential on the electrode Dl), a known current-voltage
characteristic as shown in Figure 2 is obtained between
the voltage V and a source current I. For a time from
the starting voltage 0, the current I increases showing
positive resistance characteristic as the voltage increases.
But the current also gradually shows a saturation
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characteristic so that after a peak current polnt m, at the
flrst threshold voltage Vtl, the current declines as the
voltage increases, showing a so-called negative-resistance
characteristic, i.e., between the first and second threshold
voltages Vtl and Vt2. Finally, when the voltage exceeds
the second threshold voltage Vt2~ the current I enters a
cut-off state which continues until the voltage reaches a
break-over voltage Vt3 where one of the FETs begins to
break-down and a break-down current results. In the circuit
of Figure 1, there are a first stable region of 0<V<Vtl,
and a second stable "OFF" region of Vt2<V<Vt3, with an unstable
state in the voltage range of Vtl<V<Vt2. ~ -~
Figure 3 shows a first example of a voltage drop
warning apparatus wherein a terminal B is connected to a
D.C. voltage supply, e.g., a rectifier circuit powered by
a commercial A.C. source. This voltage Vcc applied to the
terminal B is selected to be between Vt2 and Vt3. A load
resistor 2, a light-emitting diode 3 and the collector-
emitter electrodes of a transistor 4 are connected in
series across the D.C. power source Vcc. One end of a
negative-resistance device 1, such as that shown in Figure
1, can be connected through a change-over switch 5 to the
positive terminal B. The other end of the device 1 is
connected to the base of the transistor 4. A normally
closed contact 5b of the switch 5 is connected to the
~unction point A between the load resistor 2 and the diode
3.
In operation, the switch 5 is initially changed
over to the normally-open contact 5a. A voltage Vcc is
0 then directly applied to the negative-resistance device 1,
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bringing the operating point of this device to the condition
V=Vcc, I=0, in order to set the current to zero.
The switch 5 is then changed back to the normally-
closed contact Sb to await a voltage interruption to be
indicated.
If no interruption of the voltage occurs, since
the transistor 4 is held "0FF" by the zero current in the
device 1, the full source voltage Vcc is still applied to ;
the device 1. Therefore the operation point in Figure 4
10 remains at the point V=Vcc, I=0. The current through the ;
transistor 4 is zero and the light-emitting diode 3 remains
"OFF". -
If an interruption of the voltage occurs, the
voltage across the negative-resistance device 1 becomes
zero, so that the voltage-current condition of Figure 4
is brought to the point V=0, I=0, and the transistor 4
is "OFF".
Then, when the voltage supply is restored, the
D.C. voltage at the terminal B increases towards the
20 voltage Vcc. For a voltage exceeding V=VBE, at the -~
terminal B, the transistor 4 is turned "ON", a current
flowing from the terminal B through the resistor 2,
the switch 5 and the device l,to the base and emitter of
the transistor 4 and eventually to the ground. As a
result, the diode 3 is lit. As the source voltage increases,
the current through the device 1 increases along the
positive gradient part of the characteristic curve of the
device 1, and the collector current which is hFE times -
that of the base current of the transistor 4 increases
accordlngly.
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The resistance R of the load resistor 2 is so
selected that the oblique line "Q" connecting the point
V=0, I=VRc with the point V=Vcc, I=0~and representing the
load resistance R crosses the positive gradient part of
the characteristic curve at the point P. By means of
this selection of the resistance R, even when the voltage
at point B reaches Vcc, the current flowing through the
device 1 remains stable at the value represented by the
point P, and the diode 3 is lit with this steady current.
This illumination of the diode indicates that the voltage
at the terminal B has been interrupted, thus warning the
user of possible inaccuracy of the data processed or the
time indicated after such incident.
After the device 1 and the transistor have been
turned "ON", the user must reset the circuit in order to
watch for any further voltage drop. Such resetting is
achieved by applying the source voltage Vcc across the
device 1 by changing over the switch 5 to the contact 5a
to bring the device 1 to the state V=Vcc, I=0 to switch
the transistor 4 "OFF" through elimination of its base
current with consequent extinguishing of the diode 3.
The apparatus of Figure 3 is also capable of
indicating a weakening of a dry cell or battery. For such
an indication, the condition of the circuit is so selected
that the gradient of the load curve "Q" is almost equal
to or slightly gentler than the gradient between voltages Vtl and
Vt2 of the characteristic curve for the device 1 shown in Figure
4a, and the voltage Vcc of the normal state of the dry cell or
battery slightly exceeds the voltage Vt2.
When the battery or dry cell is normal, the
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oblique load curve "Q" does not intersect the curve portion
tr, and therefore the operating point is V=Vcc, I=O. Accordingly,
no base current and hence no collector current flows in the
transistor 4.
When the dry cell or battery becomes weak and the
voltage Vcc at terminal B falls below Vt2 and the oblique load -~
line "Q" for a low Vcc as is indicated by the broken line in
Figure 4a intersects the characteristic curve in the region
between VBE<V<Vtl. The operation is stable under these
10 conditions and a collector current flows through the -
transistor and the diode 3.
Figure 5 shows another example of the present -
invention having resetting means in the form of a spring
return push-button switch 6 connected between the positive-
power supply terminal B and the negative-resistance device
1. The junction between the switch 6 and the device 1 is
directly connected to the junction point A between the
resistor 2 and the light-emitting diode 3. Other parts
are identical with those of the example of Figure 3.
Resetting is achieved by depressing the switch 6 for a
short time. By this means the voltage Vcc is applied to
the device 1 and the circuit is reset in the same way as
explained with reference to Figure 3. This circuit is
easier to handle~since the resetting switch 6 is self-
restoring, reducing the risk of forgetting to return the
resetting switch to the normal operating position.
Figure 6 shows still another example of the present
invention employing a pair of light-emitting diodes, for
instance a red-emitting diode 3 and a green-emitting diode
. ,.
7. The diode 3 is connected in a manner similar to Figure
5, except that the order of the transistor 4 and the diode 3
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i8 reversed. A second transistor 8 is connected by its
emitter to the diode 7, by its collector via a resistor 10
to the terminal B, and by its base via a resistor 9 to the
~unction point A.
In Figure 6 the circuit is first reset by a re-
setting switch 6, as in the previous examples. When the
potential at point A is higher than Vt2 in Figure 4, the
device 1 and hence the first transistor 4 are "OFF". A
current flows through the resistors 2 and 9 to the base of
the second transistor 8, turning it "ON". Hence the
li~ght-emitting diode 7 is on. This green light indicates
that the power source Vcc is in order.
When an interruption takes place in the power
æupply and the potential at the terminal B falls below
Vt2, or further to zero, and is later restored to the
voltage Vcc, the device 1 turns "ON" in the manner already
described, hence turning the first transistor 4 "ON",
with its collector current represented by the point P in
Figure 4, and lighting the diode 3. This red light indicates
that the power source Vcc has suffered an interruption or
reduction. When the red light is lit, the potential at
point A is lowered. Therefore the transistor 8 is turned
"OFF", extinguishing the green light-emitting diode 7.
Thus illumination of the green light indicates
normal power supply; illumination of the red light indicates
a past interruption or diminution of the power supply; and
extinguishing of both lights indicates a current interrup-
tion of the power supply.
An example of Figure S is as follows:
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1~)36671
Negative-resistance device 1 consists of
complementary FETs, i.e., an n-channel, junction-type
FET and a p-channel, junction-type FET connected in
the manner shown in Figure 1, wherein
Vtl ----- 3V
Vt2 --~-- 7V
Vt3 ----- 22V.
Light-emitting diode 3 is a red-light emitting
diode made of a GaAsO 6Po 4 crystal- ~-
Transistor 4 is an npn-silicon planar transistor
having a D.C. current amplification factor hFE f
approximately 100.
The D.C. power source Vcc supplies lOV D.C.
The apparatus works as explained with the load `
resistance selected in a range of 400 to 1000 ohms.
An example of Figure 6 is as follows:
Negative-resistance device 1 consists of ~--
complementary FETs, i.e., an n-channel, junction-type -
FET and a p-channel, junction-type FET connected in the
manner shown in Figure 1, wherein
Vtl ----- l.OV
Vt2 ----- 2.5V
Vt3 ----- 28V.
Light-emitting diode 3 is a red-light emitting
diode made of a GaAsO.6P0.4 crystal-
Light-emitting diode 7 is a green-light emitting
diode made of a GaP crystal.
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Transistors 4 and 8 are npn-silicon planar
transistors each having a D.C. current amplification factor
hFE of approximately 200.
The D.C. power source Vcc supplies 5V D.C.
The apparatus works appropriately as explained
with
the resistance of the resistor 2 ----- 150 ohms;
the resistance of the resistor 9 ----- 33,000 ohms;
and the resistance of the resistor 10 ----- 150 ohms.
~ithin the present invention, the circuit arrange-
mènt is not confined to the abovementioned examples, and any
variation within the scope of the present invention can be
made. For instance, in the example of Figure 3 the diode
3 can be connected above the point A, i.e., between the
point B and the resistor 2.
Also, the light-emitting diodes can be replaced
by other warning means, for instance, buzzers or incande-
scent lamps.
Further, a Darlington-Connection circuit with
two transistors can be used in place of the transistor
4 or 8, if a larger output is required.
The negative-resistance device 1 can employ
insulated gate type tso-called MOS type) FETs instead of
the ~unction type PETs shown in the examples.
The apparatus is simple in circuit arrangement.
In the examples of Figures 3 and 5, the circuit has an
advantage of substantially zero power consumption under
normal conditions.
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