Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
1999-03-08
2001-03-20
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S074000, C327S063000
Reexamination Certificate
active
06204699
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a voltage detection circuit which is designed such that a voltage input into a voltage detection IC (Integrated Circuit) does not fall below a minimum operating voltage, so as to be capable of detecting the voltage correctly, while preventing malfunction of the voltage detection IC.
2. Background Art
A voltage detection circuit as shown in
FIG. 4
is known as an example of conventional voltage detection circuits.
The voltage detection circuit shown in
FIG. 4
will be described hereinafter. The voltage detection circuit
2
has a terminal A and a terminal B, and an external constant voltage source is connected to the terminal A, and a power source for measuring a voltage is connected to the terminal B.
The voltages Va and Vb are applied to terminals A and B, respectively, and the voltage Vb is input into the voltage detection circuit. The output of the voltage detection IC
1
is connected to the terminal A through the pull-up resistor R
3
. The result of the voltage detection IC
1
is output at a terminal C.
Here, an operation of the voltage detection circuit will be described. As described, the external constant voltage source is connected to the terminal A, and the voltage Va is applied to the terminal A. The terminal B is connected to the power source for measuring the voltage and the voltage Vb is applied to the terminal B.
The terminal B is connected to the voltage detection IC
1
, and the voltage Vb is input into the voltage detection IC
1
. The output end of the voltage detection IC
1
and the resistor R
3
are connected to the terminal C, and the voltage Va is applied to the pull-up resistor R
3
.
When the voltage Vb is higher than a detection voltage, a voltage at a level of “H” is output at the terminal C, and when the voltage Vb is lower than the detection voltage, a voltage at a level of “L” is output at the terminal C.
Next, the operation is described in more detail using a wave-form diagram shown in FIG.
5
.
FIG. 5
is a diagram to explain the change of the input and output voltages of the voltage detection circuit.
FIG. 5A
shows an input voltage Vb to the terminal B, and the input voltage Vb is input into the voltage detection IC
1
.
FIG. 5B
shows an output voltage of the voltage detection circuit which appears at the terminal C.
In the above figures, it is assumed that the detection voltage of the voltage detection IC
1
is 2.5 V, the minimum operating voltage of the voltage detection IC
1
is 0.5 V, and the voltage Va at the terminal A is 3.5 V.
The region a is a range wherein the voltage Vb is higher than the detection voltage of the voltage detection IC
1
. Since the voltage Vb to be input into the voltage detection IC
1
is higher than the detection voltage of the voltage detection IC
1
, the level “H” is output at the terminal A.
The region b is a range wherein the voltage Vb is lower than the detection voltage of the voltage detection IC
1
, but higher than the minimum operating voltage. Since the voltage Vb to be input in the voltage detection IC
1
is lower than the detection voltage of the voltage detection IC
1
, the level “L” is output at the terminal C.
The region c is a range wherein the voltage Vb is lower than the minimum operating voltage of the voltage detection IC
1
. Despite the voltage Vb to be input in the voltage detection IC
1
being lower than the detection voltage of the voltage detection IC
1
, since the voltage Vb is lower than the minimum operating voltage of the voltage detection IC
1
, the terminal voltage becomes unstable and causes a malfunction of the voltage detection IC
1
.
The region d is, similar to the region b, a range wherein the voltage Vb is lower than the detection voltage of the voltage detection IC
1
. Since the voltage Vb to be input into the voltage detection IC
1
is lower than the detection voltage of the voltage detection circuit IC
1
, the level “L” is output at the terminal C.
The region e is, similar to the region a, a range wherein the voltage Vb is higher than the detection voltage of the voltage detection IC
1
. Since the voltage to be input in the voltage detection IC
1
is higher than the detection voltage of the voltage detection IC
1
, the level “H” is output at the terminal C. Due to the effect of the pull-up resistor R
3
, the voltage which appears at the terminal C is Va.
As a result, change of the output voltage of the voltage detection IC
1
is obtained as shown in FIG.
5
B. The region wherein the output of the voltage detection IC
1
changes is between regions a and b as well as between regions d and e.
However, in the region c, despite the fact that the voltage Vb is lower than the minimum operating voltage of the voltage detecting IC
1
, and that the voltage Vb is lower than the detection voltage, a problem arises that it is not possible to execute a normal detection of the voltage in the region c and causes malfunction of the voltage detection IC
1
.
Although a reference voltage generating circuit which is capable of setting a very accurate detection level of a source voltage detection circuit is disclosed in Japanese Patent Application, First Publication No. Hei 06-258359, the above described problem is still remains unsolved.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above described problem and to provide a voltage detection circuit which is capable of executing the accurate detection of the voltage, while preventing the malfunction of the voltage detection IC, even when the voltage of the terminal for detecting the voltage is lower than the minimum operating voltage of the voltage detection IC.
In order to attain the above object, a voltage detection circuit by the present invention comprises:
a voltage detection IC for outputting a voltage, the level of which is made to correspond to the detection voltage by inputting a voltage which is lower than the detection voltage and which is higher than the minimum operating voltage; and
a voltage selection circuit for selecting a higher voltage among two voltages and inputting said voltage into said voltage detection IC.
The voltage detection circuit of the present invention selects a higher voltage among two voltages by the voltage selection circuit, and the thus selected voltage is input into the voltage detection IC.
Since the input voltage into the voltage detection IC is set at a voltage higher than the minimum operating voltage of the voltage detection IC and higher than the detection voltage of the voltage detection IC, it is possible to detect a low voltage, even if the voltage to be detected is lower than the minimum operating voltage of the voltage detection circuit, while preventing the malfunction of the voltage detection IC.
REFERENCES:
patent: 4617473 (1986-10-01), Bingham
patent: 4626707 (1986-12-01), Arita et al.
patent: 5378936 (1995-01-01), Kokubo et al.
patent: 5451891 (1995-09-01), Tanabe
patent: 5548227 (1996-08-01), Minami
patent: 5563546 (1996-10-01), Tsukada
patent: 5614857 (1997-03-01), Lim et al.
patent: 2 285 316 (1995-07-01), None
European Search dated Jul. 29, 1999.
Callahan Timothy P.
McGuireWoods LLP
NEC Corporation
Nguyen Hai L.
LandOfFree
Voltage detection circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Voltage detection circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Voltage detection circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2447072