Miscellaneous active electrical nonlinear devices – circuits – and – External effect – Temperature
Reexamination Certificate
1999-11-17
2001-01-30
Kim, Jung Ho (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
External effect
Temperature
C327S083000, C327S540000
Reexamination Certificate
active
06181192
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a constant voltage circuit used at a wide temperature range, such as a constant voltage circuit used in a car control circuit or the like.
2. Description of the Prior Art
FIG. 5
is a circuit diagram of a prior art constant voltage circuit for stabilizing a voltage from a DC power source. In
FIG. 5
, reference numeral
100
denotes a differential amplifier,
101
,
102
and
103
fixed resistors having resistance values R
11
, R
12
and R
13
, respectively, and
104
a Zener diode which is a temperature-dependent semiconductor element. In this constant voltage circuit, a series circuit formed on one side by connecting the fixed resistors
101
and
102
in series and a series circuit formed on the other side by connecting the fixed resistor
103
and the Zener diode
104
in series on the other side constitute a bridge circuit, a connection point between the fixed resistor
101
and the fixed resistor
103
of the bridge circuit is connected to the output terminal of the differential amplifier
100
, and a connection point between the fixed resistor
102
and the Zener diode
104
is connected to the ground. Further, the output of the connection point of the series circuit on one side is applied to the inversion input terminal of the differential amplifier
100
and the output of the connection point of the series circuit on the other side is applied to the non-inversion input terminal of the differential amplifier
100
so as to output a constant voltage from the output terminal of the differential amplifier
100
.
A description is subsequently given of the operation of the above constant voltage circuit.
The voltage V+ of the non-inversion input terminal of the differential amplifier
100
is equal to the voltage Vz at both ends of the Zener diode
104
. Therefore, the voltage V_ of the inversion input terminal of the differential amplifier
100
becomes equal to V+ and Vz. Consequently, the output voltage V
6
of the differential amplifier
100
is represented by the following equation (1).
V
6
={(
R
11
+
R
12
)/
R
12
}·
Vz
(1)
The above output voltage V
6
is a constant value determined by the resistance values R
11
and R
12
of the fixed resistors
101
and
102
and the Zener voltage Vz of the Zener diode
104
. The output voltage V
6
of the differential amplifier
100
is referred to as “constant voltage” hereinafter.
Since the Zener diode
104
is a temperature-dependent element, the voltage Vz at both ends of the Zener diode
104
is changed by temperature. The voltage Vz at both ends of the Zener diode
104
is determined by a current Iz running through the Zener diode
104
and changes &Dgr;Vz in the voltage Vz caused by a temperature variations (to be referred to as “temperature characteristics” hereinafter) are determined by the voltage Vz. That is, the temperature characteristics &Dgr;Vz of the Zener diode
104
are determined by the current Iz running through the Zener diode
104
.
The temperature characteristics of the constant voltage circuit of the prior art will be described hereinunder.
The current Iz running through the Zener diode
104
is expressed by the following equation (2).
Iz
=(
V
6
−
Vz
)/
R
13
(2)
When the temperature characteristics &Dgr;Vz of the Zener diode
104
which are determined by the current Iz running through the Zener diode
104
at a certain temperature range are taken into consideration, the voltage V_ of the inversion input terminal of the differential amplifier
100
is expressed by the equation V_=Vz+&Dgr;Vz. Therefore, the constant voltage V
6
is expressed by the following equation (3) when the temperature characteristics &Dgr;Vz of the Zener diode
104
are taken into consideration.
V
6
={(
R
11
+
R
12
)/
R
12
}·(
Vz+&Dgr;Vz
) (3)
The temperature characteristics &Dgr;V
6
of the constant voltage V
6
are expressed by the following equation (4).
&Dgr;V
6
={(
R
11
+
R
12
)/
R
12
}·&Dgr;
Vz
(4)
Therefore, it is understood that the temperature characteristics &Dgr;V
6
of the constant voltage V
6
are proportional to the temperature characteristics &Dgr;Vz of the Zener diode
104
.
SUMMARY OF THE INVENTION
Generally speaking, the value of the temperature characteristics &Dgr;Vz of the Zener diode
104
becomes the smallest when the Zener voltage is around 5V, positive when the Zener voltage is higher than 5 V and negative when the Zener voltage is lower than 5 V as shown in FIG.
6
. Therefore, in the constant voltage circuit of the prior art, a 5.1 V Zener diode is used as the Zener diode
104
in most cases. However, since the temperature characteristics &Dgr;Vz of the Zener diode
104
change like a quadratic curve at around 5 V as shown in
FIG. 7
, &Dgr;Vz is small at an ordinary use range (−10 to 80° C.) but the temperature characteristics &Dgr;V
6
of the constant voltage V
6
become large at both ends of a wide temperature range(−40 to 120° C.), that is, a high temperature side and a low temperature side, when the constant voltage circuit is used in a car control circuit, thereby making it impossible to obtain high-precision constant voltage characteristics.
It is an object of the present invention which has been made to solve the above problem to provide a constant voltage circuit having excellent temperature characteristics at a wide temperature range.
According to a first aspect of the present invention, there is provided a constant voltage circuit comprising a bridge circuit having a series circuit formed on one side by connecting resistors in series and a series circuit formed on the other side by connecting in series a resistor, a temperature-dependent semiconductor element and temperature characteristics control means including a temperature characteristics correcting element having temperature characteristics opposite to those of the temperature-dependent semiconductor element and provided between the resistor and the temperature-dependent semiconductor element, and a differential amplifier, wherein the output of the connection point of the series circuit on one side of the bridge circuit and the output of the control means on the other side are connected to the input terminal of the differential amplifier.
According to a second aspect of the present invention, there is provided a constant voltage circuit, wherein the control means comprises a temperature characteristics correcting element and a voltage dividing circuit having a series circuit connected in parallel to the temperature characteristics correcting element, and the output of the dividing point of the voltage dividing circuit is applied to the differential amplifier.
According to a third aspect of the present invention, there is provided a constant voltage circuit, wherein the temperature-dependent semiconductor element is a Zener diode having a positive temperature coefficient and the temperature characteristics correcting element is a diode.
According to a fourth aspect of the present invention, there is provided a constant voltage circuit, wherein the Zener diode has a Zener voltage of around 5 V.
According to a fifth aspect of the present invention, there is provided a constant voltage circuit, wherein the Zener current of the Zener diode is set to ensure that the temperature change of the Zener voltage becomes smaller than the temperature change of the voltage at both ends of the diode.
According to a sixth aspect of the present invention, there is provided a constant voltage circuit which is used in a car control circuit.
According to a seventh aspect of the present invention, there is provided a constant voltage circuit which is used in a heat sensitive flow sensor.
The above and other objects, features and advantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4317054 (1982-02-01), Carus
Abe Minoru
Suetake Naruki
Tohyama Ryuji
Kim Jung Ho
Mitsubishi Denki Kaibushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
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