Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2001-08-06
2003-05-20
Berhane, Adolf Deneke (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
Reexamination Certificate
active
06566852
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a voltage generator which outputs a constant voltage irrespective of temperature or power source voltage changes, an output circuit for an error detector that is used for this voltage generator, and a current generator for outputting a predetermined current. More particularly, this invention relates to a voltage generator, an output circuit for an error detector, and a current generator constituted by bipolar transistors.
BACKGROUND OF THE INVENTION
As a conventional voltage generator, there has been known a voltage generator structured by bipolar transistors.
FIG. 8
is a diagram showing a schematic structure of a conventional voltage generator structured by bipolar transistors. This voltage generator consists of a reference voltage generator
54
for generating and outputting a constant reference voltage VREF irrespective of temperature or power source voltage changes, an error detector
55
having a negative-phase input connected to an output of the reference voltage generator
54
, a PNP transistor
58
having an output of the error detector
55
connected to a base, having a high-potential side of the power source connected to an emitter, and having a collector connected to a voltage output terminal
53
, a resistor
57
disposed between the voltage output terminal
53
and a positive-phase input of the error detector
55
, and a resistor
56
disposed between the positive-phase input of the error detector
55
and a low-potential side (ground)
52
of the power source.
The reference voltage generator
54
generates a constant reference voltage VREF independent of a power source voltage and temperature. The reference voltage VREF can take only one value that satisfies a predetermined condition not to be independent of a power source voltage and temperature. As the reference voltage generator
54
has a large output impedance, an output voltage varies when a large output current flows. Therefore, only the reference voltage generator
54
is not sufficient for use as a voltage generator. Thus, the error detector
55
, the PNP transistor
58
, and the resistors
56
and
57
are also provided.
The PNP transistor
58
is disposed as an output buffer for obtaining a constant output voltage VREG
8
independent of an output current, by reducing the output impedance. The error detector
55
is disposed as a feedback amplifier that inputs the reference voltage VREF and a feedback voltage VFBK from the reference voltage generator
54
, amplifies the reference voltage VREF with a gain determined based on a ratio of a resistance R
52
to a resistance R
51
of the resistors
57
and
56
, and outputs a voltage VOP. The output voltage VREG
8
generated in the voltage output terminal
53
is expressed by equation 1.
VREG
8
=−(1+R
52
/R
51
)×
VREF
(1)
In other words, the output voltage VREG
8
is determined based on the reference voltage VREF and a resistance ratio (R
52
/R
51
) between the resistors
56
and
57
. As the reference voltage VREF has no dependency on temperature and a power source voltage, the output voltage VREG
8
does not depend on temperature and a power source voltage either. Even when the output current increases, for example, the output voltage VREG
8
is kept at a constant value shown in equation 1 based on a feedback loop of the feedback amplifier. When the error detector
55
operates from rail to rail, a set range of the output voltage VREG
8
becomes as follows. A minimum side of the range is a voltage of a low-potential side
52
of the power source becomes, and a maximum side is a voltage (VCC-Vcesat) obtained by subtracting a collector/emitter saturation voltage Vcesat (generally, about 0.3 V) of the PNP transistor
58
from a voltage VCC of a high-potential side
51
of the power source.
In other words, the output voltage of this voltage generator is set within a range from a low power source voltage (a voltage at the low-potential side of the power source) to (VCC-Vcesat). In general, a current multiplication factor of a PNP transistor is as small as about HFE=20 to 50. Therefore, for driving a large current based on the output voltage VREG
8
, a large driving capacity is necessary for the error detector
55
. When the current multiplication factor of the PNP transistor
58
is 20, and also when the driving current of the output voltage VREG
8
is 100 mA, the error detector
55
needs to have an output stage that can bear an inflow current of 5 mA.
FIG. 9
is a diagram showing a schematic structure of another conventional voltage generator structured by bipolar transistors. This voltage generator has an NPN transistor
61
in place of the PNP transistor of the voltage generator shown in
FIG. 8
, and has the input polarity of the error detector
55
changed to the opposite polarity (the reference voltage VREF is input in the positive phase, and the feedback voltage VFBK is input in the opposite phase). This voltage generator also operates in a similar manner to that of the voltage generator shown in
FIG. 8
, and outputs an output voltage VREG
9
determined by resistors
56
and
57
. However, in general, the current multiplication factor of an NPN transistor is large (HFE=about 100). Therefore, in the case of this voltage generator, the current driving capacity of an error detector
55
may be small even when a large current is driven based on the output voltage VREG
9
.
For example, when a driving current of the output voltage VREG
9
is 100 mA, it is sufficient that the input stage of the error detector
55
can bear the inflow current of 1 mA. When the error detector
55
operates from rail to rail, a set range of the output voltage VREG
9
becomes as follows. A minimum value side of the range is a low power source voltage, and a maximum side is a voltage obtained by subtracting a base/emitter voltage Vbe (generally, about 0.9 V) of the NPN transistor
61
from a high power source voltage (a voltage at the high-potential side of the power source) In other words, the output voltage of this voltage generator is set within a range from the low power source voltage to (VCC-Vbe).
Further, it is also possible to construct a current generator by providing a current source circuit at a rear stage of the voltage generator.
FIG. 10
is a diagram showing a schematic structure of a conventional current source circuit. This current source circuit consists of a voltage input terminal
71
connected to the voltage output terminal
53
of the voltage generator shown in
FIG. 8
or
FIG. 9
, for inputting the output voltage VREG
8
(or
9
) of the voltage generator, a resistor
75
(a resistance R
71
) having one end connected to the voltage input terminal
71
, an NPN transistor
73
having the other end of the resistor
75
connected to a collector and a base, a resistor
76
(a resistance R
72
) provided between an emitter of the NPN transistor
73
and a low-potential side
52
of the power source, an NPN transistor
74
having a base of the NPN transistor
73
connected to a base, and having a collector connected to a current output terminal
72
, and a resistor
77
(a resistance R
73
) provided between an emitter of the NPN transistor
74
and the low-potential side
52
of the power source.
This current source circuit outputs a current based on an input of the constant voltage VREG
8
(or
9
) independent of temperature and a voltage power source. The NPN transistors
73
and
74
constitute a current mirror current source circuit. When the sizes of the NPN transistors
73
and
74
and the resistances R
72
and R
73
of the resistors
76
and
77
are of the same values respectively, an input current Iin
8
and an output current Iout
8
of the current source circuit can be expressed by equation 2.
I
out
8
=
I
in
8
=
[
VREG8
-
Vbe
(
T
,
Ie
)
]
/
(
R71
+
R72
)
(
2
)
In equation 2, Vbe (T, Ie) represents a base/emitter voltage of the NPN transistors
73
and
74
respectively, and th
Tagami Hitoyuki
Takizawa Koichi
Berhane Adolf Deneke
Birch Stewart Kolasch & Birch, LLP.
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