Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2003-05-14
2004-08-24
Nguyen, Long (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S432000, C327S478000, C323S312000, C323S315000
Reexamination Certificate
active
06781441
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circuit for generating a very small electric current.
2. Description of the Related Art
A conventional CR oscillation circuit and load driving circuit with an over-current protection function as shown in
FIG. 9
determines a discharge time period on the basis of a very small electric current. As shown in
FIG. 9
, a pnp transistor
100
is connected in series with a resistor
101
and constant current circuit
102
between a voltage source and ground, while the base of the pnp transistor
100
is connected with the connecting point between the resistor
101
and constant current circuit
102
. The above-mentioned series circuit allows a constant current I
1
to flow. Further, a pnp transistor
103
is provided between the voltage source and ground, while the base of the pnp transistor
103
is connected with the collector of the pnp transistor
100
. Thus, the pnp transistor
103
also allows a very small electric current Ic proportional to I
1
to flow.
The CR discharge oscillation circuit as shown in
FIG. 10
can be constructed by utilizing the above-mentioned circuit as shown in FIG.
9
. The collector (through which Ic flows) of the pnp transistor
103
is connected with transistor
104
which is a part of a current mirror circuit comprises another transistor
105
which is connected with a capacitor
106
, thereby constructing through a switch
107
a charging circuit
108
. Thus, the discharge current of the capacitor
106
is determined by Ic.
Here, Ic is determined by the following formula, if the transistor
100
has the same characteristics as the transistor
103
.
Ic=I
1
/exp
((
I
1
R
1
q/kT
)),
where R
1
is a resistance value of the resistor
101
, q is the unit charge of electron, k is Boltzmann constant and T is absolute temperature.
Therefore, it is difficult to stabilize Ic within a whole defined temperature range, because Ic is strongly dependent upon the temperature.
Accordingly, the discharge time period becomes shorter at a higher temperature than at a lower temperature. If the discharge time period is designed for a higher temperature, then the lower temperature discharge time period becomes unduly long.
SUMMARY OF THE INVENTION
An object of the invention is to suppress a fluctuation in the very small electric current (in a small current generating circuit such as a CR oscillation circuit and load driving circuit with an over-current protection function) due to temperature fluctuation, thereby stabilizing the very small current.
The present invention includes several Features stated below.
According to Feature
1
, the very small current generating circuit comprises:
a first current route for a first current wherein between an internal reference voltage terminal and a ground terminal, a first resistor
10
is connected in series with a first npn transistor
11
of which collector is connected with said first resistor
10
and of which base is connected with said collector;
a second current route for a second current of a negative temperature characteristics and proportional to said first current wherein between an external voltage source and said ground terminal, a first pnp transistor
12
, a second resistor
13
, a second npn transistor
14
and a third resistor
15
are connected in series in this order, said second resistor
13
being connected with the collector of said first pnp transistor
12
, said third resistor
15
being connected with the emitter of said second npn transistor
14
, the collector of said second npn transistor
14
being connected with said second resistor
13
, the base of said first pnp transistor
12
being connected with the collector of said second npn transistor
14
, the base of said second npn transistor
14
being connected with the collector of said first npn transistor
11
; and
a third current route for a third current proportional to said second current which is outputted as a very small current wherein between said external voltage source and ground terminal, connected is a second pnp transistor
17
of which base is connected with the collector of said first pnp transistor
12
.
Thus, the very small current is stabilized inspite of the temperature fluctuation.
According to Feature
2
, the very small current generating circuit further comprises a fourth resistor
16
which is connected between said external voltage source and the emitter of said second pnp transistor
17
.
Thus, the current through the third current route is adjusted by the fourth resistor
16
.
According to Feature
3
, the very small current generating circuit further comprises a fifth resistor
18
which is connected with the emitter of said first npn transistor
11
, wherein a temperature coefficient of said fifth resistor
18
is smaller than that of said third resistor
15
.
Thus, the slope of the temperature characteristics of the current through the third current route is further adjusted.
According to Feature
4
, the very small current generating circuit further comprises a fifth resistor
18
which is connected with the emitter of said first npn transistor
11
, wherein a temperature coefficient of said fifth resistor
18
is negative and a resistance value of said third resistor
15
is negligibly smaller than that of said fifth resistor
18
.
Thus, the slope of the temperature characteristics of the current through the third current route is further adjusted.
According to Feature
5
, in the very small current generating circuit, said internal reference voltage is generated on the basis of a voltage of said external voltage source.
Thus, the current through the third current route is further stabilized due to stabilized internal and external voltages.
According to Feature
6
, in the very small current generating circuit, said second resistor
13
comprises a plurality of resistors
30
and
31
with different temperature coefficients.
Thus, the current through the third current route is finely adjusted and less temperature insensitive.
According to Feature
7
, the very small current generating circuit further comprises:
a transistor
28
constructing a current mirror circuit;
a transistor
29
constructing together with said transistor
28
said current mirror circuit and provided at an output terminal for outputting said very small current in said third current route;
a capacitor
26
connected with said transistor
28
;
a charging circuit connected with said capacitor
26
through a switch
25
for charging said capacitor
26
.
Thus, an accurate CR oscillation circuit is constructed due to the stabilized very small current (the current through the third current route).
According to Feature
8
, the very small current generating circuit further comprises:
an over-current detecting circuit
23
for switching on said switch
25
, when a current through a load
21
becomes greater than a prescribed current;
a comparator
27
for comparing a voltage of said capacitor
26
with a threshold voltage and outputting a signal for switching off a power transistor
20
on the basis of the comparison result.
Thus, a load driving circuit with an over-current protection function is constructed due to the stabilized very small current (the current through the third current route).
According to Feature
9
, in the very small current generating circuit, said threshold voltage comprises a lower threshold voltage and a higher threshold voltage.
Thus, the discharge current is stabilized and held within a prescribed range.
Further, the very small current generating circuit of the present invention can be applied to a timer circuit and filter circuit.
REFERENCES:
patent: 5557194 (1996-09-01), Kato
patent: 5760639 (1998-06-01), Hall
patent: 6271710 (2001-08-01), Ooishi
patent: 6316990 (2001-11-01), Tanizawa
patent: 6-102355 (1994-04-01), None
patent: 6-332556 (1994-12-01), None
patent: 7-191769 (1995-07-01), None
patent: 9-204773 (1997-08-01), None
patent: 2000-75945 (2000-03-01), None
Denso Corporation
Nguyen Long
Posz & Bethards, PLC
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