Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Synchronizing
Reexamination Certificate
1999-04-27
2001-02-06
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Synchronizing
C327S198000
Reexamination Certificate
active
06184731
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a reset signal generation circuit, and more particularly to a reset signal generation circuit in a battery charger, which circuit detects a voltage drop of a voltage source and generates a reset signal.
2. Description of the Related Art
FIG. 1
shows an example of a conventional reset signal generation circuit. Voltage level shift circuits
11
to
16
are cascaded. Each of the voltage level shift circuits
11
to
16
is made up of a pnp transistor Q
1
, an npn transistor Q
2
and a resistor R
1
used as a current limiter. In each of the voltage level shift circuits
11
to
16
, all of a base and a collector of the pnp transistor Q
1
and a base and a collector of the npn transistor Q
2
are connected together. An emitter of the pnp transistor Q
1
in the voltage level shift circuit
11
is connected to a voltage source Vcc (e.g., a voltage of 24 V). An emitter of the npn transistors Q
2
in each of the voltage level shift circuits
11
to
16
is connected to one end of the associated resistor R
1
. The other end of the resistor R
1
in each of the voltage level shift circuits
11
to
15
is connected to an emitter of the pnp transistor Q
1
in each of the lower voltage level shift circuits
12
to
16
, respectively. The other end of the resistor R
1
in the voltage level shift circuit
16
is connected to a ground. The voltage level shift circuits
11
to
16
respectively shift the voltage level.
A base of an npn transistor Q
3
is connected to the emitter of the pnp transistor Q
1
in the voltage level shift circuit
15
and the collector of the npn transistor Q
3
is connected to the voltage source Vcc. A base of an npn transistor Q
4
is connected to an emitter of the npn transistor Q
3
and a collector of the npn transistor Q
4
is connected to the voltage source Vcc. An emitter of the npn transistor Q
4
is connected to one end of a resistor R
2
.
The resistor R
2
, a resistor R
3
and a resistor R
4
are cascaded. The other end of the resistor R
4
is connected to the ground. A connection point between the resistors R
2
and R
3
is connected to a non-inverting input terminal of a comparator
18
and a connection point between the resistors R
3
and R
4
is connected to an inverting input terminal of the comparator
18
. An output terminal of the comparator
18
is connected to a base of an npn transistor Q
7
.
A base of the pnp transistor Q
1
in the voltage level shift circuit
11
is connected to bases of both of the pnp transistors Q
5
and Q
6
. An emitter of the pnp transistor Q
5
is connected to the voltage source Vcc and a collector of the pnp transistor Q
5
is connected to both a collector of the npn transistor Q
7
and a base of an npn transistor Q
8
. An emitter of the pnp transistor Q
6
is connected to the voltage source Vcc and a collector of the pnp transistor Q
6
is connected to a collector of the npn transistor Q
8
and an output terminal
20
. Emitters of both of the npn transistors Q
7
and Q
8
are connected to the ground.
This circuit is connected to, for example, a battery charger for Lithium batteries. Both the voltage source Vcc and the ground in
FIG. 1
are commonly connected to those of the battery charger for the Lithium batteries. As a voltage of the voltage source Vcc increases, the electric potential of an emitter of the transistor Q
1
in the voltage level shift circuit
15
increases. Then, both of the transistors Q
3
and Q
4
turn on. When a current through the resistor R
3
increases higher than a predetermined value, the output of the comparator
18
changes into a high level, so that the transistor Q
7
turns on and therefore the transistor Q
8
turns off. At the same time, when the transistor Q
1
in the voltage level shift circuit
11
turns on, both of the transistors Q
5
and Q
6
turn on because they are current mirror transistors of the transistor Q
1
. As a result, a reset signal of the high level is supplied from the output terminal
20
.
Conventionally, when the voltage source Vcc temporarily drops, the output level of the output terminal
20
becomes a low level because the transistors Q
1
, Q
5
and Q
6
temporarily turn off due to a base emitter capacitance.
FIG. 2
shows a timing chart of a conventional reset signal generation circuit. When the voltage of the voltage source Vcc temporarily drops from, for example, 24 V to 14 V at a time T
1
and recovers soon after the voltage is dropped, the voltage between the base and the emitter of the transistor Q
6
temporarily drops, as shown with a solid line in
FIG. 2
, and an electric potential of the base of the transistor Q
8
temporarily increases, as shown with an alternate short and long dash line in FIG.
2
. Though the reset signal should keep the high level because the starting voltage of the battery charging for the Lithium batteries is about 13 V, the reset signal of the output terminal
20
temporarily drops to a low level, as shown with a broken line in FIG.
2
. In other words, the erroneous reset signal is supplied to the battery charger. This results in an erroneous restart of the battery charging.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a reset signal generation circuit in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a reset signal generation circuit which prevents an erroneous reset signal for a battery charger from generating due to a voltage fluctuation of a voltage source.
The above objects of the present invention are achieved by a reset signal generation circuit which generates a power-on reset signal when a voltage of a voltage source has increased higher than a predetermined value, The reset signal generation circuit includes an output circuit which is supplied with power from a divided point between the voltage source and a ground and a voltage stabilizer which stabilizes a voltage of the divided point between the voltage source and the ground. When the voltage of the voltage source increases higher than the predetermined value, the reset signal generation circuit generates the power-on reset signal for a battery charger. In the reset signal generation circuit, the power for the output circuit is supplied from the divided point between the voltage source and the ground, and the voltage of the divided point is stabilized by the voltage stabilizer. Since the power for the output circuit is supplied from the divided point, a fluctuation of the voltage supplied to the output circuit is reduced compared to that of the voltage source. Moreover, the voltage stabilizer circuit prevents an erroneous reset signal for the battery charger from generating due to the voltage fluctuation of the voltage source.
REFERENCES:
patent: 5157270 (1992-10-01), Sakai
patent: 5177375 (1993-01-01), Ogawa et al.
patent: 5929674 (1999-07-01), Maccarrone et al.
Callahan Timothy P.
Ladas & Parry
Mitsumi Electric Co. Ltd.
Nguyen Minh
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