Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific current responsive fault sensor
Reexamination Certificate
2000-01-12
2001-09-04
Wong, Peter S. (Department: 2838)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific current responsive fault sensor
C323S908000
Reexamination Certificate
active
06285539
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a switch driver for controlling driving of a switch for controlling a charging current with respect to a secondary battery or the like. More particularly, this invention relates to a switch driver which can prevent overshooting which accompanies an abrupt rise of current upon operation of the switch.
BACKGROUND OF THE INVENTION
In recent years, apparatuses that use a secondary battery are increasing in number. This is due to the fact that the communication apparatus represented by a laptop personal computer are becoming more and more smaller, lighter and therefore portable. A secondary battery is charged in the following manner. A charge remaining in the secondary battery is detected and a control is carried out for sequentially charging based on this remaining charge.
FIG. 7
is a block diagram showing a structure of a switch driver in a conventional charge control system. As shown in
FIG. 7
, a collector of a pnp transistor TR
1
is connected to an adapter
1
via a node Pa while an emitter thereof is connected to a plus terminal of a secondary battery
2
via the node Pb. Furthermore, a base of the pnp transistor TR
1
is connected to a collector of the pnp transistor TR
2
via the node Pc while an emitter of an npn transistor TR
2
is grounded via a node Pe. A control section
3
is connected to a base of the npn transistor TR
2
via a node Pd.
The control section
3
supplies a current to the base of the npn transistor TR
2
to turn ON the npn transistor TR
2
with the result that a current flows from the collector of the npn transistor TR
2
to the emitter thereof. When the current flows with the turning ON of the npn transistor TR
2
, a base current of the pnp transistor TR
1
increases, and the pnp transistor TR
1
is turned ON with the result that a charging current iab flows to the secondary battery
2
from the adapter
1
and the secondary battery
2
is charged.
On the other hand, unless the control section
3
supplies a current to the base of the npn transistor TR
2
, the npn transistor TR
2
is maintained in an OFF state with the result that the current does not flow from the collector of the npn transistor TR
2
to the emitter thereof. As a consequence, the base current of the pnp transistor TR
1
does not flow, and the pnp transistor TR
1
is maintained in the OFF state with the result that the charging current iab does not flow from the adapter
1
to the secondary battery
2
. The ON and OFF state of the pnp transistor TR
1
is controlled with the ON and OFF control of the npn transistor TR
2
by the control section
3
, with the result that the charging of the secondary battery
2
by the charging current iab can be controlled with the ON and OFF thereof.
However, in the conventional switch driver described above, since the potential of the node Pc falls all of a sudden to a level that is nearly the grounding level because of the turning ON of the npn transistor TR
2
, the base current of the pnp transistor TR
1
also flows all of a sudden. As a consequence, the charge current iab which flows through the pnp transistor TR
1
abruptly increases and the charging current iab is overshot due to a transition phenomenon and the pnp transistor also vibrates largely.
Generally, in a charge control system that uses such a switch driver, a terminal voltage and a charging current iab of the secondary battery
2
are detected in order to protect the secondary battery
2
. When over-voltage or over-current is detected, then an operation for dealing with an unusual state, namely suspension of charging, is carried out. However, when the overshooting described above is generated then there is a problem that the charge control system erroneously detects that an over-current has generated with the result that a normal charging operation is hindered.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforementioned problems. It is an object of the present invention is to obtain a switch driver which eliminates an abrupt rise of switching in the switch driver which is used in a charge control system or the like, the switch driver being capable of preventing in advance an erroneous operation of the system due to this abrupt rise of the switching.
According to a first aspect of the present invention, when the pnp transistors are turned ON, the control unit subsequently turns ON the plurality of the npn transistors, and the base of the pnp transistor is grounded via a resistor connected in series to each of the npn transistors by the subsequent turning ON of the npn transistors one by one. As a consequence, a voltage between the base of the npn transistor and the grounding is subsequently allowed to fall with a synthesized resistance of each of the resistors which are arranged in parallel. Finally, the voltage is allowed to fall by a parallel arrangement portion of the resistance of all the resistors, and the base potential of the pnp transistor reaches approximately the grounding level and the pnp transistor is turned ON. Since the base potential of the pnp transistor is allowed to fall subsequently, it never happens that the base current of the pnp transistor abruptly increases. Thus, it never happens that the object current which flows through the pnp transistor is prevented from being overshot, either.
According to a second aspect of the present invention, when the pnp transistor is turned ON, the control unit subsequently turns ON the plurality of the npn transistors with the result that a current corresponding to a size of each of the npn transistor is allowed to flow between the pnp transistor and the grounding with the subsequent turning ON of the npn transistors. Then the base current of the pnp transistor is gradually increased thereby preventing an abrupt increase in the base current of the pnp transistor and preventing the object current from being overshot which is allowed to flow through the pnp transistor.
According to a third aspect of the present invention, when the pnp transistor is turned ON, the base current of the pnp transistor begins to flow through the plurality of third npn transistors which are connected in series for carrying out a diode operation by the control unit turning ON the first npn transistor. However, a voltage is present between the base and the emitter of each of the third npn transistor connected in series, and the base potential of the pnp transistor does not reach the grounding level. After that, the control unit subsequently turns ON each of the second npn transistor connected in parallel to each of the third npn transistor thereby decreasing a voltage fall of the third npn transistor and allowing the base potential of the pnp transistor to come close to the grounding level and gradually increasing the base current of the pnp transistor. Thus, an abrupt increase in the base current of the pnp transistor is prevented, and the object current which flows through the pnp transistor is prevent ed from being overshot.
According to a forth aspect of the present invention, when the pnp transistor is turned ON, the base current of the pnp transistor begins to flow through a plurality of resistors which are connected in series by the control unit turning ON of the first npn transistor. However, since a voltage fall of the plurality of resistors connected in series is present, the base potential of the pnp transistor does not reach the grounding level. After that, the control unit subsequently turns ON each of the second npn transistors connected in parallel to each of the resistors, decreases a voltage fall by each of the resistors, and allows the base current of the pnp transistor to gradually increase with the result that the base current of the pnp transistor is prevented from abruptly increasing and the object current which flows through the pnp transistor is prevented from being overshot.
According to a fifth aspect of the present invention, when the pnp transistor is turned ON, the control unit subsequently turns ON a switch of the power source circuit, allo
Kashimoto Koji
Saito Kazutaka
Tsuchiyama Tomonori
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Tibbits Pia
Wong Peter S.
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