Electrical transmission or interconnection systems – Switching systems – Condition responsive
Reexamination Certificate
2000-09-01
2003-02-18
Sircus, Brian (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
Condition responsive
C307S010100, C307S031000
Reexamination Certificate
active
06522034
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-voltage level power supply unit and a switching circuit employed in the power supply unit.
2. Description of the Related Art
Vehicles such as automobiles have a power supply unit for supplying loads with currents. Such a power supply unit supplies a load with the output voltage of a 14-volt power supply via the drain electrode D and the source electrode S of a field effect transistor (FET).
One of the known power supply unites is a multi-voltage level power supply unit shown in FIG.
1
. As shown in
FIG. 1
, an AC voltage generated by an alternator
121
is converted by an AC/DC converter
122
into a DC voltage, which is then transferred to a 42-volt power supply B
1
. The output of the 42-volt power supply B
1
is supplied to a load
123
such as a driving motor. The DC voltage output of the 42-volt power supply B
1
is lowered by a DC/DC converter
125
and transferred to a 14-volt power supply B
2
of which the output is supplied to a load
127
such as a lamp. By the multi-voltage levels provided with the 42-volt power supply B
1
and the 14-volt power supply B
2
, both the 42-volt system load
123
such as a driving motor and the 14-volt system load
127
such as a lamp can be driven.
The voltage output of the 42-volt power supply B
1
is substantially three times greater than that of the 14-volt power supply B
2
and its current is as small as ⅓. This permits the wire harness (W/H) in the 42-volt system circuit to be substantially ⅓ smaller in the diameter than that in the 14-volt system circuit. Accordingly, the W/H can be reduced in the weight and its load efficiency will be improved. For that reason, it is increasingly desired to activate a number of loads with the 42-volt power supply B
1
in every vehicle. In case that the motor is driven by the 42-volt power supply B
1
through a relevant relay, the use of a 42-volt system relay may increase the cost. It is hence desired to drive the motor with the 42-volt power supply B
1
, but using a 14-volt system relay.
However, when the 14-volt system relay is connected directly with the 42-volt power supply B
1
, it receives a too-high voltage and may generate an arc discharge (a spark) upon opening or closing, thus causing unwanted worn-out or meltdown on the contact.
For preventing the worn-out or meltdown of the contact so as to extend the life of the relay, an ON/OFF control circuit employing a semiconductor device and a relay is proposed in Japanese Patent Laid-open Publication S59-221921. The ON/OFF control circuit has, as shown in
FIG. 2
, a driver
205
, an AND circuit
209
, the semiconductor device
206
and the relay
207
connected in series with each other, and a timing circuit
208
for controlling the timing of switching on and off the semiconductor device
206
as well as the timing of turning on and off the relay
207
. The relay
207
is activated for turning on or off after the semiconductor device
206
is changed to the off state by the timing circuit
208
. In this circuit, the semiconductor device
206
is driven to off state before turning on and off the relay
207
, so that a flow of large current through the contact of the relay
207
can be suppressed. Accordingly, the life of tile relay
207
can be extended.
For suppressing the arc discharge in the relay so as to prevent the worn-out or meltdown on the contact, a switching apparatus is proposed in Japanese Patent Laid-open Publication S56-116238. The switching apparatus has, as shown in
FIG. 3
, an electromagnetic relay
302
having normally open contacts
302
a,
302
b,
302
c
and a triac
305
connected in series with the normally open contact
302
b.
The switching apparatus further has a normally-open push-button switch
303
and a normally-closed push-button switch
304
connected in series with the electromagnetic relay
302
. It is so set that, when the normally-open push-button switch is closed to flow current in the electromagnetic relay
302
, the normally open contact
302
b
closes first, and the normally open contact
302
c
closes so as to conduct the triac
305
. On the contrary, the normally open contact
302
c
opens first to cut off the triac
305
, and the normally open contact
302
b
opens afterwards, when the normally-closed push-button switch
304
becomes open so as to cut off the current in the electromagnetic relay
302
, thus minimizing melting-down or worn-out of the contact
302
b.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a switching circuit in which a reverse electromotive force possibly generated on a load, which will be connected to a relay serving as a component of the switching circuit, can be minimized, even if the load is an inductive load such as a motor.
Another object of the present invention is to provide a switching circuit in which a voltage applied to the relay for closing and opening operations is effectively lowered so as to allow a configuration of a multi-voltage level power supply unit, in which higher and lower voltages are supplied.
Still another object of the present invention is to provide a switching circuit in which generation of arc discharge on the relay designed to operate at lower rated voltage can be minimized even in the multi-voltage level power supply unit.
Still another object of the present invention is to provide a switching circuit in which the relay designed to operate at lower rated voltage can be operated with higher supply voltage without using any specific and complicated mechanism or apparatus designed to operate at the higher voltage.
Still another object of the present invention is to provide a multi-voltage level power supply unit in which the relay, designed to operate at lower rated voltage, can be operated with the higher voltage without using a specific mechanism or apparatus by suppressing the generation of arc discharge.
Still another object of the present invention is to provide a multi-voltage level power supply unit in which the relay, designed to operate at the lower rated voltage, can be operated with the higher voltage without giving any damage, fracture, or breakdown to the semiconductor device, which may be employed in the unit, when it is switched off.
For accomplishing the foregoing objects, the present invention is implemented by the following manners. A first aspect of the present invention inheres in a switching circuit for use in a multi-voltage level power supply unit for supplying a first voltage and a second voltage lower than the first voltage. Namely, the switching circuit of the present invention has a first relay designed to operate at the second voltage, a first semiconductor device and a control unit. The first semiconductor device has a first control electrode, a first main electrode for receiving the first voltage, a second main electrode connected to the first relay. And the control unit is connected to the first control electrode of the first semiconductor device. The control unit provides a first control signal to the first control electrode so as to increase an interelectrode voltage between the first and second main electrodes, only during transition periods between open to closed states and closed to open states. Further the control unit provides second control signal to the first control electrode so as to decrease the interelectrode voltage during steady state periods of the first relay. The first semiconductor device of the present invention is always operating in its on state, but the operation point of the first semiconductor device swings between the higher and lower interelectrode voltages.
In the first aspect of the present invention, the first semiconductor device may be a bipolar transistor (BJT), a field effect transistor (FET), a static induction transistor (SIT), insulated gate bipolar transistor (IGBT), etc. For example, if the first semiconductor device is the BJT, the first control electrode is a base electrode, the first main electrode may be emitter or collect
Sircus Brian
Yazaki -Corporation
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