Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2000-10-12
2002-12-03
Sherry, Michael (Department: 2829)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S11700H, C324S120000
Reexamination Certificate
active
06489786
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a non-isolated voltage sensor provided specifically between a high-voltage battery and a circuit having a pull-up resistance one end of which is connected to a cable while the other end thereof is connected to a reference power supply, and more particularly to a non-isolated type voltage sensor capable of sending a detected voltage accurately without considering a cable length.
2. Description of the Related Art
In a recent high-voltage vehicle containing a plurality of batteries of 12V or the like connected to each other, for example, there is such a trend that a plurality of wire harnesses are included in a junction box (J/B) and sensors, measuring circuits and the like are accommodated in this junction box if possible. The location of this junction box in a vehicle compartment varies depending on the vehicle type.
However, because a conventional voltage measuring circuit for use in automobile has a limitation on the wire harness length, there is such a problem that the locations of the voltage measuring circuit and battery controller in the vehicle compartment cannot be changed. Further, if the vehicle type is changed so that the location of the junction box is changed, there is another problem that the sensor and voltage measuring circuit cannot be accommodated in the junction box because the wire harness length is limited.
To solve this problem, Japanese Patent Application Laid-Open No. H9-257837 has disclosed a conventional voltage sensor which eliminates the necessity of considering the harness length.
A voltage sensor
10
shown in
FIG. 1
comprises a power supply line
13
for supplying an electric power from a battery
2
to a load
12
and an isolated type detector
16
having a hall device
15
in a gap of a magnetic core
14
. The power supply wire
13
passes through a through hole of the detector
16
as a primary side wire.
This voltage sensor further comprises a differential amplifying circuit
17
for differential-amplifying an output from both ends of the hall device
15
, a current buffer
18
connected to this differential amplifying circuit
17
and the like. An output wire
19
of the current buffer
18
is wound around the core
14
of the isolated type detector
16
by a predetermined number of turns as a secondary side wire. Then, a voltage signal is sent to a battery controller
22
through a harness
20
.
An end of an input circuit
23
of this battery controller
22
is connected to an input terminal of the voltage follower
24
and the harness
20
while the other end thereof is connected to the ground. This ground is a weak current ground which is different from a ground for the battery
2
and the voltage sensor
10
.
That is, when the detector
16
is used, magnetic flux proportional to a current flowing from the battery
2
to the load
12
is generated and then, the hall device
15
detects that magnetic flux as a hall voltage, so that the differential amplifying circuit
17
and a current buffer
18
supply a current in a direction which makes zero a hall voltage to the secondary wire side.
The current flowing to the secondary wire side is sent to the input circuit
23
of the battery controller
22
through the harness
20
. That is, because an output from the voltage sensor
10
becomes an output of current, the harness length can be neglected (the harness may be long).
However, because in this voltage sensor
10
, the battery voltage is not detected directly, there is a problem in terms of a detection accuracy although the harness length can be neglected. Further, there is another problem that this voltage sensor
10
necessitates the core, hall device, differential amplifying circuit and the like, the quantity of the components increases.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve the above described problems and therefore, an object of the invention is to provide a non-isolated type voltage sensor for a battery of vehicle in which the restriction on the harness length is mild, the non-isolated type voltage sensor being capable of measuring a voltage accurately without use of the hall device.
The non-isolated type voltage sensor of the present invention is a non-isolated type voltage sensor provided between a battery and a circuit containing a pull-up resistor which is connected to a reference power supply and a cable.
This non-isolated type voltage sensor comprises a voltage dividing circuit, a voltage follower and a voltage-current conversion circuit.
The voltage dividing circuit is comprised of plural resistors connected in series and connected to the battery in parallel. Then, a voltage proportional to a terminal voltage of the battery and less than the voltage of the reference power supply is obtained at a desired voltage dividing point of these plural resistors.
Because the voltage follower converts a high input impedance to a low input impedance, it takes a role as a buffer circuit for removing respective influences between the voltage dividing circuit and the voltage-current circuit. Therefore, if a voltage at the voltage dividing point of the voltage dividing circuit is inputted to the voltage follower, a low impedance output voltage is obtained.
Next, the voltage-current conversion circuit supplies a current proportional to a low impedance output voltage obtained through the voltage follower to the ground through the cable and output resistor.
This voltage-current conversion circuit comprises: a field effect transistor a source of which is connected to the cable while a drain thereof is connected to the output resistor; an output resistor which is connected to a drain of the field effect transistor and the ground, the output resistor having a resistance higher than a resistance of the pull-up resistor; and an amplifier in which an output of the voltage follower is connected to a non-inverted input thereof, an inverted input thereof is connected to the output resistor and an output thereof is connected to a gate of the field effect transistor.
Thus, if the voltage dividing circuit obtains a voltage proportional to the battery voltage at the voltage dividing point, the field effect transistor is turned ON immediately through the voltage follower.
That is, because a current supplied to the gate of the field effect transistor is made very small when the field effect transistor is turned ON, even if the voltage at the voltage dividing point is converted to current, the current flowing to the ground through the cable becomes a current accurately proportional to a detection current at the voltage dividing point.
Further, the non-isolated type voltage sensor of the present invention is a non-isolated type voltage sensor provided between a battery and a circuit having a first pull-up resistor which is connected to the ground and the cable.
This non-isolated type comprises a voltage detecting circuit and a voltage-current conversion circuit.
The voltage detecting circuit obtains a voltage proportional to a battery voltage at the voltage dividing point and supplies a first current proportional to a low impedance output voltage obtained from a voltage at this voltage dividing point to the ground through a first output resistor.
The voltage-current conversion circuit supplies a second current proportional to a voltage signal determined based on the first current to the cable using a second output resistor.
This non-isolated type voltage sensor is provided between a circuit which is connected to the same type of ground as ground of the battery and the cable and the first pull-up resistor and which has a differential amplifying circuit carrying out differential amplification with the ground as a reference and the battery.
The voltage detecting circuit comprises a voltage dividing circuit, a voltage follower and a first voltage-current conversion circuit. The first voltage-current conversion circuit comprises: a first field effect transistor a source of which is connected to an input of the second voltage-current conversion ci
Satake Syuji
Takemoto Hisashi
Amin Anand B
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Sherry Michael
Yazaki -Corporation
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