Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
2000-10-20
2001-11-13
Ton, My-Trang Nu (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C527S403000
Reexamination Certificate
active
06316967
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a current detector for detecting a supply current supplied to a load with good accuracy.
Hitherto, a high-accuracy current detector has been demanded for the purposes of finding the charge amount of a secondary battery used with a personal computer, etc., with good accuracy, monitoring a current distribution circuit in an automobile, etc. A method of placing a shunt resistor of a high-accuracy low resistance element in series with wiring through which the current to be detected flows and detecting a voltage drop occurring in the shunt resistor, thereby detecting a current value is known.
For example, in
FIG. 10
, a current I
12
proportional to a load current IL flowing into a shunt resistor Rs is formed using pnp transistors Q
11
and Q
12
and a resistor R
11
and is converted into an output current VOUT using a resistor R
12
, thereby detecting the load current IL.
Hitherto, a method of using an operational amplifier IC to differentially amplify the potential difference occurring across a shunt resistor of a high-accuracy low resistance element and output the voltage proportional to a load current has been known. In this case, however, the offset voltage of the operational amplifier IC is superposed on the output voltage, thus a problem is involved in the accuracy particularly when the load current is small. In contrast, there is also an operational amplifier IC whose output voltage can be adjusted by connecting a variable resistor to an external terminal, but the operational amplifier ICs are not suitable for mass production. A method of canceling the effect of offset voltage by a circuit shown in
FIG. 11
is known.
In
FIG. 11
, if an operational amplifier OP
1
has a sufficiently large amplification factor, the potential difference between an inversion input terminal and a noninversion input terminal of the operational amplifier OP
1
can be assumed to be zero. Therefore,
I
14
·
R
14
=(
I
13
+
IL
)·
RS≈IL·RS
where R
14
is the resistance value of a resistor R
14
, RS is the resistance value of a shunt resistor Rs, I
13
is a current flowing into the inversion input terminal of the operational amplifier OP
1
, and I
14
is a current flowing into the noninversion input terminal of the operational amplifier OP
1
.
Thus, the collector current I
14
of a pnp transistor Q
13
becomes
I
14
≈
I
1
·
RS/R
14
and a current proportional to load current IL can be output.
However, in the circuit previously described with reference to
FIG. 10
, the range in which the voltage proportional to the load current IL flowing into the shunt resistor Rs of a high-accuracy low resistance element is provided is narrow, thus to monitor a small current area and to monitor a large current area, different circuits need to be used, for example, in such a manner that the resistance value of the resistor R
12
is changed; this is a problem. In [DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS] covered later, using
FIG. 3
, comparison with the circuit forming the invention is made for the relationship between the load current and the output voltage in the circuit in FIG.
10
.
Use of the circuit previously described with reference to
FIG. 11
using the operational amplifier IC requiring a large number of circuit elements is not preferred considering implementing of the current detection circuit in IC form, the manufacturing costs, etc.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a current detector having a simple configuration capable of detecting a current with good accuracy.
According to a the invention, there is provided a current detector using a current detection resistor placed between a power supply section and a load to detect a supply current value supplied from the power supply section to the load, the current detector comprising a first resistance element having a first resistance value of a predetermined magnification of a resistance value of the current detection resistor, a first current mirror circuit made up of a plurality of negative-polarity-type transistors and having one end connected to an end part of the current detection resistor on the power supply section side thereof via the first resistance element and an opposite end connected to an end part of the current detection resistor on the load side thereof, a second current mirror circuit made up of a plurality of positive-polarity-type transistors and having both input ends connected to both output ends of the first current mirror circuit, a second resistance element placed between at least either of both output ends of the second current mirror circuit and ground and having a second resistance value, and current detection means for detecting a voltage of the second resistance element on the second current mirror circuit
8
side thereof, characterized by switch means being placed between control terminals of the transistors making up the first current mirror circuit and ground. Preferably, the current detector of the invention further includes current value detection means using the detected voltage to find the supply current value. Here, the negative-polarity-type transistors are transistors (current control elements) such as pnp transistors and p-channel FETs (field-effect transistors) of the type wherein when a current is drawn out from a control terminal, current terminals are brought into conduction, and the positive-polarity-type transistors are transistors (current control elements) such as npn transistors and n-channel FETs of the type wherein when a current is input to a control terminal, current terminals are brought into conduction. The control terminals of the transistors making up the second current mirror circuit are connected to one input end of the second current mirror circuit and the control terminals of the transistors making up the first current mirror circuit are connected to an opposite input end of the second current mirror circuit.
According to the configuration, when the circuit is activated, the control terminals of the transistors making up the first current mirror circuit are grounded through the switch means, whereby a current is forcibly made to flow into the control terminals, so that it is made possible to make the circuit operation at the activation time reliable. A part of load current is shunted with good accuracy via the first resistance element having the first resistance value of the predetermined magnification of the resistance value of the current detection resistor, the first current mirror circuit, and the second current mirror circuit, and the output end of the shunted current is grounded via the second resistance element having the second resistance value, so that an output voltage proportional to the load current can be obtained with good accuracy from the second resistance element in a simple configuration and the load current can be found with good accuracy from the output voltage.
Preferably, in the current detector of the invention, the switch means comprises a transistor circuit capable of grounding the control terminal of the transistor.
According to the configuration, the switch means can be easily implemented as transistor circuit.
Preferably, in the current detector of the invention, the switch means comprises a one-shot pulse generation circuit for activating the transistor circuit.
According to the configuration, a one-shot pulse from the one-shot pulse generation circuit can be used easily to turn off the transistor circuit after turning on the transistor circuit only for a predetermined time.
Preferably, the current detector of the invention further includes control means for controlling so that the voltage detection means detects the voltage after on/off control of the switch means is performed (in the embodiment, control means
11
or microcomputer
11
a
). Preferably, the current detector of the invention further includes control means for controlling so as to output a current detection start signal to the voltage detection means after on/off control
Endoh Takeshi
Takagi Kouichi
Autonetworks Technologies Ltd.
Nu Ton My-Trang
Oliff & Berridg,e PLC
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