1. Field of the Invention
The present invention relates to an output setting device capable of changing an output current of a constant current circuit to any current value.
2. Description of the Related Art
For example, a load such as an LED lamp or a relay coil mounted on a vehicle is activated by a constant current supplied from a constant current circuit. For an LED lamp, the current value when activated differs according to the type of an LED to use. For a relay coil, the current value when activated differs according to the resistance value of a relay coil to use. Accordingly, the output current of a constant current circuit needs to be appropriately changed according to a load.
Hence, for example, there is proposed an output setting circuit described in Patent Literature 1 (Japanese Patent Application Laid-Open Publication No. H05-259756).
However, the conventional example disclosed in Patent Literature 1 needs to provide circuits such as the EEPROM 101, the decoder 102 and the current generator 103, in order to generate a reference current, and therefore the whole device becomes expensive. Moreover, in order to change the output current value, a data write operation to the EEPROM is required, and therefore there is a problem that it takes a lot of time and efforts to change the current value.
The present invention has been made in order to solve the conventional problem, and aims to provide an output setting device of a constant current circuit, which facilitates setting of a current value and in which the device configuration can be simplified.
According to a first aspect of the present invention, there is provided an output setting device of a constant current circuit that sets a current to be supplied to a load, the output setting device comprising: a reference current generator that feeds a reference current; and a plurality of current mirror circuit groups each having at least one current mirror circuit that feeds a current proportional to the reference current, wherein one current mirror circuit group or two or more current mirror circuit groups connected in parallel to each other among the plurality of current mirror circuit groups are connected to the load to set a current to be supplied to the load.
According to a second aspect of the present invention, the plurality of current mirror circuit groups outputs current values different from each other.
According to a third aspect of the present invention, the number of the current mirror circuit groups is k (“k” is a positive integer), and when the reference current is set to Iref, the i-th current mirror circuit group (“i” is a positive integer equal to or less than k) outputs a current value of 2(i-1)·α·Iref.
According to a fourth aspect of the present invention, the output setting device of a constant current circuit further comprises a power supply terminal, a ground terminal, and a plurality of connection terminals, wherein each current mirror circuit group has a first major electrode and a second major electrode, wherein the reference current circuit has one end connected to the power supply terminal and the other end connected to the ground terminal, and wherein the first major electrode of the each current mirror circuit group is connected to the connection terminal, and the second major electrode of the each current mirror circuit group is connected to the ground terminal.
According to the first aspect of the present invention, a current value is set using the current mirror circuit groups each including at least one current mirror circuit, and therefore a desired current can be set with a simple operation, and the operability can be improved. Moreover, the device scale can be simplified.
According to the second aspect of the present invention, a plurality of current mirror circuit groups outputs current values different from each other, and therefore by appropriately selecting one or more current mirror circuit groups, a desired current value can be easily set.
According to the third aspect of the present invention, the output current values of a plurality of current mirror circuit groups are set to current values which are respectively generated by multiplying the reference current by one, two, four and eight, and therefore by appropriately selecting one or more current mirror circuit groups, a desired current value can be set in a wide range.
According to the fourth aspect of the present invention, a reference current generator and a plurality of current mirror circuit groups can be mounted on an integrated circuit having a power supply terminal, a ground terminal, and a plurality of connection terminals, and the value of a current to be supplied to a load can be set with a simple operation of selecting one or more connection terminals and connecting the same to the load.
Hereinafter, an exemplary embodiment of the present invention will be described in accordance with the accompanying drawings.
The reference current generation circuit 11 includes a current source 31 that feeds a reference current Iref and a transistor Q0. A collector and a base of the transistor Q0 are shorted.
Each of the first to fourth current mirror circuit groups 21 to 24 includes at least one transistor forming a current mirror circuit with the reference current generation circuit 11. Each of the first to fourth current mirror circuit groups 21 to 24 is set so that a current proportional to the reference current Iref flows. Specifically, a current I1 flowing through the first current mirror circuit group 21 is set so as to be a current which has a value generated by multiplying the reference current Iref by α (α is a coefficient) (i.e., I1=α·Iref), and a current I2 flowing through the second current mirror circuit group 22 is set so as to be a current which has a value generated by multiplying the current I1 by two (i.e., I2=2α·Iref).
Moreover, a current I3 flowing through the third current mirror circuit group 23 is set so as to be a current which has a value generated by multiplying the current I1 by four (i.e., I3=4α·Iref), and a current I4 flowing through the fourth current mirror circuit group 24 is set so as to be a current which has a value generated by multiplying the current I1 by eight (i.e., I4=8α·Iref). That is, the k-th current mirror circuit group (k=1 to 4) is set so as to feed a current of 2(k-1)·α·Iref.
Next, an effect of the output setting device of the constant current circuit constituted as described above will be described. Since relationships of “I1=α·Iref”, “I2=2α·Iref”, “I3=4α·Iref” and “I4=8α·Iref” are satisfied for the currents flowing through the current mirror circuit groups 21 to 24, any current can be set with a combination of these currents.
Specifically, when the value of a current to be supplied to a load (an LED lamp, a relay coil, or the like) is set to “α·Iref”, the first current mirror circuit group 21 may be connected to the load. When the current value is set to “2α·Iref”, the second current mirror circuit group 22 may be connected to the load. When the current value is set to “3α·Iref”, a parallel connection circuit of the first current mirror circuit group 21 and the second current mirror circuit group 22 may be connected to the load. In this manner, as illustrated in
A collector (the first major electrode) of the first current mirror circuit group 21 is connected to the connection terminal T1. A collector of the second current mirror circuit group 22 is connected to the connection terminal T2. A collector of the third current mirror circuit group 23 is connected to the connection terminal T3. A collector of the fourth current mirror circuit group is connected to the connection terminal T4. The reference current generation circuit 11 and the first to fourth current mirror circuit groups 21 to 24 constitute one integrated circuit 41.
Accordingly, the power supply terminal T11 is connected to the power supply VB of a battery or the like of a vehicle, the ground terminal T12 is connected to a ground line, and one or more connection terminals among the connection terminals T1 to T4 are connected to a load such as an LED lamp or a relay coil, and thereby a current flowing through the load can be set to a desired current value using either one current mirror circuit group or two or more current mirror circuit groups connected in parallel with each other among the first to fourth current mirror circuit groups 21 to 24. That is, as illustrated in
In this manner, in the output setting device of the constant current circuit according to the present embodiment, a plurality of current mirror circuit groups (the first to fourth current mirror circuit groups 21 to 24, in the present embodiment) each having a different current value are provided, and a current value is set using either one current mirror circuit group or two or more current mirror circuit groups connected in parallel with each other among the first to fourth current mirror circuit groups 21 to 24, and therefore any current value can be set with a simple operation. Moreover, since there is no need to use expensive components such as an EEPROM, unlike the conventional output setting device, the configuration can be simplified and the device scale can be reduced.
Furthermore, the currents flowing through the current mirror circuit groups 21 to 24 are set so as to be currents which have values respectively generated by multiplying the reference current Iref by α, 2α, 4α and 8α (i.e. , the current value of the k-th current mirror circuit group is 2(k-1)·α·Iref), and therefore with a combination of these, the current value can be set in a range from a times to 15α times the reference current Iref, thereby allowing the versatility to be expanded.
Next, a modified example of the output setting device of the constant current circuit according to the present embodiment will be described.
This configuration is an example of the case where the output currents of the first and second current mirror circuit groups 21 and 22 are set to αIref, the output current of the third current mirror circuit group 23 is set to 2αIref, and the output current of the fourth current mirror circuit group 24 is set to 4αIref in the circuit illustrated in
As illustrated in
As illustrated in
In the output setting device of the constant current circuit according to the present modified example, by connecting one or more connection terminals T1 to T4 to a load, it is possible to make setting so as to feed a desired current through the load. Moreover, a desired current can be supplied to each of the loads RL1 and RL2, and the versatility in setting the current value can be improved.
In the foregoing, the output setting device of the constant current circuit of the present invention has been described based on the illustrated embodiment, but the present invention is not limited thereto. The configuration of each unit can be replaced with any configuration having a similar function.
For example, in the embodiment described above, an example has been described in which the current mirror circuit groups 21 to 24 feed the currents which have values respectively generated by multiplying the reference current by α to 8α, by connecting a plurality of transistors in parallel, but the current mirror circuit groups 21 to can be also formed by one transistor which has characteristics of feeding the current which has a value generated by multiplying the reference current by α. That is, the transistors Q1 to Qm illustrated in
In the embodiment described above, an example using a bipolar transistor as the transistor constituting the current mirror circuit has been described, but other transistors such as an MOSFET can be also used. Moreover, in the embodiment described above, an example of providing four current mirror circuit groups 21 to 24 has been described, but the present invention is not limited thereto. It is also possible to provide two, three, or five or more current mirror circuit groups.
In the embodiment described above, an example has been described in which the current mirror circuit groups 21 to 24 output currents different from each other, but it is also possible for all the current mirror circuit groups 21 to 24 to feed an identical current.
In the embodiment described above, an example has been described in which the emitters of the current mirror circuit groups 21 to 24 are connected to the ground and the collectors thereof are connected to a load, but the load may be provided between the emitters and the ground.
The present invention is extremely useful in setting a desired current value with a simple operation and supplying the current to a load.
Number | Date | Country | Kind |
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2011-226466 | Oct 2011 | JP | national |
This is a continuation application based on PCT application No. PCT/JP2012/075944 filed on Oct. 5, 2012, which claims the benefit of priority from Japanese Patent Application No.2011-226466 filed on Oct. 14, 2011, the entire contents of which are incorporated by reference herein.
Number | Date | Country | |
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Parent | PCT/JP2012/075944 | Oct 2012 | US |
Child | 14250430 | US |