JP2020004018A - Constant current circuit - Google Patents

Abstract

To provide a constant current circuit capable of reducing types of elements requiring withstand pressure corresponding to power supply voltage.SOLUTION: A constant current circuit 100 comprises an output unit 102 having an output transistor Q2 in which a first terminal is electrically connected to a power supply Vd and a second terminal is electrically connected to a current output terminal OUT, and an operational amplifier U2 which controls output current flowing between the first terminal and the second terminal of the output transistor Q2 and output from the current output terminal OUT by electrically connecting an output terminal to a control terminal of the output transistor Q2 to apply negative feedback to an input terminal. Voltage obtained by dividing voltage according to reference voltage Vin2 and voltage obtained by dividing voltage occurred in resistance generated by flow of the output current is input to a non-inverting input terminal and an inverting input terminal of the operational amplifier U2.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a constant current circuit.

  Technologies relating to a constant current circuit using an operational amplifier have been developed. As the above technique, for example, a technique described in Patent Document 1 below is cited.

JP-A-4-299403

  When supplying a higher voltage to the “circuit (or element) connected to the current output terminal of the constant current circuit using an operational amplifier”, the voltage of the power supply connected to the constant current circuit (hereinafter “power supply voltage” Needs to be higher). Therefore, in the above case, among the elements constituting the constant current circuit such as the operational amplifier, the transistor, and the resistor, the element to which the power supply voltage is applied needs to have a withstand voltage corresponding to the power supply voltage.

  However, the cost of the constant current circuit increases and the size of the constant current circuit increases as the types of elements that require a withstand voltage corresponding to the power supply voltage increase.

  It is an object of the present invention to provide a new and improved constant current circuit capable of reducing the types of elements requiring a withstand voltage corresponding to a power supply voltage.

  To achieve the above object, according to one aspect of the present invention, an output transistor having a first terminal electrically connected to a power supply and a second terminal electrically connected to a current output terminal; Is electrically connected to the control terminal of the output transistor, and flows between the first terminal and the second terminal of the output transistor by applying negative feedback to the input terminal, and is output from the current output terminal. An output section having an operational amplifier for controlling an output current of the operational amplifier. A voltage obtained by dividing a voltage corresponding to a reference voltage and the output current flow through a non-inverting input terminal and an inverting input terminal of the operational amplifier. A constant current circuit is provided, to which a voltage generated by dividing a voltage generated at a resistor is input.

  In such a configuration, the voltage input to the input terminal of the operational amplifier is further reduced by the voltage division, so that the operational amplifier does not need to have a withstand voltage corresponding to the power supply voltage. Therefore, with such a configuration, it is possible to reduce the types of elements that require a withstand voltage corresponding to the power supply voltage.

  Further, the ratio of the resistance of the output section is such that the output current output in accordance with the reference voltage is such that the constant current circuit having a configuration in which the divided voltage is not input to the input terminal of the operational amplifier is connected to the reference voltage. May be set to be the same as the output current to be output accordingly.

  Further, a discharge unit having a discharge circuit provided between the second terminal of the output transistor and a reference potential point may be further provided.

  According to the present invention, it is possible to reduce the types of elements that require a withstand voltage corresponding to the power supply voltage.

FIG. 3 is an explanatory diagram illustrating an example of a configuration of a constant current circuit. FIG. 2 is an explanatory diagram illustrating an example of a configuration of a constant current circuit according to the embodiment of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted.

  Further, in the following, “to connect one component and another component” means “the one component and the other component are not interposed through another component, "Electrically connected" or "the one component and the other component are electrically connected through another component."

[1] Example of constant current circuit (comparative example)
Before describing the constant current circuit according to the embodiment of the present invention, an example of the constant current circuit will be described.

[1-1] Example of Configuration of Constant Current Circuit First, an example of the configuration of the constant current circuit will be described. FIG. 1 is an explanatory diagram illustrating an example of the configuration of the constant current circuit 10. The constant current circuit 10 includes an output unit 12 and a discharge unit 14.

  “Vd” shown in FIG. 1 indicates a power supply voltage, and the power supply voltage Vd is supplied from an arbitrary power supply. “Vin1” shown in FIG. 1 indicates one reference voltage, and the reference voltage Vin1 is supplied from an arbitrary power supply. “Vin2” shown in FIG. 1 indicates another reference voltage, and the reference voltage Vin2 is supplied from an arbitrary power supply. The reference voltage Vin1 and the reference voltage Vin2 may be supplied from the same power supply or may be supplied from different power supplies. “OUT” shown in FIG. 1 indicates a current output terminal of the constant current circuit 10.

  FIG. 1 shows an example in which the power supply voltage Vd is higher than each of the reference voltage Vin1 and the reference voltage Vin2. That is, in the constant current circuit 10, an element having a withstand voltage corresponding to the power supply voltage Vd is required to have a higher withstand voltage than an element having a withstand voltage corresponding to the reference voltage Vin1 or Vin2. Therefore, the breakdown voltage corresponding to the power supply voltage Vd is hereinafter referred to as “high breakdown voltage” for convenience of description.

  FIG. 1 shows an example in which the transistors Q1, Q2, and Q3 forming the constant current circuit 10 are N-channel MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). Note that the transistors forming the constant current circuit 10 are not limited to N-channel MOSFETs. For example, the transistors forming the constant current circuit 10 may be P-channel MOSFETs. Further, the transistor constituting the constant current circuit 10 may be, for example, another field-effect transistor such as a junction field-effect transistor (JFET) or a bipolar transistor such as an IGBT (insulated gate bipolar transistor).

[1-1-1] Discharge unit 14
The discharging unit 14 has a discharging circuit provided between the transistor Q2 (output transistor) forming the output unit 12 and the reference potential point. A current output terminal OUT is provided between the transistor Q2 and a discharge circuit forming the discharge unit 14.

  The discharge circuit forming the discharge unit 14 includes a transistor Q1, a resistor R1, and an operational amplifier U1. The first terminal of the transistor Q1 is connected to the transistor Q2 and the current output terminal OUT. The second terminal of the transistor Q1 is connected to the inverting input terminal of the operational amplifier U1 and the resistor R1. The reference voltage Vin1 is input to the non-inverting input terminal of the operational amplifier U1, and the output terminal of the operational amplifier U1 is connected to the control terminal of the transistor Q1. That is, negative feedback is applied to the inverting input terminal of the operational amplifier U1 via the transistor Q1. Therefore, the discharging circuit constituting the discharging unit 14 is a constant current circuit using the operational amplifier U1, and the magnitude (current value) of the current discharged via the transistor Q1 can be controlled by the reference voltage Vin1.

  The configuration of the discharge circuit is not limited to the example shown in FIG. 1 and may be any circuit configuration capable of discharging.

[1-1-2] Output unit 12
The output unit 12 is configured by a constant current circuit using the operational amplifier U2. The constant current circuit forming the output unit 12 includes transistors Q2 and Q3, resistors R2, R3 and R4, and operational amplifiers U2 and U3.

  A first terminal of the transistor Q2 is connected to a power supply that supplies the power supply voltage Vd via the resistor R2, and is connected to an inverting input terminal of the operational amplifier U2. The second terminal of transistor Q2 is connected to current output terminal OUT and transistor Q1. The voltage V2 corresponding to the reference voltage Vin2 is input to the non-inverting input terminal of the operational amplifier U2, and the output terminal of the operational amplifier U2 is connected to the control terminal of the transistor Q2. That is, negative feedback is applied to the inverting input terminal of the operational amplifier U2 via the transistor Q2. Therefore, the magnitude (current value) of the output current output from the current output terminal OUT via the transistor Q2 can be controlled by the reference voltage Vin2.

  The resistor R3 is connected to a power supply that supplies the power supply voltage Vd, and is connected in parallel with the resistor R2. A first terminal of the transistor Q3 is connected to a power supply that supplies the power supply voltage Vd via the resistor R3, and is connected to a non-inverting input terminal of the operational amplifier U2. The second terminal of the transistor Q3 is connected to the inverting input terminal of the operational amplifier U3 and the resistor R4. The resistor R4 is connected to the second terminal of the transistor Q3 and the reference potential point. The reference voltage Vin2 is input to the non-inverting input terminal of the operational amplifier U3, and the output terminal of the operational amplifier U3 is connected to the control terminal of the transistor Q3. That is, negative feedback is applied to the inverting input terminal of the operational amplifier U3 via the transistor Q3. Therefore, the magnitude (current value) of the current flowing between the first terminal and the second terminal of the transistor Q3 can be controlled by the reference voltage Vin2.

  In the constant current circuit forming the output unit 12, the “voltage V2 according to the reference voltage Vin2” and the “current flowing between the first terminal and the second terminal of the transistor Q2 (in the example shown in FIG. 1, the transistor Q2 The magnitude (current value) of the current output from the current output terminal OUT is controlled by directly comparing the voltage V1 ″ generated by the resistor R2 in accordance with the current source terminal OUT) with the operational amplifier U2. That is, in the constant current circuit that forms the output unit 12, the output current output from the current output terminal OUT is kept constant by keeping the reference voltage Vin2 constant.

  The constant current circuit 10 includes the output unit 12 and the discharge unit 14 each having the configuration illustrated in FIG. 1, and outputs a constant output current (that is, a constant current) corresponding to the reference voltage Vin2 from the current output terminal OUT. It is possible to do.

  Here, in the constant current circuit 10 shown in FIG. 1, the power supply voltage Vd is applied to the transistors Q1, Q2, Q3, the resistors R2, R3, and the operational amplifier U2. Therefore, in the constant current circuit 10 shown in FIG. 1, the transistors Q1, Q2, Q3, the resistors R2, R3, and the operational amplifier U2 need to be elements with high withstand voltage (withstand voltage corresponding to the power supply voltage Vd).

[1-2] Current Output from Current Output Terminal of Constant Current Circuit Next, the current output from the current output terminal of the constant current circuit will be described using the constant current circuit 10 shown in FIG. 1 as an example. . Hereinafter, the resistance value of the resistor Rx (x is a number assigned to the resistor) is referred to as “Rx”. Hereinafter, the current flowing through the resistor Rx is indicated as “Irx” (x is a number assigned to the resistor), and the voltage applied to the resistor Rx is indicated as “Vrx” (x is the number assigned to the resistor).

  The reference voltage Vin2 is represented by the following equation 1.

  The voltage V2 shown in FIG.

  The voltage Vr3 applied to the resistor R3 is represented by the following Expression 3.

  The current Ir3 flowing through the resistor R3 is represented by the following Expression 4.

  From Expressions 1 to 4, the voltage V2 is represented by Expression 5 below.

  The voltage V1 shown in FIG.

  The output current Iout output from the current output terminal OUT is represented by the following Expression 7.

  From Expressions 5 to 7, the output current Iout is represented by Expression 8 below.

  Here, “when the resistance value of the resistor R3 and the resistance value of the resistor R4 are the same” or “when the absolute value of the difference between the resistance value of the resistor R3 and the resistance value of the resistor R4 is small enough to be regarded as the same” ", The output current Iout is represented by the following equation (9).

  From Expression 9, it can be seen that in the constant current circuit 10, the magnitude (current value) of the output current Iout output from the current output terminal OUT is controlled by the reference voltage Vin2. That is, in the constant current circuit 10, the output current Iout is kept constant by keeping the reference voltage Vin2 constant.

[2] Constant current circuit according to an embodiment of the present invention Next, a constant current circuit according to an embodiment of the present invention will be described.

[2-1] Outline of Constant Current Circuit According to Embodiment of the Present Invention As described above, the cost of the constant current circuit increases as the number of types of elements that require a withstand voltage corresponding to the power supply voltage increases. The size of the current circuit is also larger. In particular, since the operational amplifier has a larger circuit scale than the transistor and the resistor, the cost is likely to increase if the operational amplifier is required to have a withstand voltage corresponding to the power supply voltage as in the constant current circuit 10 shown in FIG. Also, the size is likely to be large.

  Therefore, the constant current circuit according to the embodiment of the present invention adopts a configuration in which the operational amplifier is not required to have a withstand voltage corresponding to the power supply voltage. The types of elements that require a withstand voltage are reduced. In addition, since the types of elements that require a withstand voltage corresponding to the power supply voltage are reduced, in the constant current circuit according to the embodiment of the present invention, an increase in cost can be suppressed and the size can be reduced.

[2-2] Configuration of Constant Current Circuit According to Embodiment of the Present Invention First, an example of the configuration of the constant current circuit according to the embodiment of the present invention will be described. FIG. 2 is an explanatory diagram illustrating an example of a configuration of the constant current circuit 100 according to the embodiment of the present invention. The constant current circuit 100 includes an output unit 102 and a discharge unit 104.

  "Vd" shown in FIG. 2 indicates a power supply voltage as in FIG. "Vin1" shown in FIG. 2 indicates one reference voltage as in FIG. 1, and "Vin2" shown in FIG. 2 indicates another reference voltage as in FIG. “OUT” shown in FIG. 2 indicates a current output terminal of the constant current circuit 100.

  FIG. 2 exemplifies a case where the power supply voltage Vd is higher than each of the reference voltage Vin1 and the reference voltage Vin2, as in FIG. That is, in the constant current circuit 100, an element having a withstand voltage corresponding to the power supply voltage Vd is required to have a higher withstand voltage than an element having a withstand voltage corresponding to the reference voltage Vin1 or the reference voltage Vin2.

  FIG. 2 shows an example in which the transistors Q1, Q2, Q3, and Q4 forming the constant current circuit 100 are N-channel MOSFETs. Note that the transistors forming the constant current circuit 100 are not limited to N-channel MOSFETs. For example, the transistor constituting the constant current circuit 100 may be another field-effect transistor such as a P-channel MOSFET, a JFET, or a bipolar transistor such as an IGBT.

[2-2-1] Discharge unit 104
The discharging unit 104 has a discharging circuit provided between the transistor Q2 (output transistor) forming the output unit 102 and the reference potential point. A current output terminal OUT is provided between the transistor Q2 and a discharge circuit forming the discharge unit 104.

  The discharge circuit constituting the discharge unit 104 has, for example, the same configuration as the discharge circuit constituting the discharge unit 14 shown in FIG.

[2-2-2] Output unit 102
The output unit 102 is configured by a constant current circuit using the operational amplifier U2. The constant current circuit forming the output unit 102 includes transistors Q2, Q3, Q4, resistors R4, R5, R20, R21, R22, R30, R31, R32, and operational amplifiers U2, U3.

  The first terminal of the transistor Q2 is connected to a power supply that supplies the power supply voltage Vd via the resistor R20, and is connected to the resistor R21. The second terminal of transistor Q2 is connected to current output terminal OUT and transistor Q1. The control terminal of the transistor Q2 is connected to a power supply that supplies the power supply voltage Vd via the resistor R5, and is connected to the transistor Q4.

  The resistor R20 is connected to a power supply that supplies the power supply voltage Vd, and is connected in parallel with the resistors R5 and R30. Further, the resistor R20 is connected to the resistor R21 and the transistor Q2.

  The resistor R21 is connected in series between the resistor R20 and the resistor R22, and is connected in parallel with the transistor Q2. The resistor R22 is connected in series with the resistor R21, and is connected to a reference potential point. Further, the resistors R21 and R22 are connected to the inverting input terminal of the operational amplifier U2.

  The resistor R5 is connected to a power supply that supplies the power supply voltage Vd, and is connected in parallel with the resistors R20 and R30. A first terminal of the transistor Q4 is connected to a power supply that supplies a power supply voltage Vd via a resistor R5. The second terminal of the transistor Q4 is connected to a reference potential point. The control terminal of the transistor Q4 is connected to the output terminal of the operational amplifier U2.

  The resistor R30 is connected to a power supply that supplies the power supply voltage Vd, and is connected in parallel with the resistors R20 and R5. Further, the resistor R30 is connected to the resistor R31 and the transistor Q3.

  The resistor R31 is connected in series between the resistor R30 and the resistor R32, and is connected in parallel with the transistor Q3. The resistor R32 is connected in series with the resistor R31, and is connected to a reference potential point. Further, the resistors R31 and R32 are connected to the non-inverting input terminal of the operational amplifier U2.

  The first terminal of the transistor Q3 is connected to a power supply that supplies the power supply voltage Vd via the resistor R30, and is connected to the resistor R31. The second terminal of the transistor Q3 is connected to the inverting input terminal of the operational amplifier U3 and the resistor R4. The resistor R4 is connected to the second terminal of the transistor Q3 and the reference potential point. The reference voltage Vin2 is input to the non-inverting input terminal of the operational amplifier U3, and the output terminal of the operational amplifier U3 is connected to the control terminal of the transistor Q3. That is, negative feedback is applied to the inverting input terminal of the operational amplifier U3 via the transistor Q3. Therefore, the magnitude (current value) of the current flowing between the first terminal and the second terminal of the transistor Q3 can be controlled by the reference voltage Vin2.

  The inverting input terminal of the operational amplifier U2 is connected to the resistors R21 and R22. Therefore, the voltage divided by the resistors R21 and R22 is input to the inverting input terminal of the operational amplifier U2. The voltage divided by the resistors R21 and R22 corresponds to an example of “a voltage obtained by dividing a voltage generated in a resistor through which an output current flows”.

  The non-inverting input terminal of the operational amplifier U2 is connected to the resistors R31 and R32. Therefore, the voltage divided by the resistors R31 and R32 is input to the non-inverting input terminal of the operational amplifier U2. The voltage divided by the resistors R31 and R32 corresponds to an example of “a voltage obtained by dividing a voltage corresponding to the reference voltage Vin2”.

  The output terminal of the operational amplifier U2 is connected to the control terminal of the transistor Q4. Here, since the control terminal of the transistor Q2 is connected to the transistor Q4, the conduction state of the transistor Q4 is controlled based on the output of the operational amplifier U2, so that the conduction state of the transistor Q2 is also controlled. That is, negative feedback is applied to the inverting input terminal of the operational amplifier U2 via the transistors Q4 and Q2.

  Therefore, the magnitude (current value) of the output current output from the current output terminal OUT via the transistor Q2 can be controlled by the reference voltage Vin2.

  The constant current circuit 100 includes an output unit 102 and a discharge unit 104 each having the configuration shown in FIG. 2 to output a constant output current (that is, a constant current) corresponding to the reference voltage Vin2 from the current output terminal OUT. It is possible to do.

  Here, in the constant current circuit 100 shown in FIG. 2, the power supply voltage Vd is applied to the transistors Q1, Q2, Q3, Q4, the resistors R20, R21, R30, R31, R5. Therefore, in the constant current circuit 100 shown in FIG. 2, the transistors Q1, Q2, Q3, Q4 and the resistors R20, R21, R30, R31, R5 need to be elements with high withstand voltage (withstand voltage corresponding to the power supply voltage Vd). is there.

  On the other hand, the "input voltage of the voltage corresponding to the reference voltage Vin2" and the "voltage generated at the resistor through which the output current flows" are input to the input terminal of the operational amplifier U2 of the constant current circuit 100 shown in FIG. Is input. That is, the voltage input to the input terminal of the operational amplifier U2 shown in FIG. 2 is lower than the voltage input to the input terminal of the operational amplifier U2 shown in FIG. Therefore, in the constant current circuit 100 shown in FIG. 2, unlike the constant current circuit 10 shown in FIG. 1, the operational amplifier U2 does not need to be a high withstand voltage (withstand voltage corresponding to the power supply voltage Vd) element. More specifically, in the constant current circuit 100 shown in FIG. 2, "elements other than the transistors Q1, Q2, Q3, Q4, resistors R20, R21, R30, R31, and R5" (the operational amplifier U2 is naturally included). Any element having a withstand voltage corresponding to the voltage Vin1 or the reference voltage Vin2 may be used.

  Therefore, the constant current circuit 100 shown in FIG. 2 can reduce the types of elements that require a withstand voltage corresponding to the power supply voltage, as compared with the constant current circuit 10 shown in FIG.

  Here, in the constant current circuit 100 shown in FIG. 2, the number of transistors and the number of resistors that need to have a high withstand voltage (withstand voltage corresponding to the power supply voltage Vd) are larger than those of the constant current circuit 10 shown in FIG. . However, as described above, the operational amplifier has a larger circuit scale than the transistor and the resistor. Therefore, in the constant current circuit 100 shown in FIG. 2, an increase in cost is suppressed more than in the constant current circuit 10 shown in FIG. 1, and the size can be reduced.

  Note that the configuration of the constant current circuit according to the embodiment of the present invention is not limited to the example shown in FIG.

  For example, the constant current circuit according to the embodiment of the present invention may be an equivalent circuit of the circuit shown in FIG.

  Further, the constant current circuit according to the embodiment of the present invention may be configured not to include the discharging unit 104. Even if the configuration does not include the discharging unit 104, the constant current circuit according to the embodiment of the present invention can achieve the same effect as the constant current circuit 100 illustrated in FIG.

[2-3] Current output from current output terminal of constant current circuit according to embodiment of the present invention Next, constant current circuit 100 according to the embodiment of the present invention will be described using constant current circuit 100 shown in FIG. 2 as an example. The current output from the current output terminal of the circuit will be described.

  Focusing on the voltage Vr20 applied to the resistor R20, the voltage Vr21 applied to the resistor R21, and the voltage Vr22 applied to the resistor R22, the power supply voltage Vd is expressed by the following equation (10).

  From the above equation (10), the output current Iout is represented by the following equation (11).

  The current Ir22 flowing through the resistor R22 is represented by the following Expression 12.

  The voltage V21 shown in FIG.

  From Expressions 12 and 13, the current Ir22 flowing through the resistor R22 is represented by Expression 14 below.

  From Expressions 11 and 14, the output current Iout is represented by Expression 15 below.

  Focusing on the voltage Vr30 applied to the resistor R30, the voltage Vr31 applied to the resistor R31, and the voltage Vr32 applied to the resistor R32, the power supply voltage Vd is represented by the following equation (16).

  The voltage Vr32 applied to the resistor R32 is represented by the following equation (17).

  From the above equation 17, the current Ir32 flowing through the resistor R32 is represented by the following equation 18.

  The reference voltage Vin2 is represented by the following equation (19).

  From the above equation 19, the current Ir4 flowing through the resistor R4 is represented by the following equation 20.

  From Expressions 16, 18, and 20, the power supply voltage Vd is represented by Expression 21 below.

  From the above equation 21, the voltage V21 is represented by the following equation 22.

  From Expressions 15 and 22, the output current Iout is represented by Expression 23 below.

  When the above equation 23 is arranged, the output current Iout is expressed by the following equation 24.

Here, “when the resistance values shown in the following (a) and (b) are the same in each of the following (a) and (b)”, or “each of the following (a) and (b)” In the case where the absolute value of the difference between the resistance values shown in the following (a) and (b) is small enough to be regarded as the same, the output current Iout is expressed by the following equation (25).
(A) R22 / (R20 + R21 + R22) and R32 / (R30 + R31 + R32)
(B) R30 and R4

  Equation 25 is the same equation as Equation 9 corresponding to the constant current circuit 10. Therefore, according to Equation 25, in the constant current circuit 100, the magnitude (current value) of the output current Iout output from the current output terminal OUT can be controlled by the reference voltage Vin2, as in the constant current circuit 10. I understand. That is, in the constant current circuit 100, as in the case of the constant current circuit 10, the reference current Vin2 is kept constant, so that the output current Iout is kept constant.

  As shown in Expressions 24 and 25, the constant current circuit 100 can output the same output current Iout as the constant current circuit 10 if the conditions described with reference to the above (a) and (b) are satisfied. Is output. That is, the ratio of the resistance configuring the output unit 102 included in the constant current circuit 100 is such that the output current Iout that is output according to the reference voltage Vin2 is equal to the “constant current circuit 10 (the voltage divided into the input terminal of the operational amplifier U2). Is set so that the output current Iout "outputted in accordance with the reference voltage Vin2 is the same as that of the constant current circuit having a configuration in which the reference current Vin is not input. The output current according to the embodiment of the present invention is the same when the difference between the current values is 0 or when the difference between the current values is E (E is, for example, an allowable Is a rational number corresponding to the error ").

[3] An example of the effect obtained by using the constant current circuit according to the embodiment of the present invention By using the constant current circuit according to the embodiment of the present invention, for example, the following effects are obtained. Needless to say, the effects achieved by using the constant current circuit according to the embodiment of the present invention are not limited to the effects described below.
As described above, in the constant current circuit according to the embodiment of the present invention, the types of elements that require a withstand voltage corresponding to the power supply voltage are reduced. Therefore, the semiconductor integrated device including the constant current circuit according to the embodiment of the present invention can be manufactured using the process for a small-sized semiconductor integrated device at a lower cost.

[4] Application Example of Constant Current Circuit According to Embodiment of the Present Invention For example, a constant current circuit according to an embodiment of the present invention outputs a constant current based on a power supply voltage, such as a driving circuit for a piezoelectric element. The present invention can be applied to any driving circuit that can drive an element (or circuit) to which a constant current is supplied.

  Further, the constant current circuit according to the embodiment of the present invention may be applied to any semiconductor integrated device. Examples of a semiconductor integrated device to which the constant current circuit according to the embodiment of the present invention is applied include “an arbitrary moving object such as an automobile, an airplane, a ship, and a train”, and “a computer such as a PC (Personal Computer) or a server”. Various devices (or systems) that may require a constant current, such as "", "tablet-type device", and "communication device such as smartphone". The semiconductor integrated device to which the constant current circuit according to the embodiment of the present invention is applied may be an IC (Integrated Circuit) chip that can be mounted on the above-described device (or system).

  As described above, the preferred embodiments of the present invention have been described with reference to the accompanying drawings, but it is needless to say that the present invention is not limited to such examples. It is obvious that those skilled in the art can conceive various changes or modifications within the scope of the claims, and these naturally belong to the technical scope of the present invention. I understand.

10, 100 constant current circuit, 12, 102 output part, 14, 104 discharge part, Q1, Q2, Q3, Q4 transistor, R1, R2, R3, R4, R5, R20, R21, R22, R30, R31, R32 resistance , U1, U2, U3 operational amplifier, Vd power supply voltage, Vin1, Vin2 reference voltage

Claims (3)

An output transistor having a first terminal electrically connected to the power supply and a second terminal electrically connected to the current output terminal;
An output terminal is electrically connected to a control terminal of the output transistor, and by applying a negative feedback to an input terminal, flows between the first terminal and the second terminal of the output transistor. An operational amplifier that controls the output current that is output,
Comprising an output unit having
A voltage obtained by dividing a voltage corresponding to a reference voltage and a voltage obtained by dividing a voltage generated in a resistor through which the output current flows are input to the non-inverting input terminal and the inverting input terminal of the operational amplifier. Constant current circuit.   The ratio of the resistance of the output unit is such that the output current output according to the reference voltage is output according to the reference voltage by a constant current circuit having a configuration in which a divided voltage is not input to an input terminal of an operational amplifier. The constant current circuit according to claim 1, wherein the constant current circuit is set so as to be the same as the output current. The constant current circuit according to claim 1, further comprising a discharge unit having a discharge circuit provided between the second terminal of the output transistor and a reference potential point.

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