JP2006318337A - Constant current drive circuit, light emission device using the same, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a constant current drive circuit capable of feeding uniform drive current to a plurality of load circuits connected in parallel. <P>SOLUTION: In this constant current drive circuit 100 driving a plurality of load circuits, which are connected mutually in parallel, with a constant current, a reference current source 20 generates a reference current Iref. The constant current circuit 10 is connected to the load circuits in series. Current division parts M10-M15 distribute the reference current Iref to a plurality of constant current circuits 10. The constant current circuit 10 generates drive current Idrv based on the reference current Iref to drive the load circuit connected to a current output terminal 102. An offset voltage regulation circuit 14 regulates an offset voltage of a computing amplifier 12 to unify the drive current Idrv generated by the respective constant current circuits 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power supply device.

  In a small information terminal such as a cellular phone or PDA (Personal Digital Assistance) in recent years, a voltage higher than an output voltage of a battery such as a light emitting diode (hereinafter referred to as an LED) used for a backlight of a liquid crystal, for example. There are devices that require In these small information terminals, Li-ion batteries are often used, and the output voltage is usually about 3.5 V, and is about 4.2 V even when fully charged, but the LED has a drive voltage higher than the battery voltage. Requires high voltage. As described above, when a voltage higher than the battery voltage is required, the battery voltage is boosted by using a boost type power supply device using a charge pump circuit or the like to drive a load circuit such as an LED. Getting the required voltage.

  When driving an LED with such a power supply device, a constant current circuit is connected on the drive system path of the LED, and the current flowing through the LED is kept constant, thereby stabilizing the emission luminance control. (See Patent Document 1).

  When a plurality of white LEDs are used as the backlight of the liquid crystal, if the light emission luminance of each LED varies, the brightness of the liquid crystal becomes uneven. Therefore, the plurality of LEDs need to be driven uniformly. Since the light emission luminance of the LED is determined according to the current flowing through the LED, as shown in FIG. 2 of Patent Document 1, a plurality of LEDs are connected in series and driven by a single constant current circuit, thereby emitting light. The brightness can be made uniform.

JP 2004-22929 A

  However, as described above, when a plurality of LEDs are connected in series, there is a problem that the voltage to be supplied from the power supply circuit to the LEDs increases. For example, the forward voltage Vf of the white LED is about 4V, but when it is connected in series in four stages, a driving voltage of 16V or more is required. Such a high voltage needs to be supplied from a charge pump circuit or a switching regulator having a high step-up rate. On the other hand, when a plurality of LEDs are connected in parallel, the voltage to be supplied to the LEDs may be about 4V for one LED, so that the boosting rate of the power supply circuit can be lowered.

  Here, when a plurality of LEDs are connected in parallel, it is necessary to connect a constant current circuit for each LED. Here, in order to make the light emission luminance of each LED uniform, a constant current to be supplied to each LED is required to have a very high accuracy of about 1% to several%. However, it has been difficult from the semiconductor manufacturing process to generate such a highly accurate constant current from a plurality of constant current circuits.

  The present invention has been made in view of these problems, and an object thereof is to provide a constant current driving circuit capable of supplying a uniform driving current to a plurality of load circuits connected in parallel.

  An embodiment of the present invention relates to a constant current driving circuit that drives a plurality of load circuits connected in parallel with a constant current. The constant current driving circuit includes a reference current source that generates a predetermined reference current, a plurality of constant current circuits connected in series to a plurality of load circuits, and a current distribution unit that distributes the reference current to the plurality of constant current circuits. And comprising. Each of the plurality of constant current circuits is provided with a current output terminal to which a load circuit to be driven is connected, a first fixed voltage applied to one end and provided on a path of a reference current distributed by a current distribution unit. A resistor, an operational amplifier having a voltage appearing at the other end of the first resistor applied to the first input terminal, an output voltage of the operational amplifier applied to the control terminal, and a transistor having one end connected to the current output terminal; A second resistor connected to the other end of the transistor and having a fixed voltage applied to the other end; a feedback path for feeding back the potential at the connection point of the transistor and the second resistor to the second input terminal of the operational amplifier; An offset voltage adjusting circuit for adjusting the offset voltage.

  According to this aspect, in each constant current circuit, the reference voltage applied to the first input terminal of the operational amplifier is generated based on the reference current generated by one reference current source. A drive current is generated with a certain degree of error. Therefore, by shifting the offset voltage of each operational amplifier in a direction that cancels this several percent error, the relative error of the drive current generated by each constant current circuit can be reduced, and a plurality of loads can be reduced. The circuit can be driven with a uniform driving current.

The offset voltage adjustment circuit may adjust the differential current of the operational amplifier. The offset voltage adjustment circuit generates a main current source that generates a tail current to be supplied to the differential pair of the operational amplifier, a first variable current, and changes one of the differential currents generated by the differential pair. And a second variable current source that generates the second variable current and changes the other differential current generated by the differential pair.
By adjusting the differential current in the increasing or decreasing direction, the offset voltage can be shifted.

The main current source, the first variable current source, and the second variable current source of the offset voltage adjustment circuit are a constant current source, a current mirror circuit that adjusts the mirror ratio, and that replicates the constant current generated by the constant current source May be output to the operational amplifier as a tail current, a first variable current, and a second variable current, respectively.
In this case, the ratio of the first and second variable currents to the tail current can be changed by adjusting the mirror ratio of the current mirror circuit by trimming wiring and fuses, and the offset voltage of the operational amplifier is suitably adjusted. can do. Further, since the three currents are generated based on one constant current, it is possible to suppress relative variations.

The offset voltage adjustment circuit may include a plurality of adjustment transistors provided in parallel with transistors constituting a differential pair of the operational amplifier, and a trimmable fuse provided on a current path of each of the adjustment transistors. Good. Further, the offset voltage adjustment circuit is provided on a plurality of adjustment transistors provided in parallel with the transistors constituting the current mirror load connected to the differential pair of the operational amplifier, and on the current paths of the adjustment transistors. And a trimmable fuse.
The offset voltage of the operational amplifier can be adjusted by finely adjusting the transistor size of the differential pair or current mirror load using the adjusting transistor.

  Another embodiment of the present invention is a light-emitting device. The light emitting device includes a plurality of light emitting elements connected in parallel, a power supply circuit that supplies a driving voltage to the plurality of light emitting elements, and the above-described constant current driving circuit that drives the plurality of light emitting elements at a constant current.

  According to this aspect, since a uniform drive current can be supplied to a plurality of light emitting elements, variation in light emission luminance can be reduced.

Yet another embodiment of the present invention is an electronic device. This electronic apparatus includes a liquid crystal panel and the above-described light emitting device provided as a backlight of the liquid crystal panel.
According to this aspect, the brightness of the liquid crystal can be made uniform.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  According to the constant current drive circuit of the present invention, a uniform drive current can be supplied to a plurality of load circuits connected in parallel.

(First embodiment)
FIG. 1 is a circuit diagram showing a configuration of a constant current driving circuit 100 according to the first embodiment of the present invention. FIG. 2 is a circuit diagram showing a configuration of an electronic apparatus 300 using the constant current drive circuit 100 of FIG.
2 includes a battery 50, a light emitting device 200, and a liquid crystal panel 210. The electronic device 300 is a small information terminal such as a mobile phone or a PDA. The battery 50 is a lithium ion battery, for example, and generates a battery voltage Vbat of about 3 to 4V. This battery voltage Vbat is used as a power source in each block of the electronic device 300. The liquid crystal panel 210 provides necessary information as image data to the user of the electronic device 300. The light emitting device 200 is used as a backlight of the liquid crystal panel 210 or a flash of a camera.

  The light emitting device 200 includes a booster circuit 52, four LEDs 54 a to 54 d collectively referred to as an LED 54, and a constant current driving circuit 100. The LEDs 54 are arranged on the back surface of the liquid crystal panel 210, and the number thereof may be changed according to the size of the liquid crystal panel 210. The step-up circuit 52 is a step-up charge pump circuit or a switching regulator, and boosts the battery voltage Vbat output from the battery 50 to a voltage sufficient to drive the LED 54 and outputs the boosted voltage to the LED 54. When the LED 54 is a white LED, the forward voltage Vf is about 4V, so the booster circuit 52 outputs the output voltage Vout obtained by boosting the battery voltage Vbat to 4V or more.

Returning to FIG. 1, the configuration of the constant current drive circuit 100 will be described in detail.
The constant current drive circuit 100 includes a current distribution unit including a reference current source 20, constant current circuits 10a to 10d, and transistors M10 to M15. These components are integrated on a single semiconductor substrate. In the drawing, the internal configuration of the constant current circuit 10c is omitted for simplification.
The current output terminals 102a to 102d are terminals to which the cathode terminals of the LEDs 54a to 54d to be driven are to be connected, and the drive currents Idrva to Idrvd are passed to the LEDs 54a to 54d via the current output terminals 102a to 102d.

The reference current source 20 generates a predetermined reference current Iref. The constant current circuits 10a to 10d are connected between the current output terminals 102a to 102d and the ground terminal, respectively, and are provided on the current paths of the four LEDs 54a to 54d.
Transistors M10 to M15, which are current distribution units, constitute a current mirror circuit, and distribute the reference current Iref to the constant current circuits 10a to 10d.

Since the constant current circuits 10a to 10d have the same configuration, the configuration will be described below using the constant current circuit 10a as an example. The constant current circuit 10a includes a first resistor R1a, a second resistor R2a, a transistor M1a, an operational amplifier 12a, and an offset voltage adjustment circuit 14a.
One end of the first resistor R1a is grounded, and a ground potential is applied as a predetermined fixed voltage. The first resistor R1a is provided on the current path of the reference current Iref distributed by the current distribution unit. A voltage drop of Vx = R1a × Iref occurs due to the reference current Iref flowing in the first resistor R1a. The drop voltage Vx appearing at the other end of the first resistor R1a is applied to the non-inverting input terminal of the operational amplifier 12a.

The output voltage of the operational amplifier 12a is applied to the gate which is the control terminal of the transistor M1a, and the drain is connected to the current output terminal 102a. The second resistor R2a has one end connected to the source of the transistor M1a and the other end grounded. The potential at the connection point between the transistor M1a and the second resistor R2a is fed back to the inverting input terminal of the operational amplifier 12a.
When there is no offset voltage at the inverting input terminal and the non-inverting input terminal of the operational amplifier 12a, the drain voltage of the transistor M1a is equal to the voltage Vx appearing at the first resistor R1a. Since the drain voltage of the transistor M1a is applied to the second resistor R2a, a drive current of Idrva = Vx / R2a flows through the second resistor R2a. As described above, since Vx = R1a × Iref is established, the LED 54a connected to the current output terminal 102a can be driven with a constant current by the drive current Idrva = Iref × R1a / R2a.

In the constant current driving circuit 100, the first resistor R1a and the second resistor R2a are configured by pairing, and a relative variation of about several percent is expected. Similarly, the transistors M10 to M14, which are current distribution units, are also arranged in pairs, and the mirror ratio is expected to vary by several percent.
Therefore, the drive currents Idrva to Idrvd generated in the constant current circuits 10a to 10d have a variation obtained by multiplying these relative variations.

It is assumed that an offset voltage of ΔV is generated between the non-inverting input terminal and the inverting input terminal when the input differential pair of the operational amplifier 12a is in a completely balanced state. In this specification, the offset voltage ΔV is positive on the non-inverting input terminal side.
When the offset voltage ΔV is present in the operational amplifier 12a, a voltage of (Vx−ΔV) is applied to the second resistor R2a of the constant current circuit 10a. Therefore, the drive current Idrva is equal to Idrva = (Vx− ΔV) / R2a. Therefore, the drive current Idrva in consideration of the offset voltage of the operational amplifier 12 is given by Idrva = (R1a × Iref−ΔV) / R2a.

  As described above, since the drive current Idrva is a function of the offset voltage ΔV of the operational amplifier 12a, the drive current Idrva can be finely adjusted by adjusting the offset voltage ΔV. As a result, variations in the drive currents Idrva to 10d generated by the plurality of constant current circuits 10a to 10d can be reduced. In the constant current drive circuit 100 according to the present embodiment, the drive current Idrva is provided by providing the offset voltage adjustment circuits 14a to 14d for adjusting the offset voltage ΔV of the operational amplifiers 12a to 12d for each of the constant current circuits 10a to 10d. Reduce the relative variation of ~ Idrvd.

  FIG. 3 is a circuit diagram showing the configuration of the operational amplifier 12a and the offset voltage adjustment circuit 14a. The operational amplifier 12a includes transistors M30 to M36, constant current sources 30, 32, and 34, and an amplification stage 36. The transistors M30 and M31 form an input differential pair, and the gate terminals 40 and 42 correspond to the inverting input terminal and the non-inverting input terminal of the operational amplifier 12a. The drains of the transistors M30 and M31 are connected to a current mirror load including transistors M33 and M34 provided as constant current loads. The transistors M33 and M34 are current mirror circuits in which the gate and source are connected in common with the transistor M32, and a constant current generated by the constant current source 30 flows through each transistor.

  The drains of the transistors M33 and M34 are connected to the sources of the transistors M35 and M36, respectively. The gates of the transistors M35 and M36 are connected in common, and the gate and drain of the transistor M35 are connected. Constant current sources 32 and 34 are connected to the drains of the transistors M35 and M36, respectively. The drain of the transistor M36 is connected to the amplification stage 36. The drain current of the transistor M36 is a differential current obtained by differentially amplifying the gate voltages of the transistors M30 and M31. The amplifying stage 36 amplifies the difference between the current generated by the constant current source 34 and the drain current of the transistor M36, and outputs it from the output terminal 44 of the operational amplifier 12. Note that the configuration of the operational amplifier 12a shown in FIG. 3 is an example, and operational amplifiers of various other circuit formats may be used.

The offset voltage adjustment circuit 14a adjusts the offset voltage ΔV by adjusting the differential current of the operational amplifier 12a. The offset voltage adjustment circuit 14a includes transistors M20 to M25, fuses Rf1 to Rf4, and a constant current source 60.
The transistor M21 functions as a main current source that generates a tail current Iss to be supplied to the input differential pair (transistors M30 and M31) of the operational amplifier 12a. The transistors M22 and M23 and the fuses Rf1 and Rf2 function as a first variable current source that generates the first variable current Iv1 and increases one differential current Id1 generated by the differential pair (M30 and M31). To do.
The transistors M24 and M25 and the fuses Rf3 and Rf4 function as a second variable current source that generates the second variable current Iv2 and increases one of the differential currents Id2 generated by the differential pair (M30 and M31). To do.

  The constant current source 60 generates a constant current Ic1. The transistors M20 to M25 form a current mirror circuit in which the gate and the source are connected in common, and the constant current Ic1 is replicated according to the mirror ratio according to the size ratio of each transistor, and the tail current Iss, the first A variable current Iv1 and a second variable current Iv2 are generated. The current value of the first variable current Iv1 is variable depending on the cut state of the fuses Rf1 and Rf2. The current value of the second variable current Iv2 also changes in accordance with the cut state of the fuses Rf3 and Rf4. For example, when the size ratio of the transistors M21, M22, and M23 is set to 100: 2: 1, the first variable current Iv1 is within a range of 3%, 2%, 1%, and 0% with respect to the tail current Iss. Can be adjusted. The same applies to the transistors M24 and M25.

  The first variable current Iv1 is supplied to one transistor M30 side of the input differential pair of the operational amplifier 12a, and the second variable current Iv2 is supplied to the other transistor M31 side of the differential pair. According to the offset voltage adjustment circuit 14a of FIG. 3, the differential current of the operational amplifier 12a can be adjusted according to the cut state of the fuses Rf1 to Rf4. When the differential current of the operational amplifier is adjusted, the voltage-current characteristic of the input differential pair is shifted, so that the offset voltage ΔV can be adjusted.

  Next, a current balance method of the constant current drive circuit 100 configured as described above will be described. In general, the resistance value and transistor characteristics of a semiconductor integrated circuit vary depending on the semiconductor manufacturing process, and the magnitude of this variation varies depending on the layout of each element, the type of semiconductor manufacturing process, and the like.

  For example, it is assumed that the value of the reference current Iref generated by the reference current source 20 varies within a range of about ± 20% around the design value. Further, it is assumed that the variation in the mirror ratio of the transistors M10 to M14 which are current distribution units is about ± 2%. Furthermore, in each constant current circuit 10, it is assumed that the variation in the resistance ratio R1 / R2 of the first resistor R1 and the second resistor R2 is about ± 2%. In this case, the drive current Idrv generated by each of the constant current circuits 10a to 10d varies relatively in a range of about ± 4%.

After the constant current drive circuit 100 of FIG. 1 is manufactured, the drive currents Idrva to Idrvd output from the current output terminals 102a to 102d are measured in the inspection process. As a result, each current value varies relatively due to the process variations described above.
Therefore, the offset voltages ΔVa to ΔVd of the operational amplifiers 12a to 12d are adjusted by changing the cut states of the fuses Rf1 to Rf4 by trimming by the offset voltage adjusting circuit 14 of each constant current circuit 10. As described above, the first variable current Iv1 and the second variable current Iv2 can be adjusted in a range of 0%, 1%, 2%, and 3% with respect to the tail current Iss of the differential pair, respectively. When the fuses Rf1 and Rf2 are trimmed and when the fuses Rf3 and Rf4 are trimmed, the polarity of the offset voltage ΔV is reversed.

  As described above, the drive currents Idrva to Idrvd generated by the constant current circuits 10a to 10d are given by Idrva = (R1a × Iref−ΔV) / R2a. Therefore, by adjusting the trimming state of the fuses Rf1 to Rf4 in each of the constant current circuits 10a to 10d so that the drive currents Idrva to Idrvd are uniform, the offset voltage ΔV of the operational amplifiers 12a to 12d can be adjusted. Good. In other words, in the offset voltage adjusting circuits 14a to 14d, the size ratio of the transistors M21 to M25 that generate the tail current Iss, the first variable current Iv1, and the second variable current Iv2 is set so that the drive currents Idrva to Idrvd are ± several%. What is necessary is just to design so that it can adjust in the range of a grade.

As described above, according to the constant current drive circuit 100 according to the present embodiment, the variation of the drive currents Idrva to Idrvd can be reduced to about 1% by trimming the fuses Rf1 to Rf4 of the offset voltage adjustment circuit 14. It becomes possible. If the drive current Idrv is adjusted independently for each constant current circuit 10, several tens of steps of trimming are required. According to the constant current drive circuit 100 according to the present embodiment, several fuses are used. By trimming, high relative accuracy can be obtained.
Further, as in the present embodiment, when the LED 54 used as the backlight of the liquid crystal panel 210 is driven, it is only necessary that the light emission luminance is uniform, so that the absolute value of the drive current Idrv needs to have a very high accuracy. Not. Therefore, it is only necessary to design so that the reference current Iref generated by the reference current source 20 can be adjusted with rough accuracy.

FIG. 4 is a circuit diagram showing a modification of the operational amplifier 12a and the offset voltage adjustment circuit 14a of FIG.
In FIG. 3, the first variable current Iv1 is supplied to one transistor M30 side of the differential pair, and the second variable current Iv2 is supplied to the other transistor M31 side of the differential pair. On the other hand, in FIG. 4, the first variable current Iv1 is supplied to one transistor M35 side of the current mirror load (M35, M36) connected to the differential pair (M30, M31), and the second variable current Iv2 is , And supplied to the other transistor M36 side of the current mirror load.
Even when the differential current is adjusted in this way, the offset voltage ΔV of the operational amplifier 12a can be adjusted, and the same effect as in FIG. 3 can be obtained. The same applies when the first variable current Iv1 and the second variable current Iv2 are supplied to other positions where the differential current can be adjusted.

(Second Embodiment)
FIG. 5 is a circuit diagram showing a configuration of the operational amplifier 12a and the offset voltage adjustment circuit 14a according to the second embodiment.
The configuration of the operational amplifier 12a is the same as that shown in FIG. In the present embodiment, the offset voltage adjustment circuit 14a includes adjustment transistors M40 to M43 and fuses Rf1 to Rf4.
The adjusting transistors M40 to M43 are provided in parallel with the transistors M30 and M31 constituting the differential pair of the operational amplifier 12a. Trimmable fuses Rf1 to Rf4 are provided on the current paths of the adjusting transistors M40 to M43.

  According to the present embodiment, the size of the transistors constituting the differential pair of the operational amplifier 12a can be substantially adjusted according to the trimming state of the fuses Rf1 to Rf4, and consequently the differential current can be adjusted. . As a result, the offset voltage ΔV of the operational amplifier 12a is adjusted, and the drive currents Idrva to Idrvd can be made uniform in the constant current drive circuit 100 of FIG.

In FIG. 5, the size of the differential pair of transistors is adjusted. However, as a modification, the sizes of the transistors M33 and M34 constituting the current mirror load may be adjusted. That is, a plurality of adjustment transistors are provided in parallel with the transistors M33 and M34, and a trimmable fuse is provided on the current path of each transistor of the adjustment transistors. By forming the offset voltage adjusting circuit 14 with the adjusting transistor and the fuse and trimming the fuse, the differential current can be adjusted and the offset voltage ΔV can be adjusted.
Similarly, the sizes of the transistors M35 and M36 may be adjusted instead of the transistors M33 and M34.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In this embodiment, the case where all the transistors used in the circuit are MOS transistors has been described, but another type of transistor such as a bipolar transistor may be used. In addition, it is easily understood by those skilled in the art that the N channel and P channel of the MOS transistor and the NPN type and PNP type of the bipolar transistor can be changed. The selection of the type of transistor and the like may be determined by the design specifications required for the circuit, the semiconductor manufacturing process to be used, and the like.

  FIG. 6 is a diagram showing a modification of the constant current circuit 10a. In the constant current circuit 10a of FIG. 6, the drive current Idrva is generated with the power supply voltage Vdd as a fixed voltage. Similar to FIG. 2, the constant current circuit 10a of FIG. 6 includes a current output terminal 102a, a transistor M1a, a first resistor R1a, a second resistor R2a, and an operational amplifier 12a. The LED 54a to be driven is connected to the current output terminal 102a. The first resistor R1a is provided on a path of a reference current Iref to which a predetermined fixed voltage Vdd is applied at one end and is distributed by the current distributor. In the operational amplifier 12a, the voltage Vx1 appearing at the other end of the first resistor R1 is applied to the non-inverting input terminal. In the transistor M1a, the output voltage of the operational amplifier 12a is applied to the gate, and the source is connected to the current output terminal 102a. The second resistor R2a is connected to the source of the transistor M1a, and a fixed voltage Vdd is applied to one end thereof. The potential at the connection point between the transistor M1a and the second resistor R2a is fed back to the inverting input terminal of the operational amplifier 12a. Even when the constant current circuit 10a is configured in this way, it is possible to generate the drive current Idrv given by Idrv = Iref × R1a / R2a.

  In the present embodiment, all of the elements constituting the constant current drive circuit 100 and the light emitting device 200 may be integrated, or a part thereof may be constituted by discrete components. Which part is integrated may be determined by cost, occupied area, or the like.

  In the embodiment, the case where a plurality of LEDs are driven by the constant current driving circuit 100 has been described. However, the load circuit is not limited to this, and other light emitting elements such as an organic EL may be driven. It is also possible to drive a current driving device other than the light emitting element.

1 is a circuit diagram showing a configuration of a constant current drive circuit according to a first embodiment of the present invention. It is a circuit diagram which shows the structure of the electronic device using the constant current drive circuit of FIG. It is a circuit diagram which shows the structure of an operational amplifier and an offset voltage adjustment circuit. FIG. 4 is a circuit diagram showing a modification of the operational amplifier and the offset voltage adjustment circuit of FIG. 3. It is a circuit diagram which shows the structure of the operational amplifier and offset voltage adjustment circuit which concern on 2nd Embodiment. It is a figure which shows the modification of the constant current circuit of FIG.

Explanation of symbols

  M1 transistor, R1 first resistor, R2 second resistor, 10 constant current circuit, 12 operational amplifier, 14 offset voltage adjustment circuit, 20 reference current source, 100 constant current drive circuit, 102 current output terminal, 200 light emitting device, 210 liquid crystal Panel, 300 electronic equipment.

Claims (12)

A constant current driving circuit for driving a plurality of load circuits connected in parallel at a constant current,
A reference current source for generating a predetermined reference current;
A plurality of constant current circuits connected in series to the plurality of load circuits;
A current distribution unit that distributes the reference current to the plurality of constant current circuits, and
Each of the plurality of constant current circuits is
A current output terminal to which the load circuit to be driven is connected;
A first resistor provided on a path of a reference current applied with a predetermined fixed voltage at one end and distributed by the current distributor;
An operational amplifier in which a voltage appearing at the other end of the first resistor is applied to a first input terminal;
A transistor having an output voltage of the operational amplifier applied to a control terminal and one end connected to the current output terminal;
A second resistor connected to the other end of the transistor and having the fixed voltage applied to one end;
A feedback path for feeding back a potential at a connection point between the transistor and the second resistor to a second input terminal of the operational amplifier;
An offset voltage adjusting circuit for adjusting an offset voltage of the operational amplifier;
A constant current drive circuit comprising:   The constant current drive circuit according to claim 1, wherein the offset voltage adjustment circuit adjusts a differential current of the operational amplifier. The offset voltage adjustment circuit includes:
A main current source for generating a tail current to be supplied to the differential pair of operational amplifiers;
A first variable current source that generates a first variable current and changes one of the differential currents generated by the differential pair;
A second variable current source for generating a second variable current and changing the other differential current generated by the differential pair;
The constant current drive circuit according to claim 2, comprising: The first variable current is supplied to one transistor side of the differential pair,
The constant current drive circuit according to claim 3, wherein the second variable current is supplied to the other transistor side of the differential pair. The first variable current is supplied to one transistor side of a current mirror load connected to the differential pair,
The constant current drive circuit according to claim 3, wherein the second variable current is supplied to the other transistor side of a current mirror load connected to the differential pair. The main current source, the first variable current source, and the second variable current source of the offset voltage adjustment circuit are:
A constant current source;
A current mirror circuit capable of adjusting a mirror ratio, which replicates a constant current generated by the constant current source;
4. And a current replicated by the current mirror circuit is output to the operational amplifier as the tail current, the first variable current, and the second variable current, respectively. The constant current drive circuit described in 1. The offset voltage adjustment circuit includes:
A plurality of adjusting transistors provided in parallel with transistors constituting a differential pair of the operational amplifier;
A trimmable fuse provided on a current path of each of the plurality of adjusting transistors;
The constant current drive circuit according to claim 2, comprising: The offset voltage adjustment circuit includes:
A plurality of adjusting transistors provided in parallel with transistors constituting a current mirror load connected to the differential pair of the operational amplifier;
A trimmable fuse provided on a current path of each of the adjusting transistors;
The constant current drive circuit according to claim 2, comprising:   9. The constant current drive circuit according to claim 1, wherein the constant current drive circuit is integrated on a single semiconductor substrate. The plurality of load circuits are light emitting elements,
The constant current drive circuit according to claim 1, wherein the plurality of constant current circuits drive the plurality of light emitting elements at a constant current. A plurality of light emitting elements connected in parallel;
A power supply circuit for supplying a driving voltage to the plurality of light emitting elements;
The constant current drive circuit according to any one of claims 1 to 8, wherein the plurality of light emitting elements are driven with constant current.
A light emitting device comprising: LCD panel,
The light emitting device according to claim 11 provided as a backlight of the liquid crystal panel;
An electronic device comprising:

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