JP2009038747A - Driving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving circuit which drives a load while suppressing useless power consumption. <P>SOLUTION: A constant current driver 1 includes a constant current circuit 2 in which a constant current is made to flow to a load 5, and an internal power source 3 which outputs a driving voltage Vo to the load 5. The constant current circuit 2 includes a cascode current mirror circuit constituted of an output section 21 and an input section 22, and a voltage VA at the connecting point A of a transistor 2a and a transistor 2b is compared with a voltage VB at the connecting point B of a transistor 2c and a transistor 2d by a comparator 4. In accordance with a comparison result, the internal power source 3 controls the driving voltage Vo so that the voltage VA and the voltage VB become equal, wherein since the voltage VB is at a level of a saturation drain voltage of the transistor 2d, the transistor 2b is also operated at the level of the saturation drain voltage. Consequently, the driving voltage Vo is not boosted more than needed, and useless power consumption can be suppressed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a constant current driver (drive circuit) that is composed of a constant current circuit and an internal power supply and is characterized by low power loss.

  FIG. 8 shows a configuration of a general constant current driver 101. The constant current driver 101 includes a constant current circuit 102a, an internal power source 103 such as a DC-DC converter, and a voltage detection circuit (comparator) 104, and is built in the IC. A load 105 such as an LED, which is an external connection component, is connected between the internal power supply 103 and the constant current circuit 102. The constant current driver 101 is a method in which the constant current circuit 102 sucks current from the load 105, and based on the result of observing the output terminal voltage of the constant current circuit 102 by the voltage detection circuit 104, the internal current 103 is boosted or stepped down. By doing this, the output terminal voltage of the constant current circuit 102 is kept at a constant voltage. A detailed circuit description of the constant current driver 101 will be described below.

  When the constant current circuit 102 sinks current from the load 105, the output terminal voltage VZ of the constant current circuit 102 becomes a voltage that is lower than the drive voltage Vo of the internal power supply 103 by the voltage drop of the load 105. Here, if the drive voltage Vo of the internal power supply 103 is too low, the output terminal voltage VZ of the constant current circuit 102 is also lower than the optimum value. Conversely, if the drive voltage Vo is too high, the output terminal voltage VZ will also be higher than the target value.

  The voltage detection circuit 104 compares the output terminal voltage VZ with a reference voltage Vref inside the IC. If the output terminal voltage VZ is lower than the reference voltage Vref, the voltage detection circuit 104 increases the drive voltage Vo of the internal power supply 103 from the current level, while If the terminal voltage Vo is higher than the target value, a control signal for lowering the internal power supply than the current value is output to the internal power supply 103. Based on this control signal, the boosting or step-down control of the internal power supply 103 is performed, and the output terminal voltage VZ when a predetermined constant current flows to the load 105 is equal to the reference voltage Vref. The drive voltage Vo is also stabilized.

  Here, for example, the constant current circuit 102 includes a transistor 102d, a transistor 102b, and a constant current circuit 102c, which are NchMOS transistors, and the transistor 102d and the transistor 102b form a current mirror circuit. The transistor 102b is an output transistor of the constant current circuit 102. In this case, the output terminal of the constant current circuit 102 is on the drain side of the transistor 102b.

  FIG. 9 is a graph showing current-voltage characteristics of the Nch MOS transistor. The region where the change in the output current is small and horizontal with respect to the change in the drain voltage is called the saturation characteristic region, and the region where the drain current increases as the drain voltage increases is the non-saturation characteristic region. be called. In order for the constant current circuit 102 to absorb a constant current, the transistor 102b needs to operate in a saturation characteristic region.

  However, the saturation characteristic region fluctuates due to the ON resistance of the transistor, characteristic variation, etc., in addition to the temperature and output current. If the lower limit of the drain voltage in the saturation characteristic region is the saturated drain voltage, for example, when the operating temperature is 100 ° C., the saturated drain voltage becomes higher as shown by the solid line, and when the operating temperature is 25 ° C., the dotted line shows Thus, the saturation drain voltage is lowered. Further, the higher the gate voltage (the larger the output current), the higher the saturation drain voltage.

  Therefore, in order to always maintain the saturation characteristic region when the load 105 is driven, it is necessary to set the drain voltage of the transistor 102b in consideration of the above-described variation. Since the drain voltage of the transistor 102b is equal to the output terminal voltage VZ of the constant current circuit 102, the reference voltage input to the voltage detection circuit 104 so as to give a margin to the drain voltage of the transistor 102b in consideration of the above variation. Vref is set. For example, the reference voltage Vref is set as indicated by the vertical line in the drawing so that the transistor 102b operates in the saturation characteristic region even when the output current is large and the operating temperature is 100 ° C.

  However, even if the output current is low and the temperature is low, that is, when the saturation drain voltage is low, the output terminal voltage VZ is controlled to be approximately the same as the reference voltage Vref. Much higher than. In this case, the internal power supply 103 is unnecessarily boosted, and wasteful power is consumed between the output terminal voltage VZ of the constant current circuit 102 and the saturation drain voltage of the transistor 102b. That is, a region indicated by a triangle in the figure is wasteful power consumption.

  Therefore, a constant current driver that drives a load while suppressing wasteful power consumption has been proposed (for example, Patent Document 1).

  FIG. 10 shows a constant current driver 201 disclosed in Patent Document 1. The constant current driver 201 includes a constant current circuit 202, an internal power supply (DC-DC converter) 203, and an error amplifier circuit (comparator) 204. The constant current driver 201 serves as a load between the internal power supply 203 and the constant current circuit 202. An LED series 205 is connected.

  The constant current circuit 202 includes an N-channel MOS transistor 202a, a transistor 202b, and a constant current circuit 202c. The transistor 202a and the transistor 202b form a current mirror circuit. The output terminal of the constant current circuit 202 is the drain side of the transistor 202b.

  The error amplifier circuit 204 receives the drain voltage Vds1 of the transistor 202a and the drain voltage Vds2 of the transistor 202b. The error amplifier circuit 204 compares the voltage Vds1 and the voltage Vds2, and outputs a control signal corresponding to the comparison result to the internal power supply 203. As a result, the drive voltage Vo of the internal power supply 203 is controlled such that the voltage Vds1 and the voltage Vds2 are equal.

Since the drain voltage Vds1 is held so that the transistor 202a operates in the saturation characteristic region, the drive voltage Vo of the internal power supply 203 can be controlled in accordance with the variation amount of the constant current circuit 202c. Therefore, it is possible to suppress wasteful power consumption to some extent as compared with a configuration in which the drive voltage of the internal power supply is controlled by comparing the output terminal voltage of the constant current source with the reference voltage.
JP 2007-95907 A (released on April 12, 2007)

  However, even with the configuration of Patent Document 1, there is a problem in that a considerable amount of wasteful power consumption occurs.

  Specifically, in the constant current driver 201 illustrated in FIG. 10, the drain voltage Vds1 of the transistor 202a is Vgs of the transistor 202a. The saturated drain voltages of 202a and 202b are approximately Vgs−Vth. In the circuit of FIG. 10, the drain voltage Vds1 of the transistor 202a is not set near the saturated drain voltage of the transistor 202d.

  The present invention has been made in view of the above problems, and an object thereof is to realize a drive circuit that drives a load while suppressing wasteful power consumption.

  In order to solve the above-described problem, a drive circuit according to the present invention includes a constant current circuit that supplies a constant current to a load, and a voltage generation circuit that outputs a drive voltage to a series circuit of the load and the constant current circuit. In the driving circuit, the constant current circuit includes a cascode current mirror circuit having a constant current source as an input current, and the cascode current mirror circuit includes an output unit and an input unit, and the input unit is connected in series. One of the two transistors of the input unit is connected to the constant current source, and the voltage generation circuit includes a first voltage on the drain side of the transistor of the output unit and the input unit. The drive voltage is controlled so that the second voltage at the connection point between the two transistors becomes equal.

  According to the above configuration, the load is driven by the voltage generation circuit generating the drive voltage and the constant current circuit generating the constant current. The constant current circuit includes a cascode current mirror circuit including an output unit and an input unit. One of the two transistors in the output unit is connected to the load, and one of the two transistors in the input unit is connected to the constant current source, so that a constant current flows through the load.

  Here, in the input part of the transistor constituting the cascode current mirror circuit, the drain voltage of the transistor not connected to the constant current source is determined by the source voltage of the transistor connected to the constant current source. This source voltage, that is, the second voltage can be controlled to an arbitrary value by controlling the gate voltage of the transistor connected to the constant current source. Since the drive voltage is controlled so that the first voltage becomes equal to the second voltage, the first voltage of the output unit is also set to an arbitrary value by controlling the second voltage to an appropriate value. It is possible to control.

  As a result, even if the second voltage, that is, the drain voltage of the two transistors of the input unit that is not connected to the constant current source is set to the saturation drain voltage, the first voltage of the output unit is the same. The drive voltage is controlled so as to be about the saturation drain voltage of the transistor not connected to the load. Therefore, the drive voltage is not boosted more than necessary, and it is possible to realize a drive circuit that drives a load while suppressing wasteful power consumption.

  In the driving circuit according to the present invention, the constant current circuit may suck current from the load, and the constant current circuit may flow current into the load.

  In the drive circuit according to the present invention, the output unit is configured by two transistors connected in series, the two transistors of the output unit are a first transistor and a second transistor, and one end of the first transistor is Connected to the load, the other end of the first transistor is connected to one end of the second transistor, the other end of the second transistor is grounded, and the two transistors of the input unit are a third transistor and a fourth transistor. And the input unit further includes a fifth transistor, the constant current source is a first constant current source and a second constant current source, and one end of the third transistor is connected to the first constant current source. One end of the fifth transistor is connected to the second constant current source, and the other end of the third transistor is connected to one end of the fourth transistor. The other end of the fourth transistor and the other end of the fifth transistor are both grounded, the gate of the first transistor, the gate of the third transistor, the gate of the fifth transistor, and one end of the fifth transistor. Are preferably connected to each other, and the gate of the second transistor, one end of the third transistor, and the gate of the fourth transistor are preferably connected to each other.

  According to the above configuration, the voltage (second voltage) at the connection point between the third transistor and the fourth transistor is determined by the aspect ratio of the first to fifth transistors. Therefore, the second voltage can be set to a desired value by appropriately setting the aspect ratio of the first to fifth transistors. Here, the voltage generation circuit controls the drive voltage so that the voltage (first voltage) and the second voltage at the connection point between the first transistor and the second transistor of the output unit are equal to each other. By setting to about the saturation drain voltage, the second transistor can be operated at about the saturation drain voltage. Therefore, useless boosting by the voltage generation circuit can be suppressed.

  In the driving circuit according to the present invention, the transistor of the output unit includes a sixth transistor instead of the first transistor and the second transistor, and one end of the sixth transistor is connected to the load, and the sixth transistor The gate of the sixth transistor, the gate of the third transistor, and the gate of the fourth transistor may be connected to each other.

  In other words, the transistor of the output unit can be composed of only the sixth transistor. One end of the sixth transistor is connected to the load, the other end of the sixth transistor is grounded, the two transistors of the input unit are a third transistor and a fourth transistor, and the input unit is further 5 constant transistors, the constant current source is a first constant current source and a second constant current source, one end of the third transistor is connected to the first constant current source, the one end of the fifth transistor is the Connected to a second constant current source; the other end of the third transistor is connected to one end of the fourth transistor; the other end of the fourth transistor and the other end of the fifth transistor are both grounded; The gate of the transistor, the gate of the fifth transistor, and one end of the fifth transistor are connected to each other, and the gate of the sixth transistor and the third transistor are connected. The end and the gate of the fourth transistor of the Star are connected to each other.

  According to the above configuration, the cascode current mirror circuit is configured by the third, fourth, fifth, and sixth transistors. In the input part of the transistor constituting the cascode current mirror circuit, the drain voltage (second voltage) of the fourth transistor not connected to the constant current source is the third voltage on the side connected to the constant current source. It is determined by the source voltage of the transistor. The drive voltage is controlled so that the drain voltage (first voltage) of the sixth transistor of the output unit is equal to the second voltage. Here, since the second voltage is determined by the aspect ratio of the third to sixth transistors, the second voltage can be set to a desired value by appropriately setting the aspect ratio of the third to sixth transistors. . Similarly to the above description, by setting the second voltage to about the saturated drain voltage, the drive voltage is similarly controlled so that the first voltage of the output unit is also about the saturated drain voltage. Therefore, the drive voltage is not boosted more than necessary, and it is possible to realize a drive circuit that drives a load while suppressing wasteful power consumption.

  In this configuration, the size of the chip can be reduced by using one transistor in the output section. In addition, the driving voltage can be lowered because the transistors are not in series.

  In the drive circuit according to the present invention, the aspect ratios of the first to fourth transistors are equal to each other, the current values of the first constant current source and the second constant current source are equal, and the aspect ratio of the fifth transistor is The aspect ratio of the first to fourth transistors is preferably ¼ to 1/10.

  According to said structure, the cascode current mirror circuit is comprised by the 1st-5th transistor. Here, since the aspect ratio of the fifth transistor is ¼ to 1/10 of the aspect ratio of the first to fourth transistors, the drain voltage of the fourth transistor in the input unit is about the saturation drain voltage. The voltage generation circuit has a voltage (first voltage) at a connection point between the first transistor and the second transistor in the output unit and a voltage (second voltage) at a connection point between the third transistor and the fourth transistor in the input unit. Since the drive voltage is controlled so as to be equal, the drain voltage of the second transistor becomes equal to the drain voltage of the fourth transistor. Therefore, the second transistor also operates at a saturation drain voltage. Therefore, since boosting by the voltage generation circuit can be minimized, wasteful power consumption can be substantially suppressed.

  In addition, since the transistors constituting the cascode current mirror circuit all operate in the saturation characteristic region, the constant current circuit can generate a more stable constant current.

  Ideally, the aspect ratios of the first to fourth transistors are equal to each other, and the aspect ratio of the fifth transistor is ¼ of the aspect ratio of the first to fourth transistors.

  In the driving circuit according to the present invention, the aspect ratios of the third, fourth, and sixth transistors are equal to each other, the current values of the first constant current source and the second constant current source are equal, and the aspect ratio of the fifth transistor. The ratio is preferably 1/4 to 1/10 of the aspect ratio of the third, fourth, and sixth transistors.

  According to said structure, the cascode current mirror circuit is comprised by the 3rd-6th transistor. Here, since the aspect ratio of the fifth transistor is ¼ to 1/10 of the aspect ratio of the third, fourth, and sixth transistors, the drain voltage of the fourth transistor in the input section is about the saturated drain voltage. become. The voltage generating circuit drives the driving voltage so that the drain voltage (first voltage) of the sixth transistor in the output section is equal to the voltage (second voltage) at the connection point between the third transistor and the fourth transistor in the input section. Therefore, the drain voltage of the sixth transistor becomes equal to the drain voltage of the fourth transistor. Therefore, the sixth transistor also operates at about the saturation drain voltage. Therefore, since boosting by the voltage generation circuit can be minimized, wasteful power consumption can be suppressed.

  The aspect ratios of the third to fourth and sixth transistors are equal to each other, and the aspect ratio of the fifth transistor is ideally ¼ of the aspect ratio of the third to fourth and sixth transistors. Is. As a result, the drain voltage of the fourth transistor becomes equal to the saturation drain voltage, so that wasteful power consumption can be suppressed almost completely.

  In the drive circuit according to the present invention, the output unit is configured by two transistors connected in series, the two transistors of the output unit are a seventh transistor and an eighth transistor, and one end of the seventh transistor is The other end of the seventh transistor is connected to one end of the eighth transistor, the other end of the eighth transistor is connected to the voltage generation circuit, and the two transistors of the input unit are connected to the load, And the tenth transistor, the input unit further includes an eleventh transistor, the constant current source is a third constant current source and a fourth constant current source, and one end of the ninth transistor is connected to the first transistor. 3 is connected to a constant current source, one end of the eleventh transistor is connected to the fourth constant current source, and the other end of the ninth transistor is connected to the first transistor. The other end of the tenth transistor and the other end of the eleventh transistor are connected to the voltage generation circuit, and the gate of the seventh transistor, the gate of the ninth transistor, and the eleventh transistor are connected to one end of the transistor. Preferably, the gate of the transistor and one end of the eleventh transistor are connected to each other, and the gate of the eighth transistor, one end of the ninth transistor, and the gate of the tenth transistor are connected to each other.

  According to the above configuration, the voltage (second voltage) at the connection point between the ninth transistor and the tenth transistor is determined by the aspect ratio of the seventh to eleventh transistors. Therefore, the second voltage can be set to a desired value by appropriately setting the aspect ratio of the seventh to eleventh transistors. Here, the voltage generation circuit controls the drive voltage so that the voltage (first voltage) and the second voltage at the connection point between the seventh transistor and the eighth transistor of the output unit are equal to each other. By setting to about the saturation drain voltage, the eighth transistor can be operated at about the saturation drain voltage. Therefore, useless boosting by the voltage generation circuit can be suppressed.

  In the driving circuit according to the present invention, the transistor of the output unit includes a twelfth transistor instead of the seventh transistor and the eighth transistor, and one end of the twelfth transistor is connected to the load, and the twelfth transistor The other end of the transistor may be connected to the voltage generation circuit, and the gate of the twelfth transistor, the one end of the ninth transistor, and the gate of the tenth transistor may be connected to each other. In other words, the transistor of the output unit can be composed of only the twelfth transistor.

  According to the above configuration, the cascode current mirror circuit is configured by the ninth, tenth, eleventh and twelfth transistors. In the input part of the transistor constituting the cascode current mirror circuit, the drain voltage (second voltage) of the tenth transistor not connected to the constant current source is the ninth voltage on the side connected to the constant current source. It is determined by the source voltage of the transistor. The drive voltage is controlled so that the drain voltage (first voltage) of the twelfth transistor of the output unit is equal to the second voltage. Here, since the second voltage is determined by the aspect ratio of the ninth to twelfth transistors, the second voltage can be set to a desired value by appropriately setting the aspect ratio of the ninth to twelfth transistors. . Similarly to the above description, by setting the second voltage to about the saturated drain voltage, the drive voltage is similarly controlled so that the first voltage of the output unit is also about the saturated drain voltage. Therefore, the drive voltage is not boosted more than necessary, and it is possible to realize a drive circuit that drives a load while suppressing wasteful power consumption.

  In this configuration, the size of the chip can be reduced by using one transistor in the output section. In addition, the driving voltage can be lowered because the transistors are not in series.

In the drive circuit according to the present invention, the aspect ratios of the seventh to tenth transistors are equal to each other, and the current values of the third constant current source and the fourth constant current source are equal,
The aspect ratio of the eleventh transistor is preferably ¼ to 1/10 of the aspect ratio of the seventh to tenth transistors.

  According to the above configuration, a cascode current mirror circuit is configured by the seventh to eleventh transistors. Here, since the aspect ratio of the eleventh transistor is ¼ to 1/10 of the aspect ratio of the seventh to tenth transistors, the drain voltage of the tenth transistor in the input unit is about the saturation drain voltage. The voltage generation circuit has a voltage (first voltage) at a connection point between the seventh transistor and the eighth transistor in the output unit and a voltage (second voltage) at the connection point between the ninth transistor and the tenth transistor in the input unit. Since the drive voltage is controlled so as to be equal, the drain voltage of the eighth transistor becomes equal to the drain voltage of the tenth transistor. Therefore, the eighth transistor also operates at about the saturation drain voltage. Therefore, since boosting by the voltage generation circuit can be minimized, wasteful power consumption can be suppressed.

  In addition, since the transistors constituting the cascode current mirror circuit all operate in the saturation characteristic region, the constant current circuit can generate a more stable constant current.

  Ideally, the aspect ratios of the seventh to tenth transistors are equal to each other, and the aspect ratio of the eleventh transistor is 1/4 of the aspect ratio of the seventh to tenth transistors. As a result, the drain voltage of the tenth transistor becomes equal to the saturation drain voltage, so that wasteful power consumption can be suppressed almost completely.

  In the driving circuit according to the present invention, the aspect ratios of the ninth, tenth, and twelfth transistors are equal to each other, the current values of the third constant current source and the fourth constant current source are equal, and the aspect ratio of the eleventh transistor. The ratio is preferably ¼ to 1/10 of the aspect ratio of the ninth, tenth and twelfth transistors.

  According to the above configuration, a cascode current mirror circuit is configured by the ninth to twelfth transistors. Here, since the aspect ratio of the eleventh transistor is ¼ to 1/10 of the aspect ratio of the ninth, tenth and twelfth transistors, the drain voltage of the tenth transistor in the input section is about the saturation drain voltage. become. The voltage generation circuit drives the drive voltage so that the drain voltage (first voltage) of the twelfth transistor of the output unit is equal to the voltage (second voltage) at the connection point of the ninth transistor and the tenth transistor of the input unit. Therefore, the drain voltage of the twelfth transistor becomes equal to the drain voltage of the tenth transistor. Therefore, the twelfth transistor also operates at about the saturation drain voltage. Therefore, since boosting by the voltage generation circuit can be minimized, wasteful power consumption can be substantially suppressed.

  The aspect ratios of the ninth to tenth and twelfth transistors are equal to each other, and the aspect ratio of the eleventh transistor is ideally ¼ of the aspect ratio of the ninth to tenth and twelfth transistors. Is.

  In the drive circuit according to the present invention, a plurality of the output units are provided in parallel, and the voltage generation circuit includes the drive voltage so that the second voltage is equal to a first voltage in one of the output units. Is preferably controlled.

  According to said structure, since the output part is provided with two or more in parallel, the constant current according to the number of the output parts can be sent through load. In addition, since the voltages at the connection points of the two transistors in each output unit are equal, if the drive voltage is controlled so that the second voltage and the first voltage in one of the output units are equal, each output Of the two transistors in the section, the transistor not connected to the load operates at a voltage close to the saturation drain voltage. Therefore, it is possible to realize a drive circuit capable of flowing a constant current according to the number of output units to the load while suppressing wasteful power consumption.

  In the drive circuit according to the present invention, it is preferable that the voltage generation circuit is a DC-DC converter.

  According to the above configuration, the input voltage can be boosted to the drive voltage with high efficiency.

  In the drive circuit according to the present invention, the load may be a resistor.

  According to the above configuration, the power consumption (heat generation) at the resistor is determined by the constant current. Since the voltage generation circuit outputs a minimum driving voltage necessary for flowing a constant current through the resistor, power loss in the constant current circuit can be reduced, and power consumption in the resistor can be kept constant.

  In the drive circuit according to the present invention, the load may be a light emitting diode.

  According to the above configuration, since the forward voltage VF of the light emitting diode when a constant current is passed varies, the optimum driving voltage differs for each light emitting diode. The driving circuit according to the present invention allows a constant current to flow while outputting the minimum necessary driving voltage to the light emitting diode, so that wasteful power consumption can be reduced and constant luminance can be obtained.

  As described above, the drive circuit according to the present invention includes a cascode current mirror circuit having a constant current source as an input current, and the cascode current mirror circuit includes an output unit and an input unit. The input unit includes two transistors connected in series, one of the two transistors of the input unit is connected to the constant current source, and the voltage generation circuit is connected to the drain of the transistor of the output unit. Since the drive voltage is controlled so that the first voltage on the side and the second voltage at the connection point between the two transistors of the input unit are equal, a drive circuit that drives a load while suppressing wasteful power consumption is provided. There is an effect that it can be realized.

(Embodiment 1)
An embodiment of the present invention will be described below with reference to FIGS.

  FIG. 2 is a block diagram showing a schematic configuration of the constant current driver 1 according to the present embodiment. As shown in FIG. 2, the constant current driver 1 includes a constant current circuit 2, an internal power supply 3, and a voltage detection circuit 4, and is connected to a load 5. The voltage detection circuit 4 detects the operating voltage of the constant current circuit 2 and controls the internal power supply 3 based on the detection result, thereby driving the load 5 while suppressing power loss between the load 5 and the constant current circuit 2. .

  FIG. 1 is a circuit diagram showing a configuration of a constant current driver 1 according to the present embodiment. The constant current driver 1 has a constant current circuit 2, an internal power supply 3 and a comparator (voltage detection circuit) 4, and a load 5 is connected between the internal power supply 3 and the constant current circuit 2. The constant current circuit 2 draws a current from the load 5 and causes a constant current to flow through the load 5. The internal power supply 3 boosts the power supply voltage Vcc applied from the outside, and outputs a drive voltage Vo to the constant current circuit 2 and the load 5.

  Here, the constant current circuit 2 includes two constant current sources 23 and 24 and a cascode current mirror circuit. The cascode current mirror circuit includes an output unit 21 and an input unit 22 and generates a constant current using the constant current sources 23 and 24 as input currents. The output unit 21 includes two NchMOS transistors 2a and 2b, and the input unit 22 includes three NchMOS transistors 2c, 2d, and 2e. The sources of the transistors 2b, 2d, and 2e are grounded. The drain of the transistor 2d is connected to the source of the transistor 2c, and the drain of the transistor 2b is connected to the source of the transistor 2a. The drain of the transistor 2a is connected to the load 5, and the drains of the transistors 2c and 2e are connected to the constant current sources 23 and 24, respectively. Both gates of the transistors 2d and 2b are connected to each other and to the drain of the transistor 2c. The gates of the transistors 2a, 2c, and 2e are connected to each other and to the drain of the transistor 2e. Further, the current values of the constant current sources 23 and 24 are set to be equal to each other.

  Furthermore, with respect to the aspect ratio of the transistor (ratio W / L between the gate width W and the gate length L), the aspect ratios of the transistors 2a, 2b, 2c, and 2d are the same, but only the aspect ratio of the transistor 2e is different. ing. That is, the aspect ratio of the transistor 2e is ¼ of the aspect ratio of the transistors 2a to 2d. By setting the aspect ratio of each transistor in this way, the voltage VA at the connection point A between the drain of the transistor 2d and the source of the transistor 2c becomes about the saturation drain voltage of the transistor 2d.

  Therefore, in this embodiment, the voltage VA (first voltage) at the connection point A between the source of the transistor 2a and the drain of the transistor 2b, and the voltage VB at the connection point B between the source of the transistor 2c and the drain of the transistor 2d. (Second voltage) is input to the comparator 4. The comparator 4 compares the voltage VA and the voltage VB, and outputs a control signal corresponding to the comparison result to the internal power supply 3. The internal power supply 3 controls the drive voltage Vo based on the control signal so that the voltage VA and the voltage VB are equal.

  As described above, since the voltage VB is about the saturation drain voltage of the transistor 2d, even if the saturation drain voltage varies due to process variations and temperature, the voltage VB also varies accordingly. Furthermore, since the comparator 4 performs feedback control on the internal power supply 3 so that the voltage VA and the voltage VB are equal to each other, the voltage VA, that is, the drain voltage of the transistor 2b becomes about the saturation drain voltage of the transistor 2d. Since the transistor 2b and the transistor 2d have the same aspect ratio, the transistor characteristics are also the same. Therefore, the voltage VA is also about the saturation drain voltage of the transistor 2b.

  As described above, the internal power supply 3 is controlled so that the voltage VA is approximately equal to the saturation drain voltage of the transistor 2b regardless of process variations and temperature fluctuations. Therefore, it is necessary to boost the drive voltage Vo of the internal power supply 3. Minimized and almost no wasteful power consumption.

  Next, the principle that the voltage VB becomes approximately equal to the saturation drain voltage of the transistor 2d by setting the aspect ratios of the transistors 2a to 2e as described above will be described.

  The transistor characteristics shown in FIG. 9 are generally expressed by the following equations.

I _D ≈ (W / L) × μ × Cox ÷ 2 × (V _GS −V _T ) ² Formula (1)
V _GS = V _T + √ (2 _ID ÷ ((W / L) × μ × Cox)) (2)
Here, each parameter in the above equation is
I _D : Drain current L: Gate length W: Gate width μ: Mobility Cox: Gate oxide unit area capacitance V _GS : Gate-source voltage V _T : Threshold voltage. V _GS −V _T is called an overdrive voltage Vov, and the transistor operates in the saturation characteristic region when the drain voltage V _DS > V _GS −V _T = Vov is satisfied. That is, when operating with a saturated drain voltage, VDsat = Vov with the saturated drain voltage as VDsat.

  Next, a cascade current mirror circuit provided in the constant current circuit 2 shown in FIG. 1 will be described. In order for the constant current circuit 2 to operate as a current mirror circuit, each of the transistors 2a to 2e needs to operate in a saturation characteristic region. Here, paying attention to the voltage VK at the connection point K between the constant current circuit 2 and the load 5, when each of the transistors 2a and 2b operates in the state of VDsat = Vov, the lower limit of the voltage VK is 2VDsat. It becomes. The voltage VB at this time is VDsat.

Further, since V _DS = V _GS −V _T = Vov holds in the transistor operating at the saturation drain voltage, V _GS = V _T + Vov. Therefore, the gate voltage of the transistor 2a is
Vov + V _GS = Vov + V _T + Vov = V _T +2 Vov Equation (3)
The gate voltage of the transistor 2b is
V _GS = V _T + Vov Equation (4)
It becomes. If such a relationship can be created from the constant current sources 23 and 24, the voltage VA can be made as low as possible to operate as a current mirror circuit.

Here, when the transistor aspect ratio of the transistors 2a to 2d is W / L and the aspect ratio of the transistor 2e is W ′ / L ′, the gate voltage V _GS of the transistor 2e can be calculated from the equation (2):
V _GS = V _T + √ (2 _ID ÷ ((W ′ / L ′) × μ × Cox)) (5)
When the gate voltage of the transistor 2a and the gate voltage of the transistor 2e are equal, from the equations (3) and (5),
V _T + 2Vov = V _T + √ (2I _D ÷ ((W ′ / L ′) × μ × Cox))
_{2Vov = 2√ (2I D ÷ (} (W / L) × μ × Cox))
= √ (2I _D ÷ ((W ′ / L ′) × μ × Cox))
(W / L) × μ × Cox = 4 ((W ′ / L ′) × μ × Cox)
(W / L) = 4 (W ′ / L ′) (6)
When Expression (6) is satisfied, the gate voltage of the transistor 2d is V _T + Vov, and the drain voltage of the transistor 2d is Vov. That is, by setting the aspect ratio of the transistor 2e to ¼ of the aspect ratio of the transistors 2a to 2d, the voltage VB becomes about the saturation drain voltage of the transistor 2d.

  Note that the aspect ratio of ¼ is an ideal value, and in an actual device, the aspect ratio of the transistor 2e is 1 of the aspect ratio of the transistors 2a to 2d in consideration of variations in the manufacturing process and the like. You may comprise with a margin so that it may become about / 4-1/10.

  Next, another modification of the constant current driver according to the present embodiment will be described.

  FIG. 3 is a circuit diagram showing a configuration of the constant current driver 11 according to the present embodiment. The constant current driver 11 includes a constant current circuit 12, an internal power supply 3 and a comparator 4, and a load 5 is connected between the internal power supply 3 and the constant current circuit 12. The internal power supply 3 and the comparator 4 are the same as those in the constant current driver 1.

  The constant current circuit 12 has a configuration in which the output unit 21 is replaced with the output unit 121 in the constant current circuit 2 shown in FIG. The output unit 121 includes one NchMOS transistor 12a, the drain of the transistor 12a is connected to the load 5, and the source of the transistor 12a is grounded. The gate of the transistor 12a is connected to the gate of the transistor 2d and the drain of the transistor 2c.

  Here, the voltage VC (first voltage) at the connection point C between the drain of the transistor 12a and the load 5 and the voltage VB (second voltage) at the connection point B between the source of the transistor 2c and the drain of the transistor 2d are compared. 4 The comparator 4 compares the voltage VB with the voltage VC and outputs a control signal corresponding to the comparison result to the internal power supply 3. The internal power supply 3 controls the drive voltage Vo based on the control signal so that the voltage VB and the voltage VC are equal.

  Further, the aspect ratios of the transistors 2c and 2d and the transistor 12a are equal to each other, and the aspect ratio of the transistor 2e is set to ¼ to 1/10 of the aspect ratio of the transistors 2c and 2d and the transistor 12a. As a result, the drain voltage of the transistor 2d, that is, the voltage VB is about the saturation drain voltage. As described above, since the internal power supply 3 controls the drive voltage Vo so that the voltage VB and the voltage VC are equal, the drain voltage of the transistor 12a becomes equal to the drain voltage of the transistor 2d. Therefore, the transistor 12a also operates at about the saturation drain voltage. Accordingly, since boosting by the internal power supply 3 can be minimized, wasteful power consumption can be substantially suppressed.

  Since the drain of the transistor 12a is directly connected to the load 5, the drain voltage of the transistor 12a is likely to fluctuate due to fluctuations in the voltage drop at the load 5, and the current mirrored by the transistor 12a is also likely to fluctuate. In an actual device, in consideration of variations in the manufacturing process and the like, the aspect ratio of the transistor 2e is about 1/4 to 1/10 of the aspect ratio of the transistors 2c and 2d and the transistor 12a. You may comprise with a margin.

  FIG. 4 is a circuit diagram showing a configuration of the constant current driver 31 according to the present embodiment. The constant current driver 31 has a constant current circuit 32, an internal power supply 3 and a comparator 4, and a load 5 is connected between the internal power supply 3 and the constant current circuit 32. The internal power supply 3 and the comparator 4 are the same as those in the constant current drivers 1 and 11.

  The constant current circuit 32 includes two constant current sources 23 and 24 and a cascode current mirror circuit, similarly to the constant current circuit 2 shown in FIG. The cascode current mirror circuit includes two output units 321a and 321b and an input unit 22, and generates a constant current using the constant current sources 23 and 24 as input currents. The output unit 321a and the output unit 321b are connected in parallel. Since the output unit 321a and the input unit 22 are the same as the output unit 21 and the input unit 22 shown in FIG. 1, the same reference numerals are given to the components, and detailed description thereof is omitted. That is, the constant current circuit 32 is the same as the configuration in which the constant current circuit 2 is further provided with the output unit 321b.

  Similar to the output unit 321a, the output unit 321b includes two NchMOS transistors 2h and 2i. The source of the transistor 2i is grounded, and the drain of the transistor 2i and the source of the transistor 2h are connected. The drain of the transistor 2h is connected to the load 5 together with the drain of the transistor 2a. Thus, by providing two output units in parallel, the amount of current flowing through the load can be increased.

  In the constant current driver 31, like the constant current driver 1, the voltage VA at the connection point A between the drain of the transistor 2b and the source of the transistor 2a, and the voltage at the connection point B between the drain of the transistor 2d and the source of the transistor 2c. VB is input to the comparator 4. Thereby, the internal power supply 3 controls the drive voltage Vo so that the voltage VA and the voltage VB become equal.

  Here, since the current densities flowing in the transistors 2b, 2a, 2h, and 2i are equal, the voltage VD at the connection point D between the source of the transistor 2h and the drain of the transistor 2i is equal to the voltage VA. Therefore, since the drain voltages of the transistors 2h and 2i are both about the saturation drain voltage, useless power consumption can be suppressed.

  In addition, although the structure provided with two output parts was demonstrated in FIG. 4, you may provide three or more output parts. Even in this case, the voltage at the connection point between the two transistors in one of the output units may be set as the first voltage, and the first voltage and the second voltage may be compared.

  In the constant current driver 31, the output units 321a and 321b may be replaced with the output unit 121 shown in FIG. Even if it is such a structure, the same effect can be acquired by providing two or more output parts.

  The internal power supply 3 may be a regulator, for example, but is preferably a DC-DC converter. When the internal power supply 3 is a regulator, power loss in the regulator increases when the drive voltage is low. On the other hand, when the internal power supply 3 is a DC-DC converter, the input voltage can be boosted to the drive voltage with high efficiency.

  The load 5 is, for example, a resistor or a light emitting diode. When the load 5 is a resistor, the power consumption (heat generation) at the resistor can be kept constant. In addition, when the load 5 is a light emitting diode, a certain luminance can be obtained.

  Further, even if the drive voltage Vo of the internal power supply 3 is controlled so that the voltage at the connection point between the drain of the transistor 2a and the load is equal to the voltage at the connection point between the drain of the transistor 2c and the constant current source 23. Good. Even in this case, useless power consumption can be reduced.

(Embodiment 2)
Another embodiment of the present invention will be described below with reference to FIGS. In the first embodiment described above, the configuration in which the constant current circuit draws current from the load and causes the constant current to flow to the load has been described. However, in this embodiment, the constant current circuit causes the current to flow to the load, A configuration for supplying a constant current to the load will be described.

  FIG. 5 is a circuit diagram showing a configuration of the constant current driver 41 according to the present embodiment. The constant current driver 41 includes a constant current circuit 42, an internal power supply 3, and a comparator 4. The internal power supply 3, the constant current circuit 42, and the load 5 are connected in series in this order. The internal power supply 3 and the comparator 4 are the same as those in the constant current driver 1 shown in FIG. As described above, the constant current driver 41 has a configuration in which the constant current circuit 42 flows current into the load 5.

  The constant current circuit 42 includes a cascode current mirror circuit including two constant current sources 43 and 44, an output unit 421 and an input unit 422. The cascode current mirror circuit generates a constant current using the constant current sources 43 and 44 as input currents. The output unit 421 includes two Pch MOS transistors 42a and 42b, and the input unit 422 includes three Pch MOS transistors 42c, 42d, and 42e. The sources of the transistors 42b, 42d, and 42e are connected to the internal power supply 3. The drain of the transistor 42d is connected to the source of the transistor 42c, and the drain of the transistor 42b is connected to the source of the transistor 42a. The drain of the transistor 42a is connected to the load 5, and the drains of the transistors 42c and 42e are connected to the constant current sources 43 and 44, respectively. Both gates of the transistors 42b and 42d are connected to each other and to the drain of the transistor 42c. The gates of the transistors 42a, 42c, and 42e are connected to each other and to the drain of the transistor 42e. The current values of the constant current sources 43 and 44 are set to be equal to each other.

  Further, with respect to the aspect ratio (W / L) of the transistors, the aspect ratios of the transistors 42a, 42b, 42c, and 42d are the same, whereas the aspect ratio of the transistor 42e is 1/2 of the aspect ratio of the transistors 2a to 2d. 4. By setting the aspect ratio of each transistor in this way, the voltage VF at the connection point F between the source of the transistor 42c and the drain of the transistor 42d becomes about the saturation drain voltage of the transistor 42d.

Therefore, in this embodiment, the voltage VE (first voltage) at the connection point E between the source of the transistor 42a and the drain of the transistor 42b, and the voltage VF at the connection point F between the source of the transistor 42c and the drain of the transistor 42d. (Second voltage) is input to the comparator 4. The comparator 4 compares the voltage VE and the voltage VF, and outputs a control signal corresponding to the comparison result to the internal power supply 3. The internal power supply 3 controls the drive voltage Vo based on the control signal so that the voltage VE and the voltage VF are equal.
The voltage VE and the voltage VF are compared. The comparator 4 outputs a control signal corresponding to the comparison result to the internal power supply 3, and controls the drive voltage Vo of the internal power supply 3 so that the voltage VE and the voltage VF are equal.

  Specifically, when the voltage VE becomes lower than the voltage VF, the drive voltage Vo is boosted by the internal power supply 3, and when the voltage VE becomes higher than the voltage VF, the drive voltage Vo is lowered by the internal power supply 3.

  As described above, since the voltage VF is about the saturation drain voltage of the transistor 42d, even if the saturation drain voltage varies due to process variations or temperature, the voltage VF also varies in conjunction therewith. Furthermore, since the comparator 4 performs feedback control on the internal power supply 3 so that the voltage VE and the voltage VF are equal to each other, the voltage VE, that is, the drain voltage of the transistor 42b becomes about the saturation drain voltage of the transistor 2d. Since the transistor 42b and the transistor 42d have the same aspect ratio, the transistor characteristics are also the same. Therefore, the voltage VE is also about the saturation drain voltage of the transistor 42b.

  As described above, the internal power supply 3 is controlled so that the voltage VE is approximately equal to the saturation drain voltage of the transistor 42b regardless of process variations and temperature fluctuations. Therefore, it is necessary to boost the drive voltage Vo of the internal power supply 3. Minimized and can minimize wasteful power consumption.

  The principle that the voltage VF becomes approximately equal to the saturation drain voltage of the transistor 42d by setting the aspect ratios of the transistors 42a to 42e as described above is substantially the same as the description in the first embodiment.

  Note that the aspect ratio of 1/4 is an ideal value, and in an actual device, the aspect ratio of the transistor 42e is 1 which is one of the aspect ratios of the transistors 42a to 42d in consideration of variations in the manufacturing process. You may comprise with a margin so that it may become about / 4-1/10.

  Next, another modification of the constant current driver according to the present embodiment will be described.

  FIG. 6 is a circuit diagram showing a configuration of the constant current driver 51 according to the present embodiment. The constant current driver 51 includes a constant current circuit 52, an internal power supply 3, and a comparator 4. The internal power supply 3, the constant current circuit 52, and the load 5 are connected in series in this order. The internal power supply 3 and the comparator 4 are the same as those in the constant current driver 41.

  The constant current circuit 52 has a configuration in which the output unit 421 is replaced with the output unit 521 in the constant current circuit 42 illustrated in FIG. The output unit 521 includes one NchMOS transistor 52 a, the drain of the transistor 52 a is connected to the load 5, and the source of the transistor 52 a is connected to the internal power supply 3. The gate of the transistor 52a is connected to the gate of the transistor 42d and the drain of the transistor 42c.

  Here, the voltage VG (first voltage) at the connection point G between the drain of the transistor 52a and the load 5 and the voltage VF (second voltage) at the connection point F between the source of the transistor 42c and the drain of the transistor 42d are compared. 4 The comparator 4 compares the voltage VF and the voltage VG, and outputs a control signal corresponding to the comparison result to the internal power supply 3. The internal power supply 3 controls the drive voltage Vo based on the control signal so that the voltage VF and the voltage VG are equal.

  Further, the aspect ratios of the transistors 42c and 42d and the transistor 52a are equal to each other, and the aspect ratio of the transistor 42e is set to ¼ of the aspect ratio of the transistors 42c and 42d and the transistor 52a. Thus, the drain voltage of the transistor 42d, that is, the voltage VF is about the saturation drain voltage. As described above, since the internal power supply 3 controls the drive voltage Vo so that the voltage VF and the voltage VG are equal, the drain voltage of the transistor 52a becomes equal to the drain voltage of the transistor 42d. Therefore, the transistor 52a also operates at about the saturation drain voltage. Accordingly, since boosting by the internal power supply 3 can be minimized, wasteful power consumption can be substantially suppressed.

  Note that since the drain of the transistor 52a is directly connected to the load 5, the drain voltage of the transistor 52a is likely to fluctuate due to fluctuations in the voltage drop at the load 5, and the current mirrored by the transistor 52a is also likely to fluctuate. In an actual device, considering the variation in the manufacturing process, the aspect ratio of the transistor 52e is about 1/4 to 1/10 of the aspect ratio of the transistors 42c and 42d and the transistor 52a. You may comprise with a margin.

  FIG. 7 is a circuit diagram showing a configuration of the constant current driver 61 according to the present embodiment. The constant current driver 61 includes a constant current circuit 62, an internal power supply 3, and a comparator 4. The internal power supply 3, the constant current circuit 52, and the load 5 are connected in series in this order. The internal power supply 3 and the comparator 4 are the same as those in the constant current drivers 41 and 51.

  The constant current circuit 62 includes two constant current sources 43 and 44 and a cascode current mirror circuit, similarly to the constant current circuit 42 shown in FIG. The cascode current mirror circuit includes two output units 621a and 621b and an input unit 422, and generates a constant current using the constant current sources 43 and 44 as input currents. The output unit 621a and the output unit 621b are connected in parallel. Since the output unit 621a and the input unit 422 are the same as the output unit 421 and the input unit 422 shown in FIG. 5, the same reference numerals are given to the components, and detailed description thereof is omitted. In other words, the constant current circuit 62 has the same configuration as the constant current circuit 42 further provided with the output unit 621b.

  The output unit 621b includes two PchMOS transistors 42h and 42i, like the output unit 621a. The source of the transistor 42i is connected to the internal power supply 3, and the drain of the transistor 42i is connected to the source of the transistor 42h. The drain of the transistor 42h is connected to the load 5 together with the drain of the transistor 42a. Thus, by providing two output units in parallel, the amount of current flowing through the load can be increased.

  In the constant current driver 61, similarly to the constant current driver 41, the voltage VE at the connection point E between the drain of the transistor 42b and the source of the transistor 42a, and the voltage at the connection point F between the drain of the transistor 42d and the source of the transistor 42c. VF is input to the comparator 4. Thereby, the internal power supply 3 controls the drive voltage Vo so that the voltage VE and the voltage VF are equal.

  Here, since the current densities flowing in the transistors 42a, 42b, 42h, and 42i are equal, the voltage VH at the connection point H between the source of the transistor 42h and the drain of the transistor 42i is equal to the voltage VE. Therefore, since the drain voltages of the transistors 42h and 42i are both about the saturation drain voltage, wasteful power consumption can be suppressed.

  In addition, in FIG. 7, although the structure provided with two output parts was demonstrated, you may provide three or more output parts in parallel. Even in this case, the voltage at the connection point between two transistors connected in series in one of the output units is compared with the voltage VF, and the drive voltage Vo of the internal power supply 3 is feedback-controlled, thereby providing an output. Since the drain voltage of each of the transistors is about the saturation drain voltage, wasteful power consumption can be suppressed.

  In the constant current driver 61, the output units 621a and 621b may be replaced with the output unit 521 shown in FIG. Even if it is such a structure, the same effect can be acquired by providing two or more output parts.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The drive circuit according to the present invention can be suitably applied to a drive circuit that drives a load such as a diode.

1 is a circuit diagram showing a schematic configuration of a constant current driver according to a first embodiment of the present invention. It is a block diagram which shows schematic structure of the said constant current driver. It is a circuit diagram which shows schematic structure of the other constant current driver which concerns on the 1st Embodiment of this invention. FIG. 5 is a circuit diagram showing a schematic configuration of still another constant current driver according to the first embodiment of the present invention. It is a circuit diagram which shows schematic structure of the constant current driver which concerns on the 2nd Embodiment of this invention. It is a circuit diagram which shows schematic structure of the other constant current driver which concerns on the 2nd Embodiment of this invention. It is a circuit diagram which shows schematic structure of the further another constant current driver which concerns on the 2nd Embodiment of this invention. It is a circuit diagram which shows the structure of a general constant current driver. It is a graph which shows the current-voltage characteristic of a NchMOS transistor. It is a circuit diagram which shows the structure of the conventional constant current driver.

Explanation of symbols

1, 11, 31, 41, 51, 61 Constant current driver (drive circuit)
2, 12, 32, 42, 52, 62 Constant current circuit 3 Internal power supply (voltage generation circuit)
5 Loads 21, 121, 321a, 321b, 421, 521, 621a, 621b Output unit 22, 422 Input unit 23 Constant current source (first constant current source)
24 constant current source (second constant current source)
43 Constant current source (third constant current source)
44 Constant current source (4th constant current source)
2a transistor (first transistor)
2b transistor (second transistor)
2c transistor (third transistor)
2d transistor (fourth transistor)
2e Transistor (5th transistor)
12a transistor (sixth transistor)
42a transistor (seventh transistor)
42b Transistor (eighth transistor)
42c Transistor (9th transistor)
42d Transistor (10th transistor)
42e Transistor (11th transistor)
52a Transistor (12th transistor)

Claims (15)

A constant current circuit for supplying a constant current to the load;
In a drive circuit comprising a voltage generation circuit that outputs a drive voltage to a series circuit of the load and the constant current circuit,
The constant current circuit includes a cascode current mirror circuit having a constant current source as an input current,
The cascode current mirror circuit includes an output unit and an input unit,
The input unit has two transistors connected in series,
One of the two transistors of the input unit is connected to the constant current source,
The voltage generation circuit controls the drive voltage so that a first voltage on a drain side of a transistor in the output unit is equal to a second voltage at a connection point between two transistors in the input unit. Drive circuit.   The drive circuit according to claim 1, wherein the constant current circuit sucks current from the load. The output unit includes two transistors connected in series, the two transistors of the output unit are a first transistor and a second transistor, one end of the first transistor is connected to the load, and the first transistor The other end of one transistor is connected to one end of the second transistor, the other end of the second transistor is grounded,
The two transistors of the input unit are a third transistor and a fourth transistor, and the input unit further includes a fifth transistor,
The constant current source is a first constant current source and a second constant current source,
One end of the third transistor is connected to the first constant current source,
One end of the fifth transistor is connected to the second constant current source,
The other end of the third transistor is connected to one end of the fourth transistor;
The other end of the fourth transistor and the other end of the fifth transistor are both grounded,
A gate of the first transistor, a gate of the third transistor, a gate of the fifth transistor, and one end of the fifth transistor are connected to each other;
3. The drive circuit according to claim 2, wherein the gate of the second transistor, one end of the third transistor, and the gate of the fourth transistor are connected to each other. The transistor of the output unit includes a sixth transistor instead of the first transistor and the second transistor, one end of the sixth transistor is connected to the load, and the other end of the sixth transistor is grounded.
4. The drive circuit according to claim 3, wherein the gate of the sixth transistor, one end of the third transistor, and the gate of the fourth transistor are connected to each other. The aspect ratios of the first to fourth transistors are equal to each other, and the current values of the first constant current source and the second constant current source are equal,
4. The driving circuit according to claim 3, wherein an aspect ratio of the fifth transistor is ¼ to 1/10 of an aspect ratio of the first to fourth transistors. The aspect ratios of the third, fourth and sixth transistors are equal to each other, and the current values of the first constant current source and the second constant current source are equal,
5. The driving circuit according to claim 4, wherein an aspect ratio of the fifth transistor is ¼ to 1/10 of an aspect ratio of the third, fourth, and sixth transistors.   The drive circuit according to claim 1, wherein the constant current circuit supplies current to the load. The output unit includes two transistors connected in series. The two transistors of the output unit are a seventh transistor and an eighth transistor, and one end of the seventh transistor is connected to the load. The other end of the seventh transistor is connected to one end of the eighth transistor, and the other end of the eighth transistor is connected to the voltage generation circuit.
The two transistors of the input unit are a ninth transistor and a tenth transistor, and the input unit further includes an eleventh transistor,
The constant current sources are a third constant current source and a fourth constant current source,
One end of the ninth transistor is connected to the third constant current source,
One end of the eleventh transistor is connected to the fourth constant current source,
The other end of the ninth transistor is connected to one end of the tenth transistor;
The other end of the tenth transistor and the other end of the eleventh transistor are both connected to the voltage generation circuit,
A gate of the seventh transistor, a gate of the ninth transistor, a gate of the eleventh transistor, and one end of the eleventh transistor;
8. The drive circuit according to claim 7, wherein the gate of the eighth transistor, one end of the ninth transistor, and the gate of the tenth transistor are connected to each other. The transistor of the output unit includes a twelfth transistor instead of the seventh transistor and the eighth transistor, one end of the twelfth transistor is connected to the load, and the other end of the twelfth transistor is the voltage generation circuit. Connected to
9. The drive circuit according to claim 8, wherein the gate of the twelfth transistor, one end of the ninth transistor, and the gate of the tenth transistor are connected to each other. The aspect ratios of the seventh to tenth transistors are equal to each other, and the current values of the third constant current source and the fourth constant current source are equal,
9. The driving circuit according to claim 8, wherein an aspect ratio of the eleventh transistor is ¼ to 1/10 of an aspect ratio of the seventh to tenth transistors. The aspect ratios of the ninth, tenth and twelfth transistors are equal to each other, and the current values of the third constant current source and the fourth constant current source are equal,
10. The driving circuit according to claim 9, wherein an aspect ratio of the eleventh transistor is ¼ to 1/10 of an aspect ratio of the ninth, tenth, and twelfth transistors. A plurality of the output units are provided in parallel,
12. The voltage generation circuit controls the drive voltage so that the second voltage is equal to a first voltage at one of the output units. The driving circuit described in 1.   The drive circuit according to claim 1, wherein the voltage generation circuit is a DC-DC converter.   The drive circuit according to claim 1, wherein the load is a resistor.   The drive circuit according to claim 1, wherein the load is a light emitting diode.

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