JP2003187988A - Driving device of white light-emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the current consumption in the driver IC11 of a white light-emitting diode which is driven for lighting by impressing the input DC voltage Vin on the white light-emitting diode D by boosting by the charge pump circuit 10. <P>SOLUTION: The amount of light of the white light-emitting diode D is detected by a photodiode PD and amplified by an error amplifier OP and its feedback resistor R, and given to a logic control circuit CTL, and thereby the resistance of the variable resistor Rset is changed. On the other hand, the impressing voltage of the above variable resistor Rset is made constant by a constant voltage amplifier A and its reference voltage source B and constant voltage transistor Q1, thereby, a current Ida corresponding to the light amount is obtained, and the current Id which is returned by the current mirror circuit of the transistors Q2, Q3 is given to the white light-emitting diode D. Thereby, the unevenness of the white light-emitting diode D due to the difference of impressed voltage is suppressed, and the necessary amount of light can be obtained with the minimum current consumption. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for driving a white light emitting diode which is preferably used as a backlight of a color liquid crystal display, and more particularly to boosting a DC low power supply voltage of a portable device or the like with a boosting circuit. To the white light emitting diode.

[0002]

2. Description of the Related Art In recent years, the color liquid crystal display has come to be used in portable devices, and the white light emitting diode is used as a backlight thereof. This white light emitting diode has a forward voltage (VF) of 3 to 4 V, while the power source is, for example, a lithium ion battery.
The cell is used, from 4.2V fully charged, to 3 for mobile phones
Since it is used up to about 3.2 V, the booster circuit is built in the driver IC of the white light emitting diode.

FIG. 11 is a block diagram showing an electrical configuration of a typical prior art driver IC 1 having such a booster circuit. The driver IC1 includes a capacitor c1 for boosting operation, a capacitor c2 for smoothing the input DC power supply voltage Vin, and a capacitor c for smoothing the output voltage Vo.
3 and the feedback resistors r1 and r2 are externally attached to form a driving device for the white light emitting diode d. A plurality of white light emitting diodes d may be provided in parallel.

The driver IC1 boosts the input DC power supply voltage Vin by a charge pump operation using the capacitor c1 and outputs the output voltage Vo. Inside the driver IC1, switches s1 to s4 are provided. The control circuit 2 includes a control circuit 2 for controlling the switching of the switching circuits, and an oscillating circuit 3 for oscillating a signal for defining the switching frequency of the control circuit 2. The high-side terminal of the capacitor c1 is selectively connected to the power source of the voltage Vin via the switch s1 and to the output via the switch s2, and the low-side terminal of the capacitor c1 is connected. Is connected to GND via switch s3,
It is also selectively connected to the power source of the voltage Vin through the switch s4.

FIG. 12 is a current path diagram for explaining the charge pump operation, and FIG. 13 is a waveform diagram for explaining the switching states of the switches s1 to s4 under the control of the control circuit 2. As described above, the control circuit 2 causes the switches s1 and s3 and the switches s2 and s4 to operate in a reciprocal manner.
When 2 and s4 are in the off state, the current from the power source charges the capacitor c1 as shown by the reference numeral Ic, and the capacitor c1 is charged to the voltage Vin with reference to GND. Next, the switches s2 and s4 are turned on, and the switches s1 and
When s3 is in the off state, the low-side terminal of the capacitor c1 is raised by the voltage Vin, as indicated by reference numeral Io, Vo = 2Vin− (α + β), where α is a MOS transistor that realizes the switches s1 to s4. It is a loss at the time of charging, β is a loss at the time of discharging, and becomes Rsw × Io when the on-resistance of the MOS transistor is Rsw. In this way, the input direct-current power supply voltage Vin can be boosted to a maximum substantially doubled voltage by the charge pump operation.

On the other hand, the oscillator circuit 3 is composed of a constant voltage circuit 4 and an error amplifier 5, and the error amplifier 5 outputs the output voltage Vo to the feedback resistors r1 and r.
The feedback voltage FB divided by 2 is compared with the reference voltage Vref from the constant voltage circuit 4, and an oscillation signal having a frequency corresponding to the comparison result is given to the control circuit 2.
In this way, the switching frequencies of the switches s1 to s4 are changed according to the load, and the output voltage Vo is controlled to be constant. Also, the feedback resistance r
By changing the voltage division ratio of 1 and r2, the output voltage Vo
Is an arbitrary value between Vin and 2 Vin-α, Vo = Vref * (r1 + r2) / r1) For example, even when the input DC power supply voltage Vin from the lithium ion battery varies from 3 to 4.2V. , It can be set to 5V which can drive the light emitting diode d.

The output voltage Vo is applied to a series circuit of a white light emitting diode d and a resistor rset, and the white light emitting diode d is driven by a constant current Id. The current I
d is Id = (Vo-VF) / rset However, VF is set by the ON voltage of the white light emitting diode d, and the same applies when two or more light emitting diodes are mounted.

[0008]

In the driving device for the white light emitting diode d configured as described above, the current Id flowing through the white light emitting diode d, and hence the current Id, flowing through the white light emitting diode d due to the variation of the ON voltage VF of the white light emitting diode d. There is a problem that the brightness of the light emitting diode d varies. For example, when VF = 3.0V, Id = (Vo
-3.0) / rset, when VF = 3.5V, Id = V
o-3.5) When rset and VF = 4.0V, Id =
(Vo-4.0) / rset, and Vo = 5.0V,
When rset = 75Ω, I at VF = 3.0V
When d = 26.6 mA and VF = 3.5 V, Id = 20 m
When A and VF = 4.0V, Id = 13.3 mA.

Therefore, compared to when VF = 4.0V,
When VF = 3.0V, the brightness is about half. Therefore, when one light emitting diode d is used, the brightness of the backlight varies between products of the mobile device, and when a plurality of light emitting diodes d are used in one mobile device, the color unevenness of the backlight is caused. There is a problem that will occur.

For this reason, in many cases, the device manufacturer selects and delivers the VF value to the light emitting diode manufacturer, which results in an increase in cost and cannot completely suppress the variation. Further, in consideration of the variation, if the required brightness can be ensured even at the current level with the smallest current Id, the consumed current will flow by 30% or more at the highest current level. In particular, when a plurality of white light emitting diodes are used, the extra current is further increased, which greatly affects the battery life.

An object of the present invention is to provide a driving device for a white light emitting diode capable of reducing current consumption.

[0012]

A driving device for a white light emitting diode according to the present invention is a device for driving a white light emitting diode, wherein an input DC power supply voltage is boosted by a booster circuit and applied to the white light emitting diode to drive lighting. A difference in the on-voltage of the white light emitting diode by controlling the current applied to the white light emitting diode from the booster circuit in response to the output of the white light emitting diode and the detection means for detecting the light emission amount of the white light emitting diode. And a current control unit that suppresses the variation in light amount due to.

According to the above structure, in the driving device for the white light emitting diode, which is provided with the booster circuit to enable the lighting drive with the relatively low input DC power supply voltage for the relatively high on-voltage of the white light emitting diode, A detection unit for detecting the amount of light emitted from a white light emitting diode such as a photodiode is provided, and the current control unit controls the current from the booster circuit realized by a charge pump or the like, thereby changing the on-voltage of the white light emitting diode. It is possible to suppress the variation in the light amount due to the difference and to obtain the required amount of emitted light with the minimum current consumption.

In the driving device for a white light emitting diode according to the present invention, the current control means includes a variable impedance element interposed between the output terminal of the booster circuit and the white light emitting diode, and the detecting means. In response to the output, the control circuit changes the impedance of the variable impedance element and controls the current applied to the white light emitting diode.

According to the above structure, the control circuit changes the impedance of the variable impedance element in response to the detection result of the current flowing from the booster circuit to the white light emitting diode by the detecting means, thereby controlling the current to a prescribed light amount. Limit the level at which you can get.

Therefore, it is possible to suppress the variation in the light quantity due to the difference in the on-voltage of the white light emitting diode and to obtain the necessary light quantity with the minimum current consumption.

Further, in the driving device for a white light emitting diode according to the present invention, the current control means is interposed between the output terminal of the booster circuit and the white light emitting diode.
a channel depletion type transistor, and a control circuit for changing the gate width of the Nch depletion type transistor in response to the output from the detection means and controlling the current given to the white light emitting diode. Characterize.

According to the above configuration, the control circuit changes the gate width of the Nch depletion type transistor in response to the detection result of the current flowing from the booster circuit to the white light emitting diode by the detecting means to define the current. Limit the amount of light that can be obtained.

Therefore, it is possible to suppress the variation in the amount of light due to the difference in the on-voltage of the white light emitting diode and to obtain the required amount of light with the minimum current consumption.

Further, in the driving device for a white light emitting diode according to the present invention, a plurality of the white light emitting diodes are provided, and the detecting means is a photodiode arranged in proximity to each white light emitting diode individually, The control means is also provided individually corresponding to each of the white light emitting diodes.

According to the above configuration, when a plurality of white light emitting diodes are provided, a photodiode corresponding to each white light emitting diode is provided and the current of each white light emitting diode is controlled according to the feedback value of the photodiode. By providing each, it is possible to eliminate unevenness in the amount of light.

Furthermore, the driving device of the white light emitting diode of the present invention is formed on an integrated circuit chip, and the photodiode constituting the detecting means is formed by utilizing a PN junction in the chip. And

According to the above structure, the cost can be reduced.

In the white light emitting diode driving device of the present invention, a plurality of the white light emitting diodes are provided, and the photodiodes and the current control means are provided individually corresponding to the respective white light emitting diodes. The diode is divided into two, and one of them is used over the entire area to obtain the amount of light of the individual element of each white light emitting diode,
The other is further divided into the number of the photodiodes along the arrangement direction of the photodiodes, the average light amount of all the white light emitting diodes is obtained from the parallel output of the dividing elements of the same arrangement order, and the current control means is 6. The drive device for a white light emitting diode according to claim 5, wherein the current supplied from the booster circuit to the white light emitting diode is controlled based on a result of comparison between the average light amount and the light amount of the individual element.

According to the above configuration, when a plurality of white light emitting diodes and photodiodes corresponding to the white light emitting diodes are provided and the plurality of photodiodes are provided in the integrated circuit chip as described above, the white light emitting diode is provided. It is difficult to arrange the photodiodes that should be individually addressed in close proximity to each other.Therefore, the shape of each photodiode is formed as described above, and the current control means determines the detection result of each photodiode as described above. to correct.

Thus, the light quantity of the corresponding white light emitting diode can be feedback-controlled relatively accurately, and the light quantity variation due to the ON voltage variation can be suppressed.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a block diagram showing an electrical configuration of a driver IC 11 having a booster circuit according to the first embodiment of the present invention. The driver IC 11 includes a capacitor C1 for boosting operation, a capacitor C2 for smoothing the input DC power supply voltage Vin, and a capacitor C for smoothing the output voltage Vo.
3 and a photodiode PD for feedback are externally attached to form a driving device for the white light emitting diode D.

The driver IC 11 generally includes a charge pump circuit 10, an error amplifier OP and its feedback resistor R, a logic control circuit CTL, a variable resistor Rset, a constant voltage amplifier A and its reference voltage source B.
And a constant voltage transistor Q1 and transistors Q2 and Q3 forming a current mirror circuit.

The charge pump circuit 10 uses the capacitor C1 to generate the output voltage Vo by boosting the input DC power supply voltage Vin by the charge pump operation as shown in FIGS. 12 and 13. , The output voltage Vo is Vin to 2 Vin− (α + β)
In between, it is possible to set any value, for example, to the aforementioned 5V.

The constant voltage amplifier A and the reference voltage source B
Is to maintain the source (variable resistor Rset) side of the constant voltage transistor Q1 of the source follower at a constant voltage defined by the reference voltage from the reference voltage source B, for example, 1.2V. The error amplifier OP and the feedback resistor R are arranged adjacent to the white light emitting diode D and amplify the current flowing between the terminals of the photodiode PD driven by a bias voltage from a bias source (not shown).
The voltage is converted and given to the logic control circuit CTL. The logic control circuit CTL changes the resistance value of the variable resistor Rset connected in series to the constant current transistor Q1 in response to the output from the error amplifier OP.

FIG. 2 is a block diagram showing an example of the variable resistor Rset and the logic control circuit CTL. The variable resistor Rset is a resistor Rs connected in cascade.
, Rs2, ... And switching elements TR1, TR2, ... Short-circuiting the terminals thereof, and the resistance values of the resistors Rs1, Rs2, ... Are sequentially set to 2 using the resistance value of the resistor Rs1 as a reference value R0. Double 2R0, 4R0,
Is formed into ... The logic control circuit CTL
Drive the gates of the switching elements TR1, TR2, ... And are short-circuited. In response to the output from the error amplifier OP, the switching elements TR1, TR2 ,.
The gates of the resistors Rs1, Rs2,
Use one of ...

Therefore, the constant voltage transistor Q1
Since the voltage VR applied to the variable resistor Rset from the variable resistance changes while the resistance value changes, the current Ida flowing through the constant voltage transistor Q1 and the variable resistor Rset changes according to the amount of light received by the photodiode PD, The current Ida is turned back in the current mirror circuit including the transistors Q2 and Q3, and is supplied to the white light emitting diode D as the current Ida. Here, when the gate-source voltage due to the short-circuited switching elements TR1, TR2, ... Is Vgs and the resistance value of the selected resistor is Rset, Ida = (VR-Vgs) / Rset.

In this way, the amount of light emitted from the white light emitting diode D is monitored by the photodiode PD and fed back to the current Id flowing through the white light emitting diode D, which depends on the difference in the ON voltage VF of the white light emitting diode D. It is possible to suppress variations in light amount and obtain a required amount of emitted light with a minimum current consumption.

That is, the current Id becomes Id = Ida × γ = (Vo-VF) / Rset, and the variable resistance Rse is changed according to the difference in the on-voltage VF.
The resistance value of t is changed. However, γ is the mirror ratio of the current mirror. As a result, it is not necessary to select the white light emitting diode D in particular, the cost can be reduced, the difference in the brightness of the backlight between the products of the mobile device can be eliminated, and the battery life can be extended. Although power consumption occurs due to the constant voltage transistor Q1, the transistors Q2 and Q3, and the variable resistor Rset, these power consumptions are smaller than the power consumption of the white light emitting diode D, and the power consumption can be reduced as a whole.

FIG. 3 shows the second embodiment of the present invention.
The explanation is based on the following.

FIG. 3 is a block diagram showing an electrical configuration of a driver IC 21 with a built-in booster circuit according to the second embodiment of the present invention. This driver IC 21 is similar to the driver IC 11 described above, and corresponding parts are designated by the same reference numerals and the description thereof is omitted. It should be noted that the driver IC 21 is provided with a plurality of n white light emitting diodes D1, D2, ..., Dn, and the white light emitting diodes D1 to Dn are adjacent to each other and individually photographed. Diodes PD1, PD2, ..., PDn are provided.

In the driver IC 21, the charge pump circuit 10 described above is shared by the white light emitting diodes D1 to Dn, but the constant voltage amplifiers A1 to An and the reference voltage source are corresponding to the white light emitting diodes D1 to Dn. B
1 to Bn, constant voltage transistors Q11 to Q1n, transistors Q21 to Q2n; Q31 to Q3n, error amplifiers OP1 to OPn and feedback resistors R1 to Rn, logic control circuits CTL1 to CTLn, and variable resistors R.
set1 to Rsetn are provided.

When a plurality of white light emitting diodes D1 to Dn are provided in one portable device as described above, the corresponding photodiodes PD1 to PDn are provided and the logic control circuits CTL1 to CTLn and the variable resistors Rset1 to Rsetn, etc. are provided. It is possible to eliminate the illuminance unevenness of the backlight by respectively providing the configurations for controlling the currents Id1 to Idn of the white light emitting diodes D1 to Dn according to the feedback values of the photodiodes PD1 to PDn.

FIG. 4 shows the third embodiment of the present invention.
The following is a description with reference to FIG.

FIG. 4 is a block diagram showing an electrical configuration of a driver IC 31 having a built-in booster circuit according to the third embodiment of the present invention. This driver IC 31 is similar to the driver IC 11 described above, and corresponding parts are designated by the same reference numerals and the description thereof is omitted. It should be noted that in the driver IC 31, the current Id flowing through the white light emitting diode D is controlled by the Nch depletion type transistor Q4. Therefore, the variable resistance Rse
t, the constant voltage transistor Q1, and the transistors Q2 and Q3 for the current mirror are not provided. Instead, the voltage dividing resistors R01 and R02 for dividing the output voltage Vo and giving it to the constant voltage amplifier A, and the charge pump An oscillation circuit 32 that provides an oscillation signal to the circuit 10 is provided.

The constant voltage amplifier A includes a voltage dividing resistor R01,
The divided voltage value of the output voltage Vo from R02 is compared with the reference voltage from the reference voltage source B, and the oscillation is given from the oscillation circuit 32 to the charge pump circuit 10 so that the divided voltage value becomes the reference voltage. Change the frequency of the signal. At least one of the voltage dividing resistors R01 and R02 (only R01 in FIG. 4) is semi-fixed such as trimming.

On the other hand, an equivalent circuit of the Nch depletion type transistor Q4 is constructed, for example, as shown in FIG. The depletion type transistor has a gate,
By connecting the back gate and the source, as shown in FIG. 6, the gate-source voltage Vgs of the transistor is increased.
Is a transistor capable of flowing a drain current at the point K at 0V. The drain current at this point K is a constant current,
It is less dependent on the drain voltage and can be used as a constant current source. When the capacitance of the oxide film is Cox, the mobility is μ, the gate width is W, the effective gate length is L, and the threshold voltage is VT, the constant current value ID is ID = (μCox) / 2 × W / L (Vgs It can be represented by −VT) ² .

Therefore, as shown in FIG. 5, by changing the effective gate width W by the logic control circuit CTLa, the current Id flowing through the white light emitting diode D is changed.
It is understood that it is possible to control

The structure using the depletion type transistor Q4 can be applied to the structure including the plurality of white light emitting diodes D1 to Dn as shown in FIG.

FIG. 7 shows the fourth embodiment of the present invention.
The following is a description with reference to FIG.

FIG. 7 is a block diagram showing an electrical configuration of a driver IC 41 having a built-in booster circuit according to the fourth embodiment of the present invention. The driver IC 41 is similar to the driver IC 21 described above, and corresponding parts are designated by the same reference numerals, and description thereof will be omitted. It should be noted that in the driver IC 41, the photodiodes PD1 to PDn that detect the light emission amounts of the white light emitting diodes D1 to Dn are
That is, it is formed in the driver IC 41 by utilizing a PN junction in the driver IC 41.

Thus, in order to reduce the cost, the driver I
When a plurality of photodiodes PD1 to PDn are provided in C41, it is difficult to arrange the white light emitting diodes D1 to Dn and the photodiodes PD1 to PDn that should be individually corresponded to each other equally. Therefore, the correction method shown in FIGS. 8 and 9 is used. First, the driver IC 41, that is, the mounting positions of the photodiodes PD1 to PDn are arranged so as to be at equal distances from the white light emitting diodes D1 to Dn. Next, each photodiode PD1
The shape of each PDn is divided into two, one of which is used over the entire area to obtain the light amount of the individual element, and the other is divided into a plurality of pieces along the arrangement direction of the photodiodes PD1 to PDn (PD1 ′ to PDn). ', 4 in FIG. 8 and FIG. 9), and the parallel outputs of the dividing elements PD1 ′ to PDn ′ having the same arrangement order are obtained. Since the average light amount of each of the white light emitting diodes D1 to Dn is obtained from the parallel output, subsequently, as shown in FIG. 10, the average light amount (photocurrent) and the light amount of the individual element are After being amplified by the operational amplifiers P1 to P4 and P1 ′ to P4 ′, respectively, the two are compared by the comparators CMP1 to CMP4, and the logic control circuits CTL1 to CT based on the comparison result.
L4 changes the resistance values of the variable resistors Rset1 to Rset4.

Thus, the white light emitting diodes D1 to Dn
With the plurality of photodiodes PD1 to PDn provided in the driver IC 41 which are arranged apart from each other, the light amount of the corresponding white light emitting diodes D1 to Dn can be feedback-controlled relatively accurately, and the on-voltage can be increased. It is possible to suppress variations in the light amount due to variations in VF. In this case, the photodiodes PD1 to P
It is important for the area of Dn that the area used in the entire area and the area used in the division be equal to each other.

The depletion type transistor Q4 described above can also be used in the configuration of the driver IC 41.

By the way, in Japanese Patent Laid-Open No. 2000-40365, a voltage boosted by a booster circuit is applied to a load through a step-down circuit composed of an operational amplifier and a transistor, and the operational amplifier has a divided voltage value and a reference voltage. By applying the voltage, a semiconductor device is shown in which an arbitrary stable voltage can be obtained even if the power supply voltage is low.

However, since it is a constant voltage output, for example, it corresponds to the constant voltage amplifier A and the constant voltage transistor Q in the configuration of FIG. 1 of the present invention. In the present invention, since the current Ida corresponding to the specified light quantity is created from the constant voltage by the variable resistance Rset, the configuration of the prior art cannot cope with the variation in the ON voltage VF of the white light emitting diode D. .

[0053]

As described above, the driving device for a white light emitting diode according to the present invention boosts the lighting voltage of the white light emitting diode so that it can be driven with a relatively low input DC power supply voltage against a relatively high on-voltage. In a white light emitting diode drive device including a circuit, the amount of emitted light is detected, and the current applied to the white light emitting diode is controlled based on the result, thereby suppressing variation in the amount of light due to the difference in the ON voltage of the white light emitting diode.

Therefore, it is possible to suppress the variation in the light quantity due to the difference in the on-state voltage, and to obtain the necessary emitted light quantity with the minimum current consumption.

As described above, in the driving apparatus for a white light emitting diode according to the present invention, the current control means includes a variable impedance element interposed between the output terminal of the booster circuit and the white light emitting diode. And a control circuit that changes the impedance of the variable impedance element in response to the output from the detection means and limits the current applied to the white light emitting diode to a level at which a prescribed light amount is obtained.

Therefore, it is possible to suppress the variation in the light amount due to the difference in the on-voltage of the white light emitting diode and to obtain the necessary light amount with the minimum current consumption.

Furthermore, in the driving device for the white light emitting diode of the present invention, as described above, the current control means is interposed between the output terminal of the booster circuit and the white light emitting diode, and is an Nch depletion type transistor. And a control circuit that changes the gate width of the Nch depletion type transistor in response to the output from the detection means and limits the current applied to the white light emitting diode to a level at which a prescribed light amount is obtained. To do.

Therefore, it is possible to suppress the variation in the amount of light due to the difference in the on-voltage of the white light emitting diode, and to obtain the required amount of light with the minimum current consumption.

As described above, the driving device for a white light emitting diode according to the present invention is provided with a plurality of the white light emitting diodes, the corresponding photodiodes are provided, and each white light emission is performed according to the feedback value of the photodiode. A structure for controlling the diode current is provided.

Therefore, it is possible to eliminate unevenness in the amount of light.

Furthermore, as described above, the driving device of the white light emitting diode of the present invention is formed on the integrated circuit chip, and the photodiode constituting the detecting means is formed by utilizing the PN junction in the chip. To be done.

Therefore, the cost can be reduced.

As described above, the driving device for a white light emitting diode according to the present invention is provided with a plurality of white light emitting diodes and photodiodes corresponding thereto, and the plurality of photodiodes are integrated for cost reduction as described above. When provided in the circuit chip, the shape of each photodiode is divided into two, one of them is used over the entire area to obtain the light amount of the individual element of each white light emitting diode, and the other is further arranged along the arrangement direction of the photodiodes. The booster circuit is divided into the same number as the number of photodiodes, and the average light amount of all white light emitting diodes is obtained from the parallel outputs of the dividing elements of the same array order, and the booster circuit is based on the comparison result of the average light amount and the light amounts of the individual elements. To control the current supplied to the white light emitting diode from each.

Therefore, the light quantity of the corresponding white light emitting diode can be feedback-controlled relatively accurately, and the fluctuation of the light quantity due to the fluctuation of the ON voltage can be suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of a driver IC having a booster circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a variable resistor and a logic control circuit in the driver IC shown in FIG.

FIG. 3 is a block diagram showing an electrical configuration of a driver IC incorporating a booster circuit according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing an electrical configuration of a driver IC incorporating a booster circuit according to a third embodiment of the present invention.

5 is an equivalent circuit diagram of a depletion type transistor in the driver IC shown in FIG.

FIG. 6 is a graph showing operating characteristics of the depletion type transistor.

FIG. 7 is a block diagram showing an electrical configuration of a driver IC incorporating a booster circuit according to a fourth embodiment of the present invention.

FIG. 8 is a diagram for explaining a correction method when a photodiode is built in the driver IC.

FIG. 9 is a diagram for explaining a correction method when a photodiode is built in the driver IC.

FIG. 10 is a block diagram for explaining a configuration for correction when a photodiode is built in the driver IC.

FIG. 11 is a block diagram showing the electrical configuration of a typical prior art driver IC with a built-in booster circuit.

FIG. 12 is a current path diagram for explaining a charge pump operation.

FIG. 13 is a waveform diagram for explaining a charge pump operation.

[Explanation of symbols]

10 Charge Pump Circuit (Boosting Circuit) 11, 21, 31, 41 Driver IC (Drive Device for White Light Emitting Diode) 32 Oscillation Circuit A; A1 to An Constant Voltage Amplifier (Current Control Means) B; B1 to Bn Reference Voltage Source ( Current control means) C1 capacitor (for boost operation) C2, C3 capacitors (for smoothing) CMP1 to CMP4 Comparator CTL; CTL1 to CTLn Logic control circuit (current control means, control circuit) D; D1 to Dn White light emitting diode OP; OP1 -OPn error amplifier (current control means) P1 to P4, P1 'to P4' operational amplifier PD; PD1 to PDn; PD1 'to PDn' photodiode (detection means) Q1; Q11 to Q1n constant voltage transistor (current control means, variable Impedance element) Q2, Q3; Q21-Q2n, Q31- Q3n transistor (current control means, variable impedance element) Q4 depletion type transistor R; R1 to Rn feedback resistance (current control means) Rset; Rset1 to Rsetn variable resistance (current control means, variable impedance element) Rs1, Rs2, ... Resistance TR1 , TR2, ... Switching elements R01, R02 Voltage dividing resistors

Claims (6)

[Claims] 1. A drive device for a white light emitting diode, wherein an input DC power supply voltage is boosted by a booster circuit and applied to a white light emitting diode to drive the white light emitting diode, and a detection means for detecting the amount of light emitted from the white light emitting diode, Current control means for suppressing a light quantity variation due to a difference in ON voltage of the white light emitting diode by controlling a current given to the white light emitting diode from the booster circuit in response to an output from the detecting means. White light emitting diode drive device. 2. The current control means includes a variable impedance element interposed between the output terminal of the booster circuit and the white light emitting diode, and the variable impedance element of the variable impedance element in response to the output from the detection means. The driving device for a white light emitting diode according to claim 1, further comprising a control circuit that changes an impedance and controls a current applied to the white light emitting diode. 3. The current control means is an Nch depletion type transistor interposed between the output end of the booster circuit and the white light emitting diode, and the Nch depletion type transistor is responsive to the output from the detection means. 2. The driving device for a white light emitting diode according to claim 1, further comprising a control circuit that changes a gate width of the transistor and controls a current applied to the white light emitting diode. 4. A plurality of the white light emitting diodes are provided,
The said detection means consists of a photodiode closely arranged corresponding to each white light emitting diode, The said current control means is also provided corresponding to each said white light emitting diode individually, The 1st characterized by the above-mentioned. 4. The drive device for a white light emitting diode according to any one of 3 above. 5. The photodiode according to claim 1, which is formed on an integrated circuit chip and which constitutes the detecting means, is formed by utilizing a PN junction in the chip. White light emitting diode drive device. 6. A plurality of the white light emitting diodes are provided,
The photodiodes and current control means are also provided individually corresponding to the respective white light emitting diodes, each of the photodiodes is divided into two, and one of them is used over the entire area so that the light amount of the individual element of each white light emitting diode is The other is further divided into the number of the photodiodes along the arrangement direction of the photodiodes, the average light amount of all the white light emitting diodes is obtained from the parallel output of the dividing elements of the same arrangement order, and the current 6. The driving device for a white light emitting diode according to claim 5, wherein the control means controls a current given to the white light emitting diode from the booster circuit based on a result of comparison between the average light amount and the light amount of the individual element. .