JP2008262966A - Light emitting diode driving device - Google Patents

Light emitting diode driving device Download PDF

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JP2008262966A
JP2008262966A JP2007102566A JP2007102566A JP2008262966A JP 2008262966 A JP2008262966 A JP 2008262966A JP 2007102566 A JP2007102566 A JP 2007102566A JP 2007102566 A JP2007102566 A JP 2007102566A JP 2008262966 A JP2008262966 A JP 2008262966A
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light emitting
emitting diode
current
driving
driving device
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Mitsuru Okazaki
充 岡▲崎▼
Koichi Inoue
晃一 井上
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Rohm Co Ltd
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Rohm Co Ltd
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<P>PROBLEM TO BE SOLVED: To provide a light emitting diode driving device that can avoid simultaneous supply of driving currents when driving a plurality of light emitting diodes and suppress the heat generation amount of the device. <P>SOLUTION: The light emitting diode driving device controls pulse width modulation of driving currents (I1-I4 shown in diagram 2) that are supplied to each of the light emitting diodes in a plurality of channels. In this case, in order to avoid simultaneous turning on of the light emitting diode of at least one channel and those of the other channels, the respective turn-on timings are shifted and the driving currents are supplied thereto. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、複数チャンネルの発光ダイオードに各々駆動電流を供給する発光ダイオード駆動装置に関するものである。   The present invention relates to a light emitting diode driving apparatus that supplies a driving current to each of a plurality of channels of light emitting diodes.

従来より、発光ダイオードの輝度調整を行うべく、これに供給する駆動電流のパルス幅変調制御（以下では、ＰＷＭ［Pulse Width Modulation］制御と呼ぶ）を行う発光ダイオード駆動装置が広く一般的に用いられている。   Conventionally, in order to adjust the luminance of a light emitting diode, a light emitting diode driving device that performs pulse width modulation control (hereinafter referred to as PWM [Pulse Width Modulation] control) of a driving current supplied thereto has been widely used. ing.

図３は、発光ダイオード駆動装置の一従来例を示すブロック図であり、図４は、ＰＷＭ制御の一従来例を示す波形図である。   FIG. 3 is a block diagram showing a conventional example of a light emitting diode driving apparatus, and FIG. 4 is a waveform diagram showing a conventional example of PWM control.

なお、上記に関連する従来技術の一例として、特許文献１には、発光ダイオードに直列接続される第１のトランジスタのほかに、駆動回路（調光回路）から出力されるデューティ制御信号を増幅する第２のトランジスタを設け、第２のトランジスタの増幅出力を用いて、複数の発光ダイオードを駆動する発光ダイオード駆動回路が開示・提案されている。
特開２００３−１５２２２３号公報 As an example of the related art related to the above, in Patent Document 1, in addition to the first transistor connected in series to the light emitting diode, the duty control signal output from the drive circuit (dimming circuit) is amplified. There has been disclosed and proposed a light-emitting diode driving circuit in which a second transistor is provided and a plurality of light-emitting diodes are driven using the amplified output of the second transistor.
JP 2003-152223 A

確かに、上記従来の発光ダイオード駆動装置であれば、発光ダイオードに供給する駆動電流のＰＷＭ制御を行うことによって、所望の発光輝度を得ることが可能である。   Certainly, with the conventional light emitting diode driving device, it is possible to obtain a desired light emission luminance by performing PWM control of the driving current supplied to the light emitting diode.

ところで、図３の発光ダイオード駆動装置を用いて、ｎチャンネル（ｎ≧２）の発光ダイオードＬＥＤ１〜ＬＥＤｎを駆動する場合、従来のＰＷＭ制御方式では、一般に、全チャンネルの発光ダイオードＬＥＤ１〜ＬＥＤｎに対して、同一のタイミングで駆動電流Ｉ１〜Ｉｎ（いずれのチャンネルについても電流値ｉ）が供給されていた（図４を参照）。   By the way, when driving the n-channel (n ≧ 2) light-emitting diodes LED1 to LEDn using the light-emitting diode driving device of FIG. 3, in the conventional PWM control system, generally, the light-emitting diodes LED1 to LEDn of all the channels are compared. Thus, the drive currents I1 to In (current value i for any channel) were supplied at the same timing (see FIG. 4).

そのため、図３の発光ダイオード駆動装置では、ＰＷＭ制御のオン期間中にｎチャンネル分の駆動電流ＩＤＲＶ（＝ｎ×ｉ）が一度に流れて、発熱タイミングが一時に集中してしまうことから、各チャンネルにおける発熱量の合計分をカバーし得るだけの許容損失が必要となり、パッケージの大型化が招かれていた。   Therefore, in the LED driving device of FIG. 3, the driving current IDRV (= n × i) for n channels flows at a time during the PWM control ON period, and the heat generation timing is concentrated at one time. An allowable loss that can cover the total amount of heat generated in the channel is required, which increases the size of the package.

なお、特許文献１の従来技術は、駆動回路の出力電流値を抑える手段として、駆動回路の後段に信号増幅用のトランジスタを設けた技術であり、本発明とは、その本質的構成を異にするものであった。   The prior art disclosed in Patent Document 1 is a technique in which a transistor for signal amplification is provided in the subsequent stage of the drive circuit as means for suppressing the output current value of the drive circuit, and the essential configuration differs from the present invention. It was something to do.

また、特許文献１には、上記構成のほか、本発明に関連する内容として、第１の発光ダイオード回路を点灯させてから所定時間（点灯時差）の経過後に、第２の発光ダイオード回路を点灯させる時差点灯回路が開示されているが、特許文献１には、本発明が解決しようとする課題（駆動電流の同時供給に起因する発熱量の増大）について何ら言及がなく、また、上記の課題を解決する上で重要となる前記所定時間（点灯時差）の具体的な設定値についても説明が全くされていないことから、上記の開示内容は、本発明の動機付けとはなり得ないと考えられる。   In addition to the above-described configuration, Patent Document 1 discloses that the second light-emitting diode circuit is turned on after a predetermined time (lighting time difference) has elapsed since the first light-emitting diode circuit was turned on, as content related to the present invention. A time difference lighting circuit is disclosed. However, Patent Document 1 does not mention any problem (increased calorific value due to simultaneous supply of drive current) that the present invention intends to solve, and the problem described above. Since the specific set value of the predetermined time (lighting time difference) that is important for solving the problem is not explained at all, the above disclosure is not considered to be a motivation of the present invention. It is done.

本発明は、上記の問題点に鑑み、複数の発光ダイオードを駆動するに際して、駆動電流の同時供給を回避し、装置の発熱量を抑制することが可能な発光ダイオード駆動装置を提供することを目的とする。   SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a light emitting diode driving device capable of avoiding simultaneous supply of driving current and suppressing the amount of heat generated by the device when driving a plurality of light emitting diodes. And

上記目的を達成するために、本発明に係る発光ダイオード駆動装置は、複数チャンネルの発光ダイオードに各々供給する駆動電流のパルス幅変調制御を行う発光ダイオード駆動装置であって、少なくとも一のチャンネルの発光ダイオードと、その余のチャンネルの発光ダイオードとの同時点灯を回避するように、各々のオン期間をずらして前記駆動電流を供給する構成（第１の構成）とされている。   In order to achieve the above object, a light emitting diode driving device according to the present invention is a light emitting diode driving device that performs pulse width modulation control of a driving current supplied to each of a plurality of channels of light emitting diodes, and emits light of at least one channel. In order to avoid simultaneous lighting of the diodes and the light emitting diodes of the remaining channels, the driving current is supplied by shifting the on periods of each of them (first configuration).

なお、上記第１の構成から成る発光ダイオード駆動装置は、前記駆動電流のパルス幅変調制御とともに、前記駆動電流の電流値制御を行う構成（第２の構成）にするとよい。   The light emitting diode driving device having the first configuration may be configured to perform the current value control of the driving current (second configuration) together with the pulse width modulation control of the driving current.

また、上記第２の構成から成る発光ダイオード駆動装置は、前記駆動電流のオンデューティが所定の上限値に達していなければ、前記駆動電流のパルス幅変調制御のみを行い、前記駆動電流のオンデューティが所定の上限値に達していれば、前記駆動電流のパルス幅変調制御とともに、前記駆動電流の電流値制御を行う構成（第３の構成）にするとよい。   Further, the light emitting diode driving device having the second configuration performs only the pulse width modulation control of the driving current and the on-duty of the driving current unless the on-duty of the driving current reaches a predetermined upper limit value. If the current value reaches the predetermined upper limit value, it is preferable to adopt a configuration (third configuration) in which the current value control of the drive current is performed together with the pulse width modulation control of the drive current.

また、上記第１〜第３いずれかの構成から成る発光ダイオード駆動装置は、一のチャンネルの発光ダイオードを消灯してから他のチャンネルの発光ダイオードを点灯するまでの間に、所定の同時オフ期間を有するように、前記駆動電流の供給制御を行う構成（第４の構成）にするとよい。   The light emitting diode driving device having any one of the first to third configurations has a predetermined simultaneous off period between turning off the light emitting diode of one channel and turning on the light emitting diode of the other channel. It is preferable to adopt a configuration (fourth configuration) for controlling the supply of the drive current so as to have the above.

本発明に係る発光ダイオード駆動装置であれば、複数の発光ダイオードを駆動するに際して、駆動電流の同時供給を回避し、装置の発熱量を抑制することが可能となる。   With the light emitting diode driving device according to the present invention, when driving a plurality of light emitting diodes, it is possible to avoid simultaneous supply of driving currents and to suppress the amount of heat generated by the device.

図１は、本発明に係る発光ダイオード駆動装置を備えた電子機器の一実施形態を示すブロック図である。   FIG. 1 is a block diagram showing an embodiment of an electronic apparatus equipped with a light emitting diode driving device according to the present invention.

図１に示すように、本実施形態の電子機器は、マイコン１０と、発光ダイオード駆動装置２０と、昇降圧回路３０と、照明装置４０と、を有して成る。   As shown in FIG. 1, the electronic device of the present embodiment includes a microcomputer 10, a light emitting diode driving device 20, a step-up / down circuit 30, and a lighting device 40.

マイコン１０は、発光ダイオード駆動装置２０に所定の輝度制御命令を送出するなど、電子機器の動作を統括的に制御する手段である。   The microcomputer 10 is means for comprehensively controlling the operation of the electronic device, such as sending a predetermined luminance control command to the light emitting diode driving device 20.

発光ダイオード駆動装置２０は、シリアルインターフェイス部２１と、ＤＣ／ＤＣコンバータ部２２と、駆動電流制御部２３と、を集積化して成る半導体集積回路装置（いわゆるＬＥＤドライバＩＣ）である。   The light emitting diode driving device 20 is a semiconductor integrated circuit device (so-called LED driver IC) in which a serial interface unit 21, a DC / DC converter unit 22, and a driving current control unit 23 are integrated.

シリアルインターフェイス部２１は、マイコン１０から入力される輝度制御命令を受け取り、これを駆動電流制御部２３に伝達する手段である。なお、図１では、３線シリアルバス（Ｉ２Ｃバスなど）を介して、輝度制御命令（点灯すべき発光ダイオードやそのオンデューティ及び駆動電流値を示すデータ信号ＤＡＴＡ、クロック信号ＣＬＫ、及び、ラッチ信号ＬＡＴ）を受け取る構成を例示したが、本発明の構成はこれに限定されるものではなく、２線シリアルバスやパラレルバスなどを用いても構わない。   The serial interface unit 21 is a means for receiving a luminance control command input from the microcomputer 10 and transmitting it to the drive current control unit 23. In FIG. 1, a luminance control command (a light emitting diode to be lit, a data signal DATA indicating its on-duty and driving current value, a clock signal CLK, and a latch signal are transmitted via a three-wire serial bus (I2C bus or the like). (LAT) is exemplified, but the configuration of the present invention is not limited to this, and a two-wire serial bus, a parallel bus, or the like may be used.

ＤＣ／ＤＣコンバータ部２２は、入力電圧Ｖｉｎを安定化して所望の定常電圧Ｖｒｅｇを生成する手段である。   The DC / DC converter unit 22 is means for stabilizing the input voltage Vin and generating a desired steady voltage Vreg.

駆動電流制御部２３は、マイコン１０から入力される輝度制御命令に応じて、照明装置４０の駆動電流（照明装置４０を構成するｎチャンネル（ｎ≧２）の発光ダイオードＬＥＤ１〜ＬＥＤｎに各々供給する駆動電流Ｉ１〜Ｉｎ）を生成し、そのＰＷＭ制御を行う手段である。このようなＰＷＭ制御により、駆動電流Ｉ１〜Ｉｎの見かけ上の電流値（平均値）を可変制御して、発光ダイオードＬＥＤ１〜ＬＥＤｎの発光輝度（延いては、照明装置４０の発光輝度）を任意に調整することが可能となる。なお、駆動電流制御部２３の動作については、後ほど詳細な説明を行う。   The drive current control unit 23 supplies the drive current of the illuminating device 40 to the n-channel (n ≧ 2) light emitting diodes LED1 to LEDn constituting the illuminating device 40 in accordance with the luminance control command input from the microcomputer 10. This is means for generating drive currents I1 to In) and performing PWM control thereof. By such PWM control, the apparent current value (average value) of the drive currents I1 to In is variably controlled, and the light emission luminance of the light emitting diodes LED1 to LEDn (and the light emission luminance of the lighting device 40) is arbitrarily set. It becomes possible to adjust to. The operation of the drive current control unit 23 will be described in detail later.

昇降圧回路３０は、ＤＣ／ＤＣコンバータ２２で生成された定常電圧Ｖｒｅｇを昇圧或いは降圧して所望の駆動電圧Ｖｏｕｔを生成し、これを照明装置４０（発光ダイオードＬＥＤ１〜ＬＥＤｎのアノード端）に供給する手段である。なお、図２では、昇降圧回路３０が発光ダイオード駆動装置２０の外部に接続された構成を例示したが、本発明の構成はこれに限定されるものではなく、昇降圧回路３０を発光ダイオード駆動装置２０に内蔵しても構わない。また、入力電圧Ｖｉｎの電圧値や発光ダイオードＬＥＤ１〜ＬＥＤｎの直列段数、ないし、素子特性によっては、昇降圧回路３０を省略することも可能である。   The step-up / step-down circuit 30 increases or decreases the steady voltage Vreg generated by the DC / DC converter 22 to generate a desired drive voltage Vout, and supplies this to the lighting device 40 (the anode ends of the light emitting diodes LED1 to LEDn). It is means to do. 2 illustrates the configuration in which the step-up / step-down circuit 30 is connected to the outside of the light-emitting diode driving device 20, but the configuration of the present invention is not limited to this, and the step-up / down circuit 30 is driven by the light-emitting diode. It may be built in the device 20. Further, the step-up / step-down circuit 30 can be omitted depending on the voltage value of the input voltage Vin, the number of series stages of the light emitting diodes LED1 to LEDn, or the element characteristics.

照明装置４０は、アノードを共通端として並列に接続されたｎチャンネルの発光ダイオードＬＥＤ１〜ＬＥＤｎを有して成り、例えば、液晶テレビやカーナビ用の液晶モニタを背面から照射するバックライトとして用いられる。なお、発光ダイオードＬＥＤ１〜ＬＥＤｎの直列段数については、必ずしも複数段である必要はない。   The illuminating device 40 includes n-channel light emitting diodes LED1 to LEDn connected in parallel with an anode as a common end, and is used as a backlight for irradiating a liquid crystal television or a liquid crystal monitor for car navigation from the back. Note that the number of series stages of the light emitting diodes LED1 to LEDn is not necessarily a plurality of stages.

次に、駆動電流制御部２３による駆動電流Ｉ１〜ＩｎのＰＷＭ制御について、図２を参照しながら、詳細な説明を行う。   Next, the PWM control of the drive currents I1 to In by the drive current control unit 23 will be described in detail with reference to FIG.

図２は、ＰＷＭ制御の一実施例を示す波形図であり、本図の上段及び下段には、それぞれ、従来におけるＰＷＭ制御の様子と本発明におけるＰＷＭ制御の様子が互いの周期Ｔを一致させた形で描写されている。   FIG. 2 is a waveform diagram showing an embodiment of the PWM control. In the upper and lower parts of the figure, the state of the PWM control in the prior art and the state of the PWM control in the present invention match each other with the period T. It is depicted in the form.

なお、本図中の左端に付された符号ＰＷＭは、ＰＷＭ信号の論理状態を示しており、符号Ｉ１〜Ｉ４は、４チャンネルの発光ダイオードＬＥＤ１〜ＬＥＤ４に各々供給される駆動電流の電流波形を示している。また、符号ＩＤＲＶは、駆動電流制御部２３から照明装置４０に供給されるトータルの駆動電流ＩＤＲＶ（駆動電流Ｉ１〜Ｉ４の合計電流）の電流波形を示している。また、図中の符号Ｔは、ＰＷＭ制御の周期を示しており、符号Ｔｏｎ、Ｔｏｎ’は、ＰＷＭ制御のオン期間を示している。また、図中の符号ｉは、駆動電流Ｉ１〜Ｉ４の電流値を示している。   In addition, the code | symbol PWM attached | subjected to the left end in this figure has shown the logic state of the PWM signal, and code | symbols I1-I4 show the current waveform of the drive current each supplied to light emitting diode LED1-LED4 of 4 channels. Show. Reference sign IDRV indicates a current waveform of a total drive current IDRV (total current of the drive currents I1 to I4) supplied from the drive current control unit 23 to the illumination device 40. Further, the symbol T in the figure indicates the PWM control cycle, and the symbols Ton and Ton ′ indicate the PWM control ON period. Moreover, the symbol i in the figure indicates the current values of the drive currents I1 to I4.

本図に示すように、本実施形態の発光ダイオード駆動装置２０は、４チャンネル全ての発光ダイオードＬＥＤ１〜ＬＥＤ４について、互いの同時点灯を回避するように、各々のオン期間Ｔｏｎ’をずらして駆動電流Ｉ１〜Ｉ４（いずれのチャンネルについても電流値ｉ）を供給する構成とされている。具体的には、一のチャンネルの発光ダイオードをオンさせてから、そのオン期間Ｔｏｎ’が経過した後に、次のチャンネルの発光ダイオードをオンさせる構成とされている。   As shown in the figure, the light-emitting diode driving device 20 of the present embodiment shifts each on-period Ton ′ so as to avoid the simultaneous lighting of the light-emitting diodes LED1 to LED4 of all four channels. It is configured to supply I1 to I4 (current value i for any channel). Specifically, the light-emitting diode of the next channel is turned on after the ON period Ton 'has elapsed since the light-emitting diode of one channel is turned on.

このような構成とすることにより、４チャンネル全ての発光ダイオードＬＥＤ１〜ＬＥＤ４に対して、同一のタイミングで駆動電流Ｉ１〜Ｉ４を供給していた従来のＰＷＭ制御と異なり、ＰＷＭ制御のオン期間中に４チャンネル分の駆動電流ＩＤＲＶ（＝４×ｉ）が一度に流れることを回避して、駆動電流ＩＤＲＶのピーク値を駆動電流Ｉ１〜Ｉ４の各電流値ｉまで低減することができる。すなわち、本実施形態の構成であれば、発光ダイオード駆動装置２０の発熱タイミングが均一に分散されるので、その放熱効率が上がり、パッケージの許容損失を下げて、省スペース化やコスト削減を実現することが可能となる。   By adopting such a configuration, unlike the conventional PWM control in which the drive currents I1 to I4 are supplied to the light emitting diodes LED1 to LED4 of all four channels at the same timing, during the on period of the PWM control. The drive current IDRV (= 4 × i) for four channels can be avoided from flowing at one time, and the peak value of the drive current IDRV can be reduced to each current value i of the drive currents I1 to I4. That is, with the configuration of the present embodiment, the heat generation timing of the light emitting diode driving device 20 is uniformly distributed, so that the heat dissipation efficiency is increased, the allowable loss of the package is reduced, and space saving and cost reduction are realized. It becomes possible.

なお、人間の視覚は、単位時間当たりに与えられたエネルギの総量に応じて、輝度の大小を感じるので、本発明のＰＷＭ制御方式を採用した場合でも、体感的な輝度が著しく変化することはない。   Human vision senses the magnitude of the brightness according to the total amount of energy given per unit time, so that even if the PWM control method of the present invention is adopted, the sensible brightness will not change significantly. Absent.

また、ＰＷＭ制御の周波数（１／Ｔ）については、表示画像のフレーム数（例えば３０［ｆｐｓ］）や商用交流電源の周波数（５０／６０［Ｈｚ］）、並びに、これらの倍数と一致しない周波数に適宜設定するとよい。このような周波数設定を行うことにより、照明装置４０の点滅に起因する表示画像や照明光のチラツキを防止することが可能となる。   As for the PWM control frequency (1 / T), the number of frames of the display image (for example, 30 [fps]), the frequency of the commercial AC power supply (50/60 [Hz]), and a frequency that does not match these multiples. It may be set as appropriate. By performing such frequency setting, it is possible to prevent flickering of the display image and illumination light caused by the blinking of the illumination device 40.

ところで、従来におけるＰＷＭ制御のオンデューティをα（α≧０）、本発明におけるＰＷＭ制御のオンデューティをβ（β≧０）とした場合、従来におけるＰＷＭ制御のオン期間Ｔｏｎ、本発明におけるＰＷＭ制御のオン期間Ｔｏｎ’は、それぞれ、以下の（１）式、（２）式で表される。   By the way, when the on-duty of the conventional PWM control is α (α ≧ 0) and the on-duty of the PWM control according to the present invention is β (β ≧ 0), the on-period Ton of the conventional PWM control, the PWM control according to the present invention The ON period Ton ′ is expressed by the following equations (1) and (2), respectively.

Ｔｏｎ＝α×Ｔ … （１）
Ｔｏｎ’＝β×Ｔ … （２） Ton = α × T (1)
Ton ′ = β × T (2)

従って、発光ダイオードのチャンネル数をｎとすると、従来におけるＰＷＭ制御の空白期間Ｔｄｅｄ、及び、本発明におけるＰＷＭ制御の空白期間Ｔｄｅｄ’は、それぞれ、以下の（３）式、（４）式で表すことができる。   Therefore, when the number of light emitting diode channels is n, the conventional PWM control blank period Tded and the PWM control blank period Tded 'in the present invention are expressed by the following equations (3) and (4), respectively. be able to.

Ｔｄｅｄ＝Ｔ−Ｔｏｎ＝（１−α）×Ｔ … （３）
Ｔｄｅｄ’＝Ｔ−Ｔｏｎ’×ｎ＝（１−β×ｎ）×Ｔ … （４） Tded = T−Ton = (1−α) × T (3)
Tded ′ = T−Ton ′ × n = (1−β × n) × T (4)

ここで、空白期間Ｔｄｅｄ、Ｔｄｅｄ’は、Ｔｄｅｄ≧０、Ｔｄｅｄ’≧０でなければならないため、オンデューティα、βの設定可能範囲は、以下の（５）式、（６）式で現される形となる。   Here, since the blank periods Tded and Tded ′ must satisfy Tded ≧ 0 and Tded ′ ≧ 0, the settable ranges of the on-duty α and β are expressed by the following equations (5) and (6). It becomes a form.

０≦α≦１ … （５）
０≦β≦１／ｎ … （６） 0 ≦ α ≦ 1 (5)
0 ≦ β ≦ 1 / n (6)

上記の（５）式、（６）式から分かるように、本発明におけるＰＷＭ制御では、発光ダイオードのチャンネル数ｎに応じて、オンデューティβに上限値（１／ｎ）の制約が生じる。例えば、４チャンネルの発光ダイオードＬＥＤ１〜ＬＥＤ４を駆動する場合、オンデューティβについては、０．２５（＝１／４）までしか設定できなくなる。   As can be seen from the above formulas (5) and (6), in the PWM control according to the present invention, an upper limit (1 / n) is restricted on the on-duty β according to the number of channels n of the light emitting diodes. For example, when driving the four-channel light emitting diodes LED1 to LED4, the on-duty β can be set only up to 0.25 (= 1/4).

そのため、これ以上の発光輝度（従来のＰＷＭ制御における０．２５＜α≦１に相当する発光輝度）を得るためには、オンデューティβが所定の上限値（０．２５）に達して以後、駆動電流の電流値をｉからｉ’に増加させる必要が生じる。   Therefore, in order to obtain light emission luminance higher than this (light emission luminance corresponding to 0.25 <α ≦ 1 in the conventional PWM control), after the on-duty β reaches a predetermined upper limit value (0.25), It is necessary to increase the current value of the drive current from i to i ′.

さて、従来におけるＰＷＭ制御（チャンネル同期制御）でも、本発明におけるＰＷＭ制御（チャンネル分散制御）でも、同一の発光輝度を得るために周期Ｔで消費されるトータルの電荷（延いてはトータルの駆動電流）は等しいため、以下の（７）式が成立する。   Now, in the conventional PWM control (channel synchronous control) and the PWM control (channel dispersion control) in the present invention, the total charge (and thus the total driving current) consumed in the period T to obtain the same light emission luminance. ) Are equal, the following equation (7) holds.

ｎ×ｉ×Ｔｏｎ／Ｔ＝ｎ×ｉ’×Ｔｏｎ’／Ｔ
ｎ×ｉ×α＝ｎ×ｉ’×β … （７） n × i × Ton / T = n × i ′ × Ton ′ / T
n × i × α = n × i ′ × β (7)

上記（７）式から、必要な電流値ｉ’は、以下の（８）式で算出することができる。   From the equation (7), the necessary current value i ′ can be calculated by the following equation (8).

ｉ’＝（α／β）×ｉ … （８）       i ′ = (α / β) × i (8)

例えば、４チャンネルの発光ダイオードＬＥＤ１〜ＬＥＤ４を駆動する場合であって、本発明のＰＷＭ制御におけるオンデューティβの上限値が０．２５であるとき、従来のＰＷＭ制御におけるオンデューティα＝０．５に相当する発光輝度を得るためには、駆動電流の電流値ｉ’を２×ｉまで高めればよいことが分かる。   For example, when the four-channel light emitting diodes LED1 to LED4 are driven and the upper limit value of the on-duty β in the PWM control of the present invention is 0.25, the on-duty α in the conventional PWM control is 0.5. It can be seen that the current value i ′ of the drive current should be increased to 2 × i in order to obtain the light emission luminance corresponding to.

このように、本実施形態の発光ダイオード駆動装置２０は、駆動電流Ｉ１〜Ｉ４のオンデューティβが上限値（０．２５）に達していなければ、駆動電流Ｉ１〜Ｉ４のＰＷＭ制御のみを行い、駆動電流Ｉ１〜Ｉ４のオンデューティβが上限値（０．２５）に達していれば、駆動電流Ｉ１〜Ｉ４のＰＷＭ制御とともに、駆動電流Ｉ１〜Ｉ４の電流値制御を行う構成とされている。このような構成とすることにより、駆動電流制御部２３に流れる駆動電流ＩＤＲＶのピーク値を低減しつつ、従来と同様の設定範囲で発光輝度を幅広く可変制御することが可能となる。   Thus, the light emitting diode drive device 20 of the present embodiment performs only the PWM control of the drive currents I1 to I4 unless the on-duty β of the drive currents I1 to I4 reaches the upper limit value (0.25). If the on-duty β of the drive currents I1 to I4 has reached the upper limit (0.25), the current values of the drive currents I1 to I4 are controlled together with the PWM control of the drive currents I1 to I4. With such a configuration, it is possible to variably control the light emission luminance over a set range similar to the conventional one while reducing the peak value of the drive current IDRV flowing through the drive current control unit 23.

なお、本発明の構成は、上記実施形態のほか、発明の主旨を逸脱しない範囲で種々の変更を加えることが可能である。   The configuration of the present invention can be variously modified in addition to the above-described embodiment without departing from the gist of the invention.

例えば、上記実施形態では、４チャンネルの発光ダイオードＬＥＤ１〜ＬＥＤ４を駆動対象とする構成を例に挙げて説明を行ったが、本発明の構成はこれに限定されるものではなく、発光ダイオードのチャンネル数に関しては、適宜増減することが可能である。   For example, in the above-described embodiment, the description has been given by taking as an example a configuration in which the four-channel light emitting diodes LED1 to LED4 are driven, but the configuration of the present invention is not limited to this, and the channel of the light emitting diode is not limited thereto. The number can be increased or decreased as appropriate.

また、上記実施形態では、４チャンネル全ての発光ダイオードＬＥＤ１〜ＬＥＤ４について、互いの同時点灯を回避するように、各々のオン期間をずらして駆動電流Ｉ１〜Ｉ４を供給する構成を例に挙げて説明を行ったが、本発明の構成はこれに限定されるものではなく、少なくとも一のチャンネルの発光ダイオードと、その余のチャンネルの発光ダイオードとの同時点灯を回避するように、各々のオン期間をずらして駆動電流を供給する構成でありさえすれば、駆動電流制御部２３に流れる駆動電流ＩＤＲＶのピーク値を従来に比べて低減することが可能となる。   Further, in the above-described embodiment, a configuration in which the drive currents I1 to I4 are supplied by shifting the respective on periods so as to avoid the simultaneous lighting of the light emitting diodes LED1 to LED4 of all four channels will be described as an example. However, the configuration of the present invention is not limited to this, and each ON period is set so as to avoid simultaneous lighting of the light emitting diodes of at least one channel and the light emitting diodes of the other channels. The peak value of the drive current IDRV flowing through the drive current control unit 23 can be reduced as compared with the conventional case as long as the drive current is shifted and supplied.

また、上記実施形態では、一のチャンネルの発光ダイオードを消灯した直後に他のチャンネルの発光ダイオードを点灯する構成を例示して説明を行ったが、本発明の構成はこれに限定されるものではなく、一のチャンネルの発光ダイオードを消灯してから他のチャンネルの発光ダイオードを点灯するまでの間に、所定の同時オフ期間を有するように、駆動電流の供給制御を行う構成としてもよい。このような構成とすることにより、前チャンネルの消灯後に生じる過渡的な温度上昇が次チャンネルの点灯に伴う温度上昇と重複するのを回避して、その放熱効率を高めることが可能となる。   Further, in the above-described embodiment, the configuration in which the light emitting diodes of the other channels are turned on immediately after the light emitting diode of one channel is turned off has been described, but the configuration of the present invention is not limited to this. Alternatively, the drive current supply control may be performed so as to have a predetermined simultaneous off period between the time when the light emitting diode of one channel is turned off and the time when the light emitting diodes of the other channel are turned on. By adopting such a configuration, it is possible to avoid the transient temperature rise that occurs after the previous channel is turned off from overlapping with the temperature rise caused by the next channel being turned on, and to increase the heat dissipation efficiency.

また、上記実施形態では、駆動電流のオンデューティが所定の上限値に達してから、駆動電流の電流値制御を開始する構成を例に挙げて説明を行ったが、本発明の構成はこれに限定されるものではなく、オンデューティが上限値に達する前から、駆動電流の電流値制御を行う構成としても構わない。   In the above embodiment, the configuration in which the current value control of the drive current is started after the on-duty of the drive current reaches a predetermined upper limit has been described as an example. However, the configuration of the present invention is not limited to this. The present invention is not limited, and the drive current value control may be performed before the on-duty reaches the upper limit value.

また、上記実施形態では、マイコン１０から発光ダイオード駆動装置２０に輝度制御命令（データ信号ＤＡＴＡ、クロック信号ＣＬＫ、ラッチ信号ＬＡＴ）を入力する構成を例示して説明を行ったが、本発明の構成はこれに限定されるものではなく、マイコン１０から各チャンネル毎のＰＷＭ信号を個別に入力する構成としても構わない。   In the above embodiment, the configuration in which the luminance control command (data signal DATA, clock signal CLK, latch signal LAT) is input from the microcomputer 10 to the light emitting diode driving device 20 has been described as an example. However, the present invention is not limited to this, and the PWM signal for each channel may be individually input from the microcomputer 10.

本発明に係る発光ダイオード駆動装置は、例えば、液晶ディスプレイのバックライトを駆動する手段として利用可能である。   The light emitting diode driving device according to the present invention can be used as means for driving a backlight of a liquid crystal display, for example.

は、本発明に係る発光ダイオード駆動装置を備えた電子機器の一実施形態を示すブロック図である。These are block diagrams which show one Embodiment of the electronic device provided with the light emitting diode drive device which concerns on this invention. は、ＰＷＭ制御の一実施例を示す波形図である。These are the wave forms which show one Example of PWM control. は、発光ダイオード駆動装置の一従来例を示すブロック図である。These are block diagrams which show a prior art example of a light emitting diode drive device. は、ＰＷＭ制御の一従来例を示す波形図である。These are waveform diagrams showing a conventional example of PWM control.

符号の説明Explanation of symbols

１０ マイコン
２０ 発光ダイオード駆動装置
２１ シリアルインターフェイス部
２２ ＤＣ／ＤＣコンバータ部
２３ 駆動電流制御部
３０ 昇降圧回路
４０ 照明装置
ＬＥＤ１〜ＬＥＤｎ 発光ダイオード DESCRIPTION OF SYMBOLS 10 Microcomputer 20 Light emitting diode drive device 21 Serial interface part 22 DC / DC converter part 23 Drive current control part 30 Buck-boost circuit 40 Lighting apparatus LED1-LEDn Light emitting diode

Claims (4)

複数チャンネルの発光ダイオードに各々供給する駆動電流のパルス幅変調制御を行う発光ダイオード駆動装置であって、少なくとも一のチャンネルの発光ダイオードと、その余のチャンネルの発光ダイオードとの同時点灯を回避するように、各々のオン期間をずらして前記駆動電流を供給することを特徴とする発光ダイオード駆動装置。   A light emitting diode driving device that performs pulse width modulation control of a driving current supplied to each of a plurality of light emitting diodes, so as to avoid simultaneous lighting of at least one light emitting diode and the remaining light emitting diodes. Further, the driving current is supplied by shifting each ON period. 前記駆動電流のパルス幅変調制御とともに、前記駆動電流の電流値制御を行うことを特徴とする請求項１に記載の発光ダイオード駆動装置。   2. The light emitting diode driving device according to claim 1, wherein a current value control of the driving current is performed together with a pulse width modulation control of the driving current. 前記駆動電流のオンデューティが所定の上限値に達していなければ、前記駆動電流のパルス幅変調制御のみを行い、前記駆動電流のオンデューティが所定の上限値に達していれば、前記駆動電流のパルス幅変調制御とともに、前記駆動電流の電流値制御を行うことを特徴とする請求項２に記載の発光ダイオード駆動装置。   If the on-duty of the driving current does not reach a predetermined upper limit value, only the pulse width modulation control of the driving current is performed, and if the on-duty of the driving current reaches a predetermined upper limit value, 3. The light emitting diode driving device according to claim 2, wherein current value control of the driving current is performed together with pulse width modulation control. 一のチャンネルの発光ダイオードを消灯してから他のチャンネルの発光ダイオードを点灯するまでの間に、所定の同時オフ期間を有するように、前記駆動電流の供給制御を行うことを特徴とする請求項１〜請求項３のいずれかに記載の発光ダイオード駆動装置。   The drive current supply control is performed so as to have a predetermined simultaneous off period from when the light emitting diode of one channel is turned off until the light emitting diode of another channel is turned on. The light-emitting-diode drive device in any one of Claims 1-3.
JP2007102566A 2007-04-10 2007-04-10 Light emitting diode driving device Pending JP2008262966A (en)

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