JP2011060696A - Pwm light dimming circuit - Google Patents

Pwm light dimming circuit Download PDF

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JP2011060696A
JP2011060696A JP2009211699A JP2009211699A JP2011060696A JP 2011060696 A JP2011060696 A JP 2011060696A JP 2009211699 A JP2009211699 A JP 2009211699A JP 2009211699 A JP2009211699 A JP 2009211699A JP 2011060696 A JP2011060696 A JP 2011060696A
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pwm
switch
output voltage
emitting element
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JP5415879B2 (en
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Takayuki Shindo
崇之 進藤
Tetsuji Yamaguchi
哲二 山口
Tomoyuki Koga
智之 古賀
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Asahi Kasei Toko Power Devices Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a PWM light dimming circuit which has a small light dimming duty or can maintain a constant output voltage even in a low on-duty and flickering of a light emitting element can be reduced. <P>SOLUTION: A mode setting part 16 is provided between a load Load of the PWM light dimming circuit and an error amplifier 11. The mode setting part 16 inputs a minimum period setting signal CNT and when a dimming PWM signal is smaller than the minimum period setting signal CNT, a normal operation mode is shifted to a low duty operation mode. At the low duty operation mode, a switch 18 opens and a switch 19 closes and a non-inverted input terminal of the error amplifier 11 is cut off from a connected resistance and is connected to a ground potential. Thereby, a feed-back control is stopped and an error signal COMP becomes maximum by a signal FB of a zero potential and a DC/DC converter is operated so that an output voltage VOUT may be made large. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

本発明はＰＷＭ調光回路に関し、より詳細には、ＬＥＤ等の発光素子をＰＷＭ信号のデューティー比を変化させることで調光するＰＷＭ調光回路に関する。   The present invention relates to a PWM dimming circuit, and more particularly to a PWM dimming circuit for dimming a light emitting element such as an LED by changing a duty ratio of a PWM signal.

従来、ＬＥＤや陰極蛍光管等を駆動する駆動回路が知られており、負荷変更等の影響を受ける出力電圧や電流をフィードバック制御により一定に保つように構成され、一方、ＰＷＭのデューティー比を調整している（特許文献１参照）。   Conventionally, drive circuits for driving LEDs, cathode fluorescent tubes, etc. are known, and are configured to keep output voltage and current affected by load changes, etc. constant by feedback control, while adjusting the duty ratio of PWM (See Patent Document 1).

図３に、従来のＰＷＭ調光回路の構成を示す。ＰＷＭ信号によりＬＥＤ等の負荷Ｌｏａｄに流れる電流のオンオフを制御して、調光する回路の一例であって、ＬＥＤに流れる電流をフィードバック制御して一定の出力電圧ＶＯＵＴを生成する回路である。   FIG. 3 shows a configuration of a conventional PWM dimming circuit. It is an example of a circuit that performs dimming by controlling on / off of a current flowing in a load Load such as an LED by a PWM signal, and is a circuit that generates a constant output voltage VOUT by feedback controlling the current flowing in the LED.

外部電源ＶＩＮからインダクタンスとダイオードを介して電圧保持用のキャパシタに電荷が供給され、定電圧ＶＯＵＴが負荷Ｌｏａｄに接続されている。負荷Ｌｏａｄは、例えばＬＥＤであり、グランドとの間に抵抗とＰＷＭ信号によってオンオフされるスイッチ２４が直列に接続されている。外部から入力されるこのＰＷＭ信号は、例えば５ｍｓを１周期とし、この範囲でデューティー比が変更される。   Electric charge is supplied from the external power source VIN to the voltage holding capacitor via the inductance and the diode, and the constant voltage VOUT is connected to the load Load. The load Load is, for example, an LED, and a switch 24 that is turned on / off by a PWM signal is connected in series with the ground. The PWM signal input from the outside has, for example, 5 ms as one cycle, and the duty ratio is changed within this range.

尚、図３では１つの負荷Ｌｏａｄが接続されているが、並列または直接あるいはそれらの組み合わせで複数のＬＥＤが接続されることがある。   Although one load Load is connected in FIG. 3, a plurality of LEDs may be connected in parallel, directly, or a combination thereof.

負荷Ｌｏａｄと抵抗との間の電位が誤差増幅器２１の反転入力端子に入力されている。非反転入力端子には基準電圧Ｖｒｅｆが入力され、誤差増幅器２１から差電圧を増幅した誤差信号ＣＯＭＰが出力される。ＰＷＭコンパレータ２２に入力された誤差信号ＣＯＭＰは、のこぎり波と比較され、のこぎり波の電圧より高い場合に、ＰＷＭコンパレータ２２から「Ｈｉ」が出力される。のこぎり波は例えば、１ＭＨｚの周波数であり、ＰＷＭコンパレータ２２からは誤差信号に応じた１ＭＨｚのＰＷＭ信号が生成される。このＰＷＭ信号は、外部から入力される調光用のＰＷＭと論理積され、インダクタンスに接続されたＭＯＳトランジスタからなるスイッチを制御し、出力電圧ＶＯＵＴが一定となるようにフィードバック制御される。つまり、フィードバック制御される期間は、調光用ＰＷＭ信号がＨｉ状態になっている間であり、ＤＣ／ＤＣコンバータはバースト動作することになる。   A potential between the load Load and the resistor is input to the inverting input terminal of the error amplifier 21. The reference voltage Vref is input to the non-inverting input terminal, and an error signal COMP obtained by amplifying the difference voltage is output from the error amplifier 21. The error signal COMP input to the PWM comparator 22 is compared with a sawtooth wave, and when the voltage is higher than the sawtooth wave, “Hi” is output from the PWM comparator 22. The sawtooth wave has a frequency of 1 MHz, for example, and the PWM comparator 22 generates a 1 MHz PWM signal corresponding to the error signal. This PWM signal is logically ANDed with a dimming PWM input from the outside, and controls a switch composed of a MOS transistor connected to an inductance, and is feedback-controlled so that the output voltage VOUT becomes constant. That is, the period during which feedback control is performed is during the time when the dimming PWM signal is in the Hi state, and the DC / DC converter performs a burst operation.

また、負荷Ｌｏａｄ等に異常が発生し、例えば負荷Ｌｏａｄが切断されたような場合、誤差増幅器２１の反転入力端子はグランド電位となり、出力電圧ＶＯＵＴが上昇し続ける。過上昇した場合に安定制御するために、出力電圧ＶＯＵＴを抵抗分割した電圧と、所定の基準電圧Ｖｒｅｆとの差信号をＯＶＰ増幅器２５により増幅し、ＰＷＭコンパレータ２２に制御信号と入力することで、出力電圧ＶＯＵＴが過電圧になった場合に、ＭＯＳスイッチをオフにして、過電圧を防止する。   Further, when an abnormality occurs in the load Load and the load Load is disconnected, for example, the inverting input terminal of the error amplifier 21 becomes the ground potential, and the output voltage VOUT continues to rise. In order to perform stable control in the case of excessive rise, a difference signal between a voltage obtained by resistance-dividing the output voltage VOUT and a predetermined reference voltage Vref is amplified by the OVP amplifier 25, and a control signal is input to the PWM comparator 22, When the output voltage VOUT becomes an overvoltage, the MOS switch is turned off to prevent the overvoltage.

特開２００３−３１７９９４号公報JP 2003-317994 A

しかしながら、外部からのＰＷＭ信号のデューティー比が小さくなると、このＰＷＭ信号の１サイクルあたりにＤＣ／ＤＣコンバータがスイッチングする回数が少なくなり、出力電圧を一定に保つことができなくなる。   However, if the duty ratio of the PWM signal from the outside decreases, the number of times the DC / DC converter switches per cycle of the PWM signal decreases, and the output voltage cannot be kept constant.

このため、ＬＥＤに対して適切な電流を提供できなくなり、発光のちらつきなどの原因となるという問題があった。   For this reason, there is a problem in that an appropriate current cannot be provided to the LED, causing light emission flicker.

本発明は、このような問題に鑑みてなされたもので、調光デューティーが小さい、すなわち低いオンデューティーであっても一定の出力電圧を維持し、発光素子のちらつきを低減するＰＷＭ調光回路を提供することにある。   The present invention has been made in view of such a problem, and a PWM dimming circuit that maintains a constant output voltage even when the dimming duty is small, that is, low on-duty, and reduces flickering of the light emitting element is provided. It is to provide.

上記の課題を解決するために、請求項１に記載の発明は、ＰＷＭ信号により発光素子の駆動を制御すると共に、前記発光素子に流れる電流に基づいてフィードバック制御を行い、前記発光素子を駆動する出力電圧を生成するＤＣ／ＤＣコンバータを備えたＰＷＭ調光回路において、発光素子の発光期間の最小期間設定信号に基づいて、前記ＰＷＭ信号が前記最小期間設定信号より短い場合に、前記フィードバック制御を停止し、前記出力電圧を上昇させる制御に遷移することを特徴とする。   In order to solve the above-mentioned problem, the invention according to claim 1 controls the driving of the light emitting element by the PWM signal, and performs the feedback control based on the current flowing through the light emitting element to drive the light emitting element. In a PWM dimming circuit including a DC / DC converter that generates an output voltage, the feedback control is performed when the PWM signal is shorter than the minimum period setting signal based on a minimum period setting signal of a light emission period of a light emitting element. It stops, and it changes to control which raises the said output voltage, It is characterized by the above-mentioned.

請求項２に記載の発明は、請求項１に記載のＰＷＭ調光回路において、前記発光素子に直列に接続され、前記発光素子に出力電圧に基づいた電流を流すためのスイッチと、前記スイッチに直列に接続され、前記電流に応じた電圧を発生させる抵抗と、前記抵抗に発生する電圧と所定の基準電圧との差を増幅し、誤差信号を生成させる誤差増幅器と、前記誤差増幅器の出力に基づいて、出力電圧を生成する出力電圧発生部と、前記抵抗と前記誤差増幅器の入力端子とを切断または接続するための第２のスイッチと、を備え、前記最小期間設定信号に基づいて、前記ＰＷＭ信号が前記最小期間設定信号より短い場合に、前記第２のスイッチをオフして前記出力電圧を上昇させる制御に遷移することを特徴とする。   According to a second aspect of the present invention, in the PWM dimming circuit according to the first aspect, the switch is connected in series to the light emitting element, and a current is passed through the light emitting element based on an output voltage. A resistor that is connected in series and generates a voltage corresponding to the current, an error amplifier that amplifies a difference between the voltage generated in the resistor and a predetermined reference voltage, and generates an error signal, and an output of the error amplifier An output voltage generator for generating an output voltage, and a second switch for disconnecting or connecting the resistor and an input terminal of the error amplifier, and based on the minimum period setting signal, When the PWM signal is shorter than the minimum period setting signal, the second switch is turned off to shift to control for increasing the output voltage.

請求項３に記載の発明は、請求項２に記載のＰＷＭ調光回路において、前記誤差増幅器の入力端子をグランドに接続する第３のスイッチをさらに備え、前記第３のスイッチは、前記第２のスイッチがオフしているときにオンすることを特徴とする。   A third aspect of the present invention is the PWM dimming circuit according to the second aspect, further comprising a third switch for connecting an input terminal of the error amplifier to a ground, wherein the third switch is the second switch. It is turned on when the switch of is turned off.

請求項４に記載の発明は、請求項１乃至３のいずれかに記載のＰＷＭ調光回路において、前記最小期間設定信号は、前記ＰＷＭ信号と同期した信号であり、前記ＰＷＭ信号の１サイクルのスタートから一定の期間オフする信号であることを特徴とする。   According to a fourth aspect of the present invention, in the PWM dimming circuit according to any one of the first to third aspects, the minimum period setting signal is a signal synchronized with the PWM signal, and one cycle of the PWM signal. The signal is turned off for a certain period from the start.

本発明は、調光デューティーが小さい、すなわち低いオンデューティーであっても一定の出力電圧を維持し、発光素子のちらつきを低減する効果を奏する。   The present invention has an effect of maintaining a constant output voltage even with a small dimming duty, that is, a low on-duty, and reducing flickering of the light emitting element.

本発明の一実施形態に係るＰＷＭ調光回路の構成を示す図である。It is a figure which shows the structure of the PWM light control circuit which concerns on one Embodiment of this invention. 本発明の一実施形態に係るモード設定部の動作を示す図である。It is a figure which shows operation | movement of the mode setting part which concerns on one Embodiment of this invention. 従来のＰＷＭ調光回路の構成を示す図である。It is a figure which shows the structure of the conventional PWM dimming circuit.

以下、本発明の実施の形態について、詳細に説明する。   Hereinafter, embodiments of the present invention will be described in detail.

図１に、本発明の一実施形態に係るＰＷＭ調光回路の構成を示す。外部電源ＶＩＮからインダクタンスとダイオードを介して電圧保持用のキャパシタに電荷が供給され、定電圧ＶＯＵＴが負荷Ｌｏａｄに接続されている。負荷Ｌｏａｄは、例えばＬＥＤであり、グランドとの間に抵抗とＰＷＭ信号によってオンオフされるスイッチ１４が直列に接続されている。外部から入力されるこのＰＷＭ信号は、例えば５ｍｓを１周期とし、この範囲でデューティー比が変更される。   FIG. 1 shows a configuration of a PWM dimming circuit according to an embodiment of the present invention. Electric charge is supplied from the external power source VIN to the voltage holding capacitor via the inductance and the diode, and the constant voltage VOUT is connected to the load Load. The load Load is, for example, an LED, and a switch 14 that is turned on / off by a PWM signal is connected in series with a ground. The PWM signal input from the outside has, for example, 5 ms as one cycle, and the duty ratio is changed within this range.

尚、図１では１つの負荷Ｌｏａｄが接続されているが、並列または直接あるいはそれらの組み合わせで複数のＬＥＤが接続されることがある。   In FIG. 1, one load Load is connected, but a plurality of LEDs may be connected in parallel, directly, or a combination thereof.

負荷Ｌｏａｄと抵抗との間の電位が誤差増幅器１１の反転入力端子に入力されている。非反転入力端子には基準電圧Ｖｒｅｆが入力され、誤差増幅器１１から差電圧を増幅した誤差信号ＣＯＭＰが出力される。ＰＷＭコンパレータ１２に入力された誤差信号ＣＯＭＰは、のこぎり波と比較され、のこぎり波の電圧より高い場合に、ＰＷＭコンパレータ１２から「Ｈｉ」が出力される。のこぎり波は例えば、１ＭＨｚの周波数であり、ＰＷＭコンパレータ１２からは誤差信号に応じた１ＭＨｚのＰＷＭ信号が生成される。このＰＷＭ信号は、外部から入力される調光用のＰＷＭと論理積され、インダクタンスに接続されたＭＯＳトランジスタからなるスイッチを制御し、出力電圧ＶＯＵＴが一定となるようにフィードバック制御される。つまり、フィードバック制御される期間は、調光用ＰＷＭ信号がＨｉ状態になっている間であり、ＤＣ／ＤＣコンバータはバースト動作することになる。   A potential between the load Load and the resistor is input to the inverting input terminal of the error amplifier 11. A reference voltage Vref is input to the non-inverting input terminal, and an error signal COMP obtained by amplifying the difference voltage is output from the error amplifier 11. The error signal COMP input to the PWM comparator 12 is compared with the sawtooth wave, and when the voltage is higher than the sawtooth wave, “Hi” is output from the PWM comparator 12. The sawtooth wave has a frequency of 1 MHz, for example, and the PWM comparator 12 generates a 1 MHz PWM signal corresponding to the error signal. This PWM signal is logically ANDed with a dimming PWM input from the outside, and controls a switch composed of a MOS transistor connected to an inductance, and is feedback-controlled so that the output voltage VOUT becomes constant. That is, the period during which feedback control is performed is during the time when the dimming PWM signal is in the Hi state, and the DC / DC converter performs a burst operation.

また、負荷Ｌｏａｄ等に異常が発生し、例えば負荷Ｌｏａｄが切断されたような場合、誤差増幅器１１の反転入力端子はグランド電位となり、出力電圧ＶＯＵＴが上昇し続ける。過上昇した場合に安定制御するために、出力電圧ＶＯＵＴを抵抗分割した電圧と、所定の基準電圧Ｖｒｅｆとの差信号をＯＶＰ増幅器１５により増幅し、ＰＷＭコンパレータ１２に制御信号と入力することで、出力電圧ＶＯＵＴが過電圧になった場合に、ＭＯＳスイッチをオフにして、過電圧を防止する。   Further, when an abnormality occurs in the load Load and the load Load is disconnected, for example, the inverting input terminal of the error amplifier 11 becomes the ground potential, and the output voltage VOUT continues to rise. In order to perform stable control in the case of excessive rise, a difference signal between the voltage obtained by dividing the output voltage VOUT by resistance and a predetermined reference voltage Vref is amplified by the OVP amplifier 15 and is input to the PWM comparator 12 as a control signal. When the output voltage VOUT becomes an overvoltage, the MOS switch is turned off to prevent the overvoltage.

本発明は、ＰＷＭ調光回路の負荷Ｌｏａｄと誤差増幅器１１との間にモード設定部１６をさらに備える。このモード設定部１６は、最小周期設定信号ＣＮＴを入力することにより、調光用ＰＷＭ信号が最小周期設定信号ＣＮＴより小さい場合、通常動作モードから低デューティー動作モードに移行させる。   The present invention further includes a mode setting unit 16 between the load Load of the PWM dimming circuit and the error amplifier 11. By inputting the minimum cycle setting signal CNT, the mode setting unit 16 shifts from the normal operation mode to the low duty operation mode when the dimming PWM signal is smaller than the minimum cycle setting signal CNT.

最小周期設定信号ＣＮＴは、例えば調光用ＰＷＭ信号と同期した信号であり、調光用ＰＷＭ信号の１サイクルのスタートから一定の期間オフする信号である。   The minimum cycle setting signal CNT is, for example, a signal synchronized with the dimming PWM signal, and is a signal that is turned off for a certain period from the start of one cycle of the dimming PWM signal.

調光用ＰＷＭ信号の周期を５ｍｓとし、ＤＣ／ＤＣコンバータのスイッチング周波数を例えば１ＭＨｚとした場合、のこぎり波は１ＭＨｚの周波数となる。このとき、最小周期設定信号ＣＮＴがオフする期間を、例えば、のこぎり波１０個分の１０μｓとする。尚、最小周期設定信号ＣＮＴがオフする期間は、５μｓから２０μｓの範囲で適宜選択してもよい。   When the cycle of the dimming PWM signal is 5 ms and the switching frequency of the DC / DC converter is 1 MHz, for example, the sawtooth wave has a frequency of 1 MHz. At this time, the period during which the minimum cycle setting signal CNT is turned off is, for example, 10 μs corresponding to 10 sawtooth waves. The period during which the minimum cycle setting signal CNT is turned off may be appropriately selected within the range of 5 μs to 20 μs.

モード設定部１６では、入力された調光用ＰＷＭ信号と最小期間設定信号ＣＮＴを、論理回路を介してモードＲＥＳＥＴ信号とモードＳＥＴ信号に変換する。   The mode setting unit 16 converts the input dimming PWM signal and the minimum period setting signal CNT into a mode RESET signal and a mode SET signal via a logic circuit.

図２に、本発明の一実施形態に係るモード設定部１６の動作を示す。   FIG. 2 shows the operation of the mode setting unit 16 according to an embodiment of the present invention.

モードＲＥＳＥＴ信号は、調光用ＰＷＭ信号のオン期間が最小周期設定信号ＣＮＴのＬｏ期間より長い場合、最小周期設定信号ＣＮＴの立ち上がりでＨｉになり、調光用ＰＷＭ信号の立ち下りでＬｏになる。   When the ON period of the dimming PWM signal is longer than the Lo period of the minimum cycle setting signal CNT, the mode RESET signal becomes Hi when the minimum cycle setting signal CNT rises and becomes Lo when the dimming PWM signal falls. .

一方、モードＳＥＴ信号は、調光用ＰＷＭ信号のオン期間が最小周期設定信号ＣＮＴのＬｏ期間より短い場合、調光用ＰＷＭ信号の立ち下がりでＨｉになり、最小周期設定信号ＣＮＴの立ち上がりでＬｏになる。   On the other hand, when the ON period of the dimming PWM signal is shorter than the Lo period of the minimum cycle setting signal CNT, the mode SET signal becomes Hi when the dimming PWM signal falls, and Lo when the minimum cycle setting signal CNT rises. become.

つまり、調光用ＰＷＭ信号のオン期間が最小周期設定信号ＣＮＴのＬｏ期間より長い場合はモードＲＥＳＥＴ信号が生成され、調光用ＰＷＭ信号のオン期間が最小周期設定信号ＣＮＴのＬｏ期間より短い場合はモードＳＥＴ信号が生成される。   That is, when the ON period of the dimming PWM signal is longer than the Lo period of the minimum cycle setting signal CNT, the mode RESET signal is generated, and when the ON period of the dimming PWM signal is shorter than the Lo period of the minimum cycle setting signal CNT A mode SET signal is generated.

これらの信号はフリップフロップ１７に入力され、モードＳＥＴ信号がＨｉなることにより低デューティー動作モードに移行し、モードＲＥＳＥＴ信号がＨｉになることにより通常モードに移行する。   These signals are input to the flip-flop 17 and shift to the low duty operation mode when the mode SET signal becomes Hi, and shift to the normal mode when the mode RESET signal becomes Hi.

通常モードでは、スイッチ１８が閉じてスイッチ１９が開くことでＬＥＤに接続された抵抗に電流が流れ、この電圧降下により信号ＦＢが生成され、基準電圧ＶＲＥＦとの差が誤差増幅器１１で増幅されて誤差信号ＣＯＭＰが生成される。この誤差信号ＣＯＭＰは、位相補償回路１３を介してＰＷＭコンパレータ１２に入力され、ＰＷＭコンパレータ１２においてのこぎり波と比較される。ＰＷＭコンパレータ１２の出力信号がインダクタに接続されたＭＯＳＦＥＴをオンオフし、出力電圧ＶＯＵＴを一定となるように制御する。   In the normal mode, when the switch 18 is closed and the switch 19 is opened, a current flows through a resistor connected to the LED. This voltage drop generates a signal FB, and the difference from the reference voltage VREF is amplified by the error amplifier 11. An error signal COMP is generated. The error signal COMP is input to the PWM comparator 12 via the phase compensation circuit 13 and is compared with the sawtooth wave in the PWM comparator 12. The output signal of the PWM comparator 12 turns on and off the MOSFET connected to the inductor, and controls the output voltage VOUT to be constant.

一方、調光用ＰＷＭ信号のオンデューティーが小さくなり、最小周期設定信号ＣＮＴのオフ期間より短くなると、低デューティー動作モードに移行する。このとき、スイッチ１８が開いてスイッチ１９が閉じるので、誤差増幅器１１の比反転入力端子は、接続されていた抵抗を切断されてグランド電位に接続される。そのため、フィードバック制御は停止され、ゼロ電位の信号ＦＢにより誤差信号ＣＯＭＰが最大になり、出力電圧ＶＯＵＴを大きくするようにＤＣ／ＤＣコンバータが動作する。   On the other hand, when the on-duty of the dimming PWM signal becomes smaller and becomes shorter than the off period of the minimum cycle setting signal CNT, the mode shifts to the low-duty operation mode. At this time, since the switch 18 is opened and the switch 19 is closed, the ratio inversion input terminal of the error amplifier 11 is disconnected from the connected resistor and connected to the ground potential. Therefore, the feedback control is stopped, the error signal COMP is maximized by the zero potential signal FB, and the DC / DC converter operates so as to increase the output voltage VOUT.

従って、調光用ＰＷＭ信号のオンデューティーが短くなって、ＤＣ／ＤＣコンバータのスイッチング動作が大幅に減少しても、出力電圧ＶＯＵＴを維持することができ、十分に電荷を負荷Ｌｏａｄに供給することができる。すなわち、オンデューティーが短い場合であっても、ＬＥＤのちらつきを防止することができる。   Therefore, even when the on-duty of the dimming PWM signal is shortened and the switching operation of the DC / DC converter is greatly reduced, the output voltage VOUT can be maintained and sufficient charge is supplied to the load Load. Can do. That is, even when the on-duty is short, the flickering of the LED can be prevented.

尚、低デューティー動作モードではフィードバック制御がなされないため、最小周期設定信号ＣＮＴの設定期間によっては、出力電圧ＶＯＵＴが高くなったり、発熱したりするのではないかとの懸念もあるかもしれないが、オンデューティーはそもそも非常に短いため、最小周期設定信号ＣＮＴを最も長く設定した場合でも、出力電圧ＶＯＵＴの上昇も、発熱も無視できる程度である。   In addition, since feedback control is not performed in the low duty operation mode, there may be a concern that the output voltage VOUT may increase or generate heat depending on the setting period of the minimum cycle setting signal CNT. Since the on-duty is very short in the first place, even when the minimum cycle setting signal CNT is set to be the longest, the rise of the output voltage VOUT and the heat generation are negligible.

１１、２１ 誤差増幅器
１２、２２ ＰＷＭコンパレータ
１３、２３ 位相補償回路
１４、１８、１９、２４ スイッチ
１５、２５ ＯＶＰ増幅器
１６ モード設定部 11, 21 Error amplifier 12, 22 PWM comparator 13, 23 Phase compensation circuit 14, 18, 19, 24 Switch 15, 25 OVP amplifier 16 Mode setting unit

Claims (4)

ＰＷＭ信号により発光素子の駆動を制御すると共に、前記発光素子に流れる電流に基づいてフィードバック制御を行い、前記発光素子を駆動する出力電圧を生成するＤＣ／ＤＣコンバータを備えたＰＷＭ調光回路において、
発光素子の発光期間の最小期間設定信号に基づいて、前記ＰＷＭ信号が前記最小期間設定信号より短い場合に、前記フィードバック制御を停止し、前記出力電圧を上昇させる制御に遷移することを特徴とするＰＷＭ調光回路。 In a PWM dimming circuit including a DC / DC converter that controls driving of a light emitting element by a PWM signal, performs feedback control based on a current flowing through the light emitting element, and generates an output voltage for driving the light emitting element.
Based on a minimum period setting signal of a light emission period of a light emitting element, when the PWM signal is shorter than the minimum period setting signal, the feedback control is stopped and a transition is made to control for increasing the output voltage. PWM dimming circuit. 前記発光素子に直列に接続され、前記発光素子に出力電圧に基づいた電流を流すためのスイッチと、
前記スイッチに直列に接続され、前記電流に応じた電圧を発生させる抵抗と、
前記抵抗に発生する電圧と所定の基準電圧との差を増幅し、誤差信号を生成させる誤差増幅器と、
前記誤差増幅器の出力に基づいて、出力電圧を生成する出力電圧発生部と、
前記抵抗と前記誤差増幅器の入力端子とを切断または接続するための第２のスイッチと、
を備え、
前記最小期間設定信号に基づいて、前記ＰＷＭ信号が前記最小期間設定信号より短い場合に、前記第２のスイッチをオフして前記出力電圧を上昇させる制御に遷移することを特徴とする請求項１に記載のＰＷＭ調光回路。 A switch connected in series to the light emitting element, and a switch for passing a current based on an output voltage to the light emitting element;
A resistor connected in series to the switch and generating a voltage according to the current;
An error amplifier for amplifying a difference between a voltage generated in the resistor and a predetermined reference voltage and generating an error signal;
An output voltage generator for generating an output voltage based on the output of the error amplifier;
A second switch for disconnecting or connecting the resistor and the input terminal of the error amplifier;
With
2. The control shifts to a control for increasing the output voltage by turning off the second switch when the PWM signal is shorter than the minimum period setting signal based on the minimum period setting signal. The PWM dimming circuit according to claim 1. 前記誤差増幅器の入力端子をグランドに接続する第３のスイッチをさらに備え、
前記第３のスイッチは、前記第２のスイッチがオフしているときにオンすることを特徴とする請求項２に記載のＰＷＭ調光回路。 A third switch for connecting the input terminal of the error amplifier to the ground;
The PWM dimming circuit according to claim 2, wherein the third switch is turned on when the second switch is turned off. 前記最小期間設定信号は、前記ＰＷＭ信号と同期した信号であり、前記ＰＷＭ信号の１サイクルのスタートから一定の期間オフする信号であることを特徴とする請求項１乃至３のいずれかに記載のＰＷＭ調光回路。   4. The minimum period setting signal is a signal synchronized with the PWM signal, and is a signal that is turned off for a certain period from the start of one cycle of the PWM signal. PWM dimming circuit.
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JP2013110060A (en) * 2011-11-24 2013-06-06 Panasonic Corp Led driving device, illuminating device and illumination apparatus
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