JP2009048908A

JP2009048908A - Protection circuit and lamp driving device

Info

Publication number: JP2009048908A
Application number: JP2007214890A
Authority: JP
Inventors: Takeo Sakamoto; 竹男坂本
Original assignee: Harison Toshiba Lighting Corp
Current assignee: Toshiba Lighting and Technology Corp
Priority date: 2007-08-21
Filing date: 2007-08-21
Publication date: 2009-03-05

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protection circuit in which judgement precision of lighting status of a lamp is improved by leaps and bounds and a lamp driving device having the protection circuit. <P>SOLUTION: The protection circuit has a first detection resistor R1 connected to an electrode on low voltage side of a first lamp 30a, a second detection resistor R2 which is connected to an electrode on low voltage side of a second lamp 30b and has a resistance value equal to or higher than that of the first detection resistor R1, and a second diode D2 which is connected between the electrode on low voltage side of the first lamp 30a and the electrode on low voltage side of the second lamp 30b and shuts off passage of electric current output from the second lamp 30b. A judgment circuit 402 compares a detection voltage obtained from the electric current flowing in a region connected to the electrode on the low voltage side of the first lamp 30a to which the second diode D2 is connected with a prescribed reference voltage, and based on the comparison result, judges lighting status of the first lamp 30a and the second lamp 30b. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、ランプの点灯状態に基づいて該ランプを駆動するランプ駆動装置を保護する保護回路と、該保護回路を備えたランプ駆動装置の技術に関する。 The present invention relates to a protection circuit that protects a lamp driving device that drives the lamp based on a lighting state of the lamp, and a technology of a lamp driving device that includes the protection circuit.

通常、パソコンや液晶テレビに使用される液晶表示装置は、並列に接続された複数のランプを使用したバックライトを備えると共に、各ランプを点灯駆動させるランプ駆動装置を備えている。 In general, a liquid crystal display device used for a personal computer or a liquid crystal television includes a backlight using a plurality of lamps connected in parallel, and a lamp driving device that drives each lamp to light.

そして、このランプ駆動装置には、ランプの破損やランプの電極に接続されたリード線の断線などに起因するランプの点灯不能により、ランプに電圧電流を供給する変圧回路の出力が無負荷状態となり、出力電圧は異常に上昇して、ランプ駆動装置のプリント基板箔間などで放電現象が発生し、アークにより周辺部品の発火や焼損を防止するため、各ランプに流れる電流から得られた検出電圧を用いて、ランプに供給する電流を制御してランプ駆動装置を保護する保護回路が備えられている。 In this lamp driving device, the output of the transformer circuit that supplies the voltage / current to the lamp becomes unloaded because the lamp cannot be turned on due to the breakage of the lamp or the disconnection of the lead wire connected to the electrode of the lamp. The detection voltage obtained from the current that flows through each lamp in order to prevent the discharge voltage between the printed circuit board foils of the lamp driving device, etc. Is used to control the current supplied to the lamp to protect the lamp driving device.

図３は、ランプ駆動装置が備える従来の保護回路の構成を示す構成図である。図３に示す保護回路４０は、並列接続された第１のランプ３０ａと第２のランプ３０ｂにそれぞれ流れる電流をそれぞれ検出する第１の検出抵抗Ｒ１と第２の検出抵抗Ｒ２を設けると共に、各ランプ３０ａ，３０ｂにそれぞれ対応する第１の判定回路４０２ａと第２の判定回路４０２ｂを備えている。図３に示すこのような保護回路を備える技術は、特許文献１に開示されている。 FIG. 3 is a configuration diagram illustrating a configuration of a conventional protection circuit included in the lamp driving device. The protection circuit 40 shown in FIG. 3 includes a first detection resistor R1 and a second detection resistor R2 that detect currents flowing in the first lamp 30a and the second lamp 30b connected in parallel, respectively, A first determination circuit 402a and a second determination circuit 402b corresponding to the lamps 30a and 30b are provided. A technique including such a protection circuit shown in FIG. 3 is disclosed in Patent Document 1.

第１の判定回路４０２ａは、第１のランプ３０ａに流れる電流から得られた検出電圧を所定の基準電圧とを比較して、この比較の結果に基づいて第１のランプ３０ａの点灯状態を判定する。この基準電圧は、第１のランプ３０ａから出力された電流ＩＬ１と第１の検出抵抗Ｒ１を乗算することで算出される。第２の判定回路４０２ｂについても同様である。 The first determination circuit 402a compares the detection voltage obtained from the current flowing through the first lamp 30a with a predetermined reference voltage, and determines the lighting state of the first lamp 30a based on the result of this comparison. To do. This reference voltage is calculated by multiplying the current IL1 output from the first lamp 30a by the first detection resistor R1. The same applies to the second determination circuit 402b.

例えば、第１のランプ３０ａが点灯状態の場合において、電流ＩＬ１が５［Ａ］、第１の検出抵抗Ｒ１の抵抗値が２［Ω］とすると、検出電圧は１０［Ｖ］となる。一方、点灯していない場合には、電流ＩＬ１が０［Ａ］なので、検出電圧は０［Ｖ］となる。すなわち、異なる点灯状態時における電圧差分量は明確なので、ランプの点灯状態を確実かつ容易に判定することができる。 For example, when the first lamp 30a is in the lighting state, if the current IL1 is 5 [A] and the resistance value of the first detection resistor R1 is 2 [Ω], the detection voltage is 10 [V]. On the other hand, when it is not lit, the current IL1 is 0 [A], so the detection voltage is 0 [V]. That is, since the voltage difference amount in different lighting states is clear, the lighting state of the lamp can be determined reliably and easily.

しかしながら、特許文献１の保護回路を備えたランプ駆動装置は、ランプの数量に比例して判定回路の数量の増加に繋がり、一般的に判定回路は汎用的に販売されている集積回路（ＩＣ：Integrated Circuit）を用い場合が多いため、数量の増加に伴いランプ駆動装置の製造コストが増加する問題が存在する。また、ランプ駆動装置自体が大型化するため、薄型でコンパクトなパソコンや液晶テレビの需要に対応できない問題も並存している。 However, the lamp driving device provided with the protection circuit of Patent Document 1 leads to an increase in the number of determination circuits in proportion to the number of lamps. Generally, the determination circuits are integrated circuits (IC: In many cases, there is a problem that the manufacturing cost of the lamp driving device increases as the quantity increases. In addition, since the lamp driving device itself is increased in size, there is a problem that the demand for thin and compact personal computers and liquid crystal televisions cannot be met.

上記の問題点を回避する方法として、特許文献２には、図４に示すように、１つの判定回路４０２を用いて各ランプ３０ａ，３０ｂの点灯状態を判定する技術が開示されている。図４に示す保護回路４０は、第１のランプ３０ａの低圧側の電極と第２のランプ３０ｂの低圧側の電極とを接続し、両ランプ３０ａ，３０ｂに流れる電流を検出する検出抵抗Ｒをその接続点に接続すると共に、両ランプ３０ａ，３０ｂに対応する１つの判定回路４０２を備えている。
特開２００２−６８０９号公報特開２００２−１４１１８６号公報 As a method for avoiding the above problem, Patent Document 2 discloses a technique for determining the lighting state of each lamp 30a, 30b using one determination circuit 402 as shown in FIG. The protection circuit 40 shown in FIG. 4 connects a low-voltage electrode of the first lamp 30a and a low-voltage electrode of the second lamp 30b, and has a detection resistor R for detecting the current flowing through both the lamps 30a and 30b. One determination circuit 402 corresponding to both the lamps 30a and 30b is provided while being connected to the connection point.
Japanese Patent Laid-Open No. 2002-6809 JP 2002-141186 A

しかしながら、一方のランプが点灯不能となった場合、変圧回路が各ランプに供給していた電流の負荷分布容量等の変動により電流の出力条件が変化し、点灯しているランプには定常時よりも過大な電流が流れるため、点灯状態と点灯不能状態とで得られる検出電圧の電圧差分量が非常に小さく、点灯状態を確実に判定できないという問題があった。 However, when one of the lamps cannot be lit, the current output conditions change due to fluctuations in the load distribution capacity of the current supplied to each lamp by the transformer circuit, and the lit lamps However, since an excessive current flows, there is a problem that the voltage difference amount of the detection voltage obtained between the lighting state and the lighting impossible state is very small, and the lighting state cannot be reliably determined.

本発明は、上記を鑑みてなされたものであり、ランプの点灯状態の判定精度を飛躍的に高める保護回路と、該保護回路を備えたランプ駆動装置を提供することを課題とする。 The present invention has been made in view of the above, and it is an object of the present invention to provide a protection circuit that dramatically increases the determination accuracy of the lighting state of the lamp and a lamp driving device including the protection circuit.

第１の本発明に係る保護回路は、第１のランプの低圧側の電極に接続された第１の抵抗と、第２のランプの低圧側の電極に接続され、前記第１の抵抗の抵抗値以上の抵抗値を有する第２の抵抗と、前記第１のランプの低圧側の電極と前記第２のランプの低圧側の電極との間に接続され、前記第２のランプから出力される電流の通過をオフするダイオードと、前記ダイオードが前記第１のランプの低圧側の電極に接続された領域に流れる電流から得られた検出電圧と所定の基準電圧とを比較し、当該比較の結果に基づいて前記第１のランプおよび前記第２のランプの点灯状態を判定する判定手段と、当該判定の結果に基づいて、前記第１のランプおよび前記第２のランプに供給する電流を制御する制御手段と、を有することを要旨とする。 The protection circuit according to the first aspect of the present invention includes a first resistor connected to the low-voltage side electrode of the first lamp, and a resistance of the first resistor connected to the low-voltage side electrode of the second lamp. A second resistor having a resistance value equal to or greater than a value, and connected between a low-pressure side electrode of the first lamp and a low-pressure side electrode of the second lamp, and output from the second lamp. A comparison is made between a diode that turns off the passage of current and a detection voltage obtained from a current flowing in a region where the diode is connected to the low-voltage side electrode of the first lamp and a predetermined reference voltage. Determining means for determining the lighting state of the first lamp and the second lamp based on the control circuit, and controlling the current supplied to the first lamp and the second lamp based on the result of the determination And a control means.

本発明にあっては、第１のランプの低圧側の電極に接続された第１の抵抗と、第２のランプの低圧側の電極に接続され、第１の抵抗の抵抗値以上の抵抗値を有する第２の抵抗と、第１のランプの低圧側の電極と第２のランプの低圧側の電極との間に接続され、第２のランプから出力される電流の通過をオフするダイオードとを有し、判定手段は、ダイオードが第１のランプの低圧側の電極に接続された領域に流れる電流から得られた検出電圧と所定の基準電圧とを比較し、比較の結果に基づいて第１のランプおよび第２のランプの点灯状態を判定するため、ランプの点灯状態の判定精度を飛躍的に高めた保護回路を提供することができる。 In the present invention, the first resistor connected to the low-voltage side electrode of the first lamp and the resistance value connected to the low-voltage side electrode of the second lamp and greater than or equal to the resistance value of the first resistor. And a diode that is connected between the low-voltage side electrode of the first lamp and the low-voltage side electrode of the second lamp and that turns off the passage of the current output from the second lamp. The determination means compares the detection voltage obtained from the current flowing through the region where the diode is connected to the low-voltage side electrode of the first lamp with a predetermined reference voltage, and determines the first voltage based on the comparison result. Since the lighting states of the first lamp and the second lamp are determined, it is possible to provide a protection circuit that dramatically increases the determination accuracy of the lighting state of the lamp.

第２の本発明に係るランプ駆動装置は、直流電源を交流に変換した交流電流を発振する発振手段と、前記交流電流を所定の電流に変圧し、並列接続された第１のランプと第２のランプに供給する変圧手段と、前記第１のランプの低圧側の電極に接続された第１の抵抗と、前記第２のランプの低圧側の電極に接続され、前記第１の抵抗の抵抗値以上の抵抗値を有する第２の抵抗と、前記第１のランプの低圧側の電極と前記第２のランプの低圧側の電極との間に接続され、前記第２のランプから出力される電流の通過をオフするダイオードと、前記ダイオードが前記第１のランプの低圧側の電極に接続された領域に流れる電流から得られた検出電圧と所定の基準電圧とを比較し、当該比較の結果に基づいて前記第１のランプおよび前記第２のランプの点灯状態を判定する判定手段と、当該判定の結果に基づいて、前記第１のランプおよび前記第２のランプに供給する電流を制御する制御手段と、を有することを要旨とする。 A lamp driving apparatus according to a second aspect of the present invention includes an oscillating means that oscillates an alternating current obtained by converting a direct current power source into an alternating current, a first lamp connected in parallel by transforming the alternating current into a predetermined current, Transformer means for supplying to the lamp of the first lamp, a first resistor connected to the low-voltage side electrode of the first lamp, and a resistance of the first resistor connected to the low-voltage side electrode of the second lamp A second resistor having a resistance value equal to or greater than a value, and connected between a low-pressure side electrode of the first lamp and a low-pressure side electrode of the second lamp, and output from the second lamp. A comparison is made between a diode that turns off the passage of current and a detection voltage obtained from a current flowing in a region where the diode is connected to the low-voltage side electrode of the first lamp and a predetermined reference voltage. Based on the first ramp and the second run Judging means for judging the lighting state of, based on the result of the determination, and summarized in that and a control means for controlling the current supplied to said first lamp and said second lamp.

本発明にあっては、第１のランプの低圧側の電極に接続された第１の抵抗と、第２のランプの低圧側の電極に接続され、第１の抵抗の抵抗値以上の抵抗値を有する第２の抵抗と、第１のランプの低圧側の電極と第２のランプの低圧側の電極との間に接続され、第２のランプから出力される電流の通過をオフするダイオードとを有し、判定手段は、ダイオードが第１のランプの低圧側の電極に接続された領域に流れる電流から得られた検出電圧と所定の基準電圧とを比較し、比較の結果に基づいて第１のランプおよび第２のランプの点灯状態を判定するため、ランプの点灯状態の判定精度を飛躍的に高めた保護回路を備えたランプ駆動装置を提供することができる。 In the present invention, the first resistor connected to the low-voltage side electrode of the first lamp and the resistance value connected to the low-voltage side electrode of the second lamp and greater than or equal to the resistance value of the first resistor. And a diode that is connected between the low-voltage side electrode of the first lamp and the low-voltage side electrode of the second lamp and that turns off the passage of the current output from the second lamp. The determination means compares the detection voltage obtained from the current flowing through the region where the diode is connected to the low-voltage side electrode of the first lamp with a predetermined reference voltage, and determines the first voltage based on the comparison result. In order to determine the lighting state of the first lamp and the second lamp, it is possible to provide a lamp driving device including a protection circuit that dramatically increases the determination accuracy of the lighting state of the lamp.

本発明によれば、ランプの点灯状態の判定精度を飛躍的に高める保護回路と、該保護回路を備えたランプ駆動装置を提供することができる。 ADVANTAGE OF THE INVENTION According to this invention, the protection circuit which raises the determination precision of the lighting state of a lamp dramatically, and a lamp drive device provided with this protection circuit can be provided.

以下、本発明の実施の形態について図面を用いて説明する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

図１は、本実施の形態に係る保護回路と、該保護回路を備えたランプ駆動装置の構成を示す構成図である。この保護回路４０は、第１のランプ３０ａの低圧側の電極に接続された第１の検出抵抗Ｒ１と、第２のランプ３０ｂの低圧側の電極に接続された第２の検出抵抗Ｒ２と、第１のランプ３０ａの低圧側の電極と第２のランプ３０ｂの低圧側の電極との間に接続され、第２のランプ３０ｂから出力される電流の通過をオフする第２のダイオードＤ２と、第２のダイオードＤ２が第１のランプ３０ａの低圧側の電極に接続された接続点と判定回路４０２との間に接続され、判定回路４０２から出力される電流の通過をオフする第１のダイオードＤ１と、第１のダイオードＤ１を介して流れる電流から得られた検出電圧に基づいて、ランプの点灯状態を判定する判定回路４０２と、判定結果に基づいて、各ランプに供給する電流を制御する制御回路４０１とを備えた構成である。 FIG. 1 is a configuration diagram illustrating a configuration of a protection circuit according to the present embodiment and a lamp driving device including the protection circuit. The protection circuit 40 includes a first detection resistor R1 connected to the low-voltage side electrode of the first lamp 30a, a second detection resistor R2 connected to the low-voltage side electrode of the second lamp 30b, A second diode D2 connected between the low-voltage side electrode of the first lamp 30a and the low-voltage side electrode of the second lamp 30b, and for turning off the current output from the second lamp 30b; The first diode which is connected between the connection point where the second diode D2 is connected to the low-voltage side electrode of the first lamp 30a and the determination circuit 402 and turns off the passage of the current output from the determination circuit 402 Based on D1 and a detection voltage obtained from the current flowing through the first diode D1, a determination circuit 402 that determines the lighting state of the lamp, and controls the current supplied to each lamp based on the determination result Control circuit 4 A configuration in which a 1 and.

そして、ランプ駆動装置１は、上述した構成を備える保護回路４０と、直流電源を交流に変換した交流電流を発振する発振回路１０と、交流電流を所定の電流に変圧し、並列接続された第１のランプ３０ａと第２のランプ３０ｂに供給する変圧回路２０とを備えた構成である。 The lamp driving device 1 includes a protection circuit 40 having the above-described configuration, an oscillation circuit 10 that oscillates an alternating current obtained by converting a direct-current power supply into an alternating current, and transforms the alternating current into a predetermined current and is connected in parallel. It is the structure provided with the voltage transformation circuit 20 supplied to the 1st lamp | ramp 30a and the 2nd lamp | ramp 30b.

第１の検出抵抗Ｒ１および第２の検出抵抗Ｒ２は、各ランプ３０ａ，３０ｂに接続されていない他端をグランドに接続している。そして、第２の検出抵抗Ｒ２は、第１の検出抵抗Ｒ１の抵抗値以上の抵抗値を備えている。 In the first detection resistor R1 and the second detection resistor R2, the other ends not connected to the lamps 30a and 30b are connected to the ground. The second detection resistor R2 has a resistance value equal to or greater than the resistance value of the first detection resistor R1.

判定回路４０２は、検出電圧と所定の基準電圧とを比較し、比較の結果に基づいて第１のランプおよび第２のランプの点灯状態を判定する。この所定の基準電圧とは、変圧回路２０が第１のランプ３０ａと第２のランプ３０ｂに供給する電流から得られた電圧値であってもよいし、他の電圧値であってもよい。 The determination circuit 402 compares the detection voltage with a predetermined reference voltage, and determines the lighting state of the first lamp and the second lamp based on the comparison result. The predetermined reference voltage may be a voltage value obtained from the current supplied from the transformer circuit 20 to the first lamp 30a and the second lamp 30b, or may be another voltage value.

次に、本実施の形態における保護回路４０の作用について説明する。なお、説明の都合上、第１のランプ３０ａの電極と第２のダイオードＤ２とが接続された領域を第１の接続点Ｓ１と称し、第２のランプ３０ｂの電極と第２のダイオードＤ２とが接続された領域を第２の接続点Ｓ２と称する。また、第１のランプ３０ａに流れる電流をＩＬ１と称し、第２のランプ３０ｂに流れる電流をＩＬ２と称する。なお、電流ＩＬ１と電流ＩＬ２は、各ランプ３０ａ，３０ｂから放射される輝度を均等にするため、同じ電流値となるよう変圧回路２０により調整されている。 Next, the operation of the protection circuit 40 in the present embodiment will be described. For convenience of explanation, a region where the electrode of the first lamp 30a and the second diode D2 are connected is referred to as a first connection point S1, and the electrode of the second lamp 30b and the second diode D2 are connected to each other. The region where is connected is referred to as a second connection point S2. The current flowing through the first lamp 30a is referred to as IL1, and the current flowing through the second lamp 30b is referred to as IL2. The current IL1 and the current IL2 are adjusted by the transformer circuit 20 so as to have the same current value in order to equalize the luminance radiated from the lamps 30a and 30b.

第１の接続点Ｓ１における検出電圧Ｅ１は、第１のランプ３０ａに第１の検出抵抗Ｒ１が接続されていることから、式（１）により得ることができる。 The detection voltage E1 at the first connection point S1 can be obtained by the expression (1) because the first detection resistor R1 is connected to the first lamp 30a.

Ｅ１＝ＩＬ１×Ｒ１・・・式（１）
第２の接続点Ｓ２における検出電圧Ｅ２についても同様に、第２のランプ３０ｂに第２の検出抵抗Ｒ２が接続されていることから、式（２）により得ることができる。 E1 = IL1 × R1 Formula (1)
Similarly, the detection voltage E2 at the second connection point S2 can be obtained by the equation (2) because the second detection resistor R2 is connected to the second lamp 30b.

Ｅ２＝ＩＬ２×Ｒ２・・・式（２）
なお、第２のダイオードＤ２の存在により、第１のランプ３０ａから第２の検出抵抗Ｒ２に流れる電流の通路が存在するが、前述したように電流ＩＬ１と電流ＩＬ２の電流値が同じであり、第２の検出抵抗Ｒ２の抵抗値は第１の検出抵抗Ｒ１の抵抗値以上なので、Ｅ１≦Ｅ２の関係が成立し、電流ＩＬ１は第１の接続点Ｓ１において分流することはない。すなわち、検出電圧Ｅ２は、式（２）で示すように電流ＩＬ２と第２の検出抵抗Ｒ２から得ることができる。 E2 = IL2 × R2 Formula (2)
Note that, due to the presence of the second diode D2, there is a path of current flowing from the first lamp 30a to the second detection resistor R2, but as described above, the current values of the current IL1 and the current IL2 are the same, Since the resistance value of the second detection resistor R2 is equal to or greater than the resistance value of the first detection resistor R1, the relationship E1 ≦ E2 is established, and the current IL1 is not shunted at the first connection point S1. That is, the detection voltage E2 can be obtained from the current IL2 and the second detection resistor R2 as shown by the equation (2).

ここで、第１のランプ３０ａと第２のランプ３０ｂが共に点灯している場合、判定回路４０２で得られる検出電圧は、第２のダイオードＤ２により電流ＩＬ２が第１の検出抵抗Ｒ１に流れることはないため、式（１）で示すように、電流ＩＬ１と第１の検出抵抗Ｒ１から得ることができる。例えば、電流ＩＬ１が５［Ａ］、第１の検出抵抗Ｒ１が１０［Ω］の場合、判定回路で得られる検出電圧は５０［Ｖ］となる。 Here, when both the first lamp 30a and the second lamp 30b are lit, the detection voltage obtained by the determination circuit 402 is that the current IL2 flows to the first detection resistor R1 by the second diode D2. Therefore, as shown by the equation (1), it can be obtained from the current IL1 and the first detection resistor R1. For example, when the current IL1 is 5 [A] and the first detection resistor R1 is 10 [Ω], the detection voltage obtained by the determination circuit is 50 [V].

また、第１のランプ３０ａが点灯不能状態になった場合、判定回路４０２で得られる検出電圧は、第２のダイオードＤ２により電流ＩＬ２が第１の検出抵抗Ｒ１に流れることはなく、且つ、電流ＩＬ１が０［Ｖ］となるため、０［Ｖ］となる。 In addition, when the first lamp 30a is in an unlightable state, the detection voltage obtained by the determination circuit 402 is such that the current IL2 does not flow to the first detection resistor R1 by the second diode D2, and the current Since IL1 is 0 [V], it is 0 [V].

更に、第２のランプ３０ｂが点灯不能状態になった場合、電流ＩＬ２が０［Ｖ］となるため、第２の接続点Ｓ２における検出電圧Ｅ２は０［Ｖ］となり、Ｅ１＞Ｅ２の関係が成立し、電流ＩＬ１は第１の接続点Ｓ１において分流して第２の検出抵抗Ｒ２に流れることになる。したがって、判定回路４０２で得られる検出電圧は、電流ＩＬ１と第１の検出抵抗Ｒ１および第２の検出抵抗Ｒ２を並列接続する合成抵抗Ｒ’との関係から得ることができる。すなわち、合成抵抗Ｒ’は、式（３）により得ることができる。 In addition, when the second lamp 30b is in an unlightable state, the current IL2 is 0 [V], so the detection voltage E2 at the second connection point S2 is 0 [V], and the relationship of E1> E2 is established. The current IL1 is diverted at the first connection point S1 and flows to the second detection resistor R2. Therefore, the detection voltage obtained by the determination circuit 402 can be obtained from the relationship between the current IL1 and the combined resistor R ′ that connects the first detection resistor R1 and the second detection resistor R2 in parallel. That is, the combined resistance R ′ can be obtained by the equation (3).

Ｒ’＝（Ｒ１×Ｒ２）／（Ｒ１＋Ｒ２）・・・式（３）
例えば、電流ＩＬ１が５［Ａ］、第１の検出抵抗Ｒ１が１０［Ω］、第２の検出抵抗が２０［Ω］の場合、合成抵抗Ｒ’は約６．６６［Ω］となるため、判定回路で得られる検出電圧は３３［Ｖ］となる。 R ′ = (R1 × R2) / (R1 + R2) (3)
For example, when the current IL1 is 5 [A], the first detection resistor R1 is 10 [Ω], and the second detection resistor is 20 [Ω], the combined resistance R ′ is about 6.66 [Ω]. The detection voltage obtained by the determination circuit is 33 [V].

最後に、第１のランプ３０ａと第２のランプ３０ｂが共に点灯不能状態となった場合、判定回路４０２で得られる検出電圧は、電流ＩＬ１と電流ＩＬ２は０［Ｖ］となるため、０［Ｖ］となる。 Finally, when both the first lamp 30a and the second lamp 30b are in an unlightable state, the detection voltage obtained by the determination circuit 402 is 0 [V] because the current IL1 and the current IL2 are 0 [V]. V].

従って、判定回路４０２は、第１のランプ３０ａと第２のランプ３０ｂが共に点灯している場合に得られる検出電圧（５０［Ｖ］）に対して、少なくともいずれか一方が点灯不能状態になった場合に得られる合成抵抗に基づく検出電圧（３３［Ｖ］）もしくは０［Ｖ］の検出電圧を用いて判定するため、点灯状態と点灯不能状態とで得られる検出電圧の電圧差分量を大きくすることができ、点灯状態を確実に判定することができる。 Accordingly, at least one of the determination circuits 402 is in an unlightable state with respect to the detection voltage (50 [V]) obtained when both the first lamp 30a and the second lamp 30b are lit. Since the determination is made using the detection voltage (33 [V]) or 0 [V] based on the combined resistance obtained in this case, the voltage difference amount of the detection voltage obtained between the lighting state and the lighting impossible state is increased. The lighting state can be reliably determined.

そして、判定回路４０２は、検出電圧と比較する基準電圧を例えば４０［Ｖ］とすることで、第１のランプ３０ａと第２のランプ３０ｂの点灯状態を判定することが可能となる。判定の結果、検出電圧が基準電圧よりも小さい場合には、少なくとも１つのランプが点灯不能と判断できるので、制御回路４０１は、交流電流の発振をオフするように発振回路１０を制御する。一方、検出電圧が基準電圧よりも大きい場合には、全てのランプが点灯していると判断できるので、制御回路４０１は、何も制御することはない。なお、制御回路４０１は、発振回路１０から発振する交流電流のオンオフを制御するだけではなく、変圧回路２０での変圧幅を制御することも可能である。 And the determination circuit 402 can determine the lighting state of the 1st lamp | ramp 30a and the 2nd lamp | ramp 30b by setting the reference voltage compared with detection voltage to 40 [V], for example. As a result of the determination, if the detected voltage is smaller than the reference voltage, it can be determined that at least one lamp cannot be lit, so the control circuit 401 controls the oscillation circuit 10 to turn off the oscillation of the alternating current. On the other hand, if the detected voltage is higher than the reference voltage, it can be determined that all the lamps are lit, and the control circuit 401 does not control anything. The control circuit 401 can not only control on / off of the alternating current oscillated from the oscillation circuit 10, but can also control the transformation width in the transformation circuit 20.

なお、第１の検出抵抗Ｒ１の抵抗値に対する第２の検出抵抗Ｒ２の抵抗値の比率を大きくすることで、合成抵抗Ｒ’の値が０［Ｖ］に近づくため、更に容易に点灯状態を判定することができることは言うまでもない。 In addition, since the value of the combined resistance R ′ approaches 0 [V] by increasing the ratio of the resistance value of the second detection resistor R2 to the resistance value of the first detection resistor R1, the lighting state can be more easily changed. Needless to say, it can be judged.

本実施の形態では、２つのランプを用いた場合について説明したが、第２のランプ３０ｂと、第２のランプ３０ｂの低電圧側の電極に接続された第２の検出抵抗Ｒ２と、第２のランプから出力される電流の通過をオフする第２のダイオードＤ２とを有する構成を、図２の（ａ）、（ｂ）に示すように、更に複数備えた場合であっても得られる効果に差異はない。 In the present embodiment, the case where two lamps are used has been described. However, the second lamp 30b, the second detection resistor R2 connected to the low-voltage side electrode of the second lamp 30b, and the second The effect obtained even when a plurality of configurations having the second diode D2 that turns off the passage of the current output from the lamp are provided as shown in FIGS. There is no difference.

最後に、本実施の形態で説明した保護回路と、この保護回路を備えたランプ駆動装置は、液晶モニター、テレビ、直下式バックライトなどに利用することが可能である。 Finally, the protection circuit described in this embodiment and the lamp driving device including the protection circuit can be used for a liquid crystal monitor, a television, a direct backlight, and the like.

本実施の形態によれば、第１のランプ３０ａの低圧側の電極に接続された第１の検出抵抗Ｒ１と、第２のランプ３０ｂの低圧側の電極に接続され、第１の検出抵抗Ｒ１の抵抗値以上の抵抗値を有する第２の検出抵抗Ｒ２と、第１のランプ３０ａの低圧側の電極と第２のランプ３０ｂの低圧側の電極との間に接続され、第２のランプ３０ｂから出力される電流の通過をオフする第２のダイオードＤ２とを有し、判定回路４０２は、第２のダイオードＤ２が第１のランプ３０ａの低圧側の電極に接続された領域に流れる電流から得られた検出電圧と所定の基準電圧とを比較し、比較の結果に基づいて第１のランプ３０ａおよび第２のランプ３０ｂの点灯状態を判定するので、ランプの点灯状態の判定精度を飛躍的に高めた保護回路、及び該保護回路を備えたランプ駆動装置を提供することができる。 According to the present embodiment, the first detection resistor R1 connected to the low voltage side electrode of the first lamp 30a and the low voltage side electrode of the second lamp 30b are connected to the first detection resistor R1. The second detection resistor R2 having a resistance value equal to or greater than the resistance value of the first lamp 30a is connected between the low voltage side electrode of the first lamp 30a and the low voltage side electrode of the second lamp 30b, and the second lamp 30b. And the second circuit D2 that turns off the passage of the current output from the determination circuit 402. The determination circuit 402 is based on the current flowing in the region where the second diode D2 is connected to the low-voltage side electrode of the first lamp 30a. The obtained detection voltage is compared with a predetermined reference voltage, and the lighting state of the first lamp 30a and the second lamp 30b is determined based on the comparison result, so that the determination accuracy of the lighting state of the lamp is dramatically improved. And a protective circuit It is possible to provide a lamp driving device having a.

本実施の形態に係る保護回路と、該保護回路を備えたランプ駆動装置の構成を示す構成図である。It is a block diagram which shows the structure of the protection circuit which concerns on this Embodiment, and the lamp drive device provided with this protection circuit. 保護回路の他の構成を示す構成図である。It is a block diagram which shows the other structure of a protection circuit. ランプ駆動装置が備える従来の保護回路の構成を示す構成図である。It is a block diagram which shows the structure of the conventional protection circuit with which a lamp drive device is provided. ランプ駆動装置が備える従来の保護回路の他の構成を示す構成図である。It is a block diagram which shows the other structure of the conventional protection circuit with which a lamp drive device is provided.

Explanation of symbols

Ｒ１…第１の検出抵抗
Ｒ２…第２の検出抵抗
１…ランプ駆動装置
１０…発振回路
２０…変圧回路
３０ａ…第１のランプ
３０ｂ…第２のランプ
４０…保護回路
４０１…制御回路
４０２…判定回路
４０２ａ…第１の判定回路
４０２ｂ…第２の判定回路 R1 ... 1st detection resistance R2 ... 2nd detection resistance 1 ... Lamp drive device 10 ... Oscillation circuit 20 ... Transformer circuit 30a ... 1st lamp 30b ... 2nd lamp 40 ... Protection circuit 401 ... Control circuit 402 ... Determination Circuit 402a: first determination circuit 402b: second determination circuit

Claims

A first resistor connected to the low pressure side electrode of the first lamp;
A second resistor connected to the low voltage side electrode of the second lamp and having a resistance value equal to or greater than the resistance value of the first resistor;
A diode connected between a low-voltage side electrode of the first lamp and a low-voltage side electrode of the second lamp, and turning off a current output from the second lamp;
The diode compares the detection voltage obtained from the current flowing in the region where the diode is connected to the low-voltage side electrode of the first lamp with a predetermined reference voltage, and based on the comparison result, the first lamp and Determining means for determining a lighting state of the second lamp;
Control means for controlling the current supplied to the first lamp and the second lamp based on the result of the determination;
A protection circuit comprising:

An oscillation means for oscillating an alternating current obtained by converting a direct current power source into an alternating current;
Transform means for transforming the alternating current into a predetermined current and supplying the first lamp and the second lamp connected in parallel;
A first resistor connected to an electrode on the low pressure side of the first lamp;
A second resistor connected to the low voltage side electrode of the second lamp and having a resistance value greater than or equal to the resistance value of the first resistor;
A diode connected between a low-voltage side electrode of the first lamp and a low-voltage side electrode of the second lamp, and turning off a current output from the second lamp;
The diode compares the detection voltage obtained from the current flowing in the region where the diode is connected to the low-voltage side electrode of the first lamp with a predetermined reference voltage, and based on the comparison result, the first lamp and Determining means for determining a lighting state of the second lamp;
Control means for controlling the current supplied to the first lamp and the second lamp based on the result of the determination;
A lamp driving device comprising: