JP3834222B2 - Voltage detection circuit for resistor for current detection - Google Patents

Description

【数２】

Ｖｉｐ_ｐおよびΔＶは、波形表示装置などにより求められるので、これにより電流検出用抵抗器の実効的インダクタンスを算定できる。
【００２７】
図８及び図９は、上記測定装置および配線パターンによる低抵抗器の実効的インダクタンスＬｅの実測例を示す。図８は、抵抗値２ｍΩの電流経路が直線的で、且つ実装されるプリント基板上から電流経路までの距離が短い実効的インダクタンスを極力小さくする構造を持った抵抗器を対象としたものである。抵抗器自体の自己インダクタンスはあるが、電圧検出端子配線との相互インダクタンスがそれを打ち消すため、（a）に示すように、電流波形と電圧波形は略一致している。そして、（ｂ）に示すように、１０個のサンプルを測定した結果、実効的インダクタンスＬｅは、殆どゼロであることが分かる。これに対して、図９は、抵抗値３ｍΩで電流経路が垂直方向のトリミングカットにより曲げられた低抵抗器の測定結果を示す。（ａ）に示すように、鋸歯状波電流波形に対して、大きな誤差電圧が発生していることが分かる。この場合には、（ｂ）に示すように、この低抵抗器においては、実効的インダクタンスＬｅが０．９ｎＨ程度存在していることが分かる。
【００２８】
図９に示すように、実効的インダクタンスＬｅが大きいと、低抵抗器の合成インピーダンスが大きくなり、これにより検出電圧に大きな誤差電圧が発生することは上述した通りである。従って、この電圧検出波形に基づいてＤＣ／ＤＣコンバータの制御を行うと、その動作に支障をきたすことになる。従って、電圧検出端子配線に適当なフィルタ回路を挿入し、実効的インダクタンスによる誤差電圧波形をなくし、抵抗成分のみによる電圧波形が出力されることが望ましい。図１０は、誤差電圧波形を除去するフィルタとして、波形補正用積分器４０を設けたものである。この積分器は、抵抗ＲｉとキャパシタンスＣｉとからなり、
Ｃｉ×Ｒｉ＝Ｌｅ／Ｒ
の関係を有していることを特徴とする。
【００２９】
次に、上記フィルタ回路により、誤差電圧波形を取り除くことができる原理について説明する。図１１は、抵抗器及び電圧検出端子配線取出部４１と積分器（波形成型用フィルタ）４０の等価回路図である。積分器入力（ａ，ａ′）から右側を負荷側とし、左側を信号源とした場合に、信号源インピーダンスに対して負荷インピーダンスは一般に非常に高くなる。従って、図１２に示すようにａ，ａ′の左側を出力電圧が
Ｒ×Ｉ＋Ｌｅ×ｄＩ／ｄｔ
の電圧を発生する信号電圧源と見なすことができる。従って、図１２の下記に述べる計算に従って、積分回路（フィルタ）の出力Ｖoutは抵抗器の抵抗値Ｒと電流Ｉの積に比例した電圧出力が取り出せることが分かる。
【００３０】
図１３は、上記電流検出用抵抗器の電圧検出回路を採用したスイッチング電源回路の構成例を示す。このスイッチング電源回路は、ＤＣ／ＤＣコンバータであり、例えばＤＣ＋１２Ｖの直流電源３１から直流負荷３６にＤＣ＋１Ｖ．電流数十Ａの直流電力を供給する。このスイッチング電源回路には、電源検出用抵抗器１１が搭載され、スイッチング素子３２，３３とチョークコイル３４とコンデンサ３５とから構成される鋸歯状波発生回路の電流を検出するようになっている。即ち、スイッチング素子３２，３３を交互にオン・オフすることで、チョークコイル３４とコンデンサ３５とからなる積分回路に直線性に優れた鋸歯状波が形成され、コンデンサ３５により平滑化された低電圧の直流電圧が直流負荷３６に供給され、直流負荷の抵抗値を調整することで、上述したように数十Ａの直流電流が流れる。
【００３１】
この電流検出用抵抗器１１の両端から電圧検出端子配線１６が取り出され、上述した抵抗ＲｉとキャパシタンスＣｉとからなる積分回路４０の出力が差動増幅器またはコンパレータからなる電圧検出器１２に取り込まれる。ここで積分回路の定数は、
Ｒｉ×Ｃｉ＝Ｌｅ／Ｒ
からなる関係を満足するので、実効的インダクタンスＬｅが存在する場合でも、これによる誤差電圧を上述したように打ち消すことができる。従って、電圧検出器１２の出力には、抵抗器１１の抵抗値Ｒに流れる電流に正確に比例した電圧が取り出され、フィードバック信号としてスイッチング素子制御回路４３に送られる。そして、正しい検出電流に基づいてスイッチング素子に制御信号が送られる。これにより、スイッチング電源回路において正しい検出電流に基づいて、その動作を制御することができる。
【００３２】
図１４は、電流検出用抵抗器としてチョークコイルの一部を用いた例を示す。スイッチング電源回路には、上述したように鋸歯状波発生用のチョークコイル３４が用いられ、この一部を電流検出用の抵抗器として用いることができる。電流端子１，２間にはチョークコイル電流Ｉが流れ、タップで接続されたコイル端子ａ，ａ′間に抵抗器両端に相当する電圧が取り出される。端子ａ，ａ′は、電圧検出端子配線を構成していて、抵抗ＲｉとキャパシタンスＣｉとからなる積分回路４０を介して電圧端子１，２から抵抗器両端に生じる電圧が出力される。
【００３３】
ここで、図中破線で示すコイルは上述したように電圧取出配線の一部を構成するが、電流が流れるコイルと同様に巻回されているので、これにより実線で示すコイルの自己インダクタンスと略等しい相互インダクタンスが形成される。しかしながら、端子ａ，ａ′から見た実効的インダクタンスが存在しても、上述したようにＲｉ，Ｃｉからなる積分回路４０をフィルタとして用いることで、実効的インダクタンスによる誤差電圧成分が打ち消される。また、電圧端子１，２間の検出電圧は、電流端子１，２間を流れる電流と相似となる。このため、抵抗Ｒｉの抵抗温度係数は、抵抗Ｒの抵抗温度係数に対して逆符号で大きさが等しいことが望ましい。なお、積分回路４０の抵抗Ｒｉは、チョークコイルにおける破線で示す巻線の電気抵抗を利用してもよい。
【００３４】
なお、端子ａ，ａ′から左側を見た抵抗Ｒは、タップからｂ点までのコイルの直流抵抗分であり、実効的インダクタンスＬｅは、上記コイルの直流抵抗分の有する自己インダクタンスから、その自己インダクタンス部分と磁束が錯交する破線部の相互インダクタンスを差し引いたものとなる。このようにＤＣ／ＤＣコンバータに用いられるチョークコイルの一部を電流検出用の抵抗体として用いることで、専用の電流検出用抵抗器が不要となり、低コスト化および基板サイズの低減を図れる。
【００３５】
なお、これらの実施形態における電圧検出端子配線は、図３に示す実効的インダクタンスＬｅが殆どゼロとなるパターンを採用することが好ましいが、例えば図４に示すパターン自体が実効的インダクタンスＬｅを有するものであっても、積分回路４０によるフィルタ作用でこれを打ち消すことができるので、このようなパターンを用いることも可能である。
【００３６】
なお、本発明の電流検出用抵抗器の電圧検出回路は、上述の図示例にのみ限定されるものではなく、本発明の要旨を逸脱しない範囲内において種々変更を加え得ることは勿論である。
【００３７】
【発明の効果】
上述した本発明によれば、電流検出用抵抗器及びその測定系が実効的インダクタンスを有する場合においても、電圧検出回路に所定の関係の積分回路を配置することで、実効的インダクタンスに起因する誤差電圧を取り除くことができる。従って、電源スイッチング回路等に適用して、電流検出用抵抗器の寄生インダクタンスに起因する誤作動を防止することが可能となる。
【図面の簡単な説明】
【図１】（ａ）は電流検出用抵抗器の被測定電流の検出回路例を示す図であり、（ｂ）は電流検出用抵抗器を流れる鋸歯状波電流波形と、電圧検出端子配線から取り出される電圧波形を例示的に示す図である。
【図２】被測定抵抗器と電圧検出端子配線の等価回路図である。
【図３】電圧検出端子配線の構成例を示すパターン図である。
【図４】図３に対する比較例としての電圧検出端子配線の他の構成例を示すパターン図である。
【図５】本発明の実施形態の電流検出用抵抗器の実効的インダクタンスの測定装置を示すブロック図である。
【図６】図５の具体的回路例を示す回路図である。
【図７】実効的インダクタンスＬｅの算定のための電流及び電圧の波形図である。
【図８】実効的インダクタンスが殆ど存在していない低抵抗器における、（ａ）は電圧及び電流波形例を示し、（ｂ）は実効的インダクタンス値の測定例を示す。
【図９】実効的インダクタンスが存在する低抵抗器における、（ａ）は電圧及び電流波形例を示し、（ｂ）は実効的インダクタンス値の測定例を示す。
【図１０】本発明の実施形態の電圧検出回路を示す回路図である。
【図１１】図１０の回路の動作原理を示す等価回路図である。
【図１２】図１０の回路を４端子回路としてみた場合の等価回路図と、その動作原理の説明に付する計算式とを示している。
【図１３】本発明の実施形態のスイッチング電源回路の構成例を示す回路図である。
【図１４】電流検出用抵抗器としてチョークコイルの一部分を用いた場合の回路図である。
【符号の説明】
１１ 被測定抵抗器
１２ 電圧検出器
１３，１４ ランド
１５ ビア
１６ 電圧検出端子配線
２１ 鋸歯状波電流発生装置
２２ 配線
２３ 電流検出器
２４ 低抵抗器の実装基板
２５ リッツ線（より線）
２６ 波形表示装置
３１ 直流電源
３２，３３ スイッチング素子
３４ チョークコイル
３５ コンデンサ
３６ 直流負荷
４０ 積分回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a voltage detection circuit for a current detection resistor suitable for use in a current detection circuit of a switching power supply circuit such as a DC / DC converter.
[0002]
[Prior art]
In recent years, in electronic devices such as personal computers, switching power supplies such as DC / DC converters have been used in their power supply circuits in accordance with the increase in voltage and current of CPU chips. This switching power supply uses a current detection resistor having a very small resistance value of several mΩ or less, is used in a frequency band of several tens to several hundred kHz, and a sawtooth wave current of several A to several tens of A flows. The magnitude of the current to be measured is detected from the voltage generated across the resistor. In the current detection resistor for such applications, the resistance value needs to be as low as possible, and the parasitic inductance of the resistor and the measurement system is preferably as low as possible. This is because the resistance value of the resistor itself is small and the frequency is relatively high, so even if the inductance is as small as 1 nH, the combined impedance seen at both ends of the resistor becomes large, resulting in a voltage detection error.
[0003]
In order to evaluate the parasitic inductance that affects the detection error of the current detection resistor, conventionally, a single current detection resistor is mounted on a test fixture or the like to measure impedance. However, the inductance value calculated from the impedance thus measured does not make much sense in the design of a current detection circuit such as a DC / DC converter that is actually used. This is due to the following reason.
[0004]
Usually, the inductance of the current detection resistor is very small, about 1 nH or less, and can be measured only by an impedance analyzer or the like that uses a frequency on the order of several hundred MHz to GHz. However, the current detection resistor is actually used in a frequency band of about 10 MHz or less. The skin effect, etc., appears prominently at high frequencies, so the inductance measured at a high frequency far from the actual usage state is meaningless, unlike the inductance in the actual usage state of the current detection resistor. is there.
[0005]
Further, as described above, a current of several A to several tens of A flows through a current detection resistor of a switching power supply such as a DC / DC converter. Even if the resistance value is low, the resistor generates a large Joule heat due to a large current. This heat changes the resistivity in the resistor and changes the current path, so that the inductance is a function of the passing current. A conventional measuring instrument such as an impedance analyzer cannot handle such a large current. Therefore, there is a problem that the inductance measured by the conventional method is different from the inductance in the actual use state of the current detection resistor.
[0006]
Moreover, although the impedance between terminals can be measured with a general test fixture, the inductance measured in this way is different from the inductance in the actual use state. That is, in the actual use state, an error voltage appears for a sawtooth current in a frequency band of several tens to several hundreds kHz. In this frequency band, the skin effect and the influence of parasitic capacitance appear greatly, and therefore the impedance is different from the impedance measured by an ordinary impedance analyzer or the like. Therefore, this is not an amount that reflects the actual usage state.
[0007]
[Problems to be solved by the invention]
For the above reasons, the inductance value measured by the conventional measuring method is only a guideline for checking whether the self-inductance of the resistor itself is large or small, and directly detects the current of a DC / DC converter or the like. It cannot be applied to circuit design. Further, as described above, since a detection error in current detection occurs due to parasitic inductance, a resistor mounting structure capable of minimizing this effect has been desired.
[0008]
The present invention has been made in view of the above circumstances, and since a detection error of a current to be measured occurs due to parasitic inductance of a low resistor in a switching power supply or the like, a current detection resistor capable of minimizing this influence. An object of the present invention is to provide a voltage detection circuit.
[0009]
[Means for Solving the Problems]
The voltage detection circuit of the current detection resistor according to the present invention is connected to both ends of the current detection resistor. On board In a voltage detection circuit for a current detection resistor, comprising: a pair of lands; and a voltage detection terminal wiring for supplying a current to be measured from the lands to the resistor and detecting a voltage generated at both ends of the resistor. The voltage detection terminal wiring is Both end electrodes of the current detection resistor are fixed Said On board A pair of lands From the horizontal between the lands arranged immediately below the resistor Pulled to the center along the central axis, between the two lands vertical Bend in the direction perpendicular to the central axis, One side is connected to the back pattern with a via and folded, and is arranged parallel to the front and back surfaces of the substrate along the vertical central axis, The voltage detection terminal wiring includes an integrator composed of a resistor (Ri) and a capacitance (Ci), and the integrator is viewed from the resistor (R) of the resistor and the voltage detection terminal wiring side of the resistor. For effective inductance (Le),
Ci × Ri = Le / R
The effective inductance (Le) supplies a sawtooth current to the current detection resistor, detects the current, detects the voltage generated at both ends, and responds to the change in the current. It is characterized in that it is calculated from the change in the voltage applied.
[0010]
According to the present invention, the sawtooth current is supplied to the resistor, the current is detected, and the voltage generated by the current is detected by being coupled to both ends of the resistor. From the change and the corresponding change in the voltage, the effective inductance (Le) of the resistor can be calculated. And for the resistance (R) of the resistor and the effective inductance (Le) of the resistor,
Ci × Ri = Le / R
By disposing an integrator having the following relationship in the voltage detection circuit of the resistor, an output in which the detection error due to the parasitic inductance of the low resistor is canceled can be taken out. Therefore, even if a low resistor having a parasitic inductance is used, a current detection circuit such as a switching power supply circuit that is not affected by the error output can be manufactured.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0012]
FIG. 1A shows an example of a circuit for detecting a current to be measured of a current detection resistor. Both ends (electrodes) of the current detection resistor 11 are fixed to the lands 13 and 14, and the current I to be measured is passed through the resistor 11. Then, by extracting the potential difference (voltage) from the voltage extraction portion (voltage detection terminal) of the land with both ends of the resistor fixed, the current and voltage are in a proportional relationship with respect to the known resistance value. Detect the size of. When detecting the measured current I, ideally, the potential difference VAB extracted from between the points A and B in FIG. 1 should simply be the product of the resistance value R of the resistor and the measured current value I. . However, since the parasitic inductance L of the resistor actually generates a voltage L × (dI / dt) corresponding to the time change of the current I to be measured, this voltage becomes a detection error. That is, as shown in FIG. 1B, a sawtooth wave current indicated by a broken line flows in the resistor 11, but a voltage change ΔV occurs at the current waveform top D.
[0013]
The voltage appearing on the voltage detection terminal wirings 16a and 16b is led to the voltage comparator or voltage amplifier 12 as shown in FIG. 1A, and the voltage is detected. However, since the resistor has the self-inductance L as described above, and the lead pattern (voltage detection terminal wiring pattern) and the current I flowing through the measured current path are magnetically coupled, the actual potential difference VAB is ,
V _AB = R * I + L * (dI / dt) -M * (dI / dt)
It becomes.
[0014]
Here, M is a mutual inductance shown in the equivalent circuit of FIG. Since the current flowing to the voltage comparator or voltage amplifier 12 is almost negligible with respect to the measured current I, it is not added to the above equation. LM is an effective inductance that gives an error in an actual current detection resistor, and when expressed as Le in the sense of effective inductance,
Le = LM
V _AB = R * I + Le * (dI / dt)
And become easy. Le × (dI / dt) is the actual detection error voltage ΔV.
[0015]
In the measurement using an impedance analyzer or the like, only the self-inductance L or the impedance viewed from the voltage detection terminal can be measured. From the impedance viewed from the voltage detection terminal, the effective inductance Le cannot be calculated for the following reason.
(1) The self-impedance of the voltage detection terminal wiring itself is included.
(2) The inductance of the current detection resistor varies depending on the current value. This is because high Joule heat is generated inside the resistor because the energization current in the actual use state ranges from several to several tens of A. When the inside of the resistor generates heat, the resistance value changes according to the resistance temperature coefficient of the substance constituting the resistor, and the current path is changed. Since both the self-inductance L and the mutual inductance M have a shape-dependent property, when the current path changes, the self-inductance L and the mutual inductance M change accordingly. In addition, the same large current as that of the resistor cannot flow through the voltage detection terminal wiring physically.
(3) A resistor for detecting current is generally used in a frequency band of several tens to several hundreds kHz. The effective inductance Le is a very small value of several nH or less. When trying to measure such a value with a conventional measuring instrument such as an impedance analyzer, an AC voltage / current with a frequency of several tens to several hundreds of MHz must be used. It becomes difficult.
[0016]
FIG. 3 shows a preferred embodiment of the voltage detection terminal wiring for extracting the voltage generated across the resistor. Both end electrodes of the current detection resistor 11 are fixed to the lands 13 and 14, and a voltage detection terminal wiring 16 for voltage extraction is drawn from the lands 13 and 14. The effective inductance Le is determined by the structure of the current detection resistor and the voltage detection terminal wiring pattern on which it is mounted. Therefore, a pattern as shown in FIG. 3 in which the mutual inductance is subtracted from the self-inductance and the effective inductance Le is almost zero is preferable. The reason is as follows.
[0017]
The voltage detection terminal wiring 16 for voltage measurement is led out to the center along the horizontal central axis (the central axis of both lands) along the current of the resistor 11 (indicated by B and B 'in the figure), and between the two lands. After bending in the direction perpendicular to the central axis (vertical central axis) (indicated by A and A 'in the figure), one side is connected to the back pattern by the via 15 and folded, and parallel to the front and back surfaces of the substrate along the vertical central axis Is arranged. That is, the wiring pattern A passing only through the substrate surface of the voltage detection terminal wiring and the wiring pattern A ′ drawn to the back surface via the via 15 are overlapped on the front and back surfaces with the insulating layer of the substrate interposed therebetween in the figure. Is guided in the vertical direction. By superimposing the wiring patterns in this way, the current flowing through the resistor 11 and the magnetic flux of the current flowing through the wiring pattern do not interlink in the loop formed by the voltage detection terminal wiring 16 composed of both wiring patterns. The inductance M is not affected by the length of the lead pattern. The voltage from both voltage detection terminals is pulled out to a position where the influence of the magnetic flux generated by the current flowing through the resistor and the energization pattern is sufficiently reduced, and then connected to a litz wire (stranded wire) or the like. Is detected by the voltage detector 12.
[0018]
The voltage detection terminal wiring uses a pattern as thin as possible of about 0.2 to 0.3 mm, and the voltage detection terminal horizontal patterns B and B ′ are aligned with the horizontal central axis as much as possible. The voltage detection terminal vertical patterns A and A It is desirable that ′ is centered on the vertical central axis. As shown in FIG. 4A, when the voltage detection terminal vertical pattern is separated from the vertical center axis, the mutual inductance M decreases and the effective inductance Le increases. On the other hand, when the voltage detection terminal vertical pattern exists beyond the vertical center axis as shown in FIG. 4B, the mutual inductance M increases, and when the voltage detection terminal vertical pattern is larger than the self-inductance L, the effective inductance Le is Become negative.
[0019]
Therefore, superimposing the voltage detection terminal vertical patterns A and A ′ on the vertical central axis is important for reducing the effective inductance Le and preventing excessive coupling as shown in FIG. That is, the wiring length of the voltage detection terminal wirings B and B ′ is substantially equal to the length of the self-inductance of the resistor. Therefore, the mutual inductance due to the voltage detection terminal wiring can be substantially subtracted from the self-inductance. When you want to measure and compare the effective inductance Le of a resistor universally, it must be a voltage detection terminal pattern that ensures the reproducibility of the effective inductance Le under minimum conditions, and external magnetic flux etc. The effects of noise must be eliminated. The pattern just meets that requirement.
[0020]
The effective inductance Le measured with such a wiring pattern is an index indicating how the current detection resistor can be used for current detection without error without correction by other circuits. Further, it is desirable that the insulating layer sandwiched between the voltage detection terminal wirings 16 stacked on the front and back surfaces of the printed circuit board is as thin as possible in order to reduce the voltage error. Since the shapes of the lands 13 and 14 differ depending on the electrode shape of the current detection resistor to be measured, it is desirable to use a shape that matches the electrode shape of the current detection resistor.
[0021]
The value of the effective inductance Le obtained with such a wiring pattern is a universal and practical practical index indicating the goodness of the current detection resistor itself. That is, if the current path of the low resistor is linear and the patterns B and B ′ extend to the vertical center axis and bend as shown in FIG. 3, the self-inductance and mutual inductance of the resistor are almost equal. And the effective inductance Le is almost zero. When the current path of the resistor is curved due to trimming or the like, the self inductance and the mutual inductance are not equal, and the effective inductance Le has a value of 1 nH, for example. Of course, if a pattern for mounting a current detection resistor is specified, a specified pattern different from the universal pattern can be used. However, in this case, the universality is lost from the calculated value, but it will be a value that can be immediately reflected in the design.
[0022]
Next, a configuration example of a measurement circuit that actually measures the effective inductance Le using the voltage detection terminal wiring pattern will be described with reference to FIGS. 5 and 6.
FIG. 5 shows an apparatus for measuring the effective inductance Le of the current detection resistor. The sawtooth wave current is supplied to the resistor 11 to be measured from the sawtooth wave current source 21 in accordance with the actual use state. The sawtooth wave current generator 21 supplies a sawtooth wave current of several A to several tens of A to the measured resistor 11 having a frequency of several mΩ or less, for example, at a cycle of 2.5 μS. A wiring 22 for supplying a sawtooth wave current to the resistor 11 to be measured is provided with a current detector 23 such as a current probe which is coupled to the wiring and detects the current. The resistor 11 to be measured is mounted on the dedicated substrate 24 having the voltage detection terminal wiring described above, and the voltage generated by the sawtooth wave current is taken out from the voltage detection terminal wiring 16 coupled to both ends of the resistor to be measured. From the end of the voltage detection terminal wiring 16 of the substrate 24, it is connected to the voltage detector 12 comprising a differential amplifier or the like through a stranded wire 25 or the like, and the voltage generated at both ends of the resistor under test is detected. The output of the current detector 23 and the output of the voltage detector 12 are input to a waveform display device 26 such as an oscilloscope, and displayed in comparison with the unit according to the current or voltage.
[0023]
FIG. 6 shows an example of a measurement circuit. For example, a +12 V DC power source is alternately switched using the switching elements 32 and 33, and current is supplied alternately to the integrating circuit composed of the choke coil 34 and the capacitor 35. By adjusting the inductance value of the choke coil, the capacitance value of the capacitor, the switching frequency, the duty factor, and the like, the sawtooth wave current indicated by the broken line in FIG. A direct current of several to several tens of A is supplied to the direct current load 36 which is a resistor load by adjusting its resistance value, for example, at about 1 VDC.
[0024]
In addition to the above-mentioned adjustment being possible, the measurement circuit should be able to generate a sawtooth wave current with good linearity and constant amplitude when a constant voltage with different polarity is alternately applied to a choke coil that does not saturate. Is to be. Further, it is desirable that the common-mode voltage rejection ratio of the differential amplifier that detects the voltage across the voltage detection terminal lead wiring pattern of the current detection resistor is as high as possible. Furthermore, arrange the choke coil and the measured current detection resistor so that the leakage flux of the choke coil does not affect the measured current detection resistor within the measurement error range, or between them. It is desirable to arrange the magnetic shield so that the same effect can be obtained. Also, the voltage detection terminal wiring pattern 16 superimposed on the front and back surfaces of the substrate shown in FIG. 3 is led to the input of the differential amplifier 12, but the path is extended to a point where it is not affected by the external magnetic flux. When extending with a wire, it is desirable to use a litz wire (stranded wire) so that an external magnetic flux does not interlink between the wires. Note that the current waveform is observed using a current probe, a current transformer or the like having a sufficient bandwidth with respect to harmonics of the switching frequency.
[0025]
Next, the procedure for calculating the effective inductance Le will be described with reference to FIG.
The effective inductance of the current detection resistor is measured by supplying a sawtooth current to the resistor 11 to be measured, detecting the current, and detecting the voltage generated by the current coupled to both ends of the resistor to be measured. . Then, the effective inductance of the resistor under test is calculated from the change in the sawtooth current and the change in the voltage corresponding thereto.
[0026]
First, the voltage change ΔV at the change point (top) of the sawtooth current is defined as a resistance value R, a duty D, a period T, and currents i1 and i2 of the resistor to be measured.
ΔV = V1-V2 = i1 × R + Le (di1 / dt) -i2 × R-Le (di2 / dt)
At t = D × T, i1 = i2, so
ΔV = Le (di1 / dt) -Le (di2 / dt)
It becomes. Here, if the current change value (peak value) is Vip_p,
(di1 / dt) = Vip_p / (R × D × T)
(di2 / dt) =-Vip_p / {R × (D-1) × T}
So, if you substitute and organize these,
[Expression 1]

[Expression 2]

Since Vip_p and ΔV are obtained by a waveform display device or the like, it is possible to calculate the effective inductance of the current detection resistor.
[0027]
8 and 9 show an actual measurement example of the effective inductance Le of the low resistor by the measuring device and the wiring pattern. FIG. 8 is intended for a resistor having a structure in which the current path having a resistance value of 2 mΩ is linear, and the effective inductance is short as far as possible from the printed circuit board to be mounted to the current path. . Although there is a self-inductance of the resistor itself, since the mutual inductance with the voltage detection terminal wiring cancels it, as shown in FIG. And as shown in (b), as a result of measuring 10 samples, it turns out that the effective inductance Le is almost zero. On the other hand, FIG. 9 shows a measurement result of a low resistor having a resistance value of 3 mΩ and a current path bent by a vertical trimming cut. As shown to (a), it turns out that the big error voltage has generate | occur | produced with respect to the sawtooth wave current waveform. In this case, as shown in (b), it can be seen that in this low resistor, the effective inductance Le is about 0.9 nH.
[0028]
As shown in FIG. 9, when the effective inductance Le is large, the combined impedance of the low resistor is increased, and as a result, a large error voltage is generated in the detection voltage as described above. Therefore, when the DC / DC converter is controlled based on the voltage detection waveform, the operation is hindered. Therefore, it is desirable to insert an appropriate filter circuit in the voltage detection terminal wiring, eliminate the error voltage waveform due to effective inductance, and output a voltage waveform based only on the resistance component. In FIG. 10, a waveform correcting integrator 40 is provided as a filter for removing the error voltage waveform. This integrator consists of a resistor Ri and a capacitance Ci,
Ci × Ri = Le / R
It has the relationship of these.
[0029]
Next, the principle that the error voltage waveform can be removed by the filter circuit will be described. FIG. 11 is an equivalent circuit diagram of the resistor and voltage detection terminal wiring extraction portion 41 and the integrator (waveform shaping filter) 40. When the right side from the integrator input (a, a ') is the load side and the left side is the signal source, the load impedance is generally very high with respect to the signal source impedance. Therefore, as shown in FIG.
R x I + Le x dI / dt
Can be regarded as a signal voltage source that generates Therefore, according to the calculation described below in FIG. 12, it can be seen that the output Vout of the integrating circuit (filter) can take out a voltage output proportional to the product of the resistance value R and current I of the resistor.
[0030]
FIG. 13 shows a configuration example of a switching power supply circuit employing the voltage detection circuit of the current detection resistor. This switching power supply circuit is a DC / DC converter. For example, a DC + 1V. DC power with a current of tens of A is supplied. This switching power supply circuit is equipped with a power supply detection resistor 11 so as to detect a current of a sawtooth wave generating circuit composed of switching elements 32 and 33, a choke coil 34 and a capacitor 35. That is, when the switching elements 32 and 33 are alternately turned on and off, a sawtooth wave having excellent linearity is formed in the integrating circuit composed of the choke coil 34 and the capacitor 35, and the low voltage smoothed by the capacitor 35. Is supplied to the DC load 36, and by adjusting the resistance value of the DC load, a DC current of several tens of A flows as described above.
[0031]
The voltage detection terminal wiring 16 is taken out from both ends of the current detection resistor 11, and the output of the integration circuit 40 including the resistor Ri and the capacitance Ci is taken into the voltage detector 12 including a differential amplifier or a comparator. Here, the constant of the integration circuit is
Ri × Ci = Le / R
Therefore, even when the effective inductance Le exists, the error voltage due to this can be canceled as described above. Accordingly, a voltage that is exactly proportional to the current flowing through the resistance value R of the resistor 11 is taken out from the output of the voltage detector 12 and sent to the switching element control circuit 43 as a feedback signal. Then, a control signal is sent to the switching element based on the correct detection current. Thereby, the operation | movement can be controlled based on the correct detection current in a switching power supply circuit.
[0032]
FIG. 14 shows an example in which a part of a choke coil is used as a current detection resistor. As described above, the switching power supply circuit uses the choke coil 34 for generating a sawtooth wave, and a part of the choke coil 34 can be used as a resistor for current detection. A choke coil current I flows between the current terminals 1 and 2, and a voltage corresponding to both ends of the resistor is taken out between the coil terminals a and a ′ connected by taps. The terminals a and a 'constitute voltage detection terminal wiring, and a voltage generated at both ends of the resistor is output from the voltage terminals 1 and 2 through an integration circuit 40 including a resistor Ri and a capacitance Ci.
[0033]
Here, the coil indicated by the broken line in the figure constitutes a part of the voltage extraction wiring as described above, but is wound in the same manner as the coil through which the current flows. An equal mutual inductance is formed. However, even if there is an effective inductance viewed from the terminals a and a ′, the error voltage component due to the effective inductance is canceled by using the integration circuit 40 made of Ri and Ci as a filter as described above. The detected voltage between the voltage terminals 1 and 2 is similar to the current flowing between the current terminals 1 and 2. For this reason, it is desirable that the resistance temperature coefficient of the resistor Ri is equal in magnitude to the resistance temperature coefficient of the resistor R with an opposite sign. Note that the resistance Ri of the integrating circuit 40 may be an electrical resistance of a winding indicated by a broken line in the choke coil.
[0034]
The resistance R viewed from the terminals a and a ′ on the left side is the DC resistance of the coil from the tap to the point b, and the effective inductance Le is the self-inductance possessed by the DC resistance of the coil. It is obtained by subtracting the mutual inductance of the broken line part where the inductance part and the magnetic flux intersect. Thus, by using a part of the choke coil used for the DC / DC converter as a current detection resistor, a dedicated current detection resistor is not required, and the cost and the substrate size can be reduced.
[0035]
The voltage detection terminal wiring in these embodiments preferably employs a pattern in which the effective inductance Le shown in FIG. 3 is almost zero. For example, the pattern itself shown in FIG. 4 has an effective inductance Le. Even so, such a pattern can be used because it can be canceled out by the filter action of the integrating circuit 40.
[0036]
It should be noted that the voltage detection circuit of the current detection resistor of the present invention is not limited to the illustrated example described above, and it is needless to say that various changes can be made without departing from the scope of the present invention.
[0037]
【The invention's effect】
According to the present invention described above, even when the current detection resistor and its measurement system have an effective inductance, an error caused by the effective inductance can be obtained by arranging the integration circuit having a predetermined relationship in the voltage detection circuit. The voltage can be removed. Therefore, it is possible to prevent malfunction caused by the parasitic inductance of the current detection resistor when applied to a power supply switching circuit or the like.
[Brief description of the drawings]
FIG. 1A is a diagram illustrating an example of a circuit for detecting a current to be measured by a current detection resistor, and FIG. It is a figure which shows the voltage waveform taken out exemplarily.
FIG. 2 is an equivalent circuit diagram of a measured resistor and voltage detection terminal wiring.
FIG. 3 is a pattern diagram showing a configuration example of a voltage detection terminal wiring.
4 is a pattern diagram showing another configuration example of the voltage detection terminal wiring as a comparative example with respect to FIG. 3; FIG.
FIG. 5 is a block diagram showing an apparatus for measuring effective inductance of a current detection resistor according to an embodiment of the present invention.
6 is a circuit diagram showing a specific circuit example of FIG. 5. FIG.
FIG. 7 is a waveform diagram of current and voltage for calculating an effective inductance Le.
FIGS. 8A and 8B show examples of voltage and current waveforms, and FIG. 8B shows an example of measurement of effective inductance values in a low resistor in which there is almost no effective inductance.
9A shows an example of voltage and current waveforms, and FIG. 9B shows an example of measurement of an effective inductance value in a low resistor having an effective inductance.
FIG. 10 is a circuit diagram showing a voltage detection circuit according to an embodiment of the present invention.
11 is an equivalent circuit diagram showing the operation principle of the circuit of FIG.
FIG. 12 shows an equivalent circuit diagram when the circuit of FIG. 10 is viewed as a four-terminal circuit, and a calculation formula for explaining the operation principle thereof.
FIG. 13 is a circuit diagram showing a configuration example of a switching power supply circuit according to the embodiment of the present invention.
FIG. 14 is a circuit diagram when a part of a choke coil is used as a current detection resistor.
[Explanation of symbols]
11 Resistor to be measured
12 Voltage detector
13,14 rand
15 Via
16 Voltage detection terminal wiring
21 Sawtooth wave current generator
22 Wiring
23 Current detector
24 Low resistor mounting board
25 litz wire (stranded wire)
26 Waveform display device
31 DC power supply
32, 33 switching element
34 Choke coil
35 capacitors
36 DC load
40 Integration circuit

Claims (4)

A pair of lands on the substrate connected to both ends of the current detection resistor, and a voltage detection terminal wiring for supplying a current to be measured from the lands to the resistor and detecting a voltage generated at both ends of the resistor In the voltage detection circuit of the current detection resistor comprising:
The voltage detection terminal wiring is centered along a horizontal central axis between the lands arranged immediately below the resistor from a pair of lands on the substrate to which both end electrodes of the current detection resistor are fixed. Pulled out, bent at right angles in the vertical center axis between both lands, one side connected to the back pattern with vias and folded, arranged parallel to the front and back surfaces of the substrate along the vertical center axis,
The voltage detection terminal wiring includes an integrator composed of a resistor (Ri) and a capacitance (Ci), and the integrator is viewed from the resistor (R) of the resistor and the voltage detection terminal wiring side of the resistor. For effective inductance (Le),
Ci × Ri = Le / R
Have the relationship
The effective inductance (Le) is obtained by supplying a sawtooth wave current to the current detecting resistor, detecting the current and detecting a voltage generated at both ends, and detecting a change in current and a corresponding voltage change. A voltage detection circuit for a current detection resistor, characterized by being calculated.   A switching power supply circuit that controls opening and closing of a switching element based on a current to be measured detected by a voltage detection circuit of a current detection resistor according to claim 1. A sawtooth wave current is supplied to a current detecting resistor, the current is detected, and a voltage generated by the current is detected by a wire coupled to both ends of the resistor, and the change of the sawtooth wave current and the current are detected. The effective inductance (Le) of the resistor is calculated from the corresponding change in the voltage,
The current detection resistor is connected to a pair of lands on the substrate , and the voltage detection terminal wiring is arranged on the substrate from the land , and both ends of the current detection resistor are fixed to the voltage detection terminal wiring. From the pair of lands on the substrate to be drawn to the center along the horizontal central axis between the lands disposed immediately below the resistor, and bent in the perpendicular direction at the vertical central axis between both lands, One side is connected to the back pattern with a via and folded, and is arranged parallel to the front and back surfaces of the substrate along the vertical central axis,
For the voltage detection terminal wiring, the resistance (R) of the resistor and the effective inductance (Le) of the resistor,
Ci × Ri = Le / R
An integrator having the relationship
A voltage detection method for a current detection resistor, wherein a current to be measured is supplied to the land and a voltage generated at both ends of the resistor is detected by the voltage detection terminal wiring.   4. The voltage detection method for a current detection resistor according to claim 3, wherein a low resistance whose current path is bent by a trimming cut in a vertical direction is used as the current detection resistor.

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