JP2006184221A - Current detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current detector with reduced power loss and reduced cost. <P>SOLUTION: A current to be detected is carried to one NPN (main transistor Q1m) of a transistor Q1 having a five-layer structure of NPNPN, and a resistor 3 is connected between the base B2-emitter E2 of the other NPN (sub-transistor Q1s) to carry a bias current thereto. A detection voltage Vd1 according to a current i3 carried to the collector C2 of the sub-transistor Q1s (according to a current iL) is generated, and a transistor Q2 is driven through a resistor R1 to supply a current i2 between the base B1-collector C1 of the main transistor Q1m. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a current detection device, and more particularly to detection of a current flowing in an electric circuit such as a power circuit or an electronic device.

  There are the following methods for detecting the current flowing in the electrical circuit. In the first method, as described in Patent Document 1, a resistor having a low resistance value R is arranged in series in the current path, and the current value I = V / R is detected from the voltage V across the resistor. This method uses a shunt resistor. The second method is a method of detecting a current value α × I proportional to the current value I from a current transformer (CT) arranged in the current path. In the third method, a Hall element is arranged in the vicinity of the current path, a magnetic field generated by a current flowing through the current path is detected by the Hall element, and a voltage β × I proportional to the current value I is detected. This is a method using a Hall sensor (see FIG. 9 of Patent Document 1).

Although the shunt resistor is relatively low in cost, an I ² R power loss occurs because the shunt resistor is arranged in series with the current path. Of course, if the resistance value of the shunt resistor is lowered, the loss can be reduced. However, since the voltage generated at both ends of the shunt resistor is also reduced accordingly, the shunt resistor having a resistance value corresponding to the detected current value. is required.

  On the other hand, CT and Hall sensors that detect a current value via a magnetic field generate very little power loss compared to a shunt resistor, but the cost is higher than that of a shunt resistor.

JP 2004-53528 A

  An object of the present invention is to provide a current detection device with low power loss and low cost.

  The present invention has the following configuration as one means for achieving the above object.

  The current detection device according to the present invention has a five-layer structure of NPNPN, a bipolar element through which a current to be detected flows between the first layer (N layer) and the third layer (N layer), and the fourth layer (P Layer) and a first resistor connected between the first PN junction consisting of the third layer (N layer) and a voltage generator for generating an output voltage corresponding to the current flowing in the fifth layer (N layer) And current supply means for supplying a current corresponding to the voltage of the fifth layer (N layer) to the second PN junction consisting of the second layer (P layer) and the third (N layer). It is characterized by that.

  According to the first and second aspects of the invention, a low power loss and low cost current detection device can be provided.

  According to the invention of claim 2, in addition to the effect of the invention of claim 1, the difference between the voltage of the fifth layer (N layer) and the collector voltage of the transistor is used as the output voltage, so that the temperature dependence of the output voltage Sex can be removed.

  According to the invention of claim 3, in addition to the effect of the invention of claim 1, the peak value of the current to be detected can be detected.

  According to the invention of claim 4, in addition to the effects of the inventions of claims 1 and 3, by using the difference between the voltage of the fifth layer (N layer) and the collector voltage of the transistor as the output voltage, Temperature dependence can be removed.

  According to the invention of claim 5, in addition to the effects of the inventions of claims 1, 3, and 4, a current corresponding to the value of the current to be detected is supplied to the second PN junction, so that the current to be detected is When the AC current is large, the power loss between the first layer (N layer) and the third layer (N layer) can be reduced, and when the current to be detected is small, the current detection sensitivity can be increased. .

  According to the invention of claim 6, in addition to the effect of the invention of claim 1, the same detection characteristics can be obtained regardless of the direction of the current to be detected.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing a configuration example of the current detection device according to the first embodiment, and shows a configuration example for detecting a current i _L flowing in a circuit constituted by the DC power source 1 and the load 2.

The upper NPN portion in FIG. 1 of the bipolar transistor Q1 having the NPNPN five-layer structure shown in FIG. 1 is called a main transistor Q1m, and a current i _L to be detected flows between the emitter E1 and the collector C1. Connected to the circuit. On the other hand, although the lower NPN portion in FIG. 1 is called a sub-transistor Q1s, its emitter E2 is common to the collector C1 of the main transistor Q1m.

In FIG. 1, the positive electrode of the DC power source 3 → the resistor R1 → the base of the transistor Q2 → the emitter of the transistor Q2 → the resistor R2 → the base B1 of the main transistor Q1m → the collector C1 of the main transistor Q1m → the negative electrode of the DC power source 3 A current i1 having a value represented by the equation (1) flows in the loop.
i1 = {E3-Vbe (Q2)-Vbc (Q1m)} / (R1 + R2)… (1)
Where E3 is the voltage of DC power supply 3
Vbe (Q2) is the base-emitter voltage of transistor Q2, approximately 0.6V
Vbc (Q1m) is the base-collector voltage of the main transistor Q1m, 0.6V or more

By supplying the current i1 to the base, a current flows through the collector of the transistor Q2, and a current i2 expressed by the equation (2) flows from the emitter of the transistor Q2 to the base B1 of the main transistor Q1m.
i2 = i1 + i1 × h _FE (Q2) = (1 + h _FE ) × i1… (2)
Where h _FE (Q2) is the current gain of transistor Q2.

During emitter E1- collector C1 of the main transistor Q1m by the supply of current i2 to the base B1 is conductive, it is possible to flow a current i _L.

Further, a potential substantially equal to the potential Vb (Q1) of the base B1 is induced in the base B2 of the sub-transistor Q1s (the base potential of the transistor Q1s is also set to Vb (Q1)), and the sub-transistor Q1s is also in a communication state. Therefore, the current i3 shown in the equation (3) flows through the loop formed by the positive electrode of the DC power source 3, the resistor R1, the collector C2, the emitter E2, and the negative electrode of the DC power source 3.
i3 = h _FE (Q1s) x {Vb (Q1s) / h _IE (Q1s)-i4}
= h _FE (Q1s) × Vb (Q1) {1 / h _IE (Q1s)-1 / R3}… (3)
Where h _FE (Q1s) is the current gain of sub-transistor Q1s
h _IE (Q1s) is the input resistance of sub-transistor Q1s

  The current i3 lowers the base potential of the transistor Q2 and decreases the currents i1 and i2, but the decrease in the current i2 lowers the potential Vb (Q1), the current i3 flowing through the subtransistor Q1s, and Increase the base potential. As a result, the currents i1, i2, i3 and the potential Vb (Q1) are balanced in a certain state. Therefore, the operation state of the main transistor Q1m is maintained. Here, the potential is based on the potential of the collector C1 of the main transistor Q1m (= the potential of the emitter E2 of the subtransistor Q1s) as a reference (0V). Therefore, the potential Vb (Q1) is a voltage between the base B1 and the collector C1 of the main transistor Q1m.

In the above equilibrium state, the potential Vd1 shown in the equation (4) appears at the base of the transistor Q2 (the collector of the transistor Q1s). Vbc (Q1m) in the equation (1) indicating the current i1 is equal to Vb (Q1). Therefore, it can be seen that the potential Vd1 changes according to the potential Vb (Q1).
Vd1 = E3-(i1 + i3) × R1… (4)

FIG. 2 is a waveform diagram showing the collector current i _L , the collector-emitter voltage Vce, and the base-emitter voltage Vbe of the main transistor Q1m. For i _L (10A / div) that fluctuates around 0A, Vce (0.2V / div) is in the range of -0.1V to + 0.04V, and Vbe (0.2V / div) is + 0.6V to + It shows how it fluctuates in the range of about 0.7V. Note that the waveforms shown in FIG. 2 are measured by replacing the power supply 1 of the circuit shown in FIG. 1 with an AC power supply in order to clarify changes in Vce and Vbe with respect to i _L.

As shown in FIG. 2, Vce and Vbe are not sine waves with respect to i _L of the sine wave. This indicates that the relationship between i _L and Vce, Vbe is non-linear, and that the characteristics (for example, h _FE ) are different between when the collector current flows in the forward direction and when it flows in the reverse direction. On the other hand, the changes in Vce and Vbe match.

When the current i _L flowing between the collector and the emitter of the main transistor Q1m increases, the voltage between the collector and the emitter increases as shown in FIG. As shown in FIG. 1, since the main transistor Q1m is grounded at the collector, the base potential Vb (Q1) decreases as the absolute value of the emitter voltage increases in the negative direction. As the base potential Vb (Q1) decreases, the current i3 decreases and the currents i1 and i2 increase.

Assuming that the variation of the base potential Vb (Q1) of the main transistor Q1m is Δv, currents i1 and i3 including the variation Δv are expressed by the following equations.
i1 = {E3-Vbe (Q2)-Vb (Q1) ± Δv} / (R1 + R2)… (5)
i3 = h _FE (Q1s) × {Vb (Q1) ± Δv} / R3… (6)

Therefore, the value of the potential Vd1 shown in Equation (4) is made to vary approximately in proportion to the variation of the value of the current i _L, to measure the potential Vd1, roughly proportional to the variation of the value of the current i _L The voltage value indicating the changed can be extracted.

FIG. 3 is a waveform diagram showing the relationship between current i _L , emitter potential Ve (Q1m) of transistor Q1m, and potential Vd1. As shown in FIG. 3, when the current i _L increases, the absolute value of the emitter potential Ve (Q1m) increases in the negative direction, and a detection voltage Vd1 showing a change similar to the change in the current i _L is obtained. Of course, since the voltage Vd2 equal to the potential Vb (Q1) appears at both ends of the resistor R3, the potential Vd2 may be used instead of the potential Vd1.

[Modification]
The value of the resistor R1, by, for example, experiments, to variations in current i _L, the base current i1 of the transistor Q2 does not become 0A, and the change in the potential Vd1 corresponding to variation of the current i _L is sufficient What is necessary is just to set so that it may become a magnitude | size. For example, when the current i _L varies greatly and the base current i1 of the transistor Q2 reaches 0 A, the value of the resistor R1 may be lowered. In other words, by switching the resistance value of the resistor R1 according to the fluctuation range of the current to be detected (current i _L ) (referred to as range switching), a current detection device corresponding to the current range to be detected is obtained. Can do.

  It should be noted that the adjustment of the resistor R2 for adjusting the base current i2 of the transistor Q1m is most effective for the range switching, including the embodiments described later.

In addition, when extracting the potential Vd2, the value of the resistor R3 may be set so that the variation of the potential Vd2 corresponding to the variation of the current i _L is sufficiently large (the value of the resistor R1 is necessary if necessary). Also set).

Although FIG. 1 shows an example in which the current i _L of the circuit constituted by the DC power source 1 and the load 2 is detected, the base current i2 of the main transistor Q1m can be set appropriately so that the amplitude of the AC current is reduced. If a sufficient base current i2 is supplied, it is possible to detect an alternating current of a circuit constituted by the alternating current power source and the load. Therefore, in the following description, it is not mentioned whether the power source 1 is a DC power source or an AC power source.

  Hereinafter, a current detection apparatus according to a second embodiment of the present invention will be described. Note that the same reference numerals in the second embodiment denote the same parts as in the first embodiment, and a detailed description thereof will be omitted.

  The base potential Vb (Q1) of the main transistor Q1m varies depending on the temperature coefficient (about −2 mV / K) of the PN junction, and the base potential of the sub-transistor Q1s also varies. Therefore, the detection voltage Vd1 obtained by the current detection device described in the first embodiment has temperature dependence. Below, the structural example which compensates temperature dependence is demonstrated.

FIG. 4 is a circuit diagram illustrating a configuration example of the current detection device according to the second embodiment, and illustrates a configuration example for detecting a current i _L flowing in a circuit formed by the power source 1 and the load 2.

For example, a transistor with similar characteristics such as h _FE substantially the same as the sub-transistor Q1s is selected and used for the transistor Q3. The bias is set by the resistor R5 so that the operating point of the transistor Q3 becomes the average operating point of the transistor Q1s. Therefore, the collector potential Vc (Q3) of the transistor Q3 is constant except for the temperature dependence.

  Since the sub-transistor Q1s and the transistor Q3 have similar characteristics, the temperature dependence is considered to be almost the same, and both transistors Q1s and Q3 are placed close to each other, preferably thermally coupled, so that both transistors Q1s If the thermal conditions of Q3 are matched, the collector potential Vc (Q1s) and the collector potential Vc (Q3) show the same change with respect to the temperature. Therefore, if the differential voltage between Vc (Q1s) and Vc (Q3) is acquired as the detection voltage Vd1, the temperature dependence of the detection voltage Vd1 can be eliminated.

  FIG. 5 (a) is a diagram showing an example in which both transistors are formed on the same silicon substrate 10 in order to thermally couple the sub-transistor Q1s and the transistor Q3. FIG. 5 (b) shows an example in which a discrete transistor Q3 is bonded and thermally coupled to the package of the transistor Q1.

Also, the resistor R6 disposed between the base of the transistor Q2 and the negative electrode of the DC power supply 3 shown in FIG. 4 functions as a bleeder resistor for the transistor Q2, and is used to adjust the current gain of the transistor Q2. is there. The values may be set so that the emitter current i2 and the base voltage of the transistor Q2 become preferable values by, for example, experiments. For example, large amplitude of the current i _L, when the base voltage of the transistor Q2 will reach the supply voltage of zero or the DC power supply 3, equivalent to the current amplification factor h _FE of transistor Q2 lowers the resistance value of the resistor R6 Is reduced, the emitter current i2 of the transistor Q2 decreases, and the base voltage does not reach zero or the power supply voltage. In other words, by switching the resistance value of the resistor R6 according to the amplitude of the current to be detected (current i _L ) (range switching), it is possible to provide a current detection device according to the range of the current to be detected. It should be noted that range switching is realized even when switching is performed as described in the first embodiment in conjunction with resistors R1 and R4 without using resistor R6.

  Thus, according to the current detection device of the second embodiment, the same effect as the current detection device of the first embodiment can be obtained, and the temperature dependency of the detection voltage Vd1 due to the temperature dependency of the sub-transistor Q1s is eliminated. can do.

It is possible to obtain a detection voltage Vd1 corresponding to the peak value of the current i _L. Note that the configuration shown in FIG. 6 has a peak charge type rectifier circuit including a diode D1 and a capacitor C1, so that the detection voltage Vd1 has a value corresponding to the peak value of the current i _L. For example, the detection voltage Vd1 is in series with the diode D1. If a charging resistor is connected and a discharging resistor is connected in parallel with the capacitor C1, it becomes an average charge type rectifier circuit, and the detection voltage Vd1 becomes a value corresponding to the average value of the current i _L .

  The current detection device according to Example 3 of the present invention will be described below. Note that the same reference numerals in the third embodiment denote the same parts as in the first and second embodiments, and a detailed description thereof will be omitted.

FIG. 6 is a circuit diagram illustrating a configuration example of the current detection device according to the third embodiment, and illustrates a configuration example in which a current i _L flowing in a circuit including the power source 1 and the load 2 is detected.

  The capacitor C1 is charged with the peak value of the collector potential Vc (Q1s) of the sub-transistor Q1s via the diode D1, and the emitter current i2 of the transistor Q2 increases or decreases as the peak value increases or decreases. The charge of the capacitor C1 is discharged as the base current of the transistor Q2 and through the resistor R6. The detection voltage Vd1 extracts the difference between the potential Vc of the capacitor C1 and the collector potential of the transistor Q3.

According to such a configuration, the same effects as those of the current detection devices of Embodiments 1 and 2 can be obtained. If the power source 1 is a DC power source, the bottom side of the current i _L (the lower side of the current _L shown in FIG. 3) ), The detection voltage Vd1 corresponding to the peak value can be obtained. If the power source 1 is an AC power source and the positive and negative peak values (the peak values on the top and bottom sides) of the current i _L are the same, the peak value of the AC current can be detected.

Furthermore, if the power supply 1 is AC power supply, since the addition of current i2 which is substantially proportional to the peak value of the current i _L to the base B1 of the main transistor Q1m, increased current i2 in the region current i _L is large, the main The voltage Vec (Q1m) between the emitter E1 and the collector C1 of the transistor Q1m is lowered to reduce the power loss generated in the main transistor Q1m. On the other hand, in the region where the current i _L is small, the current i2 is decreased, and the voltage Vec (Q1m) between the emitter E1 and the collector C1 of the main transistor Q1m is increased. As a result, as understood from the waveform diagram shown in FIG. 2, the voltage Vb (Q1) between the base B1 and the collector C1 also increases, and the current detection sensitivity in the region where the current _iL is small can be increased. In other words, it is possible to provide a current detection device with low loss in a region where the detection target current is large and high sensitivity in a small region.

The power loss considered here is the power loss of the circuit through which the current i _L to be detected flows, and is the loss i _L × Vec (Q1m) generated between the emitter E1 and the collector C1 of the main transistor Q1m. It is. Needless to say, the loss i2 × Vb (Q1) generated between the base B1 and the collector C1 of the main transistor Q1m and the loss generated in the sub-transistor Q1s are not included.

[Other embodiments]
7 shows that the transistor Q4 having the same characteristics as the transistor Q1m of the current detection device shown in FIG. 1 is connected in parallel in the opposite direction (referred to as anti-parallel connection), that is, the Q1m collector and the Q4 emitter are connected, and the Q1m emitter Shown is a configuration with Q4 collector connected and both bases connected. According to such a configuration, different characteristics (for example, differences in hFE) are absorbed between the case where the collector current shown in FIG. 2 flows in the forward direction and the case where the collector current flows in the reverse direction, and uniform characteristics are obtained in both directions. be able to. Such antiparallel connection of the transistors Q1m and Q4 is effective not only for the circuit shown in FIG. 1 but also for the circuits shown in FIGS. 4 and 6.

  In the above embodiment, an example is shown in which an NPN bipolar transistor is used as the transistor Q2, but this may be replaced by, for example, an N-channel MOS FET or a junction FET. In the case of MOS FET, the base potential Vb (Q1) is divided by resistors R2 and R3, and an appropriate voltage is applied to the gate (control electrode) of Q2. In the case of junction FET, a resistor is connected to the source. For example, a negative bias is supplied to the gate.

  In addition, although an example in which an NPN transistor is used as the transistor Q2 is shown, it is extremely easy for those skilled in the art to replace an NPN transistor with a PNP transistor and an N-channel FET with a P-channel FET. In other words, any configuration that detects the current value of the current path using the voltage component Δv in which the base potential Vb of the bipolar transistor arranged in the current path changes according to the reverse transmission rate is included in the scope of the present invention. .

A circuit diagram showing a configuration example of a current detection device of Example 1, Waveform diagram showing collector current i _L , collector-emitter voltage Vce and base-emitter voltage Vbe of main transistor Q1m, Waveform diagram showing current i _L , emitter potential Ve (Q1m) of main transistor Q1m, and potential Vd1, Circuit diagram showing a configuration example of a current detection device of Example 2, The figure which shows the example of thermal coupling of subtransistor Q1s and transistor Q3, A circuit diagram showing a configuration example of a current detection device of Example 3, FIG. 2 is a circuit diagram showing a configuration example in which a transistor Q4 having the same characteristic is connected in reverse parallel to the transistor Q1m of the current detection device shown in FIG.

Claims (6)

A bipolar element having a five-layer structure of NPNPN, in which a current to be detected flows between the first layer (N layer) and the third layer (N layer);
A first resistor connected between a first PN junction comprising a fourth layer (P layer) and the third layer (N layer);
Voltage generating means for generating an output voltage corresponding to the current flowing in the fifth layer (N layer);
Current supply means for supplying a current corresponding to the voltage of the fifth layer (N layer) to the second PN junction comprising the second layer (P layer) and the third (N layer) A current detection device.   The voltage generating means corresponds to a transistor having substantially the same characteristics as NPN starting from the fifth layer (N layer), a second resistor for supplying a bias current to the transistor, and a current flowing through the collector of the transistor 2. A third resistor for generating a voltage, wherein a difference between a voltage of the fifth layer (N layer) and a collector voltage of the transistor is output as the output voltage. Current sensing device.   2. The voltage generation means includes detection means for detecting a peak value of the voltage of the fifth layer (N layer), and outputs the peak value as the output voltage. Current detection device.   The voltage generating means further includes a transistor having substantially the same characteristics as the NPN starting from the fifth layer (N layer), a second resistor for supplying a bias current to the transistor, and a current flowing through the collector of the transistor 4. The current detection device according to claim 3, further comprising a third resistor that generates a voltage corresponding to the output voltage, and outputting a difference between the peak voltage and a collector voltage of the transistor as the output voltage. .   5. The current detection device according to claim 3, wherein the current supply unit supplies a current corresponding to the peak value to the second PN junction.   The bipolar element is characterized in that the emitter, base, and collector of a transistor having the same characteristics are connected to the collector, base, and emitter of the transistor constituted by the first layer to the third layer, respectively. The current detection device according to claim 1.

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