Current detector and electric apparatus

Abstract

To provide a current detector capable of simply and accurately detecting an inductor current flowing into an inductor.SOLUTION: A current detector 10 for detecting an inductor current IL flowing into an inductor L includes a detection circuit 11 connected to the inductor IL in parallel. The detection circuit 11 is a series circuit including resistor elements Rcs1 and Rcs2 connected to both terminals of a capacitor Ccs, respectively and has a time constant set equal to that of the inductor L; and the resistor elements Rcs1 and Rcs2 connected to both terminals of the capacitor Ccs have resistance values (Rcs1=Rcs2) set equal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present disclosure relates to a current detector that detects an inductor current flowing through an inductor, and an electric device. [Background technology]

[0002] FIG. 4 shows a step-down switching regulator (electrical equipment) equipped with an inductor L. A series circuit consisting of a resistor Rcs and a capacitor Ccs is connected in parallel to the inductor L as a current detector for detecting the inductor current IL flowing through the inductor L (see, for example, Patent Document 1). This current detector detects the voltage Vccs between both terminals of the capacitor Ccs as the inductor current IL passing through the inductor L. The voltage Vccs between both terminals is proportional to the inductor current IL by setting the time constant TRC of the series circuit consisting of the resistor Rcs and the capacitor Ccs to be the same as the time constant TL of the inductor L.

[0003] The voltage Vccs between both terminals is detected by, for example, a Vccs measurement circuit using an OP amplifier, as shown in Figure 4. The voltage Vccs between both terminals is detected as Vdet by voltage division using voltage detection resistors Rdet1 to Rdet4, and Vdet is amplified by a differential amplifier to obtain inductor current information IL * Use as.

[0004] Inductor current information IL * is used for overcurrent protection, for example. * The comparator compares the inductor current information IL with the overcurrent threshold voltage to determine whether or not an overcurrent state exists. * When the overcurrent threshold voltage is exceeded, it is determined to be an overcurrent and protective functions such as stopping switching and reducing the duty are activated.

[0005] In addition, the inductor current information IL * is used to monitor the output current value. *is calculated and converted into an output current value, and transmitted to the outside via serial communication, etc. It is often used when real-time current information is required externally. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US Patent No. 5,982,160 Summary of the Invention [Problem to be solved by the invention]

[0007] As shown in Figure 5, one end of the capacitor Ccs on the output side of the switching elements Q1 and Q2 is measurement point A, and the other end on the output terminal side is measurement point B. The voltage Vb at measurement point B is the output voltage Vout of the step-down switching regulator. Since there is no impedance between the output voltage Vout and Rdet3 (current path B), connecting resistors Rdet3 and Rdet4 as a voltage divider circuit to measurement point B does not change the voltage Vb at measurement point B. Therefore, VdetB, which is the voltage Vb divided by Rdet3 and Rdet4, can be accurately measured as a value corresponding to the voltage Vb.

[0008] Meanwhile, at measurement point A, in addition to resistors Rdet1 and Rdet2, resistor Rcs also forms a series circuit between it and the output voltage Vbr of switching elements Q1 and Q2. Therefore, VdetA at measurement point A contains not only the voltage information at measurement point A, but also information about the voltage drop across resistor Rcs due to the current flowing through current path A. Furthermore, because resistor Rcs is connected to output voltage Vbr, VdetA at measurement point A also contains unnecessary voltage information about output voltage Vbr.

[0009] Figure 6 shows the voltage waveform of the output voltage Vbr. The voltage waveform of the output voltage Vbr is a square wave because it is the output of the switching elements Q1 and Q2. This square wave is averaged by an LC filter to become the output voltage Vout, and the duty cycle is controlled so that the output voltage Vout becomes the desired voltage. Therefore, the average value of the output voltage Vbr is equal to the output voltage Vout, and it can be seen that the output voltage Vbr and the output voltage Vout are equivalent. In other words, VdetA contains voltage information about the output voltage Vout, which means that VdetA fluctuates depending on the output voltage Vout.

[0010] In this way, at measurement point A, the voltage drop at resistor Rcs is added due to the connection of resistors Rdet1 to Rdet2 of the voltage divider circuit, making the potential lower than the original potential, whereas at measurement point B, there is no voltage drop even when resistors Rdet3 to Rdet4 of the voltage divider circuit are connected.

[0011] A simulation was performed on the step-down switching regulator shown in Figure 4, comparing the inductor current IL with the detected value Vdet (input voltage of the differential amplifier) ​​of the voltage Vccs between both terminals. The simulation was performed with an input voltage Vin of 24 V, Iout in the range of 1 A to 10 A, and three output voltages Vout of 5 V, 10 V, and 15 V. Figure 7 shows the plot of the detected value Vdet (average value) against the inductor current IL (average value).

[0012] As shown in Figure 7, when the current flowing through inductor L is relatively small, potential reversal can occur between the positive and negative terminals of capacitor Ccs. Because the potential across both ends of capacitor Ccs is input to a differential amplifier, the potential at the positive terminal is lower than the potential at the negative terminal, making it impossible to accurately detect the current flowing through the coil. For this reason, resistors Rdet1 to Rdet4 in the voltage divider circuit and R1 to R4 in the differential amplifier must be fine-tuned to prevent negative potentials. A large number of resistance constants must be designed with a good balance, and ultimately fine-tuning often requires trial and error.

[0013] Furthermore, as shown in Figure 7, the IL-Vdet characteristics vary depending on the output voltage Vout, and even for the same IL value, the detected value Vdet varies depending on the output voltage Vout. Therefore, to accurately measure the inductor current IL, a calculation coefficient must be provided that corresponds to the output voltage Vout. In the case of a variable output power supply, the calculation coefficient must be switched each time depending on the output voltage. Furthermore, when expanding the product lineup by output voltage Vout, it becomes necessary to implement a calculation coefficient that corresponds to the output voltage Vout for each power supply.

[0014] The present disclosure aims to provide a current detector and an electrical device that can easily and accurately detect an inductor current flowing through an inductor. [Means for solving the problem]

[0015] The current detector of the present disclosure is a current detector that detects an inductor current flowing through an inductor, and includes a detection circuit connected in parallel with the inductor. The detection circuit is a series circuit in which a resistive element is connected to each of both terminals of a capacitor, and the time constant is set equal to that of the inductor. [Effects of the Invention]

[0016] The current detector of the present disclosure can suppress the dependency of the output voltage on the voltage across the capacitor, and can therefore easily and accurately detect the inductor current flowing through the inductor based on the voltage across the capacitor. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram illustrating a configuration of an embodiment of a current detector. [Figure 2] 2 is a diagram illustrating a current path of the current detector shown in FIG. 1. FIG. [Figure 3] 2 is a diagram showing a detection result by the current detector shown in FIG. 1. FIG. [Figure 4] FIG. 1 is a diagram illustrating a configuration of a conventional current detector. [Figure 5]5 is a diagram showing a current path of the current detector shown in FIG. 4. FIG. [Figure 6] FIG. 2 is an explanatory diagram illustrating the relationship between an output voltage and a voltage at an output point. [Figure 7] 5 is a diagram showing a detection result by the current detector shown in FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

[0018] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

[0019] The electrical device of this embodiment is a power supply device 1 including an inductor L. Referring to Fig. 1, the power supply device 1 is a step-down switching regulator that receives an input voltage Vin, steps down the input voltage Vin, generates a stabilized output voltage Vout, and supplies the output voltage Vout to a load RL connected to an output terminal OUT.

[0020] The power supply device 1 includes an input capacitor Cin that smoothes the input voltage Vin. The power supply device 1 also includes a high-side switching element Q1 and a low-side switching element Q2 that are connected in series between the input voltage Vin and a reference potential. The switching elements Q1 and Q2 may be, for example, MOSFETs.

[0021] One end of the inductor L is connected to the connection point (hereinafter referred to as the output point) between the switching element Q1 and the switching element Q2, and the other end is connected to a reference potential via the output capacitor Cout. DCR shown in FIG. 1 represents the parasitic resistance of the inductor L.

[0022] The power supply device 1 includes a drive circuit 2 that alternately drives the switching elements Q1 and Q2 based on a PWM signal. The drive circuit 2 provides a dead time during which the switching elements Q1 and Q2 are simultaneously turned off for each level transition of the PWM signal.

[0023] The power supply device 1 includes a current detector 10 that detects an inductor current IL flowing through an inductor L. The current detector 10 includes a detection circuit 11 connected in parallel with the inductor L. The detection circuit 11 is a series circuit in which a resistive element is disposed on each end of a capacitor Ccs, and a first resistor Rcs1, a capacitor Ccs, and a second resistor Rcs2 are connected in series.

[0024] The detection circuit 11 is set so that the time constant TRC=Ccs×(Rcs1+Rcs2) is equal to the time constant TL=L / DCR of the inductor L. As a result, the voltage Vccs across the capacitor Ccs is proportional to the inductor current IL.

[0025] The current detector 10 includes a voltage divider circuit 12 that converts the voltage Vccs across the capacitor Ccs into a detectable detection voltage Vdet. The voltage divider circuit 12 includes resistors Rdet1 to Rdet4, and divides the voltage Vccs across the capacitor Ccs at a predetermined ratio. The resistors Rdet1 and Rdet2 are connected in series between a measurement point A, which is one end on the output terminal BR side, and a reference potential. The resistors Rdet3 and Rdet4 are connected in series between a measurement point B, which is the other end on the output terminal OUT side, and a reference potential. The voltage division ratio of the resistors Rdet1 and Rdet2 and the voltage division ratio of the resistors Rdet3 and Rdet4 are set equal, i.e., Rdet1=Rdet3, Rdet2=Rdet4.

[0026] 2, at measurement point B, resistors Rdet3 and Rdet4 of voltage-dividing circuit 12 and resistor Rcs2 of detection circuit 11 form a series circuit. Therefore, VdetB, which is obtained by dividing voltage Vb at measurement point B using resistors Rdet3 and Rdet4, contains information about the voltage drop across resistor Rcs2 due to the current flowing through current path B, in addition to voltage information about measurement point B. In other words, because resistor Rcs2 is connected to output voltage Vout, VdetB contains unnecessary voltage information about Vout in addition to voltage information about measurement point B.

[0027] At measurement point A, resistor Rcs1 of detection circuit 11 forms a series circuit in addition to resistors Rdet1 and Rdet2 of voltage divider circuit 12. Therefore, VdetA, which is obtained by dividing voltage Va at measurement point A using resistors Rdet1 and Rdet2, contains information about the voltage drop across resistor Rcs1 due to the current flowing through current path A, in addition to voltage information about measurement point A. In other words, because resistor Rcs1 is connected to voltage Vbr at output point BR, VdetA contains not only voltage information about measurement point A, but also voltage information about unwanted output point voltage Vbr.

[0028] As shown in Figure 6, the output voltage Vout and the output point voltage Vbr are equivalent. Therefore, VdetA and VdetB both contain unnecessary information about the output voltage Vout. The amount of Vout voltage information contained in VdetA and VdetB is equal when resistor Rcs1 = resistor Rcs2 in detection circuit 11.

[0029] The difference between VdetA and VdetB (detection value Vdet) is calculated (subtracted) by a differential amplifier 20 or the like, and inductor current information IL * Therefore, unnecessary information (voltage information of Vout) contained in VdetA and VdetB is deleted by calculation (subtraction), and the necessary information (voltage information of measurement point A - voltage information of measurement point B) is correctly obtained.

[0030] In the current detector 10 shown in Fig. 1, a simulation was performed on the detected value Vdet (input voltage of the differential amplifier 20) of the voltage Vccs between both terminals versus the inductor current IL. The simulation was performed with the input voltage Vin set to 24 V, Iout set to a range of 1 A to 10 A, and output voltage Vout set to three values: 5 V, 10 V, and 15 V. Fig. 3 shows the results of plotting the detected value Vdet (average value) versus the inductor current IL (average value).

[0031] As shown in FIG. 3, even in the region where the current flowing through the inductor L is relatively small, there is no region where the detection voltage Vdet becomes negative, and the shift of the detection voltage Vdet to the negative side can be prevented. This allows the current detector 10 to accurately measure the inductor current IL over a wide range, from small currents to large currents. Furthermore, the IL-Vdet characteristic does not depend on the output voltage Vout. Because the current detector 10 is not dependent on the output voltage Vout, it can accurately measure the inductor current IL without having to prepare a large number of calculation constants for different cases.

[0032] In the example shown in FIG. 1, the detection voltage Vdet detected by the current detector 10 is converted into inductor current information IL using a differential amplifier 20 (OP amplifier). * However, a microcomputer may be used instead of the differential amplifier 20.

[0033] The current detector 10 can also be used in other power supply systems, such as a step-up switching regulator equipped with an inductor L. Furthermore, the current detector 10 is not limited to switching regulators and can be used in any electrical device equipped with an inductor L.

[0034] As described above, this embodiment is a current detector 10 that detects the inductor current IL flowing through the inductor L, and includes a detection circuit 11 connected in parallel with the inductor L. The detection circuit 11 is a series circuit in which resistance elements Rcs1 and Rcs2 are connected to both terminals of the capacitor Ccs, respectively, and the time constant is set equal to that of the inductor L. This configuration makes it possible to suppress the dependency of the output voltage Vout on the voltage Vccs across the capacitor Ccs, so that the inductor current IL flowing through the inductor L can be easily and accurately detected based on the voltage Vccs across the capacitor Ccs.

[0035] Furthermore, according to this embodiment, the resistance elements Rcs1 and Rcs2 connected to both terminals of the capacitor Ccs are set to have the same resistance value (Rcs1=Rcs2). This configuration can cancel the dependency of the output voltage Vout on the voltage Vccs across the capacitor Ccs, making it possible to simply and accurately detect the inductor current IL flowing through the inductor L based on the voltage Vccs across the capacitor Ccs.

[0036] It is clear that the present invention is not limited to the above-described embodiments, and that each embodiment can be appropriately modified within the scope of the technical concept of the present invention. Furthermore, the number, position, shape, etc. of the above-described components are not limited to the above-described embodiments, and the number, position, shape, etc. can be set to be suitable for implementing the present invention. Note that the same components are denoted by the same reference numerals in each drawing. [Explanation of symbols]

[0037] 1 Power supply 2. Drive circuit 10 Current detector 11 Detection circuit 12 Voltage divider circuit 20 Differential Amplifier

Claims

1. A current detector for detecting an inductor current flowing through an inductor, a detection circuit connected in parallel with the inductor; The current detector is characterized in that the detection circuit is a series circuit in which a resistor element is connected to each of both terminals of a capacitor, and the time constant is set equal to that of the inductor.

2. 2. The current detector according to claim 1, wherein the resistance elements connected to both terminals of the capacitor are set to have the same resistance value.

3. An electrical device including an inductor, a current detector for detecting an inductor current flowing through the inductor; the current detector includes a detection circuit connected in parallel with the inductor; The electric device is characterized in that the detection circuit is a series circuit in which a resistor element is connected to each of both terminals of a capacitor, and the time constant is set equal to that of the inductor.

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