Current detector and electrical apparatus

Abstract

The invention provides a current detector and an electrical apparatus, which can simply and accurately detect inductor current flowing through an inductor. A current detector (10) for detecting an inductor current (IL) flowing through an inductor (L) has a detection circuit (11) connected in parallel with the inductor (IL), the detection circuit (11) is a series circuit in which resistor elements (Rcs1, Rcs2) are connected to both terminals of a capacitor (Ccs), respectively, and the time constant of the detection circuit (11) is set to be equal to that of the inductor (L). Resistance elements (Rcs1, Rcs2) respectively connected to both terminals of the capacitor (Ccs) are set to have the same resistance value (Rcs1 = Rcs2).

Description

Technical Field

[0001] Embodiments of this disclosure relate to a current detector and an electrical device for detecting the inductor current flowing through an inductor. Background Technology

[0002] Figure 4 This is a step-down switching regulator (electrical device) with an inductor L. As a current detector that detects the inductor current IL flowing through the inductor L, a series circuit consisting of a resistor Rcs and a capacitor Ccs is connected in parallel with the inductor L (see, for example, Patent Document 1). This current detector detects the voltage Vccs between the two terminals of the capacitor Ccs as the inductor current IL flowing through the inductor L. 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, the voltage Vccs between the two terminals is proportional to the inductor current IL.

[0003] like Figure 4 As shown, for example, regarding the detection of the voltage Vccs between the two terminals, a Vccs measurement circuit using an operational amplifier is employed. The voltage Vccs between the two terminals is detected as Vdet by using a voltage divider between voltage sensing resistors Rdet1 to Rdet4. Vdet is then amplified by a differential amplifier and used as the inductor current information IL*.

[0004] Inductor current information IL* is used, for example, for overcurrent protection. A comparator compares the inductor current information IL* with the overcurrent threshold voltage to determine if an overcurrent condition has occurred. When the inductor current information IL* exceeds the overcurrent threshold voltage, the drive circuit determines it to be an overcurrent and performs protective functions such as stopping the switch or reducing the duty cycle.

[0005] In addition, the inductor current information IL* is used to monitor the output current value. The inductor current information IL* is converted into an output current value through calculation and transmitted externally via serial communication, etc. This is frequently used when real-time current information is required externally.

[0006] Patent Document 1: Specification of US Patent No. 5982160

[0007] like Figure 5As shown, in capacitor Ccs, one end of the output terminals of switching elements Q1 and Q2 is designated as measurement point A, and the other end is designated as measurement point B. The voltage Vb at measurement point B is the output voltage Vout of the buck switching regulator. Since there is no impedance (current path B) between the output voltage Vout and Rdet3, the voltage Vb at measurement point B does not change even if resistors Rdet3 and Rdet4 are connected as a voltage divider circuit. Therefore, VdetB, obtained by dividing voltage Vb using Rdet3 and Rdet4, can be accurately measured as the value corresponding to voltage Vb.

[0008] On the other hand, regarding measurement point A, in addition to resistors Rdet1 and Rdet2, resistor Rcs also forms a series circuit with the output voltage Vbr of switching elements Q1 and Q2. Therefore, regarding VdetA of measurement point A, in addition to the voltage information of measurement point A, information about the voltage drop at resistor Rcs caused by the current flowing through current path A is also included. Furthermore, since resistor Rcs is connected to the output voltage Vbr, VdetA of measurement point A also includes unnecessary voltage information of the output voltage Vbr.

[0009] Figure 6 This is the voltage waveform of the output point voltage Vbr. Since the voltage waveform of the output point voltage Vbr is the output of switching elements Q1 and Q2, it becomes a rectangular wave. The value obtained by averaging this rectangular wave through an LC filter becomes the output voltage Vout. The duty cycle is controlled to make the output voltage Vout the desired voltage. Therefore, it can be seen that the average value of the output point voltage Vbr is equal to the output voltage Vout, and the output point voltage Vbr and the output voltage Vout are equivalent. That is, VdetA contains the voltage information of the output voltage Vout, meaning that VdetA varies according to the output voltage Vout.

[0010] Thus, measurement point A becomes lower than its original potential due to the voltage drop at resistor Rcs caused by the resistors Rdet1 to Rdet2 connected to the voltage divider circuit. In contrast, measurement point B does not experience a voltage drop even when connected to resistors Rdet3 to Rdet4 of the voltage divider circuit.

[0011] exist Figure 4 In the buck switching regulator shown, a simulation was performed on the detected value Vdet (input voltage of the differential amplifier) ​​of the voltage Vccs between the two terminals relative to the inductor current IL. The simulation was conducted with an input voltage Vin = 24V and Iout = 1A to 10A, and output voltages Vout = 5V, 10V, and 15V. Figure 7This is the result of plotting the measured value Vdet (average) relative to the inductor current IL (average).

[0012] like Figure 7 As shown, when the current flowing through inductor L is relatively small, the potentials at the positive and negative terminals of capacitor Ccs sometimes reverse. Since the potential across capacitor Ccs is input to the differential amplifier, the positive terminal has a lower potential than the negative terminal, making it impossible to accurately detect the current flowing through the coil. Therefore, it is necessary to fine-tune the resistors Rdet1 to Rdet4 in the voltage divider circuit and R1 to R4 in the differential amplifier to prevent them from becoming negative. This requires a balanced design of multiple resistance constants, and ultimately, fine-tuning is mostly achieved through a cut-and-try process.

[0013] In addition, such as Figure 7 As shown, the IL-Vdet characteristic varies depending on the output voltage Vout. Even with the same IL value, the detected value Vdet differs depending on the output voltage Vout. Therefore, to accurately measure the inductor current IL, a calculation factor corresponding to the output voltage Vout is necessary. In the case of a variable output power supply, the calculation factor must be switched according to the output voltage each time. Furthermore, when developing a product lineup based on the output voltage Vout, a calculation factor corresponding to the output voltage Vout needs to be implemented for each power supply. Summary of the Invention

[0014] This disclosure provides a current detector and electrical device that can simply and accurately detect the inductor current flowing through an inductor.

[0015] The current detector disclosed herein detects the inductor current flowing through an inductor. The current detector has a detection circuit connected in parallel with the inductor. The detection circuit is a series circuit with resistive elements connected to the two terminals of a capacitor, and its time constant is set to be equal to that of the inductor.

[0016] The current detector disclosed herein can suppress the dependence of the output voltage on the voltage between the two terminals of the capacitor, and thus can easily and accurately detect the inductor current flowing through the inductor based on the voltage between the two terminals of the capacitor. Attached Figure Description

[0017] Figure 1 This is a diagram illustrating the structure of an embodiment of the current detector.

[0018] Figure 2 It shows Figure 1 The diagram shows the current path of the current detector.

[0019] Figure 3 It shows Figure 1 The graph shows the detection results of the current detector.

[0020] Figure 4 This is a diagram showing the structure of an existing current detector.

[0021] Figure 5 It shows Figure 4 The diagram shows the current path of the current detector.

[0022] Figure 6 This is an explanatory diagram illustrating the relationship between the output voltage and the voltage at the output point.

[0023] Figure 7 It shows Figure 4 The graph shows the detection results of the current detector.

[0024] Label Explanation

[0025] 1: Power supply unit; 2: Drive circuit; 10: Current detector; 11: Detection circuit; 12: Voltage divider circuit; 20: Differential amplifier. Detailed Implementation

[0026] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0027] The electrical device in this embodiment is a power supply device 1 having an inductor L. (Refer to...) Figure 1 The power supply unit 1 is a step-down switching regulator that receives the input voltage Vin, steps it down to generate a stabilized output voltage Vout, and supplies it to the load RL connected to the output terminal OUT.

[0028] The power supply unit 1 has an input capacitor Cin that smooths the input voltage Vin. The power supply unit 1 has a switching element Q1 connected in series on the high side between the input voltage Vin and a reference potential, and a switching element Q2 on the low side. Switching elements Q1 and Q2 can be, for example, MOSFETs.

[0029] One end of the inductor L is connected to the connection point of the switching elements Q1 and Q2 (hereinafter referred to as the output point), and the other end is connected to the reference potential via the output capacitor Cout. Figure 1 The DCR shown represents the parasitic resistance of inductor L.

[0030] The power supply unit 1 has a drive circuit 2 that alternately drives switching elements Q1 and Q2 according to a PWM signal. Furthermore, the drive circuit 2 sets a dead time for simultaneously turning off switching elements Q1 and Q2 for each level transition of the PWM signal.

[0031] The power supply device 1 has a current detector 10 that detects the inductor current IL flowing through the inductor L. The current detector 10 has a detection circuit 11 connected in parallel with the inductor L. The detection circuit 11 is a series circuit in which a first resistor Rcs1, the capacitor Ccs, and the second resistor Rcs2 are connected in series across the capacitor Ccs.

[0032] The time constant TRC = Ccs × (Rcs1 + Rcs2) of the detection circuit 11 is set to be equal to the time constant TL = L / DCR of the inductor L. Therefore, the voltage Vccs between the two terminals of the capacitor Ccs is proportional to the inductor current IL.

[0033] The current detector 10 has a voltage divider circuit 12 that converts the voltage Vccs between the two terminals of capacitor Ccs into a detectable voltage Vdet. The voltage divider circuit 12 has resistors Rdet1 to Rdet4, which divide the voltage Vccs between the two terminals of capacitor Ccs in a predetermined ratio. Resistors Rdet1 and Rdet2 are connected in series at one end of the output point BR side, i.e., between measurement point A and the reference potential. Resistors Rdet3 and Rdet4 are connected in series at the other end of the output terminal OUT side, i.e., between measurement point B and the reference potential. The voltage division ratio of resistors Rdet1 and Rdet2 is equal to the voltage division ratio of resistors Rdet3 and Rdet4, and is set as Rdet1 = Rdet3 and Rdet2 = Rdet4.

[0034] Reference Figure 2 At measurement point B, in addition to resistors Rdet3 and Rdet4 of voltage divider circuit 12, resistor Rcs2 of detection circuit 11 also forms a series circuit. Therefore, VdetB, obtained by dividing the voltage Vb at measurement point B through resistors Rdet3 and Rdet4, contains not only the voltage information at measurement point B but also information about the voltage drop at resistor Rcs2 caused by the current flowing through current path B. That is, since resistor Rcs2 is connected to the output voltage Vout, VdetB contains not only the voltage information at measurement point B but also unnecessary voltage information of Vout.

[0035] At measurement point A, in addition to resistors Rdet1 and Rdet2 of voltage divider circuit 12, resistor Rcs1 of detection circuit 11 also forms a series circuit. Therefore, VdetA, obtained by dividing the voltage Va at measurement point A through resistors Rdet1 and Rdet2, contains not only the voltage information at measurement point A, but also information about the voltage drop at resistor Rcs1 caused by the current flowing through current path A. That is, since resistor Rcs1 is connected to the voltage Vbr at output point BR, VdetA contains not only the voltage information at measurement point A, but also the voltage information of the output point voltage Vbr.

[0036] If used Figure 6 As shown, the output voltage Vout is equivalent to the output point voltage Vbr. Therefore, both VdetA and VdetB contain voltage information of the output voltage Vout as unnecessary information. Moreover, the amount of voltage information of Vout contained in VdetA and VdeB is equal when the resistor Rcs1 in the detection circuit 11 is equal to the resistor Rcs2.

[0037] VdetA and VdetB are processed by differential amplifier 20 to subtract the differential value (detected value Vdet), resulting in the inductor current information IL*. Therefore, unnecessary information (voltage information of Vout) contained in VdetA and VdetB is removed through the operation (subtraction), correctly obtaining the necessary information (voltage information at measurement point A - voltage information at measurement point B).

[0038] exist Figure 1 In the current detector 10 shown, a simulation was performed on the detected value Vdet (input voltage of the differential amplifier 20) of the voltage Vccs between the two terminals of the inductor current IL. The simulation was implemented with an input voltage range of Vin = 24V and Iout = 1A to 10A, and output voltages of Vout = 5V, 10V, and 15V. Figure 3 This is the result of plotting the measured value Vdet (average) relative to the inductor current IL (average).

[0039] like Figure 3 As shown, even in regions where the current flowing through inductor L is relatively small, there is no region where the detection voltage Vdet is negative, preventing the detection voltage Vdet from shifting to the negative side. Therefore, the current detector 10 can accurately measure the inductor current IL over a wide range, from small to large currents. Furthermore, the IL-Vdet characteristic is independent of the output voltage Vout. Since the current detector 10 is independent of the output voltage Vout, it is possible to accurately measure the inductor current IL without needing to prepare multiple operational constants for different cases.

[0040] exist Figure 1In the example shown, the configuration uses a differential amplifier 20 (OP amplifier) ​​to convert the detection voltage Vdet detected by the current detector 10 into inductor current information IL*, but a microcontroller can also be used instead of the differential amplifier 20.

[0041] The current detector 10 can also be used in other power supply methods, such as boost-type switching regulators with inductors L. Furthermore, the current detector 10 is not limited to switching regulators, but can be used in all electrical devices with inductors L.

[0042] As described above, this embodiment is a current detector 10 that detects the inductor current IL flowing through the inductor L. The current detector 10 has a detection circuit 11 connected in parallel with the inductor L. The detection circuit 11 is a series circuit in which resistive elements Rcs1 and Rcs2 are connected to the two terminals of the capacitor Ccs respectively, and its time constant is set to be equal to that of the inductor L.

[0043] According to this structure, since the dependence of the output voltage Vout on the voltage Vccs between the two terminals of capacitor Ccs can be suppressed, the inductor current IL flowing through the inductor L can be detected simply and accurately based on the voltage Vccs between the two terminals of capacitor Ccs.

[0044] Furthermore, according to this embodiment, the resistive elements Rcs1 and Rcs2, which are respectively connected to the two terminals of the capacitor Ccs, are set to have equal resistance values ​​(Rcs1 = Rcs2).

[0045] According to this structure, since the dependence of the output voltage Vout on the voltage Vccs between the two terminals of capacitor Ccs can be eliminated, the inductor current IL flowing through the inductor L can be detected simply and accurately based on the voltage Vccs between the two terminals of capacitor Ccs.

[0046] Furthermore, the present invention is not limited to the embodiments described above, and it is understood that appropriate modifications can be made to each embodiment within the scope of the technical concept of the present invention. In addition, the number, position, shape, etc., of the above-described structural components are not limited to the embodiments described above, and can be any number, position, shape, etc., suitable for implementing the present invention. Furthermore, in the accompanying drawings, the same structural elements are labeled with the same reference numerals.

Claims

1. A current detector for detecting inductor current flowing through an inductor, characterized in that, The current detector has a detection circuit, which is connected in parallel with the inductor. The detection circuit is a series circuit in which resistive elements are connected to the two terminals of the capacitor, and its time constant is set to be equal to that of the inductor.

2. The current detector according to claim 1, characterized in that, The resistive elements connected to the two terminals of the capacitor are configured to have equal resistance values.

3. An electrical device comprising an inductor, characterized in that, The electrical equipment has a current detector that detects the inductor current flowing through the inductor. The current detector has a detection circuit, which is connected in parallel with the inductor. The detection circuit is a series circuit in which resistive elements are connected to the two terminals of the capacitor, and its time constant is set to be equal to that of the inductor.

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