Current parameter measuring circuit for power inductor of BUCK type DC / DC chip

Abstract

The utility model discloses a current parameter measuring circuit for a power inductor of a BUCK type DC / DC chip. The current parameter measuring circuit comprises a DC / DC chip, a power inductor, a DC resistor, a measuring resistor, a measuring capacitor, an input impedance and a current detection amplifier, the SW end of the DC / DC chip is connected with the output end VOUT through a power inductor and a direct current resistor which are connected in series; the measuring resistor and the measuring capacitor are connected in series and then connected to two ends of the power inductor and the direct-current resistor in parallel; the input end of the current detection amplifier is connected in parallel with the two ends of the measuring capacitor, and the input impedance is connected between the negative input end and the measuring capacitor. According to the utility model, the measuring resistor and the measuring capacitor are connected in parallel with the power inductor to measure the voltage change at the two ends of the capacitor to indirectly obtain the current parameter of the power inductor, which is simple and effective and has little influence on the original circuit; and voltage change at two ends of the measured capacitor is converted into voltage change at two ends of the input impedance, so that the influence of chip switching on and off on the test is reduced, and the accuracy is improved.

Description

Technical Field

[0001] The utility model relates to the technical field, in particular to a current parameter measurement circuit for a power inductor of a BUCK type DC / DC chip. Background Art

[0002] Buck type DC / DC chips, also known as buck type switching power supplies, are often used in electronic products, instrumentation, automotive power supplies, etc. They generate PWM waves by turning on and off MOS tubes to achieve output voltage control. However, due to issues such as efficiency and temperature resistance, there are requirements for the peak current passing through the power chip, and it is necessary to detect the peak current of the inductor connected to the buck type DC / DC chip.

[0003] One of the existing current detection methods for BUCK-type switching power supplies is to use the on-resistance of the high-side MOS tube inside the switching power supply to measure the peak current. However, since the on-resistance changes with temperature, the detected peak current changes continuously and the accuracy is insufficient. Another current detection method for BUCK-type switching power supply chips is to use a dedicated detection resistor in series near the inductor. However, due to the impedance effect, losses are generated, which reduces the efficiency of the overall circuit. At the same time, in actual tests, the high-side MOSFET is integrated inside the chip, and the real-time on-resistance cannot be measured. At the same time, in most BUCK-type DC / DC designs, detection resistors cannot be used due to efficiency issues. That is to say, there are at least the following two problems in the detection methods of the prior art:

[0004] 1) The detection accuracy is insufficient and may also have adverse effects on the original circuit;

[0005] 2) Detection is difficult and inefficient. Utility Model Content

[0006] In view of the above two problems, the purpose of the utility model is to propose a current parameter measurement circuit for a power inductor of a BUCK type DC / DC chip. An input impedance R2 and a measuring capacitor C2 are connected in parallel at both ends of the power inductor, and the current parameter of the power inductor can be indirectly obtained according to the voltage change at both ends of the measuring capacitor C2. The detection method is simple and effective and has little impact on the original circuit. In addition, a current detection amplifier D1 and an input impedance R2 are provided to convert the voltage change at both ends of the measuring capacitor C2 into the voltage change at both ends of the input impedance R2, thereby reducing the influence of the chip switch on the test and effectively improving the test accuracy.

[0007] This is achieved through the following technical solutions:

[0008] A current parameter measurement circuit for a power inductor of a BUCK type DC / DC chip, the measurement circuit comprises at least one test branch, each test branch comprises a DC / DC chip, a power inductor L, a DC resistance DCR of the power inductor L, a measurement resistor R1, a measurement capacitor C1, a grounded filter capacitor C2, an input impedance R2, a current detection amplifier D1 and an SMA connector; wherein the input end of the DC / DC chip is connected to an external input V IN ; The SW end of the DC / DC chip is connected to the output end V through the series power inductor L and DC resistor DCR OUT ; The measuring resistor R1 and the measuring capacitor C1 are connected in series and then connected in parallel to the two ends of the power inductor L and the DC resistor DCR; the positive input end of the current detection amplifier D1 is connected between the measuring resistor R1 and the measuring capacitor C1, and the negative input end of the current detection amplifier D1 is connected between the measuring capacitor C1 and the DC resistor DCR through the input impedance R2; the output end of the current detection amplifier D1 is connected to the SMA connector, and the grounded filter capacitor C2 is connected in parallel between the DC resistor DCR and the output end V OUT between.

[0009] The test method is simple and effective in converting the voltage change of the power inductor L into the voltage change of the measuring capacitor C1. The test method also converts the voltage change of the measuring capacitor C1 into the voltage change of the input impedance R2 of the current detection amplifier D1, thereby reducing the influence of the chip's own noise and effectively improving the accuracy.

[0010] Preferably, at the output V OUT Resistors R3 and R4 are also connected in parallel between the DC resistor DCR, which are connected in series and grounded, and the DC / DC chip is connected between the resistors R3 and R4. The DC / DC chip is connected between the resistors R3 and R4 to form a feedback loop to check whether the circuit is operating normally.

[0011] Preferably, when there are at least two test branches, the structure of each test branch is the same, and each test branch is respectively at the input terminal V IN In parallel and at the output V OUT When there is more than one DC / DC chip, each branch is tested with the same structure to reduce costs and facilitate observation.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] The technical solution of the present application connects an input impedance R2 and a measuring capacitor C2 in parallel at both ends of a power inductor, and can indirectly obtain the current parameters of the power inductor based on the voltage change at both ends of the measuring capacitor C2. The detection method is simple and effective and has little impact on the original circuit. In addition, a current detection amplifier D1 and an input impedance R2 are provided to convert the voltage change at both ends of the measuring capacitor C2 into the voltage change at both ends of the input impedance R2, thereby reducing the impact of the chip switch on the test and effectively improving the test accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of a current parameter measurement circuit for a power inductor of a BUCK type DC / DC chip;

[0015] Figure 2 The present invention is a schematic diagram of a current parameter measurement circuit for a power inductor of at least two BUCK-type DC / DC chips. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings in the embodiments of the present invention. Example

[0017] like Figure 1 As shown, it is a schematic diagram of a current parameter measurement circuit for a power inductor of a BUCK type DC / DC chip. The measurement circuit mainly includes a BUCK type DC / DC chip, a power inductor L, a DC resistance DCR of the power inductor L, a measuring resistor R1, a measuring capacitor C1, a grounded filter capacitor C2, a current detection amplifier D1, an input impedance R2 and an SMA connector.

[0018] The DC / DC chip at least includes an input terminal, a ground terminal, a SW terminal and a feedback terminal. The input terminal is connected to the external input V IN The SW terminal is used to control whether the chip outputs externally, the ground terminal is used to protect the chip, and the feedback terminal is used to receive possible feedback signals. The SW terminal of the DC / DC chip is connected to a power inductor L, and the power inductor L is connected in series with a DC resistor DCR to the output terminal V OUT It should be noted that the actual device of DC resistance DCR does not exist. It is the total DC resistance of the enameled wire used in the outer layer of the device between the two ends of the power inductor L actually used. It is just listed here as equivalent. It is actually a parameter of the power inductor L itself. There is a data sheet for the power inductor L in actual use. The value of the DC resistance can be measured based on the data sheet and the LCR meter. Here, the LCR meter is an inductance capacitance resistance meter, which can accurately measure the inductance, capacitance, resistance and other related parameters of circuit components. The LCR meter is a commonly used instrument, and the specific parameters and usage methods are not described here.

[0019] The measuring resistor R1 and the measuring capacitor C1 are connected in series and then connected to the two ends of the power inductor L and the DC resistor DCR. This is to convert the current detection of the power inductor into the voltage detection of the detection capacitor C1. The purpose of the measuring resistor R1 is to reduce the influence of its own branch on the original circuit. Specifically, when selecting the measuring resistor R1 and the measuring capacitor C1, it is necessary to satisfy R1xC1=L / DCR, so that the voltage V across the capacitor C1 can be C =IxDCR, I is the current of the power inductor L, so the current waveform of the power inductor L can be obtained. At this time, if the accuracy requirement is not high, the measuring capacitor C1 can be directly measured with a device that measures voltage changes, so as to obtain the current waveform based on V C =IxDCR to get the waveform of current I.

[0020] However, at this time, the measuring resistor R1 and the measuring capacitor C1 are very close to the SW end. The voltage change is directly measured at both ends of the measuring capacitor C1, and the noise of the DC / DC chip itself may also be introduced. The influence of this noise on the measuring capacitor C1 cannot be ignored, resulting in a large deviation in the actual measurement result. In order to reduce the influence of the noise of the DC / DC chip itself, the present embodiment also connects a branch of a current detection amplifier D1 and an input impedance R2 in parallel at both ends of the measuring capacitor C1, converts the voltage change at both ends of the measuring capacitor C1 into the voltage change at both ends of the input impedance R2, and then amplifies it using the current detection amplifier D1. Specifically, the positive input end of the current detection amplifier D1 is connected between the measuring resistor R1 and the measuring capacitor C1, and the negative input end of the current detection amplifier D1 is connected to between the measuring capacitor C1 and the DC resistance DCR through the input impedance R2, and the output end of the current detection amplifier D1 is connected to the SMA connector, and the SMA connector can be connected to other external observation instruments for easy observation.

[0021] In this embodiment, the grounded filter capacitor C2 is connected in parallel between the DC resistor DCR and the output terminal V OUT between, used to stabilize the circuit and increase the output V OUT The quality of the output signal. The number of the filter capacitor C2 can be one or more, and can be set according to actual needs.

[0022] In this embodiment, at the output terminal V OUT Resistors R3 and R4 are also connected in parallel between the DC resistor DCR. Resistors R3 and R4 are connected in series and grounded. The feedback end of the DC / DC chip is connected between resistors R3 and R4 to receive circuit feedback and check whether the circuit is operating normally.

[0023] like Figure 2As shown, it is a schematic diagram of a current parameter measurement circuit for a power inductor of at least two BUCK type DC / DC chips. The number of DC / DC chips may be one or at least two. When the number of DC / DC chips is one, the measurement circuit is set according to the above. When the number of DC / DC chips is at least two, each DC / DC chip has a current parameter measurement circuit at the input terminal V IN and output terminal V OUT The DC / DC chips are connected in parallel, and the branches corresponding to each parallel DC / DC chip are set according to the above-mentioned measurement circuit. When the number of DC / DC chips is more than one, each branch adopts the same structure for measurement, which can not only ensure the measurement accuracy, but also facilitate the actual device collection, reduce costs, and also facilitate the staff to actually connect the circuit and improve work efficiency. For example, when the number of DC / DC chips is two, DC / DC chip 1 adopts the above-mentioned power inductor L, DC resistance DCR, measurement resistance R1, measurement capacitor C1, input impedance R2, current detection amplifier D1, SMA and grounded filter capacitor C2 for corresponding connection; DC / DC chip 2 adopts power inductor L', DC resistance DCR', measurement resistance R1', measurement capacitor C1', input impedance R2', current detection amplifier D1', SMA' and grounded filter capacitor C2' for corresponding connection, the structure needs to be consistent, and the parameters of the specific device selected need to be modified accordingly according to the difference of DC / DC chips and power inductors.

[0024] In a INA240A1 series switching power supply chip, the switching power supply frequency is 20kHz, the inductance of the power inductor L at the SW end of the chip is 8.2uH, and the DC resistance DCR of the power inductor L is 27mΩ. The measuring resistor R1 is 3KΩ, and the measuring capacitor C1 is 0.1uF. The measuring resistor R1 and the measuring capacitor C1 are connected in series and then connected in parallel to the two ends of the power inductor L. The output terminal V OUT Set two grounded filter capacitors between the power inductor L, both of which are 47uF; at the output end V OUT Resistors R3 and R4 are also connected in parallel between the DC resistor DCR. Resistors R3 and R4 are connected in series and grounded. The feedback end of the DC / DC chip is connected between resistors R3 and R4 to form a feedback loop. Resistors R3 and R4 are 42KΩ and 8KΩ.

[0025] Then, the current detection amplifier D1 and the input impedance R2 are connected at both ends of the measuring resistor C2. The amplification factor of the current detection amplifier D1 is 20 times, the input impedance R2 is 1KΩ, the power supply end is powered by a 5V power supply, the positive input end is connected between the measuring resistor R1 and the measuring capacitor C1, the negative input end is connected to the other end of the measuring capacitor C2 through the input impedance R2, and the output end is connected to the SMA connector. The staff turned on the switch of the INA240A1 chip, connected the oscilloscope to the SMA connector, and successfully observed the current changes.

[0026] In summary, the utility model connects the input impedance R2 and the measuring capacitor C2 in parallel at both ends of the power inductor, and can indirectly obtain the current parameters of the power inductor according to the voltage change at both ends of the measuring capacitor C2. The detection method is simple and effective and has little impact on the original circuit. In addition, a current detection amplifier D1 and an input impedance R2 are provided to convert the voltage change at both ends of the measuring capacitor C2 into the voltage change at both ends of the input impedance R2, thereby reducing the influence of the chip switch on the test, effectively improving the test accuracy, and having significant progress.

[0027] The above embodiments are only for illustrating the technical idea of ​​the present application and cannot be used to limit the protection scope of the present application. Any changes made on the basis of the technical solution in accordance with the technical idea proposed in the present application shall fall within the protection scope of the present application.

Claims

1. A current parameter measurement circuit for a power inductor of a BUCK type DC / DC chip, characterized in that: The measuring circuit comprises at least one test branch, each of which comprises a DC / DC chip, a power inductor L, a DC resistance DCR of the power inductor L, a measuring resistor R1, a measuring capacitor C1, a grounded filter capacitor C2, an input impedance R2, a current detection amplifier D1 and an SMA connector; The input end of the DC / DC chip is connected to the external input V IN ; The SW end of the DC / DC chip is connected to the output end V through the series power inductor L and DC resistor DCR OUT ; The measuring resistor R1 and the measuring capacitor C1 are connected in series and then connected in parallel to the two ends of the power inductor L and the DC resistor DCR; the positive input end of the current detection amplifier D1 is connected between the measuring resistor R1 and the measuring capacitor C1, and the negative input end of the current detection amplifier D1 is connected between the measuring capacitor C1 and the DC resistor DCR through the input impedance R2; the output end of the current detection amplifier D1 is connected to the SMA connector, and the grounded filter capacitor C2 is connected in parallel between the DC resistor DCR and the output end V OUT between.

2. The current parameter measurement circuit for a power inductor of a BUCK type DC / DC chip according to claim 1, characterized in that: At the output V OUT A resistor R3 and a resistor R4 are connected in parallel between the DC resistor DCR. The resistor R3 and the resistor R4 are connected in series and grounded. The DC / DC chip is connected between the resistor R3 and the resistor R4.

3. The current parameter measurement circuit for a power inductor of a BUCK type DC / DC chip according to claim 1, characterized in that: When there are at least two test branches, the structure of each test branch is the same, and each test branch has a V IN parallel and at the output V OUT in parallel.

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