CN117007847A - Current detection circuit and inverter bridge - Google Patents
Current detection circuit and inverter bridge Download PDFInfo
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Abstract
The application relates to a current detection circuit and an inverter bridge. The circuit comprises: the unidirectional conduction module comprises a first unidirectional conduction device and a second unidirectional conduction device; one end of the first unidirectional conduction device is used for being connected with a load current input end of a power tube of a lower bridge arm of the inversion bridge; the conducting direction of the first unidirectional conducting device is from the other end of the first unidirectional conducting device to one end of the first unidirectional conducting device; one end of the second unidirectional conduction device is used for connecting with the grounding end of the power tube; the input end of the voltage amplifying circuit is respectively connected with the other end of the first unidirectional conduction device and the other end of the second unidirectional conduction device; the input end of the voltage amplifying circuit is used for accessing reference voltage so as to lead the first unidirectional conduction device and the second unidirectional conduction device to be conducted under the condition that the power tube is conducted; the output end of the voltage amplifying circuit outputs detection voltage used for representing the branch current where the power tube is located. The circuit can reduce current detection errors.
Description
Technical Field
The application relates to the technical field of detection circuits, in particular to a current detection circuit and an inverter bridge.
Background
In detection circuit applications, power switching tubes are often used as switches to control a load, to start or stop or to adjust its output power, speed, etc. At present, a current sampling resistor is connected in series to a branch circuit where a power switch tube is located, the current sampling resistor is connected to a voltage amplifying circuit, and the current of the branch circuit where the power switch tube is located is obtained by measuring the voltages at two ends of the current sampling resistor.
In the implementation process, the inventor finds that at least the following problems exist in the conventional technology: the current detection method or the traditional method has the problems of large current detection error and the like.
Disclosure of Invention
In view of the above, it is necessary to provide a current detection circuit and an inverter bridge capable of reducing a current detection error.
To achieve the above object, in one aspect, an embodiment of the present application provides a current detection circuit, including:
the unidirectional conduction module comprises a first unidirectional conduction device and a second unidirectional conduction device; one end of the first unidirectional conduction device is used for being connected with a load current input end of a power tube of a lower bridge arm of the inversion bridge; the conducting direction of the first unidirectional conducting device is from the other end of the first unidirectional conducting device to one end of the first unidirectional conducting device; one end of the second unidirectional conduction device is used for connecting with the grounding end of the power tube; the conducting direction of the second unidirectional conducting device is the same as that of the first unidirectional conducting device;
The input end of the voltage amplifying circuit is respectively connected with the other end of the first unidirectional conduction device and the other end of the second unidirectional conduction device; the input end of the voltage amplifying circuit is used for accessing reference voltage so that the first unidirectional conduction device and the second unidirectional conduction device are conducted under the condition that the power tube is conducted; the output end of the voltage amplifying circuit outputs detection voltage which is used for representing the branch current where the power tube is located.
In one embodiment, the voltage amplifying circuit includes an amplifying device; the amplifying device is provided with a first input end and a second input end; the first input end is used for accessing reference voltage; the first input end and the second input end are configured to be consistent in potential under the condition that the amplifying device is in an operating state;
the first input end is connected with the other end of the first unidirectional conduction device, and the second input end is connected with the other end of the second unidirectional conduction device; or alternatively, the first and second heat exchangers may be,
the first input end is connected with the other end of the second unidirectional conduction device, and the second input end is connected with the other end of the first unidirectional conduction device.
In one embodiment, the amplifying device is a differential amplifier, the first input terminal is a non-inverting input terminal of the differential amplifier, and the second input terminal is an inverting input terminal of the differential amplifier.
In one embodiment, the conduction condition of the first unidirectional conduction device includes that the first unidirectional conduction device is in a conduction state in a fluctuation range of drain-source voltage of the power tube under the condition that the power tube is conducted based on a reference voltage.
In one embodiment, the voltage amplifying circuit further comprises a first resistor, a second resistor, a third resistor and a fourth resistor; wherein,
the first input end is connected with the other end of the first unidirectional conduction device or the other end of the second unidirectional conduction device through a first resistor; the second input end is connected with the other end of the second unidirectional conduction device or the other end of the first unidirectional conduction device through a second resistor; the first input end is connected with a reference voltage through a third resistor; the second input end is connected with the output end of the voltage amplifying circuit through a fourth resistor.
In one embodiment, the reference voltage is determined based on the on-voltage of the first unidirectional conductive device, the first resistance, and the third resistance.
In one embodiment, the first resistor and the second resistor have the same resistance value; the resistance values of the third resistor and the fourth resistor are the same;
the first unidirectional conduction device and the second unidirectional conduction device are diodes with the same model.
In one embodiment, the detection voltage is a voltage output by the output end of the voltage amplifying circuit under the condition that the power tube is conducted.
In one embodiment, the unidirectional conduction module further comprises a third unidirectional conduction device, and one end of the third unidirectional conduction device is connected with the other end of the first unidirectional conduction device; the conducting direction of the third unidirectional conducting device is opposite to the conducting direction of the first unidirectional conducting device;
the circuit further comprises:
the base electrode of the triode is used for connecting with the control end of the power tube; the transmitting stage of the triode is used for grounding; the collector electrode of the triode is used for accessing the power supply voltage;
the control end of the power switch tube is connected with the collector electrode of the triode; the current input end of the power switch tube is connected with the other end of the third unidirectional conduction device; the current output end of the power switch tube is used for grounding.
In one embodiment, the transistor is an NPN transistor; the third unidirectional conduction device is a diode; the power switch tube is an N-channel MOSFET field effect tube.
On the other hand, the embodiment of the application provides an inverter bridge, wherein a power tube of a lower bridge arm of the inverter bridge is provided with a load current input end and a grounding end; the inverter bridge comprises the current detection circuit; the load current input end is connected with one end of the first unidirectional conduction device; the grounding end is connected with one end of the second unidirectional conduction device;
The inverter bridge also comprises a pull-down resistor, one end of the pull-down resistor is connected with the control end of the power tube, and the other end of the pull-down resistor is used for grounding.
In one embodiment, the inverter bridge comprises a three-phase inverter bridge;
the power tube of the lower bridge arm of the three-phase inversion bridge is a field effect tube; the drain electrode of the field effect transistor is a load current input end; the source electrode of the field effect transistor is a grounding end.
In one embodiment, the number of current detection circuits is a plurality; the current detection circuits share the same second unidirectional conducting device.
One of the above technical solutions has the following advantages and beneficial effects:
the load current input end of the power tube from the voltage amplifying circuit to the lower bridge arm of the inverter bridge is conducted unidirectionally by adopting a first unidirectionally conducting device; a second unidirectional conduction device is adopted, and unidirectional conduction is carried out from the voltage amplifying circuit to the grounding end of the power tube; the first unidirectional conduction device and the second unidirectional conduction device are conducted under the condition that the power tube is conducted through reference voltage; the current detection circuit can be applied to application scenes with a larger load voltage range by adopting the first unidirectional conduction device and the second unidirectional conduction device, so that current detection errors are reduced.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments or the conventional techniques of the present application, the drawings required for the descriptions of the embodiments or the conventional techniques will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present application, and other drawings may be obtained according to the drawings without inventive effort for those skilled in the art.
FIG. 1 is a circuit topology diagram of an MOS transistor as one of the applications of a switching power transistor;
fig. 2 is a circuit topology diagram of an MOS transistor as a switching power transistor applied to a three-phase inverter bridge;
FIG. 3 is a schematic diagram of a conventional current detection circuit;
FIG. 4 is another schematic diagram of a conventional current detection circuit;
FIG. 5 is a schematic diagram of a conventional current detection circuit;
FIG. 6 is a block diagram of a current detection circuit in one embodiment;
FIG. 7 is a schematic diagram of a current detection circuit in one embodiment;
FIG. 8 is a schematic diagram of a current detection circuit in another embodiment;
FIG. 9 is an equivalent current detection circuit in one embodiment;
FIG. 10 is an equivalent current detection circuit in another embodiment;
FIG. 11 is a circuit for detecting current in one embodiment;
FIG. 12 is a schematic diagram of another embodiment of a current sense circuit;
FIG. 13 is a three-phase inverter bridge in one embodiment;
fig. 14 is a three-phase inverter bridge in another embodiment.
Detailed Description
In order that the application may be readily understood, a more complete description of the application will be rendered by reference to the appended drawings. Embodiments of the application are illustrated in the accompanying drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.
It will be understood that the terms first, second, etc. as used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another element. It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or be connected to the other element through intervening elements. Further, "connection" in the following embodiments should be understood as "electrical connection", "communication connection", and the like if there is transmission of electrical signals or data between objects to be connected. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," and/or the like, specify the presence of stated features, integers, steps, operations, elements, components, or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof. Also, the term "and/or" as used in this specification includes any and all combinations of the associated listed items.
Currently, in applications in various fields, MOS transistors (MOSFETs) are often used as switches for switching power transistors to control loads, to start or stop or to adjust output power, speed, etc. As shown in fig. 1, the circuit topology of the MOS transistor as one of the applications of the switching power transistor is shown, wherein the direct current VBUS is generally obtained by rectifying and filtering 220V; the load RL can be a specific load such as a heating body, a direct-current motor or a primary winding of a transformer; the power transistor Q1 is typically a field effect transistor, IGBT or triode; the low-side current detection resistor Rs is used for detecting the current of the power tube Q1, and the voltage on the current detection resistor Rs is amplified by the voltage amplifying circuit and can be used for current detection, overload protection, short-circuit protection and the like. The voltage amplifying circuit may include an operational amplifier U1 and peripheral components R1 to R5 thereof (e.g., resistors); the voltage amplifying circuit may be of other forms or may not be required. As shown in fig. 2, the MOS transistor is used as a switching power transistor to be applied to a circuit topology of a three-phase inverter bridge, and the three-phase inverter bridge is widely used for driving motors such as a brushless dc motor, a permanent magnet synchronous motor, an ac induction motor, a compressor, and the like. For some products, the motor or the compressor is inconvenient to place the rotor position detection device, one method is to calculate the rotor position by independently detecting the phase currents of the UVW three phases and then matching with a specific software algorithm, so that a current detection circuit is required to be respectively added between the lower bridge arm of the three-phase inverter bridge and the ground end GND.
In order to detect phase current, a current sampling resistor Rs is added between the lower bridge arm of the three-phase inverter bridge and the ground GND, and when current flows through the current sampling resistor Rs, sampling voltage V is obtained at two ends of the current sampling resistor Rs Rs Its value is proportional to the phase current (V Rs ＝I Rs * Rs), in combination with electricityThe voltage amplifying circuit can obtain accurate phase current signals. However, the addition of the current sampling resistor Rs may have difficulty in component type selection in some application scenarios, and often cannot achieve both cost and detection precision:
(1) If a current sampling resistor Rs of lower resistance is used, the obtained sampling voltage V is obtained although the loss and the volume on the current sampling resistor Rs are smaller Rs Also smaller, if no voltage amplification circuit is used, the effective detection accuracy of the ADC (Analog to Digital Converter, analog-to-digital converter) of the MCU (Microcontroller Unit, micro control unit) will be very low; at the same time due to the sampling voltage V Rs Weak voltage, sampling voltage V Rs The voltage is more susceptible to interference. If a voltage amplifying circuit is used, the cost increases.
(2) If a current sampling resistor Rs of higher resistance is used, the sampling voltage V is increased to some extent Rs The effective detection precision of the ADC is improved, but the loss on the current sampling resistor Rs is very large, the heating of the current sampling resistor Rs is very large, and meanwhile, the high-power and large-volume sampling resistor is usually low in cost, so that the working efficiency of the driver is reduced, and the layout area of a plurality of PCBs (Printed Circuit Board, printed circuit boards) is occupied.
One of the application schemes for solving the above problems is to directly use the on-resistance R of the power tube Q1 DS_ON As shown in fig. 3, 4 or 5, the power transistor Q1 is a field effect transistor. Wherein fig. 3 employs an amplifying circuit; fig. 4 shows a voltage-limited output detection voltage Vout of the zener diode ZD 1; fig. 5 uses diode D1 and diode D2 for clamping. Fig. 3, 4 or 5 do not require the use of a current sense resistor Rs, but rather the drain-source voltage V of the fet Q1 is sampled DS Current detection is achieved. Under the condition that the field effect transistor Q1 is completely conducted, the drain-source voltage V DS And drain-source current I DS Proportional to, the relation is V DS ＝R DS(ON) *I DS Wherein R is DS(ON) The on-resistance of the field effect transistor Q1 is good, and the consistency of the on-resistance is good under the condition of deep conduction of the field effect transistorFactors such as current have little influence, and the method is suitable for equipment or products which are sensitive to cost and do not need to precisely detect the current.
However, the schemes of fig. 3, fig. 4 or fig. 5 are not suitable for application under high voltage, when the input voltage is high (for example, 220V), the rectified and filtered dc voltage VBUS will be as high as 300V or more, because the impedance of the load RL is often very low, after the fet Q1 is turned off, the voltage at the drain (point D) of the fet Q1 will be raised to the same voltage level as the dc voltage VBUS, resulting in a leakage current flowing from the voltage limiting or clamping circuit to the dc voltage VBUS through the load RL, resulting in loss. When the FET Q1 is turned on, the on-resistance R of the FET is used DS(ON) Often small (e.g., 3mΩ to 3 Ω), the resulting drain-source voltage V DS And is small but is to be used for current sampling with as high accuracy as possible. Thus, the following is caused:
(1) In the case of a high VBUS, the dynamic variation range of the drain (point D) of the fet Q1 is large, and the back-stage circuit for outputting the detection voltage Vout may be damaged by high voltage breakdown without adding the voltage limiting circuit.
(2) If the voltage limiting circuit is added, after the field effect transistor Q1 is cut off, the load end always has leakage current passing through, and the leakage current value is I RL drain ≈(VBUS-V DZ ) R1. The leakage current directly improves the standby power consumption of the driving circuit, increases unnecessary device loss, and has a power loss value of P Loss of ≈I RL drain *VBUS。
(3) In order to reduce the power loss, the resistor R1 in the subsequent stage circuit for outputting the detection voltage Vout needs to use a resistor with a higher resistance value, and the static bias current of the Input end of the GPIO (General-Purpose Input/Output) or the operational amplifier from the MCU forms a bias voltage on the resistor R1 and is superposed to the drain-source voltage V DS The drain-source voltage V detected when the FET Q1 is on DS The bias voltage formed on the resistor R1 is less than ten mV and can obviously influence the drain-source voltage V of the later-stage circuit DS Thereby resulting in current detectionFurther expansion of the measurement error.
The embodiment of the application provides a current detection circuit and an inverter bridge capable of reducing current detection errors. The present application will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present application more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.
In one embodiment, as shown in fig. 6, a current detection circuit is provided, the circuit comprising:
the unidirectional conduction module 110, the unidirectional conduction module 110 includes a first unidirectional conduction device D1 and a second unidirectional conduction device D2; one end of the first unidirectional conduction device D1 is used for being connected with a load current input end of a power tube of a lower bridge arm of the inverter bridge; the conducting direction of the first unidirectional conducting device D1 is from the other end of the first unidirectional conducting device D1 to one end of the first unidirectional conducting device D1; one end of the second unidirectional conduction device D2 is used for connecting with the grounding end of the power tube; the conducting direction of the second unidirectional conducting device D2 is the same as the conducting direction of the first unidirectional conducting device D1;
the input end of the voltage amplifying circuit 120 is respectively connected with the other end of the first unidirectional conduction device D1 and the other end of the second unidirectional conduction device D2; the input end of the voltage amplifying circuit 120 is used for accessing a reference voltage, so that the first unidirectional conduction device D1 and the second unidirectional conduction device D2 are conducted under the condition that the power tube is conducted; the output terminal of the voltage amplifying circuit 120 outputs a detection voltage, and the detection voltage is used for representing the branch current where the power tube is located.
Specifically, as shown in fig. 6, the unidirectional conduction module 110 may implement unidirectional current conduction of the voltage amplification circuit 120 to the power tube Q1; the voltage amplifying circuit 120 is used for amplifying the voltage V between the load current input end and the ground end of the power tube Q1 DS (e.g., the voltage between the load current input terminal and the ground terminal in the on state of the power transistor Q1), and outputs the detection voltage Vout through the output terminal of the voltage amplifying circuit 120. Wherein, the control end of the power tube Q1 can be connected to control powerA control signal (e.g., pulse width modulation signal PWM) for turning on and off the tube Q1; the load current input end of the power tube Q1 refers to the current input end of the power tube Q1, and when the current detection circuit is connected to the power tube of the lower bridge arm of the inverter bridge with the circuit topology shown in fig. 1, the load current of the load RL flows into the current input end of the power tube Q1; when the current detection circuit is connected to the power tube of the lower bridge arm of the inverter bridge with the circuit topology shown in fig. 2, the current input end of the power tube Q1 flows in with the phase current of the motor serving as the load; that is, the branch current where the power transistor Q1 is located is the load current; the Ground (GND) of the power transistor Q1 refers to the current output of the power transistor Q1, and the current output of the power transistor Q1 is grounded.
Further, the unidirectional conduction module 110 includes a first unidirectional conduction device D1 and a second unidirectional conduction device D2, taking a case that the current detection circuit is connected to a power tube of a lower bridge arm of the inverter bridge of the circuit topology shown in fig. 1 as an example, if the voltage of the direct current VBUS is higher, if the power tube Q1 is in a conductive state, the voltage V between the load current input end and the ground end DS Lower (typically equivalent to a voltage source of mV level) requires consideration of the conduction voltage drop VD1 of the first unidirectional conductive device D1 with respect to the voltage V DS Therefore, the second unidirectional conducting device D2 is added, and for the input end of the voltage amplifying circuit 120, the other end of the first unidirectional conducting device D1 and the other end of the second unidirectional conducting device D2 are respectively connected, that is, the other end of the first unidirectional conducting device D1 and the other end of the second unidirectional conducting device D2 are changed simultaneously relative to the input end of the voltage amplifying circuit, so that the influence of the conduction voltage drop VD1 on the detection precision of the voltage detecting circuit is favorably counteracted.
Further, the first unidirectional conduction device D1 and the second unidirectional conduction device D2 are connected to the reference voltage VCC2 through the input end of the voltage amplifying circuit 120, so as to realize the conduction of the first unidirectional conduction device D1 and the second unidirectional conduction device D2 under the condition that the power tube Q1 is conducted. With the power tube Q1 conducting, the voltage V between the load current input terminal and ground DS Load current I connected with power tube Q1 DS Is in direct proportion to satisfy V DS ＝R DS_ON *I DS The method comprises the steps of carrying out a first treatment on the surface of the Based on the detection voltage Vout, the on-resistance R of the power tube Q1 DS_ON And the amplification factor of the voltage amplifying circuit 120, a corresponding load current I can be obtained DS 。
In some examples, the first unidirectional conductive device D1 and the second unidirectional conductive device D2 may be implemented using unidirectional conductive devices such as diodes; the voltage amplifying circuit 120 may be implemented by an amplifying device such as an operational amplifier or a differential amplifier.
According to the embodiment of the application, by providing the current detection circuit shown in fig. 6, through the unidirectional conductivity of the first unidirectional conduction device D1 and the second unidirectional conduction device D2, namely, the unidirectional conduction from the voltage amplification circuit 120 to the load current input end of the power tube of the lower bridge arm of the inverter bridge is realized by adopting the first unidirectional conduction device D1; a second unidirectional conduction device D2 is adopted, and unidirectional conduction is realized from the voltage amplifying circuit 120 to the grounding end of the power tube; the first unidirectional conduction device D1 and the second unidirectional conduction device D2 are conducted under the condition of conducting the power tube by the reference voltage, so that the method can be applied to an application scene with a larger load voltage range, and the voltage V between the load current input end and the grounding end of the power tube Q1 can be greatly reduced DS Dynamic range of (2); by measuring the detection voltage output by the output end of the voltage amplifying circuit 120, the branch current of the power tube can be obtained, and an external current detection resistor RS is not required to be additionally added to the lower bridge arm of the inverter bridge, so that the material cost is reduced. Meanwhile, the problem of static power consumption or load leakage current does not exist, and further, a resistor R1 with a large resistance value (such as the resistor R1 shown in fig. 3, 4 or 5) is not needed, so that the problem that the static bias current of the input end of the GPIO or the operational amplifier forms bias voltage on the resistor R1 to influence sampling precision is solved, and the current detection error is reduced.
In one embodiment, the conduction condition of the first unidirectional conduction device D1 includes that the first unidirectional conduction device D1 is in a conduction state in a fluctuation range of a drain-source voltage of the power tube under the condition that the power tube is conducted based on a reference voltage.
Specifically, the current detection circuit is connected to the circuit topology shown in fig. 1For example, if the power tube Q1 is turned on, the power tube of the lower bridge arm of the inverter bridge is V DS The voltage value is higher, and by correspondingly adjusting the reference voltage VCC2, it can be realized that the first unidirectional conduction device D1 is in a conduction state within the fluctuation range of the drain-source voltage VDS of the power tube Q1 under the condition that the power tube Q1 is in a conduction state, so as to maintain the above relation V DS ＝R DS_ON *I DS Establishment; when the power tube Q1 is in the off state, the load current input end of the power tube Q1 is increased from a small voltage to a high voltage (for example, from mV level to hundred volt level) due to very low load RL impedance, the first unidirectional conduction device D1 is used for stopping the input end of the forward high voltage surge voltage amplifying circuit 120, VD1 is the conduction voltage drop of the first unidirectional conduction device D1, and when the voltage of the load current input end of the power tube Q1 exceeds the value of VCC2-VD1, the first unidirectional conduction device D1 is turned off without meeting the conduction condition, thus blocking the current flowing from the direct current VBUS to the voltage amplifying circuit 120 and eliminating the problems of large standby power consumption and large leakage current as shown in fig. 3, 4 or 5; further, since the reverse cut-off voltage is concentrated at both sides of the first unidirectional conductive device D1, no current flows through the rear stage circuit of the first unidirectional conductive device D1, and the problem that the rear stage circuit for outputting the detection voltage Vout may break down under the condition of high voltage of the direct current VBUS is solved.
In one embodiment, the voltage amplifying circuit 120 includes an amplifying device; the amplifying device is provided with a first input end and a second input end; the first input end is used for accessing reference voltage; the first input end and the second input end are configured to be consistent in potential under the condition that the amplifying device is in an operating state;
The first input end is connected with the other end of the first unidirectional conduction device D1, and the second input end is connected with the other end of the second unidirectional conduction device D2; or alternatively, the first and second heat exchangers may be,
the first input end is connected with the other end of the second unidirectional conduction device D2, and the second input end is connected with the other end of the first unidirectional conduction device D1.
Specifically, the first input terminal and the second input terminal are configured to be potential in the case where the amplifying device is in an operating stateIn agreement, the reference voltage VCC2 is accessed based on the input terminal of the voltage amplifying circuit 120, so that the second unidirectional conductive device D2 must also satisfy the conductive condition in the case where the first unidirectional conductive device D1 satisfies the conductive condition. In the case that the power tube Q1 is in a conducting state, the first unidirectional conducting device D1 and the second unidirectional conducting device D2 are both conducting, and the power tube Q1 loads a voltage V between a current input end and a grounding end DS The voltage value of (2) varies with the load current of the power transistor Q1. The voltage V is amplified by an amplifying device of the voltage amplifying circuit 120 DS High-magnification voltage amplification is realized to improve the accuracy of current detection.
In some examples, the amplifying device may be an operational amplifier; according to the 'virtual short' principle of the operational amplifier, under the condition that the operational amplifier works IN an amplifying state, the IN-phase input end IN+ potential is consistent with the IN-potential of the reverse input end; therefore, based on the input terminal of the voltage amplifying circuit 120 being connected to the reference voltage VCC2, the second unidirectional conductive device D2 must meet the conductive condition if the first unidirectional conductive device D1 meets the conductive condition.
In some examples, the output terminal of the voltage amplifying circuit 120 may be an output terminal of the amplifying device, that is, the detection voltage Vout may be an output voltage Vo output by the amplifying device; the output terminal of the voltage amplifying circuit 120 may be obtained by further connecting the output terminal of the amplifying device to a corresponding element or circuit, that is, the detected voltage Vout may be a voltage obtained by passing the output voltage Vo through the corresponding element or circuit.
In one embodiment, the amplifying device is a differential amplifier, the first input terminal is a non-inverting input terminal of the differential amplifier, and the second input terminal is an inverting input terminal of the differential amplifier.
Specifically, the differential amplifier may offset the conduction voltage drop VD1 of the first unidirectional conduction device D1 and the conduction voltage drop VD2 of the second unidirectional conduction device D2, so as to decouple the nonlinear voltage drop characteristics of the first unidirectional conduction device D1 and the second unidirectional conduction device D2, and achieve a good compromise between low cost and high performance.
In one embodiment, the voltage amplifying circuit 120 further includes a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4; the first input end is connected with the other end of the first unidirectional conduction device D1 or the other end of the second unidirectional conduction device D2 through a first resistor R1; the second input end is connected with the other end of the second unidirectional conduction device D2 or the other end of the first unidirectional conduction device D1 through a second resistor R2; the first input end is connected with reference voltage through a third resistor R3; the second input terminal is connected to the output terminal of the voltage amplifying circuit 120 through a fourth resistor R4.
Specifically, as shown in fig. 7, one end of the first resistor R1 is connected to the other end of the first unidirectional conduction device D1, and the other end of the first resistor R1 is connected to the non-inverting input end of the differential amplifier; one end of the second resistor R2 is connected with the other end of the second unidirectional conduction device D2, and the other end of the second resistor R2 is connected with the inverting input end of the differential amplifier; the non-inverting input end of the differential amplifier is connected with the reference voltage VCC2 through a third resistor R3; the inverting input terminal of the differential amplifier is connected to the output terminal of the voltage amplifying circuit 120 through the fourth resistor R4. The output voltage Vo of the differential amplifier is obtained according to the following equation:
Vo＝VD1+[VS+(VCC2-VD2-VS)*(R2/(R2+R4))]*(1+R3/R1)
wherein VD1 is a conduction voltage drop of the first unidirectional conduction device D1, VD2 is a conduction voltage drop of the second unidirectional conduction device D2, and VS is a voltage V between the load current input terminal and the ground terminal when the power tube Q1 is turned on DS A value; VCC2 is the pull-up reference voltage for the third resistor R3.
As shown in fig. 8, one end of the first resistor R1 is connected to the other end of the second unidirectional conduction device D2, and the other end of the first resistor R1 is connected to the non-inverting input end of the differential amplifier; one end of the second resistor R2 is connected with the other end of the first unidirectional conduction device D1, and the other end of the second resistor R2 is connected with the inverting input end of the differential amplifier; the non-inverting input end of the differential amplifier is connected with the reference voltage VCC2 through a third resistor R3; the inverting input terminal of the differential amplifier is connected to the output terminal of the voltage amplifying circuit 120 through the fourth resistor R4. Similarly, in fig. 9, the output voltage Vo of the differential amplifier is obtained according to the following formula:
Vo＝VS+VD2+[(VCC2-VD1)*(R2/(R2+R4))-VS]*(1+R3/R1)
That is, the amplification factor of the VS value can be obtained according to the resistance values of the first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4.
Further, in the case where the power transistor Q1 is turned on, the voltage V DS Load current I connected with power tube Q1 DS Is in direct proportion to satisfy V DS ＝R DS_ON *I DS Fig. 7 or 8 may be simplified to fig. 9 or 10, respectively. Voltage V between load current input terminal and ground terminal DS The voltage source can be regarded as a voltage source controlled by load current, and the change of the voltage source can lead to the change of the voltage at the point B IN fig. 9, so that the voltage division value of the IN-phase input end IN+ is influenced, the voltage change is amplified by a differential amplifier by a certain multiple to obtain the output voltage Vo, and the amplified voltage signal can obtain larger amplitude (instead of weak voltage of mV level), so that the effective sampling precision of the ADC at the later stage can be well utilized and ensured, and the current detection precision is effectively improved.
In some examples, the inverting input of the differential amplifier is connected to the output of the differential amplifier through a fourth resistor R4; the output voltage Vo of the output terminal of the differential amplifier may further output the detection voltage Vout through the fifth resistor R5.
In one embodiment, the reference voltage is determined based on the on voltage of the first unidirectional conductive device D1, the values of the first resistor R1 and the third resistor R3.
Specifically, as shown in fig. 7, the reference voltage VCC2 sequentially passes through the third resistor R3, the first resistor R1, the first unidirectional conductive device D1, the load current input end of the power tube Q1, and the ground end of the power tube Q1 to form a current path, and by reasonably selecting the resistance values of the reference voltage VCC2, the first resistor R1, and the third resistor R3, the first unidirectional conductive device D1 can be made to generate the drain-source voltage V of the power tube Q1 when the power tube Q1 is in the conductive state DS And in the fluctuation range, the two electrodes are in a conducting state.
In one embodiment, the first resistor R1 and the second resistor R2 have the same resistance value; the resistance values of the third resistor R3 and the fourth resistor R4 are the same;
the first unidirectional conduction device D1 and the second unidirectional conduction device D2 are diodes of the same model.
Specifically, as shown in fig. 7, in the case where r1=r2 and r3=r4 are satisfied, the output voltage Vo of the differential amplifier can be simplified to be obtained according to the following equation:
Vo＝VCC2+[VS*(R3/R1)]+VD1-VD2
further, the conduction voltage drop V of the diode FD Often up to 0.7V, and this on-state voltage drop V FD Is subject to temperature and current I flowing through the diode D Is also larger with respect to the voltage V after the power tube Q1 is conducted DS For a voltage source of mV only, the voltage drop V is conducted FD The influence of the conduction voltage drop VD1 of the first unidirectional conduction device D1 can be eliminated by adopting the second unidirectional conduction device D2 of the same type diode as the first unidirectional conduction device D1, so that the conduction voltage drop VD2 of the second unidirectional conduction device D2 can cancel the influence of the conduction voltage drop VD1 of the first unidirectional conduction device D1, and the conduction voltage drop VD2 of the second unidirectional conduction device D2 can be cancelled by adopting a differential amplifier. The voltage amplifying circuit 120 amplifies the VS value in a multiple relation of R3/R1 (or R4/R2), and superimposes the reference voltage VCC2 that is not amplified, to obtain the output voltage Vo of the differential amplifier. The output voltage Vo will rise with the load current connected to the power transistor Q1 on the basis of the reference voltage VCC 2.
Similarly, as shown in fig. 8, in the case where r1=r2 and r3=r4 are satisfied, the output voltage Vo of the differential amplifier can be simplified to be obtained according to the following equation:
Vo＝VS+VCC2-[VS*(1+R3/R1)]+(VD2-VD1)+(VD1-VD2)
＝VCC2-[VS*(R3/R1)]
since the on voltage drop VD1 of the first unidirectional conductive device D1 is equal to the on voltage drop VD2 of the second unidirectional conductive device D2 and cancel each other out, the voltage amplifying circuit 120 amplifies the VS value by a multiple of R3/R1 (or R4/R2), and then subtracts the amplified VS value from the reference voltage VCC2, to obtain the output voltage Vo of the differential amplifier. The output voltage Vo decreases with the increase of the load current connected to the power transistor Q1 based on the reference voltage VCC 2.
In some examples, the first unidirectional conduction device D1 and the second unidirectional conduction device D2 are of the same diode type and are placed at similar positions, and current with almost the same magnitude flows through the first unidirectional conduction device D1 and the second unidirectional conduction device D2, which may be preferably diodes of the same manufacturer and the same batch, so as to ensure that the device characteristics and the working environment of the first unidirectional conduction device D1 are the same as those of the second unidirectional conduction device D2 to the greatest extent. Amplifying the conduction voltage drop VD1 of the first unidirectional conduction device D1 and the conduction voltage drop VD2 of the second unidirectional conduction device D2 by the voltage amplifying circuit 120 with the same amplification factor, wherein the differential amplifier amplifies the first unidirectional conduction device D1 in a normal phase manner and amplifies the second unidirectional conduction device D2 in an opposite phase manner; or, the differential amplifier amplifies in an inverse manner for the first unidirectional conductive device D1 and amplifies in a normal manner for the second unidirectional conductive device D2; in this case, even if the conduction characteristics of the first unidirectional conduction device D1 and the second unidirectional conduction device D2 are nonlinear, the conduction voltage drop VD1 from the first unidirectional conduction device D1 and the conduction voltage drop VD2 from the second unidirectional conduction device D2 in the output voltage of the differential amplifier can be completely offset, so that the influence of the conduction voltage drop on the circuit sampling value of the current detection circuit is avoided.
In one embodiment, the detection voltage is a voltage output by the output terminal of the voltage amplifying circuit 120 when the power transistor is turned on.
Specifically, as shown IN fig. 7, when the power transistor Q1 is IN the off state, the first unidirectional conductive device D1 is not conductive, the first resistor R1 is suspended, the non-inverting input terminal in+ is pulled up to the voltage value of the reference voltage VCC2 by the third resistor R3, the differential amplifier U1 is IN the saturated state, and the output voltage Vo is the value of the full-scale output power supply voltage VCC.
Similarly, as shown IN fig. 8, when the power transistor Q1 is IN the off state, the first unidirectional conductive device D1 is not conductive, the second resistor R2 is suspended, the differential amplifier U1 is a voltage follower, and the output voltage Vo outputs the voltage value of the IN-phase input terminal in+, that is, the lower limit value of the output voltage of the voltage amplifying circuit 120 IN fig. 9.
Further, in the case that the power transistor Q1 is in the off state, the voltage V DS The value of (2) is greatly increased to be equal to the DC VBUS, and the voltage V DS The value of (2) no longer corresponds to the on-resistance R DS_ON Is related to the load current. Because the power tube Q1 is in an off state, the situation of overcurrent does not occur, and the meaning of detecting the load current does not exist, the specific value of the output voltage Vo at the moment is not very important, but a protection circuit or a current detection system is required to be capable of knowing when the Q1 is conducted, and the correct value of the output voltage Vo needs to be used as a judgment basis at a proper time so as to avoid the over-current protection event from being triggered by errors; when the power tube Q1 is driven by the MCU, the time period of the power tube Q1 which is conducted or cut off can be accurately judged through software, so that only the output voltage Vo value of the power tube Q1 under the condition of being in a conducting state is used as a data source of a current sampling value.
In one embodiment, the unidirectional conduction module 110 further includes a third unidirectional conduction device D3, where one end of the third unidirectional conduction device D3 is connected to the other end of the first unidirectional conduction device D1; the conduction direction of the third unidirectional conduction device D3 is opposite to the conduction direction of the first unidirectional conduction device D1;
the circuit further comprises:
the base electrode of the triode is used for connecting with the control end of the power tube; the transmitting stage of the triode is used for grounding; the collector electrode of the triode is used for accessing the power supply voltage;
the control end of the power switch tube is connected with the collector electrode of the triode; the current input end of the power switch tube is connected with the other end of the third unidirectional conduction device D3; the current output end of the power switch tube is used for grounding.
Specifically, according to the above analysis, the voltage V is applied to the power transistor Q1 in the off state DS The value of (2) no longer coincides with the on-resistance R DS_ON In relation to the load current, the output voltage Vo can be related to the driving signal of the power transistor Q1 in a hardware-improved manner.
As shown in fig. 11 or fig. 12, by adding the third unidirectional conduction device D3, the power switch Q2 and the triode Q3, when the power transistor Q1 is in the off state, since the triode Q3 and the power transistor Q1 are connected to the same control signal, the triode Q3 is turned off, and based on the triode Q3 and the reference voltage VCC2, the power switch Q2 is turned on, so that the third unidirectional conduction device D3 is grounded, that is, one end potential of the third unidirectional conduction device D3 is forced to be pulled down to the ground GND, so that the circuit is equivalent to the state when the power transistor Q1 is turned on and no load current is achieved, and the value of the output voltage Vo is equivalent to the value when the power transistor Q1 is in the on state and no load current is achieved. The improved current detection circuit is obtained without judging whether the output voltage Vo is in the conducting state of the power tube Q1.
In some examples, the base of transistor Q3 may be connected to the control terminal of power transistor Q1 through resistor R7; the collector of transistor Q3 may be connected to supply voltage VCC via resistor R6.
In one embodiment, the transistor is an NPN transistor; the third unidirectional conduction device is a diode; the power switch tube is an N-channel MOSFET field effect tube.
In one embodiment, an inverter bridge is provided, wherein power tubes of a lower bridge arm of the inverter bridge are configured with a load current input end and a ground end; the inverter bridge comprises the current detection circuit; the load current input end is connected with one end of the first unidirectional conduction device D1; the grounding end is connected with one end of the second unidirectional conduction device D2;
the inverter bridge also comprises a pull-down resistor, one end of the pull-down resistor is connected with the control end of the power tube, and the other end of the pull-down resistor is used for grounding.
Specifically, the current input end of the power tube of the lower bridge arm of the inverter bridge is configured as a load current input end, and the load current input end is connected with one end of the first unidirectional conduction device D1; the current output end of the power tube of the lower bridge arm of the inverter bridge is configured as a grounding end, and the grounding end is connected with one end of the second unidirectional conduction device D2; the control end of the power tube of the lower bridge arm of the inverter bridge is grounded through a pull-down resistor Rgs.
In one embodiment, the inverter bridge comprises a three-phase inverter bridge;
the power tube of the lower bridge arm of the three-phase inversion bridge is a field effect tube; the drain electrode of the field effect transistor is a load current input end; the source electrode of the field effect transistor is a grounding end.
Specifically, as shown in fig. 13, the three lower bridge arms of the three-phase inverter bridge are respectively connected to corresponding current detection circuits, so that three-phase currents of a motor serving as a load can be measured, 3 lower bridge arm current detection resistors can be saved, and the cost is remarkably reduced by replacing one current sampling resistor with two unidirectional conduction devices.
In one embodiment, the number of current detection circuits is a plurality; the current detection circuits share the same second unidirectional conductive device D2.
Specifically, the on-resistance R of the power tube Q1 is used DS_ON As the current detection resistor, the power transistor Q1 is preferably a field effect transistor, and is not preferably a transistor or an IGBT (Insulated Gate Bipolar Transistor ). As shown in fig. 14, the three-phase inverter bridge includes three current detection circuits, wherein reference voltages VCC2 connected to the non-inverting input terminals of the three differential amplifiers through the third resistor can be shared, and further, second unidirectional conductive devices D2 of the three current detection circuits can be combined into a shared unidirectional conductive device DF1, thereby further reducing the number of components, and further reducing the influence of uniformity differences of the devices on the current detection circuits, only 3 first unidirectional conductive devices D1 and 1 second unidirectional conductive device D2 need to be used.
In some examples, the third resistor R3 of the three current detection circuits may be combined into a pull-up resistor RF1; the 3 first unidirectional conduction devices D1 and the 1 second unidirectional conduction devices D2 can adopt diodes with the same model, and only 4 diodes with low price can be used for replacing 3 current detection resistors with relatively high price.
In summary, the embodiment of the application adopts the on-resistance R of the power tube Q1 DS_ON The current detection resistor is used, so that the current sampling resistor can be saved, and the material cost is obviously reduced; advancing oneThe difficulty in selecting the sampling resistor in a specific application occasion is avoided, and the adaptability of the current sampling circuit to high-voltage application is improved; by adopting the amplifying circuit 120 to amplify the weak voltage signal, the effective sampling precision of the post-stage ADC sampling circuit is effectively improved, and the interference is reduced; by adopting the differential amplifier, errors caused by the conduction voltage drop of the unidirectional conduction device can be counteracted, and good precision is maintained; leakage current and static power consumption are not existed, and the advantages of using a current sampling resistor are maintained; the influence of the static bias current of the input end of the GPIO or the operational amplifier is weak and can be ignored without using a resistor with a large resistance value.
In the description of the present specification, reference to the terms "some embodiments," "other embodiments," "desired embodiments," and the like, means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples illustrate only a few embodiments of the application, which are described in detail and are not to be construed as limiting the scope of the application. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of protection of the present application is to be determined by the appended claims.
Claims (13)
1. A current detection circuit, the circuit comprising:
the unidirectional conduction module comprises a first unidirectional conduction device and a second unidirectional conduction device; one end of the first unidirectional conduction device is used for being connected with a load current input end of a power tube of a lower bridge arm of the inverter bridge; the conducting direction of the first unidirectional conducting device is from the other end of the first unidirectional conducting device to one end of the first unidirectional conducting device; one end of the second unidirectional conduction device is used for being connected with the grounding end of the power tube; the conduction direction of the second unidirectional conduction device is the same as that of the first unidirectional conduction device;
the input end of the voltage amplifying circuit is respectively connected with the other end of the first unidirectional conduction device and the other end of the second unidirectional conduction device; the input end of the voltage amplifying circuit is used for accessing reference voltage so that the first unidirectional conduction device and the second unidirectional conduction device are conducted under the condition that the power tube is conducted; the output end of the voltage amplifying circuit outputs detection voltage, and the detection voltage is used for representing the branch current of the power tube.
2. The current detection circuit according to claim 1, wherein the voltage amplification circuit includes an amplification device; the amplifying device is provided with a first input end and a second input end; the first input end is used for accessing reference voltage; the first input end and the second input end are configured to have the same potential under the condition that the amplifying device is in an operating state;
the first input end is connected with the other end of the first unidirectional conduction device, and the second input end is connected with the other end of the second unidirectional conduction device; or alternatively, the first and second heat exchangers may be,
the first input end is connected with the other end of the second unidirectional conduction device, and the second input end is connected with the other end of the first unidirectional conduction device.
3. The current detection circuit of claim 2, wherein the amplifying device is a differential amplifier, the first input is a non-inverting input of the differential amplifier, and the second input is an inverting input of the differential amplifier.
4. The current detection circuit according to claim 2, wherein the conduction condition of the first unidirectional conduction device includes that the first unidirectional conduction device is in a conduction state within a fluctuation range of a drain-source voltage of the power transistor in a case where the power transistor is turned on based on the reference voltage.
5. The current detection circuit according to any one of claims 2 to 4, wherein the voltage amplification circuit further includes a first resistor, a second resistor, a third resistor, and a fourth resistor; wherein,
the first input end is connected with the other end of the first unidirectional conduction device or the other end of the second unidirectional conduction device through the first resistor; the second input end is connected with the other end of the second unidirectional conduction device or the other end of the first unidirectional conduction device through the second resistor; the first input end is connected to the reference voltage through the third resistor; the second input end is connected with the output end of the voltage amplifying circuit through the fourth resistor.
6. The current detection circuit of claim 5, wherein the reference voltage is determined based on a turn-on voltage of the first unidirectional current-conducting device, values of the first resistor and the third resistor.
7. The current detection circuit according to claim 6, wherein the first resistor and the second resistor have the same resistance value; the resistance values of the third resistor and the fourth resistor are the same;
The first unidirectional conduction device and the second unidirectional conduction device are diodes with the same model.
8. The current detection circuit according to claim 1, wherein the detection voltage is a voltage outputted from an output terminal of the voltage amplification circuit in a case where the power transistor is turned on.
9. The current detection circuit of claim 1, wherein the unidirectional conduction module further comprises a third unidirectional conduction device, one end of the third unidirectional conduction device being connected to the other end of the first unidirectional conduction device; the conduction direction of the third unidirectional conduction device is opposite to the conduction direction of the first unidirectional conduction device;
the circuit further comprises:
the base electrode of the triode is used for being connected with the control end of the power tube; the emitting stage of the triode is used for being grounded; the collector electrode of the triode is used for being connected with a power supply voltage;
the control end of the power switch tube is connected with the collector electrode of the triode; the current input end of the power switch tube is connected with the other end of the third unidirectional conduction device; the current output end of the power switch tube is used for grounding.
10. The current detection circuit of claim 9, wherein the transistor is an NPN transistor; the third unidirectional conduction device is a diode; the power switch tube is an N-channel MOSFET field effect tube.
11. An inverter bridge is characterized in that a power tube of a lower bridge arm of the inverter bridge is provided with a load current input end and a grounding end; the inverter bridge comprising the current detection circuit of any one of claims 1 to 9; the load current input end is connected with one end of the first unidirectional conduction device; the grounding end is connected with one end of the second unidirectional conduction device;
the inverter bridge further comprises a pull-down resistor, one end of the pull-down resistor is connected with the control end of the power tube, and the other end of the pull-down resistor is grounded.
12. The inverter bridge of claim 11, wherein the inverter bridge comprises a three-phase inverter bridge;
the power tube of the lower bridge arm of the three-phase inversion bridge is a field effect tube; the drain electrode of the field effect transistor is the load current input end; the source of the field effect transistor is the grounding end.
13. The inverter bridge of claim 12, wherein the number of current detection circuits is a plurality; and each current detection circuit shares the same second unidirectional conduction device.
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| CN202210467900.1A CN117007847A (en) | 2022-04-29 | 2022-04-29 | Current detection circuit and inverter bridge |
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| CN202210467900.1A CN117007847A (en) | 2022-04-29 | 2022-04-29 | Current detection circuit and inverter bridge |
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