Control method for calibration power supply of tunnel magnetoresistance current sensor

Abstract

The invention relates to a control method of a tunnel magnetoresistance current sensor calibration power supply, the calibration power supply is a CLLC resonant converter, and the method comprises the following steps: monitoring an input voltage and an output voltage of the CLLC resonant converter; judging whether the CLLC resonant converter is in a single phase shift mode or not based on the input voltage and the output voltage of the CLLC resonant converter; if the CLLC resonant converter is in a single phase shift mode, establishing time domain models of exciting current, secondary side resonant capacitor voltage, primary side resonant inductor current and secondary side resonant inductor current of the CLLC resonant converter; and solving the time domain model to obtain the secondary side synchronous rectification time of the CLLC resonant converter, and generating a synchronous rectification driving signal of a secondary side switch tube based on the secondary side synchronous rectification time.

Description

Technical Field

[0001] This invention relates to a control method for calibrating the power supply of a tunnel magnetoresistive current sensor, belonging to the field of electrical testing technology. Background Technology

[0002] With the gradual maturation of high-voltage direct current (HVDC) transmission technology, the power quality problems faced by AC distribution networks, such as large line losses, voltage dips, voltage fluctuations, and grid harmonics, are gradually being replaced by DC distribution networks. DC distribution networks offer advantages such as low line losses, high power supply reliability, no involvement in phase and frequency control, reactive power and AC charging current issues, easy access to distributed power sources and energy storage devices, and environmental friendliness.

[0003] Current sensors can detect the measured current and convert it into a usable output signal, and are widely used in DC distribution networks. Tunnel magnetoresistive (TMR) current sensors have advantages such as high sensitivity, high resolution of current changes without the magnetic field of an iron core, and high accuracy in current measurement, making them promising for applications in DC distribution networks. Currently, a large number of power semiconductor devices are used in the field of power conversion. Bidirectional CLLC resonant converters, due to their advantages such as simple structure, high efficiency, high power density, high-frequency electrical isolation, near-sinusoidal current and voltage waveforms, wide input voltage range, and ease of magnetic integration, have been widely used in the calibration power supplies for TMR current sensors.

[0004] The bidirectional CLLC resonant converter is a common bidirectional isolated DC / DC topology. Based on the LLC resonant converter, it achieves bidirectional symmetrical power flow and boasts advantages such as a wide soft-switching range, high efficiency, low control complexity, and no magnetic balance issues. In recent years, researchers have focused on further improving the efficiency of CLLC resonant converters. Synchronous rectification (SR) technology is an emerging control technique. Since the secondary side of the CLLC resonant converter uses a switching transistor, controlling the switch avoids the conduction and voltage drop of the body diode, thereby improving the converter's efficiency. However, the SR drive signal for the secondary-side switching transistor cannot be directly obtained. Therefore, achieving device-free synchronous rectification through theoretical calculations to improve efficiency and save costs has become crucial. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a control method for the calibration power supply of a tunnel magnetoresistive current sensor.

[0006] The technical solution of the present invention is as follows: On one hand, the present invention provides a control method for a calibration power supply of a tunnel magnetoresistive current sensor, wherein the calibration power supply is a CLLC resonant converter, comprising the following steps: Monitor the input and output voltages of the CLLC resonant converter; Determine whether a CLLC resonant converter is in single-phase-shift mode based on its input and output voltages; If the CLLC resonant converter is in single-phase shift mode, then establish a time-domain model of the CLLC resonant converter's excitation current, secondary-side resonant capacitor voltage, primary-side resonant inductor current, and secondary-side resonant inductor current. The synchronous rectification time of the secondary side of the CLLC resonant converter is obtained by solving the time-domain model, and the synchronous rectification drive signal of the secondary side switch is generated based on the synchronous rectification time of the secondary side.

[0007] Preferably, when the input voltage of the CLLC resonant converter is greater than the output voltage, the CLLC resonant converter is determined to be in single-phase shift mode.

[0008] Preferably, the single-phase-shifting mode of the CLLC resonant converter includes three continuous time-domain modes, namely the P mode, the OP mode, and the O mode; When constructing the time-domain model of the CLLC resonant converter, the parameters of the CLLC resonant converter are processed as follows: The equivalent inductance of the primary-side resonant inductor and the secondary-side resonant inductor is constructed as follows: ,in, This represents the equivalent inductance of the primary-side resonant inductance. Indicates the secondary side resonant inductance. This represents the primary side resonant inductance; Indicates the number of turns in the primary winding of the transformer; Indicates the secondary side resonant inductance; Construct the equivalent capacitance of the primary-side resonant capacitor and the secondary-side resonant capacitor, specifically as follows: ,in, This represents the equivalent capacitance of the primary side resonant capacitor. This represents the equivalent capacitance of the secondary-side resonant capacitor. This represents the primary side resonant capacitance; This represents the secondary side resonant capacitor; The equivalent values ​​of the primary-side resonant inductor current and the secondary-side resonant inductor current are constructed as follows: , ,in, This represents the equivalent value of the resonant inductor current on the primary side. This represents the resonant inductor current on the primary side. This represents the equivalent value of the resonant inductor current on the secondary side; The equivalent values ​​of the primary-side resonant capacitor voltage and the secondary-side resonant capacitor voltage are constructed as follows: , ,in, This represents the equivalent value of the resonant capacitor voltage on the primary side; This represents the voltage across the primary side resonant capacitor. This represents the equivalent value of the resonant capacitor voltage on the secondary side; Construct the equivalent values ​​of the input and output voltages, specifically as follows: , ,in, Indicates the equivalent value of the input voltage. Indicates the input voltage. This represents the equivalent value of the output voltage. This indicates the output voltage.

[0009] Preferably, when the single-phase-shift mode is in P mode, the time-domain model expression of the resonant inductor current on the secondary side of the CLLC resonant converter is as follows:

[0010] in: express The resonant inductor current on the secondary side at any given moment; This represents the characteristic impedance between the primary-side resonant inductor and the primary-side resonant capacitor. express Voltage of the secondary side resonant capacitor at any given moment; This represents the angular frequency of the CLLC resonant converter; Indicates the start time of mode P; The time-domain model expression of the excitation current of the CLLC resonant converter is as follows:

[0011] in: express The excitation current at any given moment; express The excitation current at any given moment; This represents the transformer magnetizing inductance of a CLLC resonant converter; The time-domain model expression of the primary-side resonant inductor current of the CLLC resonant converter is as follows:

[0012] in: express At any given moment, the resonant inductor current on the original side; The time-domain model expression for the resonant capacitor voltage on the secondary side of the CLLC resonant converter is as follows:

[0013] in: express Voltage of the secondary side resonant capacitor at any given moment; express The voltage of the secondary side resonant capacitor at that moment.

[0014] Preferably, the characteristic impedance between the primary-side resonant inductor and the primary-side resonant capacitor is calculated using the following formula: .

[0015] Preferably, when the single-phase-shift mode is in the OP mode, the time-domain models of the resonant inductor current and the excitation current on the secondary side of the CLLC resonant converter change relative to the P mode, specifically:

[0016]

[0017] in: This indicates the end time of the P mode and the start time of the OP mode; This indicates the end time of the OP mode and the start time of the O mode; express The secondary side resonant inductor current at time t; express The voltage of the secondary side resonant capacitor at time t; express The voltage of the secondary side resonant capacitor at time t; express The excitation current at any given moment.

[0018] Preferably, when the single-phase-shift mode is in the O mode, the time-domain models of the primary-side resonant inductor current and the excitation current of the CLLC resonant converter change relative to the OP mode, specifically:

[0019]

[0020] in: express The excitation current at any given moment; This indicates the end time of mode O.

[0021] Preferably, the synchronous rectification time on the secondary side of the CLLC resonant converter is obtained by symmetric solution of the time-domain model, as shown in the following formula:

[0022]

[0023] in: Indicates the secondary-side synchronous rectification time; This indicates the phase shift angle inside the primary side arm of the single-phase shift mode; Indicates the resonant period; This represents the current phase relationship obtained by solving the time-domain model symmetrically. Indicates the output resistance; The output resistance is indicated by the number of turns in the primary winding of the transformer. The equivalent resistance referred back to the original side.

[0024] On the other hand, the present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the method described in the present invention.

[0025] In another aspect, the present invention also provides a computer-readable storage medium having a computer program stored thereon that, when executed by a processor, implements the method described in the present invention.

[0026] The present invention has the following beneficial effects: 1. This invention realizes single-phase-shift control of CLLC resonant converter without device-level synchronous rectification, which has high accuracy, effectively improves the overall efficiency of the calibration power supply and saves costs. Attached Figure Description

[0027] Figure 1 This is a circuit diagram of a CLLC resonant converter, which is the controlled object used as a power supply for TMR current sensor calibration in this invention.

[0028] Figure 2 This is a schematic diagram of the single-phase-shift control waveform of the CLLC resonant converter of the present invention.

[0029] Figure 3 This is a schematic diagram of the synchronous rectification control of the secondary-side switching transistors in the CLLC resonant converter of the present invention.

[0030] Figure 4 This is a schematic diagram of the loss analysis of the present invention.

[0031] Figure 5 This is a control block diagram of the single-phase-shift control deviceless synchronous rectification strategy of the present invention.

[0032] Figure 6 The simulation waveform diagram of the synchronous rectification strategy in this invention during the load shedding process is shown. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] It should be understood that the step numbers used in the text are for ease of description only and are not intended to limit the order in which the steps are performed.

[0035] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0036] The terms “comprising” and “including” indicate the presence of the described feature, whole, step, operation, element and / or component, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0037] The term “and / or” refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes these combinations.

[0038] In some embodiments, a control method for a calibration power supply of a tunnel magnetoresistive current sensor is proposed, wherein the calibration power supply is a CLLC resonant converter, comprising the following steps: Monitor the input and output voltages of the CLLC resonant converter; Determine whether a CLLC resonant converter is in single-phase-shift mode based on its input and output voltages; If the CLLC resonant converter is in single-phase shift mode, then establish a time-domain model of the CLLC resonant converter's excitation current, secondary-side resonant capacitor voltage, primary-side resonant inductor current, and secondary-side resonant inductor current. The synchronous rectification time of the secondary side of the CLLC resonant converter is obtained by solving the time-domain model, and the synchronous rectification drive signal of the secondary side switch is generated based on the synchronous rectification time of the secondary side.

[0039] In some embodiments, when the input voltage of the CLLC resonant converter is greater than the output voltage, the CLLC resonant converter is determined to be in single-phase shift mode.

[0040] In some embodiments, the single-phase-shifting mode of the CLLC resonant converter includes three continuous time-domain modes, namely the P mode, the OP mode, and the O mode; When constructing the time-domain model of the CLLC resonant converter, the parameters of the CLLC resonant converter are processed as follows: The equivalent inductance of the primary-side resonant inductor and the secondary-side resonant inductor is constructed as follows: ,in, This represents the equivalent inductance of the primary-side resonant inductance. Indicates the secondary side resonant inductance. This represents the primary side resonant inductance; Indicates the number of turns in the primary winding of the transformer; Indicates the secondary side resonant inductance; Construct the equivalent capacitance of the primary-side resonant capacitor and the secondary-side resonant capacitor, specifically as follows: ,in, This represents the equivalent capacitance of the primary side resonant capacitor. This represents the equivalent capacitance of the secondary-side resonant capacitor. This represents the primary side resonant capacitance; This represents the secondary side resonant capacitor; The equivalent values ​​of the primary-side resonant inductor current and the secondary-side resonant inductor current are constructed as follows: , ,in, This represents the equivalent value of the resonant inductor current on the primary side. This represents the resonant inductor current on the primary side. This represents the equivalent value of the resonant inductor current on the secondary side; The equivalent values ​​of the primary-side resonant capacitor voltage and the secondary-side resonant capacitor voltage are constructed as follows: , ,in, This represents the equivalent value of the resonant capacitor voltage on the primary side; This represents the voltage across the primary side resonant capacitor. This represents the equivalent value of the resonant capacitor voltage on the secondary side; Construct the equivalent values ​​of the input and output voltages, specifically as follows: , ,in, Indicates the equivalent value of the input voltage. Indicates the input voltage. This represents the equivalent value of the output voltage. This indicates the output voltage.

[0041] In one specific embodiment, see Figure 1 This is a topology diagram of a CLLC resonant converter, used as a power supply for TMR current sensor calibration, including the switching transistors. to anti-parallel diode to Parasitic capacitance to The turns ratio is A 1-type transformer with an output capacitor. Output resistance and turns ratio is A 1-type transformer forms the resonant cavity of the CLLC resonant converter.

[0042] DC input voltage The positive terminal is simultaneously connected to the original side switch transistor. , The source is connected; DC input voltage The negative terminal is simultaneously connected to the primary side switch transistor. , Connected; Output capacitor With output resistance Parallel connection; DC output voltage For output resistance Voltage at both ends.

[0043] In some embodiments, when the single-phase-shift mode is in P-mode, the time-domain model expression of the resonant inductor current on the secondary side of the CLLC resonant converter is as follows:

[0044] in: express The resonant inductor current on the secondary side at any given moment; This represents the characteristic impedance between the primary-side resonant inductor and the primary-side resonant capacitor. express Voltage of the secondary side resonant capacitor at any given moment; This represents the angular frequency of the CLLC resonant converter; Indicates the start time of mode P; The time-domain model expression of the excitation current of the CLLC resonant converter is as follows:

[0045] in: express The excitation current at any given moment; express The excitation current at any given moment; This represents the transformer magnetizing inductance of a CLLC resonant converter; The time-domain model expression of the primary-side resonant inductor current of the CLLC resonant converter is as follows:

[0046] in: express At any given moment, the resonant inductor current on the original side; The time-domain model expression for the resonant capacitor voltage on the secondary side of the CLLC resonant converter is as follows:

[0047] in: express Voltage of the secondary side resonant capacitor at any given moment; express The voltage of the secondary side resonant capacitor at that moment.

[0048] In some embodiments, the characteristic impedance between the primary-side resonant inductor and the primary-side resonant capacitor is calculated using the following formula: .

[0049] In some embodiments, when the single-phase-shift mode is in the OP mode, the time-domain models of the resonant inductor current and the excitation current on the secondary side of the CLLC resonant converter change relative to the P mode, specifically:

[0050]

[0051] in: This indicates the end time of the P mode and the start time of the OP mode; This indicates the end time of the OP mode and the start time of the O mode; express The secondary side resonant inductor current at time t; express The voltage of the secondary side resonant capacitor at time t; express The voltage of the secondary side resonant capacitor at time t; express The excitation current at any given moment.

[0052] In some embodiments, when the single-phase-shift mode is in the O mode, the time-domain models of the primary-side resonant inductor current and the excitation current of the CLLC resonant converter change relative to the OP mode, specifically:

[0053]

[0054] in: express The excitation current at any given moment; This indicates the end time of mode O.

[0055] In some embodiments, the synchronous rectification time on the secondary side of the CLLC resonant converter is obtained by symmetric solution of the time-domain model, as shown in the following equation:

[0056]

[0057] in: Indicates the secondary-side synchronous rectification time; This indicates the phase shift angle inside the primary side arm of the single-phase shift mode; Indicates the resonant period; This represents the current phase relationship obtained by solving the time-domain model symmetrically. Indicates the output resistance; The output resistance is indicated by the number of turns in the primary winding of the transformer. The equivalent resistance referred back to the original side.

[0058] In one specific embodiment, when the converter operates with the output voltage lower than the input voltage, the CLLC resonant converter employs single-phase shift control, such as... Figure 2 As shown; See Figure 5 When the output voltage is less than the input voltage, the converter enters the single-phase-shift control mode and calculates the synchronous rectification time of the secondary-side switching transistor through the time calculation module. pass Figure 6 It can be seen that the present invention can effectively achieve synchronous rectification of the secondary-side switching transistors.

[0059] In some embodiments, an electronic device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the method as described in any embodiment of the present invention.

[0060] In some embodiments, a computer-readable storage medium is provided on which a computer program is stored, which, when executed by a processor, implements the method as described in any embodiment of the present invention.

[0061] In this application embodiment, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent the existence of A alone, A and B simultaneously, or B alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, at least one of a, b, and c can represent: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, and c can be single or multiple.

[0062] Those skilled in the art will recognize that the units and algorithm steps described in the embodiments disclosed herein can be implemented using electronic hardware, computer software, or a combination of electronic hardware and software. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0063] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0064] In the several embodiments provided in this application, any function, if implemented as a software functional unit and sold or used as an independent product, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0065] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A control method for a power supply for calibrating a tunnel magnetoresistive current sensor, characterized in that, The verification power supply is a CLLC resonant converter, and the following steps are included: Monitor the input and output voltages of the CLLC resonant converter; Determine whether a CLLC resonant converter is in single-phase-shift mode based on its input and output voltages; If the CLLC resonant converter is in single-phase shift mode, then establish a time-domain model of the CLLC resonant converter's excitation current, secondary-side resonant capacitor voltage, primary-side resonant inductor current, and secondary-side resonant inductor current. The synchronous rectification time of the secondary side of the CLLC resonant converter is obtained by solving the time-domain model, and the synchronous rectification drive signal of the secondary side switch is generated based on the synchronous rectification time of the secondary side.

2. The control method for a tunnel magnetoresistive current sensor calibration power supply according to claim 1, characterized in that, When the input voltage of a CLLC resonant converter is greater than its output voltage, the CLLC resonant converter is determined to be in single-phase shift mode.

3. The control method for a tunnel magnetoresistive current sensor calibration power supply according to claim 1, characterized in that, The single-phase-shifting mode of the CLLC resonant converter includes three continuous time-domain modes: the P mode, the OP mode, and the O mode. When constructing the time-domain model of the CLLC resonant converter, the parameters of the CLLC resonant converter are processed as follows: The equivalent inductance of the primary-side resonant inductor and the secondary-side resonant inductor is constructed as follows: ,in, This represents the equivalent inductance of the primary-side resonant inductance. Indicates the secondary side resonant inductance. This represents the primary side resonant inductance; Indicates the number of turns in the primary winding of the transformer; Indicates the secondary side resonant inductance; Construct the equivalent capacitance of the primary-side resonant capacitor and the secondary-side resonant capacitor, specifically as follows: ,in, This represents the equivalent capacitance of the primary side resonant capacitor. This represents the equivalent capacitance of the secondary-side resonant capacitor. This represents the primary side resonant capacitance; This represents the secondary side resonant capacitor; The equivalent values ​​of the primary-side resonant inductor current and the secondary-side resonant inductor current are constructed as follows: , ,in, This represents the equivalent value of the resonant inductor current on the primary side. This represents the resonant inductor current on the primary side. This represents the equivalent value of the resonant inductor current on the secondary side; The equivalent values ​​of the primary-side resonant capacitor voltage and the secondary-side resonant capacitor voltage are constructed as follows: , ,in, This represents the equivalent value of the resonant capacitor voltage on the primary side; This represents the voltage across the primary side resonant capacitor. This represents the equivalent value of the resonant capacitor voltage on the secondary side; Construct the equivalent values ​​of the input and output voltages, specifically as follows: , ,in, Indicates the equivalent value of the input voltage. Indicates the input voltage. This represents the equivalent value of the output voltage. This indicates the output voltage.

4. The control method for a tunnel magnetoresistive current sensor calibration power supply according to claim 3, characterized in that, When the single-phase-shift mode is in P mode, the time-domain model expression of the resonant inductor current on the secondary side of the CLLC resonant converter is as follows: in: express The resonant inductor current on the secondary side at any given moment; This represents the characteristic impedance between the primary-side resonant inductor and the primary-side resonant capacitor. express Voltage of the secondary side resonant capacitor at any given moment; This represents the angular frequency of the CLLC resonant converter; Indicates the start time of mode P; The time-domain model expression of the excitation current of the CLLC resonant converter is as follows: in: express The excitation current at any given moment; express The excitation current at any given moment; This represents the transformer magnetizing inductance of a CLLC resonant converter; The time-domain model expression of the primary-side resonant inductor current of the CLLC resonant converter is as follows: in: express At any given moment, the resonant inductor current on the original side; The time-domain model expression for the resonant capacitor voltage on the secondary side of the CLLC resonant converter is as follows: in: express Voltage of the secondary side resonant capacitor at any given moment; express The voltage of the secondary side resonant capacitor at that moment.

5. The control method for a tunnel magnetoresistive current sensor calibration power supply according to claim 4, characterized in that, The formula for calculating the characteristic impedance between the primary-side resonant inductor and the primary-side resonant capacitor is as follows: .

6. The control method for a tunnel magnetoresistive current sensor calibration power supply according to claim 4, characterized in that, When the single-phase-shifted mode is in the OP mode, the time-domain models of the resonant inductor current and the excitation current on the secondary side of the CLLC resonant converter change compared to the P mode, specifically: in: This indicates the end time of the P mode and the start time of the OP mode; This indicates the end time of the OP mode and the start time of the O mode; express The secondary side resonant inductor current at time t; express The voltage of the secondary side resonant capacitor at time t; express The voltage of the secondary side resonant capacitor at time t; express The excitation current at any given moment.

7. The control method for a tunnel magnetoresistive current sensor calibration power supply according to claim 6, characterized in that, When the single-phase-shifted mode is in the O mode, the time-domain models of the primary-side resonant inductor current and the excitation current of the CLLC resonant converter change relative to the OP mode, specifically: in: express The excitation current at any given moment; This indicates the end time of mode O.

8. The control method for a tunnel magnetoresistive current sensor calibration power supply according to claim 6, characterized in that, The synchronous rectification time on the secondary side of the CLLC resonant converter is obtained by symmetric solution of the time-domain model, as shown in the following equation: in: Indicates the secondary-side synchronous rectification time; This indicates the phase shift angle inside the primary side arm of the single-phase shift mode; Indicates the resonant period; This represents the current phase relationship obtained by solving the time-domain model symmetrically. Indicates the output resistance; The output resistance is indicated by the number of turns in the primary winding of the transformer. The equivalent resistance referred back to the original side.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the method as described in any one of claims 1 to 8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1 to 8.

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