Pre-charging circuit and series capacitor buck converter

Abstract

The invention provides a pre-charging circuit and a series capacitor buck converter, the pre-charging circuit provides a first current path and a second current path, a first current flows into a positive electrode of a flying capacitor through the first current path, and a second current flows to a grounding end from a negative electrode of the flying capacitor through the second current path. The first current path comprises a first high-side power tube. In the pre-charging circuit provided by the invention, the first current path and the second current path form a charging loop of the flying capacitor, so that the flying capacitor is pre-charged through the pre-charging circuit before the series capacitor buck converter is started and operated. Particularly, the pre-charging circuit multiplexes the first high-side power tube, so that the structure of the pre-charging circuit is simplified, and the production cost is reduced. Besides, the first current is equal to the second current in the pre-charging process, so that the current is prevented from flowing to the output capacitor, the bias voltage of the output capacitor is prevented from being influenced, and the operation of the load is further influenced.

Description

Technical Field

[0001] The present invention belongs to the technical field of switching power supplies, and particularly relates to a pre-charge circuit and a series capacitor buck converter. Background Art

[0002] As Figure 1 shown, a series capacitor buck converter is a DC / DC topology that combines a switched capacitor circuit and a two-phase buck converter into a single pole, and is usually used to meet the usage requirements of high-dynamic and fast slew-rate loads. The series capacitor buck converter uses two inductors (L1, L2), each inductor carrying half of the load current and operating at half of the switching frequency, which greatly reduces the switching loss. Among them, when the series capacitor buck converter operates normally, the flying capacitor Cf needs to provide half of the input voltage to supply power to one of the BUCK circuits. Therefore, when using a series buck converter, a charging circuit needs to be set to pre-charge the flying capacitor Cf before the series capacitor buck converter starts to operate, so that the voltage of the flying capacitor Cf reaches Summary of the Invention

[0003] In order to solve the technical problem that the flying capacitor needs to be pre-charged before the series capacitor buck converter starts to operate, the present invention proposes a pre-charge circuit and a series capacitor buck converter. Among them, the pre-charge circuit is used to pre-charge the flying capacitor in the series capacitor buck converter. The first-phase BUCK circuit of the series capacitor buck converter includes a first high-side power transistor, and the first high-side power transistor is connected to the input voltage and the positive electrode of the flying capacitor.

[0004] The pre-charge circuit provides a first current path and a second current path. The first current flows into the positive electrode of the flying capacitor through the first current path, and the second current flows from the negative electrode of the flying capacitor to the ground terminal through the second current path.

[0005] Among them, the first current path includes the first high-side power transistor.

[0006] Further, during pre-charging, the control unit controls the first current to be equal to the second current.

[0007] Further, the control unit controls the first high-side power transistor to operate in the saturation region according to the sampled voltage and the ramp voltage. Among them, the sampled voltage represents the voltage of the flying capacitor, and the slope of the ramp voltage is greater than zero.

[0008] Further, during pre-charging, the slope of the ramp voltage is set according to the second current and the capacitance value of the flying capacitor.

[0009] Further, the control unit performs a differential operation on the sampled voltage and the ramp voltage to obtain a compensation voltage, and controls the driving voltage of the first high-side power transistor according to the compensation voltage, so that the voltage difference between the gate voltage of the first high-side power transistor and the voltage of the flying capacitor is constant.

[0010] Further, the control unit controls the second current path to generate the second current, and determines the slope of the ramp voltage according to the ratio of the second current to the capacitance value of the flying capacitor, so that the first current is equal to the second current.

[0011] Further, the slope of the ramp voltage satisfies: the slope of the ramp voltage = k * the second current / the capacitance value of the flying capacitor, where k is greater than zero.

[0012] Further, k satisfies: k = the sampled voltage / the voltage of the flying capacitor.

[0013] Further, the control unit controls whether to perform pre-charging according to the sampled voltage and the reference voltage.

[0014] Wherein, the sampled voltage represents the voltage of the flying capacitor, and the reference voltage represents half of the input voltage.

[0015] Further, the control unit includes:

[0016] A sampling circuit connected to the flying capacitor to collect the sampled voltage;

[0017] An operational amplifier circuit that performs a differential operation on the sampled voltage and the ramp voltage to generate a compensation voltage;

[0018] A comparison circuit, the first input terminal receives the sampled voltage, the second input terminal receives the reference voltage, and the output comparison signal controls whether to generate the second current, and the reference voltage represents half of the input voltage;

[0019] A driving circuit that generates the driving voltage of the first high-side power transistor according to the compensation voltage and the comparison signal to control the conduction or cut-off of the first high-side power transistor.

[0020] Further, when the sampled voltage is less than the reference voltage, the driving circuit generates a constant driving voltage according to the compensation voltage to control the conduction of the first high-side power transistor;

[0021] When the sampled voltage is greater than the reference voltage, the driving circuit pulls down the driving voltage according to the comparison signal to control the cut-off of the first high-side power transistor.

[0022] Preferably, the second current path includes a pull-down current source, and the pull-down current source is connected to the negative electrode of the flying capacitor and the ground terminal.

[0023] A series capacitor buck converter includes the pre-charge circuit described above.

[0024] In the pre-charge circuit proposed by the present invention, the first current path and the second current path form a charging loop for the flying capacitor, so that the flying capacitor is pre-charged by the pre-charge circuit before the series capacitor buck converter starts to operate, enabling the series capacitor buck converter to start operating. In particular, the pre-charge circuit proposed by the present invention reuses the first high-side power transistor, thus simplifying the structure of the pre-charge circuit and reducing the production cost. In addition, during the pre-charging process of the flying capacitor, the first current is controlled to be equal to the second current, so that current flow to the output capacitor is avoided during this process, which affects the bias voltage of the output capacitor and further affects the operation of the load. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a structural diagram of a series capacitor buck converter;

[0026] Figure 2 is the first mode of operation of a series capacitor buck converter;

[0027] Figure 3 is the second mode of operation of a series capacitor buck converter;

[0028] Figure 4 is the third mode of operation of a series capacitor buck converter;

[0029] Figure 5 is a structural block diagram of a pre-charge circuit;

[0030] Figure 6 is a specific circuit structure diagram of a pre-charge circuit;

[0031] Figure 7 and Figure 8 are the changes of various signals during the pre-charging process. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. The preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0033] Such as Figure 1As shown in the figure, the series capacitor buck converter is a DC / DC topology that combines a switched capacitor circuit and a two-phase buck converter. Specifically, the series capacitor buck converter includes: a flying capacitor Cf, a first-phase buck circuit, and a second-phase buck circuit. Among them, the first-phase buck circuit includes a first high-side power transistor HS1, a first low-side power transistor LS1, and a first inductor L1; the second-phase buck circuit includes a second high-side power transistor HS2, a second low-side power transistor LS2, and a second inductor L2. The first end of the first high-side power transistor HS1 is connected to the input voltage Vin, the second end is connected to the positive electrode of the flying capacitor Cf, the first end of the first low-side power transistor LS1 is connected to the negative electrode of the flying capacitor Cf, the second end is grounded, and the first inductor L1 is connected to the negative electrode of the flying capacitor Cf and the output capacitor Cout. The first end of the second high-side power transistor HS2 is connected to the positive electrode of the flying capacitor Cf, the second end is connected to the second inductor L2, the other end of the second inductor L2 is connected to the output capacitor Cout, and the first end of the second low-side power transistor LS2 is connected to the connection point SW2 of the second inductor L2 and the second high-side power transistor HS2, and the second end is grounded.

[0034] As Figures 2 to 4 shown, the series capacitor buck converter can operate in the first mode, the second mode, and the third mode. As Figure 2 shown, in the first mode, the first high-side power transistor HS1 and the second low-side power transistor LS2 are controlled to conduct. As Figure 3 shown, in the second mode, the first low-side power transistor LS1 and the second high-side power transistor HS2 are controlled to conduct. As Figure 4 shown, in the third mode, the first low-side power transistor LS1 and the second low-side power transistor LS2 are controlled to conduct. In the first mode, the second mode, and the third mode, the first-phase buck circuit and the second-phase buck circuit jointly supply energy to the load. In order to ensure the simultaneous operation of the two-phase buck circuit, it is necessary to control the potential of the flying capacitor Cf to be stable at At the same time, in order to ensure the normal start-up and operation of the series capacitor buck converter, it is also necessary to ensure that the flying capacitor Cf has a certain amount of electricity at startup. Therefore, in order to ensure the normal start-up and operation of the series capacitor buck converter, it is necessary to pre-charge the flying capacitor Cf.

[0035] In summary, in order to realize the pre-charging of the flying capacitor to enable the normal start-up and operation of the series capacitor buck converter, the present invention proposes a pre-charging circuit, as Figure 5 shown, including:

[0036] A first current path, through which a first current flows into the positive electrode of the flying capacitor Cf. Specifically, the first high-side power transistor HS1 constitutes the first current path;

[0037] A second current path, through which a second current flows from the negative electrode of the flying capacitor Cf to the ground terminal.

[0038] Specifically, during pre-charging, the first current is equal to the second current.

[0039] It can be seen therefrom that in the pre-charging circuit proposed by the present invention, the first current path and the second current path constitute a charging loop for the flying capacitor, so that the flying capacitor is pre-charged by the pre-charging circuit before the series-capacitor buck converter starts to operate, enabling the series-capacitor buck converter to start operating. Specifically, the pre-charging circuit proposed by the present invention reuses the first high-side power transistor, thus simplifying the structure of the pre-charging circuit and reducing the production cost. In addition, during the pre-charging process of the flying capacitor, the first current is controlled to be equal to the second current, thereby avoiding current flowing to the output capacitor during this process, affecting the bias voltage of the output capacitor and further affecting the operation of the load.

[0040] Furthermore, in order to avoid problems such as uneven power distribution and uneven voltage stress in the early stage of operation of the series-capacitor buck converter, the present invention also proposes that when the pre-charging circuit pre-charges the flying capacitor, the voltage of the flying capacitor is controlled to be stable at Therefore, when the series-capacitor buck converter starts to operate, the voltage of the flying capacitor has reached In this way, balanced power distribution and balanced voltage stress can be achieved during system operation, enabling the series-capacitor buck converter to smoothly transition from the shutdown state to the operating state.

[0041] Furthermore, in order to ensure that the flying capacitor needs to be discharged when the series-capacitor converter operates abnormally, a third current path can also be set to discharge the flying capacitor.

[0042] It should be noted that from the solution proposed by the present invention, it can be seen that the pre-charging circuit of the flying capacitor reuses the first high-side power transistor HS1. Based on the structure of the series-capacitor converter, in order to ensure the normal operation of the converter, the breakdown voltage of the first high-side power transistor HS1 needs to reach the input voltage Vin. Thus, it can be known that the first high-side power transistor HS1 belongs to a high-voltage device. When the first high-side power transistor HS1 is fully turned on, the current flowing through the first high-side power transistor HS1 is at the ampere level. During the pre-charging process, the first high-side power transistor HS1 needs to operate in the saturation state (i.e., the saturation region) to achieve controlled conduction current and be able to operate at the milliampere level. Therefore, when reusing the first high-side power transistor HS1 as part of the pre-charging circuit, the key lies in how to control the high-voltage device, the first high-side power transistor HS1, to operate in the saturation state when it is turned on to pre-charge the flying capacitor Cf, thereby generating an accurate, stable, and controlled charging current.

[0043] To solve the difficult problems existing in the pre-charging of the flying capacitor Cf by reusing the first high-side power transistor HS1, the present invention creatively proposes that, as Figure 5 shown in

[0044] During the pre-charging process, the control unit in the pre-charging circuit controls the driving voltage of the first high-side power transistor according to the differential operation result of the sampling voltage and the ramp voltage. Among them, the sampling voltage represents the voltage of the flying capacitor, and the slope of the ramp voltage is greater than zero. Through this feedback control, the sampling voltage can follow the ramp voltage, that is, the change of the flying capacitor is controlled by the change of the ramp voltage, so as to control the voltage difference between the gate voltage and the source voltage (the source voltage is the voltage of the flying capacitor) of the first high-side power transistor to be constant. At the same time, it is obvious that the drain-source voltage of the first high-side power transistor is greater than the gate-source voltage at this time, that is, the first high-side power transistor operates in the saturation region. Therefore, the control unit realizes the constant-current conduction of the first high-side power transistor through the above feedback control, that is, the constant-current charging of the flying capacitor. Further, the control unit controls the generation of a second current, and the control unit determines the slope of the ramp voltage according to the capacitance value of the flying capacitor and the magnitude of the second current. Specifically, the slope of the ramp voltage = k * second current / capacitance value of the flying capacitor, k > 0, and k satisfies: k = sampling voltage / voltage of the flying capacitor. During the pre-charging process, the voltage Vcf of the flying capacitor satisfies: Vcf = I1 / Cf * t, where I1 represents the first current and Cf represents the capacitance value of the flying capacitor. Because the sampling voltage follows the ramp voltage in the above feedback control, and the ramp voltage Vramp satisfies: Vramp = k * I2 / Cf * t, and the sampling voltage Vc satisfies: Vc = k * Vcf = k * I1 / Cf * t, that is, Vramp = Vc = k * I2 / Cf * t = k * I1 / Cf * t. From this, it can be obtained that: I1 = I2. That is, by setting the slope of the ramp voltage through the above parameters, the first current can be made equal to the second current. Among them, the control unit controls the generation and cut-off of the second current according to the sampling voltage and the reference voltage (equivalent to the control unit controlling whether to perform pre-charging according to the sampling voltage and the reference voltage). The sampling voltage represents the voltage of the flying capacitor, and the reference voltage represents 1 / 2 of the input voltage.

[0045] Specifically, as Figure 7 or Figure 8 shown, during the pre-charging process, the sampling voltage follows the change of the ramp voltage through the feedback control of the control unit, and then the constant-current conduction of the first high-side power transistor is realized. At the same time, the slope of the ramp voltage is set according to the second current and the capacitance value of the flying capacitor to make the first current equal to the second current. Therefore, under the ramp voltage with a given slope, the gate-source voltage difference of the first high-side power transistor is finally controlled to reach a constant state and operates in the saturation region, realizing the constant-current charging of the flying capacitor and avoiding affecting the bias voltage of the output capacitor.

[0046] In summary, the pre-charge circuit proposed by the present invention perfectly solves various problems existing in the pre-charging of the flying capacitor by reusing the first high-side power transistor HS1 in the high-voltage device area, thereby simplifying the structure of the pre-charge circuit and reducing the production cost.

[0047] Specifically, the control unit includes a sampling circuit, an operational amplifier circuit, a comparison circuit, and a driving circuit. Among them, the sampling circuit is connected to the flying capacitor to collect the sampling voltage. The operational amplifier circuit performs differential amplification on the sampling voltage and the ramp voltage to generate a compensation voltage. The comparison circuit compares the sampling voltage and the reference voltage to generate a comparison signal, and the comparison signal controls whether to generate a second current. The driving circuit generates the driving voltage of the first high-side power transistor according to the compensation voltage and the comparison signal. When the sampling voltage is less than the reference voltage, the driving circuit generates a constant driving voltage according to the compensation voltage to control the conduction of the first high-side power transistor. When the sampling voltage is greater than the reference voltage, the driving circuit pulls down the driving voltage according to the comparison signal to control the turn-off of the first high-side power transistor.

[0048] Preferably, as Figure 6 shown, the second current path includes a pull-down current source Is. The pull-down current source Is is a constant current source, and the pull-down current source Is is connected to the negative electrode of the flying capacitor Cf and the ground terminal. The sampling circuit includes a differential amplifier U1. The positive input terminal of the differential amplifier U1 is connected to the positive electrode of the flying capacitor Cf, the negative input terminal is connected to the negative electrode of the flying capacitor Cf, and the output terminal of the differential amplifier U1 outputs the sampling voltage Vc. The operational amplifier circuit includes an operational amplifier U2. The positive input terminal of the operational amplifier U2 receives the ramp voltage Vramp, the negative input terminal is connected to the output terminal of the differential amplifier U1, and the operational amplifier U2 performs differential amplification on the ramp voltage Vramp and the sampling voltage Vc to output the compensation voltage Vcomp. The comparison circuit includes a comparator U3. The reverse input terminal of the comparator U3 receives the sampling voltage Vc, the forward input terminal of the comparator U3 receives the reference voltage Vref, and the comparison signal EN output by the comparator U3 controls the pull-down current source Is. The driving circuit generates the driving voltage Vgs of the first high-side power transistor HS1 according to the compensation voltage Vcomp and the comparison signal EN.

[0049] As Figure 7As shown, when the sampling voltage Vc is less than the reference voltage Vref, the comparator U3 outputs a comparison signal EN in a high-level state. The comparison signal EN enables the pull-down current source Is to generate a second current I2. The ramp generator generates a ramp voltage Vramp with a given slope. The operational amplifier U2 outputs a compensation voltage Vcomp according to the sampling voltage Vc and the ramp voltage Vramp, and the drive circuit adjusts the drive voltage Vgs according to the compensation voltage Vcomp. With the adjustment of the feedback control, it quickly enters the steady state to achieve that the sampling voltage Vc synchronously follows the ramp voltage Vramp and the drive voltage Vgs is constant, thereby driving the first high-side power transistor HS1 to conduct and operate in the saturation state. As the voltage of the flying capacitor Cf gradually increases to 1 / 2Vin, at time t1, the sampling voltage is greater than or equal to the reference voltage Vref, and the comparator U3 outputs a comparison signal EN in a low-level state to turn off the pull-down current source Is, and at the same time the drive circuit pulls down the drive voltage Vgs according to the comparison signal EN to turn off the first high-side power transistor HS1. At this time, since the slope of the ramp voltage Vramp is equal to the second current divided by the capacitance value of the flying capacitor, the slope of the ramp voltage becomes zero and Vramp no longer changes. After the pre-charging is completed, the inputs (Vc and Vramp) of the operational amplifier U2 can be short-circuited so that Vc and Vramp can keep following each other at the start stage of the next pre-charging.

[0050] It should be noted that the generation of the ramp voltage and the generation of the drive voltage are conventional technical means in the art. For example, a ramp generator can generate a ramp voltage, and by real-time collecting the voltage of the flying capacitor and performing bootstrap, a constant drive voltage can be generated, which will not be elaborated here. At the same time, during the pre-charging process, the second current can also be controlled to change in stages, such as Figure 8 shown, the second current in the time period of 0 - t1 is greater than the second current in the time period of t1 - t2, and it can also achieve a constant gate-source voltage of the first high-side power transistor.

[0051] In summary, the pre-charging circuit proposed by the present invention pre-charges the flying capacitor in the series-capacitor buck converter to ensure the normal start-up and operation of the series-capacitor buck converter. At the same time, during the pre-charging process, the first current is controlled to be equal to the second current to avoid affecting the bias voltage of the output capacitor and thus affecting the load operation. In addition, when the pre-charging circuit pre-charges the flying capacitor, it is through feedback control that the voltage of the flying capacitor reaches so as to accurately achieve the smooth transition of the series-capacitor buck converter from the shutdown state to the operating state.

[0052] The present invention also proposes a series-capacitor buck converter, which includes the pre-charging circuit proposed above.

[0053] It should be noted that the specific embodiments and corresponding illustrations given are only one way to describe the implementation method of the present invention, and do not limit the specific structure of the implementation scheme of the present invention. Without departing from the principle and essence of the present invention, various changes or modifications can be made to these implementation manners, but these changes and modifications all fall within the protection scope of the present invention.

[0054] Although the above embodiments are separately described and elaborated, regarding some common technologies, in the view of those of ordinary skill in the art, substitutions and integrations can be made between the embodiments. For the content not clearly recorded in one of the embodiments, reference can be made to another embodiment with relevant records.

[0055] The above-described implementation manners do not constitute a limitation on the protection scope of the technical solution. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the above implementation manners shall be included within the protection scope of the technical solution.

Claims

1. A pre-charge circuit for pre-charging a flying capacitor in a series-capacitor buck converter, wherein the first-phase BUCK circuit of the series-capacitor buck converter includes a first high-side power transistor, and the first high-side power transistor is connected to the input voltage and the positive electrode of the flying capacitor. The pre-charge circuit is characterized in that the pre-charge circuit provides a first current path and a second current path. The first current flows into the positive electrode of the flying capacitor through the first current path, and the second current flows from the negative electrode of the flying capacitor to the ground terminal through the second current path. wherein, the first current path includes the first high-side power transistor.

2. The pre-charge circuit according to claim 1, wherein During pre-charging, the first current is equal to the second current.

3. The pre-charging circuit according to claim 1, wherein, During pre-charging, the control unit controls the first high-side power transistor to operate in the saturation region according to the sampled voltage and the ramp voltage. wherein, the sampled voltage represents the voltage of the flying capacitor, and the slope of the ramp voltage is greater than zero.

4. The pre-charge circuit according to claim 3, characterized in that, The slope of the ramp voltage is set according to the second current and the capacitance value of the flying capacitor.

5. The pre-charge circuit according to claim 3, characterized in that, The control unit performs differential amplification on the sampled voltage and the ramp voltage to obtain a compensation voltage, and generates a driving voltage for the first high-side power transistor according to the compensation voltage.

6. The pre-charge circuit according to claim 4, wherein The control unit controls the second current path to generate the second current, and sets the slope of the ramp voltage according to the ratio of the second current to the capacitance value of the flying capacitor.

7. The pre-charge circuit according to claim 6, wherein The slope of the ramp voltage satisfies: the slope of the ramp voltage = k * the second current / the capacitance value of the flying capacitor, where k is greater than zero.

8. The pre-charge circuit according to claim 7, wherein The k satisfies: k = the sampled voltage / the voltage of the flying capacitor.

9. The pre-charge circuit according to claim 1, wherein The control unit controls whether to perform pre-charging according to the sampled voltage and the reference voltage. wherein, the sampled voltage represents the voltage of the flying capacitor, and the reference voltage represents half of the input voltage.

10. The pre-charging circuit according to claim 3, characterized in that, The control unit includes: a sampling circuit connected to the flying capacitor to collect the sampled voltage; an operational amplifier circuit that performs differential amplification on the sampled voltage and the ramp voltage to generate a compensation voltage; a comparison circuit, the first input terminal receives the sampled voltage, the second input terminal receives the reference voltage, and the output comparison signal controls whether to generate the second current. The reference voltage represents half of the input voltage; a driving circuit that generates a driving voltage for the first high-side power transistor according to the compensation voltage and the comparison signal to control the conduction or cut-off of the first high-side power transistor.

11. The pre-charge circuit according to claim 10, wherein When the sampled voltage is less than the reference voltage, the driving circuit generates a constant driving voltage according to the compensation voltage to control the conduction of the first high-side power transistor; When the sampled voltage is greater than the reference voltage, the driving circuit pulls down the driving voltage according to the comparison signal to control the cut-off of the first high-side power transistor.

12. The pre-charge circuit according to claim 1, characterized in that The second current path includes a pull-down current source, and the pull-down current source is connected to the negative electrode of the flying capacitor and the ground terminal.

13. A series capacitor buck converter, characterized in that, including the pre-charge circuit according to any one of claims 1-12.

Images