阅读说明：本技术 可动态控制最小工作周期的方法和相关半桥式升压电路 (Method for dynamically controlling minimum working period and related half-bridge type booster circuit ) 是由 王昶明 郑宗泰 王孝武 于 2021-04-02 设计创作，主要内容包括：本发明公开半桥式升压电路,包括上臂开关、下臂开关,以及一启动电容,其采用动态最小工作周期曲线来限制下臂开关的最少导通时间,以确保启动电容内存有足够的电荷以导通上臂开关。此外,依据负载的不同运作阶段,本发明可动态地设定最小工作周期曲线的值,以有效提高负载的最大输出功率。(The invention discloses a half-bridge type booster circuit, which comprises an upper arm switch, a lower arm switch and a starting capacitor, wherein the minimum conducting time of the lower arm switch is limited by adopting a dynamic minimum working period curve so as to ensure that enough charges are stored in the starting capacitor to conduct the upper arm switch. In addition, according to different operation stages of the load, the invention can dynamically set the value of the minimum duty cycle curve so as to effectively improve the maximum output power of the load.)

1. A method for dynamically controlling a minimum duty cycle, comprising:

in a charging period, an upper arm switch is turned off and a lower arm switch is turned on to charge a capacitor by a direct current voltage;

in a discharging period following the charging period, charging the parasitic capacitance of the upper arm switch by the capacitor memory energy by turning on the upper arm switch and turning off the lower arm switch to maintain the upper arm switch in a conducting state, and transmitting a bus voltage to an output terminal through the conducting upper arm switch to drive a motor;

adjusting the on-time of the upper arm switch in the discharge period according to the state of the output end; and

limiting the conduction time of the lower arm switch during the charging cycle according to a dynamic minimum duty cycle curve, wherein:

when the rotating speed of the motor is not more than a first rotating speed, the value of the dynamic minimum working period curve is not more than a maximum value;

the value of the dynamic minimum duty cycle curve is equal to the maximum value when the rotational speed of the motor is equal to the first rotational speed;

the value of the dynamic minimum duty cycle curve is not greater than the maximum value when the rotational speed of the motor is greater than the first rotational speed.

2. The method of claim 1, wherein the value of the minimum duty cycle curve increases as the rotational speed of the motor increases when the rotational speed of the motor is not greater than the first rotational speed.

3. The method of claim 2, wherein the value of the minimum duty cycle curve increases linearly, polynomial, exponential, or stepwise as the rotational speed of the motor increases when the rotational speed of the motor is not greater than the first rotational speed.

4. The method of claim 2, further comprising:

determining a rising slope of the dynamic minimum duty cycle curve when the rotation speed of the motor is not greater than the first speed according to the value of the bus voltage, the value of the capacitor, the characteristic of the upper arm switch, the characteristic of the lower arm switch, the switching manner of the upper arm switch, and/or the switching manner of the lower arm switch.

5. The method of claim 1, wherein the value of the minimum duty cycle curve decreases as the rotational speed of the motor increases when the rotational speed of the motor is greater than the first rotational speed.

6. The method of claim 5, wherein the value of the minimum duty cycle curve decreases linearly, polynomial, exponential, or stepwise as the rotational speed of the motor increases when the rotational speed of the motor is greater than the first rotational speed.

7. The method of claim 5, further comprising:

determining a falling curve of the dynamic minimum duty cycle curve when the rotation speed of the motor is greater than the first rotation speed according to the value of the bus voltage, the value of the capacitor, the characteristic of the upper arm switch, the characteristic of the lower arm switch, the switching manner of the upper arm switch, and/or the switching manner of the lower arm switch.

8. The method of claim 1, further comprising:

the minimum duty cycle curve has a value of 0 when the rotational speed of the motor is greater than a second rotational speed, wherein the first rotational speed is less than the second rotational speed.

9. The method of claim 1, further comprising:

providing a switching signal with a fixed frequency and a peak value, wherein the frequency of the switching signal is greater than the frequency of an output voltage on the output terminal;

when the level of the switching signal is greater than the level of the output voltage, turning off the upper arm switch and turning on the lower arm switch; and

when the level of the switching signal is less than the level of the output voltage, the upper arm switch is turned on and the lower arm switch is turned off.

10. The method of claim 1, wherein the lower arm switch has a conduction time within the charging cycle that is not less than a conduction time of the dynamic minimum duty cycle curve.

11. A half-bridge boost circuit with dynamically controllable minimum duty cycle, comprising:

an output end for providing an output voltage to drive a motor;

an upper arm switch for selectively conducting a signal path between a bus voltage and the output terminal;

a lower arm switch for selectively conducting a signal path between the output terminal and a ground voltage;

a capacitor, comprising:

a first terminal selectively coupled to a DC voltage; and

a second terminal coupled to the output terminal; and

a control circuit for:

turning off the upper arm switch and turning on the lower arm switch in a charging cycle to couple the output terminal to the ground voltage and allow the DC voltage to charge the capacitor;

turning on the upper arm switch and turning off the lower arm switch to couple the output terminal to the bus voltage in a discharging period following the charging period, and allowing the capacitor memory energy to charge the parasitic capacitor of the upper arm switch to maintain the upper arm switch on;

adjusting the on-time of the upper arm switch in the discharge period according to the state of the output end; and

limiting the conduction time of the lower arm switch during the charging cycle according to a dynamic minimum duty cycle curve, wherein:

when the rotating speed of the motor is not more than a first rotating speed, the value of the dynamic minimum working period curve is not more than a maximum value;

the value of the dynamic minimum duty cycle curve is equal to the maximum value when the rotational speed of the motor is equal to the first rotational speed;

when the rotating speed of the motor is greater than the first rotating speed and not greater than a second rotating speed, the value of the dynamic minimum working period curve is not greater than the maximum value;

when the rotation speed of the motor is greater than the second rotation speed, the value of the minimum duty cycle curve is 0; and is

The first rotational speed is less than the second rotational speed.

12. The half-bridge boost circuit of claim 11, further comprising a start-up diode, an anode of said start-up diode coupled to said dc voltage, and a cathode of said start-up diode coupled to said first terminal of said capacitor, wherein:

the upper arm switch includes:

a first terminal coupled to the bus voltage;

a second terminal coupled to the output terminal; and

a control end for receiving a first control signal; and is

The lower arm switch includes:

a first terminal coupled to the output terminal;

a second terminal coupled to the ground voltage; and

a control terminal for receiving a second control signal.

13. The half-bridge boost circuit of claim 11, wherein the lower arm switch has a conduction time during said charging cycle that is not less than the conduction time of said dynamic minimum duty cycle curve.

Technical Field

The present invention relates to a method for dynamically controlling a minimum duty cycle and a related half-bridge boost circuit, and more particularly, to a method for dynamically controlling a minimum duty cycle according to an operation phase of a load and a related half-bridge boost circuit.

Background

A motor is an electronic device for converting electric energy into kinetic energy, and common applications include a dc motor, an ac motor, a stepping motor, and the like. In many motor applications, pulse width modulation (pwm) is often used to adjust the current flowing through the motor, so as to save power and control the rotation speed. The pwm technique mainly adjusts the time ratio of the power supply to deliver energy to the load in a periodic square wave by high frequency switching of the power switch, and the ratio of the time of delivering energy to the period length is also called duty cycle (also called "duty cycle"). A half-bridge bootstrap (bootstrap) circuit is commonly used to drive motors, and includes a start capacitor, an upper arm switch and a lower arm switch. The upper arm switch and the lower arm switch are coupled between a bus voltage and a ground voltage in a totem pole (totem pole) manner, and an intermediate point between the two switches serves as an output terminal. When the upper arm switch is turned off and the lower arm switch is turned on, the direct-current power supply can charge the starting capacitor; when the upper arm switch is turned on and the lower arm switch is turned off, the upper arm switch is maintained in the on state by the memory energy of the start capacitor, and the bus voltage is transmitted to the output end to provide an output voltage.

To ensure that there is sufficient charge in the start-up capacitor to turn on the upper arm switch, a minimum duty cycle (MD) mechanism is typically used to limit the minimum on-time of the lower arm switch. The prior art half-bridge boost circuit uses a fixed minimum duty cycle curve to control the lower arm switches, which equivalently limits the maximum output power of the motor when the output power is higher. Therefore, a need exists for a half-bridge boost circuit that can dynamically control the minimum duty cycle.

Disclosure of Invention

The invention provides a method capable of dynamically controlling a minimum working period, which comprises the following steps that in a charging period, a direct-current voltage charges a capacitor by disconnecting an upper arm switch and conducting a lower arm switch; in a discharging period following the charging period, charging the parasitic capacitor of the upper arm switch by the capacitor memory energy by turning on the upper arm switch and turning off the lower arm switch to keep the upper arm switch on, and transmitting a bus voltage to an output end through the turned-on upper arm switch to drive a motor; adjusting the on-time of the upper arm switch in the discharge period according to the state of the output end; and limiting the conduction time of the lower arm switch in the charging period according to a dynamic minimum duty cycle curve. When the rotating speed of the motor is not more than a first rotating speed, the value of the dynamic minimum working period curve is not more than a maximum value; when the rotation speed of the motor is equal to the first rotation speed, the value of the dynamic minimum working period curve is equal to the maximum value; and when the rotating speed of the motor is greater than the first rotating speed, the value of the dynamic minimum working period curve is not greater than the maximum value.

The invention provides a half-bridge type booster circuit capable of dynamically controlling the minimum working period, which comprises an output end, an upper arm switch, a lower arm switch, a capacitor and a control circuit. The output terminal is used for providing an output voltage to drive a motor. The upper arm switch is used for selectively conducting a signal path between a bus voltage and the output end, and the lower arm switch is used for selectively conducting a signal path between the output end and a grounding voltage. The first end of the capacitor is selectively coupled to a DC voltage, and the second end of the capacitor is coupled to the output end. The control circuit is used for switching off the upper arm switch and switching on the lower arm switch in a charging period so as to couple the output end to the grounding voltage and enable the direct-current voltage to charge the capacitor; turning on the upper arm switch and turning off the lower arm switch to couple the output terminal to the bus voltage in a discharging period following the charging period, and allowing the capacitor memory energy to charge the parasitic capacitor of the upper arm switch to maintain the upper arm switch on; adjusting the on-time of the upper arm switch in the discharge period according to the state of the output end; and limiting the conduction time of the lower arm switch in the charging period according to a dynamic minimum duty cycle curve. When the rotating speed of the motor is not more than a first rotating speed, the value of the dynamic minimum working period curve is not more than a maximum value; when the rotation speed of the motor is equal to the first rotation speed, the value of the dynamic minimum working period curve is equal to the maximum value; when the rotating speed of the motor is greater than the first rotating speed and not greater than a second speed, the value of the dynamic minimum working period curve is not greater than the maximum value; when the rotating speed of the motor is greater than the second rotating speed, the value of the minimum working period curve is 0; and the first rotation speed is less than the second rotation speed.

Drawings

FIG. 1 is a schematic diagram of a half-bridge boost circuit capable of dynamically controlling a minimum duty cycle according to an embodiment of the present invention.

FIG. 2 is a signal diagram illustrating the operation of the related control circuit in the half-bridge boost circuit according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating the operation of a motor driven by a half-bridge boost circuit according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating the operation of a half-bridge boost circuit to dynamically control minimum duty cycle according to an embodiment of the present invention.

Reference numerals

10: power device

20: drive output circuit

30: control circuit

100: half-bridge type booster circuit

HSW: upper arm switch

LSW: lower arm switch

SW1-SW 4: switch with a switch body

R1, R2: resistance (RC)

C_GSH、C_GSLC1, C2: capacitor with a capacitor element

C_PH、C_PL: parasitic capacitance

D_BT: start diode

N_OUT: output end

GND: ground voltage

V_DC: direct voltage

V_BUS: bus voltage

V_OUT: output voltage

V_SW: switching signal

MD1, MD 2: minimum duty cycle curve

Po, Po': motor output power curve

TR: torque curve of motor

Detailed Description

Fig. 1 is a schematic diagram of a half-bridge boost circuit 100 capable of dynamically controlling a minimum duty cycle (minimum duty) according to an embodiment of the present invention. The half-bridge boost circuit 100 includes a power device 10, a driving output circuit 20, and a control circuit 30, which can be provided at an output end N_OUTProviding an output voltage V_OUTTo drive a load (not shown in fig. 1).

The power device 10 includes an upper arm switch HSW, a lower arm switch LSW, resistors R1 and R2, and a capacitor C_GSHAnd C_GSL. The first terminal of the upper arm switch HSW is coupled to a bus voltage V_BUSThe second terminal is coupled to the output terminal N_OUTAnd the control terminal is coupled to the driving output circuit 20 through a resistor R1 to receive the control signal VGH. The first terminal of the lower arm switch LSW is coupled to the output terminal N_OUTThe second terminal is coupled to the ground voltage GND, and the control terminal is coupled to the driving output circuit 20 through the resistor R2 to receive the control signal VGL. C_PHRepresents a parasitic capacitance between the control terminal and the second terminal of the upper arm switch HSW, and C_PLRepresenting the parasitic capacitance between the control terminal and the second terminal of the lower arm switch LSW. Capacitor C_GSHParasitic capacitance C connected in parallel with upper arm switch HSW_PHAnd a capacitor C_GSLParasitic capacitance C connected in parallel to the lower arm switch LSW_PLFor preventing malfunction of upper arm switch HSW and lower arm switch LSW and adjusting switching speed.

The driving output circuit 20 includes switches SW1-SW4, capacitors C1-C2, and a start diode D_BT. Starting diode D_BTIs coupled to a DC voltage V_DCAnd the cathode is coupled to the output terminal N through a capacitor C1_OUT. A first terminal of the switch SW1 is coupled to the start diode D_BTA second terminal coupled to the resistor R1 in the power device 10, and a control terminal coupled to the control circuit 30. The switch SW2 has a first terminal coupled to the second terminal of the switch SW1, and a second terminal coupled to the output terminal N_OUTAnd the control terminal is coupled to the control circuit 30. A first terminal of the switch SW3 is coupled to the dc voltage V_DCThe second terminal is coupled to the resistor R2 in the power device 10, and the control terminal is coupled to the control circuit 30. The switch SW4 has a first terminal coupled to the second terminal of the switch SW3, a second terminal coupled to the ground voltage GND, and a control terminal coupled to the control circuit 30. The capacitor C1 is a starting capacitor, and a first end of the starting capacitor passes through a starting diode D_BTIs coupled to a DC voltage V_DCAnd the second terminal is coupled to the output terminal N_OUT. The first terminal of the capacitor C2 is coupled to the DC voltage V_DCAnd the second terminal is coupled to the ground voltage GND.

The control circuit 30 can be based on the output terminal N_OUTSwitches SW1-SW4 are controlled to provide control signals VGH and VGL to selectively turn on or off upper arm switch HSW and lower arm switch LSW, so that half-bridge boost circuit 100 can alternately operate in the charging period and the discharging period.

During each charging cycle of half-bridge boost circuit 100, control circuit 30 controls switches SW1-SW4 of driving output circuit 20 to output control signal VGH with disable potential and control signal VGL with enable potential, thereby turning off upper arm switch HSW and turning on lower arm switch LSW. In this case, the output terminal N_OUTIs coupled to the ground voltage GND through the turned-on switch SW2_DCWill pass through the forward biased start diode D_BTTo charge the capacitor C1. In other words, the energy stored in the capacitor C1 during each charging cycle depends on the on-time of the lower arm switch LSW.

During each discharge period of half-bridge boost circuit 100, control circuit 30 controls switches SW1-SW4 of output circuit 20 to output control signal VGH with enable potential and control signal VGL with disable potential, thereby turning on upper arm switch HSW and turning off lower arm switch LSW. In this case, the output terminal N_OUTIs coupled to the bus voltage V through the conductive upper arm switch HSW_BUSSimultaneously start diode D_BTWill turn off due to reverse bias. At this time, the energy stored in the capacitor C1 during the charging period can be applied to the parasitic capacitor C of the upper arm switch HSW_PHCharging to maintain upper arm switch HSW in a conductive state and bus voltage V_BUSCan pass through the upper part of conductionArm switch HSW transfers to output terminal N_OUTTo provide an output voltage V_OUT. In other words, the output voltage V_OUTThe value of (d) depends on the on-time of the upper arm switch HSW in each discharge cycle.

The voltage required for motor operation is usually sinusoidal, so in motor driving applications, the half-bridge boost circuit 100 of the present invention provides sinusoidal output voltage V with different frequencies and peak values_OUTSo as to generate a magnetic field inside the motor to attract the magnet and further control the speed of the motor. As is known to those skilled in the art, the actual rotation direction of the motor may include forward rotation and reverse rotation, and the motor direction may be changed in a corresponding manner (e.g., changing the input voltage polarity, voltage line sequence or signal command) for different applications (e.g., dc motor, ac motor, stepping motor, etc.). For simplicity of description, the following description will be made only with respect to a single motor steering, and the present invention can also be applied to another motor steering with the same concept.

Fig. 2 is a signal diagram illustrating the operation of the related control circuit 30 in the half-bridge boost circuit of the present invention. The control circuit 30 will depend on the output voltage V_OUTAnd a switching signal V_SWTo control the on-time and off-time of the upper arm switch HSW and the lower arm switch LSW. Switching signal V_SWFor pulse signals with fixed frequency and peak value, the voltage V is output_OUTWith respect to the output power of half-bridge boost circuit 100 (with respect to motor speed in motor drive applications). To ensure the output voltage V_OUTWaveform integrity of, switching signal V_SWIs usually greater than the output voltage V_OUTIs at least 5 times. For illustrative purposes, the output voltage V shown in FIG. 2_OUTThe frequency of which is gradually increased and the output voltage V_OUTAnd a switching signal V_SWWith the same peak.

When switching signal V_SWIs greater than the output voltage V_OUTAt level (h), the control circuit 30 controls the drive output circuit 20 to turn off the upper arm switch HSW and turn on the lower arm switch LSW; when switching signal V_SWIs lower than the output voltage V_OUTAt the level of (3), the control circuit 30 will control the driving outputThe output circuit 20 turns on the upper arm switch HSW and turns off the lower arm switch LSW. As shown in fig. 2, the output voltage V_OUTThe larger the peak value of (a), the longer the on time of the upper arm switch HSW. Otherwise, the output voltage V is_OUTThe lower the peak value of (a), the longer the on time of the lower arm switch LSW. On the other hand, the output voltage V_OUTThe lower the frequency of (3), the longer the on time of the upper arm switch HSW and the more switching times.

In order to ensure that there is enough charge in the capacitor C1 to maintain the upper arm switch HSW in the conducting state during the discharging period, the control circuit 30 according to the present invention limits the minimum conducting time of the lower arm switch LSW during the charging period according to a dynamic minimum duty cycle curve, i.e. ensures that the capacitor C1 can store enough energy during the charging period. In more detail, if the time that the control signal VGL has the enable level is not less than the on-time of the dynamic minimum duty cycle curve, the maximum power output can be provided.

FIG. 3 is a diagram illustrating the operation of a motor driven by the half-bridge boost circuit 100 according to the present invention. The horizontal axis represents the motor rotation speed, the left vertical axis represents the torque (torque), the right vertical axis represents the output power, TR represents the torque of the motor as a function of the rotation speed, and Po represents the output power of the motor as a function of the rotation speed, wherein the output power Po has a value approximately equal to the product of the motor rotation speed and the torque. The region before the turning speed N1 is referred to as a constant torque region (constant torque), and the region after the turning speed N1 is referred to as a constant power region (constant power). When the motor speed is in the constant torque region, the torque TR is maintained at a constant maximum torque TR_MAX. When the motor speed enters the constant power region (i.e. after the motor speed reaches the turning speed N1), the value of the torque TR decreases as the motor speed increases, and the value of the output power Po is maintained at a constant maximum output power P_MAX. The value of the transition speed N1 is related to the bus voltage V_BUSBus voltage V_BUSThe larger the turning speed N1.

FIG. 4 is a schematic diagram illustrating the operation of the half-bridge boost circuit 100 to dynamically control minimum duty cycle. The horizontal axis represents motor speed, the left vertical axis represents MD value, and the right vertical axis represents outputPower, MD1 represents one example of a dynamic minimum duty cycle curve used by half-bridge boost circuit 100 of the present invention, MD2 represents a fixed minimum duty cycle curve used in the prior art, Po represents a curve of output power versus rotational speed for a motor driven by half-bridge boost circuit 100 of the present invention, and Po' represents a curve of output power versus rotational speed for a motor driven by the prior art. As shown in FIGS. 3 and 4, when the half-bridge boost circuit 100 of the present invention is applied to motor driving, the required MD values are different in different operation stages of the motor, so the control circuit 30 in the half-bridge boost circuit 100 of the present invention employs the dynamic minimum duty cycle curve MD1, wherein the maximum value of the dynamic minimum duty cycle curve MD1 is MD1_MAX。

When the motor speed is less than the turning speed N1, the output power does not reach the limit of the constant power region, and the corresponding output voltage V is_OUTWill be smaller than the switching signal V_SWThe on-time of the lower arm switch LSW is longer, the capacitor C1 has enough time to charge, and the value of the minimum duty cycle curve MD1 may be smaller than the maximum value MD_MAXAny value of (c). When the motor speed is between 0 and N0, the limitation of the output power of the motor by the minimum duty cycle curve MD1 has not yet been effected, and the output power Po of the motor increases with the motor speed. When the motor speed approaches the transition speed N1 and reaches N0, the value of the minimum duty cycle curve MD1 is sufficient to limit the output power Po of the motor, and the output power Po of the motor reaches the limit of the constant power region in advance, wherein the difference between N0 and N1 is determined by the setting value of the minimum duty cycle curve MD 1. In the embodiment shown in fig. 4, the value of the minimum duty cycle curve MD1 increases linearly as the motor speed increases when the motor speed is less than the breakover speed N1. In other embodiments, when the motor speed is less than the breakover speed N1, the value of the minimum duty cycle curve MD1 may increase in a polynomial, exponential, stepwise manner, or other proportion as the motor speed increases.

When the motor speed equals to the turning speed N1, the output power reaches the limit of the constant power region, corresponding to the output voltage V_OUTPeak value ofApproximately equal to the switching signal V_SWAnd therefore the on time of the lower arm switch LSW becomes short. In order to avoid that the capacitor C1 cannot be charged with enough charge to turn on the upper arm switch HSW in the next cycle in a short charging time, the minimum duty cycle curve MD1 is set to the maximum value MD_MAX. Due to the value of the turning speed N1 with respect to the bus voltage V_BUSIs normally designed at the lowest bus voltage V_BUSThe most severe condition for providing the highest output power is used to determine the turning speed N1, and then the maximum value MD is used_MAXTo ensure that the lower arm switch LSW has sufficient on-time to allow sufficient charging time for capacitor C1.

As mentioned above, the output voltage V_OUTAnd a switching signal V_SWIs dependent on the motor speed, when the motor speed is between N1 and N2 the output voltage V is made_OUTAnd a switching signal V_SWWhen the peak value is the same, the higher the motor speed, the output voltage V_OUTThe higher the frequency of (d) and the smaller the number of times the lower arm switch LSW needs to be switched, the value of the minimum duty cycle curve MD1 may be set to decrease as the motor speed increases. In the embodiment shown in fig. 4, the value of the minimum duty cycle curve MD1 decreases linearly as the motor speed increases when the motor speed is between N1 and N2. In other embodiments, the value of the minimum duty cycle curve MD1 may decrease in a polynomial, exponential, step-wise, or other proportion as the motor speed increases when the motor speed is between N1 and N2.

The rising and falling slopes of the minimum duty cycle curve MD1 may be in accordance with the bus voltage V3526 when the motor speed is between 0 and N1 and between N1 and N2_BUSThe value of the capacitor C1, the characteristics of the upper and lower arm switches, the leakage current of the drive output circuit 20, and/or the PWM switching scheme. Bus voltage V_BUSIs proportional to the transition speed N1, the bus voltage V of the present invention can be varied according to different applications_BUSTo determine the minimum duty cycle curve MD1 curve. The maximum capacity of the capacitor C1 can be correlated to its placement, ambient temperature and operating space, and the minimum duty cycle curve can be determined according to the storage capacity of the capacitor C1MD1 curve. The upper/lower arm switches periodically charge and discharge their parasitic capacitances during operation, and the minimum duty cycle curve MD1 is determined according to the parasitic capacitances caused by the switch type and the number of parallel capacitors for different applications. Since the leakage current of the driving output circuit 20 consumes the memory energy of the capacitor C1, the minimum duty cycle curve MD1 curve is determined according to the leakage current of the driving output circuit 20. In the PWM architecture, the higher the switching times, the higher the switching losses, and the different modulation will generate different energy consumption requirements at the peak, the most direct difference is the switching times, so the minimum duty cycle curve MD1 can be determined according to the PWM switching method.

When the motor speed reaches N2, the number of times the lower arm switch LSW needs to be switched is so small that the charge stored in the capacitor C1 is sufficient to satisfy the requirement of upper arm driving, and the value of the minimum duty cycle curve MD1 is set to 0.

As shown in fig. 4, the prior art uses a fixed minimum duty cycle curve MD2, which greatly limits the maximum output power (shown as curve Po') when driving the motor. In contrast, the present invention employs the dynamic minimum duty cycle curve MD1, the value of which can be set according to different operation phases of the motor, so as to increase the maximum output power of the motor (as shown by the curve Po), wherein the increase of the output power of the motor can be represented by the slope area between the curves Po and Po'.

In the embodiment of the present invention, the upper arm switch HSW, the lower arm switch LSW, and the switches SW1-SW4 may be metal-oxide-semiconductor field-effect transistors (MOSFETs), Bipolar Junction Transistors (BJTs), or other devices with similar functions. For an N-type transistor, the enable potential is high, and the disable potential is low; for a P-type transistor, the enable potential is low and the disable potential is high. However, the kind of the switch does not limit the scope of the present invention.

In summary, the half-bridge boost circuit of the present invention employs a dynamic minimum duty cycle curve to limit the minimum on-time of the lower arm switch, so as to ensure that there is enough charge in the start-up capacitor to turn on the upper arm switch. In addition, according to different operation stages of the load, the invention can dynamically set the value of the minimum duty cycle curve so as to effectively improve the maximum output power of the load.

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.