Power management system

Abstract

A power management system includes: a voltage sampling module configured to sample a voltage representing a current flowing through a BJT power tube to generate a current sensing signal; a switch control module configured to generate an off control signal based on the current sensing signal and an off reference voltage, generate an on control signal based on an output representing signal representing an output voltage or current of the power management system, and generate a pulse width modulation signal based on the on control signal and the off control signal; and a base drive module configured to generate a pre-off enable signal for controlling turning on and off of a first switch tube based on a pre-off reference voltage, the current sensing signal, and the pulse width modulation signal, control turning on and off of a second switch tube using an inverse signal of the pulse width modulation signal, and adjust the pre-off reference voltage based on the off control signal and the pre-off enable signal.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of circuit, and more particularly, to a power management system. BACKGROUND

[0002] Electronic devices have become indispensable in people's life, and power management system is an indispensable component of electronic devices. Low cost is one of the development trends of various power management systems, and bipolar junction transistor (BJT) is often used as a power device in power management system due to its low cost. SUMMARY

[0003] The power management system according to an embodiment of the present application comprises: a voltage sampling module configured to sample a voltage representing a current flowing through a BJT power transistor to generate a current sensing signal; a switch control module configured to generate an off control signal based on the current sensing signal and an off reference voltage, generate an on control signal based on an output representation signal representing an output current or an output voltage of the power management system, and generate a pulse width modulation signal based on the on control signal and the off control signal; and a base drive module including a first switch transistor for controlling the supply and shutdown of a drive current for the BJT power transistor and a second switch transistor for controlling whether a base of the BJT power transistor is pulled low to ground, and configured to generate a pre-off enable signal for controlling the on and off of the first switch transistor based on a pre-off reference voltage, the current sensing signal, and the pulse width modulation signal, control the on and off of the second switch transistor using an inverted signal of the pulse width modulation signal, and adjust the pre-off reference voltage based on the off control signal and the pre-off enable signal. BRIEF DESCRIPTION OF DRAWINGS

[0004] The present application can be better understood with reference to the following descriptions of specific embodiments in conjunction with the accompanying drawings, in which:

[0005] Figure 1 A schematic diagram of a power management system according to an embodiment of the present application is shown.

[0006] Figure 2 A schematic diagram of a power management system according to an embodiment of the present application is shown. Figure 1 A waveform diagram of a plurality of related signals in the power management system shown.

[0007] Figure 3 A schematic diagram of a base drive module used in a power management system according to an embodiment of the present application is shown. Figure 1 A schematic diagram of a base drive module used in a power management system according to an embodiment of the present application is shown.

[0008] Figure 4 A waveform diagram of a plurality of related signals in the power management system using the base drive module shown. Figure 3 A waveform diagram of a plurality of related signals in the power management system using the base drive module shown.

[0009] Figure 5 An example implementation of the off control signal detection unit is shown. Figure 3 An example implementation of the off control signal detection unit is shown.

[0010] Figure 6 An example implementation of the off control signal detection unit is shown. Figure 5 Waveform diagrams of various signals in the power management system of the abnormal detection circuit when the off control for the BJT power transistor cannot be triggered are shown.

[0011] Figure 7 An example implementation of the off control signal detection unit is shown. Figure 5 Waveform diagrams of various signals in the power management system of the abnormal timing circuit when the off control for the BJT power transistor cannot be triggered are shown.

[0012] Figure 8 An example implementation of the off control signal detection unit is shown. Figure 3 An example implementation of the off control signal detection unit is shown.

[0013] Figure 9 An example implementation of the off control signal detection unit is shown. Figure 8 Waveform diagrams of various signals in the power management system of the abnormal timing circuit when the off control for the BJT power transistor cannot be triggered are shown.

[0014] Figure 10 A flowchart of a BJT drive scheme implemented by the base drive module according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0015] The features and exemplary embodiments of the various aspects of the present application will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one of ordinary skill in the art that the present application can be practiced without some or all of these specific details. The description of the embodiments is merely illustrative of the present application and is not intended to limit the present application, as is apparent to one of ordinary skill in the art. The present application is limited only by the appended claims as interpreted in accordance with the principles of patent law. In the following detailed description of the embodiments, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one of ordinary skill in the art that the present application can be practiced without some or all of these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present application.

[0016] Figure 1 A schematic diagram of a power management system according to an embodiment of the present application is shown. As Figure 1As shown, the power management system 100 includes a voltage sampling module 102, a switch control module 104, and a base drive module 106. The voltage sampling module 102 is configured to sample the voltage representing the current Ics flowing through the BJT power transistor to generate a current sensing (CS) signal, and provide the CS signal to the switch control module 104 and the base drive module 106. The switch control module 104 is configured to generate a turn-off control signal Base_off based on the CS signal and the turn-off reference voltage Vref_off, generate a turn-on control signal Base_on based on an output characterization signal representing the output voltage or output current of the power management system 100, generate a pulse width modulation (PWM) signal based on the turn-on control signal Base_on and the turn-off control signal Base_off, and provide the PWM signal to the base drive module 106. The base drive module 106 is configured to control the supply and shutdown of the drive current Ibase for the BJT power transistor based on the PWM signal and the CS signal, thereby controlling the turn-on and turn-off of the BJT power transistor.

[0017] like Figure 1 As shown, the switch control module 104 includes a peak detection unit 1042, an output detection unit 1044, and a logic control unit 1046. The peak detection unit 1042 is configured to generate a shutdown control signal Base_off based on the CS signal and the shutdown reference voltage Vref_off, and provide the shutdown control signal Base_off to the logic control unit 1046. The output detection unit 1044 is configured to generate a conduction control signal Base_on based on an output characterization signal representing the output voltage or output current of the power management system 100, and provide the conduction control signal Base_on to the logic control unit 1046. The logic control unit 1046 is configured to generate a PWM signal based on the shutdown control signal Base_off and the conduction control signal Base_on, and provide the PWM signal to the base drive module 106. Here, when the CS signal is greater than the shutdown reference voltage Vref_off, the shutdown control signal Base_off changes from low to high, and the PWM signal changes from high to low; when the conduction control signal Base_on changes from low to high, the PWM signal changes from low to high.

[0018] Since BJT power transistors are current-driven, a sufficiently large current needs to flow into or out of the base (BASE terminal) when it is in the on-state (current flowing into the BASE terminal for NPN BJTs, current flowing out of the BASE terminal for PNP BJTs) to ensure the corresponding output power current. The faster the BJT power transistor turns off, the higher the system efficiency and the higher the constant current / constant voltage control accuracy. To turn off the BJT power transistor faster and thus more accurately control the peak current flowing through it, the base drive module 106 shuts off the drive current for the BJT power transistor before the current flowing through it reaches its peak value, i.e., when the CS signal reaches the pre-turn-off reference voltage Vref_pre. This allows the BJT power transistor to remain in the on-state using excess charge carriers. This allows for faster turn-off of the BJT power transistor, resulting in higher system efficiency and better constant current / constant voltage control accuracy.

[0019] Specifically, such as Figure 1 As shown, the base drive module 106 is further configured to: generate a pre-turn-off enable signal Base_off_pre for controlling the turn-on and turn-off of switch MN1 based on the CS signal, the pre-turn-off reference voltage Vref_pre, and the PWM signal (switch MN1 controls the supply and shutdown of the drive current Ibase for the BJT power transistor); and use the inverted signal of the PWM signal to control the turn-on and turn-off of switch MN2 (switch MN2 controls whether the base of the BJT power transistor is pulled low to ground). Here, switch MN1 is in the ON state when the pre-shutdown enable signal Base_off_pre is high and in the OFF state when the pre-shutdown enable signal Base_off_pre is low; switch MN2 is in the OFF state when the PWM signal is high and in the ON state when the PWM signal is low; when switch MN1 is ON and switch MN2 is OFF (i.e., providing the drive current Ibase for the BJT power transistor and not pulling the base of the BJT power transistor low to ground), the BJT power transistor is ON; when switch MN1 is OFF and switch MN2 is ON (i.e., turning off the drive current Ibase for the BJT power transistor and pulling the base of the BJT power transistor low to ground), the BJT power transistor is OFF.

[0020] The setting of the pre-off reference voltage Vref_pre needs to consider the system efficiency on one hand and the system stability on the other hand. Traditionally, the pre-off reference voltage Vref_pre is set as a fixed voltage. In the case that it is set relatively low, the base drive module 106 will prematurely turn off the drive current for the BJT power tube, causing the CS signal to fail to reach the off reference voltage Vref_off when the excess carriers in the BJT power tube are exhausted, so that the BJT power tube cannot be normally turned off, and finally the constant current / constant voltage control accuracy is affected.

[0021] Figure 2 The waveforms of the related signals in the power management system are shown. Figure 1 The working process of the power management system 100 is described below in combination with Figure 1 and Figure 2 .

[0022] In combination with Figure 1 and Figure 2 , it can be seen that in the case that the power management system 100 is in a normal working state: when the PWM signal changes from low to high, the pre-off enable signal Base_off_pre changes from low to high, the switch tube MN1 changes from the off state to the on state, the switch tube MN2 changes from the on state to the off state, the drive current Ibase for the BJT power tube is provided, so that the BJT power tube changes from the off state to the on state; during the period that the PWM signal is at high, when the CS signal is greater than the pre-off reference voltage Vref_pre, the pre-off enable signal Base_off_pre changes from high to low, the switch tube MN1 changes from the on state to the off state, the switch tube MN2 remains in the off state, the drive current Ibase for the BJT power tube is turned off, so that the base of the BJT power tube is in a floating state, and the BJT power tube remains in the on state by using the excess carriers; when the CS signal is greater than the off reference voltage Vref_off, the PWM signal changes from high to low, the pre-off enable signal Base_off_pre changes from low to high, the switch tube MN1 changes from the off state to the on state, the switch tube MN2 changes from the off state to the on state, the base of the BJT power tube is pulled down to the ground, so that the BJT power tube changes from the on state to the off state.

[0023] From Figure 1 and Figure 2It can be seen that when the power management system 100 is in an abnormal operating state: when the PWM signal changes from low to high, the pre-shutdown enable signal Base_off_pre remains high, switch MN1 remains in the on state, and switch MN2 changes from the on state to the off state, providing the drive current Ibase for the BJT power transistor, causing the BJT power transistor to change from the off state to the on state; during the period when the PWM signal is high, when the CS signal is greater than the pre-shutdown reference voltage Vref_pre, the pre-shutdown enable signal Base_off_pre changes from high to low, switch MN1 changes from the on state to the off state, and the switch... MN2 remains off, shutting off the drive current Ibase for the BJT power transistor, leaving the base of the BJT power transistor floating. The BJT power transistor uses excess carriers to remain on. While the pre-turn-off enable signal Base_off_pre is low, the CS signal cannot reach the turn-off reference voltage Vref_off even when the excess carriers in the BJT power transistor are depleted. The turn-off control signal Base_off remains low, preventing the PWM signal from changing from high to low. Consequently, the BJT power transistor cannot change from on to off, which degrades the constant current / constant voltage control accuracy of the power management system 100.

[0024] In view of the above, the base drive module 106 needs to be improved to automatically adjust the pre-shutdown reference voltage Vref_pre when the BJT power transistor cannot support the CS signal to reach the turn-off reference voltage Vref_off using the excess carriers in it. This will enable the BJT transistor to reliably and quickly change from the on state to the off state, ultimately resulting in higher system efficiency and better constant current / constant voltage control accuracy.

[0025] Figure 3 An example of its use according to an embodiment of the invention is shown. Figure 1 This is a schematic diagram of the base drive module in the power management system. Figure 3 As shown, the base drive module 300 according to an embodiment of the present invention is compared to Figure 1 The base drive module 106 shown adds a turn-off control signal detection unit 302 and a pre-turn-off reference voltage adjustment unit 304, which are used to adjust the pre-turn-off reference voltage Vref_pre based on the turn-off control signal Base_off and the pre-turn-off enable signal Base_off_pre. It should be noted that the composition and operation of other parts in the base drive module 300 are the same as those in the base drive module 106, and will not be described again here.

[0026] like Figure 3As shown, in some embodiments, the shutdown control signal detection unit 302 is configured to generate a pre-shutdown control signal indicating whether the CS signal can reach the shutdown reference voltage Vref_off based on the shutdown control signal Base_off and the pre-shutdown enable signal Base_off_pre; the pre-shutdown reference voltage adjustment unit 304 is configured to adjust the pre-shutdown reference voltage Vref_pre based on the pre-shutdown control signal, thereby ensuring that the CS signal can reach the shutdown reference voltage Vref_off. Here, the pre-shutdown control signal is at a low level when the CS signal can reach the shutdown reference voltage Vref_off, and at a high level when the CS signal cannot reach the shutdown reference voltage Vref_off; the pre-shutdown reference voltage adjustment unit 304 adjusts the pre-shutdown reference voltage Vref_pre when the pre-shutdown control signal is at a high level, and keeps the pre-shutdown reference voltage Vref_pre unchanged when the pre-shutdown control signal is at a low level.

[0027] In some embodiments, the shutdown control signal detection unit 302 is further configured to: determine whether the duration of the pre-shutdown enable signal Base_off_pre being at a low level reaches a fixed duration Tpre_max; and determine whether a high-level pulse appears in the shutdown control signal Base_off within the fixed duration Tpre_max, wherein, if no high-level pulse appears in the shutdown control signal Base_off within the fixed duration Tpre_max, the pre-shutdown control signal indicates that the CS signal cannot reach the shutdown reference voltage Vref_off (i.e., the pre-shutdown control signal has a high-level pulse), and if a high-level pulse appears in the shutdown control signal Base_off within the fixed duration Tpre_max, the pre-shutdown control signal indicates that the CS signal can reach the shutdown reference voltage Vref_off (i.e., the pre-shutdown control signal is at a low level).

[0028] Figure 4 It shows the use of Figure 3 The waveforms of several related signals in the power management system of the base driver module are shown below. (Followed by...) Figure 1 , Figure 3 ,and Figure 4 The working process of the power management system 100 after the base driver module 300 is used to replace the base driver module 106 will be explained.

[0029] Combination Figure 1 , Figure 3 ,and Figure 4It can be seen that during the period when the PWM signal is abnormal and at a high level: when the CS signal is not greater than the pre-shutdown reference voltage Vref_pre1, the drive current Ibase for the BJT power transistor is provided; when the CS signal is greater than the pre-shutdown reference voltage Vref_pre1, the drive current Ibase for the BJT power transistor is turned off. At this time, the excess carriers in the BJT power transistor are insufficient to support the CS signal to reach the shutdown reference voltage Vref_off. Since the shutdown control signal detection unit 302 does not detect the high-level pulse of the shutdown control signal Base_off within a fixed duration Tpre_max, it outputs a high-level pulse in the pre-shutdown control signal (in order to avoid false detection, the high-level pulse of the shutdown control signal Base_off is only output in the pre-shutdown control signal when it does not detect the high-level pulse of the shutdown control signal Base_off for several consecutive times (e.g., three times)). When the pre-shutdown reference voltage adjustment unit 304 receives the high-level pulse of the pre-shutdown control signal, it increases the pre-shutdown reference voltage Vref_pre from Vref_pre1 to Vref_pre2. Similarly, in the next cycle of the PWM signal, when the shutdown control signal detection unit 302 detects that the CS signal still cannot reach the shutdown reference voltage Vref_off, it outputs a high-level pulse in the pre-shutdown control signal; when the pre-shutdown reference voltage adjustment unit 304 receives the high-level pulse of the pre-shutdown control signal, it increases the pre-shutdown reference voltage Vref_pre from Vref_pre2 to Vref_pre3. This continues, increasing the pre-shutdown reference voltage Vref_pre until the excess carriers in the BJT power transistor are sufficient to support the CS signal reaching the shutdown reference voltage Vref_off.

[0030] Figure 5 It shows Figure 3 The diagram shows an example implementation of the shutdown control signal detection unit. Figure 5 As shown, the shutdown control signal detection unit 302 includes an anomaly detection circuit 3022 and an anomaly timing circuit 3024. The anomaly detection circuit 3022 is configured to generate an anomaly detection signal based on the pre-shutdown enable signal Base_off_pre and the shutdown substitution signal Base_off', indicating whether a high-level pulse appears in the shutdown control signal Base_off within a fixed duration Tpre_max when the pre-shutdown enable signal Base_off_pre is at a low level. The anomaly timing circuit 3024 is configured to generate a pre-shutdown control signal based on the anomaly detection signal and the shutdown control signal Base_off, wherein the shutdown substitution signal Base_off' is generated based on the anomaly detection signal and the shutdown control signal Base_off (e.g., the shutdown substitution signal Base_off' is obtained by performing a logical OR operation on the anomaly detection signal and the shutdown control signal Base_off).

[0031] That is, in Figure 5 In the example implementation shown, the abnormality detection circuit 3022 is configured to detect whether the CS signal can reach the off reference voltage Vref off. Specifically, when the CS signal reaches the pre-off reference voltage Vref pre, the abnormality detection circuit 3022 starts timing the duration that the pre-off enable signal Base off pre is at a low level, and outputs a high level pulse in the abnormality detection signal when the timing time exceeds the fixed time length Tpre max, indicating that the CS signal cannot reach the off reference voltage Vref off (i.e., the power management system 100 cannot trigger the off control for the BJT power tube). If the abnormality detection circuit 3022 receives a high level pulse of the off control signal Base off within the fixed time length Tpre max, it outputs a low level abnormality detection signal, indicating that the CS signal can reach the off reference voltage Vref off (i.e., the power management system 100 can trigger the off control for the BJT power tube). The abnormality timing circuit 3024 counts the abnormality phenomenon that the off control for the BJT power tube cannot be triggered. In order to prevent false judgment, the abnormality timing circuit 3024 only outputs a high level in the pre-off control signal when the off control for the BJT power tube cannot be triggered for three consecutive times. When the off control for the BJT power tube is triggered, the abnormality timing circuit 3024 can clear the abnormality count using the off control signal Base off.

[0032] As Figure 5 shown, in some embodiments, the off control signal detection unit 302 can be further configured to control the charging of the capacitor C by the current source Iramp based on the pre-off enable signal Base off pre and the off substitute signal Base off’ (e.g., based on the logical or result of the two); and generate the abnormality detection signal based on the comparison relationship between the voltage on the capacitor C and the predetermined voltage Va. The pre-off reference voltage adjustment unit 304 can be further configured to count the number of high level pulses of the abnormality detection signal, generate the pre-off control signal when the number of high level pulses of the abnormality detection signal reaches a predetermined number, and clear the number of high level pulses of the abnormality detection signal based on the off control signal Base off.

[0033] Figure 6 The power management system employing the abnormality detection circuit shown in Figure 5 is shown. The waveforms of multiple related signals in the power management system when the off control for the BJT power tube cannot be triggered are shown. In combination with Figure 5 and Figure 6As can be seen, when the PWM signal is high, the BJT power tube is in the on state, and the CS signal linearly increases; when the CS signal is greater than the pre-shutoff reference voltage Vref_pre, the pre-shutoff enable signal Base off pre changes from high to low, the current source Iramp starts to charge the capacitor C, and the voltage Vramp on the capacitor C linearly increases; when the voltage Vramp on the capacitor C is greater than the predetermined voltage Va, the shutoff control signal Base off is still at a low level, the comparator outputs an abnormal detection signal at a high level, and at the same time, the shutoff replacement signal Base off' changes from low to high. The switch control module 104 changes the PWM signal from high to low by using the shutoff replacement signal Base off' (that is, the switch control module 104 is further configured to generate the PWM signal based on the shutoff replacement signal Base off' and the on control signal Base on), so that the BJT power tube changes from the on state to the off state, thereby preventing the power management system 100 from being in an abnormal state for a long time.

[0034] Figure 7 An example implementation of the abnormal timing circuit is shown in Figure 5 The waveforms of a plurality of related signals in the power management system shown in FIG. 13 when the shutoff control for the BJT power tube cannot be triggered are shown in FIG. 14. The abnormal timing circuit shown in FIG. 13 is used in the power management system shown in FIG. 14. Figure 5 and Figure 7 As can be seen, when the PWM signal is high, the failure to trigger the shutoff control for the BJT power tube causes the abnormal detection signal to have a high-level pulse, and the signal A output by the D flip-flop D1 changes to high; during the time when the PWM signal is high in the next cycle, the shutoff control for the BJT power tube still cannot be triggered, the abnormal detection signal again has a high-level pulse, and the signal A output by the D flip-flop D1 changes to low; during the time when the PWM signal is high in the next cycle, the shutoff control for the BJT power tube still cannot be triggered, the abnormal detection signal again has a high-level pulse, and the signal A output by the D flip-flop D1 changes to high again, the signal B output by the D flip-flop D2 changes to high, and the pre-shutoff control signal has a high-level pulse, that is, the shutoff control for the BJT power tube cannot be triggered in three consecutive cycles.

[0035] Figure 8 An example implementation of the pre-shutoff reference voltage adjustment unit shown in Figure 4 An example implementation of the pre-shutoff reference voltage adjustment unit shown in FIG. 13 is shown in FIG. 15. As can be seen from FIG. 15, the pre-shutoff reference voltage adjustment unit includes a voltage divider circuit 1501, a comparator 1502, a D flip-flop D3, a D flip-flop D4, and a D flip-flop D5. Figure 8As shown, the pre-shutoff reference voltage adjustment unit 304 comprises a counter and a reference selection module, wherein: the counter receives the pre-shutoff control signal and outputs a control signal C according to the number of high-level pulses of the pre-shutoff control signal, the control signal C being used to control the reference selection module to select the corresponding pre-shutoff reference voltage Vref_pre. That is, the counter is configured to count the number of high-level pulses of the pre-shutoff control signal; the reference selection module is configured to adjust the pre-shutoff reference voltage Vref_pre based on the number of high-level pulses of the pre-shutoff control signal.

[0036] Figure 9 As shown Figure 8 The waveform diagram of the pre-shutoff reference voltage adjustment unit is shown. As shown Figure 9 As shown, when the pre-shutoff control signal appears a high-level pulse for the first time, C<0> becomes high level, C<1> is low level, and the pre-shutoff reference voltage Vref_pre is adjusted from Vref_pre1 to Vref_pre2. If the shutoff control for the BJT power tube cannot be triggered, when the pre-shutoff control signal appears a high-level pulse for the second time, C<0> becomes low level, C<1> is high level, and the pre-shutoff reference voltage Vref_pre is adjusted from Vref_pre2 to Vref_pre3. If the shutoff control for the BJT power tube still cannot be triggered, when the pre-shutoff control signal appears a high-level pulse for the third time, B<0> becomes high level, B<1> becomes high level, and the pre-shutoff reference voltage Vref_pre is adjusted from Vref_pre3 to Vref_pre4. Vref_pre4 is close enough to the shutoff reference voltage Vref_off, and it is ensured that when the pre-shutoff reference voltage Vref_pre is Vref_pre4, the shutoff control for the BJT power tube can be normally triggered. That is, as the number of high-level pulses of the pre-shutoff control signal increases, the pre-shutoff reference voltage Vref_pre is gradually increased.

[0037] Figure 10 As shown Figure 10 As shown, in the case where the power management system 100 adopts the base drive module 300 instead of the base drive module 106: after the power management system 100 is powered on, the BJT power tube is driven; when the power management system 100 detects that the shutoff control for the BJT power tube cannot be triggered after the BJT power tube is pre-shutoff, the pre-shutoff reference voltage Vref_pre is automatically adjusted so that the shutoff control for the BJT power tube can be normally triggered after the BJT power tube is pre-shutoff.

[0038] The application can take other specific forms without departing from the spirit or essential characteristics thereof. For example, the algorithms described in the specific embodiments can be modified without departing from the essential spirit of the application. Accordingly, the current embodiments are to be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. A power management system, comprising: a voltage sampling module configured to sample a current representative voltage representative of a current flowing through a BJT power tube to generate a current sense signal; a switch control module configured to generate an off control signal based on the current sense signal and an off reference voltage, to generate an on control signal based on an output representative signal representative of an output current or an output voltage of the power management system, and to generate a pulse width modulation signal based on the on control signal and the off control signal; and a base drive module including a first switch transistor for controlling provision and shutoff of a drive current for the BJT power tube and a second switch transistor for controlling whether a base of the BJT power tube is pulled low to ground, and configured to: generate a pre-off enable signal for controlling on and off of the first switch transistor based on a pre-off reference voltage, the current sense signal, and the pulse width modulation signal, control on and off of the second switch transistor with an inverted signal of the pulse width modulation signal, and generate a pre-off control signal indicating whether the current sense signal is able to reach the off reference voltage based on the off control signal and the pre-off enable signal, wherein generating the pre-off control signal includes determining whether a duration that the pre-off enable signal is at a low level reaches a predetermined time length and determining whether a high level pulse of the off control signal occurs within the predetermined time length, wherein the pre-off control signal indicates that the current sense signal is unable to reach the off reference voltage in a case that the high level pulse of the off control signal does not occur within the predetermined time length, and the pre-off control signal indicates that the current sense signal is able to reach the off reference voltage in a case that the high level pulse of the off control signal occurs within the predetermined time length, and adjust the pre-off reference voltage based on the pre-off control signal. the first switch transistor is in an on state when the pre-off enable signal is at a high level and in an off state when the pre-off enable signal is at a low level, and the second switch transistor is in an off state when the pulse width modulation signal is at a high level and in an on state when the pulse width modulation signal is at a low level.

2. The power management system of claim 1, wherein, the base drive module is configured to:

3. The power management system of claim 1, wherein, generate an abnormality detection signal for indicating whether a high level pulse of the off control signal occurs within a predetermined time length that the pre-off enable signal is at a low level based on the pre-off enable signal and an off substitute signal, and generate the pre-off control signal based on the abnormality detection signal and the off control signal, wherein the off substitute signal is generated based on the abnormality detection signal and the off control signal. the base drive module is configured to: control charging of a predetermined capacitor by a predetermined current source based on the pre-off enable signal and the off substitute signal, and 4. The power management system of claim 3, wherein, generate the abnormality detection signal based on a comparison relationship between a voltage on the predetermined capacitor and a predetermined voltage.

2. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

3. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

4. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

5. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

6. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

7. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

8. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

9. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

10. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

11. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

12. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

13. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

14. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

15. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

16. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

17. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

18. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

19. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

20. The power management system of claim 1, wherein the base drive module is configured to: generate the pre-off enable signal based on a comparison relationship between a voltage on a predetermined capacitor and a predetermined voltage.

5. The power management system of claim 3, wherein, The switch control module is configured to generate the pulse width modulation signal based on the turn-off replacement signal and the turn-on control signal.

6. The power management system of claim 3, wherein, The base drive module is configured to: count a number of high level pulses of the abnormality detection signal; generate the pre-turn-off control signal when the number of high level pulses of the abnormality detection signal reaches a predetermined number; and clear the number of high level pulses of the abnormality detection signal based on the turn-off control signal.

7. The power management system of claim 1, wherein, The base drive module is configured to: count a number of high level pulses of the pre-turn-off control signal; and adjust the pre-turn-off reference voltage based on the number of high level pulses of the pre-turn-off control signal.

8. The power management system of claim 7, wherein, The base drive module is configured to: gradually increase the pre-turn-off reference voltage as the number of high level pulses of the pre-turn-off control signal increases.

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