Soft driving method, soft driving circuit and switching power supply using soft driving circuit

Abstract

According to the soft driving method, the soft driving circuit and the switching power supply applying the soft driving circuit, when the driving voltage of the first switching tube in the switching module changes from the second voltage threshold to the first voltage threshold, the first current is generated based on the change of the first end voltage of the switching module; a difference value between the first reference current and the first current is used as an input of a current input operational amplifier, and an output end of the current input operational amplifier is connected with a grid electrode of a first switch tube; the change rate of the first end voltage of the switch module is stabilized at a certain value in the time period when the driving voltage is the first voltage threshold. Through the arrangement, the change rate of the first terminal voltage of the switch module can be limited to be stabilized at a certain value in the turn-on or turn-off process of the first switch tube, the system application problem caused by the too high change rate is avoided, and the requirements for other devices are also reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of switch tube driving, and in particular to a soft driving method, a circuit, and a switching power supply applying the same. Background Art

[0002] In the fields such as switching power supplies, energy conversion is carried out by controlling the conduction or cut-off of a switch tube. However, in the hard driving mode of the switch tube by a PWM square wave, usually, during the conduction or cut-off process of the switch tube, the change rate of its drain voltage is relatively fast, and such a fast change rate is not conducive to the application of the system or poses higher requirements on other devices. For example, in a flyback converter, when the voltage at the end where the primary-side switch tube is connected to the transformer changes rapidly, problems such as EMI (electromagnetic interference) and stress on the secondary-side rectifier diode will occur in the system. Therefore, it is necessary to propose a new driving scheme to solve the problems existing in the prior art. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a soft driving method, a circuit, and a switching power supply applying the same.

[0004] The present disclosure provides a soft driving method for driving a first switch tube in a switch module, where the switch module is applied to a switching power supply. The soft driving method is characterized in that it includes: When the driving voltage of the first switch tube changes from a second voltage threshold to a first voltage threshold, a first current is generated based on the change of the voltage at the first end of the switch module, and the difference between the first reference current and the first current is used as the input to an operational amplifier. The output end of the operational amplifier with the current input is connected to the gate of the first switch tube. Based on the adjustment effects of the operational amplifier with the current input and the first switch tube, the change rate of the voltage at the first end of the switch module is stabilized at a certain value during the time period when the driving voltage is the first voltage threshold; the first end is the end where the change rate needs to be controlled. Wherein, the driving voltage of the first switch tube is the absolute value of the voltage difference between its gate and source; the second voltage threshold corresponds to the driving voltage when the first switch tube is in the cut-off state or the fully-conducted state; the first voltage threshold is set close to the Miller plateau voltage.

[0005] Optionally, when the second voltage threshold corresponds to the driving voltage when the first switch tube is in the cut-off state, when the driving voltage of the first switch tube rises from the second voltage threshold to the first voltage threshold, When the first switching transistor is an N-type switching transistor, the first reference current is a pull-up current. Based on the adjustment of the current input operational amplifier and the first switching transistor, the falling rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold. When the first switching transistor is a P-type switching transistor, the first reference current is a pull-down current. Based on the adjustment of the current input operational amplifier and the first switching transistor, the rising rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold.

[0006] Optionally, when the second voltage threshold corresponds to the driving voltage in the fully-conducted state of the first switching transistor, when the driving voltage of the first switching transistor drops from the second voltage threshold to the first voltage threshold, When the first switching transistor is an N-type switching transistor, the first reference current is a pull-down current. Based on the adjustment of the current input operational amplifier and the first switching transistor, the rising rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold. When the first switching transistor is a P-type switching transistor, the first reference current is a pull-up current. Based on the adjustment of the current input operational amplifier and the first switching transistor, the falling rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold.

[0007] Optionally, when the second voltage threshold corresponds to the driving voltage in the off state of the first switching transistor, as the first switching transistor is turned on, when the voltage change rate at the first end of the switching module is lower than a preset threshold, the driving voltage of the first switching transistor is controlled to rise from the first voltage threshold to the driving voltage when the first switching transistor is fully-conducted.

[0008] Optionally, when the second voltage threshold corresponds to the driving voltage in the fully-conducted state of the first switching transistor, as the first switching transistor is turned off, after the voltage change rate at the first end of the switching module is lower than a preset threshold, the driving voltage of the first switching transistor is controlled to drop from the first voltage threshold to the driving voltage when the first switching transistor is in the off state.

[0009] This article also provides a soft drive circuit for driving the first switching transistor in a switching module. The switching module is applied to a switching power supply, and is characterized in that the soft drive circuit includes A first capacitor, arranged on the branch between the first end of the switching module and the first node; A first reference current source, which is a pull-up or pull-down current source acting on the first node; A current input operational amplifier is arranged on the branch where the gate of the first switching transistor and the first node are located; when the driving voltage of the first switching transistor changes from a second voltage threshold to a first voltage threshold, a first current is generated on a first capacitor based on the change in the voltage at the first end of the switching module, the difference signal between the first reference current and the first current is connected to the input end of the current input operational amplifier, and the output end of the current input operational amplifier is connected to the gate of the first switching transistor; based on the adjustment effect of the current input operational amplifier and the first switching transistor, the change rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold. Wherein, the driving voltage of the first switching transistor is the absolute value of the voltage difference between its gate and source; the second voltage threshold corresponds to the driving voltage when the first switching transistor is in the off state or the fully conducting state; the first voltage threshold is set close to the Miller plateau voltage.

[0010] Optionally, when the second voltage threshold corresponds to the driving voltage when the first switching transistor is in the off state, when the driving voltage of the first switching transistor rises from the second voltage threshold to the first voltage threshold, When the first switching transistor is an N-type switching transistor, the first reference current is a pull-up current, and based on the adjustment effect of the current input operational amplifier and the first switching transistor, the falling rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold. When the first switching transistor is a P-type switching transistor, the first reference current is a pull-down current, and based on the adjustment effect of the current input operational amplifier and the first switching transistor, the rising rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold.

[0011] Optionally, when the second voltage threshold corresponds to the driving voltage when the first switching transistor is in the fully conducting state, when the driving voltage of the first switching transistor drops from the second voltage threshold to the first voltage threshold, When the first switching transistor is an N-type switching transistor, the first reference current is a pull-down current, and based on the adjustment effect of the current input operational amplifier and the first switching transistor, the rising rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold. When the first switching transistor is a P-type switching transistor, the first reference current is a pull-up current, and based on the adjustment effect of the current input operational amplifier and the first switching transistor, the falling rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold.

[0012] Optionally, the soft drive circuit includes a detection circuit. When the driving voltage corresponding to the off state of the first switching tube is the second voltage threshold, as the first switching tube is turned on, when the detection circuit detects that the change rate of the voltage at the first end of the switching module is lower than a preset threshold, the driving voltage of the first switching tube is controlled to rise from the first voltage threshold to the driving voltage when the first switching tube is fully turned on; or, When the driving voltage corresponding to the fully on state of the first switching tube is the second voltage threshold, as the first switching tube is turned off, when the detection circuit detects that the change rate of the voltage at the first end of the switching module is lower than the preset threshold, the driving voltage of the first switching tube is controlled to drop from the first voltage threshold to the driving voltage when the first switching tube is in the off state.

[0013] This article also provides a switching power supply for converting an input voltage into an output voltage to supply power to a load, characterized in that the switching power supply includes the soft drive circuit described above or controls the first switching tube in the switching module based on the soft drive method described above.

[0014] The beneficial effects of the present invention at least include: For the soft drive method, circuit and the switching power supply applying the same provided in this article, when the driving voltage of the first switching tube in the switching module changes from the second voltage threshold to the first voltage threshold, a first current is generated based on the change of the voltage at the first end of the switching module, and the difference between the first reference current and the first current is used as the input of the current input operational amplifier. The output end of the current input operational amplifier is connected to the gate of the first switching tube. Based on the adjustment effects of the current input operational amplifier and the first switching tube, the change rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold; wherein, the driving voltage of the first switching tube is the absolute value of the voltage difference between the gate and the source; the second voltage threshold corresponds to the driving voltage when the first switching tube is in the off state or the fully on state; the first voltage threshold is set close to the Miller platform voltage, and it can be greater than or equal to the absolute value of the on voltage threshold of the first switching tube. Through the above settings, the present invention can limit the change rate of the voltage at the first end of the switching module to be stabilized at a certain value during the on or off process of the first switching tube, avoiding problems in system applications caused by too fast change rate, and also reducing the requirements for other devices.

[0015] It should be noted that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present invention. Description of the Drawings

[0016] Figure 1Shows the schematic diagram of the soft drive circuit provided herein; Figure 2 Shows an embodiment of the soft drive circuit during the conduction process of the N-type switching transistor provided herein; Figure 3 Shows an embodiment of the drive voltage and drive current during the conduction process of the N-type switching transistor provided herein; Figure 4 Shows an embodiment of the soft drive circuit during the turn-off process of the provided N-type switching transistor; Figure 5 Shows an embodiment of the drive voltage and drive current during the turn-off process of the N-type switching transistor provided herein; Figure 6 Shows an embodiment of the soft drive circuit during the conduction and turn-off processes of the provided N-type switching transistor. Detailed implementation mode

[0017] 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 given 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, the purpose of providing these embodiments is to make the understanding of the disclosed content of the present invention more thorough and comprehensive.

[0018] The present invention provides a soft drive method for driving a first switching transistor in a switching module, which is applied to a switching power supply. The method includes: when the drive voltage of the first switching transistor changes from a second voltage threshold to a first voltage threshold, generating a first current based on the change of the voltage at the first end of the switching module, taking the difference between the first reference current and the first current as the input to an operational amplifier, connecting the output end of the operational amplifier with the input current to the gate of the first switching transistor, and based on the adjustment of the operational amplifier with the input current and the first switching transistor, realizing that the change rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the drive voltage is the first voltage threshold; wherein, the drive voltage of the first switching transistor is the absolute value of the voltage difference between its gate and source; the second voltage threshold corresponds to the drive voltage when the first switching transistor is in the off state or the fully conducting state; the first voltage threshold is set close to the Miller plateau voltage, and it can be greater than or equal to the absolute value of the conduction voltage threshold of the switching transistor. It should be noted that being set close to the Miller plateau voltage can be understood as a value slightly less than, equal to, or slightly greater than the Miller plateau voltage. Among them, the first end is the end whose change rate needs to be controlled; for example, in the application of a flyback converter, the primary side of the transformer is connected to the ground through a switching module (a resistor can also be set between the switching module and the ground), and usually, it is necessary to limit the change rate of the end of the switching module connected to the primary side of the transformer. Therefore, the end of the switching module connected to the transformer can be regarded as the first end. Among them, the switching module described in this article includes a first switching transistor, and may or may not include other devices.

[0019] Through the above settings, the present invention can realize that during the conduction or turn-off process of the first switching transistor, the change rate of the voltage at the first end of the switching module is limited to be stabilized at a certain value, avoiding problems in system applications caused by its too fast change rate, and also reducing the requirements for other devices.

[0020] Switching transistors are usually divided into N-type switching transistors and P-type switching transistors. The following further explains. Specifically, when the second voltage threshold corresponds to the drive voltage when the first switching transistor is in the off state, when the drive voltage of the first switching transistor rises from the second voltage threshold to the first voltage threshold, when the first switching transistor is an N-type switching transistor, the first reference current is a pull-up current, and based on the adjustment of the operational amplifier with the input current and the first switching transistor, the falling rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the drive voltage is the first voltage threshold; when the first switching transistor is a P-type switching transistor, the first reference current is a pull-down current, and based on the adjustment of the operational amplifier with the input current and the first switching transistor, the rising rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the drive voltage is the first voltage threshold.

[0021] When the driving voltage corresponds to the fully - on state of the first switching transistor, when the driving voltage of the first switching transistor drops from the second voltage threshold to the first voltage threshold, and when the first switching transistor is an N - type switching transistor, the first reference current is a pull - down current. Based on the adjustment of the current - input operational amplifier and the first switching transistor, the rising rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold; when the first switching transistor is a P - type switching transistor, the first reference current is a pull - up current. Based on the adjustment of the current - input operational amplifier and the first switching transistor, the falling rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold.

[0022] Further, when the second voltage threshold corresponds to the driving voltage in the off - state of the first switching transistor, as the switching transistor is turned on, when the change rate of the voltage at the first end of the switching module is lower than the preset threshold, the driving voltage of the first switching transistor is controlled to rise from the first voltage threshold to the driving voltage when the switching transistor is fully on.

[0023] Further, when the second voltage threshold corresponds to the driving voltage in the fully - on state of the first switching transistor, as the first switching transistor is turned off, after the change rate of the voltage at the first end of the switching module is lower than the preset threshold, the driving voltage of the first switching transistor is controlled to drop from the first voltage threshold to the driving voltage when the first switching transistor is in the off - state.

[0024] This article also provides a soft - drive circuit for driving the first switching transistor in the switching module, as Figure 1As shown, the soft drive circuit includes a first capacitor C1, a first reference current source I1, a current input operational amplifier IAv, and a switch module. The switch module includes a first switch transistor, which may only include the first switch transistor or may include other devices in addition to the first switch transistor (for example, other switch transistors may be connected in series on the first switch transistor, and this switch transistor may be always on); the first capacitor C1 is disposed on the branch between the first end of the switch module (the end shown as VD in the figure) and the first node N1; the first reference current source I1 is a pull-up or pull-down current source acting on the first node N1; the current input operational amplifier is disposed on the branch between the gate of the first switch transistor and the first node N1; when the drive voltage of the first switch transistor changes from the second voltage threshold V2 to the first voltage threshold V1, a first current IC1 is generated on the first capacitor C1 based on the change in the voltage VD at the first end of the switch module. The difference signal Iin between the first reference current source I1 and the first current IC1 is connected to the input terminal of the current input operational amplifier IAv, and the output terminal of the current input operational amplifier IAv is connected to the gate of the first switch transistor (VG in the figure represents the gate of the first switch transistor); based on the adjustment of the current input operational amplifier IAv and the first switch transistor M0, the change rate of the voltage VD at the first end of the switch module is stabilized at a certain value during the period when the drive voltage is the first voltage threshold V1; wherein, the drive voltage of the first switch transistor is the absolute value of the voltage difference between its gate and source; the second voltage threshold V2 corresponds to the drive voltage when the first switch transistor is in the off state or the fully on state; the first voltage threshold V1 corresponds to the Miller plateau voltage setting, which may be greater than or equal to the absolute value of the on-voltage threshold VGSth of the switch transistor M0, and can be specifically set according to actual applications.

[0025] The following takes the case where the switch module only includes the first switch transistor and the first switch transistor is an N-type switch transistor and its conduction process as an example for illustration. At this time, the drain voltage of the first switch transistor M0 can be regarded as the voltage at the first end of the switch module described above; as Figure 2 shown, in this figure, the source of the first switch transistor M0 is grounded. Therefore, its drive voltage can be represented by VG. In other embodiments, the source of M0 can also be connected to ground through other components. For example, the source of M0 is connected to ground through a resistive element. In Figure 2 , the first reference current source I1 is a pull-up current source connected to the first node N1, Figure 3 corresponding to Figure 2An embodiment of the drive voltage VG and its gate charging current IG during the turn-on process T1 of the first switching transistor M0 in []. Before time t0, the first switching transistor M0 is in the off state, and its drive voltage VG is the second threshold voltage V2 (low-level threshold). During the time period from t0 to t1, the drive voltage VG of M0 rises from the second voltage threshold V2 to the first voltage threshold V1. Here, the first voltage threshold V1 is greater than or equal to the on-voltage threshold VGSth of the first switching transistor M0, and its specific value can be set according to actual applications. For example, when the first switching transistor M0 is in the application scenario of a flyback converter in DCM, the first voltage threshold V1 can be set to the on-voltage threshold VGSth of M0; when the first switching transistor M0 is in the application scenario of a flyback converter in CCM, the first voltage threshold V1 can be set to be greater than the on-voltage threshold VGSth of M0, and its specific value can be set according to the magnitude of the Miller plateau voltage in the system at this time. During this time period, the drive current IG acts on the gate of M0 to realize the rise of the drive voltage VG from the second voltage threshold V2 in the off state to the first voltage threshold V1. After time t1, the drain voltage VD of the first switching transistor M0 will decrease, as shown in Figure 2 shown, generating on the first capacitor C1 as shown in Figure 2A first current IC1 in the direction shown, where IC1 = C1 × dVD / dt. At this time, the current Iin input to the current-input operational amplifier IAv is Iin = I1 - IC1. The input current Iin passes through the action of the current-input operational amplifier IAv to generate an output current Iout that acts on the gate of M0. During the time period from t1 to t2, when the falling rate of the drain voltage VD of M0 is relatively fast, the value of the input current Iin will decrease, and the corresponding output current Iout will also decrease. Acting on the gate of M0, it will cause the falling rate of VD to decrease; when the falling rate of the drain voltage VD of M0 is relatively slow, the value of the input current Iin will increase, and the corresponding output current Iout will also increase. Acting on the gate of M0, it will cause the falling rate of VD to increase. Therefore, through the feedback regulation of the current-input operational amplifier IAv and M0, it can finally make the input current Iin = 0, that is, IC1 = I1. Furthermore, dVD / dt can be calculated to be equal to I1 / C1, which means that the falling rate of the drain voltage VD of M0 is stabilized at a certain value, and the driving voltage VG also remains unchanged at V1. By reasonably setting the magnitudes of I1 and C1, the falling rate of VD can be prevented from being too fast, thereby avoiding the processing difficulty in system applications. For example, when it is used in a flyback switching converter, problems such as EMI and the stress of the secondary-side rectifier diode caused by the excessive change rate of VD can be avoided. During the time period from t1 to t2, considering the application of the Miller capacitance in the switching transistor, there is also a certain current IG at its gate. At time t2, as the first switching transistor M0 turns on, its drain voltage VD drops to a potential close to zero, and the falling rate of the drain voltage VD will slow down. After the detection circuit detects that the falling rate of VD is lower than the preset threshold, a corresponding driving current IG is set to act on the gate of the first switching transistor M0. During the time period from t2 to t3, it is used to increase the driving voltage VG to achieve the full conduction of the first switching transistor M0; during the time period from t3 to t4, the first switching transistor M0 remains in the fully conducting state.

[0026] Figure 4 Taking the example of the turn-off process of the switching module including only the first switching transistor, and the first switching transistor M0 being an N-type switching transistor. Similarly, at this time, the drain voltage of the first switching transistor M0 can be regarded as the voltage at the first end of the switching module described above; different from Figure 2 the above, the first reference current source I1 is a pull-down current source connected to the first node N1. Figure 5 corresponding to Figure 4An embodiment of the driving voltage VG and its gate discharge current IG (or driving current) during the turn-off process T2 of the first switching transistor M0 in []. Before time t0, the first switching transistor M0 is in a fully conducting state, and the driving voltage VG is the second threshold voltage V2 (high-level threshold). During the time period from t0 to t1, the driving voltage VG of M0 drops from the second voltage threshold V2 to the first voltage threshold V1. The first voltage threshold V1 here is the same as that described above in the text and can be set corresponding to the Miller plateau voltage according to actual applications, and is a value close to the Miller plateau voltage. During the time period from t0 to t1, the driving current IG acts on the gate of M0 to achieve the reduction of the driving voltage VG from the second voltage threshold V2 in the conducting state to the first voltage threshold V1. After time t1, the drain voltage VD of the first switching transistor M0 will rise. As shown in Figure 4 shown, a first current IC1 in the direction shown in Figure 4 is generated on the first capacitor C1. Wherein, IC1 = C1 × dVD / dt. At this time, the current Iin acting on the current-input operational amplifier IAv is Iin = I1 - IC1 (its direction is the same as the direction of the first reference current I1). The input current Iin passes through the action of the current-input operational amplifier IAv to generate an output current Iout acting on the gate of M0. During the time period from t1 to t2, when the rising rate of the drain voltage VD of M0 is relatively fast, the value of the input current Iin will decrease, and the corresponding output current Iout will also decrease, acting on the gate of M0, which will reduce the rising rate of VD; when the rising rate of the drain voltage VD of M0 is relatively slow, the value of the input current Iin will increase, and the corresponding output current Iout will also increase, acting on the gate of M0, which will increase the rising rate of VD. Therefore, through the feedback regulation of the current-input operational amplifier IAv and M0, it can finally make the input current Iin = 0, that is, IC1 = I1, and then it can be calculated that dVD / dt is equal to I1 / C1, that is, the rising rate of the drain voltage VD of M0 is stabilized at a certain value, and the driving voltage VG also remains unchanged at V1. By reasonably setting the magnitudes of I1 and C1, the too-fast rising rate of VD can be avoided, and thus problems such as the processing difficulty in system applications can be avoided. Similarly, during the time period from t1 to t2, considering the application of the Miller capacitance in the switching transistor, there is still a certain current IG on its gate. At time t2, as the turn-off process of the first switching transistor M0 proceeds, its drain voltage VD will rise to the corresponding high potential, and the rising rate of the drain voltage VD will become slower. After the detection circuit detects that the rising rate of VD is lower than the preset threshold, a corresponding driving current IG is set to act on the gate of the first switching transistor M0. During the time period from t2 to t3, it is used to reduce the driving voltage VG to achieve the full turn-off of the first switching transistor M0; during the time period from t3 to t4, the first switching transistor M0 remains in the off state.

[0027] It should be noted that Figure 3 and Figure 5 the magnitude of the driving current IG in [reference] is only for illustration, and can be specifically set according to actual applications. In addition, the setting diagrams of the detection circuit and the corresponding circuit for generating the driving current IG are not shown in the figure, and the structures in the existing technologies can be adopted to implement them, and this article will not elaborate on them in detail. Figure 2 and Figure 4 the connection manner of the circuits in [reference] is also only the connection illustration during the time period t1 - t2. Corresponding switches can also be set, and the corresponding branches can also be disconnected by controlling the switches during other time periods; for example, a switch is set between the first reference current source I1 and the current input operational amplifier IAv. During the time period t1 - t2, the switch is closed, and during other time periods, this switch is disconnected, and the first switch tube M0 is driven by other driving currents IG; of course, the first reference current source I1 can also be used for driving during other time periods, and can be specifically set according to actual applications. Figure 3 and Figure 5 the three-stage driving voltage VG in [reference] is only one illustration in this article, and can also be set into other multi-stage driving according to actual applications. For example, a four-stage driving can also be set. For example, Figure 3 in [reference], after the time t2 and before the first switch tube M0 is fully turned on, after the driving voltage VG is raised to a certain threshold for a period of time by setting the driving current IG, the driving voltage VG is then raised to the voltage threshold when the first switch tube M0 is fully turned on by setting the driving current IG.

[0028] In the above, the switch tube is taken as an N-type switch tube as an example, and the principles for controlling the change rate of the drain voltage VD of the switch tube during its conduction process and turn-off process are respectively described. In specific applications, corresponding settings can be made only for the conduction process of the switch tube to control the change rate of the drain voltage VD, or corresponding settings can be made only for the turn-off process of the switch tube to control the change rate of the drain voltage VD, or two reference current sources can be set for both the conduction and turn-off processes of the switch tube at the same time, such as Figure 6 as shown, a pull-up reference current source I1 and a pull-down reference current source I1' are set. By switching different reference current sources (realizing the switching of different reference current sources by controlling the switches S1 and S1'), the change rate of the drain voltage VD of the switch tube during the conduction or turn-off process of the switch tube is controlled. Among them, for the conduction and turn-off processes of the switch tube, as Figure 6 shown in [reference], a common current input operational amplifier IAv can be used, or two current input operational amplifiers (not shown in the figure) can be correspondingly set.

[0029] The above description takes the switching transistor as an N-type switching transistor as an example. This article is equally applicable to P-type switching transistors. Regarding the absolute value of the voltage difference between the gate and the source of the P-type switching transistor as the driving voltage, the conduction process of the P-type switching transistor can correspond to the turn-off process of the N-type switching transistor, and the turn-off process of the P-type switching transistor can correspond to the conduction process of the N-type switching transistor. Only corresponding circuit transformations are required, and this article will not elaborate on this in detail. In addition, as described above, the switching module may also include other devices in addition to the first switching transistor.

[0030] This article also provides a switching power supply for converting an input voltage into an output voltage to supply power to a load. The switching power supply controls the first switching transistor in the switching module through the soft drive circuit or soft drive method described above.

[0031] In summary, for the soft drive method, circuit, and switching power supply applying the same provided in this article, when the driving voltage of the first switching transistor in the switching module changes from the second voltage threshold to the first voltage threshold, a first current is generated based on the change in the voltage at the first end of the switching module, and the difference between the first reference current and the first current is used as the input to the current input operational amplifier. The output terminal of the current input operational amplifier is connected to the gate of the first switching transistor. Based on the adjustment effects of the current input operational amplifier and the first switching transistor, the change rate of the voltage at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold; wherein, the driving voltage of the first switching transistor is the absolute value of the voltage difference between its gate and source; the second voltage threshold corresponds to the driving voltage when the first switching transistor is in the off state or the fully conducting state; the first voltage threshold is set close to the Miller plateau voltage, and it can be greater than or equal to the absolute value of the conduction voltage threshold of the first switching transistor. Through the above settings, the present invention can limit the change rate of the voltage at the first end of the switching module to be stabilized at a certain value during the conduction or turn-off process of the first switching transistor in the switching module, avoiding problems in system applications caused by its too fast change rate, and also reducing the requirements for other devices.

[0032] Finally, it should be noted that: Obviously, the above embodiments are only examples for clearly explaining the present invention, rather than limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A soft driving method for driving a first switching transistor in a switching module, where the switching module is applied in a switching power supply, characterized in that, The soft drive method includes: When the drive voltage of the first switching transistor changes from the second voltage threshold to the first voltage threshold, a first current is generated based on the change in the voltage at the first end of the switching module, and the difference between the first reference current and the first current is used as the input to an operational amplifier. The output terminal of the operational amplifier for the current input is connected to the gate of the first switching transistor. Based on the adjustment effect of the operational amplifier for the current input and the first switching transistor, the rate of change of the voltage at the first end of the switching module is stabilized at a certain value during the period when the drive voltage is the first voltage threshold; the first end is the end whose rate of change needs to be controlled. Wherein, the drive voltage of the first switching transistor is the absolute value of the voltage difference between its gate and source; the second voltage threshold corresponds to the drive voltage when the first switching transistor is in the off state or the fully conducting state; the first voltage threshold is set close to the Miller plateau voltage.

2. The soft drive method according to claim 1, characterized in that When the second voltage threshold corresponds to the drive voltage when the first switching transistor is in the off state, when the drive voltage of the first switching transistor rises from the second voltage threshold to the first voltage threshold, When the first switching transistor is an N-type switching transistor, the first reference current is a pull-up current. Based on the adjustment effect of the operational amplifier for the current input and the first switching transistor, the rate of decrease of the voltage at the first end of the switching module is stabilized at a certain value during the period when the drive voltage is the first voltage threshold. When the first switching transistor is a P-type switching transistor, the first reference current is a pull-down current. Based on the adjustment effect of the operational amplifier for the current input and the first switching transistor, the rate of increase of the voltage at the first end of the switching module is stabilized at a certain value during the period when the drive voltage is the first voltage threshold.

3. The soft drive method according to claim 1, characterized in that, When the second voltage threshold corresponds to the drive voltage when the first switching transistor is in the fully conducting state, when the drive voltage of the first switching transistor drops from the second voltage threshold to the first voltage threshold, When the first switching transistor is an N-type switching transistor, the first reference current is a pull-down current. Based on the adjustment effect of the operational amplifier for the current input and the first switching transistor, the rate of increase of the voltage at the first end of the switching module is stabilized at a certain value during the period when the drive voltage is the first voltage threshold. When the first switching transistor is a P-type switching transistor, the first reference current is a pull-up current. Based on the adjustment effect of the operational amplifier for the current input and the first switching transistor, the rate of decrease of the voltage at the first end of the switching module is stabilized at a certain value during the period when the drive voltage is the first voltage threshold.

4. The soft drive method according to claim 2, characterized in that When the second voltage threshold corresponds to the drive voltage when the first switching transistor is in the off state, as the first switching transistor is turned on, when the rate of change of the voltage at the first end of the switching module is lower than a preset threshold, the drive voltage of the first switching transistor is controlled to rise from the first voltage threshold to the drive voltage when the first switching transistor is fully conducting.

5. The soft drive method according to claim 3, characterized in that When the second voltage threshold corresponds to the driving voltage in the fully - on state of the first switching transistor, as the first switching transistor turns off, after the voltage change rate at the first end of the switching module is lower than a preset threshold, control the driving voltage of the first switching transistor to drop from the first voltage threshold to the driving voltage in the off state of the first switching transistor.

6. A soft drive circuit for driving a first switching transistor in a switching module, the switching module being applied to a switching power supply, characterized in that The soft - driving circuit includes a first capacitor, which is arranged on the branch between the first end of the switching module and the first node; a first reference current source, which is a pull - up or pull - down current source acting on the first node; a current - input operational amplifier, which is arranged on the branch between the gate of the first switching transistor and the first node; when the driving voltage of the first switching transistor changes from the second voltage threshold to the first voltage threshold, a first current is generated on the first capacitor based on the change in the voltage at the first end of the switching module. The difference signal between the first reference current and the first current is connected to the input end of the current - input operational amplifier, and the output end of the current - input operational amplifier is connected to the gate of the first switching transistor; based on the adjustment effects of the current - input operational amplifier and the first switching transistor, the voltage change rate at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold. Wherein, the driving voltage of the first switching transistor is the absolute value of the voltage difference between its gate and source; the second voltage threshold corresponds to the driving voltage in the off state or fully - on state of the first switching transistor; the first voltage threshold is set close to the Miller - plateau voltage.

7. The soft drive circuit according to claim 6, characterized in that, When the second voltage threshold corresponds to the driving voltage in the off state of the first switching transistor, when the driving voltage of the first switching transistor rises from the second voltage threshold to the first voltage threshold When the first switching transistor is an N - type switching transistor, the first reference current is a pull - up current. Based on the adjustment effects of the current - input operational amplifier and the first switching transistor, the voltage drop rate at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold. When the first switching transistor is a P - type switching transistor, the first reference current is a pull - down current. Based on the adjustment effects of the current - input operational amplifier and the first switching transistor, the voltage rise rate at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold.

8. The soft drive circuit according to claim 6, wherein When the second voltage threshold corresponds to the driving voltage in the fully - on state of the first switching transistor, when the driving voltage of the first switching transistor drops from the second voltage threshold to the first voltage threshold When the first switching transistor is an N - type switching transistor, the first reference current is a pull - down current. Based on the adjustment effects of the current - input operational amplifier and the first switching transistor, the voltage rise rate at the first end of the switching module is stabilized at a certain value during the period when the driving voltage is the first voltage threshold. When the first switching transistor is a P-type switching transistor, the first reference current is a pull-up current. Based on the adjustment of the current input operational amplifier and the first switching transistor, the rate of decrease of the voltage at the first end of the switching module is stabilized at a certain value during the period when the drive voltage is the first voltage threshold.

9. The soft drive circuit according to claim 6, wherein The soft drive circuit includes a detection circuit. When the second voltage threshold corresponds to the drive voltage in the off state of the first switching transistor, as the first switching transistor is turned on, when the detection circuit detects that the rate of change of the voltage at the first end of the switching module is lower than a preset threshold, the drive voltage of the first switching transistor is controlled to rise from the first voltage threshold to the drive voltage when the first switching transistor is fully turned on; or, When the second voltage threshold corresponds to the drive voltage in the fully turned-on state of the first switching transistor, as the first switching transistor is turned off, when the detection circuit detects that the rate of change of the voltage at the first end of the switching module is lower than a preset threshold, the drive voltage of the first switching transistor is controlled to drop from the first voltage threshold to the drive voltage when the first switching transistor is in the off state.

10. A switching power supply for converting an input voltage into an output voltage to supply power to a load, characterized in that, The switching power supply includes the soft drive circuit according to any one of claims 6-9 or controls the first switching transistor in the switching module based on the soft drive method according to any one of claims 1-5.

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