Active clamping control method and device and switching power supply

Abstract

The invention discloses an active clamping control method and device and a switching power supply, and the method comprises the steps: determining whether a buck-boost cascade circuit is in a no-load state or a light-load state, and enabling the working mode of the buck-boost cascade circuit to be set as a discontinuous mode, the active clamping control mode of the buck-boost cascade circuit is set as a leading edge non-complementary mode; or, the working mode of the buck-boost cascade circuit is set to be a forced continuous mode, and the active clamping control mode of the buck-boost cascade circuit is set to be a trailing edge non-complementary mode; and determining that the buck-boost cascade circuit is in a heavy load state, setting the working mode of the buck-boost cascade circuit as a continuous mode, and setting the active clamping control mode as a trailing edge non-complementary mode. Corresponding sequential logic can be matched according to different working modes, the clamping effect of peak voltage at the two ends of a switching tube is optimized, ZVS can be achieved in a continuous mode, and the efficiency of the switching power supply is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and in particular to an active clamping control method, an active clamping control device and a switching power supply. Background Art

[0002] In switching power supply products, due to wiring and other reasons, there is parasitic inductance between various devices in the circuit. Especially when the switch tube is turned off, due to the existence of parasitic inductance, a high voltage spike will be generated at both ends of the drain and source of the switch tube. This voltage spike is easy to damage the device and reduce the reliability of the circuit. In the prior art, in order to suppress the voltage spike and protect the circuit components, an absorption circuit is often used.

[0003] Conventional absorption circuits include lossy absorption and lossless absorption. Lossy absorption such as RC and RCD is suitable for small power converters. Although all the absorbed energy is consumed in the parallel resistance and cannot be transferred to the output, the loss effect can be ignored. For high power converters, the loss effect caused by absorption cannot be ignored, so lossless absorption methods such as active clamping circuits are generally used.

[0004] Please refer to Figure 1 , a Chinese patent application with publication number CN114221549A discloses a cascade circuit and a control method thereof, specifically relating to a buck-boost cascade circuit, the buck-boost cascade circuit comprising a front-stage buck-boost circuit and a rear-stage isolated switch power supply circuit, and the buck-boost mode control cascade circuit at least comprises a switch tube Q1, a switch tube Q2, a power inductor L, and an isolated switch power supply circuit, and specifically the isolated switch power supply circuit needs to include a primary switch circuit, a transformer T1, and a secondary rectifier circuit. The cascade circuit adopts a current feeding method, and the primary switch tube in the rear-stage isolated switch circuit has a common conduction part, which plays an excitation role in the boost mode and provides a freewheeling channel for the inductor current in the buck mode. The active clamping circuit composed of the clamping tube Q3 and the clamping capacitor C1 in the front-stage buck-boost circuit can reduce the voltage spike stress of the switch tube in the primary switch circuit by clamping the Vbus voltage.

[0005] Common active clamp control methods are divided into fully complementary, leading edge non-complementary mode and trailing edge non-complementary mode. Specifically, the fully complementary type means that the active clamp tube drive signal is fully turned on during the primary side switch tube is turned off (there is a dead zone), refer to Figure 2 ; The leading edge non-complementary mode type means that the driving signal of the active clamp tube is partially turned on during the off period of the switch tube, and the fixed pulse width is turned on after the dead time after the primary switch tube is turned off. Figure 3The trailing edge non-complementary mode type means that the driving signal of the active clamp tube is partially turned on during the off period of the switch tube, and after the primary switch tube is turned off for a certain period of time, the active clamp tube is turned on for a fixed pulse width and then the primary switch tube is turned on after the dead time. Figure 4 .

[0006] When the above cascade circuit works in discontinuous mode, the bus Vbus will resonate to 0 in one cycle due to the power inductance in the front-stage buck-boost circuit, the transformer T1 in the rear-stage isolation switch circuit and the parasitic capacitance on the bus. If the active clamp adopts a fully complementary type or a trailing non-complementary mode, the energy on the active clamp capacitor C1 will quickly raise the bus Vbus from 0 to the voltage drop VC1 across the active clamp capacitor C1 (VC1 ≥ Vbus), thereby causing the active clamp tube Q3 to heat up and the light no-load loss to be large. Please refer to Figure 5 ;

[0007] When the above cascade circuit works in forced continuous mode, due to the negative current of the light no-load inductor, a certain negative current will flow through the primary switch tube. If the active clamp adopts a fully complementary type or a leading-edge non-complementary mode at this time, the reverse recovery of the body diode of the primary switch tube will further aggravate the voltage spike at both ends of the primary switch tube under the combined effect of the voltage VC1 of the active clamp capacitor C1 and the primary leakage inductance energy, and the corresponding Vbus voltage spike will also become larger. Please refer to Figure 6 Therefore, an active clamping control method needs to be optimized to meet the application under different working conditions. Summary of the invention

[0008] In view of this, the present invention provides an active clamping control method, device and switching power supply. The method can match the corresponding timing logic according to different working modes, optimize the voltage spike clamping effect at both ends of the switch tube, and realize ZVS in the continuous mode, thereby improving the efficiency of the switching power supply.

[0009] The technical solution of the present invention is as follows:

[0010] In a first aspect, the present invention provides an active clamping control method, which is applied to a buck-boost cascade circuit, wherein the buck-boost cascade circuit includes a front-stage buck-boost circuit and a rear-stage isolation switch power supply circuit, wherein the output end of the front-stage buck-boost circuit is connected to the input end of the rear-stage isolation switch power supply circuit, and the active clamping control method includes:

[0011] Determining that the buck-boost cascade circuit is in a no-load state or a light-load state, setting the operating mode of the buck-boost cascade circuit to a discontinuous mode, and setting the active clamping control mode of the buck-boost cascade circuit to a leading edge non-complementary mode; or setting the operating mode of the buck-boost cascade circuit to a forced continuous mode, and setting the active clamping control mode of the buck-boost cascade circuit to a trailing edge non-complementary mode;

[0012] It is determined that the buck-boost cascade circuit is in a heavy load state, the operating mode of the buck-boost cascade circuit is set to a continuous mode, and the active clamping control mode is set to a trailing edge non-complementary mode.

[0013] Optionally, the leading edge non-complementary mode is specifically:

[0014] The driving signal of the active clamping tube of the front-stage buck-boost circuit is partially turned on during the shutdown period of the primary switch tube of the rear-stage isolation switch power supply circuit, and the active clamping tube is turned on with a fixed pulse width after the dead time after the primary switch tube is turned off.

[0015] Optionally, the trailing edge non-complementary mode is specifically:

[0016] The driving signal of the active clamping tube of the front-stage buck-boost circuit is partially turned on during the shutdown period of the primary switch tube of the rear-stage isolation switch power supply circuit, and after the primary switch tube is turned off for a certain period of time, the active clamping tube is turned on with a fixed pulse width and then turns on the primary switch tube after a dead time.

[0017] Optionally, the fixed pulse width of the active clamping tube during conduction is smaller than the turn-off time of the primary switching tube.

[0018] Optionally, the dead time between the turning off of the primary switch tube and the turning on of the active clamping tube at the leading edge is greater than the dead time between the turning off of the active clamping tube and the turning on of the primary switch tube at the trailing edge.

[0019] Optionally, the operating frequency of the active clamping tube is twice the operating frequency of the primary switching tube.

[0020] Optionally, when the trailing edge non-complementary mode is switched to the leading edge non-complementary mode, the mode is switched immediately without a filtering window; when the leading edge non-complementary mode is switched to the trailing edge non-complementary mode, a window filter is added;

[0021] The specific method of the window filtering is to switch from the leading edge non-complementary mode to the trailing edge non-complementary mode by being in the continuous mode for a certain period of time or being in the continuous mode for N switching cycles.

[0022] Optionally, the duty cycle of the primary switch tube is greater than 50%, and the switch tubes of different bridge arms are turned on alternately.

[0023] In a second aspect, the present invention application further provides an active clamping control device, which is applied to a buck-boost cascade circuit, wherein the buck-boost cascade circuit comprises a front-stage buck-boost circuit and a rear-stage isolation switch power supply circuit, wherein the output end of the front-stage buck-boost circuit is connected to the input end of the rear-stage isolation switch power supply circuit, and is characterized in that the active clamping control device comprises:

[0024] a light no-load unit, used for determining that the buck-boost cascade circuit is in a no-load state or a light-load state, setting the operation mode of the buck-boost cascade circuit to a discontinuous mode, and setting the active clamping control mode of the buck-boost cascade circuit to a leading edge non-complementary mode; or setting the operation mode of the buck-boost cascade circuit to a forced continuous mode, and setting the active clamping control mode of the buck-boost cascade circuit to a trailing edge non-complementary mode;

[0025] The overload unit is used to determine that the buck-boost cascade circuit is in an overload state, set the working mode of the buck-boost cascade circuit to a continuous mode, and set the active clamping control mode to a trailing edge non-complementary mode.

[0026] In a third aspect, the present invention further provides a switching power supply, wherein the switching power supply comprises an active clamping control device as described in the first aspect.

[0027] Compared with the existing active clamping control scheme, the present invention has the following beneficial effects:

[0028] (1) When the buck-boost cascade circuit works in a discontinuous mode, the active clamping control method of the present invention has low light no-load power consumption, small voltage stress peak of the primary switch tube under light no-load conditions, and no need to select high-voltage large-package switch devices to meet reliability requirements, thereby saving product volume and development costs. When the cascade circuit works in a continuous mode, the primary switch tube will form a ZVS opening to improve heavy-load efficiency.

[0029] (2) When the active clamping control method of the present invention operates in the forced continuous mode, the reverse recovery problem of the body diode of the primary switch tube is weakened, thereby not aggravating the voltage stress spike of the primary switch tube. The voltage stress spike of the primary switch tube is small, and the product reliability is high.

[0030] (3) The active clamping control method provided by the present invention has simple control logic and does not require the addition of external circuits, thereby reducing the cost and volume of the power supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the schematic diagram of the existing cascade circuit;

[0032] Figure 2 It is an existing fully complementary timing diagram;

[0033] Figure 3 It is a timing diagram of the existing leading-edge non-complementary mode type;

[0034] Figure 4 It is a timing diagram of the existing trailing edge non-complementary mode;

[0035] Figure 5 The Vbus waveform when the present invention adopts the trailing edge non-complementary mode in the discontinuous mode;

[0036] Figure 6 The Vbus waveform when the leading edge non-complementary mode is adopted in the forced continuous mode of the present invention;

[0037] Figure 7 The Vbus waveform when the present invention adopts the trailing edge non-complementary mode in the continuous mode;

[0038] Figure 8 This is a timing diagram of active clamping when DCM is used at light no-load in a specific embodiment of the present invention;

[0039] Fig. 9 This is a timing diagram of active clamping when FCCM is used at light no-load in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] An embodiment of the present invention provides an active clamping control method, which is applied to a buck-boost cascade circuit, wherein the buck-boost cascade circuit includes a front-stage buck-boost circuit and a rear-stage isolation switch power supply circuit, wherein the output end of the front-stage buck-boost circuit is connected to the input end of the rear-stage isolation switch power supply circuit, and the active clamping control method includes:

[0042] Determining that the buck-boost cascade circuit is in a no-load state or a light-load state, setting the operating mode of the buck-boost cascade circuit to a discontinuous mode, and setting the active clamping control mode of the buck-boost cascade circuit to a leading edge non-complementary mode; or setting the operating mode of the buck-boost cascade circuit to a forced continuous mode, and setting the active clamping control mode of the buck-boost cascade circuit to a trailing edge non-complementary mode;

[0043] It is determined that the buck-boost cascade circuit is in a heavy load state, the operating mode of the buck-boost cascade circuit is set to a continuous mode, and the active clamping control mode is set to a trailing edge non-complementary mode.

[0044] The front-stage buck-boost circuit includes an input terminal, a main switch tube, a synchronous switch tube, an inductor and an active clamping circuit, and the rear-stage isolation switch power supply circuit includes a primary side switch circuit, a transformer and a secondary side rectifier circuit.

[0045] The judgment condition of the no-load state, the light-load state or the heavy-load state may be judged by judging the load current or the load rate.

[0046] It should be noted that when the buck-boost cascade circuit works in continuous mode, the active clamp works in trailing non-complementary mode. The active clamp is turned on at the end of each primary switch working cycle, and the voltage VC1 (VC1 ≥ Vbus) of the active clamp capacitor C1 is discharged to Vbus, increasing the excitation current of the transformer. The active clamp is then turned off. Due to the characteristic that the current cannot change suddenly, resonance occurs between the front-stage power inductor, the parasitic capacitance on the bus and the transformer leakage inductance. By adjusting the dead zone, the Vds of the rear-stage primary switch is small or even close to 0 when it is turned on, thereby achieving ZVS turn-on, which can improve the efficiency under heavy load. Please refer to Figure 7 .

[0047] The active clamping control method in this embodiment is shown in Figure 8 and Fig. 9 , see the specific topology circuit diagram Figure 1 , DCM mode is discontinuous mode, CCM mode is continuous mode, FCCM is forced continuous mode, the buck-boost cascade circuit includes a front-stage buck-boost circuit and a rear-stage isolated switch power supply circuit, wherein the front-stage buck-boost circuit includes switch tube Q1, switch tube Q2, switch tube Q4, power inductor L, active clamp switch tube Q3 (PMOS) and active clamp capacitor C1; the rear-stage isolated switch power supply circuit includes: primary switch tubes Q5 and Q6, transformer T1 and secondary rectifier tubes Q7 and Q8. The buck-boost cascade circuit adopts a current feeding method, and the primary switch tubes Q5 and Q6 in the rear-stage isolated switch circuit have a common conduction part, which plays an excitation role in the boost mode and provides a freewheeling channel for the inductor current in the buck mode. The active clamp circuit composed of the active clamp tube Q3 (PMOS) and the active clamp capacitor C1 in the front-stage buck-boost circuit clamps the Vbus voltage to reduce the voltage spike stress of the switch tubes Q5 and Q6 in the primary switch circuit. This embodiment includes two types of working conditions: the light no-load control mode is a discontinuous mode and the light no-load control mode is a forced continuous mode. Specifically:

[0048] When the light no-load control mode of the above cascade circuit is the discontinuous mode, the cascade circuit has two working modes: the discontinuous mode and the continuous mode. In either mode, the primary switch tubes Q5 and Q6 will work alternately at a fixed frequency, and the duty cycle is greater than 50%. When the cascade circuit works in the discontinuous mode, the driving signal of the active clamp tube Q3 is partially turned on during the period when the primary switch tubes Q5 and Q6 are turned off, that is, the active clamp tube Q3 is turned on after a dead time of about 200ns to 300ns after the primary switch tube Q5 or Q6 is turned off. 100ns~200ns pulse width, at this time, the active clamping control method belongs to the leading edge non-complementary mode; when the cascade circuit works in the continuous mode, the driving signal of the active clamping tube Q3 is partially turned on during the shutdown period of the primary switch tubes Q5 and Q6, that is, the active clamping tube Q3 starts to turn on after the primary switch tube Q5 or Q6 is turned off for a certain period of time, and the primary switch tube Q5 or Q6 is turned on after a pulse width of about 100ns~200ns and a dead time of about 20ns~30ns. At this time, the active clamping control method belongs to the trailing edge non-complementary mode;

[0049] In the discontinuous mode, the dead time between the shutdown of the primary switch tube Q5 or Q6 and the opening of the leading active clamp tube Q3 is relatively large in order to prevent a large Vbus voltage stress spike caused by the early opening of the active clamp tube. In the continuous mode, the dead time between the shutdown of the active clamp tube Q3 and the opening of the primary switch tube Q5 or Q6 is relatively small in order to achieve the ZVS characteristics of the primary switch tube and improve the heavy-load efficiency.

[0050] Since the active clamp tube Q3 is partially turned on during the off period of the primary switch tubes Q5 and Q6, the operating frequency of the active clamp tube Q3 is twice the operating frequency of the primary switch tubes Q5 and Q6;

[0051] As the output load gradually increases, the working mode of the cascade circuit changes from the discontinuous mode to the continuous mode. If the current of the preceding power inductor is detected for 30us continuously and is judged to be in the continuous mode, or the current of the preceding power inductor is detected for 3 to 5 switching cycles continuously and is judged to be in the continuous mode, then in the next working cycle, the source clamping control mode is switched from the leading edge non-complementary mode to the trailing edge non-complementary mode. Conversely, as the load gradually decreases, the working mode of the cascade circuit returns from the continuous mode to the discontinuous mode. If the current of the preceding power inductor is detected in the previous working cycle and is judged to be in the discontinuous mode, then in the next working cycle, the active clamping control mode is immediately switched from the trailing edge non-complementary mode to the leading edge non-complementary mode.

[0052] When the light no-load control mode of the above cascade circuit is the forced continuous mode, the active clamping control mode in the full load range is the trailing edge non-complementary mode, which is the same as the control mode in the above continuous mode and will not be repeated here.

[0053] The above are only preferred embodiments of the present invention, and it should be noted that the above preferred embodiments should not be regarded as limiting the present invention. For those skilled in the art, several equivalent substitutions, improvements and modifications can be made without departing from the spirit and scope of the present invention, and these equivalent substitutions, improvements and modifications should also be regarded as the protection scope of the present invention. The embodiments will not be repeated here, and the protection scope of the present invention shall be based on the scope defined by the claims.

Claims

1. An active clamping control method, applied to a buck-boost cascade circuit, wherein the buck-boost cascade circuit comprises a front-stage buck-boost circuit and a rear-stage isolation switch power supply circuit, wherein the output end of the front-stage buck-boost circuit is connected to the input end of the rear-stage isolation switch power supply circuit, characterized in that: The active clamping control method comprises: Determining that the buck-boost cascade circuit is in a no-load state or a light-load state, setting the operating mode of the buck-boost cascade circuit to a discontinuous mode, and setting the active clamping control mode of the buck-boost cascade circuit to a leading edge non-complementary mode; or setting the operating mode of the buck-boost cascade circuit to a forced continuous mode, and setting the active clamping control mode of the buck-boost cascade circuit to a trailing edge non-complementary mode; It is determined that the buck-boost cascade circuit is in a heavy load state, the operation mode of the buck-boost cascade circuit is set to a continuous mode, and the active clamping control mode is set to a trailing edge non-complementary mode.

2. The active clamping control method according to claim 1, characterized in that: The frontier non-complementary mode is specifically: The driving signal of the active clamping tube of the front-stage buck-boost circuit is partially turned on during the shutdown period of the primary switch tube of the rear-stage isolation switch power supply circuit, and the active clamping tube is turned on with a fixed pulse width after the dead time after the primary switch tube is turned off.

3. The active clamping control method according to claim 1, characterized in that: The trailing edge non-complementary mode is specifically: The driving signal of the active clamping tube of the front-stage buck-boost circuit is partially turned on during the shutdown period of the primary switch tube of the rear-stage isolation switch power supply circuit, and after the primary switch tube is turned off for a certain period of time, the active clamping tube is turned on with a fixed pulse width and then turns on the primary switch tube after a dead time.

4. An active clamping control method according to claim 2 or 3, characterized in that: The fixed pulse width of the active clamping tube during conduction is smaller than the turn-off time of the primary switch tube.

5. An active clamping control method according to claim 2 or 3, characterized in that: The dead time between the turning off of the primary switch tube and the turning on of the active clamping tube at the leading edge is greater than the dead time between the turning off of the active clamping tube and the turning on of the primary switch tube at the trailing edge.

6. An active clamping control method according to claim 2 or 3, characterized in that: The operating frequency of the active clamping tube is twice the operating frequency of the primary switching tube.

7. The active clamping control method according to claim 1, characterized in that: When the trailing edge non-complementary mode is switched to the leading edge non-complementary mode, it is switched immediately without a filtering window; when the leading edge non-complementary mode is switched to the trailing edge non-complementary mode, window filtering is added; The specific method of the window filtering is to switch from the leading edge non-complementary mode to the trailing edge non-complementary mode by being in the continuous mode for a certain period of time or being in the continuous mode for N switching cycles.

8. An active clamping control method according to claims 2 and 3, characterized in that: The duty cycle of the primary switch tube is greater than 50%, and the switch tubes of different bridge arms are turned on alternately.

9. An active clamping control device, applied to a buck-boost cascade circuit, the buck-boost cascade circuit comprising a front-stage buck-boost circuit and a rear-stage isolation switch power supply circuit, the output end of the front-stage buck-boost circuit is connected to the input end of the rear-stage isolation switch power supply circuit, characterized in that: The active clamping control device comprises: a light no-load unit, used for determining that the buck-boost cascade circuit is in a no-load state or a light-load state, setting the operation mode of the buck-boost cascade circuit to a discontinuous mode, and setting the active clamping control mode of the buck-boost cascade circuit to a leading edge non-complementary mode; or setting the operation mode of the buck-boost cascade circuit to a forced continuous mode, and setting the active clamping control mode of the buck-boost cascade circuit to a trailing edge non-complementary mode; The overload unit is used to determine that the buck-boost cascade circuit is in an overload state, set the working mode of the buck-boost cascade circuit to a continuous mode, and set the active clamping control mode to a trailing edge non-complementary mode.

10. A switching power supply, characterized in that: The switching power supply comprises an active clamping control device as claimed in claim 9.

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