Active clamping control method, device and switching power supply

Abstract

The present invention discloses an active clamping control method, device, and switching power supply. The method includes determining that the buck-boost cascade circuit is in an unloaded or lightly loaded 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; determining that the buck-boost cascade circuit is in a heavy-loaded state, setting the operating mode of the buck-boost cascade circuit to a continuous mode, and setting the active clamping control mode to a trailing-edge non-complementary mode. The present invention can match corresponding timing logic according to different operating modes, optimizing the peak voltage clamping effect at both ends of the switch tube while also achieving ZVS in the continuous mode, thereby improving the efficiency of the switching power supply.

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, parasitic inductance exists between various components in the circuit due to wiring and other factors. Especially when the switch is turned off, due to the presence of parasitic inductance, a high voltage spike is generated across the drain and source of the switch. This voltage spike can easily damage the components and reduce circuit reliability. To suppress the voltage spike and protect the circuit components, snubber circuits are often used in existing technologies.

[0003] Conventional absorption circuits include lossy absorption and lossless absorption methods. Lossy absorption such as RC and RCD is suitable for small-power converters. Although all the absorbed energy is consumed in the parallel resistor and cannot be transferred to the output, the loss effect can be ignored. However, for high-power converters, the loss effect caused by absorption cannot be ignored. Therefore, 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 its control method, specifically a buck-boost cascade circuit. The buck-boost cascade circuit includes a front-stage buck-boost circuit and a rear-stage isolated switch power supply circuit. To achieve buck-boost mode control, the cascade circuit includes at least a switch tube Q1, a switch tube Q2, a power inductor L, and an isolated switch power supply circuit. Specifically, the isolated switch power supply circuit must include a primary switching circuit, a transformer T1, and a secondary rectifier circuit. The cascade circuit uses a current feed method. The primary switch tubes in the rear-stage isolated switch circuit have a common conduction portion, which serves as an excitation in boost mode and provides a freewheeling channel for the inductor current in 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 tubes in the primary switching 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 off period (there is a dead zone), refer to Figure 2 Leading-edge non-complementary mode means that the driving signal of the active clamp tube is partially turned on during the off period of the switch tube, and a 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 refers to the driving signal of the active clamp tube being 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 operates in discontinuous mode, the bus Vbus will resonate to 0 within one cycle due to the power inductor 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-edge non-complementary mode at this time, the energy on the active clamp capacitor C1 will cause the bus Vbus to quickly rise 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 operates in forced continuous mode, due to the negative current of the light no-load inductor, a certain negative current will also 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 primary switch tube's body diode will further aggravate the voltage spike across the primary switch tube under the combined action of the voltage VC1 of the active clamp capacitor C1 and the primary leakage inductance energy. The corresponding Vbus voltage spike will also become larger. Please refer to Figure 6 Therefore, it is necessary to optimize an active clamping control method 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 operating modes. While optimizing the voltage spike clamping effect at both ends of the switching tube, it can also achieve ZVS in continuous mode, thereby improving the efficiency of the switching power supply.

[0009] The technical solutions of the present invention are as follows:

[0010] In a first aspect, the present invention provides an active clamping control method 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 off period of the primary-side 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-side 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 off period of the primary-side switch tube of the rear-stage isolation switch power supply circuit, and after the primary-side 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-side 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 side switching tube.

[0018] Optionally, the dead time between the primary side switch tube being turned off and the active clamp tube being turned on in the leading edge non-complementary mode is greater than the dead time between the active clamp tube being turned off and the primary side switch tube being turned on in the trailing edge non-complementary mode.

[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 window filtering; when the leading edge non-complementary mode is switched to the trailing edge non-complementary mode, window filtering is added;

[0021] The specific method of the window filtering is: after the buck-boost cascade circuit is in the continuous mode for a certain period of time or is in the continuous mode for N switching cycles, it can be switched from the leading edge non-complementary mode to the trailing edge non-complementary mode.

[0022] Optionally, the duty cycle of the primary-side 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 also provides an active clamping control device, 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 is characterized in that the active clamping control device includes:

[0024] a light no-load unit, configured to determine whether the buck-boost cascade circuit is in a no-load state or a light-load state, and set the operating mode of the buck-boost cascade circuit to a discontinuous mode, and set the active clamping control mode of the buck-boost cascade circuit to a leading-edge non-complementary mode; or set the operating mode of the buck-boost cascade circuit to a forced continuous mode, and set 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, comprising 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) The active clamping control method of the present invention has the advantages that when the buck-boost cascade circuit operates in discontinuous mode, the light no-load power consumption is small, the voltage stress spike of the primary switch tube is small, and there is no need to select high-voltage large-package switch devices to meet reliability requirements, which can save product volume and development costs. When the above cascade circuit operates in continuous mode, the primary switch tube will form ZVS opening, thereby improving 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 additional external circuits, thereby reducing the cost and volume of the power supply system. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0033] Figure 3 This is the existing leading-edge non-complementary mode timing diagram;

[0034] Figure 4 This 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 present invention adopts the leading edge non-complementary mode in the forced continuous mode;

[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 under light no-load in a specific embodiment of the present invention;

[0039] Figure 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 solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to 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 intended 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. The buck-boost cascade circuit includes 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. 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. 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, light-load state or heavy-load state may be determined by judging the inductor current, load current or load rate in the preceding step-up / down circuit.

[0046] It should be noted that when the buck-boost cascade circuit operates in continuous mode, the active clamp operates in trailing-edge non-complementary mode. The active clamp is turned on at the end of each primary switch 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 made smaller or even close to 0 when it is turned on, thereby achieving ZVS turn-on, which can improve efficiency under heavy load. Please refer to Figure 7 .

[0047] The active clamping control method in this embodiment is shown in FIG. Figure 8 and Figure 9 , see the specific topology circuit diagram Figure 1 DCM is discontinuous mode, CCM is continuous mode, and FCCM is forced continuous mode. This buck-boost cascade circuit includes a front-stage buck-boost circuit and a back-stage isolated switch power supply circuit. The front-stage buck-boost circuit includes switches Q1, Q2, and Q4, a power inductor L, an active clamp switch Q3 (PMOS transistor), and an active clamp capacitor C1. The back-stage isolated switch power supply circuit includes primary-side switches Q5 and Q6, a transformer T1, and secondary-side rectifiers Q7 and Q8. This buck-boost cascade circuit uses a current-fed design. Primary-side switches Q5 and Q6 in the back-stage isolated switch circuit have a common conduction section, which serves as magnetizing circuit in boost mode and provides a freewheeling path for the inductor current in buck mode. The active clamp circuit, consisting of the active clamp Q3 (PMOS transistor) and active clamp capacitor C1 in the front-stage buck-boost circuit, clamps the Vbus voltage, thereby reducing voltage spikes on switches Q5 and Q6 in the primary-side switch circuit. This embodiment includes two operating conditions: a light no-load control mode in a discontinuous mode and a light no-load control mode in a forced continuous mode. Specifically:

[0048] When the light no-load control mode of the above cascade circuit is discontinuous mode, the cascade circuit has two working modes: discontinuous mode and 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 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, after the primary switch tube Q5 or Q6 is turned off, the active clamp tube Q3 is turned on for about 200ns to 300ns after the dead time. The pulse width is 100ns to 200ns. At this time, the active clamping control method belongs to the leading-edge non-complementary mode. When the cascade circuit operates in the continuous mode, the driving signal of the active clamping tube Q3 is partially turned on during the off period of the primary side switch tubes Q5 and Q6. That is, the active clamping tube Q3 starts to turn on after a certain period of time after the primary side switch tube Q5 or Q6 is turned off. After a pulse width of about 100ns to 200ns, the primary side switch tube Q5 or Q6 is turned on after a dead time of about 20ns to 30ns. At this time, the active clamping control method belongs to the trailing-edge non-complementary mode.

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

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

[0051] As the output load gradually increases, the operating mode of the cascade circuit enters the continuous mode from the discontinuous mode. If the current of the preceding power inductor is continuously detected for 30us and is determined to be in the continuous mode, or the current of the preceding power inductor is continuously detected for 3 to 5 switching cycles and is determined to be in the continuous mode, then in the next working cycle, the active 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 operating 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 determined 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 merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be construed as limiting the present invention. Persons skilled in the art will appreciate that equivalent substitutions, improvements, and modifications may be made without departing from the spirit and scope of the present invention. These equivalent substitutions, improvements, and modifications should also be considered within the scope of protection of the present invention. Examples will not be used here for further elaboration; the scope of protection of the present invention should be determined by the scope defined in 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 of the front-stage buck-boost circuit is connected to the input 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; Determining that the buck-boost cascade circuit is in an overload state, setting the operating mode of the buck-boost cascade circuit to a continuous mode, and setting the active clamping control mode to a trailing edge non-complementary mode; 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; The window filtering method 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.

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 off period of the primary-side 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-side switch tube is turned off.

3. The active clamping control method according to claim 1, wherein: 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 off period of the primary-side switch tube of the rear-stage isolation switch power supply circuit, and after the primary-side 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-side switch tube after a dead time.

4. The 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 shorter than the turn-off time of the primary side switching tube.

5. The active clamping control method according to claim 2 or 3, characterized in that: The dead time between the turning off of the primary side 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 side switch tube at the trailing edge.

6. The 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 side switching tube.

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

8. 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, wherein the output of the front-stage buck-boost circuit is connected to the input of the rear-stage isolation switch power supply circuit, characterized in that: The active clamping control device comprises: a light no-load unit, configured to determine whether the buck-boost cascade circuit is in a no-load state or a light-load state, and set the operating mode of the buck-boost cascade circuit to a discontinuous mode, and set the active clamping control mode of the buck-boost cascade circuit to a leading-edge non-complementary mode; or set the operating mode of the buck-boost cascade circuit to a forced continuous mode, and set the active clamping control mode of the buck-boost cascade circuit to a trailing-edge non-complementary mode; a heavy load unit, configured to determine that the buck-boost cascade circuit is in a heavy load state, set the operating 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; 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; The window filtering method 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.

9. A switching power supply, characterized in that: The switching power supply includes an active clamping control device as claimed in claim 8.

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