A source driven switching power supply and control method

Abstract

The present invention discloses a source-driven switching power supply and control method. The switching power supply includes a transformer, a first switching transistor, a second switching transistor, a third switching transistor, a bias capacitor unit, an active clamping circuit, a controller, and a secondary-side loop. The active clamping circuit generates a negative excitation current to release energy from the parasitic capacitance between the drain and source electrodes of the first and second switching transistors. The third switching transistor is then selectively turned on or off based on the voltages at the first and third terminals of the first switching transistor, thereby achieving zero-voltage conduction of the first and second switching transistors in the source-driven structure. This source-driven circuit for a switching power supply retains the technical features of the source-driven structure and reduces the withstand voltage requirements of the main power switching transistor. Furthermore, it improves system efficiency and expands the development of this topology toward higher-frequency applications.

Description

Technical Field

[0001] The present invention relates to the field of switching power supplies, and in particular to a source-driven switching power supply and a control method thereof. Background Art

[0002] The source drive method is widely used in switching power supplies due to its low power consumption and high efficiency. Its main principle is to fix the gate voltage of the switch tube at a certain value, and change the source voltage of the switch tube by controlling the switching state of the power transistor connected between the source of the switch tube and the ground, thereby controlling the switching state of the switch tube.

[0003] like Figure 1 The figure shows a circuit diagram of a switching power supply using source drive technology in the prior art. The switching power supply circuit includes a first switching tube Q1, a second switching tube Q2, a feed diode D1, a bias capacitor C1, and a transformer, wherein the anode of the feed diode is connected to the common connection point of the first switching tube and the second switching tube, and the cathode is connected to one end of the bias capacitor and the gate of the first switching tube; the drain of the first switching tube is connected to the transformer, and the source is connected to the drain of the second switching tube; the source of the second switching tube is connected to the ground. The working process of the source drive in the prior art is as follows: when the second switching tube is turned on, the source voltage of the first switching tube is rapidly pulled down. Since the gate voltage of the first switching tube is connected to a fixed bias voltage, when its gate-source voltage rises to exceed the turn-on threshold voltage, the first switching tube is turned on; when the second switching tube is turned off, the source voltage of the first switching tube rises rapidly. When its gate-source voltage drops below the turn-on threshold voltage, the first switching tube is turned off.

[0004] Due to its unique structural features, source drive technology is widely used in integrated power supply circuits for switching power supplies without auxiliary windings. However, a drawback of this existing technology is that, because the gate of the first switch Q1 is connected to a fixed bias voltage, its turn-on and turn-off are entirely determined by the drain-source voltage Vds2 of the second switch. After the second switch Q2 turns on and its drain-source voltage drops, the first switch turns on in response to the drop in Vds2 until its gate-source voltage reaches its turn-on threshold. At this point, the drain-source voltage of the first switch is still well above zero, resulting in significant junction capacitance losses when the first switch turns on. The existing source drive circuit structure prevents the first switch from achieving ZVS (zero voltage turn-on), severely impacting system efficiency and limiting the development of this topology towards higher-frequency applications. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a source-driven switching power supply and control method, which can achieve ZVS (zero voltage conduction) of the first switch tube, solve the problem of large turn-on loss of the first switch tube in the source-driven technology, and also achieve zero voltage conduction of the second switch tube, thereby expanding the application range of this topology to higher frequency fields.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] In a first aspect, a source-driven switching power supply is provided, comprising: a transformer, a source drive circuit, and a secondary-side loop, wherein the source drive circuit comprises a first switch tube, a second switch tube, a third switch tube, a bias capacitor unit, an active clamp circuit, and a controller;

[0008] The first end of the active clamping circuit is electrically connected to the same-name end of the primary winding of the transformer and is electrically connected to an input voltage, and the second end of the active clamping circuit is electrically connected to the opposite-name end of the primary winding of the transformer and the first end of the first switching tube;

[0009] The second end of the first switch tube is electrically connected to one end of the bias capacitor unit, and the second end of the first switch tube is also electrically connected to a bias voltage, and the third end of the first switch tube is connected to the third end of the third switch tube and the first end of the second switch tube;

[0010] The second end of the second switch tube is electrically connected to the first output end of the controller, and the third end of the second switch tube is electrically connected to the ground;

[0011] The first end of the third switch tube is electrically connected to one end of the bias capacitor unit, and the first end of the third switch tube is also electrically connected to a bias voltage, and the second end of the third switch tube is electrically connected to the second output end of the controller;

[0012] The other end of the bias capacitor unit is electrically connected to the ground;

[0013] The secondary winding of the transformer is electrically connected to the secondary side loop;

[0014] The controller is also electrically connected to the active clamping circuit, and is used to control the on and off of the second switch tube, the third switch tube, and the active clamping circuit.

[0015] Preferably, the active clamping circuit includes a clamping capacitor unit and a fourth switching tube, one end of the clamping capacitor unit serves as the first end of the active clamping circuit, is electrically connected to the same-name end of the primary winding of the transformer, and is electrically connected to an input voltage; the other end of the clamping capacitor unit is connected to the first end of the fourth switching tube; the second end of the fourth switching tube is connected to the third output end of the controller, and the third end of the fourth switching tube serves as the second end of the active clamping circuit, is electrically connected to the opposite-name end of the primary winding of the transformer and the first end of the first switching tube.

[0016] Preferably, the first switching tube and the second switching tube are both MOS tubes, the first end of the first switching tube and the first end of the second switching tube are both drains, the second end of the first switching tube and the second end of the second switching tube are both gates, and the third end of the first switching tube and the third end of the second switching tube are both sources.

[0017] Preferably, the capacity of the bias capacitor unit is a predetermined multiple of the capacity of the parasitic capacitance between the drain and source of the first switch, and the predetermined multiple is greater than 10.

[0018] In a second aspect, a control method for a source-driven switching power supply is provided, which includes:

[0019] an active clamping circuit turning-on step, after the magnetizing inductance of the transformer is demagnetized, controlling the first switch tube, the second switch tube, and the third switch tube to be turned off, and controlling the active clamping circuit to be turned on to generate a negative magnetizing current;

[0020] an active clamping circuit shutoff step, controlling the active clamping circuit to shut off and the third switch to turn on; when the active clamping circuit is shut off and the third switch is turned on, the negative excitation current participates in a resonance process of the transformer's excitation inductance, the parasitic capacitance between the first terminal and the third terminal of the first switch, and the parasitic capacitance between the first terminal and the third terminal of the second switch, thereby releasing energy in the parasitic capacitance; and when the voltage at the first terminal of the first switch resonates to the bias voltage, or when the voltage between the first terminal and the second terminal of the first switch resonates to zero, the controller controls the third switch to shut off;

[0021] a first switching tube turning on step, controlling the first switching tube to turn on when the negative excitation current further releases energy of the parasitic capacitance between the first terminal and the third terminal of the second switching tube so that the voltage between the first terminal and the third terminal of the first switching tube is zero or close to zero;

[0022] The second switch tube is turned on in a step of: after the first switch tube is turned on, when the negative excitation current further releases the energy of the parasitic capacitance between the first terminal and the third terminal of the second switch tube, so that the voltage between the first terminal and the third terminal of the second switch tube is zero or close to zero, the second switch tube is controlled to be turned on.

[0023] Preferably, the active clamping circuit includes a clamping capacitor unit and a fourth switching tube, one end of the clamping capacitor unit serves as the first end of the active clamping circuit, is electrically connected to the same-name end of the primary winding of the transformer, and is electrically connected to an input voltage; the other end of the clamping capacitor unit is connected to the first end of the fourth switching tube; the second end of the fourth switching tube is connected to the third output end of the controller, and the third end of the fourth switching tube serves as the second end of the active clamping circuit, is electrically connected to the opposite-name end of the primary winding of the transformer and the first end of the first switching tube; controlling the active clamping circuit to conduct to generate a negative excitation current specifically includes: controlling the fourth switching tube to conduct, so that the clamping capacitor unit discharges to generate a negative excitation current; and controlling the active clamping circuit to shut down specifically includes: controlling the fourth switching tube to shut down.

[0024] In a third aspect, a control method for a source-driven switching power supply is provided, which includes:

[0025] an active clamping circuit conducting step, after the magnetizing inductance of the transformer is demagnetized, controlling the first switch tube and the second switch tube to be turned off and the third switch tube to be turned on, and controlling the active clamping circuit to be turned on to generate a negative magnetizing current;

[0026] an active clamping circuit shutoff step, controlling the active clamping circuit to shut off; when the active clamping circuit is shut off, the negative excitation current participates in a resonance process of the transformer's excitation inductance, the parasitic capacitance between the first terminal and the third terminal of the first switching tube, and the parasitic capacitance between the first terminal and the third terminal of the second switching tube, so that energy of the parasitic capacitance is released; when the voltage at the first terminal of the first switching tube resonates to the bias voltage, or when the voltage between the first terminal and the second terminal of the first switching tube resonates to zero, the controller controls the third switching tube to shut off;

[0027] a first switching tube turning on step, controlling the first switching tube to turn on when the negative excitation current further releases energy of the parasitic capacitance between the first terminal and the third terminal of the second switching tube so that the voltage between the first terminal and the third terminal of the first switching tube is zero or close to zero;

[0028] The second switch tube is turned on in a step of: after the first switch tube is turned on, when the negative excitation current further releases the energy of the parasitic capacitance between the first terminal and the third terminal of the second switch tube, so that the voltage between the first terminal and the third terminal of the second switch tube is zero or close to zero, the second switch tube is controlled to be turned on.

[0029] Preferably, the active clamping circuit includes a clamping capacitor unit and a fourth switching tube, one end of the clamping capacitor unit serves as the first end of the active clamping circuit, is electrically connected to the same-name end of the primary winding of the transformer, and is electrically connected to an input voltage; the other end of the clamping capacitor unit is connected to the first end of the fourth switching tube; the second end of the fourth switching tube is connected to the third output end of the controller, and the third end of the fourth switching tube serves as the second end of the active clamping circuit, is electrically connected to the opposite-name end of the primary winding of the transformer and the first end of the first switching tube; controlling the active clamping circuit to conduct to generate a negative excitation current specifically includes: controlling the fourth switching tube to conduct, so that the clamping capacitor unit discharges to generate a negative excitation current; and controlling the active clamping circuit to shut down specifically includes: controlling the fourth switching tube to shut down.

[0030] Compared with the prior art, the present invention has the following technical effects:

[0031] The present invention replaces the feed diode of the traditional source drive circuit with a controllable switch tube device, and at the same time utilizes the negative excitation current generated by the active clamping circuit after the demagnetization of the transformer excitation inductance is completed. On the one hand, it retains the technical characteristics of the source drive structure and reduces the voltage resistance requirement of the main power switch tube; on the other hand, it can achieve zero-voltage turn-on of the first switch tube and the second switch tube, improve the working efficiency of the system, and expand the development of this topology structure towards higher frequency applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The invention is a source drive switching power supply in the prior art.

[0033] Figure 2 FIG. 1 is a schematic diagram of a source-driven switching power supply according to a first embodiment of the present invention.

[0034] Figure 3 This is the specific schematic diagram of the active clamping circuit.

[0035] Figure 4 FIG. 1 is a working waveform diagram of the source driver circuit according to the first embodiment of the present invention.

[0036] Figure 5 FIG. 1 is a working waveform diagram of the source driver circuit according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0037] The inventive concept of the present application is to utilize the negative excitation current generated by the active clamping circuit E1 to release the energy on the drain-source parasitic capacitance of the first switch tube Q1 and the second switch tube Q2 during each working cycle, and to select the turning on or off of the third switch tube Q3 according to the source and drain voltages of the first switch tube Q1, thereby achieving zero-voltage turn-on of the first switch tube Q1 and the second switch tube Q2 in the source drive structure and obtaining better working efficiency.

[0038] Typical embodiments embodying the features and advantages of the present disclosure will be described in detail in the following description with reference to the accompanying drawings. It should be understood that the present disclosure is capable of various variations in different embodiments without departing from the scope of the present disclosure, and the description and drawings are intended to illustrate these variations rather than to limit the present disclosure.

[0039] In addition, the figures of this disclosure are merely schematic diagrams of the present disclosure and are not necessarily drawn to scale. Identical reference numbers in the figures denote identical or similar parts, and therefore repeated descriptions thereof will be omitted. Some of the blocks shown in the figures are functional entities that do not necessarily correspond to physically or logically separate entities. These functional entities may be implemented using software, in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0040] First embodiment

[0041] See also Figure 2 , which is a schematic diagram of a source-driven switching power supply for use in a switching power supply according to a first embodiment of the present invention. In this embodiment, a source-driven switching power supply is provided, comprising: a transformer T1, a source drive circuit, and a secondary-side loop. The source drive circuit comprises a first switching transistor Q1, a second switching transistor Q2, a third switching transistor Q3, a bias capacitor unit C1, an active clamping circuit E1, and a controller E2;

[0042] A first end of the active clamping circuit E1 is electrically connected to the same-name terminal of the primary winding of the transformer T1 and is electrically connected to an input voltage. A second end of the active clamping circuit E1 is electrically connected to the opposite-name terminal of the primary winding of the transformer T1 and the first end of the first switch tube Q1.

[0043] The second end of the first switch tube Q1 is electrically connected to one end of the bias capacitor unit C1, and the second end of the first switch tube Q1 is also electrically connected to a bias voltage V1. The third end of the first switch tube Q1 is connected to the third end of the third switch tube Q3 and the first end of the second switch tube Q2.

[0044] The second end of the second switch tube Q2 is electrically connected to the first output end of the controller E2, and the third end of the second switch tube Q2 is electrically connected to the ground;

[0045] A first end of the third switch tube Q3 is electrically connected to one end of the bias capacitor unit C1, and the first end of the third switch tube Q3 is also electrically connected to a bias voltage V1, and a second end of the third switch tube Q3 is electrically connected to the second output end of the controller E2;

[0046] The other end of the bias capacitor unit C1 is electrically connected to the ground;

[0047] The secondary winding of the transformer T1 is electrically connected to the secondary side loop;

[0048] The controller E2 is also electrically connected to the active clamping circuit E1 and is used to control the on and off of the second switch tube Q2, the third switch tube Q3 and the active clamping circuit E1.

[0049] Specifically, the first output terminal of the controller E2 outputs the second control signal SW2 to control the on / off of the second switch tube Q2 , and the second output terminal of the controller E2 outputs the third control signal SW3 to control the on / off of the third switch tube Q3 .

[0050] See Figure 3 , is a circuit diagram of an active clamping circuit E1. As a specific embodiment of the active clamping circuit E1, the active clamping circuit E1 includes a clamping capacitor unit C2 and a fourth switch tube Q4. One end of the clamping capacitor unit C2 serves as the first end of the active clamping circuit E1 and is electrically connected to the same-name terminal of the primary winding of the transformer T1 and is electrically connected to an input voltage; the other end of the clamping capacitor unit C2 is connected to the first end of the fourth switch tube Q4; the second end of the fourth switch tube Q4 is connected to the third output terminal of the controller E2, and the third end of the fourth switch tube Q4 serves as the second end of the active clamping circuit E1 and is electrically connected to the opposite-name terminal of the primary winding of the transformer T1 and the first end of the first switch tube Q1.

[0051] Specifically, the third output terminal of the controller E2 outputs a fourth control signal SW4 to control the on or off of the fourth switch tube Q4; the first switch tube Q1 and the second switch tube Q2 can both be MOS tubes, or other devices that can achieve the same switching function; in a specific implementation process, the first switch tube Q1 and the second switch tube Q2 are both NMOS enhancement field effect tubes, the first terminals are both drains, the second terminals are both gates, and the third terminals are both sources.

[0052] In combination with the above-mentioned source driving circuit, in this embodiment, a control method for a source-driven switching power supply is provided, which includes:

[0053] Active clamping circuit E1 conduction step: after the magnetizing inductance of transformer T1 is demagnetized, the first switch Q1, the second switch Q2, and the third switch Q3 are all turned off, and the active clamping circuit E1 is controlled to conduct to generate a negative magnetizing current;

[0054] a step of shutting down the active clamping circuit E1, controlling the active clamping circuit E1 to shut down and the third switch tube Q3 to turn on; when the active clamping circuit is shut down and the third switch tube is turned on, a negative excitation current participates in a resonance process between the excitation inductance of the transformer T1, the parasitic capacitance between the first terminal and the third terminal of the first switch tube Q1, and the parasitic capacitance between the first terminal and the third terminal of the second switch tube Q2, thereby releasing energy from the parasitic capacitance; when the voltage at the first terminal of the first switch tube Q1 resonates to the bias voltage V1, or when the voltage between the first terminal and the second terminal of the first switch tube Q1 resonates to zero, the controller E2 controls the third switch tube Q3 to shut down;

[0055] a step of turning on the first switch tube Q1, controlling the first switch tube Q1 to turn on when the negative excitation current further releases energy of the parasitic capacitance between the first terminal and the third terminal of the second switch tube Q2, so that the voltage between the first terminal and the third terminal of the first switch tube Q1 is zero or close to zero;

[0056] In the step of turning on the second switch tube Q2, after the first switch tube Q1 is turned on, when the negative excitation current further releases the energy of the parasitic capacitance between the first terminal and the third terminal of the second switch tube Q2, so that the voltage between the first terminal and the third terminal of the second switch tube Q2 is zero or close to zero, the second switch tube Q2 is controlled to be turned on.

[0057] As a specific embodiment of the active clamping circuit E1, the active clamping circuit E1 includes a clamping capacitor unit C2 and a fourth switch tube Q4. One end of the clamping capacitor unit C2 serves as the first end of the active clamping circuit E1 and is electrically connected to the same-name terminal of the primary winding of the transformer T1 and is electrically connected to an input voltage. The other end of the clamping capacitor unit C2 is connected to the first end of the fourth switch tube Q4. The second end of the fourth switch tube Q4 is connected to the third output end of the controller E2. The third end of the fourth switch tube Q4 serves as the second end of the active clamping circuit E1 and is electrically connected to the opposite-name terminal of the primary winding of the transformer T1 and the first end of the first switch tube Q1. Controlling the active clamping circuit E1 to conduct to generate a negative excitation current specifically includes: controlling the fourth switch tube Q4 to conduct to discharge the clamping capacitor unit C2 to generate the negative excitation current. Controlling the active clamping circuit E1 to shut down specifically includes: controlling the fourth switch tube Q4 to shut down.

[0058] refer to Figure 4 , is the working waveform diagram of the source driving circuit of this embodiment, the following is combined with Figure 4 The control method of this embodiment is described in detail:

[0059] Each working cycle can be divided into six subdivided time periods according to the working state of the source driving circuit.

[0060] During the first time period (t0-t1), the first switch tube Q1, the second switch tube Q2, and the third switch tube Q3 are in the off state, the fourth switch tube Q4 is turned on, the clamping capacitor unit C2 is discharged, and the active clamping circuit E1 generates a negative excitation current;

[0061] During the second time period (t1-t2), the fourth switch tube Q4 is turned off, the third switch tube Q3 is turned on, and the bias capacitor unit C1 is equivalently connected in parallel with the drain-source parasitic capacitance of the second switch tube Q2. The negative excitation current participates in the resonance process of the excitation inductance, the equivalent parallel capacitance, and the drain-source parasitic capacitance of the first switch tube Q1, releasing the energy on the parasitic capacitance; because the equivalent parallel capacitance is much larger than the parasitic capacitance of the drain-source of the first switch tube Q1, the drain-source voltage of the first switch tube Q1 will drop rapidly. When the drain-source voltage of the first switch tube Q1 further resonates and drops to 0, or the drain voltage Vd1 of the first switch tube Q1 drops to the bias voltage V1, the third switch tube Q3 is turned off;

[0062] During the third time period (t2-t3), the negative excitation current continues to release the energy on the drain-source parasitic capacitance of the second switch tube Q2. The first switch tube Q1 is turned on in response to the drain-source voltage Vds2 of the second switch tube Q2 dropping to the point where the gate-source voltage of the first switch tube Q1 reaches its turn-on threshold voltage.

[0063] During the fourth time period (t3-t4), the negative excitation current further releases the remaining energy in the drain-source parasitic capacitance of the second switch tube Q2, providing conditions for achieving zero voltage turn-on of the second switch tube Q2. During this period, the drain voltage Vd1 of the first switch tube Q1 can be equivalently regarded as the drain-source voltage of the second switch tube Q2.

[0064] During the fifth time period (t4-t5), the drain voltage Vd1 of the first switch tube Q1 drops to 0 by resonance, and the second switch tube Q2 is turned on and is turned on at zero voltage. The magnetizing inductor is forwardly magnetized during this time period.

[0065] During the sixth time period (t5-t6), the second switch Q2 is turned off, and the first switch Q1 is turned off in response to the drain-source voltage Vds2 of the second switch Q2 rising to the point where the gate-source voltage of the first switch Q1 does not meet its turn-on threshold voltage. The energy stored in the magnetizing inductor is transferred to the secondary side, and the switching power supply operates in a normal flyback state, which will not be described in detail.

[0066] Where, I_Lm: excitation current;

[0067] Vds2: drain-source voltage of the second switch Q2;

[0068] Vd1: drain voltage waveform of the first switch tube Q1;

[0069] SW4: driving waveform of the fourth switch Q4, i.e., the fourth control signal, which is turned on when high and turned off when low;

[0070] SW3: driving waveform of the third switch Q3, i.e., the third control signal, which is turned on when high and turned off when low;

[0071] SW2: driving waveform of the second switch Q2, i.e., the second control signal, which is turned on when high and turned off when low;

[0072] SW1: driving waveform of the first switch tube Q1, which is turned on when the voltage is high and turned off when the voltage is low.

[0073] The magnetizing inductance is the primary winding of the transformer T1, and the magnetizing current is the current flowing through the primary winding of the transformer T1.

[0074] Second embodiment

[0075] The difference between this embodiment and the first embodiment lies in the operating timing of the fourth switch Q4 of the active clamp circuit E1. Therefore, in this embodiment, only the operating state of the circuit is described in detail. The connection relationship and characteristic points can be referred to the first embodiment.

[0076] In this embodiment, a control method for a source-driven switching power supply is provided, which includes:

[0077] Active clamping circuit E1 conduction step: after the magnetizing inductance of transformer T1 is demagnetized, the first switch Q1 and the second switch Q2 are turned off, and the third switch Q3 is turned on, and the active clamping circuit E1 is controlled to be turned on to generate a negative magnetizing current;

[0078] an active clamping circuit E1 shutoff step, controlling the active clamping circuit E1 to shut off. When the active clamping circuit E1 is shut off, a negative excitation current participates in a resonance process among the excitation inductance of the transformer T1, the parasitic capacitance between the first terminal and the third terminal of the first switching tube Q1, and the parasitic capacitance between the first terminal and the third terminal of the second switching tube Q2, thereby releasing energy from the parasitic capacitance. When the voltage at the first terminal of the first switching tube Q1 resonates to the bias voltage V1, or when the voltage between the first terminal and the second terminal of the first switching tube Q1 resonates to zero, the controller E2 controls the third switching tube Q3 to shut off.

[0079] a step of turning on the first switch tube Q1, controlling the first switch tube Q1 to turn on when the negative excitation current further releases energy of the parasitic capacitance between the first terminal and the third terminal of the second switch tube Q2, so that the voltage between the first terminal and the third terminal of the first switch tube Q1 is zero or close to zero;

[0080] In the step of turning on the second switch tube Q2, after the first switch tube Q1 is turned on, when the negative excitation current further releases the energy of the parasitic capacitance between the first terminal and the third terminal of the second switch tube Q2, so that the voltage between the first terminal and the third terminal of the second switch tube Q2 is zero or close to zero, the second switch tube Q2 is controlled to be turned on.

[0081] As a specific embodiment of the active clamping circuit E1, the active clamping circuit E1 includes a clamping capacitor unit C2 and a fourth switch tube Q4. One end of the clamping capacitor unit C2 serves as the first end of the active clamping circuit E1 and is electrically connected to the same-name terminal of the primary winding of the transformer T1 and is electrically connected to an input voltage. The other end of the clamping capacitor unit C2 is connected to the first end of the fourth switch tube Q4. The second end of the fourth switch tube Q4 is connected to the third output end of the controller E2. The third end of the fourth switch tube Q4 serves as the second end of the active clamping circuit E1 and is electrically connected to the opposite-name terminal of the primary winding of the transformer T1 and the first end of the first switch tube Q1. Controlling the active clamping circuit E1 to conduct to generate a negative excitation current specifically includes: controlling the fourth switch tube Q4 to conduct to discharge the clamping capacitor unit C2 to generate the negative excitation current. Controlling the active clamping circuit E1 to shut down specifically includes: controlling the fourth switch tube Q4 to shut down.

[0082] See also Figure 5 , which is a working waveform diagram of the circuit of the second embodiment of the present invention, and its detailed working states are as follows:

[0083] Each working cycle can be divided into six sub-time periods according to the working state of the circuit.

[0084] During a first time period (t0-t1), the first and second switching transistors Q1 and Q2 are in the off state, while the third switching transistor Q3 remains in the on state. The bias capacitor unit C1 is effectively connected in parallel with the drain-source parasitic capacitance of the second switching transistor Q2. The fourth switching transistor Q4 is turned on, the clamping capacitor unit C2 is discharged, and the active clamping circuit E1 generates a negative excitation current.

[0085] During the second time period (t1-t2), the fourth switch Q4 is turned off, and the negative excitation current participates in the resonance process between the excitation inductance, the equivalent parallel capacitance, and the drain-source parasitic capacitance of the first switch Q1, releasing the energy in the parasitic capacitance. Because the equivalent parallel capacitance is much larger than the drain-source parasitic capacitance of the first switch Q1, the drain-source voltage of the first switch Q1 drops rapidly. When the drain-source voltage of the first switch Q1 further resonates and drops to 0, or when the drain voltage Vd1 of the first switch Q1 drops to V1, the third switch Q3 is turned off.

[0086] During the third time period (t2-t3), the negative excitation current continues to release the energy on the drain-source parasitic capacitance of the second switch tube Q2. The first switch tube Q1 is turned on in response to the drain-source voltage Vds2 of the second switch tube Q2 dropping to the point where the gate-source voltage of the first switch tube Q1 reaches its turn-on threshold voltage.

[0087] During the fourth time period (t3-t4), the drain voltage Vd1 of the first switch tube Q1 drops to 0 by resonance, and the second switch tube Q2 is turned on at zero voltage. The magnetizing inductor is forwardly magnetized during this time period.

[0088] During the fifth time period (t4-t5), the second and third switches Q2 and Q3 are both off, and the drain voltage Vd1 of the first switch Q1 begins to rise in resonance. This period, also known as the dead time, is to prevent the second and third switches Q2 and Q3 from short-circuiting the bias voltage V1 and causing malfunctions in the converter (i.e., the source driver circuit).

[0089] During the sixth time period (t5-t6), the third switch tube Q3 is turned on, and the first switch tube Q1 is turned off in response to the drain-source voltage Vds2 of the second switch tube Q2 rising to the point where the gate-source voltage of the first switch tube Q1 does not meet its turn-on threshold voltage. The energy stored in the magnetizing inductor is transferred to the secondary side circuit, and the switching power supply operates in a normal flyback state, which will not be described in detail.

[0090] It should be understood that although specific embodiments of the present invention are described to facilitate a better understanding of the present invention, other equivalent embodiments exist. The above embodiments are provided by way of illustration and not limitation. Therefore, any modification or replacement of all or part of the technical features of the technical solutions described in the embodiments without departing from the spirit or essence of the present invention shall be deemed to be within the scope of the claims.

Claims

1. A source-driven switching power supply, characterized in that: include: A transformer, a source drive circuit and a secondary side loop, wherein the source drive circuit includes a first switch tube, a second switch tube, a third switch tube, a bias capacitor unit, an active clamping circuit and a controller; The first end of the active clamping circuit is electrically connected to the same-name end of the primary winding of the transformer and is electrically connected to an input voltage, and the second end of the active clamping circuit is electrically connected to the opposite-name end of the primary winding of the transformer and the first end of the first switching tube; The second end of the first switch tube is electrically connected to one end of the bias capacitor unit, and the second end of the first switch tube is also electrically connected to a bias voltage, and the third end of the first switch tube is connected to the third end of the third switch tube and the first end of the second switch tube; The second end of the second switch tube is electrically connected to the first output end of the controller, and the third end of the second switch tube is electrically connected to the ground; The first end of the third switch tube is electrically connected to one end of the bias capacitor unit, and the first end of the third switch tube is also electrically connected to a bias voltage, and the second end of the third switch tube is electrically connected to the second output end of the controller; The other end of the bias capacitor unit is electrically connected to the ground; The secondary winding of the transformer is electrically connected to the secondary side loop; The controller is also electrically connected to the active clamping circuit, and is used to control the conduction and shutdown of the second switching tube, the third switching tube, and the active clamping circuit. The second end of the first switching tube, the second end of the second switching tube, and the first end of the third switching tube are all gates.

2. The source-driven switching power supply according to claim 1, characterized in that: The active clamping circuit includes a clamping capacitor unit and a fourth switching tube. One end of the clamping capacitor unit serves as the first end of the active clamping circuit and is electrically connected to the same-name end of the primary winding of the transformer and is electrically connected to an input voltage. The other end of the clamping capacitor unit is connected to the first end of the fourth switching tube. The second end of the fourth switching tube is connected to the third output end of the controller. The third end of the fourth switching tube serves as the second end of the active clamping circuit and is electrically connected to the opposite-name end of the primary winding of the transformer and the first end of the first switching tube.

3. The source-driven switching power supply according to claim 1, characterized in that: The first switch tube and the second switch tube are both MOS tubes, the first end of the first switch tube and the first end of the second switch tube are both drains, and the third end of the first switch tube and the third end of the second switch tube are both sources.

4. The source-driven switching power supply according to claim 3, characterized in that: The capacity of the bias capacitor unit is a predetermined multiple of the capacity of the parasitic capacitance between the drain and source of the first switch, and the predetermined multiple is greater than 10.

5. A method for controlling a source-driven switching power supply according to any one of claims 1 to 4, characterized in that: In a single switching cycle, including: an active clamping circuit turning-on step, after the magnetizing inductance of the transformer is demagnetized, controlling the first switch tube, the second switch tube, and the third switch tube to be turned off, and controlling the active clamping circuit to be turned on to generate a negative magnetizing current; an active clamping circuit shutoff step, controlling the active clamping circuit to shut off and the third switch to turn on; when the active clamping circuit is shut off and the third switch is turned on, the negative excitation current participates in a resonance process of the transformer's excitation inductance, the parasitic capacitance between the first terminal and the third terminal of the first switch, and the parasitic capacitance between the first terminal and the third terminal of the second switch, thereby releasing energy in the parasitic capacitance; and when the voltage at the first terminal of the first switch resonates to the bias voltage, or when the voltage between the first terminal and the second terminal of the first switch resonates to zero, the controller controls the third switch to shut off; a first switching tube turning on step, controlling the first switching tube to turn on when the negative excitation current further releases energy of the parasitic capacitance between the first terminal and the third terminal of the second switching tube so that the voltage between the first terminal and the third terminal of the first switching tube is zero or close to zero; The second switch tube is turned on in a step of: after the first switch tube is turned on, when the negative excitation current further releases the energy of the parasitic capacitance between the first terminal and the third terminal of the second switch tube, so that the voltage between the first terminal and the third terminal of the second switch tube is zero or close to zero, the second switch tube is controlled to be turned on.

6. The control method of the source-driven switching power supply according to claim 5, characterized in that: The active clamping circuit includes a clamping capacitor unit and a fourth switching tube. One end of the clamping capacitor unit serves as a first end of the active clamping circuit and is electrically connected to the same-name end of the primary winding of the transformer and is electrically connected to an input voltage. The other end of the clamping capacitor unit is connected to the first end of the fourth switching tube. The second end of the fourth switching tube is connected to the third output end of the controller. The third end of the fourth switching tube serves as a second end of the active clamping circuit and is electrically connected to the opposite-name end of the primary winding of the transformer and the first end of the first switching tube. Controlling the active clamping circuit to turn on to generate a negative excitation current specifically includes: controlling the fourth switch tube to turn on, so that the clamping capacitor unit discharges to generate a negative excitation current; controlling the active clamping circuit to turn off specifically includes: controlling the fourth switch tube to turn off.

7. A method for controlling a source-driven switching power supply according to any one of claims 1 to 4, characterized in that: In a single switching cycle, including: an active clamping circuit conducting step, after the magnetizing inductance of the transformer is demagnetized, controlling the first switch tube and the second switch tube to be turned off and the third switch tube to be turned on, and controlling the active clamping circuit to be turned on to generate a negative magnetizing current; an active clamping circuit shutoff step, controlling the active clamping circuit to shut off; when the active clamping circuit is shut off, the negative excitation current participates in a resonance process of the transformer's excitation inductance, the parasitic capacitance between the first terminal and the third terminal of the first switching tube, and the parasitic capacitance between the first terminal and the third terminal of the second switching tube, so that energy of the parasitic capacitance is released; when the voltage at the first terminal of the first switching tube resonates to the bias voltage, or when the voltage between the first terminal and the second terminal of the first switching tube resonates to zero, the controller controls the third switching tube to shut off; a first switching tube turning on step, controlling the first switching tube to turn on when the negative excitation current further releases energy of the parasitic capacitance between the first terminal and the third terminal of the second switching tube so that the voltage between the first terminal and the third terminal of the first switching tube is zero or close to zero; The second switch tube is turned on in a step of: after the first switch tube is turned on, when the negative excitation current further releases the energy of the parasitic capacitance between the first terminal and the third terminal of the second switch tube, so that the voltage between the first terminal and the third terminal of the second switch tube is zero or close to zero, the second switch tube is controlled to be turned on.

8. The control method of the source-driven switching power supply according to claim 7, characterized in that: The active clamping circuit includes a clamping capacitor unit and a fourth switching tube. One end of the clamping capacitor unit serves as a first end of the active clamping circuit and is electrically connected to the same-name end of the primary winding of the transformer and is electrically connected to an input voltage. The other end of the clamping capacitor unit is connected to the first end of the fourth switching tube. The second end of the fourth switching tube is connected to the third output end of the controller. The third end of the fourth switching tube serves as a second end of the active clamping circuit and is electrically connected to the opposite-name end of the primary winding of the transformer and the first end of the first switching tube. Controlling the active clamping circuit to turn on to generate a negative excitation current specifically includes: controlling the fourth switch tube to turn on, so that the clamping capacitor unit discharges to generate a negative excitation current; controlling the active clamping circuit to turn off specifically includes: controlling the fourth switch tube to turn off.

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