ZVS forward converter without additional winding

Abstract

The present invention discloses a ZVS forward converter without additional windings. Primary power MOS transistors Q1 and Q2 are alternately turned on to ensure that the forward isolated output transformer is reset and that the primary power MOS transistor Q1 is turned on at zero voltage (ZVS). The voltage of the primary winding Np after MOS transistor Q1 is turned off is determined by the body diode of MOS transistor Q2 and the voltage across the resonant capacitor Cr. The drain-source voltage Vds1(t) of MOS transistor Q1 is the sum of the input voltage VIN and the voltage across the resonant capacitor Cr. Current is alternately exchanged between MOS transistors Q1 and Q2 within a switching cycle. The present invention reduces the winding complexity and manufacturing cost of the forward isolated output transformer. Furthermore, by eliminating additional windings and the leakage inductance between the windings, the drain-source voltage variation of the primary MOS transistor Q1 can be smoother.

Description

Technical Field

[0001] The present invention relates to a ZVS forward converter without additional winding and a control method thereof. Background Art

[0002] Forward DC-DC converters lack a reset function for their isolated output transformers, necessitating additional circuitry to accomplish this. Several reset methods are currently available, including RCD circuits, reset windings, active demagnetization reset, and resonant reset. Active demagnetization reset and resonant reset enable the isolated output transformer to operate in the first and third quadrants, further reducing its size.

[0003] The authorized invention patent "Zero Voltage Switching Forward DC-DC Converter and Control Method Thereof" (Patent No. ZL202011194205.X) provides a resonant reset method to help reset the forward isolation output transformer and enable the primary power MOS of the forward DC-DC converter to be turned on under zero voltage conditions. However, in this patent solution (such as Figure 1 As shown in Figure 1, the forward-type isolated output transformer requires an additional winding Nt to reset the resonance and enable the primary power MOS to conduct under zero-voltage conditions. Therefore, this solution still has the disadvantage of adding an additional winding Nt, which complicates the winding layout of the forward-type isolated output transformer. This is particularly true for planar transformers. Increasing the number of windings in a planar transformer design increases the transformer's complexity and manufacturing cost. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a ZVS forward converter without additional windings and a control method thereof.

[0005] To solve the above technical problems, the present invention provides a ZVS forward converter without additional windings and a control method thereof: the primary power MOS tubes Q1 and Q2 are alternately turned on (basically alternately turned on) to ensure that the forward isolation output transformer is reset and the primary power MOS tube Q1 is turned on at zero voltage ZVS.

[0006] That is, compared with the prior art, the additional winding Nt of the forward isolation output transformer is omitted.

[0007] As an improvement of the ZVS forward converter without additional winding of the present invention:

[0008] The voltage of the primary winding Np after the MOS transistor Q1 is turned off is determined by the body diode of the MOS transistor Q2 and the voltage on the resonant capacitor Cr. The drain-source voltage Vds1(t) of the MOS transistor Q1 is the sum of the input voltage VIN and the voltage on the resonant capacitor Cr.

[0009] Current is exchanged alternately between MOS Q1 and MOS Q2 during one switching cycle.

[0010] As a further improvement of the ZVS forward converter without additional winding of the present invention (this corresponds to the output inductor current operating under discontinuous current):

[0011] The forward-type isolated output transformer includes a primary winding Np and a secondary winding Ns, wherein the primary winding Np and the secondary winding Ns are tightly coupled via a magnetic core T; the output of the secondary winding Ns is connected to the cathode of the output diode D1 and the cathode of the freewheeling diode D2, respectively; the anode of the secondary output diode D1 and the anode of the freewheeling diode D2 are connected, and are connected to the negative terminal of the output filter capacitor Cf and the negative terminal of the output load; the cathode of the freewheeling diode D2 is connected to one end of the secondary output inductor L; and the other end of the secondary output inductor L is connected to the positive terminal of the filter capacitor Cf and the positive terminal of the output load.

[0012] The resonant capacitor Cr is connected in parallel with the diode Dr;

[0013] V IN is the primary input voltage, V IN It is connected to the anode of the diode Dr and the same-name terminal of the forward isolation output transformer Np; the cathode of the diode Dr is connected to the drain of the primary power MOS tube Q2, and the gate of the primary power MOS tube Q2 is connected to the output terminal DRF of the corresponding control circuit module M; the non-same-name end of the primary winding Np is connected to the source of the primary power MOS tube Q2 and the drain of the primary power MOS tube Q1; the gate of the primary power MOS tube Q1 is connected to the output terminal DR of the corresponding control circuit module M, and the source of the primary power MOS tube Q1 is grounded via the detection resistor Rs.

[0014] As a further improvement of the ZVS forward converter without additional windings of the present invention (this corresponds to the output inductor current operating in continuous current mode):

[0015] It also includes an Ls, which is a magnetic amplifier inductor Ls or a saturation inductor Ls; the output of the same-name end of the secondary winding Ns is connected to one end of Ls, and the other end of Ls is connected to the cathode of the freewheeling diode D2.

[0016] Note: The function of Ls is to provide a short blocking time to ensure that the primary power MOS tube Q1 is turned on under zero voltage conditions.

[0017] As a further improvement of the ZVS forward converter without additional windings of the present invention, the turn-on and turn-off times include the following:

[0018] The primary power MOS tube Q1 is turned off at t0;

[0019] t0~t1: When the gate drive DR of the primary power MOS tube Q1 is zero, the primary power MOS tube Q1 starts to turn off quickly, and the current in the primary side Np of the forward isolation output transformer winding is only the excitation current i of the forward isolation output transformer winding Np. Lm (t);

[0020] t1~t2: The control circuit module M outputs a DRF drive pulse to turn on the MOS tube Q2, while the MOS tube Q1 is turned off;

[0021] t2~t3: After t3, the voltage Vc(t) on the resonant capacitor Cr is zero; the forward isolation output transformer completes the reset operation;

[0022] t3-t4: The drain-source capacitance voltage of the primary power MOS tube Q1 is equal to the input DC voltage VIN. The duration from t3 to t4 is used to prepare the primary power MOS tube Q1 for zero voltage ZVS conduction.

[0023] t4-t5: Due to the reverse excitation peak current of the excitation inductor Lm, the drain-source capacitor voltage of the primary power MOS tube Q1 drops from the input DC voltage VIN to zero at time t5;

[0024] t5-t6: During t5-t6, the current in the primary winding Np of the forward isolation output transformer decreases from negative current to zero and then converts to positive current;

[0025] t6~t7: Due to the conduction of the primary power MOS tube Q1 and the input DC voltage VIN, the reverse excitation current i of the excitation inductor Lm Lm (t) decreases to zero; the secondary side output inductor L current i L (t) continue to increase;

[0026] t7~t0: The detection circuit of the control circuit module M detects the output inductor current; when the instantaneous value of the output inductor current reaches the predetermined value at time t0, the excitation current i of the excitation inductor Lm Lm (t) also reaches the positive peak, the output pulse DR of the control circuit module M is zero, the primary power MOS tube Q1 is turned off and enters the next switching cycle.

[0027] As a further improvement of the ZVS forward converter without additional winding of the present invention:

[0028] The MOS transistor Q2 is a PMOS transistor, and its source is connected to the input voltage VIN. The control circuit module M only controls the gate potential of the MOS transistor Q2 to control the on / off switching of the MOS transistor Q2. The control circuit needs to control the on / off switching of the MOS transistor Q2 in the order of t0, t0-t1, t1-t2, t2-t3, t3-t4, t4-t5, t5-t6, t6-t7, and t7-t0 (i.e., the same as above).

[0029] As a further improvement of the ZVS forward converter without additional winding of the present invention:

[0030] During the period from t4 to t5, the reverse excitation peak current in the primary winding Np of the forward-type isolated output transformer first reduces the drain-source capacitor voltage of the primary power MOSFET Q1 from the input DC voltage VIN to zero at time t5, creating the condition for MOSFET Q1 to turn on under zero-voltage conditions. At this time, Ls will be subjected to the output voltage of the secondary winding Ns of the forward-type isolated output transformer. As time passes, MOSFET Q1 completes zero-voltage turn-on, and after a fixed volt-second product, Ls switches from off to on. The secondary winding Ns of the forward-type isolated output transformer outputs current through Ls.

[0031] As a further improvement of the ZVS forward converter without additional winding of the present invention:

[0032] During the period from t4 to t5, the reverse excitation peak current in the primary winding Np of the forward-type isolated output transformer first reduces the drain-source capacitor voltage of the primary power MOSFET Q1 from the input DC voltage VIN to zero at time t5, creating the condition for MOSFET Q1 to turn on under zero-voltage conditions. At this time, Ls will be subjected to the output voltage of the secondary winding Ns of the forward-type isolated output transformer. As time passes, MOSFET Q1 completes zero-voltage turn-on, and after a fixed volt-second product, Ls switches from off to on. The secondary winding Ns of the forward-type isolated output transformer outputs current through Ls.

[0033] The main benefits of this invention are that it can eliminate one transformer winding, simplifying the transformer winding layout. Compared to ZL202011194205.X, this invention offers the following technical advantages: it reduces the winding complexity and manufacturing cost of the forward-type isolated output transformer; and, by eliminating the additional winding and the leakage inductance between the windings, it can achieve smoother changes in the drain-source voltage of the primary MOS Q1. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0035] Figure 1 This is the resonant reset circuit of ZL202011194205.X working under discontinuous current.

[0036] Figure 2 A circuit diagram of a ZVS forward converter without an additional winding in Example 1, in which the output inductor current operates at a discontinuous current;

[0037] Figure 3 To correspond Figure 2 The waveforms of MOS Q1's drain-source voltage, resonant capacitor voltage, excitation current and output inductor current;

[0038] Figure 4 This is a circuit diagram of a ZVS forward converter without an additional winding, in which the output inductor current operates at a discontinuous current according to Example 2;

[0039] Figure 5 This is a circuit diagram of a ZVS forward converter without an additional winding, in which the output inductor current of Example 3 operates at a continuous current;

[0040] Figure 6 To correspond Figure 5 The waveforms of MOS Q1's drain-source voltage, resonant capacitor voltage, excitation current and output inductor current;

[0041] Figure 7 This is a circuit diagram of a ZVS forward converter without an additional winding, in which the output inductor current of Example 4 operates at a continuous current. DETAILED DESCRIPTION

[0042] The present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0043] The present invention is based on patent ZL202011194205.X, omitting the extra winding Nt and simplifying the winding layout of the forward-type isolated output transformer.

[0044] Example 1: The output inductor current operates under discontinuous current, a ZVS forward converter without additional windings, such as Figure 2 As mentioned above, Figure 1 In comparison, the additional winding Nt of the forward isolation output transformer is omitted, and the primary power MOS tubes Q1 and Q2 are basically turned on alternately to ensure that the forward isolation output transformer is reset and the primary power MOS tube Q1 is turned on at zero voltage ZVS.

[0045] The details are as follows:

[0046] The forward-type isolated output transformer includes a primary winding Np and a secondary winding Ns, wherein the primary winding Np and the secondary winding Ns are tightly coupled via a magnetic core T; the output of the secondary winding Ns is connected to the cathode of the output diode D1 and the cathode of the freewheeling diode D2, respectively; the anode of the secondary output diode D1 and the anode of the freewheeling diode D2 are connected, and are connected to the negative end of the output filter capacitor Cf and the negative end of the output load; the cathode of the freewheeling diode D2 is connected to one end of the secondary output inductor L; and the other end of the secondary output inductor L is connected to the positive end of the filter capacitor Cf and the positive end of the output load.

[0047] The resonant capacitor Cr is connected in parallel with the diode Dr.

[0048] V IN is the primary input voltage, V IN It is connected to the anode of the diode Dr and the same-name terminal of the forward isolation output transformer Np; the cathode of the diode Dr is connected to the drain of the primary power MOS tube Q2, and the gate of the primary power MOS tube Q2 is connected to the output terminal DRF of the corresponding control circuit module M; the non-same-name end of the primary winding Np is connected to the source of the primary power MOS tube Q2 and the drain of the primary power MOS tube Q1; the gate of the primary power MOS tube Q1 is connected to the output terminal DR of the corresponding control circuit module M, and the source of the primary power MOS tube Q1 is grounded via the detection resistor Rs.

[0049] The corresponding control circuit module M is constructed using conventional technology, so it will not be elaborated in detail in the present invention.

[0050] Figure 3 is the corresponding switching waveform.

[0051] The working process of alternating conduction of the primary power MOS tubes Q1 and Q2 to ensure that the forward isolation output transformer is reset and the primary power MOS tube Q1 is turned on at zero voltage ZVS is as follows:

[0052] According to the principle of the forward-type isolated output transformer, the current i in the primary winding Np of the forward-type isolated output transformer is P (t) The current i is output from the secondary side inductor L L (t) is converted to the primary current i L (t) / N (N is the primary-to-secondary winding turns ratio of the forward-type isolated output transformer) plus the excitation current i of the primary winding Np of the forward-type isolated output transformer Lm (t), that is:

[0053] i P (t) = i Lm (t)+i L (t) / N

[0054] Assume that the secondary output inductor current works in discontinuous mode, such as Figure 3As shown in the switching waveform, the primary power MOS tube Q1 is turned off at t0.

[0055] t0~t1: Under the control of the corresponding control circuit module M, when the gate drive DR of the primary power MOS tube Q1 is zero, it starts to turn off quickly, and the current i in the primary winding Np of the forward isolation output transformer P (t) charges the drain-source capacitance of the primary power MOS tube Q1. Since the drain-source capacitance of the primary power MOS tube Q1 is low, the drain-source voltage Vds1(t) of the primary power MOS tube Q1 increases rapidly from zero to the input DC voltage VIN. When the drain-source voltage Vds1(t) of the primary power MOS tube Q1 is equal to the input DC voltage VIN, the voltage of the primary winding Np of the forward isolation output transformer drops to zero. Since the voltage of the primary winding Np drops to zero, the voltage of the secondary winding Ns also drops to zero. The current in the secondary output diode D1 drops to zero, and the current i L (t) The current is continued through the freewheeling diode D2. Since the current in the secondary output diode D1 drops to zero, the current in the primary winding Np of the forward-type isolated output transformer is only the excitation current i of the forward-type isolated output transformer winding Np. Lm (t).

[0056] t1~t2: Since the primary power MOS tube Q1 has been turned off, the excitation current i in the primary winding Np of the forward isolation output transformer Lm (t) Resonance occurs through the body diode of the primary power MOS tube Q2 and the resonant capacitor Cr. The excitation current i of the primary winding Np is Lm (t) decreases from its maximum resonance to zero; the voltage Vc(t) on the resonant capacitor Cr increases from zero resonance to the peak value. Lm (t) Through the body diode within the primary power MOS transistor Q2, the drain-source voltage Vds2 of the primary power MOS transistor Q2 is zero. During the period t1 to t2, since the drain-source voltage Vds2 of the primary power MOS transistor Q2 is zero, the primary power MOS transistor Q2 can be turned on with zero voltage. That is, the corresponding control circuit module M outputs a DRF drive pulse to turn on the MOS transistor Q2; while the MOS transistor Q1 is turned off.

[0057] t2~t3: As the primary power MOS tube Q2 continues to conduct, the resonant capacitor Cr and the excitation inductance Lm of the primary winding Np continue to resonate; the voltage Vc(t) on the resonant capacitor Cr decreases from the peak resonance to zero; the excitation current i of the excitation inductance Lm of the primary winding Np Lm (t) increases from zero reverse resonance to reverse peak. After time t3, the voltage Vc(t) on the resonant capacitor Cr is zero; thus, the forward isolation output transformer completes the reset operation. Figure 3Where t1 to t3 correspond to the resonant reset time of the forward-type isolation output transformer, which is determined by the magnetizing inductance Lm and the resonant capacitance Cr of the forward-type isolation output transformer.

[0058] t3~t4: As the primary power MOS tube Q2 continues to conduct, the resonant capacitor Cr and the magnetizing inductance Lm of the primary winding Np continue to resonate; when the voltage on the resonant capacitor Cr changes from zero to negative, the diode Dr connected in parallel with the resonant capacitor Cr conducts; thus, the voltage on the primary winding Np is the primary power MOS tube Q2 conduction voltage + the diode Dr conduction voltage, and the sum of the two is essentially zero. The voltage Vc(t) on the resonant capacitor Cr is also essentially zero; and since the voltage on the primary winding Np is essentially zero, the magnetizing current i Lm (t) Maintains a constant reverse peak current. During this duration, the drain-source capacitance voltage of the primary power MOSFET Q1 is equal to the input DC voltage VIN. The duration t3-t4 is used to prepare the primary power MOSFET Q1 for zero voltage (ZVS) turn-on.

[0059] t4-t5: Under the control of the corresponding control circuit module M, when the primary power MOS transistor Q1 is required to be turned on, the corresponding control circuit module M first outputs a pulse DRF of zero at time t4, turning off the primary power MOS transistor Q2. Due to the reverse excitation peak current of the excitation inductor Lm, the drain-source capacitor voltage of the primary power MOS transistor Q1 drops from the input DC voltage VIN to zero at time t5.

[0060] t5~t6: After t5, the drain-source capacitor voltage of the primary power MOS tube Q1 is zero, and the corresponding control circuit module M can provide a driving pulse DR to the primary power MOS tube Q1 to make the primary power MOS tube Q1 conduct at zero voltage. Lm (t) decreases. Output inductor current i L (t) starts to increase from zero, the current in the primary winding Np of the forward isolation output transformer is the excitation current i Lm (t) + secondary side output inductor L current i L (t) is converted to the primary current i L (t) / N; During the period from t5 to t6, the current in the primary winding Np of the forward isolation output transformer decreases from negative current to zero and then converts to positive current.

[0061] t6~t7: Due to the conduction of the primary power MOS tube Q1 and the input DC voltage VIN, the reverse excitation current i of the excitation inductor Lm Lm (t) decreases to zero. The secondary output inductor L current i L (t) continues to increase. The current in the primary winding Np of the forward isolation output transformer is a positive current.

[0062] t7~t0: Due to the conduction of the primary power MOS tube Q1 and the input DC voltage VIN, the excitation current i of the excitation inductor Lm Lm (t) starts to increase positively from zero, and the output inductor current i L (t) continues to increase. The corresponding control circuit module M has a corresponding detection circuit to detect the output inductor current; when the instantaneous value of the output inductor current reaches the predetermined value at time t0, the excitation current i of the excitation inductor Lm Lm (t) also reaches the positive peak value, and the corresponding output pulse DR of the control circuit module M is zero, and the primary power MOS tube Q1 is turned off and enters the next switching cycle.

[0063] like Figure 3 The output inductor current i L (t) is the discontinuous mode operation, corresponding to the above switching period from t0 to t7, Vc(t), Vds1(t), i Lm (t), i L (t) waveform;

[0064] according to Figure 3 , we can know that: Figure 2 The circuit of Example 1 is capable of resonating and resetting the windings of the forward-type isolated output transformer, and enabling MOS transistor Q1 to conduct under zero-voltage conditions. Because the additional winding Nt is omitted, the voltage across the primary winding Np of MOS transistor Q1 after it is turned off is determined by the body diode of MOS transistor Q2 and the voltage across the resonant capacitor Cr. The drain-source voltage Vds1(t) of MOS transistor Q1 is the sum of the input voltage VIN and the voltage across the resonant capacitor Cr.

[0065] like Figure 3 As shown in the figure, the duration Ton during which the output inductor current iL(t) is greater than zero varies with the output current Io and voltage Vo. The output inductor current duration Ton can be greater than or less than the forward-type isolated output transformer resonant reset time. The time period t3 to t4 is used to store the magnetizing current i of the magnetizing inductor Lm. Lm (t) Reverse peak current, that is, maintaining the reverse peak current is to provide freedom for zero voltage switching regulation of the primary power MOS tube Q1.

[0066] If the duration Ton during which the output inductor current iL(t) is greater than zero is greater than the resonant reset time of the forward isolation output transformer, it is necessary to increase the time period t3 to t4 to preserve the magnetizing current iL of the magnetizing inductor Lm. Lm (t) is the reverse peak current. So when the output inductor current i LAfter (t) drops to zero, when the primary power MOS tube Q1 starts to conduct, the excitation current i of the magnetizing inductor Lm is Lm The peak reverse current at (t) can be used to establish the zero-voltage turn-on condition for MOS transistor Q1. This requires a corresponding control circuit module M to detect the output inductor current iL(t) to determine when it decays to zero and to determine whether the forward-type isolated output transformer resonant reset is complete to determine when MOS transistor Q2 is turned off.

[0067] If the duration Ton during which the output inductor current iL(t) is greater than zero is less than the resonant reset time of the forward isolation output transformer, the time period t3 to t4 is not required to store the magnetizing current iL of the magnetizing inductor Lm. Lm (t) reverse peak current. So when the output inductor current i L After (t) drops to zero and the forward isolation output transformer resonant reset time is over, when the primary power MOS tube Q1 needs to start conducting, the excitation current i of the magnetizing inductor Lm is reduced due to the shutdown of the primary power MOS tube Q2. Lm The peak reverse current at (t) can be used to establish the zero-voltage turn-on condition for the primary-side power MOSFET Q1. This requires a corresponding control circuit module M to detect the output inductor current iL(t) to determine when it decays to zero and to determine whether the forward-type isolated output transformer resonant reset is complete to determine when MOSFET Q2 is turned off.

[0068] Figure 2 In the illustrated embodiment 1, both primary-side power MOS transistors Q1 and Q2 are NMOS transistors. MOS transistors Q1 and Q2 are cascaded, alternately conducting with a dead time. That is, after MOS transistor Q1 is turned off, a dead time must pass before MOS transistor Q2 is turned on, and vice versa. The gate and source of MOS transistor Q2 fluctuate between zero voltage and the input voltage VIN + Vcr(t) as MOS transistor Q1 turns on and off. This requires a half-bridge drive circuit in the corresponding control circuit module M to drive DR and DRF pulses to the gates of MOS transistors Q1 and Q2. Half-bridge drive circuits are conventional technology and are therefore not described in detail in this disclosure.

[0069] In summary, according to the alternating current between MOS Q1 and MOS Q2 within a switching cycle (including Figure 3 ), since the extra winding is omitted and the leakage inductance between the windings is omitted, the drain-source voltage variation of the primary MOS Q1 can be made smoother.

[0070] Example 2: Output inductor current operates at discontinuous current, another ZVS forward converter without additional winding, such as Figure 4As described above, MOS Q1 and Q2 are NMOS and PMOS respectively, and the half-bridge drive circuit can be omitted in the corresponding control circuit module M. As in Example 1, the output inductor current also operates in discontinuous mode. The drain-source voltage Vds1(t) of MOS Q1, the output inductor current iL(t), the resonant capacitor voltage Vc(t) and the excitation current i of the forward isolation output transformer are Lm (t) Waveform and Figure 3 consistent.

[0071] The details are as follows:

[0072] The forward-type isolated output transformer includes a primary winding Np and a secondary winding Ns, wherein the primary winding Np and the secondary winding Ns are tightly coupled via a magnetic core T; the output of the secondary winding Ns is connected to the cathode of the output diode D1 and the cathode of the freewheeling diode D2, respectively; the anode of the secondary output diode D1 and the anode of the freewheeling diode D2 are connected, and are connected to the negative end of the output filter capacitor Cf and the negative end of the output load; the cathode of the freewheeling diode D2 is connected to one end of the secondary output inductor L; and the other end of the secondary output inductor L is connected to the positive end of the filter capacitor Cf and the positive end of the output load.

[0073] The resonant capacitor Cr is connected in parallel with the diode Dr.

[0074] V IN is the primary input voltage, V IN The primary power MOS transistor Q2 is connected to the source and the same-name terminal of the forward isolation output transformer Np. The drain of the primary power MOS transistor Q2 is connected to the anode of the diode Dr. The gate of the primary power MOS transistor Q2 is connected to the output terminal DRF of the corresponding control circuit module M.

[0075] The cathode of the diode Dr and the non-coincident end of the primary winding Np are respectively connected to the drain of the primary power MOS transistor Q1. The gate of the primary power MOS transistor Q1 is connected to the output end DR of the corresponding control circuit module M. The source of the primary power MOS transistor Q1 is connected to the ground via the detection resistor Rs.

[0076] The operating process of Example 2 is essentially the same as that of Example 1; the only difference is that MOS transistor Q2 is a PMOS transistor. Its source is connected to the input voltage VIN. The corresponding control circuit module M can simply control the gate potential of MOS transistor Q2 to control the on / off timing of MOS transistor Q2. The corresponding control circuit only needs to control the on / off timing of MOS transistor Q2 in the same manner as MOS transistor Q2 in Example 1.

[0077] Example 3, corresponding to Example 1 Figure 2 For example, when the output inductor current is required to operate in continuous mode, a magnetic amplifier inductor Ls (or saturation inductor Ls) needs to be added; Figure 5 As shown in Figure 1, the function of the magnetic amplifier inductor Ls (or saturation inductor Ls) is to provide a short blocking time to ensure that the primary power MOS transistor Q1 is turned on under zero voltage conditions. The operating principle of this magnetic amplifier inductor Ls (or saturation inductor Ls) in the circuit is the same as that described in patent ZL202011194205.X. The output inductor current is in continuous mode. The voltage and current waveforms of the circuit are shown as follows: Figure 6 shown.

[0078] Specifically, the output of the same-name terminal of the secondary winding Ns is connected to one end of a magnetic amplifier inductor Ls (or a saturation inductor Ls), the other end of the magnetic amplifier inductor Ls (or a saturation inductor Ls) is connected to the cathode of the freewheeling diode D2, and the rest are connected to the Figure 2 Equivalent.

[0079] The operating process of Example 3 differs from that of Example 1 in that the output inductor current operates in continuous current mode. When MOS transistor Q1 begins conducting in the next switching cycle, because the current iL(t) in the output inductor L is significantly greater than zero, if the short blocking time created by the magnetic amplifier inductor Ls (or the saturation inductor Ls) were not present, the reverse excitation peak current in the primary winding Np of the forward-type isolation output transformer would immediately be coupled out through windings Np and Ns, preventing the MOS transistor Q1 from conducting under zero-voltage conditions. However, with the short blocking time created by the magnetic amplifier inductor Ls (or the saturation inductor Ls), the reverse excitation peak current in the primary winding Np of the forward-type isolation output transformer can, during the period t4 to t5, first reduce the drain-source capacitor voltage of the primary power MOS transistor Q1 from the input DC voltage VIN to zero at time t5, creating the conditions for the MOS transistor Q1 to conduct under zero-voltage conditions. At this time, the magnetic amplifier inductor Ls (or the saturated inductor Ls) will be subjected to the output voltage of the secondary winding Ns of the forward-type isolation output transformer. As time passes, the MOS tube Q1 has completed zero-voltage conduction. After a fixed volt-by-second product, the magnetic amplifier inductor Ls (or the saturated inductor Ls) switches from cutoff to conduction. The secondary winding Ns of the forward-type isolation output transformer outputs current through the magnetic amplifier inductor Ls (or the saturated inductor Ls).

[0080] Example 4, corresponding to Example 2 Figure 4 For example, when the output inductor current is required to operate in continuous mode, a magnetic amplifier inductor Ls (or saturation inductor Ls) needs to be added; Figure 7 As shown;

[0081] The function of the magnetic amplifier inductor Ls (or saturation inductor Ls) is to provide a short blocking time to ensure that MOS Q1 is turned on under zero voltage conditions. The operating principle of this magnetic amplifier inductor Ls (or saturation inductor Ls) in the circuit is the same as that described in patent ZL202011194205.X. The output inductor current is in continuous mode. The voltage and current waveforms of this circuit are as follows: Figure 6 shown.

[0082] Specifically, the output of the same-name terminal of the secondary winding Ns is connected to one end of a magnetic amplifier inductor Ls (or a saturation inductor Ls), the other end of the magnetic amplifier inductor Ls (or a saturation inductor Ls) is connected to the cathode of the freewheeling diode D2, and the rest are connected to the Figure 4 Equivalent.

[0083] The operating process of Example 4 differs from that of Example 2 in that the output inductor current operates in continuous current mode. When MOS transistor Q1 begins conducting in the next switching cycle, because the current iL(t) in the output inductor L is significantly greater than zero, if the short blocking time created by the magnetic amplifier inductor Ls (or the saturation inductor Ls) were not present, the reverse excitation peak current in the primary winding Np of the forward-type isolation output transformer would immediately be coupled out through windings Np and Ns, preventing the MOS transistor Q1 from conducting under zero-voltage conditions. However, with the short blocking time created by the magnetic amplifier inductor Ls (or the saturation inductor Ls), the reverse excitation peak current in the primary winding Np of the forward-type isolation output transformer can, during the period t4 to t5, initially reduce the drain-source capacitor voltage of the primary power MOS transistor Q1 from the input DC voltage VIN to zero at time t5, creating the conditions for the MOS transistor Q1 to conduct under zero-voltage conditions. At this time, the magnetic amplifier inductor Ls (or the saturated inductor Ls) will be subjected to the output voltage of the secondary winding Ns of the forward-type isolation output transformer. As time passes, the MOS tube Q1 has completed zero-voltage conduction. After a fixed volt-by-second product, the magnetic amplifier inductor Ls (or the saturated inductor Ls) switches from cutoff to conduction. The secondary winding Ns of the forward-type isolation output transformer outputs current through the magnetic amplifier inductor Ls (or the saturated inductor Ls).

[0084] In each embodiment, the output diode D1 and the freewheeling diode D2 have conduction losses. To reduce the conduction losses of the output diode D1 and the freewheeling diode D2, the output diode D1 and the freewheeling diode D2 can be replaced with MOS transistors to reduce the conduction losses, i.e., synchronous rectification.

[0085] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples and is subject to numerous variations. All variations that can be directly derived or conceived by a person of ordinary skill in the art from the disclosure of the present invention are considered to be within the scope of protection of the present invention.

Claims

1. A ZVS forward converter without an additional winding, characterized by: The primary power MOS tubes Q1 and Q2 are alternately turned on to ensure that the forward isolation output transformer is reset and the primary power MOS Q1 is turned on at zero voltage ZVS. The voltage across the primary winding Np after MOS transistor Q1 is turned off is determined by the body diode of MOS transistor Q2 and the voltage across the resonant capacitor Cr. The drain-source voltage Vds1(t) of MOS transistor Q1 is the sum of the input voltage VIN and the voltage across the resonant capacitor Cr. The voltage Vc(t) across the resonant capacitor Cr increases from zero resonance to peak value, and decreases from peak resonance to zero. The resonant reset time of the voltage Vc(t) across the resonant capacitor Cr is determined by the magnetizing inductance Lm of the forward isolation output transformer and the resonant capacitor Cr. Current is exchanged between MOS Q1 and MOS Q2 during one switching cycle; The MOS transistor Q2 is a PMOS transistor, and its source is connected to the input voltage VIN. The control circuit module M only controls the gate potential of the MOS transistor Q2 to control the on and off of the MOS transistor Q2. The control circuit needs to control the on and off times of the MOS transistor Q2 to be t0, t0-t1, t1-t2, t2-t3, t3-t4, t4-t5, t5-t6, t6-t7, and t7-t0. The conduction end time includes the following: The primary power MOS tube Q1 is turned off at t0; t0~t1: When the gate drive DR of the primary power MOS tube Q1 is zero, the primary power MOS tube Q1 starts to turn off quickly, and the current in the primary side Np of the forward isolation output transformer winding is only the excitation current i of the forward isolation output transformer winding Np. Lm (t); t1~t2: The control circuit module M outputs a DRF drive pulse to turn on the MOS tube Q2, while the MOS tube Q1 is turned off; t2~t3: After t3, the voltage Vc(t) on the resonant capacitor Cr is zero; the forward isolation output transformer completes the reset operation; t3-t4: The drain-source capacitance voltage of the primary power MOS tube Q1 is equal to the input DC voltage VIN. The duration from t3 to t4 is used to prepare the primary power MOS tube Q1 for zero voltage ZVS conduction. t4-t5: Due to the reverse excitation peak current of the excitation inductor Lm, the drain-source capacitor voltage of the primary power MOS tube Q1 drops from the input DC voltage VIN to zero at time t5; t5-t6: During t5-t6, the current in the primary winding Np of the forward isolation output transformer decreases from negative current to zero and then converts to positive current; t6~t7: Due to the conduction of the primary power MOS tube Q1 and the input DC voltage VIN, the reverse excitation current i of the excitation inductor Lm Lm (t) decreases to zero; Secondary side output inductor L current i L (t) continue to increase; t7~t0: The detection circuit of the control circuit module M detects the output inductor current; when the instantaneous value of the output inductor current reaches the predetermined value at time t0, the excitation current i of the excitation inductor Lm Lm (t) also reaches the positive peak, the output pulse DR of the control circuit module M is zero, the primary power MOS tube Q1 is turned off and enters the next switching cycle.

2. The ZVS forward converter without additional winding according to claim 1, wherein: The forward-type isolated output transformer includes a primary winding Np and a secondary winding Ns, wherein the primary winding Np and the secondary winding Ns are tightly coupled via a magnetic core T; the output of the secondary winding Ns is connected to the cathode of the output diode D1 and the cathode of the freewheeling diode D2, respectively; the anode of the secondary output diode D1 and the anode of the freewheeling diode D2 are connected, and are connected to the negative terminal of the output filter capacitor Cf and the negative terminal of the output load; the cathode of the freewheeling diode D2 is connected to one end of the secondary output inductor L; and the other end of the secondary output inductor L is connected to the positive terminal of the filter capacitor Cf and the positive terminal of the output load. The resonant capacitor Cr is connected in parallel with the diode Dr; V IN is the primary input voltage, V IN It is connected to the anode of the diode Dr and the same-name terminal of the forward isolation output transformer Np; the cathode of the diode Dr is connected to the drain of the primary power MOS tube Q2, and the gate of the primary power MOS tube Q2 is connected to the output terminal DRF of the corresponding control circuit module M; the non-same-name end of the primary winding Np is connected to the source of the primary power MOS tube Q2 and the drain of the primary power MOS tube Q1; the gate of the primary power MOS tube Q1 is connected to the output terminal DR of the corresponding control circuit module M, and the source of the primary power MOS tube Q1 is grounded via the detection resistor Rs.

3. The ZVS forward converter without additional winding according to claim 2, wherein: It also includes an Ls, which is a magnetic amplifier inductor Ls or a saturation inductor Ls; the output of the same-name end of the secondary winding Ns is connected to one end of Ls, and the other end of Ls is connected to the cathode of the freewheeling diode D2.

4. The ZVS forward converter without additional winding according to claim 3, wherein: During the period from t4 to t5, the reverse excitation peak current in the primary winding Np of the forward-type isolated output transformer first reduces the drain-source capacitor voltage of the primary power MOSFET Q1 from the input DC voltage VIN to zero at time t5, creating the condition for MOSFET Q1 to turn on under zero-voltage conditions. At this time, Ls will be subjected to the output voltage of the secondary winding Ns of the forward-type isolated output transformer. As time passes, MOSFET Q1 completes zero-voltage turn-on, and after a fixed volt-second product, Ls switches from off to on. The secondary winding Ns of the forward-type isolated output transformer outputs current through Ls.

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