Device and method for controlling dead time of active clamp flyback switching power supply

Abstract

The present disclosure relates to a device and method for controlling the dead time of an active clamp flyback switching power supply. A device for controlling the dead time in an active clamp flyback switching power supply comprises: a voltage signal generating module, used to: obtain the dead time of a current pulse width modulation (PWM) cycle; and generate a voltage signal based on the dead time; a reference voltage signal generating module, used to generate a reference voltage signal based on a preset reference dead time; and a control signal generating module, used to generate a control signal based on the voltage signal and the reference voltage signal, wherein the control signal is used to control the conduction time of an active clamp switch tube in the active clamp flyback switching power supply.

Description

Technical Field

[0001] The present disclosure relates to integrated circuits, and more particularly, to an apparatus and method for controlling dead time in an active clamping flyback (ACF) switching power supply. Background Art

[0002] Active clamp flyback switching power supplies can operate at higher switching frequencies. At the system level of active clamp flyback switching power supplies, the power density can be increased by reducing the size of the transformer, achieving zero voltage switching (ZVS) and improving system efficiency. Traditional active clamp flyback switching power supplies have a fixed switching frequency, and the entire system can only be designed in continuous conduction mode (CCM) or discontinuous conduction mode (DCM). The dead time in the active clamp flyback switching power supply will vary with the input voltage, output voltage and output load, resulting in the system efficiency not being optimal. Summary of the invention

[0003] In view of the above problems, the present disclosure provides a novel device and method for controlling the dead time in an active clamp flyback switching power supply.

[0004] According to one aspect of an embodiment of the present disclosure, a method for controlling the dead time in an active clamp flyback switching power supply is provided, comprising: obtaining the dead time of a current pulse width modulation (PWM) cycle; generating a voltage signal based on the dead time; generating a reference voltage signal based on a preset reference dead time; and generating a control signal based on the voltage signal and the reference voltage signal, wherein the control signal is used to control the conduction time of an active clamp switch tube in the active clamp flyback switching power supply.

[0005] According to another aspect of an embodiment of the present disclosure, a device for controlling the dead time in an active clamp flyback switching power supply is provided, comprising: a voltage signal generating module, used to: obtain the dead time of a current pulse width modulation (PWM) cycle; and generate a voltage signal based on the dead time; a reference voltage signal generating module, used to generate a reference voltage signal based on a preset reference dead time; and a control signal generating module, used to generate a control signal based on the voltage signal and the reference voltage signal, wherein the control signal is used to control the conduction time of an active clamp switch tube in the active clamp flyback switching power supply.

[0006] According to another aspect of an embodiment of the present disclosure, an active clamp flyback switching power supply is provided, comprising the apparatus for controlling the dead time in the active clamp flyback switching power supply as described above.

[0007] According to the embodiments of the present disclosure, the device and method for controlling the dead time in the active clamped flyback switching power supply can achieve precise control of the dead time in the active clamped flyback switching power supply by controlling the conduction time of the active clamped switch tube in the active clamped flyback switching power supply, so that the dead time in the active clamped flyback switching power supply does not change with the input voltage, output voltage and output load, thereby achieving ZVS, while avoiding energy consumption caused by excessive negative current of the main inductance of the transformer, thereby improving system efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present disclosure may be better understood from the following description of specific embodiments of the present disclosure in conjunction with the accompanying drawings, in which:

[0009] Figure 1 A schematic diagram of the structure of a conventional active clamp flyback switching power supply is shown;

[0010] Figure 2 Shows Figure 1 A schematic diagram of the structure of an ACF controller of an active clamp flyback switching power supply;

[0011] Figure 3 Shows Figure 1 Schematic diagram of waveforms of some signals of an active clamp flyback switching power supply;

[0012] Figure 4 A schematic structural diagram of an adaptive dead time control loop module in an ACF controller of an active clamp flyback switching power supply according to an embodiment of the present disclosure is shown;

[0013] Figure 5 A schematic diagram showing an output current and an input voltage of an error amplifier in an adaptive dead time control loop module in an ACF controller of an active clamp flyback switching power supply according to an embodiment of the present disclosure is shown;

[0014] Figure 6-7 A schematic diagram showing waveforms of some signals during the process of adjusting the dead time from a large state to a steady state in an active clamp flyback switching power supply according to an embodiment of the present disclosure is shown;

[0015] Figure 8 A schematic structural diagram of an adaptive dead time control loop module in an ACF controller of an active clamp flyback switching power supply according to an embodiment of the present disclosure is shown;

[0016] Fig. 9 A schematic structural diagram of a device for controlling the dead time in an active clamp flyback switching power supply according to an embodiment of the present disclosure is shown; and

[0017] Fig.10A flow chart of a method for controlling the dead time in an active clamp flyback switching power supply according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0018] The features and exemplary embodiments of various aspects of the present disclosure will be described in detail below with reference to the accompanying drawings. Example implementations can be implemented in a variety of forms and should not be construed as limited to the implementations set forth herein; rather, these implementations are provided to make the present disclosure more comprehensive and complete and to fully convey the concepts of the example implementations to those skilled in the art. In the accompanying drawings, the sizes of regions and components may be exaggerated for clarity. In addition, in the accompanying drawings, the same reference numerals represent the same or similar structures, and their detailed descriptions will be omitted.

[0019] In addition, the described features, structures, or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be implemented without one or more of the specific details, or other methods, components, materials, etc. may be adopted. In other cases, well-known structures, materials, or operations are not shown or described in detail to avoid blurring the main technical ideas of the present disclosure.

[0020] As mentioned above, in order to solve the problem that the dead time in the traditional active clamp flyback switching power supply varies with the input voltage, output voltage and output load, a device and method for controlling the dead time in the active clamp flyback switching power supply are proposed.

[0021] Figure 1 FIG. 1 shows a schematic diagram of the structure of a conventional active clamp flyback switching power supply. Figure 1 As shown, a conventional active clamp flyback switching power supply may include a transformer T, a main pulse width modulation (PWM) power switch tube Q L , Active clamp switch tube Q H , Active clamp capacitor C clamp , ACF controller, resistor R sense , secondary side rectifier diode D1, output capacitor C1 and error amplifier and optocoupler on the secondary side.

[0022] Figure 2 Shows Figure 1 The schematic diagram of the structure of the ACF controller of the active clamp flyback switching power supply is shown in FIG. Figure 2 As shown, Figure 1The ACF controller of the active clamp flyback switching power supply may include a VD terminal, a DEM terminal, a CS terminal, an FB input terminal, a main PWM drive output terminal GateL, and an active clamp drive output terminal GateH. The ACF controller may include a VD falling edge detection module, a peak current control module, an adaptive dead time control loop module, a main PWM drive module, and an active clamp drive module.

[0023] Figure 3 Shows Figure 1 Schematic diagram of the waveform of some signals of the active clamp flyback switching power supply. Specifically, Figure 3 The main PWM power switch tube Q L The gate drive signal GateL, the active clamp switch tube Q H The gate drive signal GateH of the transformer is M , and the main PWM power switch tube Q L The drain voltage signal V D Schematic diagram of the waveform.

[0024] like Figure 3 As shown, at time T0, the main PWM power switch tube Q L The input voltage Vin is applied to both ends of the transformer inductance, and the transformer inductance magnetizing current I M At time T1, the main PWM power switch tube Q L After a short fixed delay, the active clamp switch Q H Active clamp switch Q H When conducting, the transformer's magnetizing current I M Linearly decreases, the secondary rectifier diode D1 is turned on, and the secondary side of the transformer charges the output capacitor C1. M When it drops to zero, the energy stored in the transformer's inductance is completely released, and the secondary rectifier diode D1 is naturally disconnected. H In the on state, the transformer's main inductance and active clamping capacitor C clamp Resonant, active clamp capacitor C clamp The voltage on N*V out The reverse current is applied to both ends of the transformer's inductance, and the transformer's inductance magnetizing current I M After dropping to zero, it continues to increase linearly in the reverse direction. At time T2, the active clamp switch tube Q H Disconnect, the main inductance of the transformer resonates with the parasitic capacitance at the VD end, the parasitic capacitance discharges, and the voltage V D When the voltage V D drops to the set threshold voltage V thWhen the main PWM power switch tube Q L conduction, where the voltage V D drops to the set threshold voltage V th With the main PWM power switch tube Q L The delay time between the conduction is fixed and very small. H Disconnect to voltage V D drops to the set threshold voltage V th The time is the dead time Td, that is, T3-T2. Increase the active clamp switch tube Q H The on-time of the active clamp switch can reduce the dead time and the Q H The on-time of the transistor can increase the dead time.

[0025] Figure 4 FIG. 1 is a schematic diagram showing a structure of an adaptive dead time control loop module in an ACF controller of an active clamp flyback switching power supply according to an embodiment of the present disclosure. Figure 4 As shown, the adaptive dead time control loop module in the ACF controller of the active clamp flyback switching power supply according to one embodiment of the present disclosure takes the dead time Td_det detected in each PWM cycle and the internal preset reference dead time Td_ref as input. The dead time Td_det detected in each PWM cycle is converted into a voltage signal Vtd_det, and the preset reference dead time Td_ref is converted into a reference voltage signal Vth_ref. The resistor Rf and the capacitor Cf form a low-pass filter to filter the voltage signal Vtd_det. The filtered voltage signal Vtd_det and the reference voltage signal Vth_ref are input to the error amplifier of the GmC structure, and the generated output signal is input to the comparator together with the triangular wave signal with a fixed slope generated by the ramp generator to generate a control signal GateH off, which is used to control the shutdown of the active clamp switch tube Q H .

[0026] The ACF controller of the active clamp flyback switching power supply according to one embodiment of the present disclosure adopts the following Figure 4 The adaptive dead time control loop module shown in the figure is used to build a control loop to adjust the active clamp switch Q H The on-time of the switch can be controlled accurately to achieve the set dead time. Figure 4The adaptive dead time control loop module shown is used to control the dead time in the active clamp flyback switching power supply, which can achieve the actual dead time in the steady state to be infinitely close to the set threshold, so that the dead time can be controlled very accurately, and the dead time will not change with the input voltage, output voltage and output load, which can simplify the system design. Since the dead time can be accurately controlled at the most ideal value, ZVS can be achieved, while avoiding the energy loss caused by the excessive negative current of the main inductance of the transformer, thereby improving the efficiency of the system.

[0027] Figure 5 FIG. 1 is a schematic diagram showing the output current and input voltage of the error amplifier in the adaptive dead time control loop module in the ACF controller of the active clamp flyback switching power supply according to an embodiment of the present disclosure. Figure 4 and 5 As shown, the reverse input voltage of the error amplifier of the GmC structure is the reference voltage signal Vth_ref. When the voltage of the non-inverting input terminal of the error amplifier of the GmC structure changes linearly between Vth_L1 and Vth_H1, it corresponds to a smaller Gm value. When the voltage of the non-inverting input terminal of the error amplifier of the GmC structure changes between Vth_L2 and Vth_L1 or between Vth_H1 and Vth_H2, it corresponds to a larger Gm value, while limiting the maximum current amplitude of the output terminal. Gm is designed to have such a segmented Gm value, which can take into account the loop bandwidth in the steady state and speed up the loop response speed during dynamic switching.

[0028] Figure 6-7 The waveform diagram of some signals in the process of adjusting the dead time from too large to steady state in an active clamp flyback switching power supply according to an embodiment of the present disclosure is shown. Specifically, Figure 6-7 The waveform diagram of some signals in the process of adjusting the dead time from a large value to a steady state by using the adaptive dead time control loop module in the ACF controller of the active clamp flyback switching power supply according to an embodiment of the present disclosure is shown. Initially, the detected dead time is greater than the preset reference dead time, so the voltage Vtd_det signal input to the non-inverting input terminal of the error amplifier of the GmC structure is also greater than the reference voltage signal Vth_ref input to the reverse input terminal of the error amplifier of the GmC structure, so that the output signal (voltage Comp) of the output terminal of the error amplifier of the GmC structure gradually increases, thereby causing the active clamp switch tube Q H The conduction time of the transformer increases, and the amplitude of the negative current of the transformer inductance increases, that is, the active clamp switch tube Q H After disconnection, the discharge current amplitude to the VD terminal increases, so the absolute value of the falling slope of VD increases, that is, the falling speed is faster, thereby reducing the dead time.

[0029] Figure 8 The structure diagram of the adaptive dead time control loop module in the ACF controller of the active clamp flyback switching power supply according to an embodiment of the present disclosure is shown. When the output voltage Vout of the active clamp flyback switching power supply is different, for example, when the output voltage Vout varies between 3V and 20V, since the decreasing slope of the inductor current of the transformer is inversely proportional to the voltage N*Vout, the lower the output voltage, the lower the active clamp switch tube Q. H The longer the conduction time is. Since the range of the output signal (voltage Comp) at the output end of the GmC structure error amplifier and the slope of the triangle wave signal generated by the ramp generator are very high, it is difficult to take into account the changes in the output voltage and the changes in different output loads, that is, the output voltage has a great influence on the bandwidth of the control loop of the adaptive dead time control loop module. Figure 8 As shown, according to an embodiment of the present disclosure, the adaptive dead time control loop module in the ACF controller of the active clamp flyback switching power supply samples the output voltage through the transformer winding, and adjusts the slope of the triangular wave signal generated by the ramp generator based on the sampled output voltage. The slope of the triangular wave signal generated by the ramp generator is set to be proportional to the output voltage, thereby reducing the influence of the output voltage on the control loop of the adaptive dead time control loop module.

[0030] Fig. 9 FIG. 1 is a schematic diagram showing a structure of a device for controlling the dead time in an active clamp flyback switching power supply according to an embodiment of the present disclosure. Fig. 9 As shown, the apparatus 900 for controlling the dead time in an active clamp flyback switching power supply according to an embodiment of the present disclosure may include a voltage signal generating module 910 , a reference voltage signal generating module 920 and a control signal generating module 930 .

[0031] The voltage signal generating module 910 can be used to obtain the dead time of the current PWM cycle, and generate a voltage signal based on the obtained dead time. The reference voltage signal generating module 920 can be used to generate a reference voltage signal based on a preset reference dead time. The control signal generating module 930 can be used to generate a control signal based on the voltage signal generated by the voltage signal generating module 910 and the reference voltage signal generated by the reference voltage signal generating module 920, wherein the control signal can be used to control the conduction time of the active clamp switch tube in the active clamp flyback switching power supply.

[0032] In an example embodiment, the apparatus 900 for controlling the dead time in an active clamp flyback switching power supply according to an embodiment of the present disclosure may further include a filtering module (not shown). The filtering module may be used to filter the voltage signal generated by the voltage signal generating module 910 to generate a filtered voltage signal. The control signal generating module 920 may be used to generate a control signal based on the filtered voltage signal and a reference voltage signal.

[0033] In an example embodiment, the control signal generating module 920 may include an output signal generating submodule, a triangular wave signal generating submodule, and a control signal generating submodule. The output signal generating submodule may be used to generate an output signal based on a voltage signal and a reference voltage signal, the triangular wave signal generating submodule may be used to generate a triangular wave signal, and the control signal generating submodule may be used to generate a control signal based on the output signal generated by the output signal generating submodule and the triangular wave signal generated by the triangular wave signal generating submodule. In an example embodiment, the triangular wave signal generating submodule may be used to generate a triangular wave signal based on the output voltage of the active clamp flyback switching power supply. In another example embodiment, the triangular wave signal may have a fixed slope.

[0034] Fig.10 FIG. 1 is a flow chart of a method for controlling the dead time in an active clamp flyback switching power supply according to an embodiment of the present disclosure. Fig.10 As shown, in step 1010, the dead time of the current PWM cycle can be obtained. In step 1020, a voltage signal can be generated based on the dead time. In step 1030, a reference voltage signal can be generated based on a preset reference dead time. In step 1040, a control signal can be generated based on the voltage signal and the reference voltage signal, wherein the control signal is used to control the conduction time of the active clamp switch tube in the active clamp flyback switching power supply.

[0035] In an example embodiment, the method for controlling the dead time in an active clamp flyback switching power supply according to an embodiment of the present disclosure may also include: filtering the voltage signal generated in step 1010 to generate a filtered voltage signal, wherein generating a control signal based on the voltage signal and a reference voltage signal in step 1040 may include: generating a control signal based on the filtered voltage signal and a reference voltage signal.

[0036] In an example embodiment, generating a control signal based on the voltage signal and the reference voltage signal in step 1040 may include: generating an output signal based on the voltage signal and the reference voltage signal, generating a triangular wave signal, and generating a control signal based on the output signal and the triangular wave signal. In an example embodiment, generating a triangular wave signal includes: generating a triangular wave signal based on the output voltage of the active clamp flyback switching power supply. In another example embodiment, the triangular wave signal has a fixed slope.

[0037] Combination Fig. 9 and Fig.10 The apparatus and method for controlling the dead time in an active clamp flyback switching power supply according to the embodiments of the present disclosure can refer to the embodiments of the present disclosure described in detail above in conjunction with other figures. For the sake of brevity, some details will not be repeated. It can be understood that the functional blocks and method steps shown in the above-mentioned structure and flow chart can be implemented as hardware, software, firmware or a combination thereof.

[0038] Therefore, the device and method for controlling the dead time in the active clamped flyback switching power supply according to the embodiments of the present disclosure can achieve precise control of the dead time in the active clamped flyback switching power supply by controlling the conduction time of the active clamped switch tube in the active clamped flyback switching power supply, so that the dead time in the active clamped flyback switching power supply will not change with the input voltage, output voltage and output load, thereby achieving ZVS, while avoiding energy consumption caused by excessive negative current of the main inductance of the transformer, thereby improving system efficiency.

[0039] The present disclosure may be implemented in other specific forms without departing from its spirit and essential characteristics. Therefore, the current embodiments are considered to be illustrative and not restrictive in all aspects, the scope of the present disclosure is defined by the appended claims rather than the above description, and all changes falling within the meaning and equivalent scope of the claims are thus included in the scope of the present disclosure.

Claims

1. A method for controlling dead time in an active clamp flyback switching power supply, comprising: Get the dead time of the current pulse width modulation PWM cycle; generating a voltage signal based on the dead time; generating a reference voltage signal based on a preset reference dead time; as well as A control signal is generated based on the voltage signal and the reference voltage signal, wherein the control signal is used to control the conduction time of the active clamp switch tube in the active clamp flyback switching power supply.

2. The method according to claim 1, further comprising: filtering the voltage signal to generate a filtered voltage signal, The generating the control signal based on the voltage signal and the reference voltage signal comprises: generating the control signal based on the filtered voltage signal and the reference voltage signal.

3. The method according to claim 1, wherein: Generating the control signal based on the voltage signal and the reference voltage signal comprises: generating an output signal based on the voltage signal and the reference voltage signal; generating a triangular wave signal; and The control signal is generated based on the output signal and the triangular wave signal.

4. The method according to claim 3, wherein: The generating of the triangular wave signal includes generating the triangular wave signal based on an output voltage of the active clamp flyback switching power supply.

5. The method according to claim 3, wherein: The triangle wave signal has a fixed slope.

6. A device for controlling the dead time in an active clamp flyback switching power supply, comprising: Voltage signal generation module, used for: Get the dead time of the current pulse width modulation PWM cycle; as well as generating a voltage signal based on the dead time; A reference voltage signal generating module, used to generate a reference voltage signal based on a preset reference dead time; as well as A control signal generating module is used to generate a control signal based on the voltage signal and the reference voltage signal, wherein the control signal is used to control the conduction time of the active clamp switch tube in the active clamp flyback switching power supply.

7. The apparatus according to claim 6, further comprising: a filtering module, configured to filter the voltage signal to generate a filtered voltage signal, The control signal generating module is used to generate the control signal based on the filtered voltage signal and the reference voltage signal.

8. The device according to claim 6, wherein: The control signal generating module comprises: an output signal generating submodule, configured to generate an output signal based on the voltage signal and the reference voltage signal; A triangular wave signal generating submodule, used for generating a triangular wave signal; and A control signal generating submodule is used to generate the control signal based on the output signal and the triangular wave signal.

9. The device according to claim 8, wherein: The triangle wave signal generating submodule is used to generate the triangle wave signal based on the output voltage of the active clamp flyback switching power supply.

10. The device according to claim 8, wherein: The triangle wave signal has a fixed slope.

11. An active clamp flyback switching power supply, comprising the device for controlling the dead time in the active clamp flyback switching power supply according to any one of claims 6 to 10.

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