Control circuit of flyback converter and flyback converter

Abstract

The utility model discloses a flyback converter control circuit and a flyback converter, the flyback converter comprises a transformer and a first power tube, the first power tube is connected with a primary winding of the transformer, the control circuit is used for controlling on and off of the first power tube, the control circuit comprises a voltage partition module and a multi-mode control module, the voltage partitioning module performs voltage partitioning according to input representation voltage representing input voltage of the flyback converter, when the input representation voltage is smaller than a first threshold value, the input representation voltage is a first voltage interval, when the input representation voltage is larger than the first threshold value and smaller than a second threshold value, the input representation voltage is a second voltage interval, and when the input representation voltage is larger than the second threshold value, the input representation voltage is a third voltage interval; the multi-mode control module enters a first control mode in a first voltage interval; entering a second control mode in a second voltage interval; and entering a protection control mode in the third voltage interval. The wide input voltage range can be met, the efficiency is high in the wide input voltage range, and the EMI effect is good.

Description

Technical Field

[0001] The utility model relates to the technical field of power electronics, in particular to a control circuit of a flyback converter and a flyback converter. Background Art

[0002] From renewable energy generation, such as photovoltaics and wind power, to renewable energy consumption, such as electric vehicles and hybrid electric vehicles, renewable energy applications are becoming increasingly widespread. To improve overall energy efficiency, the bus voltage on the photovoltaic power generation side is gradually moving towards higher voltage levels, thereby reducing losses in transmission lines. Therefore, for string-type photovoltaic inverters, to account for variations in light intensity and partial shading of photovoltaic panels, the auxiliary power input range is wide, from 300V to 1500V, with an input voltage range ratio exceeding 1:5. Furthermore, supporting electronic products in industrial and commercial applications generally require both three-phase and single-phase power supply compatibility. Considering the 110Vac / 220Vac phase voltage ranges domestically and internationally, as well as undervoltage conditions on the low-voltage grid and overvoltage conditions on the high-voltage grid, the input voltage range ratio is as high as 1:9 or above. For these application scenarios, flyback converter control circuits and flyback converters that deliver excellent performance across a wide input voltage range are required.

[0003] An existing control circuit using a pulse-width modulation control mode controls the switching of the flyback converter's main power transistor based on an oscillating signal generated by an oscillator, with the switching frequency controlled by the frequency of the oscillating signal. However, when the input voltage is high, the main power transistor is hard-on at a fixed frequency, resulting in high switching losses and poor EMI performance. Furthermore, in the presence of strong magnetic field interference, the maximum output power drops significantly. Another existing control circuit using a quasi-resonant control mode controls the switching of the flyback converter's main power transistor based on a detection signal representing the valley of the drain resonant voltage waveform of the main power transistor. However, to achieve the same output power over a wide input voltage range, the peak current of the main power transistor is high, resulting in large size and high cost for the main power transistor and magnetic components. High efficiency cannot be achieved across a wide input voltage range. Furthermore, in the presence of strong magnetic field interference, the transformer's magnetizing inductance and leakage inductance are significantly reduced, resulting in excessively high switching frequency during normal operation, impacting the life of the power device. Utility Model Content

[0004] In view of this, the purpose of the present invention is to provide a control circuit and a flyback converter for a flyback converter, so as to solve the technical problem of providing a control circuit and a flyback converter that can be applied to a very wide input voltage range. Within the wide input voltage range in which the flyback converter works normally, high efficiency and good EMI effect can be obtained, and within the extremely high input voltage range, the flyback converter enters a protection control mode to ensure the safety of the flyback converter.

[0005] The technical solution of the present invention is to provide a control circuit of a flyback converter, wherein the flyback converter includes a transformer and a first power tube, wherein the first power tube is connected to the primary winding of the transformer, and the control circuit is used to control the on and off of the first power tube, and the control circuit includes a voltage partition module and a multi-mode control module.

[0006] The voltage partitioning module performs voltage partitioning according to an input characterizing voltage characterizing the input voltage of the flyback converter, wherein the input characterizing voltage is a first voltage interval when it is less than a first threshold, a second voltage interval when it is greater than the first threshold and less than a second threshold, and a third voltage interval when it is greater than the second threshold;

[0007] The multi-mode control module enters a first control mode in the first voltage range; enters a second control mode in the second voltage range; and enters a protection control mode in the third voltage range.

[0008] Optionally, the multi-mode control module includes a first oscillator and a valley detection circuit,

[0009] In the first control mode, the multi-mode control module controls the switching on of the first power tube according to the oscillation signal output by the first oscillator;

[0010] In the second control mode, the multi-mode control module controls the opening of the first power tube according to the valley detection signal output by the valley detection circuit, wherein the valley detection signal represents the valley of the drain resonant voltage waveform of the first power tube.

[0011] Optionally, the multi-mode control module receives a feedback signal representing an error between an output feedback signal of the flyback converter and a reference signal.

[0012] The first oscillator receives the feedback signal and controls the frequency of the oscillation signal according to the feedback signal.

[0013] Optionally, in the first voltage range, the multi-mode control module enters one of the Burst control mode, PFM control mode, PWM control mode, and PWM frequency doubling control mode according to the feedback signal; or enters one of the PSM control mode, PFM control mode, PWM control mode, and PWM frequency doubling control mode.

[0014] Optionally, the multi-mode control module further includes a blanking unit,

[0015] The blanking unit receives a feedback signal representing an error between an output feedback signal of the flyback converter and a reference signal to generate a blanking time, and the blanking unit controls a duration of the blanking time according to the feedback signal;

[0016] In the second control mode, the multi-mode control module controls the turn-on of the first power tube according to the valley detection signal outside the blanking time.

[0017] Optionally, in the second voltage interval, the multi-mode control module enters one of the Burst control mode and the QR control mode according to the feedback signal; or enters one of the PSM control mode and the QR control mode.

[0018] Optionally, the multi-mode control module receives a feedback signal representing an error between an output feedback signal of the flyback converter and a reference signal, and receives a first sampling signal representing a current flowing through the first power tube.

[0019] In the first control mode and the second control mode, the first power tube is controlled to be turned off according to the feedback signal and the first sampling signal.

[0020] Optionally, in the protection control mode, the multi-mode control module controls the first power tube to be turned off, so as to control the flyback converter to stop outputting.

[0021] Optionally, the voltage partitioning module includes:

[0022] a first comparator, having a first input terminal receiving the input representative voltage, a second input terminal receiving the first threshold value, and an output terminal outputting a first partition control signal;

[0023] The second comparator has a first input terminal receiving the input representative voltage, a second input terminal receiving the second threshold value, and an output terminal outputting a second partition control signal.

[0024] Optionally, the multi-mode control module further includes a first single-pole double-throw switch and a first trigger.

[0025] A first fixed terminal of the first single-pole double-throw switch is connected to the first oscillator, a second fixed terminal is connected to the valley detection circuit, a movable terminal is connected to the first input terminal of the first trigger, and a control terminal receives the first partition control signal. The movable terminal of the first single-pole double-throw switch is connected to the first fixed terminal in the first voltage range and to the second fixed terminal in the second voltage range.

[0026] The output end of the first trigger is connected to the control end of the first power tube.

[0027] Optionally, the multi-mode control module further includes:

[0028] A first logic circuit, wherein the first input end receives the second partition control signal, the second input end is connected to the active end of the first single-pole double-throw switch, and the output end is connected to the first input end of the first trigger; or, the first input end receives the second partition control signal, the second input end is connected to the output end of the first trigger, and the output end is connected to the control end of the first power tube.

[0029] Optionally, the multi-mode control module further includes:

[0030] A first frequency jittering unit outputs a first frequency jittering signal;

[0031] The first adder has a first input terminal receiving the oscillation signal, a second input terminal receiving the first frequency-jittering signal, and an output terminal connected to the first fixed terminal of the first single-pole double-throw switch.

[0032] Optionally, the multi-mode control module further includes a second single-pole double-throw switch, a peak current control unit and a third comparator.

[0033] The peak current control unit receives a feedback signal representing an error between an output feedback signal of the flyback converter and a reference signal, and controls a first peak current threshold outputted by the peak current control unit according to the feedback signal;

[0034] The first fixed terminal of the second single-pole double-throw switch receives the first peak current threshold, the second fixed terminal receives the feedback signal, the movable terminal is connected to the first input terminal of the third comparator, and the control terminal receives the first partition control signal. The movable terminal of the second single-pole double-throw switch is connected to the first fixed terminal of the second single-pole double-throw switch in the first voltage range and is connected to the second fixed terminal of the second single-pole double-throw switch in the second voltage range.

[0035] The second input terminal of the third comparator receives a first sampling signal representing the current flowing through the first power tube, and the output terminal is connected to the second input terminal of the first trigger.

[0036] Optionally, the multi-mode control module further includes:

[0037] A second frequency jittering unit outputs a second frequency jittering signal;

[0038] The second adder has a first input terminal receiving the feedback signal, a second input terminal receiving the second frequency-jittering signal, and an output terminal connected to the second fixed terminal of the second single-pole double-throw switch.

[0039] Optionally, the multi-mode control module further includes:

[0040] A second frequency jittering unit outputs a second frequency jittering signal;

[0041] a second adder, a first input terminal receiving the first sampling signal, and an output terminal connected to the second input terminal of the third comparator;

[0042] A third switch has a first end receiving the second frequency-jittering signal, a second end connected to the second input end of the second adder, and a control end receiving the first partition control signal. The third switch is disconnected in the first voltage range and closed in the second voltage range.

[0043] In a second aspect, the present invention further provides a flyback converter, comprising a power stage circuit and the control circuit.

[0044] The power stage circuit includes a transformer and a first power tube, the first power tube is connected to the primary winding of the transformer, and the control circuit is used to control the on and off of the first power tube.

[0045] The circuit structure of the present invention has the following advantages compared with the prior art: the control circuit partitions the input voltage of the flyback converter, enters a first control mode in a first voltage interval representing that the input voltage is in a low voltage segment, enters a second control mode in a second voltage interval representing that the input voltage is in a high voltage segment, and enters a protection control mode in a third voltage interval representing that the input voltage is in an extremely high voltage segment. It can be applied to flyback converters with a very wide input voltage range, can obtain high efficiency and good EMI effect in both the first voltage interval and the second voltage interval, and can ensure the safety of the flyback converter in the third voltage interval. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a schematic diagram of the circuit structure of an embodiment of a flyback converter of the present utility model;

[0047] Figure 2 Based on Figure 1 A circuit block diagram of a control circuit of a flyback converter;

[0048] Figure 3 Based on Figure 1 A circuit diagram of an embodiment of a control circuit for a flyback converter;

[0049] Figure 4 This is a schematic diagram of a control mode of an embodiment of a control circuit of a flyback converter of the present invention;

[0050] Figure 5 A schematic diagram of a frequency curve of a feedback signal and an oscillation signal of an embodiment of the first oscillator of the present invention;

[0051] Figure 6 A schematic diagram of a feedback signal-first peak current threshold curve of an embodiment of a peak current control unit of the present invention;

[0052] Figure 7 A schematic diagram of a feedback signal-blanking time curve of an embodiment of a blanking time unit of the present invention;

[0053] Figure 8 Schematic diagram of the feedback signal-switching frequency of the flyback converter in the second control mode according to an embodiment of the present invention. DETAILED DESCRIPTION

[0054] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments and covers any substitutions, modifications, equivalent methods and solutions made within the spirit and scope of the present invention.

[0055] In order to enable the public to have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0056] The following paragraphs describe the present invention in more detail by way of example with reference to the accompanying drawings. It should be noted that the drawings are simplified and not to exact proportions, and are only used for the purpose of conveniently and clearly explaining the embodiments of the present invention.

[0057] like Figure 1 As shown, in one embodiment of the present invention, a flyback converter 10 includes a power stage circuit and a control circuit 100. The power stage circuit includes a transformer T1, a first power transistor Q1, and a freewheeling diode D1. The transformer T1 includes a primary winding Np and a secondary winding Ns. The first power transistor Q1 is connected to the primary winding Np, and the freewheeling diode D1 is connected to the secondary winding Ns. Of course, in other embodiments, the freewheeling diode D1 can also be replaced with a synchronous rectifier. The control circuit 100 is used to control the on and off of the first power transistor Q1. The first terminal (source) of the first power transistor Q1 is grounded through a sampling resistor Rcs, the second terminal (drain) is connected to the primary winding Np, and the control terminal (gate) is connected to the primary control circuit 100. The AC source AC forms an input voltage Vin after passing through a rectifier bridge 101, and the output terminal of the flyback converter 10 outputs an output voltage Vout. The flyback converter 10 further includes a first sampling circuit, an auxiliary winding Na, a second sampling circuit, and a feedback module 102. The first sampling circuit includes a first resistor R1 and a second resistor R2 connected in series. One end of the first resistor R1 receives the input voltage Vin, and one end of the second resistor R2 is grounded. The second sampling circuit includes a third resistor R3 and a fourth resistor R4 connected in series between the two ends of the auxiliary winding Na. The feedback module 102 is connected to the output end of the flyback converter to output a feedback signal V representing the error between the output feedback signal of the flyback converter and the reference signal.FB In one embodiment, the feedback module 102 amplifies the error between the output feedback signal of the flyback converter and the reference signal, and uses the error amplification result as the feedback signal V through the isolation module. FB Output. The primary side control circuit 100 includes multiple pins, such as a Line pin, a DRV pin, a ZCD pin, a CS pin, etc. The Line pin is connected to the common end of the first resistor R1 and the second resistor R2 to receive the input representative voltage V_line representing the input voltage Vin; the ZCD pin is connected to the common end of the third resistor R3 and the fourth resistor R4 to receive the second sampling voltage V ZCD The CS pin is connected to the common end of the sampling resistor Rcs and the first power tube Q1 to receive the first sampling signal Vcs representing the current flowing through the first power tube Q1; the DRV pin is connected to the control end of the first power tube Q1 to control the on and off of the first power tube Q1 according to the drive signal V_g; the FB pin receives the feedback signal V FB .

[0058] Figure 2 Shown according to Figure 1 The circuit block diagram of the control circuit of the flyback converter is shown. The control circuit 100 includes a voltage partitioning module 110 and a multi-mode control module 120. The voltage partitioning module 110 performs voltage partitioning according to the input characterization voltage V_line. When the input characterization voltage V_line is less than the first threshold value VL1, it is a first voltage interval. When the input characterization voltage V_line is greater than the first threshold value VL1 and less than the second threshold value VL2, it is a second voltage interval. When the input characterization voltage V_line is greater than the second threshold value VL2, it is a third voltage interval. The multi-mode control module 120 enters a first control mode in the first voltage interval, enters a second control mode in the second voltage interval, and enters a protection control mode in the third voltage interval.

[0059] refer to Figure 3 The control circuit 100 of the flyback converter of the present invention includes a voltage partitioning module 110 and a multi-mode control module 120. For example, the voltage partitioning module 110 includes a first comparator U1 and a second comparator U2. The first input terminal of the first comparator U1 receives an input representative voltage V_line, the second input terminal receives a first threshold value VL1, and the output terminal outputs a first partition control signal S_vin1; the first input terminal of the second comparator U2 receives an input representative voltage V_line, the second input terminal receives a second threshold value VL2, and the output terminal outputs a second partition control signal S_vin2. The multi-mode control module 120 includes a first oscillator U6, a valley detection circuit U9, a first single-pole double-throw switch S1, and a first trigger U4. The first oscillator U6 outputs an oscillation signal; the valley detection circuit U9 generates an oscillation signal based on the second sampling voltage V ZCDA valley detection signal representing the valley of the drain resonant voltage waveform of the first power transistor is output; a first fixed terminal of the first single-pole double-throw switch S1 is connected to the first oscillator U6 to receive the oscillation signal, a second fixed terminal is connected to the valley detection circuit to receive the valley detection signal, a movable terminal is connected to the first input terminal of the first trigger U4, and a control terminal receives the first partition control signal S_vin1. The movable terminal of the first single-pole double-throw switch S1 is connected to the first fixed terminal in a first voltage range where the input representative voltage V_line is less than the first threshold value VL1, and is connected to the second fixed terminal in a second voltage range where the input representative voltage V_line is greater than the first threshold value VL1 and less than the second threshold value VL2. The present invention does not limit the specific signal received by the control terminal of the first single-pole double-throw switch S1. In other embodiments, a logic circuit (not shown) may also be included. The logic circuit performs logical processing on the first partition control signal S_vin1 and the second partition control signal S_vin2. The control terminal of the first single-pole double-throw switch S1 receives the signal output by the logic circuit; the output terminal of the first trigger U4 is connected to the control terminal of the first power transistor Q1. In this manner, the multi-mode control module 120 can enter a first control mode during a first voltage interval, indicating that the input voltage Vin is in the low voltage range, and control the first power transistor Q1 based on the oscillation signal output by the first oscillator U6. In a second voltage interval, indicating that the input voltage Vin is in the high voltage range, the multi-mode control module 120 can enter a second control mode, and control the first power transistor Q1 based on the valley detection signal output by the valley detection circuit U9. Furthermore, the multi-mode control module 120 also includes a first logic circuit LG1. In one embodiment, the first logic circuit LG1 can be configured to have a first input terminal receiving the second partition control signal VL2, a second input terminal connected to the active terminal of the first single-pole double-throw switch S1, and an output terminal connected to the first input terminal of the first flip-flop U4. For example, the first logic circuit LG1 includes an AND gate, wherein the first input terminal of the AND gate receives the negation of the second partition control signal VL2, the second input terminal receives the signal output from the active terminal of the first single-pole double-throw switch S1, and the output terminal is connected to the first input terminal of the first flip-flop U4. In another embodiment, the first input end of the first logic circuit LG1 can also be set to receive the second partition control signal VL2, the second input end is connected to the output end of the first trigger U4, and the output end is connected to the control end of the first power tube Q1 (not shown in the figure). In this way, the multi-mode control module 120 can enter the protection control mode in the third voltage interval representing that the input voltage Vin is in the extremely high voltage segment, control the first power tube to shut down, and control the flyback converter to stop output. Therefore, the control circuit 100 of this embodiment can be applied to flyback converters with a very wide input voltage range, and can obtain high efficiency and good EMI effect when the input voltage is in the low voltage segment and the high voltage segment. At the same time, it can obtain high load capacity in the case of strong magnetic field interference, and can also ensure the safety of the flyback converter when the input voltage is in the extremely high voltage segment.

[0060] Please continue to refer to Figure 3 In some embodiments, the first oscillator U6 receives the feedback signal V FB , and according to the feedback signal V FB Control the frequency of the oscillation signal outputted by it. In one embodiment, it can be set to have different relationships between the frequency of the oscillation signal and the feedback signal within at least two different feedback signal ranges. In some embodiments, the multi-mode control module 120 further includes a blanking unit U8, which is used to receive the feedback signal V FB Generate blanking time according to the feedback signal V FB The duration of the blanking time is controlled; in a second control mode, the multi-mode control module controls the turning on of the first power transistor Q1 based on the valley detection signal outside the blanking time. In one embodiment, the relationship between the duration of the blanking time and the feedback signal can be set to be different within at least two different feedback signal ranges. For example, in one embodiment, the blanking unit U8 also receives the drive signal V_g, detects the falling edge of the drive signal V_g, and starts the blanking time timing at the falling edge. In one embodiment, the second logic circuit LG2 is further included. The second logic circuit LG2 receives the valley detection signal output by the valley detection circuit U9 and the signal output by the blanking unit U8, and its output is connected to the second fixed terminal of the first single-pole double-throw switch S1. For example, the second logic circuit LG2 includes an AND gate. In another embodiment, the second logic circuit LG2 may not be included. The valley detection circuit U9 receives the signal output by the blanking unit U8. The valley detection circuit U9 is disabled during the blanking time and enabled outside the blanking time. It is understandable that the blanking unit U8 may also include a counting unit (not shown in the figure), which generates a counting threshold according to the feedback signal. In the second control mode, the multi-mode control module controls the opening of the first power tube according to the valley detection signal that reaches the counting threshold. Furthermore, the multi-mode control module 120 controls the opening of the first power tube according to the feedback signal V FB and the first sampling signal Vcs to control the turn-off of the first power tube Q1. In one embodiment, the multi-mode control module 120 further includes a second single-pole double-throw switch S2, a peak current control unit U5 and a third comparator U3. The peak current control unit U5 receives the feedback signal V FB , and according to the feedback signal V FBIn one embodiment, the first peak current threshold Vpk1 of the output can be set within at least two different feedback signal ranges, with the first peak current threshold and the feedback signal having different relationships. The first fixed terminal of the second single-pole double-throw switch S2 receives the first peak current threshold Vpk1, the second fixed terminal receives the feedback signal, and the movable terminal is connected to the first input terminal of the third comparator U3. The control terminal receives the first partition control signal S_vin1, which controls the movable terminal of the second single-pole double-throw switch S2 to be connected to its first fixed terminal in the first voltage range and to its second fixed terminal in the second voltage range. The second input terminal of the third comparator U3 receives the first sampling signal Vcs, and the output terminal is connected to the second input terminal of the first trigger U4. To further optimize EMI, frequency jittering control can be performed. On the one hand, to implement frequency jittering in the first control mode, in some embodiments, the multi-mode control module 120 further includes a first frequency jittering unit U7 and a first adder A1. The first frequency jittering unit U7 outputs a first frequency jittering signal. The first adder A1 has a first input terminal receiving the oscillation signal output by the first oscillator U6, a second input terminal receiving the first frequency jittering signal, and an output terminal connected to the first fixed terminal of the first single-pole double-throw switch S1. On the other hand, to implement frequency jittering in the second control mode, in some embodiments, the multi-mode control module 120 further includes a second frequency jittering unit U10, a second adder A2, and a third switch S3. The second frequency jittering unit U10 outputs a second frequency jittering signal. The second adder A2 has a first input terminal receiving the first sampling signal Vcs, and an output terminal connected to the second input terminal of the third comparator U3. The third switch S3 has a first terminal receiving the second frequency jittering signal, a second terminal connected to the second input terminal of the second adder A2, and a control terminal receiving the first partition control signal S_vin1. The third switch S3 is open in the first voltage range and closed in the second voltage range. In other embodiments, the multi-mode control module 120 may not include the third switch, but instead configure the second frequency jittering unit to output the second frequency jittering signal, and the first input terminal of the second adder receives the feedback signal V FB The second input end receives the second frequency-jittering signal, and the output end is connected to the second fixed end of the second single-pole double-throw switch S2 (not shown in the figure).

[0061] The following combination Figures 4 to 8 ,right Figure 3 The working principle of the control circuit of the flyback converter shown is introduced. Figure 4 1 is a control mode diagram of an embodiment of a flyback converter control circuit 100, wherein V FB represents the feedback signal, V_line represents the input characterization voltage, VL1 represents the first threshold, and VL2 represents the second threshold; Figure 5 is the feedback signal V of an embodiment of the first oscillator U6 FB - Schematic diagram of the frequency fsw curve of the oscillation signal, where V FBrepresents the feedback signal, fsw represents the frequency of the oscillation signal; Figure 6 The feedback signal V is an embodiment of the peak current control unit U5. FB - Schematic diagram of the first peak current threshold Vpk1 curve, where V FB represents the feedback signal, Vpk1 represents the first peak current threshold; Figure 7 The feedback signal V of the blanking time unit U9 is an embodiment of the present invention. FB -Blanking time Tblank curve diagram, where V FB represents the feedback signal, Tblank represents the blanking time; Figure 8 The feedback signal V in the second control mode of an embodiment is FB - Schematic diagram of the switching frequency Fsw of the flyback converter, where V FB represents the feedback signal, and Fsw represents the switching frequency of the flyback converter.

[0062] When the input voltage Vin is in the low voltage range and the input characteristic voltage V_line is less than the first threshold VL1, it is the first voltage interval. The first comparator U1 outputs the first partition control signal S_vin1 as "0" (low level), and the second comparator U2 outputs the second partition control signal S_vin2 as "0". The first partition control signal S_vin1 controls the connection between the active terminal of the first single-pole double-throw switch S1 and its first fixed terminal, connecting the first adder A1 and the first logic circuit LG1; controls the connection between the active terminal of the second single-pole double-throw switch S2 and its first fixed terminal, connecting the current control unit U5 and the third comparator U3; and controls the disconnection of the third switch S3. Since the second partition control signal S_vin2 is "0", the signal output by the first logic circuit LG1 is consistent with the signal at the active terminal of the first single-pole double-throw switch S1. At this time, the multi-mode control module 120 enters the first control mode and controls the opening of the first power transistor according to the signal obtained by superimposing the oscillation signal output by the first oscillator U6 on the first frequency-jittering signal output by the first frequency-jittering unit U7. Specifically, the signal after the oscillation signal is superimposed on the first frequency-jittering signal is transmitted to the first input terminal (set pin "S") of the first trigger U4 through the first single-pole double-throw switch S1 and the first logic circuit LG1 as an opening control signal for controlling the opening of the first power tube Q1. At the same time, the peak current control unit U5 is based on the feedback signal V FBThe output corresponds to the first peak current threshold Vpk1, which is transmitted to the first input terminal of the third comparator U3 through the second single-pole double-throw switch S2; when the turn-on control signal is generated, the output drive signal V_g of the first trigger U4 controls the first power tube Q1 to turn on, the excitation current of the primary winding Np of the transformer T1 increases linearly, and the first sampling signal Vcs increases accordingly. When the first sampling signal Vcs reaches the first peak current threshold Vpk1, the third comparator U3 outputs "1" (high level) and transmits it to the second input terminal (reset pin "R") of the first trigger U4, that is, the signal output by the third comparator U3 is used as the shutdown control signal, and the output drive signal V_g of the first trigger U4 controls the first power tube Q1 to turn off.

[0063] Further, refer to Figures 4 to 6 In the first voltage range, when the feedback signal V FB When the flyback converter is in a light load range, for example, the load can be set to be less than 10% of the full load as a light load. The light load range includes the following: Figure 5 and Figure 6 The V shown in BUR_L -V BUR_H In the burst control mode, the multi-mode control module 120 enters the burst control mode and controls the flyback converter to be in the burst mode. In the burst control mode, the switching frequency of the first power tube Q1 is controlled to be maintained at the frequency of the lower oscillation signal superimposed on the frequency of the first frequency-jittering signal, which can prevent the frequency of the flyback converter from entering the human ear audio range. After the flyback converter is turned on for several cycles, the feedback signal V FB Further reduce to V BUR_L , the converter starts to stop working until the feedback signal V FB Rising to V BUR_H , the flyback converter continues to drive the first power tube Q1 at the frequency in the Burst mode to complete the energy transfer. The Burst control mode can ensure that the converter can still operate at a high efficiency when the load is light and avoid audio noise. Of course, in another embodiment, the feedback signal V FB When in the light load range, the multi-mode control module 120 can also be set to enter the pulse skip modulation (PSM) control mode. FB At V PFM -V PWM range, such as V PWM The corresponding load can be set to about 40% of the full load, such as Figure 5 As shown, the frequency fsw of the oscillation signal output by the first oscillator U6 changes with the feedback signal V FB For example, the frequency fsw of the oscillation signal can be increased from fMIN linearly rise to f NOM ;like Figure 6 As shown, the peak current control unit U5 outputs a fixed value equal to Vpk1 NOM When the first peak current threshold Vpk1 is reached, the multi-mode control module 120 enters the pulse frequency modulation (PFM) control mode. The PFM control mode is beneficial for terminal electronic products in the actual EMI test environment. The load is not under heavy load and the switching frequency is relatively low, so that the flyback converter can obtain better EMI electromagnetic interference characteristics. FB At V PWM -V Meg range, such as V Meg The corresponding load can be set to about 100% of the full load, such as Figure 5 As shown, the frequency fsw of the oscillation signal output by the first oscillator U6 is equal to f NOM A fixed value; such as Figure 6 As shown, the first peak current threshold Vpk1 output by the peak current control unit U5 changes with the feedback signal V FB For example, the first peak current threshold Vpk1 can be increased from Vpk1 NOM Linear rise to Vpk1 MAX , the multi-mode control module 120 enters the pulse width modulation (PWM) control mode. The PWM control mode is beneficial to the terminal electronic products when they are actually under heavy load. The switching frequency remains relatively unchanged, and only the transformer excitation current is increased to achieve the output power improvement, thus avoiding the challenges of system stability caused by the change of switching frequency. FB is greater than V Meg When the range is Figure 5 As shown, the frequency fsw of the oscillation signal output by the first oscillator U6 is the frequency f corresponding to the PWM control mode. NOM The present invention does not limit the rising method and the doubling multiple. For example, the frequency of the oscillation signal can be increased from f NOM Linearly rising to 2*f NOM , then keep 2*f NOM Of course, in other embodiments, a nonlinear rising method can also be adopted, or when the feedback signal V FB Reach V Meg When doubled directly; Figure 6 As shown, the peak current control unit U5 outputs the maximum current limit Vpk1 MAX(Ensure that the current is within a safe range, avoid saturation of the transformer T1 core and exceeding the current carrying capacity of the first power tube Q1). The utility model names the control mode entered by the multi-mode control module 120 at this time as the pulse width modulation (PWM) frequency doubling control mode. The PWM frequency doubling control mode is beneficial to terminal electronic products when there is a magnetic field or other interference from the outside world. The magnetic saturation of the transformer T1 causes the slope of the excitation current change to become steeper. By increasing the switching frequency of the flyback converter to output sufficient power to the load, the load is ensured to operate stably. In the first voltage range, the switching frequency of the flyback converter of this embodiment depends on the frequency of the first oscillator in the first control mode. Therefore, in the first control mode, the feedback signal-switching frequency curve of the flyback converter can be referred to. Figure 5 .

[0064] In summary, in the first voltage range, in one embodiment, the multi-mode control module 120 can control the feedback signal V FB Enter one of the Burst control mode, PFM control mode, PWM control mode, and PWM frequency multiplication control mode; in another embodiment, the multi-mode control module 120 can also enter one of the Burst control mode, PFM control mode, PWM control mode, and PWM frequency multiplication control mode according to the feedback signal V FB Enter one of the PSM control mode, PFM control mode, PWM control mode, and PWM frequency multiplication control mode. It is understandable that in some other embodiments, some control modes may be deleted to sacrifice some excellent performance.

[0065] When the input voltage Vin is in the high voltage range and the input characteristic voltage V_line is greater than the first threshold VL1 and less than the second threshold, the second voltage range is reached. The first comparator U1 outputs a first partition control signal S_vin1 of "1," and the second comparator U2 outputs a second partition control signal S_vin2 of "0." The first partition control signal S_vin1 connects the active terminal of the first single-pole double-throw switch S1 to its second fixed terminal, thereby connecting the second logic circuit LG2 and the first logic circuit LG1. It also connects the active terminal of the second single-pole double-throw switch S2 to its second fixed terminal, thereby connecting the FB pin and the third comparator U3. Finally, it controls the closing of the third switch S3. Because the second partition control signal S_vin2 is "0," the signal output by the first logic circuit LG1 is consistent with the signal at the active terminal of the first single-pole double-throw switch S1. At this point, the multi-mode control module 120 enters the second control mode, controlling the turn-on of the first power transistor based on the valley detection signal outside the blanking period. The multi-mode control module 120 operates in a quasi-resonant (QR) control mode. Specifically, the valley detection signal outside the blanking time is transmitted to the first input terminal (set pin "S") of the first trigger U4 through the first single-pole double-throw switch S1 and the first logic circuit LG1 as a turn-on control signal for controlling the turn-on of the first power tube Q1. At the same time, the feedback signal V FB As the second peak current threshold Vpk2, it is transmitted to the first input terminal of the third comparator U3 through the second single-pole double-throw switch S2; when the turn-on control signal is generated, the output drive signal V_g of the first trigger U4 controls the first power tube Q1 to turn on, and the first sampling signal Vcs increases. When the first sampling signal Vcs is superimposed on the second frequency-jittering signal, it reaches the second peak current threshold Vpk2, the third comparator U3 outputs "1" and transmits it to the second input terminal of the first trigger U4 (reset pin "R"), that is, the signal output by the third comparator U3 is used as the shutdown control signal, and the output drive signal V_g of the first trigger U4 controls the first power tube Q1 to turn off.

[0066] Further, refer to Figure 4 、 Figure 7 and Figure 8 In the second voltage range, when the feedback signal V FB When the flyback converter is in the light load range, such as Figure 7 As shown, the blanking time Tblank is the time when the feedback signal V FB At V BUR_L -V BUR_H interval, there is a hysteresis characteristic, such as Figure 8 As shown, the switching frequency Fsw of the flyback converter is FB At V BUR_L -V BUR_Hinterval, there is a hysteresis characteristic, that is, when the feedback signal V FB In the light load range, the multi-mode control module 120 enters the Burst control mode based on the quasi-resonant (QR) control mode, which can achieve higher efficiency. Of course, in another embodiment, the feedback signal V FB When in the light load range, the multi-mode control module 120 can also be set to enter the pulse skip modulation (PSM) control mode based on the QR control mode. FB When in the range representing non-light load, the multi-mode control module 120 performs quasi-resonant (QR) control mode. In the QR control mode, the first power tube Q1 is turned on at the bottom of the drain resonant voltage waveform. On the one hand, the turn-on loss of the power tube Q1 is reduced. On the other hand, the drain voltage of the first power tube Q1 is used as a high-frequency jump voltage signal. Reducing the jump amplitude is beneficial to reducing the EMI interference caused by the converter to the outside. Among them, since the QR control mode does not use an oscillator, in order to further reduce EMI interference, by setting the third switch S3 to be closed, the signal after the first sampling signal Vcs is superimposed on the second frequency-jittering signal is compared with the second peak current threshold Vpk2, thereby presenting an expansion of the switching spectrum to achieve excellent EMI characteristics. In the second voltage range and the second control mode of the flyback converter of this embodiment, its switching frequency Fsw is relative to the feedback signal V FB Changes such as Figure 8 As shown above, it can be seen that in the second voltage range, in one embodiment, the multi-mode control module 120 can control the second voltage range according to the feedback signal V FB Enter one of the Burst control mode and the QR control mode; in another embodiment, the multi-mode control module 120 can also enter the Burst control mode and the QR control mode according to the feedback signal V FB Entering one of the FSM control mode and the QR control mode. It is understandable that in some other embodiments, only the QR control mode may be performed in the second voltage interval.

[0067] When the input voltage Vin is in the extremely high voltage range and the input representative voltage V_line is greater than the second threshold VL2, the third voltage interval is reached. The second comparator U2 outputs the second partition control signal S_vin2 as "1," and accordingly, the first logic circuit LG1 outputs "0." Therefore, if the first power transistor Q1 is in the off period when entering the third voltage interval, it remains off and does not turn on again during the third voltage interval. If the first power transistor Q1 is in the off period when entering the third voltage interval, it is shut down in response to the shutdown control signal output by the third comparator U3, and does not turn on again during the third voltage interval after shutting down. This means that the multi-mode control module 120 enters a protection control mode, shutting down the first power transistor and stopping the flyback converter's output. As the input voltage Vin decreases until the input representative voltage V_line falls below the second threshold VL2, the multi-mode control module 120 begins to enter the corresponding control mode, enabling the flyback converter to operate normally. The protection control mode is beneficial for stopping the flyback converter when the input voltage Vin fluctuates beyond the rated range due to external influences, thereby ensuring that the flyback converter is not damaged by the excessively high input voltage Vin and improving system reliability.

[0068] In summary, the control circuit of the flyback converter of the present invention partitions the input voltage of the flyback converter and enters the first control mode, the second control mode or the protection control mode according to the partitioning result. It can meet a very wide input voltage range and obtain high efficiency and good EMI effect when the input voltage is in the low voltage segment and the high voltage segment. At the same time, it obtains high load capacity when there is strong magnetic field interference, and can also ensure the safety of the flyback converter when the input voltage is in the extremely high voltage segment. Compared with the existing control circuit using the pulse width modulation control mode, the present invention has higher efficiency and better EMI effect when the input voltage Vin is in the high voltage segment, and has higher load power under strong magnetic field interference. Compared with the existing control circuit using the quasi-resonant control mode, the current stress of the first power tube of the present invention can be greatly reduced, and the volume of the first power tube and the transformer is reduced under the same load capacity. On the basis of partitioning the input voltage of the flyback converter, the feedback signal is partitioned in the first voltage interval and the second voltage interval respectively to enter different control modes. This can make the design of the transformer and the first power tube more excellent in each mode, so that it is not difficult to take into account a wide range in a single mode. It has the advantages of high efficiency, good EMI effect and high load power under strong magnetic field interference in the full input voltage range and full power range.

[0069] The above-described embodiments do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the above-described embodiments shall be included in the scope of protection of this technical solution.

Claims

1. A control circuit for a flyback converter, the flyback converter comprising a transformer and a first power transistor, the first power transistor being connected to a primary winding of the transformer, the control circuit being configured to control the on / off switching of the first power transistor, wherein: The control circuit includes a voltage partition module and a multi-mode control module, The voltage partitioning module performs voltage partitioning according to an input characterizing voltage characterizing the input voltage of the flyback converter, wherein the input characterizing voltage is a first voltage interval when it is less than a first threshold, a second voltage interval when it is greater than the first threshold and less than a second threshold, and a third voltage interval when it is greater than the second threshold; The multi-mode control module enters a first control mode in the first voltage range; enters a second control mode in the second voltage range; and enters a protection control mode in the third voltage range; In the first voltage interval, the multi-mode control module enters one of the Burst control mode, the PFM control mode, the PWM control mode, and the PWM frequency multiplication control mode according to a feedback signal representing an error between an output feedback signal of the flyback converter and a reference signal; or enters one of the PSM control mode, the PFM control mode, the PWM control mode, and the PWM frequency multiplication control mode; In the second voltage range, the multi-mode control module enters one of the Burst control mode and the QR control mode according to the feedback signal; or enters one of the PSM control mode and the QR control mode; In the protection control mode, the multi-mode control module controls the first power tube to be turned off, so as to control the flyback converter to stop outputting.

2. The control circuit according to claim 1, wherein: The multi-mode control module includes a first oscillator and a valley detection circuit, In the first control mode, the multi-mode control module controls the switching on of the first power tube according to the oscillation signal output by the first oscillator; In the second control mode, the multi-mode control module controls the opening of the first power tube according to the valley detection signal output by the valley detection circuit, wherein the valley detection signal represents the valley of the drain resonant voltage waveform of the first power tube.

3. The control circuit according to claim 2, characterized in that: The multi-mode control module receives the feedback signal, The first oscillator receives the feedback signal and controls the frequency of the oscillation signal according to the feedback signal.

4. The control circuit according to claim 2, characterized in that: The multi-mode control module further includes a blanking unit, The blanking unit receives the feedback signal to generate a blanking time, and the blanking unit controls the duration of the blanking time according to the feedback signal; In the second control mode, the multi-mode control module controls the turn-on of the first power tube according to the valley detection signal outside the blanking time.

5. The control circuit according to claim 1, wherein: The multi-mode control module receives the feedback signal and a first sampling signal representing the current flowing through the first power tube. In the first control mode and the second control mode, the first power tube is controlled to be turned off according to the feedback signal and the first sampling signal.

6. The control circuit according to claim 2, characterized in that: The voltage partition module includes: a first comparator, having a first input terminal receiving the input representative voltage, a second input terminal receiving the first threshold value, and an output terminal outputting a first partition control signal; The second comparator has a first input terminal receiving the input representative voltage, a second input terminal receiving the second threshold value, and an output terminal outputting a second partition control signal.

7. The control circuit according to claim 6, characterized in that: The multi-mode control module further includes a first single-pole double-throw switch and a first trigger, A first fixed terminal of the first single-pole double-throw switch is connected to the first oscillator, a second fixed terminal is connected to the valley detection circuit, a movable terminal is connected to the first input terminal of the first trigger, and a control terminal receives the first partition control signal. The movable terminal of the first single-pole double-throw switch is connected to the first fixed terminal in the first voltage range and to the second fixed terminal in the second voltage range. The output end of the first trigger is connected to the control end of the first power tube.

8. The control circuit according to claim 7, characterized in that: The multi-mode control module further includes: A first logic circuit, wherein the first input end receives the second partition control signal, the second input end is connected to the active end of the first single-pole double-throw switch, and the output end is connected to the first input end of the first trigger; or, the first input end receives the second partition control signal, the second input end is connected to the output end of the first trigger, and the output end is connected to the control end of the first power tube.

9. The control circuit according to claim 7, characterized in that: The multi-mode control module further includes: A first frequency jittering unit outputs a first frequency jittering signal; The first adder has a first input terminal receiving the oscillation signal, a second input terminal receiving the first frequency-jittering signal, and an output terminal connected to the first fixed terminal of the first single-pole double-throw switch.

10. The control circuit according to claim 7, characterized in that: The multi-mode control module further includes a second single-pole double-throw switch, a peak current control unit and a third comparator. The peak current control unit receives the feedback signal and controls a first peak current threshold outputted by the peak current control unit according to the feedback signal; The first fixed terminal of the second single-pole double-throw switch receives the first peak current threshold, the second fixed terminal receives the feedback signal, the movable terminal is connected to the first input terminal of the third comparator, and the control terminal receives the first partition control signal. The movable terminal of the second single-pole double-throw switch is connected to the first fixed terminal of the second single-pole double-throw switch in the first voltage range and is connected to the second fixed terminal of the second single-pole double-throw switch in the second voltage range. The second input terminal of the third comparator receives a first sampling signal representing the current flowing through the first power tube, and the output terminal is connected to the second input terminal of the first trigger.

11. The control circuit according to claim 10, characterized in that: The multi-mode control module further includes: A second frequency jittering unit outputs a second frequency jittering signal; The second adder has a first input terminal receiving the feedback signal, a second input terminal receiving the second frequency-jittering signal, and an output terminal connected to the second fixed terminal of the second single-pole double-throw switch.

12. The control circuit according to claim 10, characterized in that: The multi-mode control module further includes: A second frequency jittering unit outputs a second frequency jittering signal; a second adder, a first input terminal receiving the first sampling signal, and an output terminal connected to the second input terminal of the third comparator; A third switch has a first end receiving the second frequency-jittering signal, a second end connected to the second input end of the second adder, and a control end receiving the first partition control signal. The third switch is disconnected in the first voltage range and closed in the second voltage range.

13. A flyback converter, characterized in that: comprising a power stage circuit and a control circuit as claimed in any one of claims 1 to 12, The power stage circuit includes a transformer and a first power tube, the first power tube is connected to the primary winding of the transformer, and the control circuit is used to control the on and off of the first power tube.

Images