Half-bridge resonant topology flyback conversion circuit and resonant capacitor voltage self-balancing method

Abstract

The embodiment of the present invention relates to a half-bridge resonant topology flyback conversion circuit and a resonant capacitor voltage self-balancing method. The conversion circuit includes: a controller, which performs control processing according to a power supply voltage signal and a feedback signal to determine whether to control the flyback converter to enter a resonant capacitor voltage self-balancing mode; in this mode, the controller outputs a specific converter switch control signal; the flyback converter controls the main power tube to remain off according to the received specific converter switch control signal, and controls the resonant power tube to be periodically turned on / off, so that the energy on the resonant capacitor is released to the secondary side circuit through the periodic on / off of the resonant power tube, accelerating the discharge of the resonant capacitor, thereby quickly reducing the voltage difference between the voltage Vcr on the resonant capacitor and the reflected voltage Vor l converted from the second output voltage; a protocol module, which is used to generate a first feedback signal through a feedback circuit and send it to the controller when an output step-down instruction is detected or a USB load is unplugged.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a half-bridge resonant topology flyback conversion circuit and a resonant capacitor voltage self-balancing method. Background Art

[0002] With the iteration and upgrade of electronic products, electronic products have put forward high requirements for battery life. Due to the limitation of battery capacity, fast charging speed has become one of the best solutions at present. In order to reduce charging time and increase charging rate, fast charging uses handshake protocol to change the output voltage and realize power supply for different loads. In 2021, the USB-IF Association released the latest USB PD3.1 fast charging standard, which increased the charging power from the original 100W to 240W, and supported a maximum voltage output of 48V and a minimum voltage output of 3.3V, meeting the fast-paced life needs of contemporary people.

[0003] Half-bridge resonant topologies such as the active clamp flyback (ACF) topology and the asymmetric half-bridge (AHB) topology can achieve efficient power conversion because the primary power tube can achieve zero voltage switch-on (ZVS) and the secondary power tube zero current switch-off (ZCS). At the same time, thanks to soft switching, the power supply can operate at a higher switching frequency and the power density has been greatly improved, so AHB / ACF circuits are widely used.

[0004] In fast charging applications, the output voltage Vout of the switching power supply circuit usually has a large range of variation (for example, under the PD3.1 protocol, Vout is allowed to vary between 3.3V-48V). When the protocol module detects an output step-down instruction or the USB load is unplugged, the output discharge function is started (that is, the output voltage is adjusted from the high voltage Voh to the low voltage Vol). During the output voltage discharge period, the flyback converter control enters the standby mode. When the traditional flyback converter control circuit detects the standby mode, it will not turn on the resonant power tube, and the voltage Vcr of the resonant capacitor will maintain the higher reflected voltage before the output discharge function is started. When the protocol module adjusts the voltage from Voh to Vol, the flyback converter will exit the standby mode and enter the normal working mode. When the flyback converter control circuit turns on the resonant power tube again, there is a large voltage difference between the resonant capacitor voltage Vcr and the reflected voltage Vorl converted from Vol (Vor l=n×Vo l, where n is the primary-to-secondary turns ratio of the transformer), and there will be a large current pulse when the resonant power tube is turned on. If the working stress exceeds the power tube safe operating area (SOA), the resonant power tube may be damaged. Therefore, it is particularly important to accelerate the discharge of the resonant capacitor Cr during the discharge of the output voltage of the AHB / ACF flyback converter from high voltage to low voltage. Summary of the invention

[0005] The purpose of the present invention is to provide a half-bridge resonant topology flyback conversion circuit and a resonant capacitor voltage self-balancing method in view of the defects existing in the prior art. The circuit determines whether the circuit needs to enter the resonant capacitor voltage self-balancing mode according to the real-time monitoring and control logic processing of whether the power supply signal and the output voltage are stepped down and the connection state of the USB load (hereinafter referred to as the load), and in the resonant capacitor voltage self-balancing mode, the resonant power tube is controlled to be continuously turned on and off for a certain period of time with a periodic signal of a certain frequency and a certain pulse width, so that the energy on the resonant capacitor Cr can be released to the secondary side circuit through the transformer, thereby accelerating the discharge of the resonant capacitor Cr. This solves the problem that when the conversion circuit is powered on again in a short time after power failure in the prior art, the protocol chip controls the output voltage discharge according to the requirements and the output voltage is switched from high voltage to low voltage, the voltage difference between the resonant capacitor voltage and the output reflected voltage (Vor l) is too high due to the slow discharge of the resonant capacitor voltage, resulting in the generation of pulse peak current during the conduction of the resonant power tube.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a half-bridge resonant topology flyback converter circuit, comprising:

[0007] a controller that performs control processing according to a power supply voltage signal at a first input terminal and a feedback signal at a second input terminal to determine whether to control the flyback converter to enter a resonant capacitor voltage self-balancing mode; when it is determined that the flyback converter is controlled to enter the resonant capacitor voltage self-balancing mode, the controller outputs a specific converter switch control signal;

[0008] A flyback converter, comprising a primary side circuit and a secondary side circuit, wherein the primary side circuit comprises a resonant capacitor, a primary winding, a resonant power tube and a main power tube; the secondary side circuit is inductively coupled to the primary side circuit through the secondary winding, and outputs a DC voltage signal to a load; the flyback converter controls the main power tube to remain turned off according to the received specific converter switch control signal, and the resonant power tube is periodically turned on / off, so that the energy on the resonant capacitor is released to the secondary side circuit through the periodic turning on / off of the resonant power tube, thereby accelerating the discharge of the resonant capacitor, thereby quickly reducing the voltage difference between the voltage Vcr on the resonant capacitor and the reflected voltage Vorl converted from the second output voltage;

[0009] A protocol module, used to detect whether the half-bridge resonant topology flyback conversion circuit receives an output step-down instruction or whether the connected USB load is unplugged, and output a first detection signal when the output step-down instruction or the load is unplugged is detected;

[0010] A feedback circuit, the input end of which is connected to the output of the protocol module, and the output end of which is connected to the second input end; the feedback circuit is used to generate a first feedback signal according to the first detection signal and send it to the second input end.

[0011] Preferably, when the controller determines that a power input voltage failure occurs in the half-bridge resonant topology flyback converter circuit according to the power voltage signal at the first input terminal, the controller outputs the specific converter switch control signal to control the flyback converter to enter a resonant capacitor voltage self-balancing mode; or,

[0012] When the protocol module detects an output step-down instruction of the half-bridge resonant topology flyback converter circuit or the connected USB load is unplugged, it outputs a first detection signal to the feedback circuit, the feedback circuit generates the first feedback signal according to the first detection signal, and the controller controls the flyback converter to enter a resonant capacitor voltage self-balancing mode according to the first feedback signal.

[0013] Preferably, the protocol module is also used to, when the protocol module detects the output voltage reduction instruction or the load is unplugged, start the output discharge function, and adjust the output voltage of the half-bridge resonant topology flyback conversion circuit from the first DC voltage signal Voh to the second DC voltage signal Vol; the second DC voltage signal Vol is less than the first DC voltage signal Voh.

[0014] Further preferably, the reflected voltage Vor l converted from the second output voltage is specifically: Vor l=n×Vol; wherein n is the primary-to-secondary turns ratio of the transformer.

[0015] Preferably, the controller comprises an input detection module, a control logic module and a driver;

[0016] The input detection module is connected to the first input terminal, and is used to perform power failure detection according to the power supply voltage signal input from the first input terminal, and output a power failure detection result signal;

[0017] The control logic module receives the power-off detection result signal and the feedback signal, performs control logic processing, and outputs a driving signal to send to the driver;

[0018] The driver outputs the converter switch control signal according to the drive signal.

[0019] Preferably, in the primary side circuit of the flyback converter, the resonant power tube and the main power tube are connected in series, and the primary winding is coupled to the resonant power tube in parallel; the resonant capacitor and the primary winding form an LC resonant circuit.

[0020] Preferably, the flyback converter is specifically a flyback converter based on a half-bridge resonant AHB topology, or a flyback converter based on a half-bridge resonant ACF topology.

[0021] In a second aspect, an embodiment of the present invention provides a method for self-balancing the resonant capacitor voltage of the half-bridge resonant topology flyback conversion circuit described in the first aspect, the method comprising:

[0022] The controller monitors the power supply voltage signal to determine whether a power supply input voltage power failure occurs; when the power supply input voltage power failure does not occur, the controller controls the flyback converter to operate in a normal working mode; when the power supply input voltage power failure occurs, the controller controls the flyback converter to enter a resonant capacitor voltage self-balancing mode;

[0023] In the normal working mode, the protocol module monitors whether the output voltage reduction instruction of the conversion circuit or the USB load is unplugged, and generates a first feedback signal through the feedback circuit when the output voltage reduction instruction or the load is unplugged is detected;

[0024] The controller monitors the feedback signal, and when the feedback signal is the first feedback signal, the protocol module adjusts the output voltage of the half-bridge resonant topology flyback converter circuit from the first DC voltage signal Voh to the second DC voltage signal Vol, and the controller controls the flyback converter to enter the resonant capacitor voltage self-balancing mode; otherwise, the controller controls the flyback converter to operate in the normal working mode, and the half-bridge resonant topology flyback converter circuit outputs the first DC voltage signal Voh;

[0025] In the resonant capacitor voltage self-balancing mode, in the primary side circuit of the flyback converter, the main power tube remains turned off, and the resonant power tube is periodically turned on / off, and the energy on the resonant capacitor of the flyback converter is released to the secondary side circuit through the periodic turning on / off of the resonant power tube, thereby accelerating the discharge of the resonant capacitor, so as to quickly reduce the voltage difference between the voltage Vcr on the resonant capacitor and the reflected voltage Vor l converted from the second output voltage; the reflected voltage Vor l converted from the second output voltage is specifically: Vor l=n×Vo l; wherein n is the primary-to-secondary turns ratio of the transformer.

[0026] Preferably, the method also includes: in the normal working mode, the controller outputs a pulse width modulation PWM signal to control the resonant power tube and the main power tube of the flyback converter to be alternately turned on and off, so that the conversion circuit outputs the first DC voltage signal Voh.

[0027] Preferably, after the output voltage is adjusted from the first DC voltage signal Voh to the second DC voltage signal Vo l, the feedback circuit generates a second feedback signal, and the controller controls the flyback converter to exit the resonant capacitor self-balancing mode according to the second feedback signal.

[0028] The half-bridge resonant topology flyback conversion circuit provided by the embodiment of the present invention determines whether the circuit needs to enter the resonant capacitor voltage self-balancing mode according to the real-time monitoring and control logic processing of the input power supply voltage signal, the output voltage reduction instruction and the load connection state, and in the resonant capacitor voltage self-balancing mode, controls the resonant power tube to be continuously turned on and off for a certain period of time with a periodic signal of a certain frequency and a certain pulse width, so that the energy on the resonant capacitor Cr can be released to the secondary side circuit through the transformer, thereby accelerating the discharge of the resonant capacitor Cr, greatly reducing the voltage difference between the resonant capacitor Cr voltage and the Vor voltage in the flyback converter such as AHB or ACF after the output voltage is switched or the input power is powered off, thereby avoiding the generation of large current pulses when the resonant power tube is turned on again in a short time. This solves the problem that when the conversion circuit is powered on again in a short time after power failure in the prior art, the protocol chip controls the output voltage discharge according to requirements and the output voltage is switched from high voltage to low voltage, the voltage difference between the resonant capacitor voltage and the output reflected voltage (Vor l) is too high due to the slow discharge of the resonant capacitor voltage, resulting in the generation of pulse peak current during the conduction of the resonant power tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A circuit structure block diagram of a half-bridge resonant topology flyback converter circuit provided in an embodiment of the present invention;

[0030] Figure 2 A block diagram of the internal structure of a controller in a half-bridge resonant topology flyback conversion circuit provided by an embodiment of the present invention;

[0031] Figure 3 A specific implementation circuit in which the converter in the half-bridge resonant topology flyback conversion circuit provided in an embodiment of the present invention is an AHB flyback converter;

[0032] Figure 4 A specific implementation circuit in which the converter in the half-bridge resonant topology flyback conversion circuit provided in an embodiment of the present invention is an ACF flyback converter;

[0033] Figure 5 A flow chart of a control method for self-balancing the resonant capacitor voltage provided by an embodiment of the present invention;

[0034] Figure 6 One of the signal waveform diagrams in the half-bridge resonant topology flyback conversion circuit provided by an embodiment of the present invention;

[0035] Figure 7 The second signal waveform diagram of the half-bridge resonant topology flyback conversion circuit provided by the embodiment of the present invention;

[0036] Figure 8 A curve diagram of the voltage change of the resonant capacitor Cr and the resonant current change during the first PWM cycle from entering to exiting the resonant capacitor self-balancing mode of the half-bridge resonant topology flyback conversion circuit provided by an embodiment of the present invention;

[0037] Fig. 9 This is a curve diagram of the voltage change of the resonant capacitor Cr and the resonant current change in the half-bridge resonant topology flyback conversion circuit provided in the comparative example of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments.

[0040] The embodiment of the present invention provides a half-bridge resonant topology flyback converter circuit. Figure 1 As shown, it includes: a controller 1, a flyback converter 2, a protocol module 3 and a feedback circuit 4.

[0041] The controller 1 performs control processing according to the power supply voltage signal Vin at the first input terminal and the feedback signal FB at the second input terminal to determine whether to control the flyback converter 2 to enter the resonant capacitor voltage self-balancing mode or to operate in the normal working mode.

[0042] The controller 1 is as follows Figure 2 As shown, it includes an input detection module 11, a control logic module 12 and a driver 13.

[0043] The input detection module 11 is connected to the first input terminal, and is used for performing power-off detection according to the power voltage signal Vin inputted from the first input terminal, and outputting a power-off detection result signal Brnout.

[0044] The control logic module 12 receives the power-off detection result signal Brnout and the feedback signal FB, performs control logic processing, and outputs driving signals GTH and GTL to send to the driver.

[0045] The driver 13 outputs a converter switch control signal according to the driving signal.

[0046] The driving signal GTH is converted into the driving signal GH for controlling the gate of the resonant power tube of the flyback converter 2 by the driver 13 , and the driving signal GTL is converted into the driving signal GL for controlling the gate of the main power tube of the flyback converter 2 by the driver 13 .

[0047] When it is determined that the flyback converter 2 needs to be controlled to operate in the normal working mode, the drive signals GH and GL output by the controller 1 are pulse width modulation (PWM) signals, which control the resonant power tube and the main power tube of the flyback converter 2 to be alternately turned on and off, so that the half-bridge resonant topology flyback conversion circuit outputs the first DC voltage signal Voh.

[0048] When it is determined that the flyback converter 2 needs to be controlled to enter the resonant capacitor voltage self-balancing mode, the controller 1 stops generating the PWM signal and outputs a specific converter switch control signal. The specific converter switch control signal includes: a multi-cycle square wave signal sequence for controlling the resonant power tube of the flyback converter 2 to be periodically turned on / off, and a level signal for controlling the main power tube of the flyback converter 2 to be turned off. Specifically, whether it is a high level or a low level can be determined according to the type of the main power tube being controlled. In this example, a low level signal is used.

[0049] The flyback converter 2 may specifically be a flyback converter based on an AHB topology, or a flyback converter based on an ACF topology.

[0050] For ease of understanding, combined Figure 3 The flyback converter based on AHB topology shown in Figure 4 The flyback converter based on the ACF topology shown is explained.

[0051] The flyback converter 2 includes a primary side circuit and a secondary side circuit.

[0052] The primary side circuit includes a resonant capacitor Cr, a primary winding, a resonant power tube QH and a main power tube QL; in the primary side circuit of the flyback converter, the resonant power tube QH and the main power tube QL are connected in series, and the primary winding is coupled to the resonant power tube in parallel; the resonant capacitor Cr and the primary winding form an LC resonant circuit.

[0053] The secondary side circuit is inductively coupled to the primary side circuit through the secondary winding and outputs a DC voltage signal to the load.

[0054] In normal working mode, the flyback converter 2 receives the pulse width modulation (PWM) signal output by the controller 1, and the resonant power tube QH and the main power tube QL are alternately turned on and off, so that the half-bridge resonant topology flyback conversion circuit outputs a first DC voltage signal Voh.

[0055] When the flyback converter 2 receives a specific converter switch control signal, the main power tube QL will remain off, and the resonant power tube QH will be periodically turned on / off according to the multi-cycle square wave signal sequence, thereby releasing the energy on the resonant capacitor Cr to the secondary side circuit through the periodic on / off of the resonant power tube QH, accelerating the discharge of the resonant capacitor Cr, thereby quickly reducing the voltage difference between the voltage Vcr on the resonant capacitor Cr and the reflected voltage Vor l converted from the second output voltage; the reflected voltage Vor l converted from the second output voltage is specifically: Vor l=n×Vo l; where n is the primary-to-secondary turns ratio of the transformer. Vol is the output voltage of the set half-bridge resonant topology flyback converter circuit under the output discharge function.

[0056] For example Figure 1 The protocol module 3 is used to detect whether the half-bridge resonant topology flyback converter circuit receives an output voltage step-down instruction and to detect whether the load connected to the half-bridge resonant topology flyback converter circuit is unplugged, and outputs a first detection signal when an output voltage step-down instruction or load unplugging is detected.

[0057] The output voltage reduction instruction is generated by the USB interface module, and the output voltage is reduced by the output voltage reduction instruction. For example, this process occurs when the load is fully charged and then switched to voltage clamp trickle charging.

[0058] The protocol module 3 is also used to, when the protocol module detects an output voltage step-down instruction or the load is unplugged, and starts the output discharge function, adjusts the output voltage of the half-bridge resonant topology flyback converter circuit from the first DC voltage signal Voh (such as 48V) to the second DC voltage signal Vol (such as 5V); the second DC voltage signal Vol is less than the first DC voltage signal Voh. The specific voltage signal parameters are based on the protocol of the fast charging application.

[0059] The feedback circuit 4 has an input end connected to the output of the protocol module 3 and an output end connected to the second input end; the feedback circuit is used to generate a first feedback signal according to the first detection signal and send it to the second input end.

[0060] In this embodiment, based on the above circuit structure, when the controller 1 determines that the power input voltage of the half-bridge resonant topology flyback converter circuit is powered off according to the power voltage signal Vin at the first input terminal, the controller 1 outputs a specific converter switch control signal to control the flyback converter 2 to enter the resonant capacitor voltage self-balancing mode; or, when the protocol module 3 detects an output voltage step-down instruction or a load disconnection connected to the half-bridge resonant topology flyback converter circuit, the protocol module 3 outputs a first detection signal to the feedback circuit 4, the feedback circuit 4 generates a first feedback signal according to the first detection signal, and the controller 1 controls the flyback converter 2 to enter the resonant capacitor voltage self-balancing mode according to the first feedback signal.

[0061] The half-bridge resonant topology flyback conversion circuit provided by the embodiment of the present invention determines whether the circuit needs to enter the resonant capacitor voltage self-balancing mode according to the real-time monitoring and control logic processing of whether the power supply signal and the output voltage are stepped down and the load connection state, and can quickly enter the resonant capacitor voltage self-balancing mode in the case of power failure, output step-down or load unplugging. The resonant power tube is controlled to continuously turn on and off for a certain period of time with a periodic signal of a certain frequency and a certain pulse width, so that the energy on the resonant capacitor Cr can be released to the secondary side circuit through the transformer, thereby accelerating the discharge of the resonant capacitor Cr, and further avoiding the instantaneous generation of a large current pulse when the resonant power tube is turned on again in a short time (for example, in the case of power jitter). Thus, it solves the problem in the prior art that when the conversion circuit is powered on again within a short time after power failure, the protocol chip controls the output voltage to discharge according to the requirements, and after the output voltage switches from high voltage to low voltage, due to the slow discharge of the resonant capacitor voltage, the voltage difference between the resonant capacitor voltage and the output reflected voltage (Vor l) is too high, resulting in a pulsed spike current during the conduction period of the resonant power tube.

[0062] The above introduces the half-bridge resonant topology flyback conversion circuit of the present invention. Next, the method for realizing the self-balancing of the resonant capacitor voltage based on this circuit will be described in detail, and combined with the waveform diagram analysis, the changes in the resonant current in the circuit when the resonant power tube is turned on again after power jitter, output step-down or load unplugging in the prior art will be explained.

[0063] Figure 5 It is a flowchart of the control method for the self-balancing of the resonant capacitor voltage provided by the embodiment of the present invention. Next, in combination with Figure 5 , according to the following step flow, the technical solution of the present invention will be described with specific embodiments.

[0064] Step 510, monitor the input power supply voltage signal through the input detection module of the controller.

[0065] When the power supply voltage signal Vin < Vin_brn, a high-level power failure detection signal Brnout is generated; when the power supply voltage signal Vin > Vin_brn, a low-level Brnout signal is generated. Vin_brn is a reference voltage, which can be set to not less than 80% of the working voltage, and the specific parameters can be set by those skilled in the art according to actual needs in practical applications.

[0066] Step 520, the control logic module of the controller determines whether the power input voltage has a power failure according to the monitoring result.

[0067] When Brnout is at a low level, it is considered that no power input voltage drop occurs, and the flyback converter operates in a normal working mode, and step 530 is continued to be executed; when Brnout is at a high level, it is considered that a power input voltage drop occurs, and the flyback converter enters a resonant capacitor voltage self-balancing mode, and step 560 is executed.

[0068] Step 530 : The protocol module monitors whether the half-bridge resonant topology flyback converter circuit receives an output voltage reduction instruction or whether the load is unplugged.

[0069] If no output voltage step-down instruction is detected or the load is unplugged, the flyback converter operates in the normal working mode and step 540 is executed; if an output voltage step-down instruction is detected or the load is unplugged, steps 550 and 560 are executed.

[0070] Step 540: The flyback converter operates in a normal operating mode, and the half-bridge resonant topology flyback converter circuit outputs a first DC voltage signal.

[0071] In the normal working mode, the controller outputs a pulse width modulation PWM signal to control the resonant power tube and the main power tube of the flyback converter to be alternately turned on and off, so that the conversion circuit outputs a first DC voltage signal Voh.

[0072] Step 550: The protocol module starts output discharge.

[0073] After the output discharge is completed, the output voltage of the half-bridge resonant topology flyback converter circuit is adjusted from the first DC voltage signal Voh to the second DC voltage signal Vo l.

[0074] In step 560 , the controller controls the flyback converter to enter a resonant capacitor voltage self-balancing mode.

[0075] The above step 560 is executed synchronously with step 550. In the resonant capacitor voltage self-balancing mode, in the primary side circuit of the flyback converter, the main power tube remains off, and the resonant power tube is periodically turned on / off, and the energy on the resonant capacitor of the flyback converter is released to the secondary side circuit through the periodic on / off of the resonant power tube, accelerating the discharge of the resonant capacitor, thereby quickly reducing the voltage difference between the voltage Vcr on the resonant capacitor and the reflected voltage Vorl converted from the second output voltage. The reflected voltage Vorl converted from the second output voltage is specifically: Vorl = n×Vol; where n is the primary-to-secondary turns ratio of the transformer.

[0076] Furthermore, the exit mechanism of the resonant capacitor self-balancing mode may vary depending on its entry mechanism. If the controller enters the resonant capacitor self-balancing mode because it detects that the power supply is powered off, then the controller exits the resonant capacitor self-balancing mode when it detects that the power is on (when Brnout changes from a high level to a low level). If the controller enters the resonant capacitor self-balancing mode because it detects that the feedback signal changes to a low level, then after the output voltage is adjusted from the first DC voltage signal Voh to the second DC voltage signal Vol, the feedback circuit generates a second feedback signal to enable the controller to control the flyback converter to exit the resonant capacitor self-balancing mode.

[0077] The frequency of periodic opening / closing of the resonant power tube involved in the above specific steps of the method can be set by those skilled in the art according to the actual circuit application environment. Based on the technical solution of the present invention, the setting can be obtained without creative work by those skilled in the art. Therefore, no specific numerical value is limited here.

[0078] According to the above method, it can be known that, since the continuous on and off of the resonant power tube is controlled, the energy on the resonant capacitor Cr can be released to the secondary side circuit through the transformer, thereby accelerating the discharge of the resonant capacitor Cr. The voltage difference between the voltage Vcr on the resonant capacitor and the reflected voltage Vor l converted from the low output voltage (i.e., Vo l) will decrease until it is close to 0V, reducing the generation of pulse peak current when the resonant power tube is turned on again after the flyback converter exits the standby mode.

[0079] Regarding the above step 530, the protocol module monitors the situation that the load of the half-bridge resonant topology flyback converter circuit is unplugged. The specific processing process is described as follows. The voltage waveform diagram of the half-bridge resonant topology flyback converter circuit executing this method is as follows: Figure 6 shown.

[0080] from Figure 6 It can be seen that before time t2, it is in normal working mode. According to the law of conservation of energy, the Cr capacitor voltage Vcr is approximately equal to Vorh=n×Voh. Therefore, in normal working mode, the voltage difference between Vcr and the reflected voltage Vorh converted from the high output voltage (ie, Voh) is approximately zero, and there is no large peak current during the opening of the resonant power tube.

[0081] At time t2, the protocol module detects the output step-down instruction or the load is unplugged, starts output discharge, the output voltage Vout begins to decrease, and the FB voltage generated by the feedback circuit becomes lower; the controller controls the flyback converter to enter the resonant capacitor self-balancing mode, and the energy on the resonant capacitor Cr is released to the secondary side circuit through the transformer, thereby accelerating the discharge of the resonant capacitor.

[0082] At t4, after the output voltage Vout drops from Voh to the low voltage Vol, the voltage Vcr on the resonant capacitor decreases due to the rapid discharge of the resonant capacitor. The voltage Vcr on the resonant capacitor also drops to Vcr 1. The specific value of Vcr 1 is related to the output discharge time of the protocol module and the frequency of the periodic opening / closing of the resonant power tube. Different frequency values ​​can be selected according to different application parameters to minimize the voltage difference between Vcr and the reflected voltage Vor 1 converted from the second output voltage when the resonant power tube is turned on again, thereby reducing the pulse peak current generated when the resonant power tube is turned on again after the output voltage drops to the target value Vol. At t4, the FB signal becomes high, causing the flyback converter to exit the resonant capacitor self-balancing mode.

[0083] Regarding the above step 520, the specific processing process is described as follows: the voltage waveform of the half-bridge resonant topology flyback converter circuit in the implementation of the present method is as follows: Figure 7 shown.

[0084] In the technical solution of the present invention, when the power supply is unplugged, the controller will detect that the power supply input voltage is powered off. When it is determined that the power supply input voltage is powered off, the control logic circuit stops generating the PWM signal and switches to outputting a specific converter switch control signal.

[0085] Figure 7 It shows the changing relationship between the input voltage Vin, the output voltage Vout and the voltage Vcr on the resonant capacitor. As shown in the figure:

[0086] Before time t1, it is in normal working mode. According to the law of conservation of energy, the Cr capacitor voltage Vcr is approximately equal to Vorh=n×Voh, so the voltage difference between Vcr and Vorh is approximately zero in normal working mode, and there is no large peak current during the opening of the resonant power tube.

[0087] At time t1, the power supply is unplugged and the input voltage Vin starts to drop;

[0088] At time t2, Vin drops to the reference threshold Vin_brn, and the controller of the flyback converter detects that the power supply voltage is off, stops outputting the PWM signal, and switches to outputting a specific converter switch control signal to control the flyback converter to enter the resonant capacitor self-balancing mode. Because the main power tube remains off, the converter cannot obtain energy from the power supply Vin, and Vout begins to drop; when the load is heavy, the output voltage Vout will quickly discharge to 0V, and at the same time, the energy on the resonant capacitor Cr is released to the secondary side circuit through the transformer in the resonant capacitor self-balancing mode;

[0089] At time t3, the power supply is plugged in and the input voltage Vin starts to rise;

[0090] At t4, Vin rises to the reference threshold Vin_brn, and the controller detects that the power supply voltage is powered on. When the controller re-outputs the PWM signal to control the resonant power tube to turn on, the voltage Vcr on the resonant capacitor has dropped to Vcr l, close to 0V, and the voltage difference between Vcr and the reflected voltage Vor l (n×Vo l, n is the transformer primary-to-secondary turns ratio) converted from the low output voltage is already very small, thereby reducing the pulse peak current generated when the resonant power tube is turned on again after the power supply is unplugged and then quickly plugged in.

[0091] Figure 8 A curve diagram of the voltage change of the resonant capacitor Cr and the resonant current change during the first PWM cycle after the half-bridge resonant topology flyback conversion circuit provided by the embodiment of the present invention enters and exits the resonant capacitor self-balancing mode.

[0092] Further, according to Figure 8 It can be seen that the t2 moment corresponds to Figure 6 and Figure 7 Before t2, Vcr = Vorh. At t2, the resonant capacitor enters the self-balancing mode, stops outputting PWM signals, and switches to outputting specific converter switch control signals, i.e., the multi-cycle square wave signal sequence in the figure. The protocol module detects the output step-down command or the load is unplugged, and the control logic detects the power failure of Vin power supply, which will cause the output voltage Vout to drop. The energy on the resonant capacitor of the flyback converter is released to the secondary side circuit through the periodic opening / closing of the resonant power tube, which accelerates the discharge of the resonant capacitor and Vcr decreases rapidly. The t4 moment corresponds to Figure 6 and Figure 7 At t4, the normal working mode is entered, and the first PWM cycle is turned on (the main power tube is turned on first, and the resonant power tube is turned on after the main power tube is turned off). At t5, the resonant power tube is turned on again, and at t6, the resonant power tube is turned off. During the period when the resonant power tube is turned on, the peak value of the resonant current I Lr is small.

[0093] In the prior art, when the protocol module detects an output voltage reduction instruction or the load is unplugged, and the control logic detects that the power supply is powered off, the main power tube and the resonant power tube of the flyback converter all enter the shutdown state (such as Fig. 9The output voltage Vout drops rapidly (especially when the input power fails and the output load is overloaded, the output voltage Vout will quickly discharge to 0V), while the voltage Vcr on the resonant capacitor will maintain the higher reflected voltage before the power is unplugged. If the power failure is a continuous plug-in and unplug situation at this time (for example, voltage jitter when the power is plugged in will be recognized by the circuit as continuous plug-in and unplugging), the controller of the flyback converter will stop generating PWM signals after the power is unplugged, and generate PWM signals again after the next power plug-in, which will cause the resonant power tube to be quickly turned on again. Since the voltage Vcr on the resonant capacitor is still maintained at a higher reflected voltage at this time, there is a large voltage difference with the reflected voltage converted from the low output voltage (close to 0V or has reached 0V), and the impedance in the loop is very small at the moment the resonant power tube is turned on, a large current pulse will be generated. If this large current pulse exceeds the safe operating area (SOA) of the resonant power tube, it may cause damage to the resonant power tube.

[0094] Its waveform Fig. 9 As shown: before t2, Vcr = Vorh. At t2, the protocol module detects the output voltage reduction command or the load is unplugged, and the control logic detects the power failure. The controller of the flyback converter stops outputting the PWM signal, and the output voltage Vout will drop rapidly (especially when the power is off and the output load is under heavy load, the output voltage Vout will quickly discharge to 0V). Because the Vcr voltage takes a long time to discharge from a high voltage, the voltage difference between Vcr and Vor is large. When Vout drops to Vol due to output discharge, or when the power is turned on again in a short time after power failure, the PWM signal is restarted, that is, the main power tube is turned on for a certain time at t4, and the resonant power tube is turned on at t5 after the main power tube is turned off, and the resonant power tube is turned off at t6. During the conduction period of the resonant power tube, the peak value of the resonant current I Lr is relatively high. If the safe working area of ​​the power tube is exceeded, the resonant power tube is easily damaged.

[0095] It can be seen that the resonant capacitor voltage self-balancing method proposed in the present invention can greatly reduce the voltage difference between the resonant capacitor Cr voltage and the Vor voltage in the flyback converter such as AHB or ACF after the output voltage is switched and the input power is off, and reduce the pulse peak current generated when the resonant power tube is turned on again, making the system safer and more reliable.

[0096] The professionals should further realize that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to the function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0097] The steps of the method or algorithm described in conjunction with the embodiments disclosed herein may be implemented using hardware, a software module executed by a processor, or a combination of the two. The software module may be placed in a random access memory (RAM), a memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

[0098] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A half-bridge resonant topology flyback converter circuit, characterized in that: The half-bridge resonant topology flyback conversion circuit comprises: The controller performs control processing according to the power supply voltage signal of the first input terminal and the feedback signal of the second input terminal, and determines whether to control the flyback converter to enter the resonant capacitor voltage self-balancing mode; when it is determined that the flyback converter is controlled to enter the resonant capacitor voltage self-balancing mode, the controller outputs a specific converter switch control signal; wherein the controller includes an input detection module, a control logic module and a driver; the input detection module is connected to the first input terminal, and is used to perform power-off detection according to the power supply voltage signal input by the first input terminal, and output a power-off detection result signal; the control logic module receives the power-off detection result signal and the feedback signal, performs control logic processing, and outputs a drive signal to the driver; the driver outputs the converter switch control signal according to the drive signal; A flyback converter, comprising a primary side circuit and a secondary side circuit, wherein the primary side circuit comprises a resonant capacitor, a primary winding, a resonant power tube and a main power tube; wherein, in the primary side circuit of the flyback converter, the resonant power tube and the main power tube are connected in series, and the primary winding is coupled to the resonant power tube in parallel; the resonant capacitor and the primary winding constitute an LC resonant circuit; the secondary side circuit is inductively coupled to the primary side circuit through the secondary winding, and outputs a DC voltage signal to a load; the flyback converter controls the main power tube to remain turned off according to the received specific converter switch control signal, and the resonant power tube is periodically turned on / off, so that the energy on the resonant capacitor is released to the secondary side circuit through the periodic turning on / off of the resonant power tube, thereby accelerating the discharge of the resonant capacitor, thereby rapidly reducing the voltage difference between the voltage Vcr on the resonant capacitor and the reflected voltage Vorl converted from the second output voltage; A protocol module, used to detect whether an output voltage reduction instruction is received or whether a USB load connected to the half-bridge resonant topology flyback conversion circuit is unplugged, and output a first detection signal when the output voltage reduction instruction or the load is unplugged is detected; A feedback circuit, the input end of which is connected to the output of the protocol module, and the output end of which is connected to the second input end; the feedback circuit is used to generate a first feedback signal according to the first detection signal and send it to the second input end.

2. The half-bridge resonant topology flyback converter circuit according to claim 1, characterized in that: When the controller determines that the power input voltage of the half-bridge resonant topology flyback converter circuit is powered off according to the power voltage signal at the first input terminal, the controller outputs the specific converter switch control signal to control the flyback converter to enter the resonant capacitor voltage self-balancing mode; or, When the protocol module detects an output step-down instruction of the half-bridge resonant topology flyback converter circuit or the connected USB load is unplugged, it outputs a first detection signal to the feedback circuit, the feedback circuit generates the first feedback signal according to the first detection signal, and the controller controls the flyback converter to enter a resonant capacitor voltage self-balancing mode according to the first feedback signal.

3. The half-bridge resonant topology flyback converter circuit according to claim 1, characterized in that: The protocol module is also used to start the output discharge function when the protocol module detects the output voltage reduction instruction or the load is unplugged, and adjust the output voltage of the half-bridge resonant topology flyback conversion circuit from the first DC voltage signal Voh to the second DC voltage signal Vol; the second DC voltage signal Vol is less than the first DC voltage signal Voh.

4. The half-bridge resonant topology flyback converter circuit according to claim 3, characterized in that: The reflected voltage Vorl converted from the second output voltage is specifically: Vorl=n×Vol; wherein n is the primary-to-secondary turns ratio of the transformer.

5. The half-bridge resonant topology flyback converter circuit according to claim 1, characterized in that: The flyback converter is specifically a flyback converter based on a half-bridge resonant AHB topology, or a flyback converter based on a half-bridge resonant ACF topology.

6. A method for self-balancing the resonant capacitor voltage based on the half-bridge resonant topology flyback converter circuit according to claim 1, characterized in that: The method comprises: The controller monitors the power supply voltage signal to determine whether a power supply input voltage power failure occurs; when the power supply input voltage power failure does not occur, the controller controls the flyback converter to operate in a normal working mode; when the power supply input voltage power failure occurs, the controller controls the flyback converter to enter a resonant capacitor voltage self-balancing mode; In the normal working mode, the protocol module monitors whether the output voltage reduction instruction of the conversion circuit or the USB load is unplugged, and generates a first feedback signal through the feedback circuit when the output voltage reduction instruction or the load is unplugged is detected; The controller monitors the feedback signal, and when the feedback signal is the first feedback signal, the protocol module adjusts the output voltage of the half-bridge resonant topology flyback converter circuit from the first DC voltage signal Voh to the second DC voltage signal Vol, and the controller controls the flyback converter to enter the resonant capacitor voltage self-balancing mode; otherwise, the controller controls the flyback converter to operate in the normal working mode, and the half-bridge resonant topology flyback converter circuit outputs the first DC voltage signal Voh; In the resonant capacitor voltage self-balancing mode, in the primary side circuit of the flyback converter, the main power tube remains turned off, and the resonant power tube is periodically turned on / off, and the energy on the resonant capacitor of the flyback converter is released to the secondary side circuit through the periodic turning on / off of the resonant power tube, thereby accelerating the discharge of the resonant capacitor, so as to quickly reduce the voltage difference between the voltage Vcr on the resonant capacitor and the reflected voltage Vorl converted from the second output voltage; the reflected voltage Vorl converted from the second output voltage is specifically: Vorl = n×Vol; wherein n is the primary-to-secondary turns ratio of the transformer.

7. The resonant capacitor voltage self-balancing method according to claim 6, characterized in that: The method also includes: in the normal working mode, the controller outputs a pulse width modulation (PWM) signal to control the resonant power tube and the main power tube of the flyback converter to be alternately turned on and off, so that the conversion circuit outputs the first DC voltage signal Voh.

8. The resonant capacitor voltage self-balancing method according to claim 7, characterized in that: The method further includes: after the output voltage is adjusted from the first DC voltage signal Voh to the second DC voltage signal Vol, the feedback circuit generates a second feedback signal, and the controller controls the flyback converter to exit the resonant capacitor self-balancing mode according to the second feedback signal.

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