A low temperature start-up optimization circuit for LLC resonant converter

Abstract

The utility model discloses a low temperature starting optimization circuit for LLC resonant converter relates to power electronics technical field, on the converter of LLC resonant cavity, controller chip and current detection resistance Risen constitution foundation, add temperature sampling unit, control unit and impedance adjusting unit, temperature sampling unit is divided by negative temperature coefficient thermistor and fixed resistance voltage division, and the environmental temperature is perceived and is output sampling signal, and after RC filtering, transmission control unit, control unit is by voltage comparator and precision voltage reference source composition, compare sampling signal with preset threshold value, and output control signal, impedance adjusting unit passes through MOSFET and compensation resistance, and according to control signal dynamic adjustment current detection network equivalent impedance. The utility model realizes reliable starting under low temperature, and the original detection impedance is automatically recovered when normal temperature, and is applicable to the scene of communication equipment, industrial control and other need extremely low temperature power supply.

Description

Technical Field

[0001] This utility model relates to the field of power electronics technology, specifically to a low-temperature startup optimization circuit for LLC resonant converters. Background Technology

[0002] In the field of power electronics, power supplies based on highly integrated PFC+LLC control chips such as the Silergy SY5055A have been widely used in communication equipment, industrial control devices, consumer electronics, and many other fields due to their core advantages of high efficiency and high power density. As application scenarios continue to expand, the demand for reliable operation of these power supplies in extreme low-temperature environments is becoming increasingly prominent. For example, in outdoor equipment in high-latitude regions, cold chain transportation control systems, and aerospace auxiliary power supply scenarios, they often face low-temperature conditions of -35℃ or even -40℃, posing stringent challenges to the power supply's startup performance and stability.

[0003] In practical testing and applications, it has been found that traditionally designed LLC resonant converters are prone to startup failures and repeated restarts in low-temperature environments, severely affecting the normal operation of the equipment. The root cause lies in the fact that low temperatures induce a series of changes in the characteristics of key components: the on-resistance Rds(on) of the power MOSFET increases significantly, leading to increased conduction losses; the permeability of magnetic components such as transformers and inductors changes, increasing hysteresis losses; and the capacitance of the resonant capacitor decays due to low-temperature characteristics. These changes collectively result in extremely weak initial oscillation energy of the LLC resonant cavity.

[0004] Insufficient oscillation energy directly results in an excessively low amplitude and poor signal-to-noise ratio of the detection signal (Visen) on the current sensing resistor (Risen), making it impossible for the controller to accurately perform zero-voltage switching (ZVS) judgment and cycle-by-cycle current limit control. When the detection signal fails to meet the controller's recognition threshold, the system will falsely trigger the protection logic, thus entering a dead loop of start-protection-restart. This not only prevents normal power supply but may also cause additional wear and tear on the internal components of the power supply due to frequent start-stop cycles, shortening its lifespan.

[0005] Existing solutions to this problem have significant drawbacks. A common approach is to simply reduce the resistance of the current sensing resistor (Risen) to improve detection sensitivity, but this static adjustment method is destructive. At room temperature, an excessively small Risen value can cause abnormal operating modes of the LLC converter, such as switching from continuous conduction mode (CCM) to discontinuous conduction mode (DCM), resulting in a significant decrease in power efficiency. Simultaneously, the overcurrent protection point shifts as the Risen resistance decreases, reducing the power supply's protection capability under overload conditions. This makes it impossible to balance low-temperature startup reliability with room-temperature steady-state performance. Therefore, an optimized solution that can adapt to ambient temperature and intelligently adjust detection sensitivity is urgently needed. Utility Model Content

[0006] To address the aforementioned technical problems, this application discloses a low-temperature startup optimization circuit for LLC resonant converters, comprising an LLC resonant cavity, a controller chip, and a current sensing resistor R for detecting the resonant current. isen The controller chip is equipped with a current detection resistor R. isen Connected current sensing pin I sen The LLC resonant cavity, controller chip, and sensing resistor R isen An LLC resonant converter is characterized by comprising a temperature sampling unit, a control unit, and an impedance adjustment unit.

[0007] The temperature sampling unit is used to sense the ambient temperature of the LLC resonant converter and output a sampling signal corresponding to the ambient temperature.

[0008] The control unit is electrically connected to the temperature sampling unit, and is used to receive the sampling signal, compare the sampling signal with a preset threshold, and output a corresponding control signal according to the comparison result.

[0009] The impedance adjustment unit is connected to the control unit and the current detection resistor R respectively. isen An electrical connection is provided for receiving the control signal and dynamically adjusting the current detection resistor R according to the control signal. isen The equivalent impedance of the detection network.

[0010] Preferably, the temperature sampling unit includes a negative temperature coefficient thermistor RT1, a fixed resistor R1, and a fixed resistor R2; one end of the fixed resistor R1 is connected to the power supply VCC, and the other end is connected to one end of the negative temperature coefficient thermistor RT1 and one end of the fixed resistor R2 respectively; the other end of the negative temperature coefficient thermistor RT1 is grounded.

[0011] Preferably, the control unit includes a voltage comparator U1 and a reference voltage source; the non-inverting input of the voltage comparator U1 is connected to the output of the temperature sampling unit for receiving the sampling signal; the inverting input of the voltage comparator U1 is connected to the output of the reference voltage source for receiving a reference voltage V corresponding to a preset threshold. ref The output terminal of the voltage comparator U1 serves as the output terminal of the control unit, used to output the control signal.

[0012] Preferably, the reference voltage source includes a precision voltage reference chip U2; the input terminal of the precision voltage reference chip U2 is connected to the power supply VCC, and the output terminal serves as the output terminal of the reference voltage source, connected to the inverting input terminal of the voltage comparator U1; the ground terminal of the precision voltage reference chip U2 is grounded, and a filter capacitor C1 is connected in parallel between the ground terminal and the output terminal to stabilize the reference voltage V. ref The output of .

[0013] Preferably, the voltage comparator U1 is further provided with a hysteresis adjustment pin, which is connected to the power supply VCC through a resistor to prevent abnormal jitter of the control signal when the sampling signal fluctuates near a preset threshold.

[0014] Preferably, the impedance adjustment unit includes a switching device Q2 and a compensation resistor R. comp The first electrode of the switching device Q2 is connected to the compensation resistor R. comp One end of the circuit is connected, and the second electrode of the switching device Q2 is grounded; the compensation resistor R comp The other end is connected to the current sensing resistor R isen One end is connected; the current sensing resistor R isen The other end is connected to the LLC resonant cavity, and the current sensing resistor R isen With compensation resistor R comp One end of the connection is also connected to the current detection pin I of the controller chip. sen Connection; the control electrode of the switching device Q2 is connected to the output terminal of the control unit for receiving the control signal.

[0015] Preferably, the switching device Q2 is an N-channel MOSFET; the drain of the N-channel MOSFET serves as the first electrode of the switching device Q2, and is connected to the compensation resistor R. comp The source of the N-channel MOSFET serves as the second electrode of the switching device Q2 and is grounded; the gate of the N-channel MOSFET serves as the control electrode of the switching device Q2 and is connected to the output terminal of the control unit.

[0016] Preferably, the impedance adjustment unit further includes a current-limiting resistor R5; one end of the current-limiting resistor R5 is connected to the output terminal of the control unit, and the other end is connected to the control electrode of the switching device Q2, for limiting the current flowing into the control electrode of the switching device Q2.

[0017] Preferably, the controller chip is a SY5055A chip; the Isen pin of the SY5055A chip serves as a current sensing pin, connected to the current sensing resistor R. isen Connection: The VCC pin of the SY5055A chip is connected to the power supply, the GND pin is grounded, and a decoupling capacitor C3 is connected in parallel between the VCC pin and the GND pin to stabilize the chip's power supply voltage.

[0018] Compared with the prior art, the technical solution of this application has the following technical effects:

[0019] This invention solves the startup problem of LLC resonant converters in extreme low-temperature environments. By sensing the ambient temperature in real time through a temperature sampling unit, and cooperating with the control unit and impedance adjustment unit to dynamically adjust the equivalent impedance of the current detection network, the amplitude of the resonant current detection signal and the signal-to-noise ratio are significantly improved at low temperatures. This ensures that the controller can accurately complete zero-voltage switching judgment and cyclic current limiting, avoids false triggering of protection logic, completely breaks the dead loop of "start-protection-restart", and achieves reliable startup under low-temperature conditions of -35℃ to -40℃.

[0020] This invention balances the low-temperature start-up reliability and room-temperature steady-state performance of LLC resonant converters, overcoming the shortcomings of existing technologies that statically reduce the resistance value of the current detection resistor. At room temperature, the impedance adjustment unit disconnects the compensation resistor, and the equivalent impedance of the detection network is restored to the original current detection resistor value. This avoids problems such as abnormal converter operating mode, efficiency reduction, and overcurrent protection point offset, ensuring that the power supply maintains a high-efficiency and stable operating state at room temperature, achieving a synergy between "high sensitivity at low temperature" and "high performance at room temperature".

[0021] This invention boasts advantages such as low cost, ease of implementation, and adaptability. It optimizes the circuit by adding low-cost components such as negative temperature coefficient thermistors, voltage comparators, and switching devices, without requiring modification to the controller chip itself, and can be easily integrated into existing power supply designs. The entire adjustment process requires no software intervention and can automatically switch detection sensitivity based on ambient temperature, exhibiting fast response and high reliability. While improving low-temperature start-up performance, it reduces R&D and production costs, making it widely applicable.

[0022] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the preferred embodiments of this application are described in detail below with reference to the accompanying drawings.

[0023] The above and other objects, advantages and features of this application will become more apparent to those skilled in the art from the following detailed description of specific embodiments in conjunction with the accompanying drawings. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0025] Based on the description of the figures and their corresponding technical content in the document, the titles of the figures are as follows:

[0026] Figure 1 This is a schematic diagram of the complete circuit connection of a low-temperature startup optimization circuit for LLC resonant converters. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. In the following description, specific details such as specific configurations and components are provided merely to help fully understand the embodiments of this application. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. In addition, for clarity and brevity, descriptions of known functions and structures are omitted in the embodiments.

[0028] It should be understood that the phrase "an embodiment" or "this embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "an embodiment" or "this embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0029] Furthermore, reference numerals and / or letters may be repeated in different examples within this application. Such repetition is for the purpose of simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or settings discussed.

[0030] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. The term " / and" in this article describes another type of relationship between related objects, indicating that two relationships can exist. For example, A / and B can mean: A exists alone, and A and B exist alone. In addition, the character " / " in this article generally indicates that the related objects before and after it are in an "or" relationship.

[0031] In this article, the term "at least one" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, "at least one of A and B" can mean: A exists alone, A and B exist simultaneously, or B exists alone.

[0032] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion.

[0033] Example 1

[0034] This embodiment mainly describes a low-temperature startup optimization circuit for LLC resonant converters, such as... Figure 1 As shown, it includes an LLC resonant cavity, a controller chip, and a current sensing resistor R for detecting the resonant current. isen The controller chip is equipped with a current detection resistor R. isen Connected current sensing pin I sen The LLC resonant cavity, controller chip, and sensing resistor R isen The low-temperature startup optimization circuit, which constitutes an LLC resonant converter, includes a temperature sampling unit, a control unit, and an impedance adjustment unit.

[0035] The temperature sampling unit is used to sense the ambient temperature of the LLC resonant converter and output a sampling signal corresponding to the ambient temperature.

[0036] The control unit is electrically connected to the temperature sampling unit, and is used to receive the sampling signal, compare the sampling signal with a preset threshold, and output a corresponding control signal according to the comparison result.

[0037] The impedance adjustment unit is connected to the control unit and the current detection resistor R respectively. isen An electrical connection is provided for receiving the control signal and dynamically adjusting the current detection resistor R according to the control signal. isen The equivalent impedance of the detection network.

[0038] Furthermore, the temperature sampling unit uses a negative temperature coefficient thermistor RT1 as its core sensing element, and forms a voltage divider network with fixed resistors R1 and R2 to convert temperature into voltage signals. One end of the fixed resistor R1 is directly connected to the power supply VCC for power, while the other end serves as a voltage divider node, sharing a common connection with one end of the negative temperature coefficient thermistor RT1 and one end of the fixed resistor R2. The other end of the negative temperature coefficient thermistor RT1 is directly grounded, forming the lower branch of the voltage divider circuit. The other end of the fixed resistor R2 serves as the signal output terminal of the entire temperature sampling unit, which is directly connected to the signal input terminal of the subsequent control unit to transmit the temperature-varying voltage divider signal (i.e., the sampling signal) to the control unit. This voltage divider structure utilizes the characteristic of RT1 that "the lower the temperature, the higher the resistance, and the higher the temperature, the lower the resistance," so that the output sampling signal voltage is inversely linearly correlated with the change in ambient temperature, providing accurate electrical signal basis for temperature judgment.

[0039] Furthermore, the control unit consists of a voltage comparator U1 and a reference voltage source, which compares the sampled signal with a preset threshold. The pin connections of the voltage comparator U1 are as follows: its non-inverting input (+) is connected to the output of the temperature sampling unit (the other end of the fixed resistor R2) through the filter resistor R4 mentioned above, specifically to receive the filtered temperature sampling signal; its inverting input (-) is directly connected to the output of the reference voltage source, receiving the reference voltage V used to determine the temperature threshold. ref The output of voltage comparator U1 serves as the final signal output of the control unit, directly connected to the control terminal of the subsequent impedance adjustment unit, and is used to output high and low level control signals.

[0040] The reference voltage source is built around the precision voltage reference chip U2 to ensure the reference voltage V. ref The stability of the precision voltage reference chip U2 is ensured by the following pin connections: its input terminal (VIN) is directly connected to the power supply VCC to obtain the operating voltage; its output terminal (VOUT) serves as the signal output terminal of the reference voltage source and is directly connected to the inverting input terminal of the voltage comparator U1 to provide a stable reference voltage Vref; its ground terminal (GND) is directly grounded, and a filter capacitor C1 is connected in parallel between the ground terminal and the output terminal. One end of the filter capacitor C1 is connected to the output terminal of U2, and the other end is connected to the ground terminal of U2. This capacitor can suppress the fluctuation of the reference voltage Vref, further improving the stability of the reference voltage and ensuring the threshold judgment accuracy of the voltage comparator U1.

[0041] To prevent abnormal control signal jitter caused by the sampling signal repeatedly crossing the threshold when the ambient temperature fluctuates slightly around a preset threshold, a hysteresis adjustment circuit is added to the voltage comparator U1. Specifically, the hysteresis adjustment pin of the voltage comparator U1 (usually labeled HYST or H) is connected to the power supply VCC via a dedicated resistor. One end of this resistor is connected to the power supply VCC, and the other end is directly connected to the hysteresis adjustment pin of U1, forming a voltage divider circuit for the hysteresis voltage. By configuring the resistance value of this resistor, a reasonable hysteresis voltage range can be set, so that the voltage comparator U1 uses a higher trigger voltage when the sampling signal crosses the threshold from low to high, and a lower trigger voltage when the sampling signal falls back from high to low. The difference between the two is the hysteresis voltage. This design effectively avoids frequent switching of the control signal around the threshold, ensuring the stability and reliability of the control signal output by the control unit, and thus preventing the impedance adjustment unit from experiencing frequent on / off abnormalities.

[0042] Furthermore, the impedance adjustment unit consists of a switching device Q2 and a compensation resistor R. comp The core function of the switching device Q2 is to change the equivalent impedance of the current detection network by controlling its on / off state. The first electrode of the switching device Q2 is connected to the compensation resistor R. comp One end of the circuit is connected at a common point; the second electrode of the switching device Q2 is directly grounded, forming the common terminal of the circuit; the compensation resistor R comp The other end is connected to the current sensing resistor R. isen One end is connected at a common point; current sensing resistor R isen The other end is directly connected to the current output terminal of the LLC resonant cavity to obtain the resonant current signal; simultaneously, the current sensing resistor R... isen With compensation resistor R comp The common point of connection is also directly connected to the current sensing pin (I) of the controller chip. sen The common point is connected to the current detection signal acquisition point and the compensation resistor access point. The control electrode of the switching device Q2 (the pin used to receive control signals) is directly connected to the output terminal of the control unit (the output terminal of the voltage comparator U1), and is turned on or off by receiving high and low level control signals.

[0043] When the switching device Q2 is an N-channel MOSFET, its pin connection relationship is clearer: the drain (D) of the N-channel MOSFET serves as the first electrode of the switching device, connected to the compensation resistor R. compOne end is connected; the source (S) serves as the second electrode and is directly grounded; the gate (G) serves as the control electrode and is connected to the output of the control unit. This connection method conforms to the operating characteristics of an N-channel MOSFET: "the drain and source are turned on when a positive voltage (high level) is applied to the gate, and the drain and source are turned off when zero voltage or a negative voltage (low level) is applied to the gate," ensuring the effectiveness of the switching control.

[0044] To prevent excessive control signal current from damaging the control electrode (such as the gate of a MOSFET) of the switching device Q2, a current-limiting resistor R5 is added to the impedance adjustment unit. Specifically, the current-limiting resistor R5 is connected in series between the output terminal of the control unit (the output terminal of voltage comparator U1) and the control electrode of the switching device Q2. That is, one end of the current-limiting resistor R5 is directly connected to the output terminal of U1, and the other end is directly connected to the control electrode of Q2. By selecting a suitable current-limiting resistor R5, the current flowing into the control electrode of the switching device can be limited to a safe range, preventing the control electrode from burning out due to excessive control signal current, while not affecting the level of the control signal, ensuring that the switching device can normally receive the control commands for conduction or cutoff.

[0045] The controller chip uses the SY5055A chip, whose pin connections are closely related to the LLC resonant converter and optimization circuit, making it the control core of the entire system. Specifically, the connection method is as follows: the current detection pin (I...) of the SY5055A chip... sen Directly connected to the current sensing resistor R isen The signal acquisition terminal (i.e., R) isen With compensation resistor R comp The common point of connection is used to collect current sensing resistor R. isen Voltage signal (V) isen This allows for the detection of resonant current. The chip's power supply pin (VCC) is directly connected to the power supply, providing the chip with its operating voltage. The chip's ground pin (GND) is directly grounded, forming the circuit's common reference terminal. Simultaneously, a decoupling capacitor C3 is connected in parallel between the power supply pin (VCC) and the ground pin (GND). One end of the decoupling capacitor C3 is connected to the chip's VCC pin, and the other end is connected to the chip's GND pin. This decoupling capacitor C3 suppresses power supply voltage fluctuations, filters out high-frequency noise generated during chip operation, stabilizes the chip's supply voltage, and ensures that the SY5055A chip can normally perform its core functions of zero-voltage switching (ZVS) judgment and cycle current limiting, avoiding abnormal chip operation due to unstable power supply.

[0046] This implementation constructs a complete low-temperature startup optimized hardware architecture by clearly defining the specific circuit connections of the temperature sampling unit, control unit, and impedance adjustment unit. It uses a negative temperature coefficient thermistor for voltage division to sample the temperature, coupled with RC filtering to ensure signal stability. It achieves accurate threshold judgment through a voltage comparator and a precision reference source, and then uses MOSFETs and compensation resistors to dynamically adjust the detection impedance. At the same time, it adds current limiting and decoupling protection circuits, so that it can provide reliable hardware support for subsequent operating condition adaptation without modifying the controller chip. It can be integrated with low-cost components, effectively solving the hardware design defects of traditional static resistance adjustment that cannot take into account both low-temperature and normal-temperature performance.

[0047] Based on Example 1, this example details the working mechanism of the low-temperature startup optimization circuit for LLC resonant converters. Through the coordinated action of the temperature sampling unit, control unit, and impedance adjustment unit, it dynamically adapts to changes in ambient temperature, solving the low-temperature startup problem while ensuring performance at room temperature. The specific working mechanism is divided into low-temperature operating conditions, room temperature / post-startup operating conditions, and anti-interference protection, as follows:

[0048] The startup optimization mechanism under low-temperature conditions is based on an ambient temperature ≤ a preset threshold. When the LLC resonant converter is in an extreme low-temperature environment of -35℃ to -40℃, the temperature sampling unit first completes the acquisition and conversion of the temperature signal. In the temperature sampling unit, the resistance of the negative temperature coefficient thermistor RT1 increases significantly due to its low-temperature characteristics, and the voltage divider network formed by it and the fixed resistors R1 and R2 changes: one end of the fixed resistor R1 is connected to the power supply VCC, and the other end is connected at the same point as RT1 and R2. The other end of RT1 is grounded, and the other end of R2 serves as the output terminal. As the resistance of RT1 increases, the voltage at the voltage divider point (i.e., the sampling signal Vtemp) of the voltage divider network increases accordingly. This signal is filtered by the RC filter circuit composed of the filter resistor R4 and the filter capacitor C2 to remove interference, and then transmitted to the non-inverting input terminal of the voltage comparator U1 of the control unit.

[0049] In the control unit, the precision voltage reference chip U2 (with its input terminal connected to VCC, its ground terminal grounded, and a filter capacitor C1 connected in parallel between the ground terminal and the output terminal to stabilize the voltage) outputs a fixed reference voltage V. ref The signal is connected to the inverting input of voltage comparator U1. At this time, the sampled signal V... temp Higher than the reference voltage V ref The voltage comparator U1 outputs a high-level control signal, which is then limited by the current-limiting resistor R3 and transmitted to the gate of the N-channel MOSFET (switching device Q2) in the impedance adjustment unit.

[0050] The N-channel MOSFET turns on after receiving a high-level signal at its gate, and its drain is connected to a compensation resistor R. comp The following circuit is then connected: compensation resistor R comp One end is connected to the drain of the MOSFET, and the other end is connected to the current sensing resistor R.isen One end, the controller chip (SY5055A) I sen Pins are connected at a common point, R isen The other end is connected to the LLC resonant cavity, and the MOSFET source is grounded. At this time, the compensation resistor R... comp With R isen By forming a parallel connection, the equivalent impedance of the current sensing network is significantly reduced; the problem of weak oscillation energy in the LLC resonant cavity due to low temperature is improved with the reduced equivalent impedance—the same resonant current can generate a higher amplitude detection signal V. isen This signal is transmitted through I sen The pins transmit data to the SY5055A chip, ensuring that the chip can accurately perform zero-voltage switching (ZVS) judgment and cycle-by-cycle current limit, avoiding false triggering of protection logic, while transferring more energy to the output terminal, enabling reliable startup of the converter at low temperatures.

[0051] The performance guarantee mechanism under normal temperature / start-up conditions is as follows: when the ambient temperature is greater than the preset threshold, or when the converter completes low-temperature start-up and enters a stable operating state, the resistance of the negative temperature coefficient thermistor RT1 of the temperature sampling unit decreases with increasing temperature, resulting in a decrease in the sampling signal V output by the voltage divider network. temp Synchronous decrease. After processing by the RC filter circuit, V temp The voltage is transmitted to the non-inverting input of voltage comparator U1, at which point V temp Lower than the reference voltage V at the inverting input terminal ref The voltage comparator U1 outputs a low-level control signal.

[0052] A low-level signal is transmitted to the gate of the N-channel MOSFET via the current-limiting resistor R3. The MOSFET gate is turned off due to the lack of a forward voltage trigger, and its drain is connected to the compensation resistor R. comp The connection to the circuit has been completely disconnected. The equivalent impedance of the current sensing network has been restored to the original current sensing resistor R. isen The resistance value, the controller chip SY5055A through I sen Pin acquisition R isen The detection signal V on isen At this point, the circuit parameters return to their optimal state at room temperature—avoiding problems such as abnormal LLC operating mode (e.g., switching from continuous conduction mode CCM to intermittent conduction mode DCM), efficiency degradation, and overcurrent protection point offset caused by long-term connection of the compensation resistor, thus ensuring that the converter maintains high efficiency and high stability steady-state operation at room temperature.

[0053] The hysteresis function's anti-jitter protection is designed to prevent small fluctuations in ambient temperature around a preset threshold (such as alternating between around 0°C) from affecting the sampling signal V.temp Repeatedly crossing the reference voltage V ref This leads to frequent switching of control signals and abnormal switching of the impedance adjustment unit. Voltage comparator U1 is equipped with a hysteresis adjustment function. Specifically, this is achieved by connecting a resistor in series between the hysteresis adjustment pin of U1 and the power supply VCC: one end of the resistor is connected to VCC, and the other end is connected to the hysteresis adjustment pin of U1. A reasonable hysteresis voltage range is set by configuring the resistance value.

[0054] As the temperature rises from low to high and approaches the threshold, voltage comparator U1 needs to be at V... temp Reaching the upper limit trigger voltage (above V) ref It only switches to low level when the temperature approaches the threshold from high to low; when the temperature decreases from high to low, it needs to switch to low level at V. temp Drop to the "lower trigger voltage" (below V) ref The signal only switches to high level when the threshold voltage is reached. The difference between the upper and lower trigger voltages forms a hysteresis range, which effectively avoids abnormal jitter of the control signal near the threshold, ensures the stability of the on / off state of the impedance adjustment unit, and further guarantees the operational reliability of the LLC resonant converter in the temperature critical region.

[0055] This embodiment details the dynamic adjustment logic that adapts to low temperatures and recovers to normal temperatures, completely solving the problem of starting at extreme low temperatures. At low temperatures, the impedance is reduced by temperature sampling, which increases the amplitude of the detection signal, ensuring accurate judgment by the controller and breaking the dead loop of the start-protection-restart strategy, achieving reliable start-up from -35℃ to -40℃. At normal temperature or after start-up, the compensation resistor is automatically disconnected to restore the original detection impedance, avoiding abnormal working modes and efficiency reduction, perfectly balancing low-temperature reliability and high performance at normal temperature.

[0056] The above are merely preferred embodiments of the present utility model, and are not intended to limit the scope of protection of the present utility model. For those skilled in the art, the present utility model can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter changes made to these embodiments within the spirit and principles of the present utility model, without departing from the principles and spirit of the present utility model, through conventional substitutions or to achieve the same function, shall fall within the scope of protection of the present utility model.

Claims

1. A low-temperature startup optimization circuit for an LLC resonant converter, comprising an LLC resonant cavity, a controller chip, and a current sensing resistor R for detecting the resonant current. isen The controller chip is equipped with a current detection resistor R. isen Connected current sensing pin I sen The LLC resonant cavity, controller chip, and sensing resistor R isen The LLC resonant converter is characterized by, Includes a temperature sampling unit, a control unit, and an impedance adjustment unit: The temperature sampling unit is used to sense the ambient temperature of the LLC resonant converter and output a sampling signal corresponding to the ambient temperature. The control unit is electrically connected to the temperature sampling unit, and is used to receive the sampling signal, compare the sampling signal with a preset threshold, and output a corresponding control signal according to the comparison result. The impedance adjustment unit is connected to the control unit and the current detection resistor R respectively. isen An electrical connection is provided for receiving the control signal and dynamically adjusting the current detection resistor R according to the control signal. isen The equivalent impedance of the detection network.

2. The low-temperature startup optimization circuit for an LLC resonant converter according to claim 1, characterized in that, The temperature sampling unit includes a negative temperature coefficient thermistor RT1, a fixed resistor R1, and a fixed resistor R2; one end of the fixed resistor R1 is connected to the power supply VCC, and the other end is connected to one end of the negative temperature coefficient thermistor RT1 and one end of the fixed resistor R2 respectively; the other end of the negative temperature coefficient thermistor RT1 is grounded.

3. The low-temperature startup optimization circuit for an LLC resonant converter according to claim 1, characterized in that, The control unit includes a voltage comparator U1 and a reference voltage source; the non-inverting input of the voltage comparator U1 is connected to the output of the temperature sampling unit for receiving the sampling signal; the inverting input of the voltage comparator U1 is connected to the output of the reference voltage source for receiving a reference voltage V corresponding to a preset threshold. ref The output terminal of the voltage comparator U1 serves as the output terminal of the control unit, used to output the control signal.

4. The low-temperature startup optimization circuit for an LLC resonant converter according to claim 3, characterized in that, The reference voltage source includes a precision voltage reference chip U2; the input terminal of the precision voltage reference chip U2 is connected to the power supply VCC, and the output terminal serves as the output terminal of the reference voltage source, connected to the inverting input terminal of the voltage comparator U1; the ground terminal of the precision voltage reference chip U2 is grounded, and a filter capacitor C1 is connected in parallel between the ground terminal and the output terminal to stabilize the reference voltage V. ref The output of .

5. A low-temperature startup optimization circuit for an LLC resonant converter according to claim 4, characterized in that, The voltage comparator U1 is also provided with a hysteresis adjustment pin, which is connected to the power supply VCC through a resistor to prevent abnormal jitter of the control signal when the sampling signal fluctuates near a preset threshold.

6. The low-temperature startup optimization circuit for an LLC resonant converter according to claim 1, characterized in that, The impedance adjustment unit includes a switching device Q2 and a compensation resistor R. comp The first electrode of the switching device Q2 is connected to the compensation resistor R. comp One end of the circuit is connected, and the second electrode of the switching device Q2 is grounded; the compensation resistor R comp The other end is connected to the current sensing resistor R isen One end is connected; the current sensing resistor R isen The other end is connected to the LLC resonant cavity, and the current sensing resistor R isen With compensation resistor R comp One end of the connection is also connected to the current detection pin I of the controller chip. sen Connection; the control electrode of the switching device Q2 is connected to the output terminal of the control unit for receiving the control signal.

7. A low-temperature startup optimization circuit for an LLC resonant converter according to claim 6, characterized in that, The switching device Q2 is an N-channel MOSFET; the drain of the N-channel MOSFET serves as the first electrode of the switching device Q2, and is connected to the compensation resistor R. comp The source of the N-channel MOSFET serves as the second electrode of the switching device Q2 and is grounded; the gate of the N-channel MOSFET serves as the control electrode of the switching device Q2 and is connected to the output terminal of the control unit.

8. A low-temperature startup optimization circuit for an LLC resonant converter according to claim 1 or 7, characterized in that, The impedance adjustment unit also includes a current-limiting resistor R5; one end of the current-limiting resistor R5 is connected to the output terminal of the control unit, and the other end is connected to the control electrode of the switching device Q2, which is used to limit the current flowing into the control electrode of the switching device Q2.

9. A low-temperature startup optimization circuit for an LLC resonant converter according to claim 1, characterized in that, The controller chip is a SY5055A chip; the Isen pin of the SY5055A chip serves as a current sensing pin, connected to the current sensing resistor R. isen Connection: The VCC pin of the SY5055A chip is connected to the power supply, the GND pin is grounded, and a decoupling capacitor C3 is connected in parallel between the VCC pin and the GND pin to stabilize the chip's power supply voltage.

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