Switching power supply device

Abstract

The invention provides a switching power supply device comprising a transformer which comprises a primary winding and a secondary winding and is used for converting an input voltage into an output voltage; the primary switching tube is connected with the primary winding and controls the on-off of the primary winding; the rectifying unit is connected with the secondary winding and rectifies the output of the secondary winding, and the rectifying unit comprises a semiconductor field effect transistor; the control unit is connected with the rectification unit and generates a control signal so as to control the switch of the semiconductor field effect transistor through the control signal; the current detection unit detects the output current and generates a current detection signal; the control unit receives the current detection signal and adjusts the control signal according to the current detection signal. According to the device, the COOLMOS with small internal resistance and high switching speed is adopted, the switching loss is reduced, the switching signal is dynamically adjusted by the control unit according to the real-time output current, the rectification conduction loss and the switching noise are reduced, the power supply conversion efficiency is improved, and the electromagnetic interference is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of circuit control, and in particular to a switching power supply device. BACKGROUND

[0002] The refrigerator high-power switching power supply realizes high-frequency energy transmission to the compressor and other key loads through alternating current mains rectification chopping, needs to meet the continuous output stability and energy efficiency conversion economy, and the flyback topology becomes the mainstream technology architecture of the refrigerator power supply due to the compact structure and electrical isolation characteristics. The high-frequency transformer connects the primary side power switch tube and the secondary side rectifier device, the secondary rectifier tube selects the fast recovery diode, the super-fast recovery diode or the Schottky diode, and the rectifier device is limited by the semiconductor conduction characteristic, and a significant forward voltage drop is generated during work. The heat generated by the rectifier unit causes the overall temperature rise to intensify, and the upper limit of the conversion efficiency is limited by the physical bottleneck of the tube voltage drop.

[0003] The voltage drop of the rectifier device itself affects the system energy efficiency, the fast recovery diode has a high conduction voltage drop, the Schottky diode is slightly improved, but still brings energy loss that cannot be ignored, the reverse recovery characteristic in the rectification process causes current spikes, increases the electromagnetic compatibility risk, and in the medium and high power application scene, the proportion of rectifier device loss increases, and the heat accumulation phenomenon is prominent. The material characteristics limit makes it difficult to break through the overall conversion efficiency of the system.

[0004] In summary, the inherent voltage drop of the rectifier device leads to low energy conversion efficiency, a large amount of input electrical energy is converted into invalid heat energy, and the device has high temperature rise and large loss. SUMMARY

[0005] The present application provides a switching power supply device to solve the problems of low energy conversion efficiency, high device temperature rise and large loss.

[0006] The present application provides a switching power supply device, comprising:

[0007] A transformer comprising a primary winding and a secondary winding, for converting an input voltage into an output voltage;

[0008] A primary switch tube connected to the primary winding for controlling the on-off of the primary winding;

[0009] A rectifier unit connected to the secondary winding for rectifying the output of the secondary winding, wherein the rectifier unit comprises a semiconductor field effect transistor;

[0010] A control unit connected to the rectifier unit for generating a control signal to control the switching of the semiconductor field effect transistor through the control signal;

[0011] A current detection unit for detecting an output current and generating a current detection signal;

[0012] The control unit is further configured to receive the current detection signal and adjust the control signal according to the current detection signal.

[0013] In some possible embodiments, the first temperature control switch is further included.

[0014] The first temperature control switch is connected in series in a control loop between the control unit and the primary switch tube.

[0015] The first temperature control switch is configured to detect the temperature of the primary switch tube.

[0016] The first temperature control switch is configured to disconnect the control loop between the control unit and the primary switch tube when the temperature of the primary switch tube is greater than a first temperature threshold.

[0017] In some possible embodiments, the second temperature control switch is further included.

[0018] The second temperature control switch is connected in series in a control loop between the control unit and the semiconductor field effect transistor.

[0019] The second temperature control switch is configured to detect the temperature of the semiconductor field effect transistor.

[0020] The second temperature control switch is configured to disconnect the control loop between the control unit and the semiconductor field effect transistor when the temperature of the semiconductor field effect transistor is greater than a second temperature threshold.

[0021] In some possible embodiments, the control unit includes a microcontroller and a PWM controller, and the microcontroller is configured to:

[0022] output a first PWM signal to the semiconductor field effect transistor to control switching of the semiconductor field effect transistor;

[0023] obtain power information of a load to be connected, and adjust a duty cycle of the first PWM signal according to the power information;

[0024] compare the current detection signal with a current range of a preset load power, and turn off the first PWM signal when the current detection signal exceeds the current range.

[0025] In some possible embodiments, the current detection unit further includes a current detection element.

[0026] The current detection element is arranged in a secondary output loop and configured to detect an output current.

[0027] The microcontroller is connected with the current detection element, for receiving the signal outputted by the current detection element, to generate the current detection signal.

[0028] In some possible embodiments, the control unit comprises a PWM controller, which is configured to:

[0029] output a second PWM signal to the primary switch tube, to control the switching of the primary switch tube;

[0030] receive a feedback signal, and adjust the duty cycle of the second PWM signal according to the feedback signal;

[0031] monitor the voltage of the power supply pin of the PWM controller, the current flowing through the primary switch tube, and the feedback signal, and stop outputting the second PWM signal when an abnormality is detected.

[0032] In some possible embodiments, the PWM controller is further configured to:

[0033] stop outputting the second PWM signal when the voltage of the power supply pin is lower than a first voltage threshold or higher than a second voltage threshold;

[0034] stop outputting the second PWM signal when the current flowing through the primary switch tube exceeds a current threshold;

[0035] stop outputting the second PWM signal when the feedback signal indicates that the output voltage is lower than a first output threshold or higher than a second output threshold.

[0036] In some possible embodiments, further comprising a first absorption circuit and a second absorption circuit;

[0037] the first absorption circuit is connected in parallel between the drain and the source of the primary switch tube, and is configured to absorb the voltage spike generated by the primary switch tube when it is turned off;

[0038] the second absorption circuit is connected in parallel between the drain and the source of the semiconductor field effect transistor, and is configured to absorb the voltage spike generated by the semiconductor field effect transistor when it is turned off.

[0039] In some possible embodiments, further comprising an output filter circuit;

[0040] the output filter circuit is connected in parallel at the output end of the rectification unit;

[0041] the output filter circuit comprises an electrolytic capacitor and a high-frequency decoupling capacitor;

[0042] The electrolytic capacitor is used for energy storage and smoothing low frequency ripple; the high frequency decoupling capacitor is used for suppressing high frequency noise.

[0043] In some possible embodiments, further comprising a safety capacitor;

[0044] The safety capacitor is connected between the primary side ground and the secondary side ground.

[0045] The safety capacitor is used for suppressing common mode electromagnetic interference.

[0046] From the above technical solutions, the application provides a switching power supply device, comprising: a transformer comprising a primary winding and a secondary winding, for converting an input voltage into an output voltage; a primary switch tube connected to the primary winding, for controlling the on-off of the primary winding; a rectification unit connected to the secondary winding, for rectifying the output of the secondary winding, wherein the rectification unit comprises a semiconductor field effect transistor; a control unit connected to the rectification unit, for generating a control signal to control the switching of the semiconductor field effect transistor through the control signal; a current detection unit for detecting an output current and generating a current detection signal; the control unit is further configured to receive the current detection signal and adjust the control signal according to the current detection signal. In the device, the semiconductor field effect transistor and the primary switch tube both use COOLMOS with small internal resistance and fast switching speed, thereby reducing switching loss; at the same time, according to the control unit, the switching time of the rectification element is controlled according to the output load power, so that the output power runs in a reasonable range, and the temperature rise of the power device is monitored through the temperature control switch to avoid over-temperature abnormality. BRIEF DESCRIPTION OF DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed in the embodiments. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0048] Figure 1 The circuit diagram of the switching power supply device provided by the embodiments of the present application. DETAILED DESCRIPTION

[0049] The embodiments will be described in detail below, and examples are shown in the drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementation described in the following embodiments does not represent all the implementations consistent with the present application. It is only an example of the system and method consistent with some aspects of the present application as described in detail in the claims.

[0050] As Figure 1As shown, the embodiment of the present application provides a switching power supply device, comprising:

[0051] The transformer BK100 is an electrical device for changing AC voltage by electromagnetic induction. The transformer comprises a primary winding and a secondary winding, which are used to convert input voltage into output voltage. The primary winding receives power from the input power supply, and the secondary winding generates induced electromotive force through electromagnetic induction effect, thereby converting the input voltage into output voltage with different amplitude, realizing electrical isolation and energy transmission.

[0052] The primary switch tube Q100 is a controlled semiconductor power device that is turned on and off. It is connected to the primary winding and used to control the on-off of the primary winding. Its control end receives a driving signal. The main circuit is connected in series or parallel in the power supply circuit of the primary winding. When the primary switch tube is turned on, current flows through the primary winding and stores energy. When the primary switch tube is turned off, the current in the primary winding is cut off, and the stored energy is released through the secondary winding. The primary switch tube can be a metal oxide semiconductor field effect transistor COOLMOS.

[0053] The rectifier unit is connected to the secondary winding and is used to rectify the output of the secondary winding. The rectifier unit is a circuit component for converting AC to DC. Its input end is connected to the secondary winding of the transformer, and its output end provides DC. The rectifier unit includes a semiconductor field effect transistor Q200, which is used as a synchronous rectifier. By controlling its switching state, it is turned on to transfer energy when the transformer secondary winding outputs forward voltage and is turned off to block reverse current when the voltage is reversed, thereby achieving high-efficiency rectification.

[0054] The control unit U100 is a circuit module that generates and outputs control signals. Its output end is connected to the control end of the semiconductor field effect transistor in the rectifier unit. It is connected to the rectifier unit and used to generate control signals to control the switching of the semiconductor field effect transistor through the control signals. The control unit generates control signals with specific timing and duty cycle according to the working state of the power supply device, accurately controls the on-off time of the semiconductor field effect transistor through the control signals, and realizes the function of synchronous rectification.

[0055] The current detection unit is used to detect the output current. Its detection end is connected in the output circuit of the power supply device, and it generates a current detection signal. The current detection unit converts the output current into a voltage signal or a digital signal through sampling resistors, current transformers, or Hall sensors, etc. It generates a current detection signal that can reflect the size of the output current. The current detection signal is transmitted to the control unit for analysis and processing.

[0056] The control unit is also provided with a signal input end connected with the output end of the current detection unit, for receiving the current detection signal generated by the current detection unit. The control unit internally contains a signal processing and logic judging circuit, which can calculate the current output power or load state in real time according to the received current detection signal, and dynamically adjust the parameters of the control signal output to the semiconductor field effect transistor, such as adjusting the switching frequency or duty cycle, so as to match the output of the power supply device with the load demand.

[0057] The embodiment of the present application provides a switching power supply device, which operates based on an isolated flyback conversion topology, realizes energy transmission and voltage conversion through high-frequency switching operation, and adopts a synchronous rectification technology to replace a traditional diode rectification, aiming to improve the conversion efficiency and dynamic response performance of the power supply device.

[0058] In operation, an input voltage is applied to the primary winding of the transformer. The control unit outputs a driving signal to periodically turn on and off the primary switch. When the primary switch is turned on, the input voltage is applied across the primary winding, and the current linearly rises, and the electrical energy is stored in the transformer in the form of a magnetic field. At this time, the voltage induced in the secondary winding reverses the bias of the semiconductor field effect transistor in the rectification unit. When the primary switch is turned off, the stored energy in the transformer is released through the secondary winding, and the voltage polarity of the secondary winding reverses, and the semiconductor field effect transistor in the rectification unit enters a forward bias condition.

[0059] The control signal generated by the control unit drives the semiconductor field effect transistor to enter a conduction state at this moment, providing a low-impedance path for the secondary current, and the electrical energy is delivered to the output end. Since the on-state resistance of the semiconductor field effect transistor is much lower than the on-state voltage drop of the traditional rectification diode when it is turned on, the conduction loss generated during the rectification process is significantly reduced. The current detection unit continuously monitors the current in the output loop and feeds back a current detection signal representing the current size to the control unit.

[0060] After receiving the current detection signal, the control algorithm in the control unit processes the signal according to the preset regulation. The control unit analyzes the trend or absolute value of the current detection signal to determine the load condition or whether an abnormality occurs. Based on this determination, the control unit dynamically adjusts the timing or pulse width of the control signal output to the semiconductor field effect transistor. Under heavy load conditions, the control unit can extend the effective pulse width of the control signal to ensure sufficient energy transmission; under light load or no-load conditions, the control unit can shorten the pulse width or skip the period to reduce switching loss, thereby optimizing the efficiency of the power supply device in the entire load range.

[0061] For example, when the load power requirement increases, resulting in an increase in output current, the current detection unit generates a current detection signal with a corresponding increase in amplitude. After receiving the increased signal, the control unit increases the duty cycle of the output control signal, allowing the semiconductor field effect transistor to conduct for a longer time during each switching cycle, thereby allowing more energy to be transferred from the transformer to the output to support the increased load current and maintain the stability of the output voltage. Conversely, when the load is reduced, the control unit reduces the duty cycle of the control signal to reduce energy transfer and prevent the output voltage from being too high.

[0062] In some embodiments, the control unit includes a microcontroller and a PWM controller. The microcontroller is a single-chip microcomputer that integrates a processor core, memory, and various input and output interfaces. In this embodiment, the microcontroller serves as the intelligent control core, with specific control algorithm programs built in. External sensing signals are received through the input port, logical operations and judgments are performed through the internal program, and finally control instructions are issued through the output port, especially the output pin with PWM signal generation function, to achieve complex power management functions.

[0063] The PWM controller is an integrated circuit chip for switching power supply control, which integrates an oscillator, an error amplifier, a comparator, a logic control circuit, and a drive output stage. The PWM controller obtains operating power from the auxiliary winding or the starting circuit through its power supply pin, receives isolated feedback signals from the secondary side through its feedback pin, issues control instructions through its output pin, and monitors the primary side current through its current sampling pin. The internal logic synthesizes all information to generate a stable pulse width modulation signal.

[0064] The PWM controller is a current-mode PWM drive controller suitable for wide voltage output and integrated high-voltage starting function. For high-performance current-mode PWM controllers for offline flyback converters, it integrates high-voltage starting, input power-down detection, and X-capacitor discharge functions, meeting the requirements of fast starting and ultra-low standby. It adopts green energy-saving mode, hiccup mode, medium-load valley conduction mode, and heavy-load CCM mode to optimize system efficiency and easily meet the six-level energy efficiency requirements.

[0065] PWM controller built-in high-precision high-frequency switching frequency oscillator, integrated slope compensation, soft start, jitter frequency technology, loop gain adjustment and other functions. The stability, reliability and electromagnetic compatibility of the power system are greatly improved. At the same time, it integrates complete protection functions, including VDD undervoltage protection (UVLO), VDD overvoltage protection (VDD OVP), input undervoltage protection (Brownout), X capacitor discharge protection, output overvoltage protection (OVP), output undervoltage protection (UVP), cycle-by-cycle current limit (0CP), overload protection (OLP), short circuit protection (SCP), built-in overheat protection, abnormal overcurrent protection (AOCP), front porch blanking (LEB), CS pin open circuit protection, VDD clamp protection, etc. By controlling the external MOS tube Q100 and the switching transformer, the isolated optocoupler feedback control main power V K Constant voltage output.

[0066] The microcontroller is configured to:

[0067] output a first PWM signal to the semiconductor field effect transistor to control switching of the semiconductor field effect transistor;

[0068] obtain power information of a load to be connected, and adjust a duty cycle of the first PWM signal according to the power information;

[0069] compare the current detection signal with a current range of a preset load power, and turn off the first PWM signal when the current detection signal exceeds the range.

[0070] When the device is running, the microcontroller continuously runs its internal control algorithm, first generates a first PWM signal and outputs it to the gate of the semiconductor field effect transistor, the generation of the first PWM signal is based on the voltage phase of the secondary winding of the transformer, and the microcontroller senses the zero-crossing point and polarity change of the secondary voltage through an auxiliary winding or a voltage sampling circuit, to ensure that the first PWM signal drives the semiconductor field effect transistor to turn on and off at the correct time, and completes the synchronous rectification process, thereby replacing the traditional diode and reducing the conduction loss.

[0071] Before starting any new load, the microcontroller first queries the power information of the load to be connected from the internal memory or through the communication interface. According to the power information, and in combination with the feedback of the current input voltage and output voltage, the microcontroller calculates the approximate current value required to meet the load power in real time through the internal algorithm. According to this, the microcontroller dynamically adjusts the duty cycle of the first PWM signal it is about to output, and sets the initial conduction time in advance, to prepare for the smooth connection of the load and avoid the dramatic fluctuation of the output voltage when the load is suddenly added.

[0072] During normal operation of the load, the microcontroller monitors in real time, the current detection unit converts the real-time collected output current signal into a current detection signal and transmits it to the microcontroller. The internal ADC module of the microcontroller converts this analog signal into a digital quantity and compares it with the current range of the preset load power.

[0073] As long as the current detection signal is within the preset range, the microcontroller still maintains the output of the first PWM signal. When the microcontroller judges that the current detection signal is lower than the lower limit of the range, it indicates that the load may be open or disconnected; if it is higher than the upper limit of the range, it indicates that the load may be short-circuited or severely overloaded. For these two abnormal states, the microcontroller turns off the first PWM signal, forcing the semiconductor field effect transistor to turn off, thereby stopping energy delivery and achieving rapid protection.

[0074] In some embodiments, the PWM controller is used for:

[0075] outputting a second PWM signal to the primary switch tube to control the switching of the primary switch tube;

[0076] receiving a feedback signal and adjusting the duty cycle of the second PWM signal according to the feedback signal;

[0077] monitoring the voltage of the power supply pin of the PWM controller, the current flowing through the primary switch tube, and the feedback signal, and stopping outputting the second PWM signal when an abnormality is detected.

[0078] The second PWM signal is a square wave driving signal generated by the PWM controller with a frequency and a duty cycle. The voltage amplitude and waveform characteristics of the signal are used to drive and control the gate of the primary switch tube, ensuring that it can turn on and off. The PWM controller adjusts the duty cycle of the signal, i.e. adjusts the on-time of the primary switch tube in each switching period, thereby achieving stable regulation of the output voltage.

[0079] The feedback signal is an electrical signal that represents the real-time state of the output voltage of the switching power supply device. The signal is derived from the output voltage sampling network on the secondary side, and is transmitted to the feedback pin of the PWM controller after electrical isolation via an optocoupler. The feedback signal can be a voltage value, a current value, or a frequency modulation signal, whose trend is opposite to that of the output voltage, for example, when the output voltage rises, the feedback signal indicates a decrease.

[0080] After the PWM controller starts working, it generates a second PWM signal and outputs it to the gate of the primary switch tube. The signal drives the primary switch tube to perform high-frequency switching action. When the primary switch tube is turned on, electrical energy is stored in the transformer; when it is turned off, electrical energy is released to the secondary side. The PWM controller controls the amount of stored energy in each switching period by precisely controlling the duty cycle of the second PWM signal.

[0081] To achieve accurate voltage regulation, the PWM controller needs to receive a feedback signal from the secondary side. The feedback signal is generated by a secondary output voltage sampling circuit and transmitted to the feedback pin of the PWM controller through an optocoupler after isolation. The error amplifier inside the PWM controller compares this feedback signal with its precise internal reference source to generate an error voltage. The magnitude and polarity of the error voltage represent the degree and direction of the output voltage deviation from the preset value.

[0082] Based on the error voltage, the PWM controller performs duty cycle adjustment. Within a switching cycle, a comparator inside the PWM controller compares the error voltage with a ramp signal representing the primary current. When the magnitude of the ramp signal reaches the threshold set by the error voltage, the comparator output flips, and the logic control circuit immediately turns off the second PWM signal, thereby terminating the conduction of the primary switch. If the output voltage decreases, the feedback signal decreases, and the error voltage increases, causing the threshold of the comparator to rise, and the conduction time of the second PWM signal to extend, allowing more energy to be transferred to the secondary, which helps to restore the output voltage.

[0083] In addition to voltage regulation control, the PWM controller continuously monitors the voltage at its own power supply pin to ensure it operates within the rated range, and continuously monitors the peak current flowing through the primary switch through an external current sampling resistor.

[0084] In some embodiments, the PWM controller is further configured to:

[0085] stop outputting the second PWM signal when the voltage at the power supply pin is below a first voltage threshold or above a second voltage threshold;

[0086] stop outputting the second PWM signal when the current flowing through the primary switch exceeds a current threshold;

[0087] stop outputting the second PWM signal when the feedback signal indicates that the output voltage is below a first output threshold or above a second output threshold.

[0088] The first voltage threshold is the minimum operating voltage threshold set by the protection circuit inside the PWM controller, corresponding to the minimum supply voltage at which the PWM controller can maintain normal and stable operation. When the PWM controller detects that the voltage at its power supply pin is below this first voltage threshold, it is determined to be in an under-voltage condition, known as under-voltage lockout, which can cause the PWM controller's internal circuit to malfunction and the output drive signal to distort, resulting in the primary switch operating in the non-saturation region and generating excessive heat loss.

[0089] The second voltage threshold is the highest operating voltage limit set by the protection circuit within the PWM controller, corresponding to the maximum safe voltage that the internal components of the PWM controller can withstand. When the PWM controller monitors the voltage at its power pin and finds it higher than the second voltage threshold, it determines that an overvoltage surge has occurred. Excessively high voltage can immediately damage the internal delicate circuits of the PWM controller, or cause the output drive signal voltage to be excessively high, which in turn jeopardizes the gate oxide insulation reliability of the primary switch.

[0090] The current threshold is the current limit set by the overcurrent protection circuit within the PWM controller, which is slightly higher than the expected peak current flowing through the primary switch under maximum load conditions of the power supply device, with a proper safety margin, serving as the core reference for determining whether an abnormal overcurrent has occurred in the power loop, such as an output short circuit or a sudden load surge.

[0091] For example, when the power supply device is connected to a load with a very large capacitance, a sudden drop in input voltage may occur at the moment of power-on. The voltage at the power pin of the PWM controller decreases accordingly, and if it is lower than the first voltage threshold, the undervoltage protection is activated, stopping all switching operations. After the input voltage returns to normal and the voltage at the power pin is re-established, the controller resumes the soft-start process. For another example, when the feedback optocoupler is open-circuited due to failure, the feedback loop is broken and the output voltage rises uncontrollably. The voltage at the feedback pin of the PWM controller is thus pulled up to an abnormal level, and when it exceeds the voltage corresponding to the second output threshold, the output overvoltage protection is triggered immediately, locking the output and effectively preventing the high voltage from damaging the load device.

[0092] In some embodiments, the current detection unit further comprises a current detection element A200; the current detection element is arranged in the secondary output loop for detecting the output current; the microcontroller is connected with the current detection element for receiving the signal output by the current detection element to generate the current detection signal.

[0093] The current detection element is used to collect and convert current parameters, and is arranged in the main power output loop on the secondary side of the switching power supply device, connected in series or with a low resistance sampling method to the output positive or negative line, and can directly sense the total current flowing through the load. The current detection element converts the output current into a low-amplitude voltage signal or digital code that is easy to process and has a linear proportional relationship with the output current.

[0094] The secondary output loop refers to the complete electrical energy transmission path from the transformer secondary winding, through the rectifier unit and the filter network, to the output terminal. This loop carries all the operating currents provided by the power supply device to the load. The output terminal of the current detection element, i.e. its signal pin, is directly connected to a specific input channel pin of the analog-to-digital converter (ADC) built into the microcontroller through PCB wiring.

[0095] On the secondary side of the switching power supply device, the electrical energy is rectified by the rectifier unit and smoothed by the filter circuit, and then transmitted to the load through the secondary output circuit. The signal output by the current detection element is transmitted to the microcontroller, which periodically samples the voltage on the input pin. The analog-to-digital converter discretizes the analog signal at a rate much higher than the switching frequency, converting the continuous voltage waveform into a series of discrete digital codes.

[0096] These digital codes are read by the firmware program of the microcontroller, which first performs software filtering to suppress high-frequency noise that may be introduced during sampling. Subsequently, the calibrated coefficients stored in the memory are called to calculate and calibrate the filtered data. This calculation process maps the numerical values of the digital codes to the real current values, ultimately generating the current detection signal.

[0097] The current detection signal is the basis for the microcontroller to perform its advanced control functions. The microcontroller compares this signal with the preset current range based on the power information of the load to be connected. The comparison result is the basis for the microcontroller to determine whether the system is currently in a normal working state, a light load state, an overload state, or a short circuit state, and to decide whether to maintain, adjust, or shut down the first PWM signal.

[0098] The switching power supply device provided in this embodiment solves the technical problem of low energy conversion efficiency caused by the inherent on-state voltage drop of traditional diode rectification by using a semiconductor field effect transistor to form the rectifier unit and synchronously driving it by the control unit. The semiconductor field effect transistor exhibits low resistance characteristics in the on-state, and its on-state loss is significantly lower than the forward voltage drop loss of the diode, thereby reducing the invalid conversion of electrical energy to heat energy and improving the energy utilization efficiency of the device.

[0099] At the same time, since the semiconductor field effect transistor is a controlled switching device, its switching timing can be accurately controlled by the control signal, avoiding the reverse recovery problem caused by carrier recombination in diode rectification. Therefore, the device effectively suppresses the high-frequency harmonic oscillation and electromagnetic interference caused by reverse recovery current, reduces the harmonic pollution to the power grid, and improves the electromagnetic compatibility of the power supply device.

[0100] In addition, the control unit adjusts the control strategy by receiving the current detection signal, realizing real-time management of the output power. This closed-loop control method enables the power supply device to quickly adapt to load changes, maintain high efficiency in a wide load range, and improve the dynamic performance and reliability of the device. The reduction of loss directly reduces the heat generation of the internal device, especially the rectifier unit, alleviates the heat accumulation effect, and helps to improve the long-term operation stability and power density of the medium and high power power supply system.

[0101] In some embodiments, a first temperature control switch 100 and a second temperature control switch 200 are further included; the first temperature control switch is configured to detect the temperature of the primary switch tube; and the second temperature control switch is configured to detect the temperature of the semiconductor field effect transistor.

[0102] The first temperature control switch and the second temperature control switch are both protection devices that change their on-off states based on temperature changes, and internally include temperature sensing elements and mechanical contacts or electronic switch circuits. Taking the first temperature control switch as an example, the temperature sensing element is directly or indirectly attached to the surface of the primary switch tube or the surface of the heat sink, and is used to sense the real-time working temperature of the primary switch tube. The first temperature control switch has a preset first temperature threshold, which is set according to the maximum allowed working junction temperature of the primary switch tube. When the detected temperature exceeds the threshold, the internal mechanism will act, thereby changing the switch state.

[0103] The first temperature control switch is connected in series in the control loop between the control unit and the primary switch tube; and the first temperature control switch is configured to disconnect the control loop between the control unit and the primary switch tube when the temperature of the primary switch tube is greater than the first temperature threshold.

[0104] The control loop is an electrical path connecting the control unit and the control end of the primary switch tube, and the driving signal generated by the control unit is transmitted to the primary switch tube through the loop to control its conduction and shutdown. The contacts or electronic switch of the first temperature control switch are connected in series in the physical circuit of the control loop, and the on-off state of the first temperature control switch determines the physical on-off of the control loop, thereby determining whether the driving signal can reach the primary switch tube.

[0105] When the device is working normally, the primary switch tube will generate heat due to its switching process and conduction loss, causing its temperature to rise. The first temperature control switch continuously monitors the temperature of the primary switch tube through its temperature sensing element. As long as the monitored temperature is below the preset first temperature threshold, the first temperature control switch maintains the closed state of its contacts, and the second PWM signal generated by the control unit can pass through the complete control loop without obstruction, normally driving the primary switch tube to perform switching operations, and the power supply device is in a normal working state.

[0106] When the power supply device encounters abnormal working conditions such as overload, poor heat dissipation, or high ambient temperature, the power consumption of the primary switch tube increases or the heat dissipation capacity decreases, and its temperature starts to rise continuously. The first temperature control switch tracks this temperature change in real time, and as soon as the temperature of the primary switch tube rises to and exceeds the first temperature threshold set inside the first temperature control switch, the first temperature control switch is triggered.

[0107] The first temperature control switch, after being triggered, will disconnect its mechanical contact in series in the control loop, or make its electronic switch in off state, thus cutting off the driving signal path from the control unit to the control electrode of the primary switch tube. No matter whether the control unit outputs driving signal at this time, the driving signal cannot reach the primary switch tube any more due to the physical path being cut off. The primary switch tube will inevitably enter off state due to the loss of driving voltage, its current is cut off, power dissipation stops, temperature stops rising and starts to gradually drop, thus avoiding the risk of the primary switch tube being burned due to overheating.

[0108] For example, due to the failure of the heat dissipation fan, the heat dissipation condition of the primary switch tube deteriorates, and its temperature will continue to accumulate and rise. When the temperature reaches 130°C, the first temperature control switch acts and cuts off the control loop. The primary switch tube is forced to be off, and the entire power supply device stops working, and the temperature no longer rises. Only after the device is powered off and the temperature of the primary switch tube is sufficiently cooled below the safe range, the contact of the first temperature control switch will automatically reset and close, ready for the next start.

[0109] Unlike the first temperature control switch, the second temperature control switch is used to monitor the operating temperature of the semiconductor field effect transistor in the rectifier unit, wherein the temperature sensing element is in thermal coupling relationship with the tube shell of the semiconductor field effect transistor or its heat sink, and can respond to the temperature change of the semiconductor field effect transistor due to power loss. The second temperature control switch is internally provided with a second temperature threshold value, which is usually lower than the damage temperature of the semiconductor field effect transistor and has a safety margin according to the maximum allowed operating junction temperature of the semiconductor field effect transistor.

[0110] In some embodiments, the second temperature control switch is connected in series in the control loop between the control unit and the semiconductor field effect transistor; the second temperature control switch is configured to disconnect the control loop between the control unit and the semiconductor field effect transistor when the temperature of the semiconductor field effect transistor is greater than the second temperature threshold value.

[0111] Between the control unit and the semiconductor field effect transistor, there is a control loop for transmitting the first PWM signal. This control loop is the basic path for the control unit to realize synchronous rectification control of the rectifier unit. The contact of the second temperature control switch is connected in series in the physical wire of this control loop, and its on-off state directly determines the integrity of this signal path. Only when the second temperature control switch is in the closed state, the first PWM signal generated by the control unit can reach the gate of the semiconductor field effect transistor smoothly.

[0112] When the temperature of the semiconductor field effect transistor continues to rise and exceeds the preset second temperature threshold, the temperature sensing element in the second temperature control switch drives the mechanism to act, so that the normally closed contact is quickly disconnected, thereby physically cutting off the transmission path of the first PWM signal, the semiconductor field effect transistor is immediately turned off due to the loss of gate drive voltage, the rectification function is stopped, and further heating of the device is blocked, so as to realize the over-temperature protection of the hardware.

[0113] During normal operation of the power supply device, the semiconductor field effect transistor acts as a synchronous rectifier, and during its conduction period, the on-state resistance causes conduction loss, and during its switching process, switching loss is generated, which is ultimately converted into heat. The second temperature control switch continuously senses the temperature of the device, and as long as the temperature is maintained below the second temperature threshold, the second temperature control switch maintains the closed state of its contact, and the first PWM signal output by the control unit can pass through the control loop to accurately control the synchronous rectification action of the semiconductor field effect transistor, thereby ensuring efficient energy conversion.

[0114] When an abnormal situation occurs, for example, the output current increases sharply due to load short circuit, the heat dissipation path is blocked, or the ambient temperature is too high, the power consumption of the semiconductor field effect transistor will increase sharply or the heat dissipation efficiency will decrease, causing the junction temperature to rise rapidly. Once the second temperature control switch detects that the temperature exceeds the second temperature threshold, the protection mechanism is activated.

[0115] The second temperature control switch will disconnect its contact in series in the control loop, so that the transmission path of the first PWM signal is interrupted. At this time, the semiconductor field effect transistor enters the off state because it cannot receive any driving signal, its conduction is forcibly terminated, the current path is cut off, and the heat source disappears, thereby effectively preventing the performance degradation or thermal breakdown failure of the semiconductor field effect transistor due to overheating.

[0116] In some embodiments, a first absorption circuit RC100 and a second absorption circuit RC200 are further included; the first absorption circuit is connected in parallel between the drain and the source of the primary switch tube; the first absorption circuit is used to absorb the voltage spike generated by the primary switch tube when it is turned off; the second absorption circuit is connected in parallel between the drain and the source of the semiconductor field effect transistor; and the second absorption circuit is used to absorb the voltage spike generated by the semiconductor field effect transistor when it is turned off.

[0117] The first absorption circuit is used to provide a high-frequency impedance path relative to the switching frequency, limit the rate of change of the drain voltage of the primary switch tube at the moment of turning off, and absorb the spike energy generated by the resonance of the transformer leakage inductance and the circuit parasitic parameters.

[0118] Voltage spike is a pulse waveform with extremely short duration but much higher amplitude than the voltage in normal circuit operation. In a switching power supply device, when the primary switch is controlled to turn off, the leakage inductance of the transformer primary winding and the parasitic inductance in the circuit will try to maintain the current unchanged, thus inducing a high voltage pulse superimposed on the DC bus voltage. If the voltage spike is not effectively suppressed, its amplitude may exceed the rated withstand voltage of the primary switch, causing avalanche breakdown or electromagnetic interference radiation.

[0119] The second absorption circuit is an energy absorption network equivalent to the first absorption circuit in circuit structure and function, and the second absorption circuit and the semiconductor field effect transistor jointly bear the voltage stress on the secondary side, and aims to manage the voltage overshoot of the semiconductor field effect transistor in the off operation due to the interaction of its own parasitic inductance and the leakage inductance of the transformer secondary.

[0120] The voltage spike generated during the off state is an inevitable phenomenon of the power metal oxide semiconductor field effect transistor in the high-speed switching process. When the control signal drives the device to change from the on state to the off state, the rapid change of the current will induce a counter electromotive force on the series parasitic inductance, and the induced voltage is superimposed on the DC voltage at this time, and is applied to the drain-source of the device, forming a steep voltage spike. The role of the absorption circuit is to controllably dissipate or transfer the spike energy.

[0121] The first absorption circuit and the second absorption circuit work cooperatively, do not participate in the normal energy transmission function, and are only activated in the extremely short time of switching transient state to process the oscillation and overshoot energy caused by parasitic parameters.

[0122] At the end of a switching cycle, the primary switch receives a turn-off signal, and the drain voltage begins to rise from the on-state voltage close to zero. Due to the influence of circuit parasitic parameters, the voltage rising waveform is not smooth, and an obvious overshoot appears on the front edge. The first absorption circuit absorbs the overshoot energy at this time, so that the voltage waveform becomes smooth, and the maximum voltage value is limited within the DC bus voltage plus an acceptable threshold, thereby protecting the primary switch. The semiconductor field effect transistor on the secondary side is the same, and is protected by the second absorption circuit.

[0123] In some embodiments, an output filter circuit is further included, which is connected in parallel to the output end of the rectifying unit. The output filter circuit is a passive network connected between the output end of the rectifying unit and the load, and its input end receives the pulsed DC voltage after rectification but before smoothing, and its output end provides smooth and stable DC voltage.

[0124] The output filter circuit includes an electrolytic capacitor C201 and a high-frequency decoupling capacitor C202; the electrolytic capacitor is used to store energy and smooth low-frequency ripples; and the high-frequency decoupling capacitor is used to suppress high-frequency noise.

[0125] In the output filter circuit, the electrolytic capacitor, due to its large capacity value, serves the low-frequency band, can store electrical energy during the conduction of the rectifier tube, and release the stored electrical energy to the load during the turn-off of the rectifier tube, thereby filling the intermittent period of energy transmission, maintaining the output voltage at a relatively stable level, and smoothing the low-frequency ripple component in the output voltage.

[0126] The high-frequency decoupling capacitor is a capacitor element with small capacity but extremely low parasitic parameters. In the output filter circuit, the high-frequency decoupling capacitor is arranged close to the rectifier tube or the load. Due to its very small equivalent series inductance and equivalent series resistance, it exhibits extremely low impedance characteristics at high frequencies, and can provide a local, low-impedance discharge path for the high-frequency current spikes and noise generated during the high-speed switching of the switch tube, thereby effectively suppressing the superposition of high-frequency interference on the output end.

[0127] During the short time when the semiconductor field effect transistor in the rectifier unit is turned on, the current charges the electrolytic capacitor, storing electrical energy in its electric field. During the longer time when the semiconductor field effect transistor is turned off, the continuous current required by the load is provided by the discharge of the electrolytic capacitor. This periodic charging and discharging process greatly smooths the pulsation of the output current and suppresses the low-frequency ripple amplitude of the output voltage to a very low level, ensuring that the load can obtain continuous and stable energy supply.

[0128] The high-frequency decoupling capacitor is responsible for filtering high-frequency noise. Although the electrolytic capacitor can effectively smooth low-frequency ripples, its own parasitic inductance increases its impedance at high frequencies, making it unable to effectively filter switching noise. The high-frequency decoupling capacitor is arranged close to the output end of the semiconductor field effect transistor or the input pin of the load power supply. The nanosecond current spikes and extremely high frequency electromagnetic interference generated during the high-speed switching of the semiconductor field effect transistor are immediately absorbed by the nearby high-frequency decoupling capacitor. The high-frequency decoupling capacitor provides a short-term local discharge path to prevent these high-frequency noises from propagating through the power supply line to the entire output circuit, thereby ensuring the high-frequency purity of the output DC.

[0129] In some embodiments, a safety capacitor CY100 is also included, connected between the primary side ground and the secondary side ground, and used to suppress common-mode electromagnetic interference.

[0130] When the power switch and the synchronous rectifier are switched at high frequency, the voltage and current will change sharply. These changes will be coupled to the reference ground through the parasitic capacitance between the power device and the heat sink, the parasitic capacitance between the transformer windings, etc., forming a common-mode noise current. If these noise currents are not guided and controlled, they will be conducted outward through the power input line or output line, and will also be radiated outward through the chassis, causing interference to the power grid and other electronic devices.

[0131] The safety capacitor is arranged between the primary side ground and the secondary side ground, and is arranged across the isolation boundary of the transformer. When the high-frequency common-mode noise generated by the primary side power switch attempts to be coupled to the secondary side ground through the parasitic capacitance, or the noise generated by the secondary side synchronous rectifier attempts to be coupled to the primary side ground, the safety capacitor provides a low-impedance path for these noise currents.

[0132] Because the safety capacitor presents a low-impedance characteristic to high-frequency signals, the common-mode noise current preferentially selects the safety capacitor to form a loop and flows back to the noise source. This process effectively absorbs or shunts the common-mode noise that is to be propagated through stray parasitic paths, so that it is limited within the device and attenuated, rather than being conducted or radiated to the external environment.

[0133] U100 outputs a PWM signal through the gate to control Q100 switching, and θ100 is connected in series between U100 and Q100, and is disconnected when the temperature of the heat sink to which Q100 is attached exceeds the set temperature of θ100, so as to avoid abnormality caused by uncontrolled temperature rise of Q100. K The load capacity is controlled by the main control MCU according to the load condition (no load, light load, heavy load). The PWM signal output by the MCU reasonably controls the switching of Q200, so that the voltage of V K The load capacity is controlled within a reasonable range to reduce energy loss. When the actual current of the refrigerator load is significantly higher or lower than A200, load short circuit or open circuit may occur, the MCU will immediately shut off the control signal output, and will transmit the fault information to the display through data, so as to remind in time. At the same time, when the temperature of the heat sink of Q200 detected by the temperature control switch θ200 exceeds the set value, Q200 is immediately disconnected, so as to avoid uncontrolled situations such as damage to Q200 caused by uncontrolled temperature rise. RC100 and RC200 are used to absorb high-voltage spikes and static electricity to avoid damage to MOS (Q100, Q200).

[0134] BK100 is rectified by Q200 (another COOLMOSFET) instead of a traditional diode. Q200 is controlled by the PWM signal of the main control MCU to realize synchronous rectification. The filter capacitor C200 series smoothes the output to supply power to the load. The feedback loop transmits the output state back to the FB pin of U100 through the optocoupler isolation, forming a closed-loop control.

[0135] Current detection is realized by CS pin sampling resistance to achieve over-current protection; temperature control switch θ100 and θ200 are connected in series in the key loop to cut off the circuit when the temperature is too high. The main control MCU also detects the current through AD, predicts the load and adjusts PWM.

[0136] The application provides a COOLMOSFET working synchronously with a main switch tube as a rectifying element to replace a conventional diode. The COOLMOSFET has small internal resistance and low switching loss. The microcontroller MCU outputs a PWM signal to control the MOS switch according to the size of the load, so that the power consumption and temperature rise of the system can be reduced, the conversion efficiency can be improved, and the load power can be compared with the output current. If the output current is obviously lower or higher than the load power, it indicates that the load is open or short-circuited. The MCU will immediately stop the output of the load control signal, consume the power, and report the fault information through communication for display, so that the fault can be repaired in time. At the same time, the temperature control switch is used to monitor the temperature rise of the radiator to avoid overheating, so that the refrigerator power supply system works more reliably and is suitable for application in a refrigerator and a high-power switching power supply.

[0137] The similar parts among the embodiments provided in the application can be referred to each other. The specific embodiments provided above are only a few examples under the general concept of the application, and do not limit the protection scope of the application. Any other embodiments extended according to the application scheme without creative labor belong to the protection scope of the application.

Claims

1. A switching power supply device, characterized in that, include: A transformer, consisting of a primary winding and a secondary winding, is used to convert an input voltage into an output voltage. A primary switching transistor, connected to the primary winding, is used to control the on / off state of the primary winding; A rectifier unit, connected to the secondary winding, is used to rectify the output of the secondary winding, wherein the rectifier unit includes a semiconductor field-effect transistor; A control unit, connected to the rectifier unit, is used to generate a control signal to control the switching of the semiconductor field-effect transistor. The current detection unit is used to detect the output current and generate a current detection signal; The control unit is further configured to receive the current detection signal and adjust the control signal according to the current detection signal.

2. The switching power supply device according to claim 1, characterized in that, It also includes the first temperature control switch; The first temperature control switch is connected in series in the control loop between the control unit and the primary switching transistor; The first temperature control switch is used to detect the temperature of the primary switching transistor; The first temperature control switch is configured to disconnect the control loop between the control unit and the primary switching transistor when the temperature of the primary switching transistor is greater than a first temperature threshold.

3. The switching power supply device according to claim 1, characterized in that, It also includes a second temperature control switch; The second temperature control switch is connected in series in the control loop between the control unit and the semiconductor field-effect transistor; The second temperature control switch is used to detect the temperature of the semiconductor field-effect transistor; The second temperature control switch is configured to disconnect the control loop between the control unit and the semiconductor field-effect transistor when the temperature of the semiconductor field-effect transistor is greater than a second temperature threshold.

4. The switching power supply device according to claim 1, characterized in that, The control unit includes a microcontroller; the microcontroller is configured to: A first PWM signal is output to the semiconductor field-effect transistor to control the switching of the semiconductor field-effect transistor; Obtain the power information of the load to be connected, and adjust the duty cycle of the first PWM signal according to the power information; By comparing the current detection signal with the current range of the preset load power, the first PWM signal is turned off when the current detection signal exceeds the current range.

5. The switching power supply device according to claim 4, characterized in that, The current detection unit also includes a current detection element; The current sensing element is installed in the secondary output circuit and is used to detect the output current; The microcontroller is connected to the current sensing element and is used to receive the signal output by the current sensing element in order to generate the current sensing signal.

6. The switching power supply device according to claim 1, characterized in that, The control unit includes a PWM controller, which is used for: A second PWM signal is output to the primary switching transistor to control the switching of the primary switching transistor; Receive feedback signals and adjust the duty cycle of the second PWM signal according to the feedback signals; The voltage of the power supply pin of the PWM controller, the current flowing through the primary switching transistor, and the feedback signal are monitored, and the output of the second PWM signal is stopped when an abnormality is detected.

7. The switching power supply device according to claim 6, characterized in that, The PWM controller is also used for: When the pin voltage of the power supply is lower than the first voltage threshold or higher than the second voltage threshold, the output of the second PWM signal is stopped; When the current flowing through the primary switch exceeds the current threshold, the output of the second PWM signal is stopped; When the feedback signal indicates that the output voltage is lower than the first output threshold or higher than the second output threshold, the output of the second PWM signal is stopped.

8. The switching power supply device according to claim 1, characterized in that, It also includes a first absorption circuit and a second absorption circuit; The first absorption circuit is connected in parallel between the drain and source of the primary switching transistor; the first absorption circuit is used to absorb the voltage spike generated by the primary switching transistor when it is turned off. The second absorption circuit is connected in parallel between the drain and source of the semiconductor field-effect transistor; the second absorption circuit is used to absorb the voltage spike generated by the semiconductor field-effect transistor when it is turned off.

9. The switching power supply device according to claim 1, characterized in that, It also includes an output filter circuit; The output filter circuit is connected in parallel to the output terminal of the rectifier unit; The output filter circuit includes an electrolytic capacitor and a high-frequency decoupling capacitor. The electrolytic capacitor is used for energy storage and smoothing low-frequency ripple; the high-frequency decoupling capacitor is used to suppress high-frequency noise.

10. The switching power supply device according to claim 1, characterized in that, It also includes safety capacitors; The safety capacitor is connected between the primary side ground and the secondary side ground; The safety capacitor is used to suppress common-mode electromagnetic interference.

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