Low-temperature starting circuit of switching power supply and electronic device

Abstract

A low-temperature startup circuit and electronic device for a switching power supply, belonging to the field of power supply technology, is connected to a switching power supply that provides output DC power. A switching control circuit, in response to an ambient temperature lower than a first preset temperature and the output DC power being lower than a preset voltage, disconnects the switching control signal; and in response to an output DC power being greater than or equal to the preset voltage, outputs the switching control signal. A first switching circuit, in response to the switching control signal, transmits the output DC power to the load, and in response to the disconnection of the switching control signal, disconnects the output DC power. This reduces the power consumption of the control chip in the switching power supply during startup, reduces the likelihood of protection functions being triggered during startup, and reduces the impact of electrolytic capacitor performance degradation at low temperatures on the startup of the switching power supply, thus expanding the application scenarios of the switching power supply.

Description

Technical Field

[0001] This application belongs to the field of power supply technology, and in particular relates to a low-temperature startup circuit and electronic device for a switching power supply. Background Technology

[0002] my country has a vast territory, and extreme low temperatures of -30 to -40°C can occur in regions such as Heilongjiang and Inner Mongolia. Ambient temperature has a great impact on the performance of switching power supplies. For example, ultra-low temperature environments can cause switching power supplies to fail to start. In switching power supplies, electrolytic capacitors are used for energy storage and filtering. At low temperatures, electrolytic capacitors will experience changes such as reduced capacity, increased leakage current, and increased ESR (equivalent series resistance). Specifically, the following reasons may cause switching power supplies to fail to start: (1) It causes unstable power supply to the control circuit. Moreover, the heavier the load, the greater the power consumption of the chip in the control circuit, and the longer it takes to establish a stable power supply. If the output voltage has not reached the preset value within a certain time, the chip protection function will be triggered, resulting in failure to start; (2) The increased ESR of the output electrolytic capacitor will change the loop response characteristics of the power supply, severely weakening the load-carrying capacity of the power supply under heavy load. In severe cases, it may be impossible to start under heavy load.

[0003] There are usually two solutions to this problem: (1) Use electrolytic capacitors made of low-temperature materials. These capacitors are more expensive than conventional capacitors. Their performance changes at low temperatures are relatively smaller than those of conventional capacitors. However, their parameters still change significantly compared to those at room temperature. For example, the ESR of conventional capacitors at -40℃ is hundreds of times that at room temperature. Ultra-low temperature capacitors are better, but their ESR is still tens or even hundreds of times greater than that at room temperature. This can only improve the problem of low-temperature startup (the load that can be carried by low-temperature startup is heavier, but it cannot be driven by full load or even overload startup. It is necessary to change the loop design to solve this problem. However, the loop design is different for different models. It is not a universal solution, so the hardware design is complicated); (2) Use an additional heating method. When the ambient temperature reaches -40℃, turn on the heating module to heat the electrolytic capacitor. After preheating, start the machine. At this time, the startup can be successful. However, this method requires an additional low-temperature detection circuit and heating circuit. It is also necessary to prepare an additional power supply device that can work at ultra-low temperatures. The cost is high and the hardware design is complicated.

[0004] Therefore, the hardware design of the low-temperature startup circuit for related switching power supplies is complex and costly. Summary of the Invention

[0005] The purpose of this application is to provide a low-temperature startup circuit and electronic device for a switching power supply, aiming to solve the problems of complex and costly hardware design of related low-temperature startup circuits for switching power supplies.

[0006] This application provides a low-temperature startup circuit for a switching power supply, connected to a switching power supply that provides DC output power, including: An on / off control circuit, connected to the switching power supply, is configured to: disconnect the on / off control signal in response to an ambient temperature lower than a first preset temperature and an output DC voltage lower than a preset voltage; and output an on / off control signal in response to an output DC voltage greater than or equal to the preset voltage. A first switching circuit, connected to the on / off control circuit and the switching power supply, is configured to: transmit the output DC power to the load in response to the on / off control signal; and disconnect the output DC power in response to the disconnection of the on / off control signal.

[0007] In one embodiment, the on / off control circuit is further configured to output the on / off control signal in response to an ambient temperature greater than or equal to the first preset temperature.

[0008] In one embodiment, the on / off control circuit includes: The first voltage divider circuit includes a first thermistor and a first resistor assembly connected in series, configured to receive a power supply voltage and divide the power supply voltage to output a first divided voltage from a first node; the first node is a common connection point of the first thermistor and the first resistor assembly. The regulating circuit includes a second resistor assembly. The regulating circuit is connected to the switching power supply and is configured to connect the second resistor assembly in parallel with the first thermistor in response to the output DC voltage being greater than or equal to the preset voltage, so that the first voltage divider circuit outputs the regulated first voltage divider voltage. The decision circuit, connected to the first voltage divider circuit, is configured to: output the on / off control signal in response to the first voltage divider voltage being greater than or equal to a first threshold voltage; and disconnect the output of the on / off control signal in response to the first voltage divider voltage being less than the first threshold voltage. Wherein, when the ambient temperature is less than the first preset temperature, the first voltage divider voltage before adjustment is less than the first threshold voltage; when the ambient temperature is greater than or equal to the first preset temperature, the first voltage divider voltage before adjustment is greater than or equal to the first threshold voltage.

[0009] In one embodiment, the first thermistor includes a first NTC thermistor, and the first resistor assembly includes a first resistor; The first terminal of the first NTC thermistor forms the input terminal of the first voltage divider circuit and is connected to the adjustment circuit to receive the power supply voltage; The second end of the first NTC thermistor and the first end of the first resistor are connected and together form the output terminal of the first voltage divider circuit, which is connected to the adjustment circuit and the decision circuit to output the first voltage divider voltage; The second end of the first resistor is connected to the power supply ground.

[0010] In one embodiment, the adjustment circuit includes a first optocoupler, a second resistor, and a third resistor; wherein the second resistor assembly includes the second resistor; The first end of the third resistor is connected to the positive terminal of the first optocoupler, the negative terminal of the first optocoupler is connected to the signal ground, the first end of the second resistor is connected to the first thermistor and the first resistor assembly, the collector of the first optocoupler is connected to the first thermistor, and the second end of the second resistor is connected to the emitter of the first optocoupler. The second end of the third resistor forms the input terminal of the adjustment circuit and is connected to the switching power supply to receive the output DC power.

[0011] In one embodiment, the decision circuit includes a second optocoupler, a first transistor, a first Zener diode, a fourth resistor, and a fifth resistor; The first end of the fourth resistor constitutes the input terminal of the decision circuit, and is connected to the first voltage divider circuit and the adjustment circuit to receive the first voltage divider voltage. The second end of the fourth resistor is connected to the negative terminal of the first Zener diode, the positive terminal of the first Zener diode is connected to the base of the first transistor, and the emitter of the first transistor is connected to the first end of the fifth resistor and the positive terminal of the second optocoupler. The collector of the first transistor forms the power supply terminal of the decision circuit and is connected to the first voltage divider circuit to receive the power supply voltage; The collector of the second optocoupler forms the output terminal of the decision circuit and is connected to the first switching circuit to output the on / off control signal.

[0012] In one embodiment, the switching power supply includes: A rectifier and filter circuit is configured to receive an input AC power and convert the input AC power into the input DC power. A voltage conversion circuit, connected to the rectifier and filter circuit, is configured to convert the input DC power into the output DC power and the auxiliary DC power according to the conversion control signal; A feedback circuit, connected to the voltage conversion circuit, is configured to sample the voltage of the output DC power to output a sampled voltage; A conversion control circuit, connected to the voltage conversion circuit and the feedback circuit, is configured to output the conversion control signal based on the auxiliary DC power supply and the feedback of the sampled voltage. The conversion control signal is configured to regulate the output DC power. The low-temperature start-up circuit also includes: The charging circuit, connected to the rectifier filter circuit and the voltage conversion circuit, is configured to transmit the input DC power to the conversion control circuit in response to the ambient temperature being lower than the second preset temperature. The conversion control circuit is further configured to be powered by the auxiliary DC power and the input DC power, and to output the conversion control signal based on the feedback of the sampled voltage.

[0013] In one embodiment, the charging circuit includes: The second voltage divider circuit includes a second thermistor and a third resistor assembly connected in series, configured to divide the supply voltage to output a second divided voltage from a second node; the second node is a common connection point of the second thermistor and the third resistor assembly. A second switching circuit, connected to the second voltage divider circuit, is configured to transmit the input DC power to the conversion control circuit in response to the second voltage divider voltage being greater than the second threshold voltage. Wherein, when the ambient temperature is lower than the second preset temperature, the second voltage divider voltage is greater than the second threshold voltage.

[0014] In one embodiment, it further includes: The power supply circuit is configured to receive an input AC power and convert the input AC power into a supply voltage.

[0015] This invention also provides an electronic device, which includes the low-temperature startup circuit of the switching power supply described above.

[0016] The beneficial effects of this invention compared to the prior art are as follows: Because the on / off control circuit responds to an ambient temperature lower than a first preset temperature and an output DC current lower than a preset voltage, it disconnects the on / off control signal, causing the first switching circuit to disconnect the output DC current in response to the disconnection of the on / off control signal; the switching power supply provides the output DC current; the on / off control circuit responds to an output DC current greater than or equal to a preset voltage, outputting the on / off control signal, causing the first switching circuit to transmit the output DC current to the load in response to the on / off control signal; thus, when the ambient temperature is lower than the first preset temperature, the first switching circuit disconnects the load from the switching power supply before the switching power supply starts successfully, allowing the switching power supply to start under no-load conditions. After the switching power supply starts, the first switching circuit connects the load to the switching power supply to supply power to the load, thereby reducing the power consumption of the control chip in the switching power supply during startup, reducing the possibility of protection function triggering during startup, and reducing the impact of electrolytic capacitor performance degradation at low temperatures on the startup of the switching power supply, thus expanding the application scenarios of the switching power supply. Attached Figure Description

[0017] To more clearly illustrate the technical inventions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of a low-temperature startup circuit for a switching power supply provided in an embodiment of this application; Figure 2 This is a schematic diagram of another structure of the on / off control circuit in the low-temperature startup circuit of the switching power supply provided in an embodiment of this application; Figure 3 Another schematic diagram of a low-temperature startup circuit for a switching power supply provided in an embodiment of this application; Figure 4 A schematic diagram of a charging circuit in a low-temperature startup circuit of a switching power supply provided in an embodiment of this application; Figure 5 Another schematic diagram of a low-temperature startup circuit for a switching power supply provided in an embodiment of this application; Figure 6 This is a partial example circuit diagram of a low-temperature startup circuit for a switching power supply provided in an embodiment of this application. Detailed Implementation

[0019] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0020] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0021] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0022] Furthermore, the terms "first" and "second" are configured for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0023] Figure 1 A schematic diagram of the low-temperature startup circuit of the switching power supply provided in a preferred embodiment of this application is shown. For ease of explanation, only the parts relevant to this embodiment are shown, and are described in detail below: The low-temperature start-up circuit of the aforementioned switching power supply is connected to the switching power supply 100 that provides output DC power, and includes an on / off control circuit 10 and a first switching circuit 20.

[0024] The on / off control circuit 10 is connected to the switching power supply 100 and is configured to: disconnect the on / off control signal in response to the ambient temperature being lower than a first preset temperature and the output DC voltage being lower than a preset voltage; and output the on / off control signal in response to the output DC voltage being greater than or equal to the preset voltage. The first switching circuit 20 is connected to the on / off control circuit 10 and the switching power supply 100, and is configured to: transmit output DC power to the load in response to the on / off control signal; and disconnect the output DC power in response to the disconnection of the on / off control signal.

[0025] The first switching circuit 20 may include a switching transistor and an isolation device.

[0026] In response to the ambient temperature being lower than a first preset temperature and the output DC power being lower than a preset voltage, the on / off control circuit 10 disconnects the on / off control signal, causing the first switching circuit 20 to disconnect the output DC power in response to the disconnection of the on / off control signal; the switching power supply 100 provides the output DC power; in response to the output DC power being greater than or equal to the preset voltage, the on / off control circuit 10 outputs the on / off control signal, causing the first switching circuit 20 to transmit the output DC power to the load in response to the on / off control signal; thus, when the ambient temperature is lower than the first preset temperature, the first switching circuit 20 disconnects the load from the switching power supply 100 before the switching power supply 100 starts successfully, allowing the switching power supply 100 to start in an unloaded state, and after the switching power supply 100 starts, the first switching circuit 20 connects the load to the switching power supply 100 to supply power to the load, thereby reducing the power consumption of the control chip in the switching power supply 100 during startup, reducing the possibility of the protection function being triggered during startup, and reducing the impact of the performance degradation of the electrolytic capacitor at low temperatures on the startup of the switching power supply 100, thus expanding the application scenarios of the switching power supply 100.

[0027] It should be noted that the on / off control circuit 10 is also configured to output an on / off control signal in response to an ambient temperature greater than or equal to a first preset temperature.

[0028] Through the above technical solution, when the ambient temperature is greater than or equal to the first preset temperature, an on / off control signal is output to turn on the first switching circuit 20, thereby connecting the switching power supply 100 and the load, and realizing the normal load start-up of the switching power supply 100.

[0029] like Figure 2 As shown, the on / off control circuit 10 includes a first voltage divider circuit 11, an adjustment circuit 12, and a decision circuit 13.

[0030] The first voltage divider circuit 11 includes a first thermistor and a first resistor assembly connected in series, configured to receive a power supply voltage and divide the power supply voltage to output a first divided voltage from a first node; the first node is a common connection point of the first thermistor and the first resistor assembly. The regulating circuit 12 includes a second resistor assembly. The regulating circuit 12 is connected to the switching power supply 100 and is configured to connect the second resistor assembly in parallel with the first thermistor in response to the output DC voltage being greater than or equal to a preset voltage, so that the first voltage divider circuit 11 outputs the regulated first voltage divider voltage. The decision circuit 13, connected to the first voltage divider circuit 11, is configured to: output an on / off control signal in response to the first voltage divider voltage being greater than or equal to the first threshold voltage; and disconnect the output of the on / off control signal in response to the first voltage divider voltage being less than the first threshold voltage. Specifically, when the ambient temperature is lower than the first preset temperature, the first voltage divider voltage before adjustment is lower than the first threshold voltage; when the ambient temperature is greater than or equal to the first preset temperature, the first voltage divider voltage before adjustment is greater than or equal to the first threshold voltage.

[0031] The above technical solution enables ambient temperature detection based on a thermistor, and the switching between no-load start control and load control after the switching power supply 100 starts is achieved through the adjustment circuit 12, which simplifies the hardware design and reduces the cost.

[0032] like Figure 3 As shown, the switching power supply 100 includes a rectifier and filter circuit 200, a voltage conversion circuit 110, a feedback circuit 120, and a conversion control circuit 130.

[0033] The rectifier and filter circuit 200 is configured to receive input AC power and convert the input AC power into input DC power. The voltage conversion circuit 110 is connected to the rectifier and filter circuit 200 and is configured to convert the input DC power into the output DC power and the auxiliary DC power according to the conversion control signal. Feedback circuit 120, connected to voltage conversion circuit 110, is configured to sample the voltage of the output DC power supply to output the sampled voltage; The conversion control circuit 130 is connected to the voltage conversion circuit 110 and the feedback circuit 120, and is configured to be powered by auxiliary DC power and output a conversion control signal based on the feedback of the sampled voltage.

[0034] The conversion control signal is configured to regulate the output DC power. The low-temperature start-up circuit also includes a charging circuit 30.

[0035] The charging circuit 30 is connected to the rectifier and filter circuit 200 and the voltage conversion circuit 110, and is configured to transmit input DC power to the conversion control circuit 130 in response to the ambient temperature being lower than a second preset temperature. The conversion control circuit 130 is also configured to be powered by auxiliary DC and input DC, and to output a conversion control signal based on the feedback of the sampled voltage.

[0036] By using the above technical solution, when the ambient temperature is lower than the second preset temperature, the conversion control circuit 130 in the switching power supply 100 is supplied with supplemental power, which reduces the possibility that the chip in the conversion control circuit 130 cannot start due to low temperature.

[0037] like Figure 4 As shown, the charging circuit 30 includes a second voltage divider circuit 31 and a second switching circuit 32.

[0038] The second voltage divider circuit 31 includes a second thermistor and a third resistor assembly connected in series, configured to divide the supply voltage to output a second divided voltage from a second node; the second node is a common connection point of the second thermistor and the third resistor assembly. The second switching circuit 32 is connected to the second voltage divider circuit 31 and is configured to transmit input DC power to the conversion control circuit 130 in response to the second voltage divider voltage being greater than the second threshold voltage. Specifically, when the ambient temperature is lower than the second preset temperature, the second voltage divider voltage is greater than the second threshold voltage.

[0039] The above technical solution enables ambient temperature detection based on a thermistor and provides supplementary power through a second switching circuit 32, simplifying hardware design and reducing costs.

[0040] like Figure 5 As shown, the low-temperature startup circuit of the switching power supply also includes a power supply circuit 40 and a rectifier and filter circuit 200.

[0041] The power supply circuit 40 is configured to receive input AC power and convert the input AC power into the power supply voltage.

[0042] The above technical solution provides a power supply voltage based on the input AC power (such as mains power), expanding the application scenarios of the low-temperature start-up circuit of the switching power supply.

[0043] Figure 6 The present invention illustrates a partial example circuit structure of a low-temperature startup circuit for a switching power supply provided in an embodiment of the present invention. For ease of explanation, only the parts relevant to the embodiment of the present invention are shown, and are described in detail below: The first thermistor includes a first negative temperature coefficient (NTC) thermistor RT1, and the first resistor assembly includes a first resistor R1; The first terminal of the first NTC thermistor RT1 forms the input terminal of the first voltage divider circuit 11 and is connected to the adjustment circuit 12 to receive the power supply voltage; the second terminal of the first NTC thermistor RT1 and the first terminal of the first resistor R1 are connected and together form the output terminal of the first voltage divider circuit 11, which is connected to the adjustment circuit 12 and the decision circuit 13 to output the first voltage divider voltage; the second terminal of the first resistor R1 is connected to the power supply ground.

[0044] The adjustment circuit 12 includes a first optocoupler U1, a second resistor R2, and a third resistor R3; wherein the second resistor assembly includes the second resistor R2. The first end of the third resistor R3 is connected to the positive terminal of the first optocoupler U1, and the negative terminal of the first optocoupler U1 is connected to the signal ground. The first end of the second resistor R2 is connected to the first thermistor and the first resistor assembly. The collector of the first optocoupler U1 is connected to the first thermistor. The second end of the second resistor R2 is connected to the emitter of the first optocoupler U1. The second end of the third resistor R3 constitutes the input terminal of the adjustment circuit 12 and is connected to the switching power supply 100 to receive the output DC power.

[0045] The decision circuit 13 includes a second optocoupler U2, a first transistor Q1, a first Zener diode Z1, a fourth resistor R4, and a fifth resistor R5; The first end of the fourth resistor R4 forms the input terminal of the decision circuit 13, and is connected to the first voltage divider circuit 11 and the adjustment circuit 12 to receive the first voltage divider voltage; the second end of the fourth resistor R4 is connected to the negative terminal of the first Zener diode Z1, the positive terminal of the first Zener diode Z1 is connected to the base of the first transistor Q1, and the emitter of the first transistor Q1 is connected to the first end of the fifth resistor R5 and the positive terminal of the second optocoupler U2; the collector of the first transistor Q1 forms the power supply terminal of the decision circuit 13, and is connected to the first voltage divider circuit 11 to receive the power supply voltage; the collector of the second optocoupler U2 forms the output terminal of the decision circuit 13, and is connected to the first switching circuit 20 to output the on / off control signal.

[0046] The first switching circuit 20 includes a first field-effect transistor M1, a sixth resistor R6, a seventh resistor R7, and an eighth resistor R8; The source of the first field-effect transistor M1 and the first end of the seventh resistor R7 are connected and together form the input terminal of the first switching circuit 20, which is connected to the switching power supply 100 and the on / off control circuit 10 to receive the output DC power; the first end of the sixth resistor R6 forms the control terminal of the first switching circuit 20 and is connected to the on / off control circuit 10 to receive the on / off control signal; the gate of the first field-effect transistor M1 is connected to the first end of the eighth resistor R8, and the second end of the eighth resistor R8 is connected to the second end of the sixth resistor R6 and the second end of the seventh resistor R7; the drain of the first field-effect transistor M1 forms the output terminal of the first switching circuit 20 and is connected to the load to output DC power.

[0047] The second thermistor includes a second NTC thermistor RT2, and the third resistor assembly includes a ninth resistor R9; The first end of the ninth resistor R9 forms the input terminal of the second voltage divider circuit 31 to be connected to the power supply voltage; the second end of the ninth resistor R9 is connected to the first end of the second NTC thermistor RT2 and together forms the output terminal of the second voltage divider circuit 31, which is connected to the second switching circuit 32 to output the second voltage divider voltage; the second end of the second NTC thermistor RT2 is connected to the power supply ground.

[0048] The second switching circuit 32 includes a second transistor Q2, a second Zener diode Z2, a tenth resistor R10, and an eleventh resistor R11; The first end of the tenth resistor R10 forms the control terminal of the second switching circuit 32 and is connected to the second voltage divider circuit 31 to receive the second voltage divider voltage; the first end of the eleventh resistor R11 forms the input terminal of the second switching circuit 32 and is connected to the switching power supply 100 to receive the input DC power; the second end of the eleventh resistor R11 is connected to the collector of the second transistor Q2, the second end of the tenth resistor R10 is connected to the negative terminal of the second Zener diode Z2, and the positive terminal of the second Zener diode Z2 is connected to the base of the second transistor Q2; the emitter of the second transistor Q2 forms the output terminal of the second switching circuit 32 and is connected to the conversion control circuit 130 to output the input DC power.

[0049] The power supply circuit 40 includes a third transistor Q3, a third Zener diode Z3, a first diode D1, a second diode D2, a first capacitor C1, and a twelfth resistor R12; The anodes of the first diode D1 and the second diode D2 together form the input terminal of the power supply circuit 40 to receive AC power. The cathodes of the first diode D1, the second diode D2, the first terminal of the first capacitor C1, the collector of the third transistor Q3, the first terminal of the twelfth resistor R12, and the collector of the third transistor Q3 are connected together. The base of the third transistor Q3 is connected to the second terminal of the twelfth resistor R12 and the cathode of the third Zener diode Z3. The anode of the third Zener diode Z3 and the second terminal of the first capacitor C1 are connected to the power supply ground. The emitter of the third transistor Q3 forms the output terminal of the power supply circuit 40 and is connected to the first voltage divider circuit 11 and the second voltage divider circuit 31 to output the power supply voltage.

[0050] The following is based on the working principle. Figure 6 Further explanation is provided below: The first diode D1 and the second diode D2 rectify the input AC power to output the first DC power. The first capacitor C1 filters the first DC power. The filtered first DC power is then regulated by the third transistor Q3, the third Zener diode Z3, and the twelfth resistor R12 to output the supply voltage. At the same time, the rectifier and filter circuit 200 also rectifies the input AC power to output the input DC power.

[0051] When the ambient temperature is lower than the first preset temperature, the resistance of the first NTC thermistor RT1 is relatively large. The first NTC thermistor RT1 and the first resistor R1 divide the supply voltage, resulting in a smaller first divided voltage. Therefore, the gate voltage of the first transistor Q1 is less than the threshold voltage of the first transistor Q1, and the first transistor Q1 is cut off. The positive terminal of the second optocoupler U2 is pulled low by the fifth resistor R5, and the collector of the second optocoupler U2 disconnects the output of the on / off control signal. The first field-effect transistor M1 is cut off, thereby disconnecting the connection between the switching power supply 100 and the load. The switching power supply 100 starts under no-load (the voltage conversion circuit 110 converts the input DC power into output DC power and auxiliary DC power according to the conversion control signal; the feedback circuit 120 samples the voltage of the output DC power to output the sampled voltage; the conversion control circuit 130 is powered by the auxiliary DC power and according to...). (Feedback output conversion control signal of sampling voltage), after startup, the switching power supply 100 outputs DC power, the positive terminal of the first optocoupler U1 is at a high level, the emitter and collector of the first optocoupler U1 are connected, the second resistor R2 is connected in parallel to the two ends of the first NTC thermistor RT1, the equivalent resistance of the first NTC thermistor RT1 and the second resistor R2 after parallel connection is small, so the first voltage divider voltage is large, so the gate voltage of the first transistor Q1 is greater than or equal to the threshold voltage of the first transistor Q1, the first transistor Q1 is turned on, the positive terminal of the second optocoupler U2 is at a high level, the collector of the second optocoupler U2 outputs on / off control signal, the first field-effect transistor M1 is turned on, thus connecting the switching power supply 100 and the load, the output DC power of the switching power supply 100 supplies power to the load through the first field-effect transistor M1.

[0052] When the ambient temperature is greater than or equal to the first preset temperature, the resistance of the first NTC thermistor RT1 is small. The first NTC thermistor RT1 and the first resistor R1 divide the supply voltage, resulting in a larger first voltage divider. Therefore, the gate voltage of the first transistor Q1 is greater than or equal to the threshold voltage of the first transistor Q1, and the first transistor Q1 is turned on. The positive terminal of the second optocoupler U2 is at a high level, and the collector of the second optocoupler U2 outputs an on / off control signal. The first field-effect transistor M1 is turned on, thereby connecting the switching power supply 100 and the load. The output DC power from the switching power supply 100 supplies power to the load through the first field-effect transistor M1.

[0053] It should be noted that when the ambient temperature is lower than the second preset temperature, the resistance of the second NTC thermistor RT2 is relatively large. The second NTC thermistor RT2 and the ninth resistor R9 divide the supply voltage, resulting in a larger second voltage divider. Therefore, the gate voltage of the second transistor Q2 is greater than or equal to the threshold voltage of the second transistor Q2. The first transistor Q1 is turned on and transmits the input DC power to the power supply terminal of the conversion control circuit 130. The conversion control circuit 130 is powered by the auxiliary DC power and the input DC power, and outputs the conversion control signal according to the feedback of the sampled voltage.

[0054] When the ambient temperature is greater than or equal to the second preset temperature, the resistance of the second NTC thermistor RT2 is small. The second NTC thermistor RT2 and the ninth resistor R9 divide the supply voltage, resulting in a smaller second voltage divider. Therefore, the gate voltage of the second transistor Q2 is less than the threshold voltage of the second transistor Q2. The first transistor Q1 is turned off and stops transmitting the input DC power to the power supply terminal of the conversion control circuit 130. The conversion control circuit 130 is powered by auxiliary DC power and outputs a conversion control signal based on the feedback of the sampled voltage.

[0055] This invention also provides an electronic device that includes the low-temperature startup circuit of the switching power supply described above.

[0056] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0057] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A low-temperature startup circuit for a switching power supply, characterized in that, Connected to a switching power supply that provides DC output power, including: An on / off control circuit, connected to the switching power supply, is configured to: disconnect the on / off control signal in response to an ambient temperature lower than a first preset temperature and an output DC voltage lower than a preset voltage; and output an on / off control signal in response to an output DC voltage greater than or equal to the preset voltage. A first switching circuit, connected to the on / off control circuit and the switching power supply, is configured to: transmit the output DC power to the load in response to the on / off control signal; and disconnect the output DC power in response to the disconnection of the on / off control signal.

2. The low-temperature startup circuit of the switching power supply as described in claim 1, characterized in that, The on / off control circuit is further configured to output the on / off control signal in response to an ambient temperature greater than or equal to the first preset temperature.

3. The low-temperature startup circuit of the switching power supply as described in claim 2, characterized in that, The on / off control circuit includes: The first voltage divider circuit includes a first thermistor and a first resistor assembly connected in series, configured to receive a power supply voltage and divide the power supply voltage to output a first divided voltage from a first node; the first node is a common connection point of the first thermistor and the first resistor assembly. The regulating circuit includes a second resistor assembly. The regulating circuit is connected to the switching power supply and is configured to connect the second resistor assembly in parallel with the first thermistor in response to the output DC voltage being greater than or equal to the preset voltage, so that the first voltage divider circuit outputs the regulated first voltage divider voltage. The decision circuit, connected to the first voltage divider circuit, is configured to: output the on / off control signal in response to the first voltage divider voltage being greater than or equal to a first threshold voltage; and disconnect the output of the on / off control signal in response to the first voltage divider voltage being less than the first threshold voltage. Wherein, when the ambient temperature is less than the first preset temperature, the first voltage divider voltage before adjustment is less than the first threshold voltage; when the ambient temperature is greater than or equal to the first preset temperature, the first voltage divider voltage before adjustment is greater than or equal to the first threshold voltage.

4. The low-temperature startup circuit of the switching power supply as described in claim 3, characterized in that, The first thermistor includes a first NTC thermistor, and the first resistor assembly includes a first resistor; The first terminal of the first NTC thermistor forms the input terminal of the first voltage divider circuit and is connected to the adjustment circuit to receive the power supply voltage; The second end of the first NTC thermistor and the first end of the first resistor are connected and together form the output terminal of the first voltage divider circuit, which is connected to the adjustment circuit and the decision circuit to output the first voltage divider voltage; The second end of the first resistor is connected to the power supply ground.

5. The low-temperature startup circuit of the switching power supply as described in claim 3, characterized in that, The adjustment circuit includes a first optocoupler, a second resistor, and a third resistor; wherein the second resistor assembly includes the second resistor. The first end of the third resistor is connected to the positive terminal of the first optocoupler, the negative terminal of the first optocoupler is connected to the signal ground, the first end of the second resistor is connected to the first thermistor and the first resistor assembly, the collector of the first optocoupler is connected to the first thermistor, and the second end of the second resistor is connected to the emitter of the first optocoupler. The second end of the third resistor forms the input terminal of the adjustment circuit and is connected to the switching power supply to receive the output DC power.

6. The low-temperature startup circuit of the switching power supply as described in claim 3, characterized in that, The decision circuit includes a second optocoupler, a first transistor, a first Zener diode, a fourth resistor, and a fifth resistor; The first end of the fourth resistor constitutes the input terminal of the decision circuit, and is connected to the first voltage divider circuit and the adjustment circuit to receive the first voltage divider voltage. The second end of the fourth resistor is connected to the negative terminal of the first Zener diode, the positive terminal of the first Zener diode is connected to the base of the first transistor, and the emitter of the first transistor is connected to the first end of the fifth resistor and the positive terminal of the second optocoupler. The collector of the first transistor forms the power supply terminal of the decision circuit and is connected to the first voltage divider circuit to receive the power supply voltage; The collector of the second optocoupler forms the output terminal of the decision circuit and is connected to the first switching circuit to output the on / off control signal.

7. The low-temperature startup circuit of the switching power supply as described in claim 1, characterized in that, The switching power supply includes: A rectifier and filter circuit is configured to receive an input AC power and convert the input AC power into the input DC power. A voltage conversion circuit, connected to the rectifier and filter circuit, is configured to convert the input DC power into the output DC power and the auxiliary DC power according to the conversion control signal; A feedback circuit, connected to the voltage conversion circuit, is configured to sample the voltage of the output DC power to output a sampled voltage; A conversion control circuit, connected to the voltage conversion circuit and the feedback circuit, is configured to output the conversion control signal based on the auxiliary DC power supply and the feedback of the sampled voltage. The conversion control signal is configured to regulate the output DC power. The low-temperature start-up circuit also includes: The charging circuit is configured to transmit the input DC power to the conversion control circuit in response to the ambient temperature being lower than a second preset temperature. The conversion control circuit is further configured to be powered by the auxiliary DC power and the input DC power, and to output the conversion control signal based on the feedback of the sampled voltage.

8. The low-temperature startup circuit of the switching power supply as described in claim 7, characterized in that, The charging circuit includes: The second voltage divider circuit includes a second thermistor and a third resistor assembly connected in series, configured to divide the supply voltage to output a second divided voltage from a second node; the second node is a common connection point of the second thermistor and the third resistor assembly. A second switching circuit, connected to the second voltage divider circuit, is configured to transmit the input DC power to the conversion control circuit in response to the second voltage divider voltage being greater than the second threshold voltage. Wherein, when the ambient temperature is lower than the second preset temperature, the second voltage divider voltage is greater than the second threshold voltage.

9. The low-temperature startup circuit of the switching power supply as described in any one of claims 1 to 8, characterized in that, Also includes: The power supply circuit is configured to receive an input AC power and convert the input AC power into a supply voltage.

10. An electronic device, characterized in that, The electronic device includes a low-temperature startup circuit for a switching power supply as described in any one of claims 1 to 9.

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