Protection device of PFC (Power Factor Correction) circuit and electric equipment

Abstract

The invention relates to a protection device of a PFC (Power Factor Correction) circuit and electric equipment. In the protection device, a current detection circuit is used for detecting a voltage difference value between a current input end and a current output end of a power switch in a PFC circuit, and forming a current detection signal positively correlated with a current flowing through the power switch; the current protection circuit is used for comparing the current detection signal with a current protection threshold value to form a current protection signal. The current detection circuit is used for current detection, the current protection circuit is used for current protection, a special current sampling resistor and a detection circuit do not need to be arranged in the PFC circuit, the circuit design is simplified, when a current detection signal exceeds a current exceeding threshold value, the protection circuit can rapidly turn off the PFC circuit, the reliability is high, and the circuit is convenient to use. And the safety of the PFC circuit can be improved. The electric equipment comprises a PFC circuit and the protection device.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and particularly to a protection device for a PFC circuit and an electrical equipment. Background Art

[0002] Power factor correction (PFC) is generally divided into active power factor correction (APFC) and passive power factor correction (PPFC) according to the implementation method. With the development of power electronics technology, active power factor correction has gradually become the mainstream. Usually, a PFC circuit includes a power switch. By controlling the conduction and turn-off of the power switch, sinusoidal change of current can be achieved, which has the advantages of small volume, light weight, and high power factor.

[0003] The power switch in the PFC circuit is easily damaged or even fails due to overvoltage or overcurrent. Usually, a dedicated current sampling resistor and a detection circuit are provided in the PFC circuit to detect the current flowing through the power switch, and the circuit design is relatively complex. In addition, the current hardware protection circuit for PFC does not fully consider the influence of temperature, and the reliability is still insufficient. Summary of the Invention

[0004] The present invention provides a protection device for a PFC circuit, which can detect the current flowing through the power switch in the PFC circuit and form a current detection signal, simplifies the circuit design compared with the prior art, and can also perform current protection by using the current detection signal. The present invention also provides an electrical equipment.

[0005] On the one hand, the present invention provides a protection device for a PFC circuit. The PFC circuit includes a power switch and converts the rectified signal output by the power supply module into a corresponding output voltage. The protection device includes:

[0006] A current detection circuit, configured to detect the voltage difference between the current input end and the current output end of the power switch in the PFC circuit, and amplify the voltage difference to form a current detection signal that is positively correlated with the current flowing through the power switch; and

[0007] A current protection circuit, configured to compare the current detection signal with a current protection threshold to form a current protection signal. When the current detection signal is greater than the current protection threshold, the current protection signal turns off the power switch.

[0008] Optionally, the current detection circuit includes:

[0009] A first operational amplifier;

[0010] The first input sub - circuit includes an input control switch, a first resistor, and a second resistor. The input terminal of the input control switch is coupled to the current input terminal of the power switch. The output terminal of the input control switch is coupled to one end of the first resistor. The other end of the first resistor is coupled to the non - inverting input terminal of the first operational amplifier. Both ends of the second resistor are respectively coupled to the non - inverting input terminal of the first operational amplifier and ground. Wherein, the current output terminal of the power switch is grounded, and the input control switch and the power switch are turned on and off in response to the same PFC control signal;

[0011] The second input sub - circuit includes a third resistor, a fourth resistor, and a fifth resistor. The third resistor and the fourth resistor are sequentially connected in series between ground and the inverting input terminal of the operational amplifier. Both ends of the fifth resistor are respectively coupled to the inverting input terminal and the output terminal of the first operational amplifier;

[0012] Wherein, the sum of the on - resistance of the input control switch and the resistance value of the first resistor is equal to the sum of the resistance values of the third resistor and the fourth resistor; the resistance values of the second resistor and the fifth resistor are equal.

[0013] Optionally, the on - resistance of the input control switch is equal to the resistance value of the third resistor.

[0014] Optionally, the current protection circuit includes:

[0015] A first comparator, with the inverting input terminal coupled to the current detection signal and the non - inverting input terminal coupled to the current protection threshold; and

[0016] A first diode, with the negative terminal coupled to the output terminal of the first comparator and the positive terminal coupled to the control terminal of the power switch.

[0017] Optionally, the protection device further includes:

[0018] A temperature detection circuit for detecting the temperature of the power switch and outputting a temperature signal.

[0019] Optionally, the protection device further includes a control module, and the control module includes:

[0020] A storage unit storing a temperature - on - resistance comparison table, which reflects the corresponding relationship between the device temperature and the on - resistance value of the power switch;

[0021] A temperature processing unit for collecting the temperature signal output by the temperature detection circuit, performing analog - to - digital conversion, and obtaining the current on - resistance value of the power switch according to the temperature - on - resistance comparison table; and

[0022] A current processing unit is configured to collect the current detection signal, perform analog-to-digital conversion, and calculate the current flowing through the power switch based on the current detection signal and the current on-resistance value obtained by the temperature processing unit.

[0023] Optionally, the temperature detection circuit includes:

[0024] A Wheatstone bridge including a first bridge arm and a second bridge arm coupled between a power supply voltage and ground. The first bridge arm includes a sixth resistor and a seventh resistor connected in series, and the second bridge arm includes an eighth resistor and a thermistor unit connected in series; and

[0025] A second operational amplifier coupled to the first bridge arm and the second bridge arm of the Wheatstone bridge and configured to generate the temperature signal. Wherein, the connection point of the sixth resistor and the seventh resistor is coupled to the non-inverting input terminal of the second operational amplifier, and the connection point of the eighth resistor and the thermistor unit is coupled to the inverting input terminal of the second operational amplifier.

[0026] Optionally, the protection device further includes:

[0027] A temperature protection circuit configured to compare the temperature signal with a safety temperature threshold to form a temperature protection signal. When the temperature signal is greater than the safety temperature threshold, the temperature protection signal turns off the power switch.

[0028] Optionally, the temperature protection circuit includes:

[0029] A second comparator having an inverting input terminal coupled to the temperature signal and a non-inverting input terminal coupled to the safety temperature threshold, and the second comparator outputs the temperature protection signal; and

[0030] A second diode having a negative terminal coupled to the temperature protection signal and a positive terminal coupled to the control terminal of the power switch.

[0031] On the other hand, the present invention provides an electrical device. The electrical device includes a PFC circuit and the above protection device. The PFC circuit includes a power switch. The protection device is at least configured to detect the voltage difference between the current input terminal and the current output terminal of the power switch and output a current detection signal that is positively correlated with the current flowing through the power switch.

[0032] The protection device for the PFC circuit provided by the present invention includes a current detection circuit and a current protection circuit. The current detection circuit is used to detect the voltage difference between the current input end and the current output end of the power switch in the PFC circuit, and amplify the voltage difference to form a current detection signal that is positively correlated with the current flowing through the power switch. The current protection circuit is used to compare the current detection signal with a current protection threshold to form a current protection signal. When the current detection signal is greater than the current protection threshold, the current protection signal turns off the power switch. Since the power switch has a conduction internal resistance, the voltage difference between the current input end and the current output end of the power switch is the product of the current flowing through the power switch and the conduction internal resistance of the power switch. The voltage difference and its amplified value are positively correlated with the current flowing through the power switch. Therefore, the current detection signal can reflect the magnitude of the current flowing through the power switch, and the current detection signal can be used for overcurrent detection and calculating the value of the current flowing through the power switch. Using the current detection circuit for current detection and the current protection circuit for current protection does not require setting a dedicated current sampling resistor and detection circuit in the PFC circuit, which helps to simplify the circuit design. And when the current detection signal exceeds the current protection threshold, the current protection circuit can quickly turn off the PFC circuit, with high reliability, which helps to improve the safety of the PFC circuit.

[0033] Further, the protection device may further include a temperature detection circuit, a temperature protection circuit, and a control module. Using the temperature protection circuit for temperature protection has high reliability and helps to improve the safety of the PFC circuit. The control module can collect the current detection signal and calculate the current flowing through the power switch, and can also collect the temperature signal generated by the temperature detection circuit and calculate the current temperature of the power switch. Considering that the conduction internal resistance of the power switch is related to temperature, an appropriate conduction internal resistance value can be selected according to the current temperature of the power switch to calculate the current flowing through the power switch, which helps to improve the current detection accuracy.

[0034] The electrical equipment provided by the present invention includes a PFC circuit and the above protection device, and has the same or similar advantages as the protection device. Description of the Drawings

[0035] Figure 1 It is a connection schematic diagram of a power supply module, a PFC circuit, a load, and a protection device in an embodiment of the present invention.

[0036] Figure 2 It is a circuit schematic diagram of a power supply module, a PFC circuit, and a load in an embodiment of the present invention.

[0037] Figure 3 It is a circuit schematic diagram of the protection device for the PFC circuit in an embodiment of the present invention. Detailed Implementation Modes

[0038] The protection device for the PFC circuit and the electrical equipment of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are all in very simplified forms and use non-precise scales, only for conveniently and clearly assisting in explaining the purpose of the embodiments of the present invention.

[0039] Figure 1 The connection relationship of the power supply module 10, the PFC circuit 20, the load 30, and the protection device 100 is shown, where the solid line represents the circuit connection and the dotted line represents the protected object. Refer to Figure 1 , the protection device 100 is coupled to the PFC circuit 20; the PFC circuit 20 is respectively coupled to the power supply module 10 and the load 30 to perform power factor correction (PFC) on the rectified signal output by the power supply module 10, and the generated output voltage is delivered to the load 30.

[0040] Refer to Figure 2 , as an example, the power supply module 10 includes a rectifier VC1, one input terminal of the rectifier VC1 is coupled to the live wire of the AC power grid and the other input terminal is coupled to the neutral wire of the AC power grid to convert the AC signal into a DC signal. The PFC circuit 20 is coupled to the output terminal of the rectifier VC1. The PFC circuit 20 can adopt a boost topology, a buck topology, a buck-boost topology, a forward topology, or a flyback topology, which can be specifically set according to needs. In the following embodiments, the PFC circuit 20 is, for example, a boost topology (boost).

[0041] As an example, the PFC circuit 20 includes an inductor L1, a power switch VT1, a fast recovery diode D1, and an energy storage capacitor E1. Among them, the power switch VT1 is, for example, an NMOS transistor. Specifically, one end of the inductor L1 is coupled to the positive output terminal of the rectifier VC1, and the other end is coupled to the positive extreme of the fast recovery diode D and the drain extreme of the power switch VT1. The control terminal of the power switch VT1 is coupled to a PFC control signal; the upper plate of the energy storage capacitor E1 is coupled to the negative extreme of the fast recovery diode D, and the lower plate is coupled to the source extreme of the power switch VT1 and grounded. When the PFC circuit 20 is working, the power switch VT1 is alternately turned on and off through the PFC control signal, so that the inductor L alternately stores and releases energy to form an output voltage. The PFC control signal can be formed by a hardware circuit and / or by a software program. As Figure 1 shown, the protection device 100 may include a control module 130, and the PFC control signal can be output through the control module 130. The control module 130 includes, for example, an MCU.

[0042] As Figure 1and Figure 2 As shown, the load 30 is coupled to the output terminal of the PFC circuit 20, specifically between the upper and lower plates of the energy storage capacitor E1. The load 30 has a load resistor R load , and the load resistor R load The voltage value across both ends is the output voltage value of the PFC circuit 20.

[0043] Figure 3 The circuit of the protection device 100 of the PFC circuit is shown. In this embodiment, the protection device 100 can be used to obtain a signal related to the current flowing through the power switch VT1 in the PFC circuit 20 while keeping the circuit simple, so as to detect the current and further perform current protection. Refer to Figures 1 to 3 , the protection device 100 includes a current detection circuit 110. The current detection circuit 110 is used to detect the voltage difference between the current input terminal and the current output terminal of the power switch VT1 in the PFC circuit 20, and amplify the voltage difference to form a current detection signal that is positively correlated with the current flowing through the power switch VT1.

[0044] Since the power switch VT1 has a conduction internal resistance, the voltage difference between the current input terminal and the current output terminal of the power switch VT1 can be regarded as the product of the current flowing through the power switch VT1 and the corresponding conduction internal resistance. Thus, after the current detection circuit 110 detects the voltage difference between the current input terminal (i.e., the high voltage terminal) and the current output terminal (i.e., the low voltage terminal) of the power switch VT1 in the PFC circuit 20, the voltage difference is positively correlated with the current flowing through the power switch VT1. By amplifying the voltage difference, a current detection signal that is positively correlated with the current flowing through the power switch VT1 can be obtained. In this embodiment, the current output terminal of the power switch VT1 is grounded, and the voltage difference is the voltage of the current input terminal of the power switch VT1.

[0045] Refer to Figure 3 , as an example, the current detection circuit 110 includes a first operational amplifier U1, a first input sub-circuit, and a second input sub-circuit. The first operational amplifier U1 is used to calculate the voltage difference between the current input terminal and the current output terminal of the power switch VT1 in the PFC circuit 20 and amplify the voltage difference. Among them, the first input circuit is coupled to the current input terminal and the non-inverting input terminal of the first operational amplifier U1, and the second input circuit is coupled to the current output terminal of the power switch VT1 (grounded in this embodiment). Specifically, the first input sub-circuit includes an input control switch Q1, a first resistor R1, and a second resistor R2. The input terminal of the input control switch Q1 is coupled to the current input terminal of the power switch VT1 to obtain as Figure 2 and Figure 3The shown current input sampling signal (the current input signal is a voltage signal), the output end of the input control switch Q1 is coupled to one end of the first resistor R1, the other end of the first resistor R1 is coupled to the non-inverting input end of the first operational amplifier U1, and both ends of the second resistor R2 are respectively coupled to the non-inverting input end of the first operational amplifier U1 and the ground; the second input sub-circuit includes a third resistor R3, a fourth resistor R4, and a fifth resistor R5. The third resistor R3 and the fourth resistor R4 are sequentially connected in series between the ground and the inverting input end of the first operational amplifier U1, and both ends of the fifth resistor R5 are respectively coupled to the inverting input end and the output end of the first operational amplifier U1.

[0046] Since in the PFC circuit 20, when the power switch VT1 is turned off, the voltage at its current input end is relatively high and may exceed the maximum voltage allowed for input by the first operational amplifier U1. To protect the first operational amplifier U1, the first input sub-circuit has an input control switch Q1. The input control switch Q1 and the power switch VT1 are turned on and off in response to the same PFC control signal. In this way, when the PFC control signal controls the power switch VT1 to turn on, it also controls the input control switch Q1 to turn on simultaneously, so that the sampled value at the current input end, that is, the current input sampling signal, is output to the first operational amplifier U1. When the PFC control signal controls the power switch VT1 to turn off, it also controls the input control switch Q1 to turn off simultaneously, thereby protecting the first operational amplifier U1. The input control switch Q1 has an on-resistance. The sum of the on-resistance of the input control switch Q1 and the resistance value of the first resistor R1 is equal to the sum of the resistance values of the third resistor R3 and the fourth resistor R4. In addition, the resistance values of the second resistor R2 and the fifth resistor R5 are equal, thus forming a symmetric amplifier circuit, which can improve the accuracy of the current detection signal. Further, the on-resistance of the input control switch Q1 and the resistance value of the third resistor R3 are, for example, equal, and the resistance values of the first resistor R1 and the fourth resistor R4 are, for example, equal.

[0047] The current detection signal generated by the above current detection circuit 110 can be used for overcurrent protection. Refer to Figure 1 and Figure 3 , the protection device 100 further includes a current protection circuit 120. The current protection circuit 120 is used to compare the current detection signal with a current protection threshold to form a current protection signal. When the current detection signal is greater than the current protection threshold, the current protection signal turns off the power switch VT1, thereby reducing the impact of overcurrent on the power switch VT1 and the PFC circuit 20 through a hardware protection method.

[0048] Specifically, as Figure 3As shown, by way of example, the current protection circuit 120 includes a first comparator U2 and a first diode D2. The inverting input terminal of the first comparator U2 is coupled to the current detection signal output by the current detection circuit 110, and the non-inverting input terminal is coupled to the current protection threshold. The negative terminal of the first diode D2 is coupled to the output terminal of the first comparator U2, and the positive terminal is coupled to the control terminal of the power switch VT1 (i.e., coupled to the PFC control signal). The current protection threshold can be set and output by the control module 130, or can be generated by a hardware circuit. Here, for example, it is the latter. By way of example, the current protection circuit 120 further includes a first voltage-dividing resistor R6 and a second voltage-dividing resistor R7 connected in series between the power supply voltage VCC and the ground. The voltage at the connection point of the first voltage-dividing resistor R6 and the second voltage-dividing resistor R7 is used as the current protection threshold. By adjusting the resistance values of the first voltage-dividing resistor R6 and the second voltage-dividing resistor R7, the current protection threshold can be adjusted. In addition, the current protection circuit 120 may further include a pull-up resistor R8 coupled between the power supply voltage VCC and the output terminal of the first comparator U2 to ensure that the signal at the output terminal of the first comparator U2 does not appear abnormally.

[0049] The working principle of the current protection circuit 120 is as follows: The signal at the output terminal of the first comparator U2 is the current protection signal. When the current detection signal output by the current detection circuit 110 does not exceed the current protection threshold, the current protection signal is at a high level. At this time, due to the blocking of the first diode D2, the current protection signal does not affect the PFC control signal, and the PFC circuit 20 is in a working state. When the current detection signal exceeds the current protection threshold, the current protection signal is at a low level, the first diode D2 conducts, the PFC control signal is pulled low, so that the power switch VT1 is forced to turn off, and the PFC circuit 20 stops working.

[0050] By collecting the above-mentioned current detection signals and appropriately processing them, the current actually flowing through the power switch VT1 can be detected. Specifically, in the protection device 100, the control module 130 may include a current processing unit (not shown in the figure), and the current processing unit is used to collect the current detection signals and perform analog-to-digital conversion, and calculate the current flowing through the power switch VT1 based on the current detection signals and the on-resistance value of the power switch VT1. In a further embodiment, when collecting the current detection signals, corresponding thresholds may be set to perform software protection on the PFC circuit 20. Specifically, when the current flowing through the power switch VT1 exceeds the corresponding threshold set by the program in the control module 130 (i.e., the software threshold for the on-current of the power switch VT1), the PFC control signal can be automatically stopped from being output through the program, so that the PFC circuit 20 stops working. Optionally, the software threshold for the on-current of the power switch VT1 is lower than or equal to the aforementioned current protection threshold set by the hardware circuit.

[0051] The control module 130 includes, for example, an MCU. The current acquisition unit can collect the current detection signals through the corresponding ADC in the MCU and perform analog-to-digital conversion, and calculate the current flowing through the power switch VT1 by using the processor in the MCU based on the current detection signals and the on-resistance value of the power switch VT1. The control module 130 may further include a storage unit (not shown in the figure). The on-resistance value of the power switch VT1 can be stored in the storage unit, and the storage unit can be integrated in the MCU or coupled to the MCU. To avoid the influence of the voltage magnitude of the PFC control signal on the on-resistance value of the power switch VT1, each time the power switch VT1 is turned on, the PFC control signal adopts the same voltage value.

[0052] In this embodiment, the protection device 100 may further include a temperature detection circuit 140 and a temperature protection circuit 150 to obtain a temperature signal reflecting the temperature of the power switch VT1 and reduce the over-temperature risk through a hardware protection method. Moreover, the control module 130 can correct the on-resistance of the power switch VT1 by using the temperature signal and calculate the actual current flowing through the power switch VT1 by using the corrected on-resistance, which can improve the current detection accuracy. The specific description is as follows.

[0053] The temperature detection circuit 140 is used to detect the temperature of the power switch VT1 and output a temperature signal. Before temperature measurement, the temperature detection circuit 140 can be placed near the power switch VT1 to be measured. For example, the thermistor used to sense temperature in the temperature detection circuit 140 is tightly fixed to the power switch VT1. In this embodiment, in order to improve the accuracy and sensitivity of temperature detection and meet the temperature protection requirements of the PFC circuit 20, the temperature detection circuit 140 adopts a Wheatstone bridge.

[0054] Specifically, as Figure 3 shown, the temperature detection circuit 140 includes a Wheatstone bridge and a second operational amplifier U3. The Wheatstone bridge includes a first bridge arm and a second bridge arm coupled between a power supply voltage VCC and ground. The first bridge arm includes a resistor R9 (denoted as the sixth resistor) and a resistor R10 (denoted as the seventh resistor) connected in series. The second bridge arm includes a resistor R11 (denoted as the eighth resistor) and a thermistor unit RT connected in series. When the temperature of the power switch VT1 changes, the resistance value of the thermistor unit RT changes accordingly. Subsequently, the voltage difference between the connection point of the resistors R9 and R10 on the first bridge arm and the connection point of the resistor R11 and the thermistor unit RT on the second bridge arm changes, so that the temperature change is converted into a high-precision voltage change. This voltage change is compared and amplified by the second operational amplifier U3 to generate a corresponding temperature signal containing the temperature information of the power switch VT1. Specifically, the second operational amplifier U3 is configured to be coupled to the first bridge arm and the second bridge arm of the Wheatstone bridge and generate a corresponding temperature signal. Among them, the connection point of the resistors R9 and R10 is coupled to the non-inverting input terminal of the second operational amplifier U3, and the connection point of the resistor R11 and the thermistor unit is coupled to the inverting input terminal of the second operational amplifier U3. In this embodiment, a resistor R12 is coupled between the connection point of the resistors R9 and R10 and the non-inverting input terminal of the second operational amplifier U3, a resistor R13 is coupled between the connection point of the resistor R11 and the thermistor unit RT and the inverting input terminal of the second operational amplifier U3, a resistor R14 is coupled between the inverting input terminal and the output terminal of the second operational amplifier U3, and a resistor R15 is coupled between the non-inverting input terminal of the second operational amplifier U3 and ground.

[0055] In this embodiment, an NTC thermistor (i.e., a negative temperature coefficient thermistor, Negative Temperature Coefficient Thermistor) is used to detect the temperature change of the heating device. Considering that the resistance value of the NTC thermistor and the temperature are in a non-linear relationship, in order to reduce the influence of measurement error on the system, the thermistor unit RT includes an NTC thermistor RT1 and a resistor R16 connected in parallel to perform hardware compensation using the resistor R16. Thus, when the temperature of the power switch VT1 changes, the change in the resistance value of the parallel resistor formed by the NTC thermistor RT1 and the resistor R16 is lower than the change in the resistance value of the NTC thermistor when only the NTC thermistor is used, thereby reducing the influence of the non-linear relationship. The present invention is not limited to this. In another embodiment, after collecting the temperature signal, the influence of the above non-linear relationship can be reduced by a calculation fitting method (i.e., software compensation), and relatively accurate temperature information can also be obtained.

[0056] The temperature protection circuit 150 is used to compare the temperature signal generated by the temperature detection circuit 140 with a safety temperature threshold to form a temperature protection signal. When the temperature signal is greater than the safety temperature threshold, the temperature protection signal turns off the power switch VT1. The safety temperature threshold can be set and output by the control module 130 or generated by a hardware circuit.

[0057] Referring to Figure 3 , as an example, the temperature protection circuit 150 includes a second comparator U4 and a second diode D3. The inverting input terminal of the second comparator U4 is coupled to the output terminal of the second operational amplifier U3. A third voltage-dividing resistor R16 and a fourth voltage-dividing resistor R17 are connected in series between the power supply voltage VCC and the output terminal of the second comparator U4. The safety temperature threshold is the voltage value at the connection point of the third voltage-dividing resistor R16 and the fourth voltage-dividing resistor R17. The second comparator D3 outputs a temperature protection signal. The negative terminal of the second diode D3 is coupled to the temperature protection signal and the positive terminal is coupled to the control terminal of the power switch VT1 (i.e., coupled to the PFC control signal). In addition, the temperature protection circuit 150 may further include a pull-up resistor R18 coupled between the power supply voltage VCC and the output terminal of the second comparator U4 to ensure that the signal at the output terminal of the second comparator U4 does not show abnormalities.

[0058] The working principle of the temperature protection circuit 150 is as follows: When the temperature signal output by the temperature detection circuit 140 does not exceed the safety temperature threshold, the temperature protection signal formed by passing through the second comparator U4 is at a high level. At this time, due to the blocking of the second diode D3, the temperature protection signal does not affect the PFC control signal, and the PFC circuit 20 is in a working state; when the temperature signal exceeds the safety temperature threshold, the temperature protection signal formed by passing through the second comparator U4 is at a low level, and the second diode D3 conducts, pulling down the PFC control signal, so that the power switch VT1 is forced to turn off and the PFC circuit 20 stops working. In this embodiment, the second comparator D3 is a hysteresis comparator. After the PFC circuit 20 stops working, the temperature of the power switch VT1 gradually decreases. When the temperature drops until the temperature signal returns to the lower temperature limit value in the hysteresis curve of the hysteresis comparator, the temperature protection signal returns to a high level. At this time, due to the blocking of the second diode D3, the temperature protection signal does not affect the PFC control signal, and the PFC circuit 20 resumes working. It can be seen that by using the temperature protection circuit 150, the PFC circuit 20 is allowed to work only after ensuring that the temperature of the power switch VT1 is stably lower than the safety temperature threshold, so as to protect the power switch VT1 and the PFC circuit 20 and reduce the impact of overheating on the power switch VT1 and the PFC circuit 20.

[0059] The temperature signal generated by the temperature detection circuit 140 can be collected by the control module 130 to obtain the current temperature value of the power switch VT1. To avoid adverse effects on the control module 130 caused by excessive temperature, when collecting the temperature signal, corresponding thresholds can be set to perform software protection on the PFC circuit 20. Specifically, when the temperature signal exceeds the corresponding threshold (software threshold regarding the operating temperature of the power switch VT1) set by the program in the control module 130, the program can automatically stop outputting the PFC control signal, thereby causing the PFC circuit 20 to stop working. Optionally, the software threshold regarding the operating temperature of the power switch VT1 is lower than or equal to the aforementioned safety temperature threshold set by the hardware circuit.

[0060] In the control module 130, the above storage unit may store a temperature internal resistance comparison table, which reflects the correspondence between the device temperature of the power switch VT1 and the on-resistance value of the power switch VT1. The temperature internal resistance comparison table can be obtained based on the curve of the on-resistance and temperature of the power switch VT1. The control module 130 may further include a temperature processing unit, which is configured to collect the temperature signal output by the temperature detection circuit 140 and perform analog-to-digital conversion, and obtain the current on-resistance value of the power switch VT1 according to the temperature internal resistance comparison table. The temperature processing unit may collect the temperature signal generated by the temperature detection circuit 140 through the corresponding ADC in the MCU and perform analog-to-digital conversion, and calculate the current on-resistance value of the power switch VT1 by using the processor in the MCU according to the temperature internal resistance comparison table. When calculating the current flowing through the power switch VT1, the above current processing unit may calculate based on the current on-resistance value of the power switch VT1 obtained by the temperature processing unit, thereby improving the current detection accuracy.

[0061] It can be understood that the storage unit, the temperature processing unit, and the current processing unit in the control module 130 can be implemented in one unit, or any one of them can be split into multiple units, or at least part of the functions of one or more of these units can be combined with at least part of the functions of other units and implemented in one unit. According to the embodiments of the present invention, any one of the storage unit, the temperature processing unit, and the current processing unit can be at least partially implemented by software or at least partially implemented by a hardware circuit. Whether in the form of software or a hardware circuit, the individual parts can be implemented by those skilled in the fields of electronics and software, and therefore, the details are not elaborated in this specification.

[0062] The current protection signal obtained by the above-mentioned current protection circuit 120 and / or the temperature protection signal obtained by the temperature protection circuit 150 can be collected by the control module 130. By collecting the temperature protection signal or the voltage protection signal, it is convenient for the staff to judge whether it is caused by current protection or temperature protection when the power switch VT1 is forced to turn off, which is convenient for the staff to analyze and troubleshoot.

[0063] Optionally, the protection device 100 may include an overtemperature alarm and / or an overcurrent alarm. The overtemperature alarm is coupled to the temperature protection signal. Wherein, when the temperature signal is greater than the safe temperature threshold, the temperature protection signal controls the overtemperature alarm to emit a warning light and / or a warning sound. The overcurrent alarm is coupled to the current protection signal. Wherein, when the current detection signal is greater than the current protection threshold, the current protection signal controls the overcurrent alarm to emit a warning light and / or a warning sound. By using the overtemperature alarm and the overcurrent alarm, information on whether the temperature is too high and whether the current is too high can be obtained more intuitively.

[0064] In the protection device 100 described in the above embodiment, the current detection circuit 110 is used to detect the voltage difference between the current input end and the current output end of the power switch VT1 in the PFC circuit 20, and form a current detection signal that is positively correlated with the current flowing through the power switch. Since the power switch VT1 has a conduction internal resistance, the voltage difference is the product of the current flowing through the power switch VT1 and the conduction internal resistance of the power switch VT1. The voltage difference and its amplified value are positively correlated with the current flowing through the power switch VT1. Therefore, the current detection signal can reflect the magnitude of the current flowing through the power switch VT1, and the current detection signal can be used for overcurrent detection and calculation of the current value flowing through the power switch VT1. The protection device 100 further includes a current protection circuit 120. Using the current detection circuit 110 to obtain a current detection signal and using the current protection circuit 120 for current protection does not require a dedicated current sampling resistor and detection circuit to be provided in the PFC circuit 20, which helps to simplify the circuit design. And when the current detection signal exceeds the current protection threshold, the current protection circuit can quickly turn off the PFC circuit 20, with high reliability, which helps to improve the safety of the PFC circuit 20.

[0065] The protection device 100 may further include a temperature detection circuit 140, a temperature protection circuit 150, and a control module 130. The temperature protection circuit 150 is used for temperature protection, which has relatively high reliability and helps improve the safety of the PFC circuit 20. The control module can collect the current detection signal and calculate the current flowing through the power switch VT1. It can also collect the temperature signal generated by the temperature detection circuit 140 and calculate the current temperature of the power switch VT1. Moreover, considering that the on-resistance of the power switch VT1 is related to temperature, a more accurate on-resistance value can be selected according to the calculated current temperature of the power switch VT1 to calculate the current flowing through the power switch VT1, which helps improve the current detection accuracy.

[0066] An embodiment of the present invention further relates to an electrical device, referring to Figures 1 to 3 , the electrical device includes a PFC circuit 20 and the protection device 100 described in the above embodiment. The electrical device can be various devices that use the PFC circuit 20 for power factor correction, such as household appliances, like air conditioners.

[0067] In the electrical device, the PFC circuit 20 includes a power switch. The protection device 100 is at least used to detect the voltage difference between the current input end and the current output end of the power switch, and output a current detection signal that is positively correlated with the current flowing through the power switch. The PFC circuit 20 can convert the rectified signal output by the power supply module 10 into a corresponding output voltage. In the protection device 100, the current detection circuit 110 can form a current detection signal that is positively correlated with the current flowing through the power switch VT1 in the PFC circuit 20. The current detection signal reflects the current flowing through the power switch VT1, and can be used to detect overcurrent and calculate the current flowing through the power switch VT1. This not only helps simplify the circuit design, but also helps improve the reliability and safety of the PFC circuit 20 and the electrical device, thereby ensuring the normal operation of the PFC circuit 20 and the electrical device.

[0068] It should be noted that the embodiments in this specification are described in a progressive manner. Each part focuses on the differences from the previous part, and the same and similar parts between each part can be understood by reference.

[0069] The above description is only a description of the preferred embodiments of the present invention, and does not limit the scope of the rights of the present invention in any way. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modification, equivalent change, and modification made to the above embodiments according to the technical essence of the present invention without departing from the technical solutions of the present invention all belong to the protection scope of the technical solutions of the present invention.

Claims

1. A protection device for a PFC circuit, characterized in that The PFC circuit includes a power switch and converts the rectified signal output by the power supply module into a corresponding output voltage. The protection device includes: a current detection circuit configured to detect a voltage difference between a current input end and a current output end of the power switch in the PFC circuit and amplify the voltage difference to form a current detection signal that is positively correlated with the current flowing through the power switch; and a current protection circuit configured to compare the current detection signal with a current protection threshold to form a current protection signal, and when the current detection signal is greater than the current protection threshold, the current protection signal turns off the power switch.

2. The protection device according to claim 1, characterized in that, The current detection circuit includes: a first operational amplifier; a first input sub-circuit including an input control switch, a first resistor, and a second resistor. An input end of the input control switch is coupled to the current input end of the power switch, an output end of the input control switch is coupled to one end of the first resistor, the other end of the first resistor is coupled to the non-inverting input end of the first operational amplifier, and two ends of the second resistor are respectively coupled to the non-inverting input end of the first operational amplifier and ground. Wherein, the current output end of the power switch is grounded, and the input control switch and the power switch are turned on and off in response to the same PFC control signal; a second input sub-circuit including a third resistor, a fourth resistor, and a fifth resistor. The third resistor and the fourth resistor are sequentially connected in series between ground and the inverting input end of the operational amplifier, and two ends of the fifth resistor are respectively coupled to the inverting input end and the output end of the first operational amplifier; wherein, the sum of the on-resistance of the input control switch and the resistance value of the first resistor is equal to the sum of the resistance values of the third resistor and the fourth resistor; the resistance values of the second resistor and the fifth resistor are equal.

3. The protection device according to claim 2, wherein, The on-resistance of the input control switch is equal to the resistance value of the third resistor.

4. The protection device according to claim 1, characterized in that, The current protection circuit includes: a first comparator with its inverting input end coupled to the current detection signal and its non-inverting input end coupled to the current protection threshold; and a first diode with its negative terminal coupled to the output end of the first comparator and its positive terminal coupled to the control end of the power switch.

5. The protection device according to claim 1, characterized in that, Further included is: a temperature detection circuit configured to detect the temperature of the power switch and output a temperature signal.

6. The protection device according to claim 5, characterized in that, Further included is a control module, and the control module includes: a storage unit storing a temperature-on-resistance look-up table that reflects the corresponding relationship between the device temperature and the on-resistance value of the power switch; a temperature processing unit configured to collect the temperature signal output by the temperature detection circuit and perform analog-to-digital conversion, and obtain the current on-resistance value of the power switch according to the temperature-on-resistance look-up table; and a current processing unit configured to collect the current detection signal and perform analog-to-digital conversion, and calculate the current flowing through the power switch based on the current detection signal and the current on-resistance value obtained by the temperature processing unit.

7. The protection device according to claim 5, characterized in that, The temperature detection circuit includes: A Wheatstone bridge, including a first bridge arm and a second bridge arm coupled between a power supply voltage and ground, the first bridge arm including a sixth resistor and a seventh resistor connected in series, and the second bridge arm including an eighth resistor and a thermistor unit connected in series; and A second operational amplifier, coupled to the first bridge arm and the second bridge arm of the Wheatstone bridge and generating the temperature signal, wherein a connection point of the sixth resistor and the seventh resistor is coupled to the non-inverting input terminal of the second operational amplifier, and a connection point of the eighth resistor and the thermistor unit is coupled to the inverting input terminal of the second operational amplifier.

8. The protection device according to claim 5, wherein, Further comprising: A temperature protection circuit for comparing the temperature signal with a safety temperature threshold to form a temperature protection signal, and when the temperature signal is greater than the safety temperature threshold, the temperature protection signal turns off the power switch.

9. The protection device according to claim 8, characterized in that, The temperature protection circuit includes: A second comparator, with the inverting input terminal coupled to the temperature signal and the non-inverting input terminal coupled to the safety temperature threshold, and the second comparator outputs the temperature protection signal; and A second diode, with the negative terminal coupled to the temperature protection signal and the positive terminal coupled to the control terminal of the power switch.

10. An electrical device, characterized in that, Comprising: A PFC circuit, including a power switch; And The protection device according to any one of claims 1 to 9, the protection device is at least used to detect the voltage difference between the current input terminal and the current output terminal of the power switch, and output a current detection signal that is positively correlated with the current flowing through the power switch.

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