A startup circuit for an AC-DC power supply

Abstract

The present invention discloses a startup circuit for an AC-DC power supply. The operational amplifier AMP1 is used for AC voltage sampling and amplification, isolates the impedance of the voltage division network at the input end from the impedance of the comparator circuit at the rear end, and amplifies the rectified voltage processed by the RC filter circuit to the peak value. The operational amplifier AMP2 is used for bus voltage sampling, and the upper voltage division resistor is connected to the PFC bus, isolating the impedance of the voltage division network at the input end from the impedance of the comparator circuit at the rear end. The comparator U1 is used to compare the input voltage with the input undervoltage protection point reference value Uvref as input undervoltage protection. The comparator U2 is used to compare the input voltage with the input overvoltage protection point reference value as input overvoltage protection. The comparator U3 is used to compare the input voltage with the bus voltage to determine whether the bus capacitor is effectively fully charged. This circuit eliminates the primary side single-chip microcomputer through the method of analog circuit inspection, simplifying the complex control method.

Description

Technical Field

[0001] The present invention relates to the technical field of power circuits, and particularly to a starting circuit for an ACDC power supply. Background Art

[0002] Primary power supplies (ACDC power supplies connected to the power grid) are very common in the industrial field in our country, such as communication power supplies, electric vehicle charging power supplies, etc. Since the power of such switching power supplies is relatively large (generally greater than 1000W), a power factor correction circuit is basically required to reduce the impact of the device on the power grid after it is connected to the power grid. Due to the presence of PFC, such power supplies have clear requirements for starting logic and starting timing. Currently, there are the following several ways to start an ACDC power supply:

[0003] Way 1: Place a single-chip microcomputer on both the primary side and the secondary side. The single-chip microcomputer on the primary side is responsible for sampling the AC voltage and the PFC bus voltage, controlling the PFC enable, controlling the soft-start relay, and communicating with the single-chip microcomputer on the secondary side at the same time; the single-chip microcomputer on the secondary side is mainly responsible for controlling the enable of the subsequent DCDC.

[0004] Way 2: Only the single-chip microcomputer on the secondary side exists. The single-chip microcomputer on the secondary side controls the PFC enable and the closing of the soft-start relay through an optocoupler, and is also responsible for enabling the subsequent DCDC, etc.

[0005] The main disadvantages of the above solutions are as follows: For Way 1, the circuit is complex and the cost is high; for Way 2, due to the lack of isolated sampling, a timing start method is generally adopted, and the soft-start resistor generally uses a PTC. When the repeated start intervals are relatively short, the resistance value of the PTC becomes larger, resulting in an increase in the pre-charge time. When the relay is closed regularly, since the pre-charge is not completed, the relay closes when the bus capacitor is not fully charged, so that the contacts stick together, thereby reducing the power supply reliability. Summary of the Invention

[0006] The purpose of the present invention is to provide a starting circuit for an ACDC power supply. This circuit eliminates the single-chip microcomputer on the primary side through an analog circuit inspection method, simplifies the complex control method, and reduces the system cost without sacrificing the product reliability.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A starting circuit for an ACDC power supply, the circuit includes two operational amplifiers AMP1 and AMP2; three comparators U1, U2, and U3, where:

[0009] One input terminal of the operational amplifier AMP1 is connected to a resistor R2, and the other input terminal is connected to an RC filter circuit composed of a resistor R1 and a capacitor C1. The other end of the resistor R1 is connected to voltage-dividing resistors RinH and RinL;

[0010] The output terminal of the operational amplifier AMP1 is connected to a comparator circuit composed of three comparators U1, U2, and U3;

[0011] The operational amplifier AMP1 is used for AC voltage sampling and amplification. Specifically, it isolates the impedance of the voltage division network at the input terminal from the impedance of the comparator circuit at the back end, and amplifies the rectified voltage processed by the RC filter circuit to the peak value to facilitate the subsequent parameter design;

[0012] The voltage division network composed of the voltage division resistors RinH and RinL attenuates the input high voltage Vin+ to a relatively low voltage value, which is convenient for the subsequent control circuit to use;

[0013] The RC filter circuit is used to convert the input bun-shaped voltage wave into a rectified voltage and input it to the operational amplifier AMP1;

[0014] One input terminal of the operational amplifier AMP2 is connected with a resistor R4 and a capacitor C2. The other end of the resistor R4 is connected to the voltage division resistors RbusH and RbusL. The voltage division network composed of the voltage division resistors RbusH and RbusL attenuates the bus high voltage to a relatively low voltage value, which is convenient for the control circuit to use;

[0015] The resistor R4 and the capacitor C2 form an RC filter circuit, which is used to filter out the bus ripple;

[0016] The output terminal of the operational amplifier AMP2 is connected to the input terminal of the comparator U3. A voltage division network composed of resistors R11 and R12 is also arranged between the operational amplifier AMP2 and the comparator U3. The purpose of this voltage division network is to facilitate the later debugging;

[0017] The operational amplifier AMP2 is used for bus voltage sampling. The upper voltage division resistor is connected to the bus. Specifically, it isolates the impedance of the voltage division network at the input terminal from the impedance of the comparator circuit at the back end;

[0018] The inverting input terminal of the comparator U1 is connected to the undervoltage reference UVref, and the non-inverting input terminal is connected to the output terminal of AMP1. The hysteresis is set through the resistors R5 and R6. The function of this comparator U1 is to compare the input voltage with the input undervoltage protection point reference value Uvref as the input undervoltage protection;

[0019] The non-inverting input terminal of the comparator U2 is connected to the overvoltage reference UVref, and the inverting input terminal is connected to the output terminal of AMP1. The hysteresis is set through the resistors R8 and R9. The function of this comparator U2 is to compare the input voltage with the input overvoltage protection point reference value as the input overvoltage protection;

[0020] The non-inverting input terminal of the comparator U3 is connected to Vbus+ which reflects the bus voltage value, and the inverting input terminal is connected to Vinsp which reflects the input voltage value, and is used to compare the input voltage Vin+ with the bus voltage Vbus+ to determine whether the bus capacitor is effectively charged;

[0021] Specifically, when the system is powered on, the optocoupler is in the conducting state. The three comparators U1, U2, and U3 are used to determine whether the input voltage is not overvoltage, not undervoltage, and whether the bus capacitor is effectively charged. If both conditions are met, the optocoupler is cut off; after the subsequent single-chip microcomputer obtains the cut-off signal, it executes operations according to the system power-on logic, that is, closing the relay - turning on the PFC - turning on the ACDC power supply.

[0022] It can be seen from the technical solution provided by the present invention described above that the above circuit eliminates the primary-side single-chip microcomputer through the analog circuit inspection method, simplifies the complex control method, and reduces the system cost without sacrificing the product reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 FIG. is a schematic diagram of the overall structure of the startup circuit of the ACDC power supply provided by the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments, which do not constitute a limitation to the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the protection scope of the present invention.

[0026] As Figure 1 shown is a schematic diagram of the overall structure of the startup circuit of the ACDC power supply provided by the embodiment of the present invention. The circuit mainly includes two operational amplifiers AMP1 and AMP2; three comparators U1, U2, and U3, where:

[0027] One input terminal of the operational amplifier AMP1 is connected to a resistor R2, and the other input terminal is connected to an RC filter circuit composed of a resistor R1 and a capacitor C1. The other end of the resistor R1 is connected to the voltage-dividing resistors RinH and RinL;

[0028] The output terminal of the operational amplifier AMP1 is connected to a comparator circuit composed of three comparators U1, U2, and U3;

[0029] The operational amplifier AMP1 is used for AC voltage sampling and amplification. Specifically, it isolates the impedance of the voltage division network at the input end from the impedance of the comparator circuit at the back end, and amplifies the rectified voltage (representing the average value of the input voltage here) processed by the RC filter circuit to the peak value, which is convenient for subsequent parameter design;

[0030] The voltage division network composed of the voltage division resistors RinH and RinL attenuates the input high voltage Vin+ to a relatively low voltage value, which is convenient for the subsequent control circuit to use;

[0031] The RC filter circuit is used to convert the input steamed bun-shaped voltage wave into a rectified voltage and input it to the operational amplifier AMP1;

[0032] One input terminal of the operational amplifier AMP2 is connected with a resistor R4 and a capacitor C2. The other end of the resistor R4 is connected to the voltage division resistors RbusH and RbusL. The voltage division network composed of the voltage division resistors RbusH and RbusL attenuates the bus high voltage to a relatively low voltage value, which is convenient for the control circuit to use;

[0033] The resistor R4 and the capacitor C2 form an RC filter circuit, which is used to filter out the bus ripple;

[0034] The output terminal of the operational amplifier AMP2 is connected to the input terminal of the comparator U3. A voltage division network composed of resistors R11 and R12 is also provided between the operational amplifier AMP2 and the comparator U3. The purpose of this voltage division network is to facilitate later debugging;

[0035] The operational amplifier AMP2 is used for bus voltage sampling. The upper voltage division resistor is connected to the bus. Specifically, it isolates the impedance of the voltage division network at the input end from the impedance of the comparator circuit at the back end;

[0036] The inverting input terminal of the comparator U1 is connected to the undervoltage reference UVref, and the non-inverting input terminal is connected to the output terminal of AMP1. The hysteresis value is set through the resistors R5 and R6. The function of this comparator U1 is to compare the input voltage with the input undervoltage protection point reference value Uvref as the input undervoltage protection;

[0037] The non-inverting input terminal of the comparator U2 is connected to the overvoltage reference UVref, and the inverting input terminal is connected to the output terminal of AMP1. The hysteresis value is set through the resistors R8 and R9. The function of this comparator U2 is to compare the input voltage with the input overvoltage protection point reference value as the input overvoltage protection;

[0038] The non-inverting input terminal of comparator U3 is connected to Vbus+ which reflects the bus voltage value, and the inverting input terminal is connected to Vinsp which reflects the input voltage value, and is used to compare the input voltage Vin+ with the bus voltage Vbus+ to determine whether the bus capacitor is effectively charged; in a specific implementation, the bus capacitor is placed between Vbus+ and the system ground in the system, and its main functions are energy storage and filtering.( Figure 1 (not shown in the figure); through comparator U3, the magnitude relationship between Vbus+ and Vinsp can be judged, and then it can be judged whether the bus capacitor voltage has risen to a level close to the peak value of the input voltage. Since the DC voltage after the system rectifies through the bridge rectification method is close to the peak value of the input voltage, it is necessary to cooperate with resistors R11 and R12 to realize the comparison function of comparator U3, that is, the bus capacitor voltage mentioned above is approximately raised to the level of the peak value of the input voltage.

[0039] Specifically, when the system is powered on, the optocoupler is in the conducting state, and three comparators U1, U2, and U3 are used to judge whether the input voltage is not overvoltage, not undervoltage, and whether the bus capacitor is effectively charged. If both conditions are met, the optocoupler will turn off; after the subsequent single-chip microcomputer receives the cut-off signal, it will execute operations according to the system power-on logic, that is, close the relay - turn on the PFC - turn on the ACDC power supply.

[0040] In a specific implementation, set the voltage division attenuation coefficient of the voltage division resistor in the circuit to K, and set the resistance value of resistor RinH to RinH, the resistance value of resistor RinL to RinL, the resistance value of resistor RbusH to RbusH, and the resistance value of resistor RbusL to RbusL, then there is the following relationship:

[0041]

[0042] In addition, set the output voltage of operational amplifier AMP1 to the peak value of the input AC voltage, then there is the relational expression:

[0043]

[0044] Among them, resistors R2 and R3 and operational amplifier AMP1 form a non-inverting proportional amplifier, and this formula means that the average value of the input voltage is amplified by the amplifier and becomes the peak value of the input voltage.

[0045] In addition, as Figure 1 shown, it is also possible to set the input over- and under-voltage protection points and the corresponding hysteresis. Specifically, the specific parameters of resistors R5, R6, R7, R8, and R9 can be set according to needs. This setting belongs to the standard hysteresis comparator circuit, and the specific design method will not be repeated.

[0046] As Figure 1As shown, in the process of using the comparator U3 to determine whether the bus capacitor is effectively filled, the ratio of the resistors R11 and R12 can be adjusted as a determination condition for whether the bus capacitor is effectively filled. Specifically:

[0047] When the voltage of the bus capacitor is 0.95 times the input peak voltage, it is judged that the bus capacitor is effectively fully charged, and the following relationship exists:

[0048]

[0049] The resistance of the resistor R13 is much greater than that of R11 and R12, so it can be ignored.

[0050] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to professional and technical personnel in the field.

[0051] In summary, the circuit described in the embodiment of the present invention has a simple structure, low cost, and can effectively save space; at the same time, it does not require front-end and back-end communication and saves the work of writing a single-chip microcomputer code, thereby improving development efficiency. Compared with the traditional solution of a timed start-up of a back-end single-chip microcomputer, the system reliability is improved.

[0052] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A startup circuit for an AC-DC power supply, characterized in that, The circuit includes two operational amplifiers AMP1 and AMP2; three comparators U1, U2, and U3, where: One input terminal of operational amplifier AMP1 is connected to resistor R2, and the other input terminal is connected to an RC filter circuit composed of resistor R1 and capacitor C1. The other end of resistor R1 is connected to voltage-dividing resistors RinH and RinL; The output terminal of operational amplifier AMP1 is connected to a comparator circuit composed of three comparators U1, U2, and U3; The operational amplifier AMP1 is used for AC voltage sampling and amplification. Specifically, it isolates the impedance of the voltage-dividing network at the input terminal from the impedance of the comparator circuit at the back end, and amplifies the rectified voltage processed by the RC filter circuit to the peak value to facilitate the subsequent parameter design; The voltage-dividing network composed of voltage-dividing resistors RinH and RinL attenuates the input high voltage Vin+ to a relatively low voltage value to facilitate the use of the subsequent control circuit; The RC filter circuit is used to convert the input bun-shaped voltage wave into a rectified voltage and input it to operational amplifier AMP1; One input terminal of operational amplifier AMP2 is connected to resistor R4 and capacitor C2. The other end of resistor R4 is connected to voltage-dividing resistors RbusH and RbusL. The voltage-dividing network composed of voltage-dividing resistors RbusH and RbusL attenuates the bus high voltage to a relatively low voltage value to facilitate the use of the control circuit; Resistor R4 and capacitor C2 form an RC filter circuit for filtering out the bus ripple; The output terminal of operational amplifier AMP2 is connected to the input terminal of comparator U3. A voltage-dividing network composed of resistors R11 and R12 is also provided between operational amplifier AMP2 and comparator U3. The purpose of this voltage-dividing network is to facilitate the subsequent debugging; The operational amplifier AMP2 is used for bus voltage sampling. The upper voltage-dividing resistor is connected to the bus. Specifically, it isolates the impedance of the voltage-dividing network at the input terminal from the impedance of the comparator circuit at the back end; The inverting input terminal of comparator U1 is connected to the undervoltage reference UVref, and the non-inverting input terminal is connected to the output terminal of AMP1. The hysteresis value is set through resistors R5 and R6. The function of this comparator U1 is to compare the input voltage with the input undervoltage protection point reference value Uvref as the input undervoltage protection; The non-inverting input terminal of comparator U2 is connected to the overvoltage reference UVref, and the inverting input terminal is connected to the output terminal of AMP1. The hysteresis value is set through resistors R8 and R9. The function of this comparator U2 is to compare the input voltage with the input overvoltage protection point reference value as the input overvoltage protection; The non-inverting input terminal of comparator U3 is connected to Vbus+ reflecting the bus voltage value, and the inverting input terminal is connected to Vinsp reflecting the input voltage value. It is used to compare the input voltage Vin+ with the bus voltage Vbus+ to determine whether the bus capacitor is effectively charged; Specifically, when the system is powered on, the optocoupler is in the conducting state. Three comparators U1, U2, and U3 are used to determine whether the input voltage is not overvoltage, not undervoltage, and whether the bus capacitor is effectively charged. If all conditions are met simultaneously, the optocoupler is turned off. After the subsequent microcontroller receives the cut-off signal, it performs operations according to the system power-on logic, that is, closing the relay - turning on the PFC - turning on the ACDC power supply.

2. The startup circuit of the AC-DC power supply according to claim 1, wherein Set the voltage division attenuation coefficient of the voltage division resistor in the circuit to K, and set the resistance value of resistor RinH to RinH, the resistance value of resistor RinL to RinL, the resistance value of resistor RbusH to RbusH, and the resistance value of resistor RbusL to RbusL. Then, the following relationship exists:

3. The starting circuit of the AC-DC power supply according to claim 1, characterized in that, Set the output voltage of operational amplifier AMP1 to the peak value of the input AC voltage. Then, there is the relational expression: Among them, resistors R2 and R3 and operational amplifier AMP1 form a non-inverting proportional amplifier. This relational expression means that the average value of the input voltage is amplified by the amplifier and then becomes the peak value of the input voltage.

4. The starting circuit of the AC-DC power supply according to claim 1, characterized in that, In the process of using comparator U3 to determine whether the bus capacitor is effectively charged, the ratio of resistors R11 and R12 is adjusted as the determination condition for whether the bus capacitor is effectively charged. Specifically: When the voltage of the bus capacitor is 0.95 times the input peak voltage, it is determined that the bus capacitor is effectively charged. Then, the following relational expression exists:

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