Wide-range output AC-DC converter based on PFC feedback regulation

Abstract

The utility model provides a wide-range output AC-DC converter based on PFC feedback regulation. The wide-range output AC-DC converter comprises a transformer circuit used for converting a first DC voltage into a second DC voltage and outputting the second DC voltage to an input end of a BUCK circuit; the PWM control circuit is used for sampling the first DC voltage and the output DC voltage to obtain an actual load voltage, adjusting the duty ratio and the gain value of the first PWM signal according to the actual load voltage, and adjusting the input end voltage of the feedback circuit according to the output gain; the feedback circuit is used for outputting a feedback voltage signal with a corresponding size to the PFC control circuit according to the input end voltage; and the PFC control circuit is connected with the input end of the transformer circuit and is used for adjusting the PFC voltage according to the feedback voltage signal so as to improve the power factor. According to the utility model, the load voltage is monitored, and the PWM signal duty ratio and the PFC voltage of the BUCK circuit are adjusted according to the current load voltage, so that the voltage conversion efficiency and the power factor are improved under the condition of lower output voltage.

Description

Technical Field

[0001] This utility model relates to the field of circuit design technology, specifically to a wide-range output AC-DC converter based on PFC feedback regulation. Background Technology

[0002] Currently, in many power supply applications, such as LED driver power supplies and communication power supplies, AC-DC converters with a wide range of output voltages are required to meet the usage requirements. Furthermore, PFC circuits must be added to the AC-DC conversion circuit to improve the power factor of the power supply. This allows the power supply to effectively manage reactive power while consuming active power, thereby reducing unnecessary losses on the power grid and improving the overall efficiency of the power system.

[0003] Existing wide-range AC-DC converters are used to provide constant output current, such as 15% to 100% programmable constant output current within a wide output voltage range of 10V to 55V. In this case, when the BUCK circuit is used for buck conversion in the AC-DC converter, the BUCK circuit can only control the input current when the AC input voltage is higher than the DC output voltage, and the PFC circuit within it has a fixed voltage output. At this time, the conversion circuit will encounter two contradictory problems:

[0004] (1) To ensure a high power factor, the output voltage of the conversion circuit should be as low as possible.

[0005] (2) If the output voltage is low, the duty cycle of the power supply PWM control signal will be very low when the input voltage is high, such as before and after the peak of the input power supply, resulting in a large power loss and causing the circuit's conversion efficiency to not reach the optimal state.

[0006] Regarding the above problem (2), if the input voltage of the conversion circuit cannot be reduced or changed under the condition of relatively equal power, then reducing the output voltage may mean reducing the working efficiency and will also increase the standby power consumption of the power supply device.

[0007] Therefore, it is necessary to design a wide-range output AC-DC converter that can monitor and adjust the PFC voltage, so as to ensure high conversion efficiency of the circuit even at low output voltage, thereby greatly reducing the standby power consumption of the power supply equipment. Utility Model Content

[0008] This utility model provides a wide-range output AC-DC converter based on PFC feedback regulation, which is mainly used to solve the problems in existing AC-DC converters, such as reduced working efficiency and increased standby power consumption of power supply equipment due to the fixed voltage output of the PFC circuit. It achieves the effect of monitoring and regulating the PFC voltage, ensuring high conversion efficiency of the circuit under low output voltage conditions, and reducing the standby power consumption of power supply equipment.

[0009] This utility model achieves the above objectives through the following technical solutions:

[0010] A wide-range output AC-DC converter based on PFC feedback regulation includes a first rectifier and filter circuit, a PWM control circuit, a power switch circuit, and a BUCK circuit. The first rectifier and filter circuit is connected to an AC power supply and is used to filter and rectify the AC power supply, and outputs a first DC voltage to the input terminal of the BUCK circuit through the power switch circuit. The PWM control circuit is used to control and output a first PWM signal with a variable duty cycle. The power switch circuit is used to switch the on / off state according to the duty cycle of the first PWM signal to control the output DC voltage of the BUCK circuit.

[0011] It also includes a transformer circuit, a feedback circuit, and a PFC control circuit. The transformer circuit converts the first DC voltage into a second DC voltage and outputs it to the input terminal of the BUCK circuit. The PWM control circuit samples the first DC voltage and the output DC voltage to obtain the actual load voltage, adjusts the duty cycle and gain value of the first PWM signal according to the actual load voltage, and adjusts the input terminal voltage of the feedback circuit according to the output gain. The feedback circuit outputs a feedback voltage signal of corresponding magnitude to the PFC control circuit according to the input terminal voltage. The PFC control circuit is connected to the input terminal of the transformer circuit and adjusts its PFC voltage according to the feedback voltage signal to improve the power factor.

[0012] A further solution includes a lightning protection circuit and an EMI filter circuit. The lightning protection circuit includes several varistors, which are used to dissipate the high-voltage energy introduced into the AC power supply from the power grid during a lightning strike, thereby protecting the circuit.

[0013] The EMI filter circuit is used to suppress electromagnetic interference in the AC power supply.

[0014] A further embodiment is that the transformer circuit includes a multi-winding transformer and a second rectifier and filter circuit. The multi-winding transformer is used to output different voltage levels by adjusting the turns ratio. The input terminal of the second rectifier circuit is connected to the output terminal of the multi-winding transformer to suppress interference and harmonics to obtain a stable second DC signal.

[0015] A further embodiment is that the PWM control circuit further includes a first sampling circuit, which is connected to the output winding of the transformer circuit. The first sampling circuit includes a first sampling resistor and a second sampling resistor that constitute a voltage divider circuit, and is used to sample the midpoint voltage of the voltage divider circuit as the first DC voltage.

[0016] A further embodiment is that the PWM control circuit further includes a second sampling circuit, which is connected to the output terminal of the BUCK circuit. The second sampling circuit includes a third sampling resistor and a fourth sampling resistor that constitute a voltage divider circuit, and is used to sample the midpoint voltage of the voltage divider circuit as the output DC voltage.

[0017] A further embodiment is that the PWM control circuit also includes a microprocessor and its peripheral circuits. The microprocessor is set with an initial gain value, and the gain value output by its gain control terminal is inversely proportional to the magnitude of the PFC voltage.

[0018] A further embodiment is that the microprocessor has a voltage sampling period, and in each voltage sampling period, the voltage is sampled by the sampling circuit. Its two analog signal input terminals respectively input the first DC voltage and output the DC voltage, and calculate the actual load voltage according to the voltage division relationship of the sampling resistor.

[0019] A further embodiment is that the microprocessor is provided with a storage module and a logic judgment module. The storage module is used to store the load voltage. The logic judgment module compares the current actual load voltage with the load voltage stored in the previous voltage sampling period, and calibrates the PFC voltage according to the comparison result.

[0020] A further embodiment is that the feedback circuit includes a voltage regulator chip and an optocoupler. The reference terminal of the voltage regulator chip is connected to the gain control terminal of the microprocessor, its cathode is grounded, and its anode is connected to the input terminal of the optocoupler, which is used to adjust the input current of the optocoupler according to the magnitude of the input voltage. The optocoupler is used to adjust the magnitude of the output current according to its current transfer ratio and feed it back to the PFC control circuit.

[0021] A further embodiment is that the PFC control circuit includes a PFC circuit, a first voltage divider circuit, a PFC control chip and its peripheral circuits. The feedback input terminal of the PFC control chip is connected to the output terminal of the optocoupler through the first voltage divider circuit, and is used to output a second PWM signal to adjust the power switching circuit of the PFC circuit, thereby adjusting the power factor of the circuit.

[0022] Therefore, the present invention has the following beneficial effects: by monitoring the load voltage and adjusting the duty cycle of the PWM signal and the PFC voltage of the BUCK circuit according to the current load voltage, the present invention can improve the voltage conversion efficiency and power factor under the condition of lower output voltage.

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a wide-range output AC-DC converter according to an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of the lightning protection circuit and EMI filter circuit of this utility model embodiment.

[0026] Figure 3 This is a schematic diagram of the transformer circuit and PFC control circuit of this utility model embodiment.

[0027] Figure 4 This is a schematic diagram of the sampling circuit for implementing this utility model.

[0028] Figure 5 This is a schematic diagram of the PWM control circuit and feedback circuit of an embodiment of this utility model.

[0029] Figure 6 This is an equivalent schematic diagram of the sampling circuit implemented in this utility model. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. All other embodiments obtained by those skilled in the art based on the described embodiments of this utility model without creative effort are within the scope of protection of this utility model.

[0031] An embodiment of a wide-range output AC-DC converter based on PFC feedback regulation

[0032] See Figure 1The present invention relates to a wide-range output AC-DC converter based on PFC feedback regulation, comprising a first rectifier and filter circuit 10, a PWM control circuit 60, a power switch circuit 20, and a BUCK circuit 50. The first rectifier and filter circuit 10 is connected to an AC power supply and is used to filter and rectify the AC power supply, and outputs a first DC voltage to the input terminal of the BUCK circuit 50 through the power switch circuit 20. The PWM control circuit 60 is used to control and output a first PWM signal with a variable duty cycle. The power switch circuit 20 is used to switch the on / off state according to the duty cycle of the first PWM signal to control the output DC voltage of the BUCK circuit 50.

[0033] It also includes a transformer circuit 30, a feedback circuit 70, and a PFC control circuit 80. The transformer circuit 30 is used to convert the first DC voltage into a second DC voltage and output it to the input terminal of the BUCK circuit 50. The PWM control circuit 60 is used to sample the first DC voltage and the output DC voltage to obtain the actual load voltage, and to adjust the duty cycle and gain value of the first PWM signal according to the actual load voltage, and to adjust the input terminal voltage of the feedback circuit 70 according to the output gain. The feedback circuit 70 is used to output a feedback voltage signal of a corresponding magnitude to the PFC control circuit 80 according to the input terminal voltage. The PFC control circuit 80 is connected to the input terminal of the transformer circuit 30 and is used to adjust its PFC voltage according to the feedback voltage signal to improve the power factor.

[0034] See Figure 2 In this embodiment, a lightning protection circuit 11 and an EMI filter circuit 12 are also included. The lightning protection circuit 11 includes several varistors, which are used to dissipate the high-voltage energy introduced into the AC power supply through the power grid during a lightning strike, thereby protecting the circuit.

[0035] The EMI filter circuit 12 is used to suppress electromagnetic interference in the AC power supply.

[0036] Specifically, the surge protection circuit 11 in this embodiment includes varistors MV1 to MV3, fuse F1, and resistor RT3. Varistors MV1 and MV2 are connected in parallel across the AC power supply, and MV1 is connected in parallel across the output of rectifier bridge D1. Fuse F1 and resistor RT3 are connected in series across the AC input. When the AC power supply voltage applied across the varistor exceeds its operating voltage, its resistance decreases, causing high-voltage energy to be consumed by the varistor. If the current is too large, fuse F1 burns out as a downstream circuit to protect the circuit.

[0037] Specifically, in this embodiment, resistor RT3 is used to prevent surges. When the power is turned on, C1 needs to be charged. Due to the large instantaneous current, a surge current is generated, and all the instantaneous energy is consumed by resistor RT3. After a certain period of time, the resistance of RT3 decreases as the temperature rises. At this time, the energy consumed is very small, allowing the subsequent circuit to work normally. Among them, resistor RT3 is a negative temperature coefficient element.

[0038] Specifically, the EMI filter circuit 12 in this embodiment includes capacitors C1, C5, C6 and inductor L1. The capacitors C1, C5, C6 and inductor L1 form a dual-type filter network, which is used to suppress the electromagnetic noise and noise signals of the AC power supply, and at the same time prevent the high-frequency noise generated by the power supply itself from interfering with the power grid.

[0039] Specifically, in this embodiment, the first rectifier and filter circuit 10 includes a rectifier bridge D1 and a resistor-capacitor filter circuit composed of C4 and R2. After the AC power supply is rectified by the rectifier bridge D1, it is filtered by C4 to obtain a relatively pure DC voltage; however, if the capacitance of C4 decreases, the output AC ripple will increase.

[0040] See Figure 3-4 In this embodiment, the transformer circuit 30 includes a multi-winding transformer and a second rectifier and filter circuit 40. The multi-winding transformer is used to output different levels of voltage by adjusting the turns ratio. The input terminal of the second rectifier circuit is connected to the output terminal of the multi-winding transformer to suppress interference and harmonics to obtain a stable second DC signal.

[0041] Specifically, in this embodiment, the second rectifier filter circuit 40 adopts a full-wave rectification method with two diodes connected in parallel, namely D4 in the figure.

[0042] In this embodiment, the PWM control circuit 60 further includes a first sampling circuit, which is connected to the output winding of the transformer circuit 30. The first sampling circuit includes a first sampling resistor R164 and a second sampling resistor R165 that constitute a voltage divider circuit, and is used to sample the midpoint voltage of the voltage divider circuit as the first DC voltage.

[0043] In this embodiment, the PWM control circuit 60 further includes a second sampling circuit, which is connected to the output terminal of the BUCK circuit 50. The second sampling circuit includes a third sampling resistor R6 and a fourth sampling resistor R18 that constitute a voltage divider circuit, and is used to sample the midpoint voltage of the voltage divider circuit as the output DC voltage.

[0044] See Figure 5 In this embodiment, the PWM control circuit 60 also includes a microprocessor IC14 and its peripheral circuits. The microprocessor IC14 is set with an initial gain value, and the gain value output by its gain control terminal is inversely proportional to the magnitude of the PFC voltage.

[0045] Specifically, in this embodiment, if the gain value output by the microprocessor IC14 is larger, the feedback voltage signal output by the feedback circuit 70 will pull the potential of the FB terminal of the PFC controller higher. At this time, the PFC controller will reduce the PFC voltage by adjusting the duty cycle of the second PWM signal. Conversely, if the potential of the FB terminal is pulled lower, the output duty cycle will be adjusted to increase the PFC voltage.

[0046] In this embodiment, the microprocessor IC14 has a voltage sampling period. During each voltage sampling period, the voltage is sampled by a sampling circuit. Its two analog signal input terminals respectively input the first DC voltage and output the DC voltage. The actual load voltage is calculated based on the voltage division relationship of the sampling resistors. (See [link to relevant documentation]). Figure 6 According to the equivalent schematic diagram of the sampling circuit, we can see that:

[0047] The first DC voltage is:

[0048]

[0049] Among them, V PFC The PFC voltage is mentioned above.

[0050] The formula for calculating the output DC voltage is:

[0051]

[0052] Among them, V LED The actual load voltage is denoted as .

[0053] As can be seen, the actual load voltage value can be obtained by using the above two calculation formulas and based on the values ​​of the first DC voltage PFAIL_HR and the output DC voltage VOUT_PFAIL obtained from the sampling.

[0054] In this embodiment, the microprocessor IC14 is provided with a storage module and a logic judgment module. The storage module is used to store the load voltage. The logic judgment module compares the current actual load voltage with the load voltage stored in the previous voltage sampling period, and calibrates the PFC voltage according to the comparison result.

[0055] Specifically, in this embodiment, the storage module uses Flash memory to store data, which is used to quickly read the load voltage saved before the last power outage.

[0056] Specifically, the judgment process of the logic judgment module described in this embodiment includes:

[0057] a1: Input AC power and read the load voltage V stored in Flash before the last power outage. LED1 And set the current PFC voltage to: V PFC =VLED1 +Δ.

[0058] b1: Recalculate the current actual load voltage V after one detection cycle. LED2 .

[0059] c1: If the current actual load voltage V LED2 Not equal to the previously saved load voltage value V LED1 If the output gain is equal to the value of the load, it is assumed that the user has changed the load, and the PFC voltage is recalibrated; if the output gain is equal to the value of the load, the current output gain and PFC voltage are maintained.

[0060] Specifically, the PFC voltage calibration process in this embodiment includes:

[0061] a2: Set the PFC voltage to the maximum value to ensure the load functions properly.

[0062] b2: Recalculate the current actual load voltage V LED2 .

[0063] c2: Reset the PFC voltage to: V PFC =V LED2 +Δ. It will also save the current actual load voltage V. LED2 To Flash.

[0064] e2: Repeat steps a1 to c1 to periodically power on and monitor whether the load has changed. If it has changed, execute steps a2 to c2.

[0065] In this embodiment, the feedback circuit 70 includes a voltage regulator chip IC25 and an optocoupler IC2. The reference terminal of the voltage regulator chip IC25 is connected to the gain control terminal of the microprocessor IC14, its cathode is grounded, and its anode is connected to the input terminal of the optocoupler IC2. It is used to adjust the input current of the optocoupler IC2 according to the magnitude of the input voltage. The optocoupler IC2 is used to adjust the magnitude of the output current according to its current transfer ratio and feed it back to the PFC control circuit 80.

[0066] Specifically, the feedback circuit 70 in this embodiment also includes a diode D8 and a resistor R32. The diode D8 and the resistor R32 are connected in parallel to the input terminal of the voltage regulator chip IC25. When the feedback circuit 70 receives a first PWM signal with a different duty cycle, the input voltage value will be changed through the resistor R32.

[0067] Specifically, the voltage regulator IC25 uses the TL431.

[0068] In this embodiment, the PFC control circuit 80 includes a PFC circuit, a first voltage divider circuit, a PFC control chip IC1 and its peripheral circuits. The feedback input terminal of the PFC control chip IC1 is connected to the output terminal of the optocoupler IC2 through the first voltage divider circuit, and is used to output a second PWM signal to adjust the power switching circuit 20 of the PFC circuit, thereby adjusting the power factor of the circuit.

[0069] The above embodiments are merely preferred embodiments of this utility model and should not be construed as limiting the scope of protection of this utility model. Any non-substantial changes and substitutions made by those skilled in the art based on this utility model shall fall within the scope of protection claimed by this utility model.

Claims

1. A wide-range output AC-DC converter based on PFC feedback regulation, comprising a first rectifier-filter circuit, a PWM control circuit, a power switch circuit, and a BUCK circuit; the first rectifier-filter circuit is connected to an AC power supply and is used to filter and rectify the AC power supply, and outputs a first DC voltage to the input terminal of the BUCK circuit through the power switch circuit; the PWM control circuit is used to control and output a first PWM signal with a variable duty cycle; the power switch circuit is used to switch the on / off state according to the duty cycle of the first PWM signal to control the output DC voltage of the BUCK circuit; characterized in that, Also includes: The system includes a transformer circuit, a feedback circuit, and a PFC control circuit. The transformer circuit converts the first DC voltage into a second DC voltage and outputs it to the input terminal of the BUCK circuit. The PWM control circuit samples the first DC voltage and the output DC voltage to obtain the actual load voltage, adjusts the duty cycle and gain of the first PWM signal according to the actual load voltage, and adjusts the input voltage of the feedback circuit according to the output gain. The feedback circuit outputs a feedback voltage signal of appropriate magnitude to the PFC control circuit based on the input voltage. The PFC control circuit is connected to the input terminal of the transformer circuit and adjusts its PFC voltage according to the feedback voltage signal to improve the power factor.

2. The wide-range output AC-DC converter based on PFC feedback regulation according to claim 1, characterized in that: It also includes a lightning protection circuit and an EMI filter circuit. The lightning protection circuit includes several varistors, which are used to dissipate the high-voltage energy introduced into the AC power supply through the power grid during a lightning strike, thereby protecting the circuit. The EMI filter circuit is used to suppress electromagnetic interference in the AC power supply.

3. The wide-range output AC-DC converter based on PFC feedback regulation according to claim 1, characterized in that: The transformer circuit includes a multi-winding transformer and a second rectifier and filter circuit. The multi-winding transformer is used to output different voltage levels by adjusting the turns ratio. The input terminal of the second rectifier and filter circuit is connected to the output terminal of the multi-winding transformer to suppress interference and harmonics to obtain a stable second DC voltage.

4. The wide-range output AC-DC converter based on PFC feedback regulation according to claim 1, characterized in that: The PWM control circuit further includes a first sampling circuit, which is connected to the output winding of the transformer circuit. The first sampling circuit includes a first sampling resistor and a second sampling resistor that constitute a voltage divider circuit, and is used to sample the midpoint voltage of the voltage divider circuit as the first DC voltage.

5. The wide-range output AC-DC converter based on PFC feedback regulation according to claim 4, characterized in that: The PWM control circuit further includes a second sampling circuit, which is connected to the output terminal of the BUCK circuit. The second sampling circuit includes a third sampling resistor and a fourth sampling resistor that constitute a voltage divider circuit, and is used to sample the midpoint voltage of the voltage divider circuit as the output DC voltage.

6. The wide-range output AC-DC converter based on PFC feedback regulation according to claim 5, characterized in that: The PWM control circuit also includes a microprocessor and its peripheral circuits. The microprocessor is set with an initial gain value, and the gain value output by its gain control terminal is inversely proportional to the magnitude of the PFC voltage.

7. The wide-range output AC-DC converter based on PFC feedback regulation according to claim 6, characterized in that: The microprocessor has a voltage sampling period. In each voltage sampling period, the voltage is sampled by the sampling circuit. Its two analog signal input terminals respectively input the first DC voltage and output the DC voltage, and calculate the actual load voltage according to the voltage division relationship of the sampling resistor.

8. The wide-range output AC-DC converter based on PFC feedback regulation according to claim 7, characterized in that: The microprocessor includes a storage module and a logic judgment module. The storage module is used to store the load voltage. The logic judgment module compares the current actual load voltage with the load voltage stored in the previous voltage sampling period and calibrates the PFC voltage based on the comparison result.

9. The wide-range output AC-DC converter based on PFC feedback regulation according to claim 6, characterized in that: The feedback circuit includes a voltage regulator chip and an optocoupler. The reference terminal of the voltage regulator chip is connected to the gain control terminal of the microprocessor, its cathode is grounded, and its anode is connected to the input terminal of the optocoupler. The voltage regulator chip is used to adjust the input current of the optocoupler according to the magnitude of the input voltage. The optocoupler is used to adjust the output current according to its current transfer ratio and feed it back to the PFC control circuit.

10. The wide-range output AC-DC converter based on PFC feedback regulation according to claim 9, characterized in that: The PFC control circuit includes a PFC circuit, a first voltage divider circuit, a PFC control chip and its peripheral circuits. The feedback input terminal of the PFC control chip is connected to the output terminal of the optocoupler through the first voltage divider circuit, and is used to output a second PWM signal to adjust the power switching circuit of the PFC circuit, thereby adjusting the power factor of the circuit.

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