CN114123741A - Harmonic suppression circuit of flyback power supply - Google Patents
Harmonic suppression circuit of flyback power supply Download PDFInfo
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- CN114123741A CN114123741A CN202111338151.4A CN202111338151A CN114123741A CN 114123741 A CN114123741 A CN 114123741A CN 202111338151 A CN202111338151 A CN 202111338151A CN 114123741 A CN114123741 A CN 114123741A
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- 230000001629 suppression Effects 0.000 title claims abstract description 39
- 239000003990 capacitor Substances 0.000 claims description 47
- 230000035699 permeability Effects 0.000 description 7
- 238000012360 testing method Methods 0.000 description 5
- 238000010586 diagram Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000001914 filtration Methods 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 2
- 230000002159 abnormal effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- QELJHCBNGDEXLD-UHFFFAOYSA-N nickel zinc Chemical compound [Ni].[Zn] QELJHCBNGDEXLD-UHFFFAOYSA-N 0.000 description 1
- 230000010349 pulsation Effects 0.000 description 1
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
- H02M1/126—Arrangements for reducing harmonics from ac input or output using passive filters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
- H02M1/4208—Arrangements for improving power factor of AC input
- H02M1/4266—Arrangements for improving power factor of AC input using passive elements
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Rectifiers (AREA)
- Dc-Dc Converters (AREA)
Abstract
The invention discloses a harmonic suppression circuit of a flyback power supply, which aims to solve the technical problem of being suitable for a small-sized switching power supply and reducing the cost. The invention adopts the following technical scheme: a harmonic suppression circuit of a flyback power supply is provided with a rectifier bridge, the harmonic suppression circuit of the flyback power supply is used for a flyback switching power supply below 200W, the harmonic suppression circuit is formed by combining a thermistor, a primary LC filter and a pi-type filter, and the thermistor, the primary LC filter, the rectifier bridge and the pi-type filter are sequentially connected. Compared with the prior art, the invention adopts the combination of the thermistor, the first-stage LC filter and the pi-type filter to inhibit harmonic waves, has the advantages of simple circuit and low cost, has small volume of the switching power supply, and meets the requirements of the switching power supply on the development towards miniaturization and high power density.
Description
Technical Field
The invention relates to a switching power supply, in particular to a flyback switching power supply.
Technical Field
According to the requirement of standard IEC61000-3-2, the harmonic wave test is required when the input power is more than 75W, and the harmonic wave generation is that the switching power supply adopts bridge rectification and large-capacitance filter capacitorThe input current becomes a spike due to the conduction characteristic of the rectifier diode, and a higher harmonic component is generated. Therefore, a harmonic suppression device or a harmonic suppression circuit is provided for a switching power supply having an input power of 75W or more. Hazards of harmonics include: the input current is distorted, the power factor is reduced, and the power grid is polluted. The harmonic suppression devices or harmonic suppression circuits in the prior art have two main ways to suppress harmonics: active PFC and passive PFC. As shown in fig. 1, the active PFC is connected with a large capacitor behind a bridge rectifier circuit, the active PFC circuit boosts voltage by using direct current, and after the rectifier bridge, the boost circuit is composed of an inductor, a control switch tube, a diode and an electrolytic capacitor, converts sine wave voltage into constant direct current voltage, detects input grid current waveform through a boost control integrated circuit IC connected to the boost circuit, controls the on-time of the switch tube, detects input voltage waveform, and adjusts boost current by an adjustment control IC, so that the current and voltage waveforms are kept consistent, and the voltage is kept consistent with the input voltage Vac. The active PFC circuit has a complex structure, so that the cost is high, a control IC is required to be connected, and electromagnetic interference is brought to the booster circuit. The passive PFC includes an inductance compensation PFC and a valley fill PFC. As shown in fig. 2, an industrial frequency inductor L1 is connected in series between the inductor compensation PFC and the filter capacitor C1 after the bridge rectifier circuit, and the industrial frequency inductor L1 can cancel part of the capacitive reactance of the filter capacitor C1, so that the ac input voltage V is obtainedACThe phase difference with the current waveform is reduced, and the purpose of increasing the power factor is achieved. The power frequency inductor L1 required in the inductance compensation type PFC circuit is large in size, low in efficiency and incapable of meeting the miniaturization requirement of a switching power supply. As shown in fig. 3, the valley-filled PFC uses a valley-filling circuit connected after the bridge rectifier to greatly increase the conduction angle of the bridge rectifier, and fills the valley region in the peak pulse current waveform to change the input current from the peak pulse to a waveform close to a sine wave, thereby improving the power factor and significantly reducing the total harmonic distortion. The valley-fill PFC outputs a direct-current voltage V because charging is carried out by connecting C1 and C2 in series, and discharging is carried out by connecting C1 and C2 in parallelOOnly half of bridge rectified voltage is supplied to the main circuitThe peak ratio of the direct current voltage of the switching tube in the flyback circuit (the ratio of the peak value of the direct current voltage to the effective value) is large, and the peak ratio of the output current is also large, so that the flyback switching power supply is not suitable for being used as a buck switching power supply, because the valley value of the output voltage of the valley filling circuit filtering circuit between the rectified flyback circuit and the rear-end flyback circuit is only half of the valley value of the C1 and C2 electrolytic filtering circuit in the valley filling circuit.
Disclosure of Invention
The invention aims to provide a harmonic suppression circuit of a flyback power supply, and aims to solve the technical problem of being suitable for a small-sized switching power supply and reducing the cost.
The invention adopts the following technical scheme: a harmonic suppression circuit of a flyback power supply is provided with a rectifier bridge, the harmonic suppression circuit of the flyback power supply is used for a flyback switching power supply below 200W, the harmonic suppression circuit is formed by combining a thermistor, a primary LC filter and a pi-type filter, and the thermistor, the primary LC filter, the rectifier bridge and the pi-type filter are sequentially connected.
The primary LC filter of the invention is formed by connecting a capacitor and a common mode inductor.
The pi-type filter is formed by connecting a first electrolytic capacitor, a second electrolytic capacitor and a differential mode inductor.
According to the 80W flyback power supply, 1-5 ohms of a thermistor, 0.02-0.47 uF of a capacitor, 20-35 mH of a common-mode inductor, 1000V and 3A diodes are adopted in a rectifier bridge to form the rectifier bridge, 400V and 27uF are adopted in a first electrolytic capacitor and a second electrolytic capacitor, and 10-20 mH of a differential-mode inductor are adopted.
The harmonic suppression circuit of the flyback power supply is used for the flyback switching power supply of 80-200W.
The harmonic suppression circuit of the flyback power supply is used for an 80W flyback switching power supply.
The capacitor (CX1) is connected with a discharge resistor, the discharge resistor is connected with two ends of the capacitor in parallel after a first resistor and a third resistor are connected in series and a second resistor and a fourth resistor are connected in series, and the other ends of the first resistor, the second resistor, the third resistor and the fourth resistor are connected.
Compared with the prior art, the invention adopts the combination of the thermistor, the first-stage LC filter and the pi-type filter to inhibit harmonic waves, has the advantages of simple circuit and low cost, has small volume of the switching power supply, and meets the requirements of the switching power supply on the development towards miniaturization and high power density.
Drawings
Fig. 1 is a circuit schematic diagram of an active PFC of the prior art.
Fig. 2 is a circuit schematic of a prior art inductance compensated PFC.
Fig. 3 is a circuit schematic of a prior art valley-filled PFC.
Fig. 4 is a circuit schematic of the present invention.
Fig. 5 is a diagram of current and voltage phase after common mode inductance permeability is suppressed from harmonics according to an embodiment of the present invention.
FIG. 6 is a graph of thermistor resistance versus harmonic suppression results for an embodiment of the present invention.
FIG. 7 is a schematic circuit diagram of the flyback switching power supply of 80-200W in accordance with the present invention.
Fig. 7-1 is an enlarged view of portion 1 of fig. 7.
Fig. 7-2 is an enlarged view of portion 2 of fig. 7.
Fig. 7-3 is an enlarged view of portion 3 of fig. 7.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. As shown in fig. 4, the harmonic suppression circuit of the flyback power supply of the present invention is connected with a fuse F1, a thermistor RT1, a primary LC filter, a rectifier bridge, and a pi filter in sequence from an ac input terminal to an output terminal.
The F1 fuse is used to protect against abnormal conditions occurring inside the switching power supply.
The thermistor RT1 is used to suppress the startup surge of the switching power supply from the ac input terminal, and on the other hand, because the thermistor increases the impedance of the switching power supply input terminal, it can better suppress the conversion of ac into dc, which is the higher harmonic generated by the diode conduction characteristic. The larger the resistance of the thermistor is, the better the effect of reducing harmonic components is.
The primary LC filter is formed by connecting a capacitor CX1 and a common mode inductor LF1 and is used for inhibiting electromagnetic compatibility EMC differential mode and common mode interference brought by harmonic waves generated by the conduction characteristic of a diode and electromagnetic interference generated by the high-frequency switching characteristic of a flyback power supply when alternating current is converted into direct current. The leakage inductance of the common mode inductor LF1 is equivalent to a differential mode inductor, and in the process of transmitting the harmonic from the power supply to the grid side, the capacitor CX1 is on the grid side, and is equivalent to the leakage inductance of the capacitor CX1 and the common mode inductor LF1, so as to form an LC filter, that is, the capacitor CX1 and the inductor LF1 form a filter, which is helpful for filtering the harmonic and reducing the harmonic component.
The first resistor R1 is connected in series with the third resistor R3, the second resistor R2 is connected in series with the fourth resistor R4, and then the first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 are connected in parallel at two ends of the capacitor CX1, and the other ends of the first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 are connected to form a discharge resistor of the capacitor CX 1. In operation, the capacitor CX1 has a charging process, and when the power supply is disconnected, the residual voltage of the current plug must be reduced to the safe voltage of the human body within a specified time according to the safety standard, so a discharge resistor is connected in parallel at two ends of the capacitor CX 1.
The rectifier bridge is composed of a first diode D1, a second diode D2, a third diode D3 and a fourth diode D4 and is used for converting alternating-current voltage into direct-current voltage, and the rectifier bridge and electrolytic capacitors of the pi-type filter are reasons for generating high-order harmonics.
The pi-type filter is formed by connecting a first electrolytic capacitor EC1, a second electrolytic capacitor EC2 and a differential mode inductor L2, wherein the differential mode inductor L2 is used for suppressing electromagnetic interference (EMI) of a high-frequency flyback power supply, and the inductance and the material of the differential mode inductor L2 are reasonably selected, so that the pi-type filter has a good suppression effect on suppressing harmonic waves generated by the conduction characteristic of diodes when alternating current is converted into direct current, and the harmonic wave components can be reduced.
The working process of the harmonic suppression circuit of the flyback power supply combining the thermistor RT1, the primary LC filter and the pi-type filter is as follows: the input alternating current passes through the thermistor RT1, the high impedance of the thermistor RT1 reduces the surge current of the alternating current AC input end, and simultaneously inhibits the harmonic component of the AC input end. And an LC filter consisting of the capacitor CX1 and the common-mode inductor LF1 is used for further suppressing higher harmonic components generated by alternating current. After rectification by the rectifying bridge, the first electrolytic capacitor EC1, the second electrolytic capacitor EC2 and the differential mode inductor L2 form a pi-type filter, unnecessary harmonic waves generated by the conduction characteristics of the diode are removed, the pulsation of current is reduced, and the output current is smoother.
The working principle of the harmonic suppression circuit of the flyback power supply comprises the following steps: 100-240V alternating current is input, passes through a fuse F1 and then passes through a thermistor RT1, and because the thermistor increases the impedance of the input end of the switching power supply, higher harmonics of 100-240V alternating current 50 or 60hz from the input end can be well suppressed. The harmonic-suppressed current passes through a first-stage LC filter formed of a capacitor CX1 and a common-mode inductor L3, and the harmonic is further filtered. The direct current rectified by the rectifier bridge passes through a pi-type filter to filter harmonic waves generated by the conduction characteristic of the diode. So that the harmonic waves of the input 100-240V alternating current are effectively suppressed.
In the embodiment, for an 80W flyback power supply, 1-5 ohms of the thermistor RT1, 0.02-0.47 uF of the capacitor CX1, 20-35 mH of the common-mode inductor LF1, 1000V and 3A of diodes of the rectifier bridge form the rectifier bridge, 400V and 27uF of the first electrolytic capacitor EC1 and the second electrolytic capacitor EC2 are used, and 10-20 mH of the differential-mode inductor L2 are used.
The common mode inductor LF1 is made of nickel-zinc material with low initial permeability, the inductance is adjusted to be 100-3 mH, and 1-0 to 30 harmonics can be well suppressed.
As shown in fig. 5, the LF1 has different magnetic permeability and obviously changes the harmonic suppression, and in this embodiment, under the condition of full-load ac 220V input, through tests, the initial magnetic permeability is 200 to 2000ui, and has a good suppression effect on the odd harmonic of the input ac of 100 to 240V. The input voltage is positive sine wave alternating current, the input current is pulse, the voltage waveform and the current waveform keep the same phase, and the representative power factor is good.
Taking an 80W flyback power supply as an example, the magnetic permeability of LF1 is 300ui, the resistance value of a thermistor RT1 is 2 ohms, EC1 EC2, EC3 is 400V27uF, CX1 is 0.1uF, the resistance value of RT1, the inductance value of L2 and the capacitance of CX1 are adjusted, under the condition that the efficiency is not influenced, the resistance value and the inductance value of RT1 are properly increased, the harmonic component can be further reduced, and the power can be expanded to be within 200W.
As shown in fig. 6, the resistance of the thermistor NTC has a significant effect on the harmonic suppression result, and when the 120W flyback power supply is used as an example and tested under the working conditions of input ac 220V and output dc 20V, 6A, the larger the resistance of the thermistor is, the significant effect on the odd harmonic suppression is achieved, the harmonic frequency is from 2 to 40, and the harmonic current is reduced from 3.5A to 0.0. The test results are shown in Table 1.
TABLE 1LF1 inductance 300uH, initial permeability 600ui, thermistor resistance 2 ohm, harmonic suppression results
It can be seen that the larger the thermistor resistance, the lower the harmonic current.
According to the requirements of IEC61000-3-2 standard, there are corresponding limits for harmonic currents for different orders of harmonics.
TABLE 2 thermistor resistance vs. odd harmonic suppression
| NTC resistance ohm | 13Harms(avg) | 15Harms(avg) | 17Harms(avg) |
| 1 | 0.186 | 0.131 | 0.093 |
| 2 | 0.133 | 0.122 | 0.071 |
| 3 | 0.103 | 0.093 | 0.023 |
The combination of the thermistor, the first-stage LC filter and the pi-type filter of the harmonic suppression circuit of the flyback power supply is adopted to suppress harmonic waves, the inductance value of LF1 is 300uH, the initial permeability is 600ui, and the resistance value of the thermistor is 2 ohms. Therefore, the current and voltage analog signals obtained by measurement are converted into digital signals, Fourier decomposition is carried out, and the size, distortion rate and phase data of each order of harmonic can be obtained, and the harmonic analyzer is used for testing, so that the requirements of IEC61000-3-2 are met.
The harmonic suppression circuit of the flyback power supply does not need an active PFC control circuit, does not have energy loss of the PFC circuit, and has higher efficiency of the switching power supply. As shown in fig. 7, 7-1, 7-2 and 7-3, for an 80-120W flyback switching power supply, a thermistor RT1 is located between a fuse and a port of a capacitor CX1, one end of the thermistor is connected with a fuse F1, the other end of the thermistor is connected with a capacitor CX1, the capacitor CX1 is bridged between the thermistor RT1 and a zero line N of an input power line, an input port of a common mode inductor LF1 is connected with the thermistor RT1 and the capacitor CX1, an output port of the common mode inductor is connected with an input end of a rectifier bridge, an anode and a cathode of an output end of the rectifier bridge are respectively connected with an anode and a cathode of a first electrolytic capacitor EC1, an anode of the first electrolytic capacitor EC1 is connected with one end of a differential mode inductor L2, an anode of a second electrolytic capacitor EC2 is connected with the other end of the differential mode inductor L2, and cathodes of the first electrolytic capacitor EC1 and the second electrolytic capacitor EC2 are connected together. Taking an 80W flyback switching power supply as an example, the input is AC 115V and AC 23V respectively, and the average efficiency of the combination of the active PFC and the combination of the thermistor, the primary LC filter and the pi-type filter is tested. The average efficiency is the ratio of output power to input power at 100%, 75%, 50%, 25% load, and the values of 100%, 75%, 50%, 25% efficiency are added and divided by 4, and the test results are shown in table 3.
Average efficiency of table 380W flyback switching power supply
| Average efficiency | Switching power supply with active PFC | Switch power supply using the invention |
| 115V | 90.1％ | 90.78％ |
| 23V | 90.57％ | 91.26％ |
By comparison of table 3, it can be seen that the average efficiency of the present invention can be improved by 0.6%.
Compared with an active PFC and a passive PFC, the invention has the advantages of simple circuit, low cost, no need of an additional PFC control circuit, avoidance of a large inductance mode, small size of the switching power supply and capability of meeting the requirements of the switching power supply on the development towards miniaturization and high power density.
The invention is suitable for flyback switching power supplies below 200W.
Claims (7)
1. The utility model provides a harmonic suppression circuit of flyback power supply, is equipped with rectifier bridge, its characterized in that: the harmonic suppression circuit of the flyback power supply is used for a flyback switching power supply below 200W, and is formed by combining a thermistor (RT1), a primary LC filter and a pi-type filter, wherein the thermistor (RT1), the primary LC filter, a rectifier bridge and the pi-type filter are sequentially connected.
2. The harmonic suppression circuit of the flyback power supply of claim 1, wherein: the primary LC filter is formed by connecting a capacitor (CX1) and a common-mode inductor (LF 1).
3. The harmonic suppression circuit of the flyback power supply of claim 2, wherein: the pi-type filter is formed by connecting a first electrolytic capacitor (EC1), a second electrolytic capacitor (EC2) and a differential mode inductor (L2).
4. The harmonic suppression circuit of the flyback power supply of claim 3, wherein: the flyback power supply comprises an 80W flyback power supply, wherein a thermistor (RT1) adopts 1-5 ohms, a capacitor (CX1) adopts 0.02-0.47 uF, a common mode inductor (LF1) adopts 20 uH-35 mH, a rectifier bridge adopts 1000V and 3A diodes to form a rectifier bridge, a first electrolytic capacitor (EC1) and a second electrolytic capacitor (EC2) adopt 400V and 27uF, and a differential mode inductor (L2) adopts 10 uH-20 mH.
5. The harmonic suppression circuit of the flyback power supply of claim 4, wherein: the harmonic suppression circuit of the flyback power supply is used for the flyback switching power supply of 80-200W.
6. The harmonic suppression circuit of the flyback power supply of claim 5, wherein: the harmonic suppression circuit of the flyback power supply is used for an 80W flyback switching power supply.
7. The harmonic suppression circuit of the flyback power supply of claim 6, wherein: the capacitor (CX1) is connected with a discharge resistor, the discharge resistor is connected with the two ends of the capacitor (CX1) in parallel after being connected with the first resistor (R1) and the third resistor (R3) in series and the second resistor (R2) and the fourth resistor (R4) in series, and the other ends of the first resistor (R1), the second resistor (R2), the third resistor (R3) and the fourth resistor (R4) are connected.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202111338151.4A CN114123741A (en) | 2021-11-12 | 2021-11-12 | Harmonic suppression circuit of flyback power supply |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202111338151.4A CN114123741A (en) | 2021-11-12 | 2021-11-12 | Harmonic suppression circuit of flyback power supply |
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20130141004A1 (en) * | 2011-12-01 | 2013-06-06 | RAB Lighting Inc. | Led driver protection circuit |
| CN104283411A (en) * | 2014-09-26 | 2015-01-14 | 广东美的制冷设备有限公司 | AC/DC converter circuit and power supply system of household appliance |
| CN213243810U (en) * | 2020-10-26 | 2021-05-18 | 中山市宝利金电子有限公司 | Efficient harmonic filtering circuit |
| CN112888109A (en) * | 2021-03-24 | 2021-06-01 | 东莞市皇品光电科技有限公司 | LED driving switch power supply circuit with high PF and low THD |
| CN213547366U (en) * | 2020-11-03 | 2021-06-25 | 厦门市科力电子有限公司 | Circuit for effectively inhibiting EMI (electro-magnetic interference) of switching power supply |
-
2021
- 2021-11-12 CN CN202111338151.4A patent/CN114123741A/en active Pending
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20130141004A1 (en) * | 2011-12-01 | 2013-06-06 | RAB Lighting Inc. | Led driver protection circuit |
| CN104283411A (en) * | 2014-09-26 | 2015-01-14 | 广东美的制冷设备有限公司 | AC/DC converter circuit and power supply system of household appliance |
| CN213243810U (en) * | 2020-10-26 | 2021-05-18 | 中山市宝利金电子有限公司 | Efficient harmonic filtering circuit |
| CN213547366U (en) * | 2020-11-03 | 2021-06-25 | 厦门市科力电子有限公司 | Circuit for effectively inhibiting EMI (electro-magnetic interference) of switching power supply |
| CN112888109A (en) * | 2021-03-24 | 2021-06-01 | 东莞市皇品光电科技有限公司 | LED driving switch power supply circuit with high PF and low THD |
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Application publication date: 20220301 |