CN110829809A - Harmonic suppression device for switching power supply - Google Patents

Abstract

The invention provides a switching power supply harmonic suppression device, comprising: a rectifier bridge, a filter and a high-frequency transformer, the output end of the rectifier bridge is connected to the input end of the filter, and the output end of the filter is connected to the input end of the high frequency transformer, so the The output end of the high-frequency transformer is connected to the inverter of the switching power supply; the filter includes a first capacitor, a second capacitor, a third capacitor, a fourth capacitor and an inductor; the first capacitor is connected in parallel with the input end of the inductor; the The second capacitor is connected in parallel with the output end of the inductor; the series branch of the third capacitor and the fourth capacitor is connected in parallel with the second capacitor; a ground wire is arranged between the third capacitor and the fourth capacitor; The second capacitor is a differential mode interference filtering capacitor; the third capacitor and the third and fourth capacitors are common mode interference filtering capacitors. The invention utilizes the characteristics of the flyback conversion circuit to design a multi-terminal flyback switching power supply, which can provide two output voltages, and maximizes the efficiency of the power supply in order to make the output voltage more stable.

Description

A switching power supply harmonic suppression device

technical field

The invention belongs to the technical field of switching power supplies, and in particular relates to a device for suppressing harmonics of switching power supplies.

Background technique

Currently in the period of high-tech development, switching power supplies have been widely used and have a very important position in daily life. At present, with the continuous development of power supply technology, switching power supply has begun to develop towards integration and high efficiency, and the requirements for high performance and high power factor power supply technology have gradually increased. Although the design of switching power supply is more complicated, and some indicators may not be as good as linear regulators, high-frequency switching regulated power supplies are widely used because of their outstanding advantages such as small size, light weight, high efficiency, and stable performance. The efficiency value of modern switching power supplies is usually 65 to 95 percent, which is much higher than the efficiency of traditional linear regulated power supplies, which is the main reason why modern switching power supplies are gradually replacing traditional power supplies.

At present, switching power supplies at home and abroad are more inclined to miniaturization, high frequency and light weight, higher efficiency and reliability, and more digitization. In the primary rectifier bridge of the switching power supply, due to the nonlinear period, the current is a sine half-wave with very serious distortion and rich harmonics, which leads to a series of conducted interference and radiation interference. Therefore, the output voltage of the existing switching power supply is not stable, which limits the use of the initial power supply in some fields.

SUMMARY OF THE INVENTION

In view of the above-mentioned shortcomings of the prior art, the present invention provides a switching power supply harmonic suppression device to solve the above-mentioned technical problems.

An embodiment of the present application provides a device for suppressing harmonics of a switching power supply, including: a rectifier bridge, a filter and a high-frequency transformer, the output end of the rectifier bridge is connected to the input end of the filter, and the output end of the filter is connected to the input end of the high frequency transformer , the output end of the high-frequency transformer is connected to the inverter of the switching power supply; the filter includes a first capacitor, a second capacitor, a third capacitor, a fourth capacitor and an inductor; the first capacitor is connected in parallel with the input end of the inductor; the second capacitor is connected in parallel with the output end of the inductor; the series branch of the third capacitor and the fourth capacitor is connected in parallel with the second capacitor; a ground wire is arranged between the third capacitor and the fourth capacitor; the first capacitor and the second capacitor are differential mode interference filtering capacitors; the third capacitor and the third and fourth capacitors are common mode interference filtering capacitors.

In an embodiment of the present application, the differential mode interference filtering capacitor adopts a film capacitor with a capacity of 0.1 μF; the common mode interference filtering capacitor adopts a ceramic capacitor with a capacity of 2.2 nF; An inductor with a size of 6mH, a rated voltage of 250V and a rated current of 6A.

In an embodiment of the present application, the input end of the rectifier bridge is connected to a pre-stage protection circuit, and the pre-stage protection circuit includes a 2A/250V fuse, a negative temperature thermistor and a varistor; the fuse is connected to The negative temperature thermistor is connected in parallel; one end of the varistor is connected to the output end of the fuse tube, and the other end is connected to the output end of the negative temperature thermistor.

In an embodiment of the present application, the withstand voltage value of the rectifier bridge exceeds 442V.

In an embodiment of the present application, the rectifier bridge selects a rectifier bridge with a specification of 6A/600V.

In an embodiment of the present application, the output end of the rectifier bridge is connected in parallel with a filter capacitor, and the size of the filter capacitor is 12 μF.

The beneficial effect of the present invention is that,

The switching power supply harmonic suppression device provided by the present invention utilizes the characteristics of the flyback conversion circuit to design a multi-terminal flyback switching power supply, which can provide two output voltages. In order to make the output voltage more stable and maximize the improvement of the efficiency of the power supply.

In addition, the present invention has reliable design principle and simple structure, and has a very wide application prospect.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. In other words, other drawings can also be obtained based on these drawings without creative labor.

1 is a schematic diagram of a filter structure of a device according to an embodiment of the present application;

2 is a schematic structural diagram of a front-stage protection circuit of a device according to an embodiment of the present application;

FIG. 3 is a schematic structural diagram of a rectifier bridge of an apparatus according to an embodiment of the present application.

Detailed ways

In order to make those skilled in the art better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described The embodiments are only some of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that the embodiments of the present invention and the features of the embodiments may be combined with each other under the condition of no conflict.

In the description of the present invention, the terms "first", "second", etc. are only used for description purposes, and cannot be understood as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined as "first", "second", etc., may expressly or implicitly include one or more of that feature. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

In the description of the present invention, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense, unless otherwise expressly specified and limited, for example, it may be a fixed connection or a detachable connection Connection, or integral connection; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

Example 1

This embodiment provides a switching power supply harmonic suppression device, including: a rectifier bridge, a filter and a high-frequency transformer, the output end of the rectifier bridge is connected to the input end of the filter, the output end of the filter is connected to the input end of the high frequency transformer, The output end of the high frequency transformer is connected to the inverter of the switching power supply.

Please refer to FIG. 1, the filter includes a first capacitor, a second capacitor, a third capacitor, a fourth capacitor and an inductor; the first capacitor is connected in parallel with the input end of the inductor; the second capacitor is connected in parallel with the output end of the inductor; the The series branch of the third capacitor and the fourth capacitor is connected in parallel with the second capacitor; a ground wire is arranged between the third capacitor and the fourth capacitor; the first capacitor and the second capacitor are differential mode interference filtering capacitors; The third capacitor and the third and fourth capacitors are common mode interference filtering capacitors.

① Selection of X capacitor: It is connected between the live wire and the neutral wire. The capacitor used to eliminate differential mode interference is called X capacitor, which includes three types: X1, X2, and X3. The capacitance range of X2 is 1nF-1uF and is often used in EMI filters. In the switching power supply circuit, the optimal capacitor is 0.1~0.33uF. The two X2 capacitors, C1 and C2, in the EMI filter in Figure 1, this design uses a film capacitor with a capacity of 0.1μF [30].

②The choice of Y capacitor: There are four types of Y capacitors: Y1, Y2, Y3, and Y4. Commonly used in switching power supplies are Y1 and Y2 capacitors. The capacitor connected across the two ends of the safety insulation area, that is, between the primary side and the secondary side, is the Y1 capacitor, and its rated voltage is AC 250V. The role of the Y1 capacitor is to provide a loop path for the current to couple from the primary side to the secondary side, while also preventing the current from being coupled to the ground through the secondary side. Its common capacity range is 1~3nF. Experience shows that appropriately increasing the capacity of Y1 capacitor can reduce common-mode EMI noise, but at the same time, the leakage current to the ground will increase, so this design uses a ceramic capacitor with a capacity of 2.2nF, which is A relatively compromised approach.

③Choice of common mode inductance: In the common mode inductance, its main function is to filter out common mode interference and restrain itself from emitting interference, so as to avoid other reasons from affecting the normal operation of the equipment. It is actually a bidirectional filter, with two coils wound around the same iron core, and the number of turns and phases of the coils are the same [31]. When a current passes through, it is equivalent to a large inductance. The magnetic flux of the common mode signal generated on the coil is mutually strengthened, and the magnetic flux of the differential mode signal will cancel each other in the iron core. In the same type of circuit design, the typical value of common mode inductance is generally 10~33mH, usually 5~33mH. This design takes 6mH based on experience, the rated voltage is 250V, and the rated current is 6A. Finally, it has been verified that the circuit works well, and each component has no bad phenomena such as excessive heat.

Example 2

This embodiment provides a switching power supply harmonic suppression device, including: a rectifier bridge, a filter and a high-frequency transformer, the output end of the rectifier bridge is connected to the input end of the filter, the output end of the filter is connected to the input end of the high frequency transformer, The output end of the high frequency transformer is connected to the inverter of the switching power supply.

Connect the front-stage protection circuit at the input end of the rectifier bridge, and the front-stage protection circuit is shown in Figure 2. The safety and reliability of the switching power supply are largely determined by the protection circuit, so the protection circuit at the input end is particularly important. The pre-stage protection circuit of this embodiment uses a 2A/250V fuse tube instead of its fuse wire, selects NTCl0D-9 as the negative temperature thermistor, and selects MYG14K471 as the varistor. Among them, 2A/250V fuse tube plays the role of overcurrent protection, NTCl0D-9 can perform overcurrent protection at the moment of power-on, and MYG14K471 is used to absorb surge voltage and protect against lightning strike. The fuse tube is connected in parallel with the negative temperature thermistor; one end of the varistor is connected to the output end of the fuse tube, and the other end is connected to the output end of the negative temperature thermistor.

Example 3

This embodiment provides a switching power supply harmonic suppression device, including: a rectifier bridge, a filter and a high-frequency transformer, the output end of the rectifier bridge is connected to the input end of the filter, the output end of the filter is connected to the input end of the high frequency transformer, The output end of the high frequency transformer is connected to the inverter of the switching power supply.

As shown in Figure 3, the rectifier bridge includes two AC input terminals and two DC output terminals, and a total of four terminals. In order to obtain a DC voltage with a smaller ripple, the ripple and harmonic components can be reduced after adding LC filtering. It can be seen from Figure 3 that if current is to be supplied to the load, the value of iac is greater than zero only when the peak voltage amplitude at the input end of the power supply is greater than the secondary voltage at both ends of the filter capacitor, that is, the power grid can supply current to the load. The input current iac is in the form of a sharp pulse, which is out of phase with the voltage. After Fourier decomposition of the current, a series of harmonics will be obtained, resulting in a low power factor of 0.6 to 0.7 for the input power supply. The frequency of the grid AC voltage is 50 Hz. Theoretically, in order to provide a DC current with a small ripple to the load in Figure 3, a large inductor needs to be connected to the rectifier output, so that the load DC is approximately DC Id. The inductor current cannot be abruptly changed, and the switch has rise and fall times when it is turned on or off. Single-phase rectified load currents contain odd harmonics. The phase relationship between the single-phase rectifier input voltage and current and the harmonic components of the single-phase rectifier load current are analyzed. There are high-order harmonics at the single-phase rectifier input and load ends. Similarly, there are high-order harmonics at the input end and load end of the three-phase uncontrolled rectifier. The above analysis is uncontrolled rectification, but in the rectifier power supply, controllable rectification is usually used, that is, the output voltage is controlled by controlling the conduction angle of the thyristor, whether it is single-phase controllable rectification or three-phase controllable rectification, its The conduction of the switch tube is not zero-crossing conduction. If closed-loop control is used, its conduction angle changes at any time. Therefore, in the controlled rectification, the harmonic components existing at the input end and the load end are higher than those of the uncontrolled rectification. The ingredients are large.

The main parameters of the rectifier bridge mainly include the maximum reverse leakage current IR(μA), reverse peak voltage URM(V), forward voltage drop UF(V), forward peak surge current IFSM(A) and average rectifier current Id(A).

According to the literature, the reverse breakdown voltage UBR of the rectifier bridge should meet the following requirements

According to the design of the maximum AC voltage of 250V, the calculation can be obtained according to the above formula

Therefore, a rectifier bridge with a withstand voltage value greater than 442V should be selected. In this design, Umax is 250V. In order to further improve the withstand voltage value, the margin is about 1.5 times. Therefore, the reverse breakdown voltage of the rectifier bridge is generally about 600V through calculation. It should be pointed out that if four silicon rectifier tubes are used to form a rectifier bridge, the rectifier bridge needs to be further improved. According to the principle of choosing higher voltage than lower, the rectifier bridge can work more safely and reliably.

The rated effective current value of the rectifier bridge is set as IBR below, and the effective value of the input current is IRMS, which should meet the requirement of I _BR ≥ 2I _RMS . The formula for calculating IRMS is as follows

Among them, P ₀ is the output power of the switching power supply;

η is the efficiency of the power supply;

U _min is the minimum value of the AC input voltage;

是开关电源的功率因数[34]。

is the power factor of the switching power supply [34].

又有I_BR≥2I_RMS≈0.628A。在选择时，要留有一定的余量，所以本设计选择低成本的整流桥6A/600V。As can be seen from the design,

And I _BR ≥ 2I _RMS ≈ 0.628A. When choosing, a certain margin should be left, so this design chooses a low-cost rectifier bridge 6A/600V.

In the filter circuit, the input voltage is filtered by the rectifier bridge, and after the filter is charged and discharged, the output ripple will be greatly reduced, so the voltage waveform will become more stable and smooth. However, due to the large capacity of the filter capacitor in the rectifier circuit, if the capacitance value added to it is too low, it will affect the voltage pulsation, which will increase the cost of the capacitor [35]. Electrolytic capacitors are used as filter capacitors in most cases. It is the filter waveform of the rectifier filter capacitor, and the dotted line represents the filtered waveform after rectification. At the time of 2tc, that is, in the frequency range of 50Hz, the capacitor is charged twice.

The specific method for calculating C5 is introduced below: let "Umin" be the minimum value of the AC voltage U, after bridge rectification and C5 filtering, input the voltage waveform under the condition of U=Umin, when the input power reaches the maximum value (P0=Pm ), the power supply efficiency η=85%, when the turn-on response time tc of the rectifier bridge is set to 2.5ms, the minimum value V(min) of the DC high voltage is also superimposed by the input capacitor C5, the amplitude formed during the discharge process is the primary side pulsating voltage of VR. The value of C5 can be calculated by formula (3.4)

Substitute the data

After leaving a certain margin, the filter capacitor C5 is 12 μF in this embodiment.

Example 4

This embodiment provides a switching power supply harmonic suppression device, including: a rectifier bridge, a filter and a high-frequency transformer, the output end of the rectifier bridge is connected to the input end of the filter, the output end of the filter is connected to the input end of the high frequency transformer, The output end of the high frequency transformer is connected to the inverter of the switching power supply.

The specifications and parameters of the high-frequency transformer are determined by the AP method. The specific process is as follows:

(1) Determine the transformation ratio N

Among them, the voltage drop V _D of the output diode is 1V, N _p is the number of primary turns, N _s is the number of secondary turns, and the turns ratio can be obtained

(2) The estimated output power of input and output power can be obtained according to the magnitude of input and output voltage and current:

P ₀ =U ₀₁ I ₀₁ +U ₀₂ I ₀₂ =12×2+5×0.5=26.5W

(3) Calculate the maximum value of DC input voltage and current

(4) Determine the duty cycle Dmax According to the AC input voltage, the minimum input DC voltage and the maximum input DC voltage can be obtained by calculation

So choose a duty cycle of 0.5. The table below shows the reference voltage selection based on the input operating voltage range.

Table 3.1 Selection of Input Voltage

Table.3.1 Input Voltage Selection

(5) Select the magnetic core

The most commonly used soft magnetic material for most switching power supplies is ferrite material, mainly because it not only has a relatively high resistivity, but also has a relatively low price and low eddy current loss. In order to simplify the design process, AP method is adopted in this design. The AP method has been introduced earlier. If the area is in square millimeters, the corresponding AP unit is the fourth power in millimeters [41]. Using the area product method, the rated power of the transformer core can be easily calculated. The size of the core can be selected when designing the choke coil. Other important parameters of the transformer can also be calculated by the AP value method.

In the formula, AP is the area product, A _e is the intimate cross-sectional area, A _w is the intimate window area, B _m is the working magnetic induction intensity, P _in is the input power, f is the frequency, and generally ranges from 0.1 to 0.25; J is the The current density is generally 4; Ku is the window utilization coefficient, which is generally a value (0.2 to 0.4); _Ki is the core gap coefficient, which is generally 1.0. so

Looking up the table, the selected magnetic core model is EE22, L _e is 39.40mm ² , and A _e is 41.00mm ² .

Table 3.2 Core AP value table

Table.3.2 core values form AP

The choice of the magnetic core is to choose a suitable AP value that makes it within the rated temperature range when delivering power.

(6) Primary inductance

The primary peak current is

therefore,

(7) Calculate the number of primary turns n _P

Among them, Ae is the cross-sectional area of the magnetic core, f is the frequency, Bm is the working magnetic induction intensity, and the number of primary turns is 94 turns.

Calculate the winding turns ns1, ns2 on the secondary side of the output 12V and 5V

When ns1 is taken as 8 turns, the number of voltages per turn can be obtained

So output 5V winding turns

Take ns2 as 3 turns.

Although the present invention has been described in detail in conjunction with the preferred embodiments with reference to the accompanying drawings, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions should all fall within the scope of the present invention/any Those skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included within 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.

Claims (6)

1. A switching power supply harmonic suppression device is characterized in that, comprising: a rectifier bridge, a filter and a high frequency transformer, the output end of the rectifier bridge is connected to the input end of the filter, and the output end of the filter is connected to the input end of the high frequency transformer The output end of the high-frequency transformer is connected to the inverter of the switching power supply; the filter includes a first capacitor, a second capacitor, a third capacitor, a fourth capacitor and an inductor; the first capacitor is connected in parallel with the input end of the inductor ; the second capacitor is connected in parallel with the output end of the inductor; the series branch of the third capacitor and the fourth capacitor is connected in parallel with the second capacitor; a ground wire is arranged between the third capacitor and the fourth capacitor; the first The capacitor and the second capacitor are differential mode interference filtering capacitors; the third capacitor and the third and fourth capacitors are common mode interference filtering capacitors. 2. The switching power supply harmonic suppression device according to claim 1, wherein the differential mode interference filtering capacitor adopts a film capacitor with a capacity of 0.1 μF; the common mode interference filtering capacitor adopts a capacity of 0.1 μF. 2.2nF ceramic capacitor; the inductance is 6mH, the rated voltage is 250V, and the rated current is 6A. 3 . The switching power supply harmonic suppression device according to claim 1 , wherein the input end of the rectifier bridge is connected to a pre-stage protection circuit, and the pre-stage protection circuit comprises a 2A/250V fuse tube and a negative temperature thermistor. 4 . and the varistor; the fuse tube is connected in parallel with the negative temperature thermistor; one end of the varistor is connected to the output end of the fuse tube, and the other end is connected to the output end of the negative temperature thermistor. 4. The switching power supply harmonic suppression device according to claim 1, wherein the withstand voltage value of the rectifier bridge exceeds 442V. 5 . The switching power supply harmonic suppression device according to claim 1 , wherein the rectifier bridge adopts a rectifier bridge with a specification of 6A/600V. 6 . 6 . The device for suppressing harmonics of a switching power supply according to claim 1 , wherein the output end of the rectifier bridge is connected in parallel with a filter capacitor, and the size of the filter capacitor is 12 μF. 7 .

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