CN103730249A - Flyback transformer designing method for preventing interference of external high-intensity magnetic field - Google Patents

Abstract

The invention relates to a flyback transformer designing method for preventing the interference of an external high-intensity magnetic field. The electromagnetic parameters of a transformer are optimized according to the magnetizing curve of a transformer magnetic core at the flyback transformer designing stage, the anti-magnetic capability of the transformer can be improved, and the magnetic field coupled to the transformer magnetic core is blocked or weakened by optimizing the structure of the flyback transformer, additionally adding a soft iron material below a transformer framework and carrying out other auxiliary means according to the actual demands. According to the flyback transformer designing method, the purpose of preventing the interference of the high-intensity magnetism can be achieved only by adopting one or two means on many occasions. The flyback transformer designing method is suitable for intelligent electric meters capable of being prevented from being falsified by the external high-intensity magnetic field or suitable for other application occasions with the similar requirements for preventing the external high-intensity magnetism. The flyback transformer designing method is simple, scientific, high in high-intensity magnetism interference preventing capability and wide in application range.

Description

A kind of flyback transformer method for designing that realizes anti-outside high-intensity magnetic field interference

Technical field

The present invention relates to design of transformer field, specifically a kind of flyback transformer method for designing that realizes anti-outside high-intensity magnetic field interference.

Background technology

In recent years, the Switching Power Supply especially occupation rate of market of the Switching Power Supply of small-power reverse exciting topological structure improves year by year, and this mainly should give the credit to the incomparable advantages of other power supplys such as the distinctive volume of Switching Power Supply is little, efficiency is high, cost is low.But in some application scenarios high to power requirement reliability such as intelligent electric meters, may there is artificial intentional or unintentional destruction.And a kind of common method of tamper switch power supply smart ammeter, with strong external magnetic field, disturb exactly, because the saturation flux density of Ferrite Material is lower, conventional FERRITE CORE saturation flux density is about 5000 Gausses, external magnetic field can be coupled to the magnetic core of transformer and be made magnetic core be easy to reach capacity, and therefore adopts the mentality of designing of common flyback transformer and structure to be difficult to meet the requirement of anti-outside high-intensity magnetic field.

Around this difficult problem, some solutions are arisen at the historic moment at present.Air-core transformer is one of them solution, and it is saturated never, but needs a large amount of winding turns, and result is brought high-copper core loss and leakage inductance, can greatly lower efficiency like this (being about 20%).If the shell of transformer is placed in a box making of magnetic shielding material, make magnetic flux away from magnetic core of transformer, prevent saturatedly, can use the ferrite transformer of standard, this has increased cost and complexity undoubtedly, and is difficult to meet the requirement of safety and production technology simultaneously.Another method is to replace FERRITE CORE to solve the problems referred to above by using with the high magnetic resistance ferrocart core material of distributed air gaps.This magnetic core has lower relative permeability (μ, between 10 to 35), compares with ferrite (magnetic flux density 5000 Gausses, 0.5T), and ferrocart core has higher saturation flux density (15000 Gausses, 1.5T), and saturation characteristic is more weak.But the producer of processing ferrocart core material magnetic core of transformer is also considerably less both at home and abroad at present, therefore also there is no general applicability, and under the condition of identical power output, the volume of the transformer of ferrocart core magnetic core is more much larger than the volume of the transformer of common FERRITE CORE.Therefore current, also do not have a kind of proper and be easy to the method for designing of anti-strong external magnetic field transformer realizing.

Summary of the invention

The present invention is directed to the existing technical problem of prior art; avoid the weak point of current some anti-outside high-intensity magnetic field solutions; based on current monolithic off-line type switch chip mostly all with the function of overcurrent protection; propose one without adopting special core material (as ferrocart core or sendust core), and be structurally easy to realize and can easily meet the flyback transformer method for designing that disturb the anti-external magnetic field of realizing of safety standard and technological requirement.

The present invention is mainly solved by following technical proposals above-mentioned technical problem:

Realize the flyback transformer method for designing that anti-outside high-intensity magnetic field disturbs, it adopts Ferrite Material as magnetic core of transformer, comprises the following steps:

Step 1, the selection of monolithic off-line type switch chip: selection has quick current-limiting defencive function and meets the monolithic off-line type switch chip of demanded power output;

Step 2, the design of flyback transformer: described flyback transformer is the flyback transformer of primary current continuous mode, adjusts the design parameter of described flyback transformer according to power specification; The design parameter of flyback transformer need meet: at the peakflux density B of flyback transformer _mvalue is less than 3000 Gausses, switch chip current-limiting points I _lIMITtime magnetic flux density B _pvalue is greater than or equal to FERRITE CORE saturation flux density B _scondition under, Δ B=B _s-B _mcalculated value maximum, and now other design parameter of transformer is also all in rational scope, (how many as big or small in wire diameter and number of share of stocks need meet transformer temperature rise requirement, and size of gaps need meet the designing requirement of the conventional flyback transformers such as transformer manufacture process requirement).

More excellent, also comprise step 3, whether the flyback transformer of designing in detecting step 2 meets the strong magnetic requirement in anti-outside, satisfied finish, and does not meet and carries out next step;

Step 4, flyback transformer below encapsulation soft iron: lengthen the pin of flyback transformer, use the soft iron material of material package that meets dielectric voltage withstand requirement below flyback transformer.

As a kind of preferred embodiment, the volume of described soft iron material is as much as possible little under the prerequisite that meets antimagnetic requirement.

More specifically, describedly meet antimagnetic requirement for meeting the outside strong magnetic of anti-300mT.

It is more specifically, described that to meet antimagnetic requirement be to meet the antimagnetic requirement of setting in advance according to specific environment factor.

As a kind of preferred embodiment, the described material that meets dielectric voltage withstand requirement is plastics.

As a kind of preferred embodiment, the packaged type of described soft iron material is: two sides are encapsulated in plastic housing inside from left and right directions by soft iron material with the plastic housing of snap close.

As a kind of preferred embodiment, the top and bottom of described plastic housing respectively have the hole corresponding with flyback transformer pin, and the pin of flyback transformer is fixed on printed circuit board (PCB) after inserting from the hole of top and passing from the hole of below.

Tool of the present invention has the following advantages: use common FERRITE CORE and without adopting the magnetic core of other special substance just can reach the object of the strong magnetic in anti-outside 1.; 2. the flyback transformer mentality of designing that the present invention proposes can make full use of the saturation point of FERRITE CORE self, reach substantially the effect of the strong magnetic in anti-outside, may not need the measure of step 3-4, just can meet antimagnetic requirement, save in order to solve the antimagnetic extra cost of bringing; 3. in the situation that step 2 method can not meet the demands, can select to adopt step 3-4, in this step, transformer device structure is simple, is easy to realize.

Accompanying drawing explanation

Accompanying drawing 1 is master-plan flow chart of the present invention

Accompanying drawing 2 is flyback transformer parameter designing flow chart of the present invention

Accompanying drawing 3 is for needing to encapsulate the structural design drawing in soft iron situation below flyback transformer in the present invention

Accompanying drawing 4 is the locus schematic diagram of flyback transformer in the present invention in intelligent electric meter application

Description of reference numerals:

1-snap close; 2-plastic housing; 3-soft iron material; 4-hole; 5-flyback transformer magnetic core; 6-flyback transformer pin; 7-table cover; 8-Switching Power Supply wiring board; 9-gauge stand.

Embodiment

Below by embodiment, and by reference to the accompanying drawings, technical scheme of the present invention is described in further detail

Embodiment is designed to example with the flyback transformer of primary current continuous mode technical scheme of the present invention is described:

Step 1, first selects a monolithic off-line type switch chip that meets demanded power output and have quick current-limiting defencive function.Can guarantee like this just in case while there is to cause because magnetic core is saturated situation that primary current sharply rises; the consequence that there will not be switch chip to damage; if changed, do the switching device that there is no this function; when occurring disturbing with strong external magnetic field; this magnetic Field Coupling is to the magnetic core of transformer and while making situation that magnetic core reaches capacity; will there is because of overcurrent destructive malfunction in the MOSFET of switch chip, selecting will provide protection to inner MOSFET with the device of quick current-limiting defencive function.

Step 2, according to the design parameter of power specification adjustment flyback transformer, carries out the flyback transformer design of primary current continuous mode.Specifically comprise following some steps:

1 zero. determine system requirements: minimum ac input voltage V _aCMIN(unit: volt); Maximum ac input voltage V _aCMAX(unit: volt); Input voltage frequency f _l(unit: hertz); Output voltage V _o(unit: volt); Power output P _o(unit: watt); Power-efficient η; Loss allocation factor Z.

Wherein about Loss allocation factor Z: if Z=1 illustrates that institute is lossy all in primary side.If Z=0, illustrates that institute is lossy all in primary side.If there is no better reference data, can use Z=0.5, i.e. primary and secondary side loss respectively accounts for 50%.

2.. based on input voltage and P _oselect input storage capacitance C _iNcapacity, determine minimum and maximum DC input voitage V _mIN(unit: volt) and V _mAX(unit: volt).

3.. determine the output voltage V of reflection _oR(unit: volt) and clamp voltage-stabiliser tube voltage V _cLO(unit: volt).

4.. corresponding corresponding mode of operation and current waveform are set current waveform parameter K _p, work as K _p≤ 1.0, be continuous mode.

$K_P=\frac{I_R}{I_R}$

Wherein I _rfor elementary ripple current, I _pfor peak primary currents.

5.. according to V _mINand V _oRdetermine D _mAX.

$D_{\mathrm{MAX}}=\frac{V_{\mathrm{OR}}}{(V_{\mathrm{MIN}}-V_{\mathrm{DS}})+V_{\mathrm{OR}}}$

Wherein V _dSfor the conducting voltage between the drain electrode of monolithic off-line type switch chip and the source electrode set; Take volt as unit.

6.. calculate input average current I _aVG(unit: ampere) and peak primary currents I _p(unit: ampere).

$I_{\mathrm{AVG}}=\frac{P_O}{\mathrm{\η}*V_{\mathrm{MIN}}}$

7.. calculate primary current effective value I _rMS(unit: ampere).

$I_{\mathrm{RMS}}=I_P*\sqrt{D_{\mathrm{MAX}}*(\frac{K_{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="HDA0000449954750000031.png"\; state="\{\{state\}\}">P</figure-callout>}}^2}{3}-K_P+1)}$

8.. calculate primary electrical sensibility reciprocal L _p(unit: microhenry).

$L_P=\frac{{10}^6*P_O}{I_{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="HDA0000449954750000031.png"\; state="\{\{state\}\}">P</figure-callout>}}^2*K_P*(1-\frac{K_P}{2})*f_S}*\frac{Z*(1-\mathrm{\&eta;})+\mathrm{\&eta;}}{\mathrm{\&eta;}}$

9.. according to the switching frequency f of monolithic off-line type switch chip _s(unit: hertz) and P _oselect magnetic core and skeleton, then obtain from the databook of magnetic core and skeleton: magnetic core equivalent cross-sectional area A _e(unit: square centimeter); Magnetic core equivalent periodic line length L _e(unit: centimetre); Magnetic core is without the equivalent electric sensibility reciprocal A of air gap _l(unit: nanohenry/circle ²); Skeleton width B W(unit: millimeter).

10.. set number of plies L and the secondary winding number of turns N of armature winding _s(may need the process through iteration).

Wherein L value, from L=2, keeps 1.0≤L≤2.0 in whole iterative process.

Wherein N _svalue is from N _s=0.6 circle/volt starts.

. calculate armature winding number of turns N _p(unit: circle) and biasing winding number of turns N _b(unit: circle).

$N_P=N_S*\frac{V_{\mathrm{OR}}}{V_O+V_D}$

$N_B=N_S*\frac{V_B+V_{\mathrm{DB}}}{V_O+V_D}$

Wherein V _dfor output rectifying tube forward voltage, take volt as unit; V _dBfor biasing winding rectifying tube forward voltage, take volt as unit; V _bfor requiring according to feedback circuit and output the bias voltage of choosing, take volt as unit.

. determine armature winding wire diameter parameter: bare wire conductor diameter DIA (unit: millimeter); Elementary by line AWG specification.

. check peakflux density B _m(unit: Gauss); Primary winding current density CMA(unit: circular mil/ampere); And gas length L _g(unit: millimeter).

$B_M=\frac{100*I_P*L_P}{N_P*A_e}$

$L_g=40*\mathrm{\&pi;}*A_e*(\frac{{\mathrm{<figure-callout\; id="2"\; label="N\; P"\; filenames="HDA0000449954750000031.png"\; state="\{\{state\}\}">N</figure-callout>}}_P^{}}{100*L_P}-\frac{1}{A_L})$

$C\mathrm{MA}=\frac{1.27*{\mathrm{<figure-callout\; id="2"\; label="DIA"\; filenames="HDA0000449954750000031.png"\; state="\{\{state\}\}">DIA</figure-callout>}}^2*\frac{\mathrm{\&pi;}}{4}}{I_{\mathrm{RMS}}}*{\left(\frac{1000}{25.4}\right)}^2$

This step need to check whether meet L _g>=0.1; 200≤CMA≤500.Do not meet by changing L, N _s, or the method for magnetic core/skeleton carry out iteration.

. computing chip current-limiting points I _lIMITmagnetic flux density B when (unit: ampere) _p(unit: Gauss).

$B_P=\frac{I_{\mathrm{LIMIT}}}{I_P}*B_M$

. calculate secondary peak value electric current I _sP(unit: ampere), secondary effective value electric current I _sRMS(unit: ampere).

$I_{\mathrm{SP}}=I_P*\frac{N_P}{N_S}$

$I_{\mathrm{SRMS}}=I_{\mathrm{SP}}*\sqrt{(1-D_{\mathrm{MAX}})*(\frac{{\mathrm{<figure-callout\; id="2"\; label="K\; P"\; filenames="HDA0000449954750000031.png"\; state="\{\{state\}\}">K</figure-callout>}}_P^{}}{3}-K_P+1)}$

. determine secondary winding wire diameter parameter: bare wire conductor diameter DIA _s; The secondary line AWG that uses _sspecification.

In above-mentioned steps 9. and 10., by changing K _p, L, N _s, or the method for magnetic core/skeleton it is iterated, making B _m(peakflux density) value is less than 3000 Gausses, B _p(switch chip current-limiting points I _lIMITtime magnetic flux density) value is greater than or equal to B _s(FERRITE CORE saturation flux density, the B of PC40 material _sbe about 5000 Gausses) situation under, make Δ B=B _s-B _mcalculated value reach maximum, and now other design parameter of transformer is also all in rational scope, when this method for designing can make normally to work, transformer operates in the region that magnetization curve is lower, when outside magnetic interference, when magnetic core starts to enter zone of saturation, inductance value reduces, and primary current increases, if the B of design _pvalue is less than B _s, at the magnetic core saturation value that also do not reach capacity, primary current will reach the current-limiting points of switching device and protect so, and output voltage disappears; So just can not make full use of the intrinsic magnetic saturation density value of FERRITE CORE; And if the B of design _pbe greater than or equal to B _s, so can realize after magnetic core reaches capacity saturation value, former limit inductance value sharply reduces, and electric current surge, causes primary current to reach the current-limiting points of switching device and protects, and so just can realize the design of transformer stage to reach the antimagnetic object of maximization.

Step 3, whether the flyback transformer of designing in detecting step 2 meets the standard of the strong magnetic in anti-outside, satisfied finish, and does not meet and carries out next step.

Step 4, lengthen the pin 6 of flyback transformer, below transformer, with plastic material (for meeting the requirement of dielectric voltage withstand), encapsulate a soft iron material 3, make the magnetic line of force that can be coupled to magnetic core of transformer originally produce distortion and change direction, soft iron is just as " black hole ", near the magnetic line of force " swallowing up ", thus the magnetic line of force that can be coupled to magnetic core of transformer originally greatly reduced.The volume of soft iron material is as much as possible little under the prerequisite that meets antimagnetic requirement.

The execution mode encapsulating as a kind of soft iron material 3, adopts two sides from left and right directions, soft iron material 3 to be encapsulated in to plastic housing 2 inside with the plastic housing 2 of snap close 1.The top and bottom of plastic housing 2 respectively have the hole corresponding with flyback transformer pin 64, and flyback transformer pin 6 is fixed on printed circuit board (PCB) after inserting from the hole 4 of top and passing from the hole 4 of below.

The flyback transformer that the present invention is designed is specifically applied in a kind of electric energy meter as shown in Figure 4, comprises table cover 7, flyback transformer magnetic core 5, flyback transformer pin 6, Switching Power Supply wiring board 8 and gauge stand 9.Lengthen flyback transformer pin 6, be fixed on Switching Power Supply wiring board 8 after making it pass from hole 4, and then reach the object of the strong magnetic in anti-outside.

Specific embodiment described herein is only that spirit of the present invention is illustrated.Those skilled in the art can make various modifications or supplement or adopt similar mode to substitute described specific embodiment, but can't depart from spirit of the present invention or surmount the defined scope of appended claims.

Claims (8)

1. realize the flyback transformer method for designing that anti-outside high-intensity magnetic field disturbs, it is characterized in that it adopts Ferrite Material as magnetic core of transformer, comprises the following steps:

Step 1, the selection of monolithic off-line type switch chip: selection has quick current-limiting defencive function and meets the monolithic off-line type switch chip of demanded power output;

Step 2, the design of flyback transformer: described flyback transformer is the flyback transformer of primary current continuous mode, adjusts the design parameter of described flyback transformer according to power specification; The design parameter of flyback transformer need meet: at the peakflux density B of flyback transformer _mvalue is less than 3000 Gausses, switch chip current-limiting points I _lIMITtime magnetic flux density B _pvalue is greater than or equal to FERRITE CORE saturation flux density B _scondition under, Δ B=B _s-B _mcalculated value maximum.

2. a kind of flyback transformer method for designing that anti-outside high-intensity magnetic field disturbs that realizes according to claim 1, is characterized in that it also comprises:

Step 3, whether the flyback transformer of designing in detecting step 2 meets the strong magnetic requirement in anti-outside in application scenario, satisfied finish, and does not meet and carries out next step;

Step 4, flyback transformer below encapsulation soft iron: lengthen the pin of flyback transformer, and use a soft iron material of material package (3) that meets dielectric voltage withstand requirement below flyback transformer.

3. according to any described in claim 1-2, realize the flyback transformer method for designing that anti-outside high-intensity magnetic field disturbs, it is characterized in that describedly meeting antimagnetic requirement for meeting the outside magnetic by force of anti-300mT.

4. according to any described in claim 1-2, realize the flyback transformer method for designing that anti-outside high-intensity magnetic field disturbs, it is characterized in that described to meet antimagnetic requirement be to meet the antimagnetic requirement of setting in advance according to specific environment factor.

5. a kind of flyback transformer method for designing that anti-outside high-intensity magnetic field disturbs that realizes according to claim 2, is characterized in that in step 4, and the volume of described soft iron material (3) is as much as possible little under the prerequisite that meets antimagnetic requirement.

6. according to claim 2 any realized the flyback transformer method for designing that anti-outside high-intensity magnetic field disturbs, and it is characterized in that the described material that meets dielectric voltage withstand requirement is plastics.

7. a kind of flyback transformer method for designing that anti-outside high-intensity magnetic field disturbs that realizes according to claim 6, is characterized in that the packaged type of described soft iron material is: two sides are encapsulated in plastic housing (2) inside from left and right directions by soft iron material (3) with the plastic housing (2) of snap close (1).

8. a kind of flyback transformer method for designing that anti-outside high-intensity magnetic field disturbs that realizes according to claim 7, the top and bottom that it is characterized in that described plastic housing (2) respectively have the hole (4) corresponding with flyback transformer pin (6), and flyback transformer pin (6) is fixed on printed circuit board (PCB) after inserting from the hole (4) of top and passing from the hole (4) of below.

Images