CN103730249B - A kind of flyback transformer method for designing realizing anti-outside 300mT magnetic interference - Google Patents

Abstract

The present invention relates to a kind of flyback transformer method for designing realizing anti-outside 300mT magnetic interference, this method just optimizes the electromagnetic parameter of transformer from the flyback transformer design phase according to the magnetization curve of magnetic core of transformer, improve self antimagnetic ability of transformer, auxiliary with the structure by optimizing flyback transformer according to actual needs, increase the means such as soft iron material below transformer framework, block or weaken the magnetic field of being coupled to magnetic core of transformer.This invention only may need adopt a kind of object that just may reach anti-strong magnetic disturbance to two means wherein in a lot of occasion, and the present invention is applicable to intelligent electric meter that anti-strong external magnetic field distorts or other has the application scenario that the strong magnetic in similar anti-outside requires.The simple science of this flyback transformer method for designing, anti-strong magnetic disturbance ability is strong, applied widely.

Description

A kind of flyback transformer method for designing realizing anti-outside 300mT magnetic interference

Technical field

The present invention relates to design of transformer field, specifically a kind of flyback transformer method for designing realizing anti-outside 300mT magnetic interference.

Background technology

In recent years, the occupation rate of market of the Switching Power Supply especially Switching Power Supply of small-power reverse exciting topological structure improves year by year, and this mainly should give the credit to the incomparable advantage 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, artificial intentional or unintentional destruction may be there is.And a kind of common method of tamper switch power supply smart ammeter, disturb with strong external magnetic field 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-strong external magnetic field.

At present around this difficult problem, some solutions are arisen at the historic moment.Air-core transformer is one of them solution, and it is saturated never, but needs a large amount of winding turns, and result brings 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 made of magnetic shielding material, make magnetic flux away from magnetic core of transformer, prevent saturated, then can use the ferrite transformer of standard, this adds cost and complexity undoubtedly, and is difficult to the requirement simultaneously meeting safety and production technology.Another method is by using the high magnetic resistance ferrocart core material with distributed air gaps to replace FERRITE CORE to solve the problems referred to above.This magnetic core has lower relative permeability (μ, between 10 to 35), with ferrite (magnetic flux density 5000 Gauss, 0.5T) compare, 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 general applicability is not also had, 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 that realizes.

Summary of the invention

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

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

Realize a flyback transformer method for designing for anti-outside 300mT magnetic interference, it adopts Ferrite Material as magnetic core of transformer, comprises the following steps:

Step 1, the selection of monolithic off-line type switch chip: select there is quick current-limiting defencive function and the monolithic off-line type switch chip meeting 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, (as how many wire diameter size and number of share of stocks need meet transformer temperature increase requirement, size of gaps need meet the designing requirement of the conventional flyback transformers such as transformer manufacturing technological requirement).

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

Step 4, encapsulates soft iron below flyback transformer: the pin lengthening flyback transformer, by the material package one piece of soft iron material meeting dielectric voltage withstand requirement below flyback transformer.

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

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

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

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

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

As a kind of preferred embodiment, the top and bottom of described plastic housing respectively have the hole corresponding with flyback transformer pin, the pin of flyback transformer insert from the hole of top and pass in hole from below rear fixing on a printed circuit.

Tool of the present invention has the following advantages: 1. use common FERRITE CORE and object without the need to adopting the magnetic core of other special substance just can reach the strong magnetic in anti-outside; 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 the effect of the strong magnetic in anti-outside substantially, the measure of step 3-4 may not being needed, just can meet antimagnetic requirement, saving to solve the antimagnetic extra cost brought; 3. when 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 the structural design drawing needed below flyback transformer in the present invention to encapsulate in soft iron situation

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

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 and is described technical scheme of the present invention:

Step 1, first selects aly meet demanded power output and have the monolithic off-line type switch chip of quick current-limiting defencive function.Can ensure when the situation causing primary current sharply to rise because magnetic core is saturated occurs contingency like this; there will not be the consequence that switch chip damages; if change the switching device doing and do not have this function; when occurring disturbing with strong external magnetic field; this magnetic Field Coupling to the magnetic core of transformer and the situation that magnetic core is reached capacity time; will there is destructive malfunction because of overcurrent in the MOSFET of switch chip, select the device with quick current-limiting defencive function will provide protection to inner MOSFET.

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.. certainty annuity requires: 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, illustrate that institute is lossy all in primary side.If Z=0, illustrate that institute is lossy all in primary side.If do not have better reference data, can use Z=0.5, namely the loss of primary and secondary side 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 reflected _oR(unit: volt) and clamp voltage-stabiliser tube voltage V _cLO(unit: volt).

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

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

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

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

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

Wherein V _dSfor setting monolithic off-line type switch chip drain electrode and source electrode between conducting voltage; In units of volt.

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

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

$I_P=\frac{I_{AVG}}{(1-\frac{K_P}{2})*D_{MAX}}$

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

$I_{RMS}=I_P*\sqrt{D_{MAX}*(\frac{K_P^2}{3}-K_P+1)}$

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

$L_P=\frac{{10}^6*P_O}{I_P^2*K_P*(1-\frac{K_P}{2})*f_S}*\frac{Z*(1-\mathrm{\η})+\mathrm{\η}}{\mathrm{\η}}$

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); The equivalent electric sensibility reciprocal A of magnetic core air-gap-free _l(unit: nanohenry/circle ²); Skeleton width B W (unit: millimeter).

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

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

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

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

$N_P=N_S*\frac{V_{OR}}{V_0+V_D}$

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

Wherein V _dfor exporting rectifying tube forward voltage, in units of volt; V _dBfor biased winding rectifying tube forward voltage, in units of volt; V _bfor requiring the bias voltage chosen according to feedback circuit and output, in units of volt.

. determine armature winding wire diameter parameter: bared wire conductor diameter DIA (unit: millimeter); Elementary 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).

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

$L_g=40*\mathrm{\π}*A_e*(\frac{N_P^2}{1000*L_P}-\frac{1}{A_L})$

$CMA=\frac{1.27*{\mathrm{DIA}}^2*\frac{\mathrm{\π}}{4}}{I_{RMS}}*{\left(\frac{1000}{25.4}\right)}^2$

This step needs check whether and meet L _g>=0.1; 200≤CMA≤500.Do not meet then 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 time (unit: ampere) _p(unit: Gauss).

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

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

$\begin{array}{c}{I}_{SP}=I_p*\frac{N_P}{N_S}\\ I_{SRMS}=I_{SP}*\sqrt{(1-D_{MAX})*(\frac{K_P^2}{3}-K_P+1)}\end{array}$

. determine secondary winding wire diameter parameter: bared wire conductor diameter DIA _s; Secondary line AWG _sspecification.

Above-mentioned steps 9. and 10. in, 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) when, 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 lower region of magnetization curve, when outside magnetic interference, time 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, so also not reach capacity saturation value at magnetic core, primary current will reach the current-limiting points of switching device and protect, and output voltage disappears; So just can not make full use of the magnetic saturation density value that FERRITE CORE is intrinsic; 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 reach the current-limiting points of switching device and protect, and so just can realize the design of transformer stage to reach the antimagnetic object of maximization.

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

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

As the execution mode that a kind of soft iron material 3 encapsulates, two sides are adopted from left and right directions, soft iron material 3 to be encapsulated in 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 4 corresponding with flyback transformer pin 6, flyback transformer pin 6 insert from the hole 4 of top and pass in hole 4 from below rear fixing on a printed circuit.

Flyback transformer the present invention designed is particularly applicable 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 illustrate spirit of the present invention.Those skilled in the art can make various amendment or supplement or adopt similar mode to substitute to described specific embodiment, but can't depart from spirit of the present invention or surmount the scope that appended claims defines.

Claims (6)

1. realize a flyback transformer method for designing for anti-outside 300mT magnetic interference, it is characterized in that it adopts Ferrite Material as magnetic core of transformer, comprise the following steps:

Step 1, the selection of monolithic off-line type switch chip: select there is quick current-limiting defencive function and the monolithic off-line type switch chip meeting 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, comprises following some steps:

1.. certainty annuity requires: minimum ac input voltage V _aCMIN, maximum ac input voltage V _aCMAX, input voltage frequency f _l, output voltage V _o, power output P _o, power-efficient η, Loss allocation factor Z,

Wherein about Loss allocation factor Z: if Z=1, illustrate that institute is lossy all in primary side; If Z=0, illustrate that institute is lossy all in primary side; If do not have better reference data, use Z=0.5, namely the loss of primary and secondary side 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 _mINand V _mAX;

3.. determine the output voltage V reflected _oRand clamp voltage-stabiliser tube voltage V _cLO;

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

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

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

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

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

Wherein V _dSfor setting monolithic off-line type switch chip drain electrode and source electrode between conducting voltage;

6.. calculate input average current I _aVGwith peak primary currents I _p:

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

$I_P=\frac{I_{AVG}}{(1-\frac{K_P}{2})*D_{MAX}}$

7.. calculate primary current effective value I _rMS:

$I_{RMS}=I_P*\sqrt{D_{MAX}*(\frac{K_P^2}{3}-K_P+1)}$

8.. calculate primary electrical sensibility reciprocal L _p:

$L_P=\frac{{10}^6*P_O}{I_P^2*K_P*(1-\frac{K_P}{2})*f_S}*\frac{Z*(1-\mathrm{\η})+\mathrm{\η}}{\mathrm{\η}}$

9.. according to the switching frequency f of monolithic off-line type switch chip _sand P _oselect magnetic core and skeleton, then obtain from the databook of magnetic core and skeleton: magnetic core equivalent cross-sectional area A _e, magnetic core equivalent periodic line length L _e, magnetic core air-gap-free equivalent electric sensibility reciprocal A _l, skeleton width B W;

10.. the number of plies L of setting armature winding and secondary winding number of turns N _s, need the process through iteration;

Wherein L value is from L=2, in whole iterative process, keep 1.0≤L≤2.0;

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

. calculate armature winding number of turns N _pand biased number of winding turns N _b:

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

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

Wherein V _dfor exporting rectifying tube forward voltage, V _dBfor biased winding rectifying tube forward voltage, V _bfor requiring the bias voltage chosen according to feedback circuit and output;

. determine armature winding wire diameter parameter: bared wire conductor diameter DIA, elementary line AWG specification;

. check peakflux density B _m, primary winding current density CMA and gas length L _g:

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

$L_g=40*\mathrm{\π}*A_e*(\frac{N_P^2}{1000*L_P}-\frac{1}{A_L})$

$CMA=\frac{1.27*{\mathrm{DIA}}^2*\frac{\mathrm{\π}}{4}}{I_{RMS}}*{\left(\frac{1000}{25.4}\right)}^2$

This step needs check whether and meet L _g>=0.1,200≤CMA≤500, do not meet then by changing L and N _sor carry out iteration by the method changing magnetic core and skeleton;

. computing chip current-limiting points I _lIMITtime magnetic flux density B _p:

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

. calculate secondary peak value electric current I _sP, secondary effective value electric current I _sRMS:

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

$I_{SRMS}=I_{SP}*\sqrt{(1-D_{MAX})*(\frac{K_P^2}{3}-K_P+1)}$

. determine secondary winding wire diameter parameter: bared wire conductor diameter DIA _s, secondary line AWG _sspecification,

Above-mentioned steps 9. and 10. in, by changing K _p, L and N _sor it is iterated, at peakflux density B by the method changing magnetic core and skeleton _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 _swhen, make Δ B=B _s-B _mcalculated value reach maximum.

2. a kind of flyback transformer method for designing realizing anti-outside 300mT magnetic interference according to claim 1, is characterized in that it also comprises:

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

Step 4, encapsulates soft iron below flyback transformer: the pin lengthening flyback transformer, and with the material package one piece of soft iron material (3) meeting dielectric voltage withstand requirement below flyback transformer.

3. a kind of flyback transformer method for designing realizing anti-outside 300mT magnetic interference according to claim 2, it is characterized in that in step 4, the volume of described soft iron material (3) is little as much as possible under the prerequisite meeting antimagnetic requirement.

4. a kind of flyback transformer method for designing realizing anti-outside 300mT magnetic interference according to claim 2, is characterized in that the described material meeting dielectric voltage withstand requirement is plastics.

5. a kind of flyback transformer method for designing realizing anti-outside 300mT magnetic interference according to claim 4, is characterized in that the packaged type of described soft iron material is: it is inner that soft iron material (3) to be encapsulated in plastic housing (2) with the plastic housing (2) of snap close (1) from left and right directions by two sides.

6. a kind of flyback transformer method for designing realizing anti-outside 300mT magnetic interference according to claim 5, it is characterized in that the top and bottom of described plastic housing (2) respectively have the hole (4) corresponding with flyback transformer pin (6), flyback transformer pin (6) insert from the hole (4) of top and pass in hole (4) from below rear fixing on a printed circuit.