The working principle of electronic transformers Electronic transformer materials and classification
Electronic transformersIntroduction
Electronic transformer, input is AC220V, output is AC12V, power can reach 50W. It is mainly a transformer circuit developed on the basis of high-frequency electronic ballast circuit. It has stable performance, small size and high power, thus overcoming the shortcomings of traditional silicon steel sheet transformers such as large body, bulkiness and high price.
The working principle of an electronic transformer
The working principle is similar to that of a switching power supply. The diodes VD1 ~ VD4 form a rectifier bridge to transform the mains power into The high-frequency oscillation circuit composed of oscillation transformer T1 and transistors VT1 and VT2 turns the pulsating DC into high-frequency current, and then the ferrite output transformer T2 steps down the high-frequency and high-voltage pulses to obtain the required voltage and power. R1 is the current limiting resistor. Resistor R2, capacitor C1 and bidirectional trigger diode VD5 constitute the start trigger circuit. Transistors VT1 and VT2 are S13005, and their B is 15 to 20 times. High-power transistors with BUceo>=35OV such as C3093 can also be used. The trigger diode VD5 should be DB3 or VR60 with around 32V. The oscillation transformer can be made by yourself, and the audio wire is wound around the H7X10X6 magnetic ring. TIa and T1b are wound with 3 turns, and Tc is wound with 1 turn. The ferrite output transformer T2 also needs to be homemade, and the magnetic core is made of EI type ferrite with a side length of 27mm, a width of 20mm, and a thickness of 10mm. T2a is wound with 100 turns of high-strength enameled wire with a diameter of 0.45mm, and T2b is wound with 8 turns of high-strength enameled wire with a diameter of 1.25mm. The diodes VD1~VD4 are of the IN4007 type, the bidirectional trigger diodes are of the DB3 type, and the capacitors C1~C3 are polypropylene polyester polyester capacitors with a withstand voltage of 250V.
When the circuit is working, the working voltage of point A is about 12V; point B is about 25V; point C is about 105V; point D is about 10V. If the voltage does not meet the above values, or the circuit does not oscillate, you should check whether there are mis-soldering, missing soldering or weak soldering in the circuit. Then check whether VT1 and VT2 are in good condition, and whether the phases of T1a and T1b are correct. After the entire circuit is successfully installed, it can be placed in a small box made of metal material to facilitate shielding and heat dissipation, but attention must be paid to the insulation between the circuit and the casing. By changing the number of turns of the two coils T2a and b, the output high-frequency voltage can be changed.
The role of electronic transformer
It plays the functions of boost, step-down, isolation, rectification, frequency conversion, phase inversion, impedance matching and inversion in electronic circuits , energy storage, filtering and other functions.
Electronic TransformersClassification
A Classification by working frequency:
Industrial frequency transformer: working frequency is 50Hz or 60Hz
Medium frequency transformer: working frequency is 400Hz or 1KHz
Audio transformer: working frequency is 20Hz or 20KHz
Super audio transformer: above 20KHz, not exceeding 100KHz
High frequency transformer: working frequency is usually It is above KHz to hundreds of KHz.
B Classification by use:
Power transformer: Transformer used to provide power required for electronic equipment
Audio transformer: Used for audio amplification circuits and audio equipment Transformer
Pulse transformer: a transformer working in a pulse circuit, its waveform is generally a unipolar rectangular pulse wave
Special transformer: a transformer with a special function , such as parametric transformers, voltage stabilizing transformers, ultra-isolation transformers, transmission line transformers, magnetic leakage transformers
Switching power supply transformers: used in transformers in switching power supply circuits
Communication transformers: used Transformers used for DC blocking and filtering in communication networks
Materials and classification
1) Electronic transformer materials mainly include
Bobbin, Base, Case
Wire (CopperWire)
Magnetic core (FerriteCore, SI-SteelLamination)
Copper foil (CopperFoil)
Insulating tape (Tape)
Safety tape, also called MarginTape
Tube
Chemical materials: solder (SolderBar), insulating oil (Varnish), Epoxy, Glue, Thinner, ScalingPowder, Ink
1. Magnetic core:
There are several main categories of magnetic cores:
1. Steel Lamination (SI-STEEL, PERMALLOY);
2. Soft ferrite (FERRITECORE);
3. Iron Powder;
4. Kool, Mu or Sendust;
5. High Flux;
6 Iron-nickel-molybdenum magnetic powder core (MppCore);
7. Amorphous (Amorphous).
1) Ferromagnetic core (IronPowder): widely used in the RF field, using its inherent air gap distribution characteristics, suitable forVarious energy storage inductors, such as DC output chokes, split-state input chokes, power factor correction (PFC) inductors, pulse transformers, DCtoDC converters, continuous state relaxation inductors, dimming chokes and EMI/ in the RFI circuit. Its shape is usually circular.
Materials are usually distinguished by color code (ColorCode), and their specifications are named in the form T*-XX*. For example: in T130-26B, T stands for Toroid, 130 stands for 1.3-inch outer diameter, 26 stands for 26-inch material, and B stands for the same outer diameter but different thickness types. Suppliers are usually Mircometal, Jiacheng, Keda and Koda.
2) Iron-nickel-molybdenum magnetic powder core (MPPmolypermalloypowder): The material with the lowest magnetic loss among powder cores. It is made of 79% nickel, 17% iron, and 4% molybdenum. A ring-shaped magnetic core with distributed gaps in the magnetic powder.
MPP core has excellent electromagnetic properties in many aspects:
High resistance coefficient: low hysteresis and low eddy current loss; under high DC magnetization or DC bias conditions, the inductance is stable; It has the widest optional range of magnetic permeability and is the best choice material for DC output filters in switching power supplies. The materials of MPP are mainly divided into ui: 26, 60, 125, 147, 160, 173, 200.
Mainly used in high-Q inductors, low-loss filters, drive coils, radio frequency (RFI) filters, transformers and inductor coils, etc.
3) High magnetic permeability powder core (HighFluxCore): It is a ring shape made of 50% nickel and 50% iron alloy powder. There are air gaps inside the core. It is a powder magnetic powder with the best bias ability. Core material, magnetic flux density up to 15,000 Gauss, loss is significantly lower than iron powder core. It is ideal for switching power supply modulation inductors, line noise filters, pulse transformers and flyback transformer cores. Especially in large DC current situations, the use of HF magnetic powder core can effectively reduce the size of the inductor.
2. Skeleton:
Functionally divided into three categories: 1. Bobbin (BOBBIN), 2. Base (BASE), 3 .Coat (CASE)
In terms of materials, it is mainly divided into: PHENOLIC, PBT, PET, LCP, PPHS, PA66 and so on.
In terms of form, it is mainly divided into: vertical (VERTICAL), horizontal (HORIZONTAL)
It can also be divided into two types: surface mount device (SMD) and plug-in (Lead-throughorThroughHole) kind. The role of BOBBIN: a type of material used as a winding carrier for coils and insulating between the coil and the magnetic core.
The role of BASE: a type of material used to fix the coil and position the leads to facilitate its installation on the circuit board. Available with or without PIN.
The role of CASE: used to fix, protect and isolate the coil, and position the leads to facilitate their installation on the circuit board. Mostly used for coil potting.
Phenolic resin: commonly known as bakelite (PHENOLIC), is a thermoset (Thermoset) material.
Features: 1. Not easy to deform; 2. Resistant to high temperature and high temperature soldering; high strength. Disadvantages: brittle and easy to break. There are many bakelite materials currently in use, with different properties and different costs. Such as: T375j, 1403G4, M9630, AM-113, CPJ-860, etc. The different performance makes it suitable for different skeleton types.
PET: Polybutylene terephthalate (Polybutylene terephthalate), a thermoplastic material.
Features: 1. Not easy to deform; 2. High-temperature solder has certain melting loss; 3. High strength; 4. High cost.
There are many types of PET materials, and each manufacturer names PET differently, such as: T102, T102G30, FR530L(f1), FR-515, etc.
PBT: It is a thermoplastic (Thermoset) material.
Features: 1. Easy to deform; 2. Easy to melt and damage; 3. Low cost; 4. Has certain toughness.
Materials such as: 4115, 420SEO, 4115, etc.
LCP: (Liquidcrystalpolyester), a thermosetting material.
Features: High strength, not damaged later, higher cost. It is mostly used to drive high-voltage transformers for backlights, such as UI, EE, EPC and other multi-slot skeletons. Materials such as: E4008, E4010, E4810, etc.
NYLON (PA66: Ployamidetype66nylon): Nylon, a thermoplastic material.
Features: 1. Greater toughness; 2. High temperature solder has certain melting loss; 3. Late deformation (glass fiber can be added to increase strength). Materials such as: 101L, TE250F6, A3X2G7, KF4357G6, etc.
One thing to be clear is that thermoplastic and thermosetting molds are not universal
3. Wire (WIRE): The main types include enameled wire, multi-layer insulated wire, and wire wrapped wire. Wire, PVC wire
Commonly used wire gauges (WireGauge): mmG (Japanese gauge), AWG (American gauge), SWG (British gauge), the wire gauge here refers to the diameter of the bare wire Area
1) EnamelledwierorMagnetwire:
According to the enameled film, it is divided into:
A Polyurethane enameled wire (UEW), according to the enameled film Film thicknessDecreasingly divided into 0UEW (Triple), 1UEW (Heavy or Double), 2UEW (Single), UEW is the most widely used line type, among which 2UEW and 1UEW are the most commonly used.
Its features are: no need to remove the paint in advance before soldering, and can be directly immersed in the tin furnace for soldering.
It is divided into three categories: single strand, multi-strand stranded wire (LITZ, also known as Li branch line) and silk covered wire (UTSC). Among them, LITZ refers to one-time twisting or multiple twisting, which aims to reduce the influence of skin effect and reduce the difficulty of production operation due to excessive hardness of copper wires. UTSC refers to multi-strand untwisted wires wrapped with glass fiber, which has strong mechanical strength. and wear resistance, it also has the advantages of reducing the skin effect and facilitating operation.
From the temperature level, it is usually divided into two types: B grade 130℃ (NEMAMW-C) 5F grade 155℃ (MW7C9)
UEW patent leather can be added with a layer of Nylon film. Enhance its mechanical strength and wear resistance, which can be expressed as UEW+NY, among which Class B 130℃ (MW2C8) Class F (MW8C0)
B. Polyester enameled wire (PEW), according to the enameled film The decreasing thickness is divided into 0PEW (Triple), 1PEW (Heavy or Double), 2PEW (Single), which is a widely used line type. At higher operating temperatures, the insulation layer has good stability, and the patent leather Good wear resistance.
The characteristics are: the paint needs to be removed before soldering.
There are two types of single-strand and multi-strand stranded wires.
A layer of Nylon film can be added to the outside of PEW patent leather to enhance its mechanical strength and wear resistance, which can be expressed as PEW+NY, F grade 155℃ (MW2C4)
C. Other types such as PVE, EIW, EAIW and other wires are rarely used, so they will not be introduced
2) Multi-layer insulated wire: mainly double-layer insulated wire (DIW: Doubleinsulatdewire) and triple-layer insulated wire (TIW: tripleinsulatedwire).
Sanming system method:
For example: primary—-secondary—-primary
Primary (densely wound) Secondary (sparsely wound) Primary (densely wound)
Rubadue: The insulation layer material is DuPont ETFET, EFFEZPELTEPEONTEFC material. Copper wire is available in single and multiple strands, and its insulation can be in a variety of colors. The insulation layer must be removed with wire strippers.
The commonly used ETFET insulation layer thicknesses are divided into five types: 0.0015”, 0.0002”, 0.0003”, 0.0005”, 0.0007”, and their breakdown voltages are 9,000VRMS, 10,000VRMS and 12,000VRM respectively.S, the temperature grade is F grade 155℃. Furukawa three-layer insulated wire is the TEX series, of which the temperature grades of TEX-E, TEX-B, and TEX-F are 105°C, 130°C, and 150°C respectively.
A STANDARDTYPE (TEX-E, TEX-B, TEX-F)
The colors of the insulation layer are yellow, brown and white.
TEX-E is a three-layer insulation made of weldable, thermal resistance resin and polyamine resin. TEX-E is the most commonly used line type, and the insulation layer thickness is 100mm.
B SELR-BONDINGTYPE (TEX-ECEW3)
C CITZWIRETYPE (TEX-ELZ)
Twisted wire type: The appearance of multi-stranded wire is covered with three layers of insulation , can reduce high-frequency impedance. This type of wire is used less frequently.
4. Copper foil (COPPERFOIL): Copper foil functions as a winding (WINDING) or shielding layer (SHIELD)
Its characteristics are as The windings can pass large currents to reduce the influence of skin effect and leakage inductance. They are insulated by wrapping insulating paper or Mylar tape; when used as a shielding layer between windings, they are insulated by wrapping insulation or Mylar tape. The ends overlap and must be isolated. And usually use a good phase wire to ground the starting end of the shielded copper foil; when the copper foil is used as the external shield, use copper foil to wrap the wire package and the magnetic core with a layer, and solder the ends to the magnetic core. The lead can be soldered to the ground or not. Leads
There are three specifications for copper foil:
1. Thickness: expressed in inches (INCH) or millimeters (MM)
2. Width: millimeters ( MM) means
3. Hardness: divided into three types: hard, medium hard and soft
The copper foil is made of soft and thick material for winding, and medium hard is used for internal shielding. And thin materials, use hard and thin materials for external shielding
5. Insulating tape (TAPE): tape used for insulation between windings, commonly used Mylar tape (polyester film), Luo There are three types of paper (NOMEX) and Kaptontape. Among them, MylarTape is the most commonly used and has the lowest cost. Its temperature grade is B grade 130℃, Lome paper is N grade 200℃, and Kapt tape temperature grade is H grade 180℃ and F grade 150℃. . Its characteristics are: higher temperature resistance than acetate film tape, good shape quotient, excellent resistance to chemicals and moisture, and can withstand cutting and abrasion.
6. Safety tape (MARGINTAPE): also called retaining wall, used in conjunction with casing to ensure safe distance (CREEPDISTANCE). The usual manufacturers are 3M44#, NTTOP245, Yahua non-woven fabric WF, etc. The thickness of 44# anjiao is divided into three types: 1 layer 1L, 2 layers 2L, 3 layers 3L. Yahua is divided into 0.2mm, 0.35mm two kinds. The thickness of the glue and the number of turns are selected based on the design to facilitate production operations.
7. Casing (TUBE): The commonly used ones are heat shrink tubing (HEATSHRINKTUBE), Teflon tubing (TEFLONTUBE), silicone tubing (SILICONTUBE) and epoxy fiberglass tubing. Among them, heat shrinkable sleeves are divided into two categories: PVC heat shrinkable sleeves and UL heat shrinkable sleeves. The temperature grade of UL heat shrinkable casing is 125℃ and 105℃, and the temperature grade of Teflon casing is 200℃. Its wall thickness is divided into L type, S type and T type, and the thickness increases in sequence.
8. Solder (SOLDERBAR): It is a tin (Sn) lead (Pb) alloy. The commonly used ratios are Sn63/Pb37, Sn60/Pb40, Sn50/Pb50. A small amount of other materials such as silver can also be added to improve smoothness and other properties. Tin bars are also divided into high-temperature tin and low-temperature tin, with operating humidity of 390-440℃ and 26-80℃ respectively.
9. Insulating oil (VARNISH): also known as VARNISH, its functions are insulation, thermal conductivity, fixation, and moisture-proof; impregnation usually has two forms: natural impregnation (DIPVARNISH) and vacuum impregnation (VACUUM) . Magnetic toroid coils are usually naturally impregnated, and their model specifications and physical properties vary depending on the model and manufacturer. For transformer impregnation, some manufacturers perform vacuum impregnation with epoxy resin (such as 486-FC), which greatly improves its insulation, thermal conductivity, fixation, moisture-proof and other properties, but the corresponding process difficulty increases.
10. Fixing glue: There are two commonly used fixing glues: epoxy glue (EPOXY) and other glues (GLUE)
Epoxy glue is usually a blended glue. The curing agent is mixed and used in a certain proportion, and a certain amount of idle time is required after mixing and dispensing. It can be naturally dried in the shade or baked to harden. Epoxy resin glue is usually used for potting devices and bonding parts. Potting glue and adhesive glue have different ingredients and additives, and their properties and uses are different and cannot be mixed. One-component glue (GLD) is usually used for bonding between magnetic cores, magnetic cores and bone or coils. The method of use and baking after direct dispensing.
11. Potting Glue (POTTINGGLUE): Commonly used potting glues include epoxy resin (such as Huili 9001A/B) and silica gel (Dow Corning 170A/B). Epoxy resin glue has high stress and strength; silica gel has low stress and strength. Its purpose The insulation is filled with glue, and all potting glues should be UL certified.
Temperature grades of insulating materials: Insulating materials are divided into the following temperature grades according to their performance and usage requirements
Insulation temperature grades: Class A (105℃) Class E (120℃) Class B (130℃) Class H (180℃) Class N (200℃) Class C (220℃).
Materials with temperature grades mainly include: tape, retaining wall, copper wire with insulation layer, skeleton material powder, Fanli water and casing, etc..
Electronic transformerProcess flow
1) Pre-processing, such as copper foil, skeleton, etc.; (beforehandprocess)
2) Winding; (windingcoil)
3) Wiring (termianlleadwire);
4) Solder one; (dipsolder1)
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5) Assembled magnetic core, including dispensing glue and wrapping tape; (assembly)
6) Test 1; (test1)
7) Baking glue; (bakeglue )
8)Impregnation;(dipvarnishedorvacuumedvarnish)
9)Bakevarnish;(bakevarnish)
10)Solder 2;(dipsolder2)
11) Test 2; (test2)
12) Appearance inspection and cleaning; (inspection&cleaning)
13) Finished product packaging; (packing)
Note: This process is a general process, and some processes can be deleted for specific products
Performance indicators
Performance indicators of electronic transformers (ELECTRICALCHARACTER):
A. Inductance (Inductance)
B. Leakage Inductance (LeakageInductance)
C. DC Resistance (DCResistance)
D. Turn Ratio (TurnRadio)
E. Withstand voltage (Hi-POT)
F. Insulation resistance (InsulationResistance)
G. Mechanical Dimension (MechanicalDimension)
H. Interlayer insulation (LayerInsulation)
I. Online test (InCircuitTest)
A: Inductance L=AL*N2
where AL is the magnetic permeability, which Determined by factors such as the ui magnetic circuit length and cross-sectional area of the magnetic core, N is the number of coil turns.
B: Leakage inductance LK
As the amount of magnetic leakage, its size is determined by the designed winding structure and production process, such as: whether there is a retaining wall bushing, winding integrity, There are many factors such as the density of winding, the number of layers of interlayer tape and the tightness of winding.
C: DC resistance DCR=ρL/πR2
Where ρ is the conductivity, L is the length of the copper wire, πR2 the cross-sectional area of the copper wire, the length of the copper wire is determined by the number of winding turns and Winding diameter.
D: Turn ratio TurnRadio (TR for short)
The basic principle of a transformer: the voltage ratio between the primary and secondary input and output is equal to the ratio of the primary and secondary turns. Its function: it is used to test whether the number of windings meets the requirements;
Testing principle: primary input-high-frequency sine wave signal is measured with an ammeter to measure its voltage value, and secondary is measured to measure its no-load output voltage , the voltage ratio between the two is the turns ratio.
Usually the test conditions are 20KHz, 1V
E: Withstand voltage HI-POT (destructive test)
Function: used to test the safety of the transformer, A project of reliability.
Usually the test positions are primary and secondary (PRITOSEC) and primary and primary core (SECTOCORE); the parameters set include power supply type: AC or DC (ACORDC), voltage value (Voltage), leakage current (Leakagecurrent), test time (Time), usually AC high voltage test is used. The voltage and leakage current are usually specified by the customer or tested according to relevant safety regulations.
Testing principle: Add high voltage between the test parts, and test whether the leakage current exceeds the requirements. When the parts to be tested fail to meet the requirements, the insulation part between the parts to be tested may be broken down. At this time, the leakage current will be much greater than the requirements; sometimes the insulation degree is in a critical state and the high voltage cannot breakdown it, and the leakage current may be slightly greater than requirements, it is also judged as defective at this time.
F: Insulation resistance Insulationresistance
Function: An item used to test the degree of insulation.
Testing principle: Add a DC voltage of 500VDC between the test parts and test the impedance therebetween, which is usually 100MΩMIN.
Although HI-POT and IR testing methods are different, they are very closely related. Usually the same defective cause will cause HI-POT and IR to be defective at the same time: In some cases, one type of project defect will also occur.
G: Interlayer insulation Layerinsulation
Function: For some drive transformers (DriveTransformer) or ACTODC main transformers, due to their large number of turns and layers of windings, the starting line and When the voltage between the terminal wires is very high and the insulation level of the enameled wire coating is close to or fails to meet the requirements, it is necessary to conduct this test on the product to ensure the reliability of the product.
Testing principle: Instantly add oscillation signals at the beginning and end of the winding to form a damped oscillation in the coil of the signal. Observe its oscillation waveform through the display; if a short circuit occurs in the coil, the rigid waveform will instantly attenuate. , rather than a damped oscillation. In the design, multi-slot and primary coil distribution or interlayer tape are usually used for processing.
H: Online test InCircuitTest
Function: Customers ensure the dynamic characteristics of the components used during normal useThis test is added to meet the requirements.
Testing principle: Directly install the transformer on the machine board and test whether the input and output characteristics meet the design requirements during operation.
Analysis of causes of defective transformer manufacturing process and solving techniques
1. Defective inductor
A: Extremely high
The number of coil turns is much larger than the specification Requirements, reduce the number of turns as required.
The magnetic core is used incorrectly, use a magnetic core made of high μ value material, and use the required magnetic core.
The magnetic cores are not paired. They are all assembled with NOGAP magnetic cores. Use the cores when paired.
The test instrument settings are incorrect, such as frequency, test voltage, etc. Reset the test instrument.
B: Too high
The number of coil turns slightly exceeds the specification requirements. Reduce the number of turns as required.
The core GAP is too small, so grind off a little of the middle part of the core.
The magnetic core is used incorrectly. Use a magnetic core made of a material with a slightly higher μ value. Use the required magnetic core.
If the test instrument settings and operations are incorrect or there are instrument errors, retest or retest with other instruments.
Environmental conditions do not match, such as temperature, humidity, etc., test under normal conditions.
C: Low
The number of coil turns is slightly lower than the specification requirement. Increase the number of turns as required.
The GAP of the magnetic core is too large, so grind off a little bit of both sides of the magnetic core.
The legs of the magnetic core are short and the core is not tightly closed when assembled.
The magnetic core is used incorrectly. Use a magnetic core made of a material with a slightly lower μ value. Use the required magnetic core.
If the test instrument settings and operations are incorrect or there are instrument errors, retest or retest with other instruments.
Environmental conditions do not match, such as temperature, humidity, etc., test under normal conditions.
D: Extremely low
The number of coil turns is far less than the specification requirement. Increase the number of turns as required.
The magnetic core is used incorrectly. Use a magnetic core made of a material with a slightly lower μ value. Use the required magnetic core.
The magnetic cores are not paired, they are all assembled with GAPED magnetic cores, and the magnetic cores are used in pairs.
The test instrument settings are incorrect, such as frequency, test voltage, etc. Reset the test instrument.
Interlayer short circuit occurs in the coil, such as: multi-strand wire leads are wrapped in the wrong pin position; solder short circuit; enameled film is damaged and short circuit; shielding copper foil is short circuited from beginning to end; copper foil lead crushes the copper foil outer tape and causes Cause short circuit to itself, etc.
2. Poor leakage inductance (leakage inductance is an indicator of magnetic leakage, and the smaller the value of the leakage inductance, the better)
A: Extremely high
The instrument settings are incorrect. Correct the settings.
If the short circuit is bad, re-short it to make it complete.
B: Too high
The wiring is poor. Correct the wiring to make it even and smooth. Use sparse winding if it is less than one layer.
Try not to overlap too much between layers of tape, usually 5 to 10mm.
The tape is smooth and the wire package is tight.
Low inductance.
3. Bad DC resistance
A: Extremely high
The test frame has poor contact, with open circuit or point contact.
The lead wire is wrapped in the wrong pin position.
B: High
The test frame has poor contact and point contact occurs.
The number of windings is too high.
Partial breakage of multiple strands occurred.
The test instrument was not reset to zero correctly.
The wire diameter of the enameled wire is too small.
C: Low
The number of windings is small.
The number of multi-strand lines is too high.
The test instrument was not reset to zero correctly.
The wire diameter of the enameled wire is too large.
The corresponding winding part of the coil is short-circuited.
D: Extremely low
The corresponding winding is short-circuited.
The lead wire is wrapped in the wrong pin position.
The PIN pins are soldered.
4. Poor lap ratio
A: Extremely high
Wrong test method.
The test frame has poor contact.
B: On the high side
The number of coil turns is too many
C: On the low side
The number of coil turns is too few.
There is a GAP in the magnetic core during testing. Usually GAP has an impact on the TR value. The TR value is subject to the NOGAP magnetic core test or to seek consistency.
A short circuit occurs between coil layers.
D: Extremely low
The lead wires are soldered from end to end.
The test frame has poor contact.
5. HI-POTNG (pressure-resistant NG)
A: The design and requirements are unreasonable.
B: The number of layers of interlayer tape is not enough.
C: TEFLONTUBE is not installed.
D: The width of MARGINTAPE (tape) is not enough (ie: the distance along the surface is not enough).
E: The leakage current setting is too small.
F: The PIN pin of the lead wire is wrapped incorrectly.
G: Soldering.
H: Enameled wire welding.
I: The coil is fat, and the magnetic core assembly is worn through the outer TAPE and enameled film.
6. IRNG (insulation resistance)
A: The PIN pin of the lead wire is wrapped wrongly.
B: Soldering.
C: The enameled wire is damaged.
D: The coil is fat, and the magnetic core assembly is worn through the outer TAPE and enameled film.
E: VARNISH has not been baked yet.
7. LayerInsulationNG (interlayer insulation)
A: The enameled wire is damaged and the damaged area is in contact.
B: The potential difference between the starting end and the ending end of the winding is too large, the coil has no inter-layer isolation measures, and the voltage resistance of the enameled film of the first and last wires cannot withstand the potential difference at the contact point.
8. InCircuitTestNG (online test)
Also known as PCBATest, the reasons for its failure are complex. However, this problem can be avoided if the performance indicators of the products produced can be close to the theoretical values or as good as possible.
According to the different driving methods of high-frequency switching tubes, they can be divided into self-excited oscillation type and separately excited type.
Principles of electronic transformersClassification introduction
Self-excited oscillation working principle
The principle of the electronic transformer is similar to the working principle of the switching power supply. The diodes VD1~VD4 form a rectifier bridge to convert the mains power into DC power. The high-frequency oscillation circuit composed of the oscillation transformer T1 and transistors VT1 and VT2 converts the pulsating DC into high frequency. The current is then stepped down by the ferrite output transformer T2 to obtain the required voltage and power. R1 is the current limiting resistor. Resistor R2, capacitor C1 and bidirectional trigger diode VD5 constitute the start trigger circuit. Transistors VT1 and VT2 are S13005, and their B is 15 to 20 times. High-power transistors with BUceo>=35OV such as C3093 can also be used. The trigger diode VD5 should be DB3 or VR60 with around 32V. The oscillation transformer can be made by yourself, and the audio wire is wound around the H7X10X6 magnetic ring. TIa and T1b are wound with 3 turns, and Tc is wound with 1 turn. The ferrite output transformer T2 also needs to be homemade, and the magnetic core is made of EI type ferrite with a side length of 27mm, a width of 20mm, and a thickness of 10mm. T2a is wound with 100 turns of high-strength enameled wire with a diameter of 0.45mm, and T2b is wound with 8 turns of high-strength enameled wire with a diameter of 1.25mm. The diodes VD1~VD4 are of the IN4007 type, the bidirectional trigger diodes are of the DB3 type, and the capacitors C1~C3 are polypropylene polyester polyester capacitors with a withstand voltage of 250V.
When the circuit is working, the working voltage of point A is about 12V; point B is about 25V; point C is about 105V; point D is about 10V. If the voltage does not meet the above values, or the circuit does not oscillate, you should check whether there are mis-soldering, missing soldering or weak soldering in the circuit. Then check whether VT1 and VT2 are in good condition, and whether the phases of T1a and T1b are correct. After the entire circuit is successfully installed, it can be placed in a small box made of metal material to facilitate shielding and heat dissipation, but attention must be paid to the insulation between the circuit and the casing. By changing the number of turns of the two coils T2a and b, the output high-frequency voltage can be changed.
Principle of separately excited electronic transformer
Separately excited electronic transformer
When the power frequency is connected After the mains power is supplied, the current through Rs of the bridge rectifier, except for the starting current flowing into the IC pin VCC, most of the remaining current charges the capacitor CVCC1. When the voltage on the IC pin VCC reaches the startup threshold (11.8V), the IC starts to work. Once the IC is started, the charge pump circuit consisting of CSNUB, DCP1 and DCP2 isIC pin VCC feeds current. Bootstrap diode DB and capacitor CB power the IC’s high-side driver circuit. Zener diode DZ is used to shunt excess IC current to prevent IC damage.
The resistance of the halogen lamp filament has a positive temperature coefficient, and the “cold resistance” at room temperature is much smaller than the “hot resistance” when the lamp is working. When the lamp is started, a large surge current will be generated, which will affect the lamp life. However, IR2161 provides soft-start operation to avoid surge current. During lamp start-up, IR2161 outputs a high frequency of 125kHz. Since the primary leakage inductance of the output high-frequency transformer T1 in the system is fixed, it exhibits higher impedance at higher frequencies and the voltage on the primary winding is lower. As a result, the output voltage of the transformer is lower, the lamp current is smaller, and the protection circuit is prevented from being triggered. After about 1 second, the circuit runs at a lower frequency. During this process, the voltage on the external capacitor CSD at IC pin 3 increases from OV to 5V.
When no-load, VCSD=OV, the oscillator frequency is about 60kHz. Under maximum load, VCSD=5V, the oscillator frequency is about 30kHz. When the output is short-circuited, a large current flows through the half-bridge and is sensed by RCS. As long as the voltage on IC pin 4 (CS) exceeds the threshold level of 1V for more than 50ms, the system will shut down. If the load exceeds 50% of the maximum load, the voltage on IC pin 4 will exceed the lower threshold voltage of O5V. After 0.5S, the system will shut down. Whether it is short circuit protection or overload protection, it can be automatically reset. The IR2161 also provides an overtemperature shutdown feature. When the chip junction temperature exceeds the over-temperature limit of 135°C, the half-bridge switch will stop working to avoid MOSFET burnout.
The relationship between role and calculation in power supply technology. Power supply devices, whether DC power supply or AC power supply, use electronic transformers (soft magnetic electromagnetic components) made of soft magnetic cores. Although there are already air-core electronic transformers and piezoelectric ceramic transformers that do not use soft magnetic cores, up to now, the vast majority of electronic transformers in power supply devices still use soft magnetic cores.
Therefore, discuss the relationship between power supply technology and electronic transformers: the role of electronic transformers in power supply technology, the requirements of power supply technology for electronic transformers, the use of new soft magnetic materials and new magnetic core structures in electronic transformers. The impact of the development of power supply technology will definitely arouse the interest of friends in the power supply industry and soft magnetic materials industry. Baidu Encyclopedia puts forward some opinions in order to promote dialogue, mutual exchange and common development between the power supply industry, the electronic transformer industry and the soft magnetic material industry on issues related to electronic transformers and soft magnetic materials.
2. Requirements of power supply technology for electronic transformers
The requirements of power supply technology for electronic transformers, like all commercial products, are to complete specific functions under specific conditions of use. Pursue the best performance-price ratio. Sometimes it may focus on price and cost, and sometimes it may focus on efficiency and performance. Now, light, thin, short and small have become the development direction of electronic transformers.It emphasizes cost reduction. Starting from the general requirements, four specific requirements can be drawn for electronic transformers: conditions of use, completion of functions, improvement of efficiency, and reduction of costs.
2. Conditions of use The conditions for use of electronic transformers include two aspects:
Reliability and electromagnetic compatibility. In the past, only reliability was paid attention to, but now due to the increased awareness of environmental protection, electromagnetic compatibility must be paid attention to. Reliability means that under specific conditions of use, the electronic transformer can work normally until its service life. Among general usage conditions, the greatest impact on electronic transformers is ambient temperature. The parameter that determines the strength of the electronic transformer affected by temperature is the Curie point of the soft magnetic material. Soft magnetic materials have a high Curie point and are less affected by temperature; soft magnetic materials have a low Curie point and are sensitive to temperature changes and are greatly affected by temperature.
For example: the Curie point of manganese-zinc ferrite is only 215℃, which is relatively low. The magnetic flux density, magnetic permeability and loss all change with temperature. In addition to the normal temperature of 25℃, Various parameter data at 60℃, 80℃ and 100℃ are given. Therefore, the operating temperature of manganese-zinc ferrite cores is generally limited to below 100°C, that is, when the ambient temperature is 40°C, the temperature rise must be lower than 60°C. The Curie point of cobalt-based amorphous alloy is 205°C, which is also low, and the use temperature is also limited to below 100°C. The Curie point of iron-based amorphous alloy is 370°C and can be used below 150°C to 180°C. The Curie point of high magnetic permeability permalloy is 460°C to 480°C and can be used below 200°C to 250°C. The Curie point of microcrystalline and nanocrystalline alloy is 600°C, and the Curie point of oriented silicon steel is 730°C, and can be used at 300°C to 400°C. (Electromagnetic compatibility means that an electronic transformer neither produces electromagnetic interference to the outside world, but can withstand electromagnetic interference from the outside world. Electromagnetic interference includes: audible audio noise and inaudible high-frequency noise. The main reason why electronic transformers produce electromagnetic interference It is the magnetostriction of the magnetic core. Soft magnetic materials with large magnetostrictive coefficients produce large electromagnetic interference.) The magnetostrictive coefficient of iron-based amorphous alloys is usually the maximum (27~30)×10-6, and must be taken Measures to reduce noise suppression interference. The magnetostriction coefficient of high magnetic permeability Ni50 permalloy is 25×10-6, and the magnetostriction coefficient of manganese-zinc ferrite is 21×10-6. The above three types of soft magnetic materials are materials that are prone to electromagnetic interference, so care should be taken during application. The magnetostriction coefficient of 3% oriented silicon steel is (1~3)×10-6, and the magnetostriction coefficient of microcrystalline and nanocrystalline alloy is (0.5~2)×10-6. These two types of soft magnetic materials are materials that are relatively prone to electromagnetic interference. The magnetostriction coefficient of 6.5% silicon steel is 0.1×10-6, the magnetostriction coefficient of high-permeability Ni80 permalloy is (0.1~0.5)×10-6, and the magnetostriction coefficient of cobalt-based amorphous alloy is 0.1 ×10-6 or less. These three soft magnetic materials are materials that are less prone to electromagnetic interference. The frequency of electromagnetic interference generated by magnetostriction is generally the same as the operating frequency of electronic transformers. If there isElectromagnetic interference below or above the operating frequency is caused by other reasons.
3. Complete functions. Electronic transformers are mainly divided into two types: transformers and inductors.
The functions completed by special components are discussed separately.
The transformer has three functions: power transmission, voltage conversion, and insulation isolation;
The inductor has two functions: power transmission and ripple suppression. There are 2 ways of power transfer.
The first is the transformer transmission method, that is, the alternating voltage applied to the original winding of the transformer produces magnetic flux changes in the magnetic core, causing the secondary winding to induce voltage and add it to the load, thereby increasing the electric power. Transfer from primary side to secondary side. The size of the transmitted power is determined by the induced voltage, that is, it is determined by the magnetic flux density variable ΔB per unit time. ΔB has nothing to do with magnetic permeability, but is related to saturation magnetic flux density Bs and residual magnetic flux density Br. From the perspective of saturation magnetic flux density, the Bs of various soft magnetic materials in descending order are: iron-cobalt alloy is 2.3~2.4T, silicon steel is 1.75~2.2T, iron-based amorphous alloy is 1.25~1.75T, The iron-based microcrystalline nanocrystalline alloy is 1.1~1.5T, the iron-silicon aluminum alloy is 1.0~1.6T, the high magnetic permeability iron-nickel permalloy is 0.8~1.6T, the cobalt-based amorphous alloy is 0.5~1.4T, iron-aluminum alloy The alloy is 0.7~1.3T, the iron-nickel-based amorphous alloy is 0.4~0.7T, and the manganese-zinc ferrite is 0.3~0.7T. As core materials for electronic transformers, silicon steel and iron-based amorphous alloys are dominant, while manganese-zinc ferrite is at a disadvantage. The second method of power transmission is the inductor transmission method, that is, the electric energy input to the inductor winding causes the magnetic core to be excited, converted into magnetic energy and stored, and then converted into electrical energy through demagnetization and released to the load. The amount of transmitted power is determined by the energy storage of the inductor core, that is, it is determined by the inductance of the inductor. The inductance is not directly related to the saturation magnetic flux density, but to the magnetic permeability. High magnetic permeability means large inductance, large energy storage, and large transmission power. The magnetic permeability of various soft magnetic materials in descending order is: Ni80 permalloy is (1.2~3)×106, cobalt-based amorphous alloy is (1~1.5)×106, iron-based microcrystalline nanocrystalline alloy It is (5～8)×105, iron-based amorphous alloy is (2～5)×105, Ni50 permalloy is (1～3)×105, silicon steel is (2～9)×104, manganese zinc ferrite The size is (1~3)×104. As the core materials for inductors, Ni80 permalloy, cobalt-based amorphous alloys, and iron-based microcrystalline and nanocrystalline alloys are dominant, while silicon steel and manganese-zinc ferrite are at a disadvantage. The transmission power is also related to the number of transmissions per unit time, that is, to the operating frequency of the electronic transformer. The higher the operating frequency, the greater the power transmitted under the same size core and coil parameters. Voltage conversion is completed by the turns ratio of the primary winding and the secondary winding of the transformer. Regardless of the size of the power transfer, the voltage conversion ratio of the primary side and the secondary side is equal to the turns ratio of the primary winding and the secondary winding. Insulation isolation through the transformer primary winding and secondaryThe insulation structure of the winding is completed. The complexity of the insulation structure is related to the magnitude of the applied and converted voltage. The higher the voltage, the more complex the insulation structure is. Ripple suppression is achieved through the self-induced potential of the inductor. As long as the current through the inductor changes, the magnetic flux generated by the coil in the magnetic core will also change, causing a self-induced potential to appear at both ends of the coil of the inductor, with its direction opposite to the direction of the applied voltage, thus preventing the change of current. The changing frequency of the ripple is higher than the fundamental frequency, and the current frequency of the current ripple is greater than the fundamental frequency. Therefore, it can be more suppressed by the self-induced potential generated by the inductor. The ability of the inductor to suppress ripples depends on the size of the self-inductance potential, that is, the size of the inductance, which is related to the magnetic permeability of the magnetic core. Ni80 permalloy, cobalt-based amorphous alloy, iron-based microcrystalline nanocrystalline alloy The high magnetic permeability is an advantage, while the low magnetic permeability of silicon steel and manganese-zinc ferrite is a disadvantage.
4. Improve efficiency Improving efficiency is a common requirement for power supplies and electronic transformers.
a. Improve the efficiency of electronic transformers.
For example: When the efficiency of a 100VA power transformer is 98%, the loss is only 2W, which is not much. But with hundreds of thousands or millions of power transformers, the total loss may reach hundreds of thousands of watts or even millions of watts. In addition, many power transformers have been running for a long time, and the total annual loss is considerable, possibly reaching tens of millions of kWh. Obviously, improving the efficiency of electronic transformers can save electricity. By saving electricity, fewer power stations can be built. By building fewer power stations, we can consume less coal and oil, emit less CO2, SO2, NOx, waste gas, sewage, soot and ash, and reduce environmental pollution. It not only saves energy but also protects the environment. Therefore, increasing efficiency is a major requirement for electronic transformers.
b. Design of electronic transformer
The losses of electronic transformers include core loss (iron loss) and coil loss (copper loss). Iron loss will always exist as long as the electronic transformer is put into operation and is the main part of the loss of the electronic transformer. Therefore, selecting magnetic core materials based on iron loss is the main content of electronic transformer design, and iron loss has also become a major parameter for evaluating soft magnetic materials. Iron loss is related to the operating magnetic flux density and operating frequency of the electronic transformer core. When introducing the iron loss of soft magnetic materials, it must be explained what the operating magnetic flux density and operating frequency are.
For example: P0.5/400, represents the iron loss at an operating magnetic flux density of 0.5T and an operating frequency of 400Hz. P0.1/100k represents the iron loss at an operating magnetic flux density of 0.1T and an operating frequency of 100kHz. Soft magnetic materials include hysteresis loss, eddy current loss and residual loss. Eddy current losses are inversely proportional to the resistivity ρ of the material. The larger ρ is, the smaller the eddy current loss is. The ρ of various soft magnetic materials in descending order is: manganese-zinc ferrite is 108~109μΩ?cm, iron-nickel-based amorphous alloy is 150-180μΩ?cm, and iron-based amorphous alloy is 130~150μΩ?cm. cm, cobalt-based amorphous alloy is 120~140μΩ?cm, high magnetic permeability permalloy is 40-80μΩ?cm, iron-silicon-aluminum alloy is 40-60μΩ?cm, iron-aluminum alloy is 30-60μΩ?cm, silicon steel is 40-50μΩ?cm, iron-cobalt alloy is 20～40μΩ?cm. Therefore, the ρ of manganese-zinc ferrite is 106 to 107 times higher than that of metal soft magnetic materials. It has small eddy currents at high frequencies and has an advantage in applications. But when the operating frequency exceeds a certain value, the insulator within the magnetic particles of manganese-zinc ferrite is broken down and melted, ρ becomes quite small, and the loss quickly rises to a very high level. This operating frequency is the operating frequency of manganese-zinc ferrite. Extreme operating frequency.
Electronic transformerFunction of each part
Electronic transformer for spotlights, downlights, etc. used in general store lighting. 220v AC to DC 12v50W, there is a magnet coil with 7 terminals inside. 3 resistors, 6 diodes, 4 capacitors, 2 transistors. Their functions are:
Resistors: 1 starting resistor, 2 current limiting resistor, 3 voltage stabilizing resistor
Diodes: Four diodes are used for rectification, and the remaining two are also used. Rectifier
Capacitor: Filter
Transistor: One is a switching transistor, and the other is a starting inductor. The function and calculation formula of the inductor is L=μN*NS/l (2-108)
Among them:
L: The inductance of the transformer coil [H]
l: The average length of the magnetic circuit of the transformer core [m]
N: Number of turns of the coil
S: Cross-sectional area of the magnetic circuit of the transformer core [m2]
μ: Magnetic permeability of the transformer core [H/m]
1. In the case of the same number: the inductance should be high or low, depending on the core material selected. For example, if the magnetic permeability is from 1k to 10k, the change in inductance is basically 10 times. However, you will find that due to the properties of various materials, as the magnetic permeability increases, the Curie temperature will drop sharply, or The loss will rise sharply, and there are always other parameters that are so bad that you cannot consider that the magnetic permeability cannot be blindly high, so other factors may become the main contradiction at this time and must be weighed;
2. Different turns: principles In other words, the turns ratio is guaranteed. For example, 1:2, 2:4, 4:8, and 20:40 can be chosen. Which one to choose may be based on a certain material selected. Only 4:8 may be suitable. At this number of turns, the inductor can satisfy the customer. The minimum value given can also ensure the minimum copper loss, etc. If it is less than this number of turns, the leakage inductance may be too large, and if it is more than this number of turns, the copper loss may be too severe
3. Inductance The level has nothing to do with saturation
As for the level of inductance: it may be that the level of inductance corresponds to the material, and is related to the magnetic permeability of the material to a certain extent. Generally speaking, materials with high magnetic permeability have smaller saturation magnetic induction intensity;
Saturation of the magnetic core: because the external magnetic field that magnetizes the core is too large, causing the internal magnetic moment of the material to be maximized in the same direction.
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