Definition, Function, and Classification of Power Transformers.
2026-05-09
Transformer is a device composed of a magnetic core (iron core) and two or more coils, which do not change positions with each other. It converts alternating current from one or more circuits through electromagnetic induction into voltage and current, and supplies a certain number of cycles of alternating current to another or two circuits.
Functions: In power supply lines, it plays roles such as voltage boosting, voltage reducing, isolation, rectification, frequency conversion, inversion, impedance matching, inverter, energy storage, and filtering.
1.Category:
①Classified by working frequency:
Power frequency transformer: operating frequency of 50Hz or 60Hz
Medium frequency transformer: operating frequency of 400Hz or 1KHz
Audio Transformer: Operating frequency of 20Hz or 20KHz
Super audio transformer: above 20KHz, not exceeding 100KHz
High frequency transformer: The operating frequency is usually above KHz to hundreds of KHz.
②Classified by purpose:
Power transformer: a transformer used to provide the power required by electronic devices
Audio transformer: a transformer used in audio amplification circuits and audio equipment
Pulse transformer: a transformer working in a pulse circuit, whose waveform is generally a unipolar rectangular pulse wave
Special transformer: a transformer with a special function, such as parametric transformer, voltage regulator transformer, super isolation transformer, transmission line transformer, leakage magnetic transformer
Switching power transformer: a transformer used in switching power circuits
Communication transformer: a transformer used for DC isolation and filtering in communication networks
①Classified by working frequency:
Power frequency transformer: operating frequency of 50Hz or 60Hz
Medium frequency transformer: operating frequency of 400Hz or 1KHz
Audio Transformer: Operating frequency of 20Hz or 20KHz
Super audio transformer: above 20KHz, not exceeding 100KHz
High frequency transformer: The operating frequency is usually above KHz to hundreds of KHz.
②Classified by purpose:
Power transformer: a transformer used to provide the power required by electronic devices
Audio transformer: a transformer used in audio amplification circuits and audio equipment
Pulse transformer: a transformer working in a pulse circuit, whose waveform is generally a unipolar rectangular pulse wave
Special transformer: a transformer with a special function, such as parametric transformer, voltage regulator transformer, super isolation transformer, transmission line transformer, leakage magnetic transformer
Switching power transformer: a transformer used in switching power circuits
Communication transformer: a transformer used for DC isolation and filtering in communication networks
2.Materials and classification of power transformers:
A. The main materials for power transformers are:
Skeleton (Bobbin, Base, Case)
Copper Wire
Magnetic Core (SI Steel Lamination)
Copper foil
Insulation tape (Tape)
Safety tape, also known as margin tape
Tube
Chemical materials: Solder Bar, Varnish, Epoxy, Glue, Thinner, Scaling Powder, Ink
A. The main materials for power transformers are:
Skeleton (Bobbin, Base, Case)
Copper Wire
Magnetic Core (SI Steel Lamination)
Copper foil
Insulation tape (Tape)
Safety tape, also known as margin tape
Tube
Chemical materials: Solder Bar, Varnish, Epoxy, Glue, Thinner, Scaling Powder, Ink
● Magnetic core: The main types of magnetic cores are:
①Steel sheet laminate (SI-STEEL, PERMALLOY);
②Soft magnetic ferrite materials (FERRITE CORE);
③Iron Powder Core; Widely used in the RF field, utilizing its inherent air gap distribution characteristics, it is suitable for various energy storage inductors, such as DC output chokes, split state input chokes, power factor correction (PFC) inductors, pulse transformers, DC to DC converters, continuous state relaxation inductors, dimming chokes, and EMI/RFI circuits. Its shape is usually circular.
Materials are usually distinguished by their Color Code, and their specifications are named in the form of T * - XX *. For example, in T130-26B, T represents Toroid, 130 represents a 1.3-inch outer diameter, 26 represents a 26 inch material, and B represents a type with the same outer diameter but different thicknesses. Suppliers are usually Mircomet, Jiacheng, Keda, and Keda.
④Iron silicon aluminum (Kool, Mu or Sendust); ARNOLD was first developed to replace iron powder core magnetic rings, with lower core losses, higher energy storage capacity than MPP, and better DC bias performance than Iron Powder. It is an ideal choice for energy storage and filtering inductor cores in switch mode power supplies.
The materials of iron silicon aluminum magnetic cores are mainly divided into ui: 26, 60, 90, 125.
⑤High Flux Core; It is a ring-shaped magnetic core material made of 50% nickel and 50% iron alloy powder, with air gaps distributed inside the core. It is the powder core material with the best bias ability, with a magnetic flux density of up to 15000 Gauss and significantly lower loss than iron powder cores. It is an ideal choice for modulating inductors in switching power supplies, line noise filters, pulse transformers, and flyback transformer cores. Especially in high DC current situations, the use of HF magnetic powder cores can effectively reduce the size of inductors.
The materials of high permeability magnetic cores are mainly divided into ui: 26, 60, 125, 147.
⑥Iron Nickel Molybdenum Magnetic Powder Core (Mpp Core); The material with the lowest magnetic loss in the powder core is a ring-shaped magnetic core composed of 79% nickel, 17% iron, and 4% molybdenum, with gaps distributed in the magnetic powder.
MPP magnetic cores have excellent electromagnetic properties in multiple aspects:
High resistance coefficient: low hysteresis and low eddy current loss; Inductance stability under high DC magnetization or DC bias conditions; It has the widest range of magnetic permeability options and is the best choice material for DC output filters in switching power supplies. The materials of MPP are mainly divided into ui: 26, 60125147160173200.
Mainly used in high-Q inductors, low loss filters, drive coils, radio frequency (RFI) filters, transformers, and inductor coils, etc.
⑦Amorphous state; It has the characteristics of high saturation magnetic induction intensity, high magnetic permeability, low loss, small size, strong resistance to strong electric interference, excellent frequency characteristics, and high temperature stability. Commonly used in PFC, energy storage inductors, current transformers, and so on. Amorphous materials are divided into two types: amorphous ribbon and amorphous powder magnetic core.
①Steel sheet laminate (SI-STEEL, PERMALLOY);
②Soft magnetic ferrite materials (FERRITE CORE);
③Iron Powder Core; Widely used in the RF field, utilizing its inherent air gap distribution characteristics, it is suitable for various energy storage inductors, such as DC output chokes, split state input chokes, power factor correction (PFC) inductors, pulse transformers, DC to DC converters, continuous state relaxation inductors, dimming chokes, and EMI/RFI circuits. Its shape is usually circular.
Materials are usually distinguished by their Color Code, and their specifications are named in the form of T * - XX *. For example, in T130-26B, T represents Toroid, 130 represents a 1.3-inch outer diameter, 26 represents a 26 inch material, and B represents a type with the same outer diameter but different thicknesses. Suppliers are usually Mircomet, Jiacheng, Keda, and Keda.
④Iron silicon aluminum (Kool, Mu or Sendust); ARNOLD was first developed to replace iron powder core magnetic rings, with lower core losses, higher energy storage capacity than MPP, and better DC bias performance than Iron Powder. It is an ideal choice for energy storage and filtering inductor cores in switch mode power supplies.
The materials of iron silicon aluminum magnetic cores are mainly divided into ui: 26, 60, 90, 125.
⑤High Flux Core; It is a ring-shaped magnetic core material made of 50% nickel and 50% iron alloy powder, with air gaps distributed inside the core. It is the powder core material with the best bias ability, with a magnetic flux density of up to 15000 Gauss and significantly lower loss than iron powder cores. It is an ideal choice for modulating inductors in switching power supplies, line noise filters, pulse transformers, and flyback transformer cores. Especially in high DC current situations, the use of HF magnetic powder cores can effectively reduce the size of inductors.
The materials of high permeability magnetic cores are mainly divided into ui: 26, 60, 125, 147.
⑥Iron Nickel Molybdenum Magnetic Powder Core (Mpp Core); The material with the lowest magnetic loss in the powder core is a ring-shaped magnetic core composed of 79% nickel, 17% iron, and 4% molybdenum, with gaps distributed in the magnetic powder.
MPP magnetic cores have excellent electromagnetic properties in multiple aspects:
High resistance coefficient: low hysteresis and low eddy current loss; Inductance stability under high DC magnetization or DC bias conditions; It has the widest range of magnetic permeability options and is the best choice material for DC output filters in switching power supplies. The materials of MPP are mainly divided into ui: 26, 60125147160173200.
Mainly used in high-Q inductors, low loss filters, drive coils, radio frequency (RFI) filters, transformers, and inductor coils, etc.
⑦Amorphous state; It has the characteristics of high saturation magnetic induction intensity, high magnetic permeability, low loss, small size, strong resistance to strong electric interference, excellent frequency characteristics, and high temperature stability. Commonly used in PFC, energy storage inductors, current transformers, and so on. Amorphous materials are divided into two types: amorphous ribbon and amorphous powder magnetic core.
●Skeleton: functionally divided into three categories: 1. Bobbin, 2. BASE, 3. CASE
The function of BOBBIN: It is a type of material used as a winding carrier for coils and to insulate the coil from the magnetic core.
The function of BASE: It is a type of material used to fix coils and position leads for easy installation on circuit boards. There are two options: with or without a PIN.
The function of CASE is to fix, protect, and isolate coils, and to position leads for easy installation on circuit boards. Mostly used for coil sealing.
In terms of materials, it is mainly divided into PHENOLIC, PBT, PET, LCP, PPHS, PA66, and so on.
①PET: Polybutylene terephthalate, a thermoplastic material.
Characteristics: A is not easily deformed; High temperature soldering has a certain degree of melting loss; C has high strength; The cost is relatively high.
②There are many types of PET materials, and each manufacturer has different names for PET, such as T102, T102G30, FR530L (f1), FR-515, and so on
PBT: belongs to thermoplastic materials.
Characteristics: a is prone to deformation; B is prone to melting damage; Low cost; D has a certain degree of resilience.
Materials such as 4115420SEO, 4115, etc
③LCP：（Liquid crystal polyester）， Belongs to thermosetting materials.
Features: High strength, not too late to break, high cost. High voltage transformers commonly used to drive backlight sources, such as UI, EE, EPC, and other multi slot skeletons. Materials such as E4008, E4010, E4810, etc.
④NYLON (PA66: Ployamide type 66 nylon): Nylon is a thermoplastic material.
Characteristics: a. High toughness; High temperature soldering has a certain degree of melting loss; Late deformation (glass fiber can be added to increase strength). Materials such as 101L, TE250F6, A3X2G7, KF4357G6, etc.
It should be clarified that thermoplastic and thermosetting molds are not interchangeable.
⑤Phenolic resin: commonly known as PHENOLIC, belongs to thermosetting materials.
Characteristics: A is not easily deformed; B High temperature resistance and high-temperature soldering; High intensity. Disadvantage: It is brittle and easily damaged. There are many electric wood materials currently used, each with different properties and costs. For example, T375j, 1403G4, M9630, AM-113, CPJ-860, etc., the different performance makes them suitable for different types of skeletons.
The function of BOBBIN: It is a type of material used as a winding carrier for coils and to insulate the coil from the magnetic core.
The function of BASE: It is a type of material used to fix coils and position leads for easy installation on circuit boards. There are two options: with or without a PIN.
The function of CASE is to fix, protect, and isolate coils, and to position leads for easy installation on circuit boards. Mostly used for coil sealing.
In terms of materials, it is mainly divided into PHENOLIC, PBT, PET, LCP, PPHS, PA66, and so on.
①PET: Polybutylene terephthalate, a thermoplastic material.
Characteristics: A is not easily deformed; High temperature soldering has a certain degree of melting loss; C has high strength; The cost is relatively high.
②There are many types of PET materials, and each manufacturer has different names for PET, such as T102, T102G30, FR530L (f1), FR-515, and so on
PBT: belongs to thermoplastic materials.
Characteristics: a is prone to deformation; B is prone to melting damage; Low cost; D has a certain degree of resilience.
Materials such as 4115420SEO, 4115, etc
③LCP：（Liquid crystal polyester）， Belongs to thermosetting materials.
Features: High strength, not too late to break, high cost. High voltage transformers commonly used to drive backlight sources, such as UI, EE, EPC, and other multi slot skeletons. Materials such as E4008, E4010, E4810, etc.
④NYLON (PA66: Ployamide type 66 nylon): Nylon is a thermoplastic material.
Characteristics: a. High toughness; High temperature soldering has a certain degree of melting loss; Late deformation (glass fiber can be added to increase strength). Materials such as 101L, TE250F6, A3X2G7, KF4357G6, etc.
It should be clarified that thermoplastic and thermosetting molds are not interchangeable.
⑤Phenolic resin: commonly known as PHENOLIC, belongs to thermosetting materials.
Characteristics: A is not easily deformed; B High temperature resistance and high-temperature soldering; High intensity. Disadvantage: It is brittle and easily damaged. There are many electric wood materials currently used, each with different properties and costs. For example, T375j, 1403G4, M9630, AM-113, CPJ-860, etc., the different performance makes them suitable for different types of skeletons.
Formally, it is mainly divided into vertical (VERTICAL) and horizontal (HORIZONTAL)
It can also be divided into two categories: Surface Mount Devices (SMD) and Plug ins (Lead through or Through Hole).
●Wire: Its types mainly include enameled wire, multi-layer insulated wire, wrapped wire, and PVC wire
Common wire gauges: mmG (Japanese gauge), AWG (American gauge), SWG (British gauge), where wire gauge refers to the area of the diameter of bare wire
1) Enamelled wire or Magnet wire:
Divided by paint coating:
Polyurethane enameled wire (UEW) is divided into 0UEW (Triple), 1UEW (Heavy or Double), and 2UEW (Single) according to the decreasing thickness of the coating. UEW is the most widely used wire type, with 2UEW and 1UEW being the most commonly used.
Its characteristic is that it does not require pre stripping before soldering, and can be directly immersed in a soldering furnace for soldering.
In terms of form, it can be divided into three categories: single strand, multi strand twisted wire (LITZ also known as Li branch line), and wire wrapped wire (UTSC). Among them, LITZ refers to one-time or multiple twisting, with the aim of reducing the impact of skin effect and reducing the hardness of copper wire that is difficult to produce. UTSC refers to the use of glass fiber to wrap multiple strands of untwisted wire.
It can also be divided into two categories: Surface Mount Devices (SMD) and Plug ins (Lead through or Through Hole).
●Wire: Its types mainly include enameled wire, multi-layer insulated wire, wrapped wire, and PVC wire
Common wire gauges: mmG (Japanese gauge), AWG (American gauge), SWG (British gauge), where wire gauge refers to the area of the diameter of bare wire
1) Enamelled wire or Magnet wire:
Divided by paint coating:
Polyurethane enameled wire (UEW) is divided into 0UEW (Triple), 1UEW (Heavy or Double), and 2UEW (Single) according to the decreasing thickness of the coating. UEW is the most widely used wire type, with 2UEW and 1UEW being the most commonly used.
Its characteristic is that it does not require pre stripping before soldering, and can be directly immersed in a soldering furnace for soldering.
In terms of form, it can be divided into three categories: single strand, multi strand twisted wire (LITZ also known as Li branch line), and wire wrapped wire (UTSC). Among them, LITZ refers to one-time or multiple twisting, with the aim of reducing the impact of skin effect and reducing the hardness of copper wire that is difficult to produce. UTSC refers to the use of glass fiber to wrap multiple strands of untwisted wire.
Complete classification of transformers
Regarding Low-frequency Transformers.
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