Bobbin is mainly functioned as a support for winding, generally made by plastic, which has a variety of types, for example, PHONIC, NYLON, NYLON-66, PBT, PET, LCP or so. PBT, PET, LCP are the most commonly used.

The simply distinguish of bobbin that several commonly used as below：

Phonic black withstand high-temperatures   high bad, fragile non-recyclable middle

Nylon transparent thermo-labile, heat deformation bad, easily deformed good recyclable high

PBT, PET white, black, yellow amid phonic and nylon recyclable low

Nylon bobbin will be given fiberglass to increase its hardness.

Most of Phonic bobbin contains urea can produce urea acid that has an etching to cooper wires. Given that, part of product with thin wires is labeled to use phonic bobbin without urea that the main ingredient is phonic powder. Commonly used phonic powder as below:

Changchun phonic powder: T373, T357, T375

Zhuyou phonic powder: PM-9820, PM-9630

Dubang phonic powder: PE9087

They are distinguished from thermotolerance, liquidity, moisture content.

Example with Changchun phonic powder

Liquidity: T373(Great)>T357>T375

Thermotolerance: T375(High)>T357>T373

Moisture content: T375(Less)>T357>T373

So sometimes, when some clients asking high-quality take transformer to do environmental experiments, they designate specific phonic powder for bobbin. Quotation needs to be rechecked on the basis of clients’ requirements.

Pertaining to PBT and PET, they are poor at heat-resistance and try to avoid using them. The largest reason is easily distortion of PIN after tinning, which brings numerous troubles to later procedures. But due to itsfragile character of thin guard of multiple groove bobbin in the middle as well as PBT and PET material used for bobbin of low-frequency transformer going with PIN, bobbin that kinds of material has a certain share in the market so far.

For example: Dubang: FR530

Qiyi: 420-SEO

At present, there has a refined material called LCP to replace PBT,PET. It is largely improved in heat-resistance, widely applied to base of SMD inductor. PBT is less heat-resistance than PET，Bobbin is made with windows in the top of PIN given that those material.(As figured) Now the upcoming internet transformer produced will adapt DAP as its bobbin material, acting more excellent than LCP.

PIN varying in amount will be assembled in the coil shield to link winding wires as a good conductor after being soldered in PC board.

The testing items of bobbin

A.     Material   distinguish it from color, chart above for reference, second is to burn it with open flames, phonic material is ash-like, falling loop by loop, no flame. Nylon is combustible and easy to deform in between PBT and PET.

B.      Dimensions b-1. PIN distance, rank distance

b-2. length, width, height of bobbin

b-3. The area of window

b-4. breadth

C.      Appearance Currently it tends to be light, thin, small, but no burrs and angle R has better to do not over 2mm so as to keeping winding easy. In addition, paying attention to safe regulations is in conformity to products.

D.     Voltage-endurance requirement

AC 3.5KV/5mA/60Sec, no punch-though phenomenon

E.      Solderability

Put PINs into high-temperature tin stove about 2~3 seconds, take it perpendicularly, PINs are not allowed to be knock-kneed, emerged, sinked; PIN polished, no yellow or black spots, no icicles.

Specifications of bobbin

Bobbin usually is dubbed according to its matched core.

For example, one bobbin, matched with EC35(EER35) core, will be called EC35(EER35). Except that, bobbin has two shapes in the appearance: single groove and multi-groove. See picture below:

So it is not enough that we only specify specifications when talking bobbin, is it vertical type or horizontal type? How many pitches? Bounded type or pin-indexed type? Single groove or multi-groove? Clapboard between grooves is regular(approximately 1.0mm) or thickening(approximately 1.5~2mm)? How long of rank distance and PIN distance? If necessary, drawings are good to express it clearly.

Method to identify PIN

Generally speaking, PIN1 is labeled in the process of making. The first step is to spot it.

Depicted by sectional plane, as figure

Depicted by Embossed spot in the top, as figure

Depicted by debossed plane, as figure

Depicted BY different pitches, as figure

A few bobbin has number marker in PIN need to be followed; No marking, the mark it in order to wrong PIN winding. Apart from, bobbin of EP type has two approaches to count PIN, general one and computing one.

Above are common pitch-counting method, sometimes customers require others standards what the criteria are for us.

Anti-fire class

It means the flammability class of material itself, dividing into 4 ranks: HB, V1,V2, V0.

HB: Non-fire class

V0: not ignite cotton, but burning doesn’t last 10s per piece

V1: not ignite cotton, but burning last over 10s/piece

V2: will ignite cotton.

Core

Classification of core

The major material of core for high-frequency transformer is FERRITE. The major material for low-frequency is copper. How to distinguish them from each other, as below:

Advantages of FERRITE:

1.      Be of high-impedance

2.      Low magnetic loss

3.      Apply to higher frequency

4.      Excellent winding combination

5.      Installment easily

6.      High Q-value

Disadvantages:

1.      Low Curie temperature

2.      Lower saturated magnetic flux density.

Curie temperature：the temperature at which certain materials lose their permanent magnetic properties, to be replaced by induced magnetism.

What can  be divided into in term of construction:

LaminationSi,Fe annealed sintering (50~10KHz)

Non-annealed non-sintering (50-10KHz)

Ni,Fe PC(Taiwan, South Korea) 78%~80% Ni-content

Working frequency can be ranged from 50KHz to 300KHz

PB(English, Japan) 45%~50% Ni-content

FerriteNiZn : working spectrum can reach 250MHz

MnZn: high-permeability

High Bs, Low Po

High Q-value

MgZn: Low cost, low performance

Mental powder  Fe powder core：different color with others, low permeability.

Compound：MPP：grey, low Po. Great thermostability, but high cost.

High-flux: tan, great DC superimposition characteristic

Sendust: Black, great DC superimposition characteristic

Amorphous state nanocrystalline: High-Bs, High-u great low-frequency figure, excellent thermosteability.

Amorphous state: high Bs, low Po, amazing anti-DC superimposition characteristic

Performance Comparison of common cores

Material  loss DC superimposition character relatively cost range of frequency saturated magnetic-flux density thermosteability