How to design choke transformer

Brief discussion on how to design choke transformer

choke transformer is a special type of transformer, which is usually used to connect DC and AC inductive coils ", plus the iron core to form a filter transformer, which can reduce the peak voltage, reduce the invalid power, and improve the filter electrical components of effective power. It is widely used in electronic circuits. Among the electrical products that have been updated day by day, the requirements for their electrical characteristics are more stringent. How to make the quality better, it is very necessary to add choke transformer. Therefore, how to better design a product with good performance puts forward higher requirements for designers. The design method provided in this paper is how to design a choke transformer with good cost performance, and how to reasonably select and estimate the output power, skeleton model, wire diameter, temperature rise, etc

as we all know, there are many inductance calculation methods, and the general calculation formula is as follows:

L = inductance value (H Henry)

n = number of coils

= permeability

AE = cross-sectional area of core (cm2)

LC = magnetic circuit length (CM)

I = current (a)

so there are many factors that affect the inductance value, which are directly proportional to the permeability, the square of the number of coils, and the cross-sectional area of core, and inversely proportional to the average magnetic circuit length

if you want to determine the size of the choke transformer, you need to calculate according to the following calculation formula:

calculate the capacity of the choke transformer va=li2

the adjustment method is if there is no gap iron core:

li2=3.35ae2 (empirical formula)

if there is EI iron, this formula can be transformed into:

where: l= inductance value (H Henry), i= current value (a); Ae= sectional area of core (cm2)

ae=a B 0.9 (cm2) (a= length of middle core cm, b= thickness of core cm)

as shown in Figure 1

in order to explain the above problems in more detail, this paper gives an example of the design method of EI choke transformer

the specification conditions of this transformer are as follows:

① inductance l=0.5h

so as to improve the dispersion of filler and improve the storage length of glass fiber ② frequency of use f=50hz

③ current a=70ma (DC)

④ DC resistance =35 10%

1. First, determine the size of iron core by capacity:

according to the above formula:

ei-28-a0 (thickness 11mm) s=1.1 0.8 0.9=0.8 cm2)

2 The core volume is

v= (2.5 2. (0.6 1.7)) 1.1 0.9=4.91 (cm3)

3, the magnetic circuit length lc=6.2cm

see Figure 2 for details of EI28 core size

4. The curve chart in the annex can be obtained (see Figure 4 on the next page):

according to figure 4, the following results and gap length values can be quickly obtained:

n "thin-walled", that is, the wall thickness of the reduced product = 6.2 11.5/0.07=1018 (circles)

5. Calculate the wire diameter: below 70 ℃ temperature rise, the current density needs to be below 5a, and the optional wire diameter is 0.18, but it is still necessary to confirm whether the coil occupation rate can be met

6, rdc= the value of 0.18/km of the average winding length

=5.26 1018 715/100000=37.6

actual measurement: 35.2

7. Due to the need for clearance, clearance pieces are required between iron cores E and I for isolation, so according to experience, the combination of iron cores is as follows:

① when there is no clearance piece l=0.25h (when the current is 0.5A)

② 025mf1 (between 0.025mm thick), l=0.47h (when the current is 0.5A)

③ 45k1 (between 0.45mm thick),the, L=0.5h (when the current is 0.5A)

④ 45k1+025g1 (between 0.475mm thick), l=0.43h (when the current is 0.5A)

the combination method is as follows:

this transformer uses a 45k insulating cardboard as a clearance piece, which can meet the above requirements

of course, if you open a certain gap length in the e-piece of the core, and then weld the E and I pieces together, the anti vibration effect is better. If the core is quite large, you need to add a special special material gap piece for anti vibration. Therefore, in order to design a good choke transformer, it needs long-term experience summary and continuous improvement, so as to meet the requirements of customers satisfactorily