Key points of transformer design

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Key points of transformer design [Copy link]

Key points of transformer design

(1) Both the pulse source and the load are field effect tubes, and their input capacitance is relatively large. Usually, the magnetic reset is accelerated by reducing L△, but reducing the inductance is likely to cause under-damped oscillation. In severe cases, it will cause the secondary conduction or cutoff of the V2 field effect tube to be insufficient. Therefore, the primary inductance value must be controlled to ensure that the transformer can achieve magnetic reset and does not have under-damped oscillation.

Oscillation, when controlling the inductance value cannot achieve satisfactory results, the secondary parallel resistance R1 can be adjusted; when R1 is reduced, the oscillation will disappear, but the recovery time will be prolonged, so there should be an adjustment range between the circuit and the transformer to ensure that the magnetic state of the transformer is reset without oscillation. The optimal state should be the critical state, but it is difficult to design the circuit to work in the critical state.

(2) When designing a single-ended forward excitation transformer, the core selection is also very important. Generally, the core is required to have a higher flux density increment.

△B value, smaller core loss and lower pulse magnetic permeability μP value; the core materials that can be used for excitation transformers include ferrite, iron-based amorphous, 1J6721, 1J34Kh, etc. When the frequency is higher, ferrite pot-shaped cores can be used, and when the frequency is lower, iron-based amorphous, 1J6721, 1J34Kh and other cores can be used.

(3) The design of the feedback winding mainly depends on the withstand voltage of V1, but the number of turns of the feedback winding should satisfy the following relationship:

Upτpmax<（Np1/Np2）Up(T－τpmax)

　　The current of the feedback winding is basically equal to the magnetizing current, generally only 50% of the primary current, and sometimes close to the primary current, which mainly depends on the working magnetic flux density △B value and the primary inductance value.

　　(4) When designing a higher voltage switching power supply, Ec2 is generally higher. In order to improve the reliability of the low-voltage excitation circuit, the primary and secondary of the excitation transformer are shielded and grounded, which will effectively ensure that the low-voltage excitation circuit will not be damaged.

　　The above points are the key points in designing a single-ended forward excitation transformer. When designing, the influence of high-frequency skin effect on wire resistance, as well as preventing instantaneous saturation of the transformer and reducing leakage inductance should be considered; the calculation and analysis of these issues can refer to the general pulse transformer design.