Points to be aware of when selecting transformers

A transformer is a device that uses the principle of electromagnetic induction to change the AC voltage. The main functions are: voltage conversion, current conversion, impedance transformation, isolation, voltage regulation (magnetic saturation transformer), etc., which are the most common parts of the circuit. To make the circuit stable, choose the right transformer. Here are some questions for transformer selection:

First, in the production of transformers, what are the advantages and disadvantages of coil winding and manual winding?

The advantage of the machine-wound transformer is that it is efficient and beautiful in appearance, but the toroidal transformer that winds a small hole is troublesome, and the reliability of the insulation process is not as good as the manual winding. Manual winding can make the leakage magnetic flux of the transformer very small. It can be adjusted at any time during the winding process for the layout of the coil turns. Therefore, the real Hi-END transformer must be hand-wound, hand-wound. The only drawback is the low efficiency and slow speed.

Second, the ring type, EI type, R type, C type of power transformers which one is best?

They all have their own advantages and disadvantages, and no one has the best, so strictly speaking which kind of transformer can do the best. Structurally speaking, the ring type can achieve the least magnetic leakage, but the EI type can make the medium frequency density better. In terms of magnetic saturation alone, the EI type is stronger than the ring type, but in terms of efficiency, the ring type is superior to the EI type. Nevertheless, the key to the problem is whether you can make the best of their strengths by taking advantage of their strengths and avoiding weaknesses. This is the most fundamental thing to do with transformers.

In the current imported amplifiers, the application of toroidal transformers is still the mainstream, which basically illustrates a problem. Enthusiasts should be objective and fair in evaluating the transformer. You can't take a bad reference and say it is not good. Some people say that a toroidal transformer is easy to magnetically saturated, so why not try to make it difficult to magnetically saturate it? This can be done by technical means. If you don't have to work hard or simply save money, then it is easy to magnetically saturated. In the same way, as long as you carefully make, the efficiency of the EI-type transformer can also be very high.

The quality of the transformer has a great influence on the sound, because the transmission energy of the transformer is closely related to the iron core and the coil, and the transmission rate plays a decisive role in the influence of the sound. Like the EI type transformer, people usually think that its intermediate frequency is thicker and the high frequency is more slender. Why? Because its transmission speed is relatively slow. And what about the ring? The low frequency is fierce, and the middle and high frequency are slightly weaker. Why? Because it transmits faster, but if you change the structure through an effective structure, you can do both the ring and the EI, so the key is to see how you do it.

But at least for sure, the R-type transformer is not too easy to do. It can also be used to make a small current preamplifier and CD player power supply. If it is used as a power supply for the post amplifier, there are serious defects. Because the structure of the R-type transformer itself is not easy to change, the ring type and the EI type are relatively easy to change the structure to achieve the humming purpose. Power amplifier power supplies made with R-type transformers usually have a very low-pitched sound and lack aura. The low-frequency is often harder without bounce.

Third, the silicon core of the transformer core, the greater the silicon content, the better?

It is not seen that the amount of silicon contained in the silicon steel sheet has little effect on the quality of the transformer, and the orientation and non-orientation are related to the type of the iron core. Secondly, even if the same type of iron core is not well processed, the quality difference is very large, and the difference is sometimes as high as 40%.

A good iron core and the same material are critical for the heat treatment and wire winding process. A good heat treatment requires only a small 10 mA excitation current to reach 15,000 gauss, while a poor heat treatment may require a 50 mA excitation current. The corresponding 15,000 Gauss, the difference between the two is very large. Judging from the professional point of view, the core is good and bad, mainly through the excitation current, iron loss, saturation parameters of several indicators to carry out comprehensive * price.

Fourth, if the ribbon type silicon steel sheet of the toroidal transformer adopts the splicing process, does it mean that the quality is definitely not good?

It can't be generalized, but the spliced ​​break head is not too much, because there is one more magnetic leakage point for one more break, so the joint point should not exceed 2–3. In the production process, the broken ends should be pre-treated by pickling, but the ring-type transformers for the manufacture of high-end audio equipment are strictly the best, and the quality of the process is more guaranteed.

5. What is the stress of the silicon steel sheet material in the transformer?

Since the loss of silicon steel in the alternating magnetic field is small, the transformer mainly uses silicon steel sheets as magnetic materials. Silicon steel sheets can be divided into hot rolling and cold rolling. Cold rolled silicon steel strips have the advantages of small volume, light weight and high efficiency due to their high magnetic permeability and low loss. The performance of hot rolled silicon steel strips is slightly inferior to that of cold rolled silicon steel strips.

Ordinary EI type transformers are made of silicon steel plate into 0.35–0.5mm thick E-type and I-type films, which are heat-treated and then inserted into the winding wire package. These cores are mostly made of hot-rolled silicon steel sheets (silicon content). Very high quality silicon steel sheets are D41, D42, D43, D301). The cores of the ring-type and C-type transformers are formed by winding a cold-rolled silicon steel strip, wherein the C-type transformer is formed by heat-treating and varnishing.

The leakage inductance of the transformer is generated by magnetic flux that does not pass through the primary and secondary coils, and these magnetic fluxes pass through the air to self-close the magnetic circuit. Enhancing the coupling density between the primary and secondary of the transformer can reduce the leakage inductance. A good transformer has a leakage inductance of no more than 1/100 of the primary coil inductance, and a high-fidelity Hi-Fi amplifier output transformer should not exceed 1/500.

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