Medium Frequency Transformer

Medium Frequency Transformer Product Introduction：

IF transformers are generally paired with capacitors to form a tuned circuit. IF transformer is divided into single-tuned and double-tuned two kinds. Only the primary coil and the capacitor form a tuned loop is called single-tuned IF transformer, if the tuned loop with capacitive or inductive coupling is called double-tuned IF transformer. General transistor radio has three single-tuned IF transformers, three positions are not interchangeable.

Medium Frequency Transformer Working Principle：

The IF transformer (commonly known as mid-period) is a transformer with a fixed resonance circuit unique to super-aberratic transistor radios, but the resonance circuit can be fine-tuned within certain limitations in order to achieve an uncluttered resonance frequency (465kHz) when connected to the circuit. Fine tuning is accomplished with the aid of a change in the relative position of the magnetic core. Its mechanism is that most of the IF transformers in radios are single-tuned, simpler in structure and occupy less space. Due to the low input and output impedance of the transistor, in order to make the IF transformer match the input and output impedance of the transistor, the primary has a tap and has a secondary coupling coil with few turns. The advantage of double-tuning type is better selectivity and wider passband, mostly used in high-performance radios.

The role of medium frequency transformer：

The function of IF transformer is to transform the power supply voltage of IF generator (such as silicon controlled IF power supply, IF generator or electron tube oscillator, etc.) into the voltage required by quenching induction coil or other devices.

IF transformers are generally dry type and cooled in water. When high-frequency current passes through a conductor, the current distribution on the cross-section of the conductor is not uniform by the influence of the sub-collector effect and the neighbourhood effect. The skin depth of the current within the copper is:

So its primary and secondary windings are wound with rectangular hollow copper tubes, which are cooled by water. The current density is chosen with respect to the water flow up to several + amperes per square millimetre. The windings can be wound into cylindrical or pancake type, and when the secondary current is large, copper plate can also be used to weld into cylindrical windings. Copper tube should be able to withstand 490kPa (5kgf/cm), 5min pressure test, copper plate welded windings should be able to withstand 196kPa (2kgf/cm), 5min pressure test without leakage. When the primary and secondary windings are cake type, the two overlapping arrangement; with cylinder type, the concentric arrangement.

Iron core with 0.2mm or thinner electrical steel sheet stacked, due to the intermediate frequency is much higher than the frequency, the core will produce a large eddy current and hysteresis loss, so the flux density can not be too high. When the frequency is 2500Hz, the magnetic density of 0.75T and below; when the frequency is 8000Hz, take 0.3T and below. And the core of the stack needs to be placed between the appropriate welding of rectangular hollow copper tube heat sink, using water-cooled structure. Heat sink made of 1mm thick copper plate, welded around the square copper pipe, two neighbouring heat sinks between the stack thickness is generally about 15mm.

If the use of high saturation, low unit loss, moisture resistance and resistance to thermal aging of the ferrite for the core of the material, you can reduce the temperature rise of the core. The new manganese-zinc ferrite Mn-Zn-4000 is one of them.

This type of ferrite is produced in a dry process. In mass production, it can be wound into shape in a chain winding furnace. However, as far as quality is concerned, it is preferable to produce them by the wet method of precipitation and winding them in a vacuum furnace.

In order to reduce the excitation current, the core can be stacked, lap structure, and with 618 epoxy resin mixed with ferrite powder to fill the gap. Taking into account the high porosity of ferrite (0.1 ~ 10%), the core must be dipped in paint to improve moisture resistance. In this way, 1000kVA transformer ferrite core and electrical steel sheet core compared to the no-load loss reduction of 4.2kW, only 7% of the original value, while the excitation current only increased by 4.2A, for the original value of 1.72 times, the core does not use water cooling to meet the temperature rise requirements.

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