Overview
For pulse transformers, the main consideration is the waveform transmission problem. Even if it is the same wide-band transformer, as long as the waveform can meet the design requirements, the core can also work in the non-linear region. Therefore, its appearance can be made much smaller than a communication transformer. Also, except for passing high-power pulses, the transmission loss of the transformer is generally not large. Therefore, the size of the magnetic core taken depends on whether the magnetic flux is saturated when the pulse passes, or whether the temperature rise caused by the iron loss exceeds the allowable value. The latest analysis method of pulse transformers today is to process pulse transformers in a distributed parameter manner, which is called transmission type pulse transformers.
Structure
The structure of the pulse transformer is similar to the general control transformer, and the core part of the pulse transformer is formed by the conductive winding and the magnetic core. However, most of the pulse transformer cores are made into a ring, and the material is generally permalloy or manganese-zinc-iron magnetic ceramics; the windings are double-sided or triple-sided, and the third winding is generally set to improve certain performance. The characteristic of the winding is to change the polarity of the pulse signal at the output terminal by changing the winding direction of the secondary winding.
Working principle
The working principle of pulse transformer uses iron core The magnetic saturation performance of the transformer turns the input sine wave voltage into a narrow pulse-shaped output voltage. It can be used for burner ignition, thyristor triggering, etc. The structure of the pulse transformer is that the original winding is sleeved on a core column made of silicon steel sheets with a larger section, and the secondary winding is sleeved on a core column made of permalloy material with a smaller section, which is easy to be highly saturated. It can be placed between the two columns. Set the magnetic shunt. The relationship between voltage and magnetic flux, the input voltage u1 is a sine wave, and a sine magnetic flux Φ1 is generated in the iron core on the left. The magnetic flux Φ2 in the iron core on the right is highly saturated and is a flat-top wave. It only changes near the zero value and is immediately saturated to reach a fixed value. At the moment when Φ2 crosses the zero value, a very steep narrow pulse electromotive force e2 is induced in the secondary winding. There is an air gap in the magnetic shunt, and Φσ basically changes linearly, which is similar to magnetic leakage. Its function is to ensure that Φ1 is a sine wave.
Comparison of the two
The basic principle of all pulse transformers is the same as that of ordinary transformers (such as audio transformers, power transformers, power transformers, etc.), but with regard to the magnetization process of the magnetic core It seems that there is a difference, the analysis is as follows:
(1) The pulse transformer is a transformer that works in a transient state, that is, the pulse process occurs in a short period of time, and it is a smooth top Square wave, while the general common transformer works in continuous and unchanging magnetization, and its alternating signal changes according to a sine wave.
(2) The pulse signal is a repetitive period, at a certain interval, and only The positive or negative voltage, and the alternating signal is continuously repeated, with both positive and negative voltage values.
(3) Pulse transformers require that the waveform be transmitted without distortion, that is, the leading edge of the waveform and the top drop should be as small as possible. However, these two indicators are contradictory.
Main uses
Pulse transformers are widely used in radar and conversion technology; the matching of load resistance and the characteristic impedance of the feeder; increasing or decreasing the pulse voltage; changing the polarity of the pulse; The isolation of the primary circuit and the primary circuit uses several secondary windings to obtain the phase relationship; isolates the DC component of the power supply; in the transistor (or tube) pulse oscillator, the collector (anode) and the base (gate) are obtained Strong coupling; several secondary windings are used to obtain several pulses of different amplitudes, so that the plate loop and gate loop of the electron tube, or the collector and base of the transistor form a positive feedback to generate self-excited oscillation; As power synthesis and conversion components, etc.