What Is a Pulse Transformer?

The so-called pulse transformer is a broadband transformer. For communication transformers, nonlinear distortion is an extremely important indicator. Therefore, the transformer is required to work at the initial permeability of the magnetic core, so that even if the transformer has a very small power like the input transformer, the shape has to be quite large. . In addition to the frequency characteristics of the transformer, how to reduce losses is also a concern.

For the pulse transformer, it mainly considers the waveform transmission problem. Even if it is also a 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 shape can be made much smaller than a communication transformer. In addition, except for passing high-power pulses, the transmission loss of the transformer is generally not large. Therefore, the size of the core taken depends on whether the magnetic flux is saturated when the pulse passes, or whether the temperature rise caused by iron loss exceeds the allowable value. The latest analysis method of pulse transformers today is to treat pulse transformers in a distributed parameter manner, which is called transmission pulse transformers ^[1]

The structure of a pulse transformer is similar to that of a general control transformer. It consists of a conductive winding and a magnetically permeable core.

The working principle of the pulse transformer uses the magnetic saturation performance of the iron core to transform the input sine wave voltage into a narrow pulse-shaped output voltage transformer. It can be used for ignition of burner and trigger of thyristor. The structure of the pulse transformer is that the original winding is sleeved on a core pillar made of silicon steel sheets with a large cross section, and the secondary winding is sleeved on a core pillar made of permalloy material with a small cross section and easily highly saturated. Set the magnetic shunt. The relationship between voltage and magnetic flux, the input voltage u1 is a sine wave, and a sine magnetic flux 1 is generated in the left core. The magnetic flux 2 in the iron core on the right is highly saturated and is a flat-topped wave. It changes only around zero and immediately saturates to a fixed value. At the moment of 2 zero crossing value, a very steep narrow pulse electromotive force e2 is induced in the secondary winding. There is an air gap in the magnetic shunt. basically changes linearly, similar to the magnetic leakage. Its role is to ensure that 1 is a sine wave.

The basic principle of all pulse transformers is the same as general transformers (such as audio transformers, power transformers,

Pulse transformers are widely used in radar and conversion technology; matching of load resistance and feeder characteristic impedance; raising or lowering the pulse voltage; changing the polarity of the pulse; isolation of the transformer secondary circuit and the primary circuit using several secondary windings to obtain the phase Relationship; isolate the DC component of the power supply part; make strong coupling between the collector (anode) and base (gate) in the transistor (or tube) pulse oscillator; use several secondary windings to get several different amplitudes The value of the pulse makes the plate circuit and gate circuit of the tube, or the positive feedback between the collector and the base of the transistor in order to generate self-excited oscillation; as a power synthesis and conversion element, etc. ^[1]