A pulse transformer is a special type of transformer that is enhanced to produce electrical pulses with minimum distortion. These transformers are designed to efficiently transfer energy in the form of short-duration, high-voltage pulses between circuits.

Features of Pulse Transformers

High-Frequency Operation: Pulse transformers operate over a wide frequency range, typically from a few kilohertz to several megahertz. They are designed to handle short-duration pulses ranging from nanoseconds to microseconds.

Isolation: They provide electrical isolation between different stages of a circuit, which is crucial in many high-voltage applications. This isolation helps prevent noise and interference from affecting sensitive electronic components.

Small Size and Lightweight: These transformers are compact and lightweight, making them suitable for integration into various electronic devices and systems.

Construction and Working

A pulse transformer consists of primary and secondary windings. The primary winding is connected to the input circuit, and the secondary winding is connected to the output circuit. The core is usually toroidal and is typically made of ferrite or other high-permeability materials to minimize core losses and maximize the transformer's efficiency.

The operation of a pulse transformer is based on the principle of electromagnetic induction. When a pulse is applied to the primary winding, an electromagnetic field is generated in the core. This magnetic field induces a voltage in the secondary winding, which is proportional to the number of turns in the primary and secondary windings. The voltage-to-current ratio of the pulse transformer is determined by the turns ratio of the primary and secondary windings. This ratio can be designed to be 1:1, 1:5, or other ratios depending on the application.

The above schematic of the pulse transformer explains its working when used in an SCR gate drive circuit. A constant voltage supply is provided to operate the pulse generator circuit. The pulse generator circuit can be a microcontroller or a 555 timer that generates pulses of suitable duration.  To transfer the pulses from one circuit to another and to maintain the isolation between the low-power and high-power circuit, we use a pulse transformer. The diode in the circuit conducts only in one direction and prevents the reverse current to the gate terminal of SCR. The resistor is used to adjust the holding current of SCR.

Types of Pulse Transformers

Pulse transformers are of two main types:

Power pulse transformers: These transformers are used to provide controlled power in the form of pulses to devices like heating elements or power drivers.

Signal pulse transformers: These transformers are used to transmit low-power control signals while providing isolation, usually for driving circuits like FETs or SCRs.

Pulse Transformer V/S Conventional Power Transformer

Applications of Pulse Transformer

Pulse transformers are integral in switching power supplies and converters, providing isolation while transferring high-frequency voltage pulses. They are used for signal transmission and isolation in both digital and analog communication lines. Pulse transformers are used in various test and measurement devices, such as pulse generators, to produce precise voltage pulses for testing electronic components.

Click here to learn more about Pulse Transformers listed on everything PE.