Pulse transformers interface a pulse forming network (PFN) and a load. They match the impedance of the load to the PFN in order to maximize power-transfer efficiency. Pulse forming networks (PFNs) collect electrical energy over a relatively long period of time and then release this stored energy quickly, as a short-duration, relatively-square pulse. Typically, applications which use pulse transformers have an output pulse whose peak power is measured in megawatts (MW) or terawatts (TW). Often, the combination of a high-voltage source, high-voltage switch, PFN, and pulse transformer is called a power modulator or pulser. Technologies which use pulsed transformers include radar, medical equipment and laser systems.
There are two main types of pulse transformers: power and signal. Power transformers convert power-level voltages from one level or phase configuration to another. They are available in either single-phase or three-phase primary configurations, and differ with regard to how the winding is connected. Signal transformers are pulse transformers which use electromagnetic induction to transfer information from one circuit to another. Often, they are used to increase or decrease the voltage from one side of a power transformer to the other. With signal transformers, the turn ratio of the number of windings determines the change in voltage.
Pulse transformers have low-loss cores and are designed to operate at high frequencies. To minimize parasitic elements such as leakage inductance and winding capacitance, the winding configuration is designed to optimize coupling. Performance specifications for pulse transformers include range, repetition rate, pulse width, current, input voltage, output voltage, frequency, duty cycle, and physical dimensions such as length, width and height. Pulse repetition rate or frequency is the average number of pulses per unit of time (typically seconds) during a specified period. Pulse width or pulse length is the interval between the first and last instances that that instantaneous amplitude reaches a specified fraction of peak pulse amplitude.
Approvals and Specifications
Pulse transformers differ in terms of approvals. Some products bear marks from the Canadian Standards Association (CSA) or Underwriters Laboratories (UL). Others meet standards or specifications from the International Electrotechnical Commission. Pulse transformers that are sold in Europe should comply with European Union (EU) Directives such as Restriction of Hazardous Substances (RoHS) and Waste Electrical and Electronics Equipment (WEEE). Pulse transformers with marks from national European organizations such as VDE are also available.