Pulse transformers are used in high frequency power converters, when it is required to trasfer an electrical pulse from the control to the power stage, keeping the galvanic isolation between the circuits, according to the safety standards related to each different application fields.
The electrical signal is applied to the primary side and transferred to the secondary side, to fire power BJTs, power MOSFETs, IGBTs, SCRs, GTOs, TRIACs.
In high frequency power conversion systems, several control techniques are available and they differ from each other because of the striking apparatus parameters, like rated power, rated voltages and currents, field of application.
After the developer has chosen the firing topology for his application, he has the chance to find the most suitable pulse transformer, by considering its main parameters.
Main features of a pulse transformer are the following ones:
- n primary to secondary turns ratio
- Vt minimum voltage*time area (called transfer area) that can be trasferred at the secondary side with unipolar pulse, without causing the core saturation, referred to the temperature of 25°C
- LP primary winding inductance
- Ck coupling capacity between windings
- Ls primary leakage inductance, it is the inductance value measured at the primary side, with the secondary winding short-circuited
- RP primary winding resistance
- RS secondary winding resistance
- tr rise time, it is the time that takes to trasfer the pulse when the rated load resistance is connected at the secondary side; this value is tightly connected to the leakage inductance value
- Imax maximum secondary current, available with a rise time equal to tr (rated load resistance connected to the secondary winding)
- Ip rated primary effective current (thermal current)
- fn rated working frequency (or optimum frequency range)
- Uis maximum working voltage between two windings
- Up isolation voltage between two windings
Sirio pulse transformers are classified by dimensions and production profiles and grouped in Families. Some Standard Pulse and Drive Transformers are available, they are listed on a family by family basis. They can be used for many applications but, as the solution possibilities are so many, it is sometimes necessary to develop a custom product (see the Custom Design sheet). By looking through the standard codes table it is easy to understand the general features of each pulse/drive transformer size.