Reset Behavior of High Duty Cycle Pulse Transformers

Magnetic core pulse transformers operating in a repetitive mode must maintain the core flux density within the saturation bounds of the magnetic material to provide satisfactory performance. The instantaneous flux is established by the time integration of the induced winding voltage. Alternatively, the flux is also determined by the net instantaneous magneto-motive force acting on the core in relation to the core dimensions and material hysteresis characteristics. Core material is typically non-linear and is awkward to model, so the preferred method of flux determination is via the induced voltage integration method. During the output pulse duration, this induced voltage is forced on the core via the winding by the pulsed power source and establishes the instantaneous flux and flux time derivative during the pulse. In the steady state, the integration of the induced voltage that occurs between load pulses, commonly called the back-swing period, must equal the value established by the output or load portion of the pulse to avoid saturation. This back-swing period can be driven by an external forced re-set source or by the stored energy in the transformer acting through the equivalent circuit impedance. In this paper only the stored energy re-set process is analyzed