Investigation of Forward Conduction of High Voltage Diodes at Short High-Current Pulses

This paper investigates the characteristics of forward conduction of high voltage fast recovery rectifiers at short duration high-current pulses. In these regimes, the devices' datasheets do not provide data on forward voltage drop. Four relevant HV fast recovery rectifiers are reported here: BYX104G, UX-FOB, 1N6519, DH 60-18A. For the experimental investigation, a low-inductive breadboard was assembled. Forward current pulses with rise times of several ns and durations of hundreds of ns were applied to the diodes. The diode voltage drop waveforms were recorded for several different current pulse levels. Experimental set-up and results, and Volt-Ampere (VA) charts showing the dependency on the pulse shape are presented. The examination of these waveforms revealed the occurrence of high voltage overshoot during turn-on. Only partially, these overshoots pertain to the circuit parasitic inductance. A detailed description of the physics behind this phenomenon is analyzed. It is shown that the overshoot is determined by the time of flight delay of electrons and holes injected into the pn layers of the p⁺pnn ⁺ diode from p⁺ and n⁺ layers. The effect manifests itself as a quasi-inductance. Such effect is well known for low frequency. The low current density case for diffusion transfer delay. At high current nanosecond pulses, the effect is due to drift of carriers in strong electric field. As a real test-case of an application employing these diodes, a high power, high voltage pulsed power supply (PPS) generating 4-J pulses of 50 kV, 100 ns, on a 100-Omega load, at a PRF of up to 1 kHz is given. Two rectifier arrays, each based on one type of the tested diodes (BYX104G and UX-FOB), were assembled and tested, and a comparison of their performance is given. A conclusion has been obtained that the UX-FOB diode is preferable for this application