Discharge circuits and loads Page: 21 of 62
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DISCHARGE CIRCUITS AMD LOADS
High-pulse fidelity pulse-transformer design is still a compromise of
efficiency against pulse fidelity (Fig. 7). Flatness is predominantly con-
trolled by three factors: resonances in the transformer structure, flux
saturation level and the time taken to reach saturation (which is material
dependent), and the amount of energy that flows into the magnetizing induc-
tance. For very long pulses, it is the magnetizing inductance that shunts
away the desired energy from the PFN. The cost of large, high-quality
lse transformers goes up very rapidly with pulse width. Unless absolute-
ly necessary, pulse transformers are an expensive route far pulses Monger
than 20 to 25 us.
B, Pulse Transformer Limitations
Given a load like a magnetron or a direct-discharge-pumped gas laser,
as the current and the voltage start to decrease, the sustaining voltage is
passed and the current suddenly ceases to flow in the load, except for the
current flow in the recharging inductance or resistance across the load.
The falltime limit is then determined by the total loop inductance L, which
for pulse transformer drive can easily be'400 to 500 nH, and the P"N imped-
ance, resulting in fairly long falltimes. When a laser switches off, the
energy stored in this shunt inductance and in the transformer leakage
inductance discharges in a resonant fashion into the inductance/capaci-
tance loop (Fig. 7). Another problem is that since this is a resonart
discharge there can b3 a voltage reversal at the load point. The amount
can be determined through a nonlinear analysis for high-power pulse trans-
formers, but it is difficult to do. The amount of reversal is not constant
as the load impedance changes. The load and the pulse transformer are
For very fast pulses, coaxial cable transformers can be used to pro-
vide voltage gains of two to four times, but they are always rather high im-
pedance. Cable transformers experimentally give much lower multiplications
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Sarjeant, W.J. Discharge circuits and loads, report, October 15, 1980; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1061299/m1/21/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.