Panasonic GPH5D - Manual (Page 29)

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The Sustain pulse is developed using a similar circuit as the Scan Pulse. A series
of specifically timed pulses are applied to FET drivers creating the distinctive
sustain pulse. The drivers switch the voltages (150V, 155V and 175V) at selected
intervals determined by the D2 board. The basic waveform remains constant but
the exact number of sustain pulses is determined by the amount of luminance
required, see figure 28.