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Flyback Sustainer

IP.com Disclosure Number: IPCOM000050130D
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 35K

Publishing Venue

IBM

Related People

Duspiva, WS: AUTHOR [+2]

Abstract

Gas panels require that specific waveforms be applied to them to properly fulfill their data retention and display functions. These requisite waveforms are typically generated by separate circuits which produce the sustain, high voltage regulation, and write/erase functions. This article describes a method of accomplishing both the sustain and high voltage regulation functions in a single circuit, and with a single output transistor.

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Flyback Sustainer

Gas panels require that specific waveforms be applied to them to properly fulfill their data retention and display functions. These requisite waveforms are typically generated by separate circuits which produce the sustain, high voltage regulation, and write/erase functions. This article describes a method of accomplishing both the sustain and high voltage regulation functions in a single circuit, and with a single output transistor.

Figure 1 illustrates the circuit topology used to achieve the stated objective. Capacitor 1 represents the load capacitance presented to the circuit by the gas panel. Diodes 2 and 3 are diodes within the panel driver modules, while diode 4 provides a shunt path for currents to bypass the driver module. Capacitor 5 is the output filter required for the high voltage regulator. To understand the operation of the circuit, assume that capacitor 5 is initially charged to the desired sustain voltage (e.g. 185 volts), that the panel voltage 1 is also at this level, that inductor 6 has no current flow in it, and that transistor 9 is initially open. At this initial instant transistor 9 is turned on by its control circuits 10, discharging the panel capacitance 1 through the same diodes in the normal manner.

When the transistor 9 turns on, inductor 6 will have a voltage Vcc placed across it, and thus its current will begin to build through diodes 7, 4, and 8. The various voltage and current waveforms are shown in Fig. 2. As this current builds up linearly from the assumed zero initial level, it will still be small as the avalanche current flows through transistor 9. At time T (off) in Fig. 2, transistor 9 is turned off again, breaking the inductor current path to ground, causing the voltage across the inductor to reverse until its node is clamped to capacitor 5 through diodes 7 and 13. As the inductor voltage reverses and climbs toward the desired sustain level, some of its current serves to charge the panel 1 through diodes 7 and 2. When inductor 6 is clamped to the sustain voltage level by capacitor 5, it also holds the panel to that same level. As a result of this voltage transition, the panel will again avalanche, the avalanche current being supported by the current from the inductor 6 through diodes 2 and 7. To have this system operate, it is only necessary that the current present in the inductor when the transistor is first opened be greater than the maximum avalanche current which can flo...