Preheating and starting circuit and method for a fluorescent lamp
First Claim
1. A preheating and ignition circuit for use with a fluorescent lamp which has cathodes and a medium which is ionizable into a conductive plasma by voltage and current applied in half-cycles from a power source through a ballast to the lamp, comprising:
- a control module adapted to be connected to the cathodes of the lamp;
the control module including a controllable switch which is connected in series with the cathodes upon connection of the control module to the cathodes, the switch conducts substantially all of the current applied to the cathodes from the power source when the switch is conductive, the switch having a characteristic holding current level, the switch remaining conductive after being triggered when the current flow therethrough exceeds the holding current level, the switch commutating into a non-conductive state if not triggered upon the current therethrough decreasing below the holding current level;
the control module further including a controller for controlling the conductivity of the switch relative to the current flow therethrough by supplying signals to trigger the switch;
the controller including information defining a warm-up time period of predetermined time duration of two or more complete applied half-cycles during which the cathodes are heated prior to attempting to ignite the lamp;
the controller delivering a conductive interval start signal to trigger the switch into a conductive state during a predetermined conductive time interval during each applied half-cycle occurring during the warm-up time period, the switch conducting current through the cathodes and thereby heating the cathodes during the conductive time interval of each applied half-cycle during the predetermined warm-up time period;
the controller causing the switch to commutate into a nonconductive state at the end of the conductive time interval occurring in the next half-cycle after the expiration of the warm-up time period as a result of current conducted through the switch decreasing to below the holding current level, the commutation of the switch into the non-conductive state upon the current conducted therethrough decreasing to below the holding current level creating a change in current per change in time (di/dt) effect at the ballast which applies a high voltage ignition pulse to the cathodes; and
the controller delivering a suppression signal in addition to the interval start signal during each applied half-cycle occurring during the warm-up time period, the suppression signal triggering the switch into a conductive state prior to the end of the conductive time interval and while the current conducted through the switch reaches the holding current level during each applied half-cycle of the predetermined warm-up time period.
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Accused Products
Abstract
The cathodes of a fluorescent lamp are preheating and the medium between the cathodes is ignited into a plasma by heating the cathodes for a predetermined warm-up time period by conducting current from a supply power source through the cathodes for a conductive time interval, and applying a relatively high voltage starting pulse to the cathodes at the end of the conductive time interval or alternatively suppressing the high voltage starting pulse during the predetermined warm-up time period. Suppressing the high voltage starting pulse during the warm-up time period, thereby preventing erosion the thermionic coating of the cathodes due to positive ion bombardment. A controllable semiconductor switch is connected to the cathodes to control the current flow through them. The high voltage starting pulse is derived from commutating the semiconductor switch into a nonconductive state when the applied current level drops to the characteristic holding current value of the switch. The high voltage starting pulse is suppressed by triggering the semiconductor switch at the time when it would otherwise be commutating to the nonconductive state.
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Citations
25 Claims
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1. A preheating and ignition circuit for use with a fluorescent lamp which has cathodes and a medium which is ionizable into a conductive plasma by voltage and current applied in half-cycles from a power source through a ballast to the lamp, comprising:
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a control module adapted to be connected to the cathodes of the lamp; the control module including a controllable switch which is connected in series with the cathodes upon connection of the control module to the cathodes, the switch conducts substantially all of the current applied to the cathodes from the power source when the switch is conductive, the switch having a characteristic holding current level, the switch remaining conductive after being triggered when the current flow therethrough exceeds the holding current level, the switch commutating into a non-conductive state if not triggered upon the current therethrough decreasing below the holding current level; the control module further including a controller for controlling the conductivity of the switch relative to the current flow therethrough by supplying signals to trigger the switch; the controller including information defining a warm-up time period of predetermined time duration of two or more complete applied half-cycles during which the cathodes are heated prior to attempting to ignite the lamp; the controller delivering a conductive interval start signal to trigger the switch into a conductive state during a predetermined conductive time interval during each applied half-cycle occurring during the warm-up time period, the switch conducting current through the cathodes and thereby heating the cathodes during the conductive time interval of each applied half-cycle during the predetermined warm-up time period; the controller causing the switch to commutate into a nonconductive state at the end of the conductive time interval occurring in the next half-cycle after the expiration of the warm-up time period as a result of current conducted through the switch decreasing to below the holding current level, the commutation of the switch into the non-conductive state upon the current conducted therethrough decreasing to below the holding current level creating a change in current per change in time (di/dt) effect at the ballast which applies a high voltage ignition pulse to the cathodes; and the controller delivering a suppression signal in addition to the interval start signal during each applied half-cycle occurring during the warm-up time period, the suppression signal triggering the switch into a conductive state prior to the end of the conductive time interval and while the current conducted through the switch reaches the holding current level during each applied half-cycle of the predetermined warm-up time period. - View Dependent Claims (4, 5, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16, 17, 18, 19)
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2. A method of preheating and ingniting a plasma in a fluorescent lamp which has cathodes and a medium which is ionizable into the plasma, comprising the steps of:
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connecting a ballast between an AC power source and the lamp; applying voltage and current in half-cycles from the AC power source to the cathodes; heating the cathodes for a predetermined warm-up time period extending over two or more complete applied half-cycles of current by conducting current from the source through the cathodes for a predetermined conductive time interval of each applied half-cycle of current during the warm-up time period; conducting current from the source through the cathodes for the predetermined conductive time interval of a half-cycle of current occurring immediately after the warm-up time period; generating a relatively high voltage starting pulse by creating a relatively large decrease in current conducted through the ballast in a relatively short time (di/dt effect) at the end of the conductive time interval; suppressing the high voltage starting pulse by suppressing the di/dt effect at the end of each conductive time interval occurring during the predetermined warm-up time period; applying the relatively high voltage starting pulse to the cathodes at the end of the conductive time interval occurring in the half-cycle occurring immediately after the warm-up time period; connecting a controllable switch to the cathodes to conduct substantially all of the current applied to the cathodes through the cathodes when the switch is triggered into a conductive state during the conductive time interval, the switch having a characteristic holding current level, the switch remaining conductive after being triggered when current flow therethorugh exceeds the holding current level, the switch commutating into a non-conductive state if not triggered when the current therethrough decreases below the holding current level; delivering a conductive start signal during each half-cycle of applied current during the warm-up time period to trigger the switch into a conductive state at the start of the conductive time interval; and delivering a suppression signal during each half-cycle of the warm-up time period to trigger the switch into the conductive state prior to and during the end of the conductive time interval during each half-cycle of the warm-up time period, the suppression signal existing when the current conducted through the switch reaches the holding current level. - View Dependent Claims (3, 11, 20, 21, 22, 23, 24, 25)
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Specification