Sample and hold method to achieve square-wave PWM current source for light emitting diode arrays
First Claim
1. An apparatus for controlling voltage and current in a switched LED array that is energized via a switched voltage converter, comprising:
- a semiconductor switching device for connecting the LED array to a voltage biasing rail from the switched voltage converter;
a current detecting means for generating a signal proportional to a current being conducted through the LED array during an activation time; and
a sample and hold means for retaining the generated signal during an inactivation time.
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Abstract
An apparatus for controlling overshoots in the switching of LED arrays in a system having a switching voltage converter providing the biasing voltage for the LED array. By synchronizing a switching converter to an LED turn-on signal, loading on the voltage converter can be controlled such that output conduction of the converter only occurs when LEDs that are to be displayed are switched on to provide loading to the output of the converter. A Sample and hold method is employed to effectively store the current information in a previous “on” interval and use it for the current control in a following interval with inhibited current overshoot.
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Citations
18 Claims
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1. An apparatus for controlling voltage and current in a switched LED array that is energized via a switched voltage converter, comprising:
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a semiconductor switching device for connecting the LED array to a voltage biasing rail from the switched voltage converter;
a current detecting means for generating a signal proportional to a current being conducted through the LED array during an activation time; and
a sample and hold means for retaining the generated signal during an inactivation time. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An apparatus for transferring energy from a source to a load, comprising:
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a first semiconductor switching device;
an energy storage element coupled to the first semiconductor switching device;
a second semiconductor switching device coupled to the energy storage element;
a timing control means for activating the first and second semiconductor switching devices; and
a synchronizing means for aligning the time of activation and deactivation of the first and second semiconductor switching devices to a predetermined time. - View Dependent Claims (13, 14)
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15. A method for synchronizing a switching LED driver to a switched voltage converter having an activation time period and an inactivation time period, comprising:
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a) activating the switched LED driver simultaneously with the activation time period of the switched voltage converter;
b) storing a signal corresponding to the peak current conducted through the LED during that activation time period;
c) inactivating the LED driver simultaneously with the inactivation time period of the switched voltage converter; and
d) inhibiting discharge of the stored peak current signal. - View Dependent Claims (16)
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17. An apparatus, comprising:
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a semiconductor switch for connecting an LED array to a voltage biasing rail from a switched voltage converter;
a current detector for generating a signal proportional to a current being conducted through the LED array during an activation time; and
a sample and hold circuit for retaining the signal during an inactivation time.
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18. An apparatus, comprising:
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a first semiconductor switch;
an energy storage element coupled to the first semiconductor switch;
a second semiconductor switch coupled to the energy storage element;
a timing controller for activating the first and second semiconductor switches; and
a synchronizer for aligning the time of activation and deactivation of the first and second semiconductor switches to a predetermined time.
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Specification