Overcurrent protection for solid state switching system
First Claim
1. A PWM switching power supply with overcurrent protection, said power supply receiving AC power from a power source and providing output current for powering a load, said PWM switching power supply comprising:
- a series switching section having a series solid state switch in series with the load, and a clamp switching section shunting the load;
a programmable controller supplying a PWM control signal having a duty cycle with power on segments;
a driver system receiving said PWM control signal and providing PWM operating signals for alternate conduction of said series and clamp switching sections;
a current sensing resistor connected to said series solid state switch and sensing output current during power on cycles;
a comparator connected to said current sensing resistor for comparing sensed output current with a threshold value and providing an overcurrent indication if the output current exceeds the threshold value in a PWM power on duty cycle segment;
a logic circuit for overriding said driver system and rendering said series switching section nonconductive and rendering said clamp switching section conductive in response to said overcurrent indication; and
an optocoupler connected to said logic circuit for providing an overcurrent signal in response to said overcurrent indication.
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Accused Products
Abstract
Current sensing resistors are connected directly to output terminals of MOSFETs forming the series switching stage of a PWM sinewave dimmer. An analog sensed current signal is coupled through an EMI resistant current link to comparators that provide an overcurrent indication in response to an overcurrent condition. A logic circuit overrides PWM control signals from a programmable controller, and operates drivers to render the series switching stage nonconductive and to render a clamp switching stage conductive until after the end of the current PWM duty cycle power on segment. The logic circuit sends an overcurrent signal through an optocoupler to an input of the programmable controller. The input of the controller is polled at a clock frequency for overcurrent signals and if the count exceeds a limit in any half cycle, or a maximum sum in sixteen half cycles of the AC supply, the series switching stage is rendered nonconductive and the clamp switching stage is rendered conductive pending a reset signal.
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Citations
46 Claims
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1. A PWM switching power supply with overcurrent protection, said power supply receiving AC power from a power source and providing output current for powering a load, said PWM switching power supply comprising:
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a series switching section having a series solid state switch in series with the load, and a clamp switching section shunting the load;
a programmable controller supplying a PWM control signal having a duty cycle with power on segments;
a driver system receiving said PWM control signal and providing PWM operating signals for alternate conduction of said series and clamp switching sections;
a current sensing resistor connected to said series solid state switch and sensing output current during power on cycles;
a comparator connected to said current sensing resistor for comparing sensed output current with a threshold value and providing an overcurrent indication if the output current exceeds the threshold value in a PWM power on duty cycle segment;
a logic circuit for overriding said driver system and rendering said series switching section nonconductive and rendering said clamp switching section conductive in response to said overcurrent indication; and
an optocoupler connected to said logic circuit for providing an overcurrent signal in response to said overcurrent indication. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An overcurrent protection system for a high power, high frequency solid state switch having an output terminal supplying an output current to a load, said overcurrent protection system comprising:
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a high current, low resistance current sensing resister connected directly to the output terminal of the solid state switch;
a comparator establishing a threshold output current level;
a conductive link interconnecting said current sensing resistor to said comparator; and
a logic circuit connected to said comparator for rendering the solid state switch nonconductive if the sensed output current reaches said threshold
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9. A PWM power supply with overcurrent protection, said power supply providing output current for powering a load, said PWM power supply comprising:
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at least one high power, high frequency solid state series switching device connected in series with the load and switching the output current on and off;
an output current sensing resistor connected in series with the series switching device;
an overload detection logic section;
a circuit link connecting said current sensing resistor to said logic section;
said logic section including a first circuit operable to an overcurrent state in response to a sensed output current exceeding a threshold amplitude;
said logic section having a second circuit for rendering said series switching device nonconductive in response to operation of said first circuit to said overcurrent state. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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18. A power module package for a high frequency switching system supplying power to a load, said power module package comprising:
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a heat sink having a flat, planar, surface having generally the shape of a rectangle;
a power circuit board structure mounted on said heat sink surface;
a first pair of solid state switches mounted on said power circuit board structure and located in first and second corners of said rectangle to one side of a central region of said rectangle;
a second pair of solid state switches mounted on said power circuit board structure and located in third and fourth corners of said rectangle to the other side of said central region;
a driver board supported above said heat sink surface and including drivers for said solid state switches, said driver board including a main board portion overlying said central region;
a current sensing resistor mounted on said power circuit board structure between said first pair of solid state switches;
said driver board having a tongue portion projecting from said main portion to overlie said current sensing resistor;
overcurrent detection logic mounted on said tongue portion; and
a circuit link connecting said current sensing resister to said overcurrent detection logic. - View Dependent Claims (19, 20, 21, 22)
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23. An overcurrent protected power supply for supplying an output current to a load, said overcurrent protected power supply comprising:
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a series solid state switching stage in series with the load;
a clamp solid state switching stage shunting the load;
a source of PWM signals having a duty cycle with a power on segment;
a series driver for switching said series solid state switching stage in accordance with said duty cycle;
a clamp driver for switching said clamp solid state switching stage in accordance with the inverse of said duty cycle;
a current sensor in series with the series solid state switching stage providing an output current responsive signal during said power on segment;
a comparator comparing said output current responsive signal with a threshold value and providing an overcurrent indication if said output current responsive signal exceeds said threshold value;
a series override circuit operable in response to said overcurrent indication for removing said series driver from PWM control and placing said series driver in a state for holding said series solid state switching stage in a nonconductive condition; and
a clamp override circuit operable in response to said overcurrent indication for removing said clamp driver from PWM control and placing said clamp driver in a state for holding said clamp solid state switching stage in a conductive condition. - View Dependent Claims (24, 25)
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26. A method for overcurrent protection of a solid state switching power supply, said method comprising:
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sensing current at an output terminal of a series solid state switch of the power supply;
comparing the sensed current with a threshold value;
providing an overcurrent indication if the sensed current exceeds the threshold value; and
switching the series solid state switch to a nonconductive condition in response to the overcurrent indication. - View Dependent Claims (27, 28, 29)
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30. A method for overcurrent protection of a solid state PWM switching sinewave dimmer power supply, said method comprising:
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operating first and second series solid state switches in accordance with a PWM control signal;
operating a clamp switch section in accordance with the inverse of the PWM signal;
sensing current in the power supply by detecting current during positive half cycles of a power source waveform with a first sensing resistor connected to an output terminal of the first series solid state switch of the power supply and detecting current during negative half cycles of the power source waveform with a second sensing resistor connected to an output terminal of the second series solid state switch of the power supply;
comparing the sensed current with a threshold value;
providing an overcurrent indication if the sensed current exceeds the threshold value; and
removing the first and second series solid state switches from PWM control and switching the first and second series solid state switches to a nonconductive condition in response to the overcurrent indication. - View Dependent Claims (31, 32, 33, 34, 35, 36, 37, 38)
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39. A method for overcurrent protection of a solid state PWM switching power supply, said method comprising:
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switching a solid state switch on and off in accordance with a PWM control signal having power on segments;
sensing current in the solid state switch;
providing an overcurrent indication if the sensed current exceeds a threshold value in a power on segment;
overriding the PWM control signal and switching off the solid state switch for the duration of said power on segment in response to the overcurrent indication; and
reinstating the PWM control signal after said power on segment. - View Dependent Claims (40, 41, 42)
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43. A method for protecting a power supply with an AC source from output overcurrent damage comprising:
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driving the power supply with a control signal from a microprocessor based programmable controller sensing output current in the power supply;
applying an overcurrent signal to an input of the controller when the sensed current exceeds a threshold;
polling the input terminal at a clock frequency and maintaining an overcurrent count equal to instances of overcurrent signal presence at the input terminal;
resetting the count to zero at time intervals; and
interrupting the control signal if the overcurrent count reaches a limit value. - View Dependent Claims (44, 45, 46)
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Specification