Overcurrent protection for solid state switching system

• US 20050185353A1
• Filed: 01/31/2005
• Published: 08/25/2005
• Est. Priority Date: 06/06/2003
• Status: Active Grant

• Current Assignee: Electronic Theatre Controls Incorporated
• Original Assignee: Electronic Theatre Controls Incorporated
• Inventors: Suomi, Eric W., Rasmussen, Eric G., Thurk, John P.
• Granted Patent: US 7,369,386 B2
• Time in Patent Office: Days
• US Class Current: 361/93.900
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 5/293 using semiconductor devices only
• CPC Class Codes: H05B 39/00 Circuit arrangements or apparatus for operating incandescent light sources structurally associated with the incandescent lamps H01K1/62
• CPC Class Codes: H05B 39/044 continuously H05B39/042 takes precedence
• CPC Class Codes: H05K 1/0306 Inorganic insulating substrates, e.g. ceramic, glass
• CPC Class Codes: H05K 1/14 Structural association of two or more printed circuits providing electric connection to or between printed circuits H05K1/11, H01R12/00
• CPC Class Codes: H05K 1/144 Stacked arrangements of planar printed circuit boards
• CPC Class Codes: H05K 2201/10166 Transistor
• CPC Class Codes: H05K 3/0061 onto a metallic substrate, e.g. a heat sink heat sinks for electric apparatus H05K7/20
• CPC Class Codes: H05K 3/222 Completing of printed circuits by adding non-printed jumper connections printed jumper connections H05K3/4685
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

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.

Claims

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.

2. The PWM switching power supply of claim 1, comprising two said series solid state switches;

two said sensing resistors each connected to one of said series solid state switches; and

two said comparators each connected to one said current sensing resistor.

3. The PWM switching power supply of claim 1, said logic circuit returning said driver circuit to PWM control following said PWM power on duty cycle segment.

4. The PWM switching power supply of claim 3, said controller having an input connected to said optocoupler for receiving said overcurrent signal;

said controller having a counter programmed to poll said input with a clock frequency and to hold a count of instances of the presence of the overcurrent signal at the input during a predetermined time interval; and

said controller having an interrupt routine for discontinuing said PWM control signals, holding said series solid state switch non conductive and holding said clamp switching section conductive in response to said count reaching a limit value.

5. The PWM switching power supply of claim 4, said controller having a summing routine for summing said count for a predetermined number of said time intervals and calling said interrupt routine if the sum reaches a maximum value.

6. The PWM switching power supply of claim 1, said series solid state switch being a high power, high frequency solid state switch, namely a MOSFET or an IGBT.

7. The PWM switching power supply of claim 6, said series solid state switch being a MOSFET.

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:

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

9. A PWM power supply with overcurrent protection, said power supply providing output current for powering a load, said PWM power supply comprising:

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.

10. The PWM power supply of claim 9, further comprising a power circuit board supporting said series switching device;

said current sensing resistor being mounted on said power circuit board;

a driver circuit board;

said logic system being mounted on said driver circuit board; and

said circuit link extending between said power and driver circuit boards.

11. The PWM power supply of claim 10 further comprising a driver chip mounted on said driver circuit board for sending PWM power on duty cycle segment operating signals to said series switching device;

a third circuit on said driver circuit board for transferring PWM duty cycle control signals to said driver chip; and

said second circuit overriding said duty cycle control signals in response to operation of said first circuit to said overcurrent state.

12. The PWM power supply of claim 10, said first circuit including a comparator having a first input for receiving a threshold value and a second input for receiving an analog signal from said current sensing resistor through said circuit link.

13. The PWM power supply of claim 12, said driver circuit board being mounted parallel to said power circuit board, and said first circuit on said driver circuit board overlying said current sensing resistor on said power circuit board.

14. The PWM power supply of claim 13, said driver circuit board being spaced from said power circuit board by a distance of less than about one-half inch.

15. The PWM power supply of claim 13, said circuit link including a massive terminal post extending between said power circuit board and said driver circuit board.

16. The PWM power supply of claim 15, said massive terminal post having a cross sectional area of at least about 0.05 inch.

17. The PWM power supply of claim 12, said circuit link forming an analog signal path from said current sensing resistor to said first circuit, said signal path having a length of less than about one inch.

18. A power module package for a high frequency switching system supplying power to a load, said power module package comprising:

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.

19. The power module package of claim 18, said power circuit board structure including two power circuit boards mounted at opposite sides of said central region.

20. The power module package of claim 18, where in two said sensing resistors are mounted on said power circuit board structure between said first pair of solid state switches.

21. The power module package of claim 18 wherein said first pair of solid state switches is in series with the load and the second pair of solid state switches shunts the load;

said drivers include a series driver for said first pair of solid state switches and a second driver for said second pair of solid state switches; and

said overcurrent detection logic operates in response to a threshold current detected by said current sensing resistor to switch said first driver to a state for rendering said first pair of solid state switches nonconductive and to switch said second driver to a state for rendering said second pair of solid state switches conductive.

22. The power module package of claim 21 wherein said overcurrent detection circuit includes an output terminal for outputting an overcurrent signal for external processing.

23. An overcurrent protected power supply for supplying an output current to a load, said overcurrent protected power supply comprising:

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.

24. The overcurrent protected power supply of claim 23, further comprising a logic circuit connected between said comparator and said series and clamp override circuits, said logic circuit returning said series and clamp drivers to PWM control following said power on segment of said duty cycle.

25. The overcurrent protected power supply of claim 24, further comprising a programmable controller including said source of PWM signals;

said logic circuit having an output for providing an overcurrent signal in response to said output indication; and

an optocoupler for coupling said overcurrent signal to said controller.

26. A method for overcurrent protection of a solid state switching power supply, said method comprising:

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.

27. A method as claimed in claim 26, wherein said switching step includes interrupting a PWM series switch drive signal

28. A method as claimed in claim 26, further comprising switching a clamp solid state switch to a conductive condition in response to the overcurrent indication.

29. A method as claimed in claim 28, wherein said step of switching a clamp solid state switch includes interrupting an inverse PWM clamp switch drive signal.

30. A method for overcurrent protection of a solid state PWM switching sinewave dimmer power supply, said method comprising:

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.

31. A method as claimed in claim 30, further comprising removing the clamp switch section from inverse PWM control and switching the clamp switch section to a conductive condition in response to the overcurrent indication.

32. A method as claimed in claim 31, further comprising returning the first and second series solid state switches to PWM control and returning the clamp switch section to inverse PWM control at the end of the current power on segment of the PWM control signal.

33. A method as claimed in claim 32, further comprising providing an overcurrent signal to an input of a microprocessor based programmable controller in response to the overcurrent indication.

34. A method as claimed in claim 33 wherein said providing step includes transferring the overcurrent signal through an optocoupler.

35. A method as claimed in claim 33 further comprising polling the controller input with a clock frequency and holding a count of instances of the presence of the overcurrent signal at the input during a predetermined time interval.

36. A method as claimed in claim 35 wherein the clock frequency is faster than the frequency of the PWM control signal.

37. A method as claimed in claim 35 further comprising shutting down the sinewave dimmer power supply if the count reaches a limit.

38. A method as claimed in claim 37 further comprising maintaining a sum of the counts for a predetermined number of time intervals and shutting down the sinewave dimmer power supply if the sum reaches a maximum.

39. A method for overcurrent protection of a solid state PWM switching power supply, said method comprising:

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.

40. The method of claim 39 further comprising counting instances of the overcurrent indications and switching off the solid state switch if the count reaches a limit during a time interval.

41. The method of claim 40 further comprising summing the count for a predetermined number of time intervals and switching off the solid state switch if the sum reaches a maximum.

42. The method of claim 41 further comprising reinstating the PWM control signal in response to a reset signal.

43. A method for protecting a power supply with an AC source from output overcurrent damage comprising:

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.

44. A method for protecting as claimed in claim 43, further comprising summing the overcurrent count for a predetermined number of time intervals, and interrupting the control signal if the sum of overcurrent counts reaches a maximum value.

45. A method for protecting as claimed in claim 43 wherein the time interval is one half cycle of the AC source.

46. A method for protecting as claimed in claim 45 wherein the predetermined number of time intervals is sixteen.