Overcurrent protection for solid state switching system

• US 7,369,386 B2
• Filed: 01/31/2005
• Issued: 05/06/2008
• 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.
• Primary Examiner(s): Deberadinis; Robert L.
• Assistant Examiner(s): ROMAN, LUIS ENRIQUE
• Application Number:
  US11/048,123
• Publication Number:
  US 20050185353A1
• Time in Patent Office: 1,191 Days
• Field of Search: 361/93.9, 361/93.1
• US Class Current: 361/93.9
• 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;

an optocoupler connected to said logic circuit for providing an overcurrent signal in response to said overcurrent indication;

said logic circuit returning said driver circuit to PWM control following said PWM power on duty cycle segment

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.

2. The PWM switching power supply of claim 1, 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.

3. 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.

4. The PWM switching power supply of claim 3, said series solid state switch being a MOSFET.

5. 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

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

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, and

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.

6. The PWM power supply of claim 5 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.

7. The PWM power supply of claim 5, said driver circuit board being spaced from said power circuit board by a distance of less than about one-half inch.

8. The PWM power supply of claim 5, said circuit link including a massive terminal post extending between said power circuit board and said driver circuit board.

9. The PWM power supply of claim 8, said massive terminal post having a cross sectional area of at least about 0.05 inch.

10. The PWM power supply of claim 5, 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.

11. 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;

producing an overcurrent indication if the sensed current exceeds the threshold value;

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;

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;

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;

providing an overcurrent signal to an input of a microprocessor based programmable controller in response to the overcurrent indication, said providing step including transferring the overcurrent signal through an optocoupler; and

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.

12. A method as claimed in claim 11 wherein the clock frequency is faster than the frequency of the PWM control signal.

13. A method as claimed in claim 11 further comprising shutting down the sinewave dimmer power supply if the count reaches a limit.

14. A method as claimed in claim 13 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.

15. 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;

reinstating the PWM control signal after said power on segment;

counting instances of the overcurrent indications and shutting down the PWM power supply if the count reaches a limit during a time interval; and

summing the count for a predetermined number of time intervals and shutting down the PWM power supply if the sum reaches a maximum.

16. The method of claim 15 further comprising, after shutting down of the PWM power supply, reinstating the PWM control signal in response to a reset signal.

17. A method for overcurrent protection as claimed in claim 15 wherein the time interval is one half cycle of the AC source.

18. A method for overcurrent protection as claimed in claim 17 wherein the predetermined number of time intervals is sixteen.