Method of Detecting a Fault Condition of a Load Control Device
First Claim
1. A method of detecting a fault condition of a first semiconductor switch in a load control device operable to be electrically coupled between an alternating-current (AC) power source and a load for control of the load to an on state or an off state, the first semiconductor switch coupled in anti-series connection with a second semiconductor switch, the method comprising the steps of:
- measuring a first voltage across the first semiconductor switch during a first half cycle of the AC power source;
comparing the first measured voltage to a first voltage threshold and a second voltage threshold greater than the first voltage threshold;
measuring a second voltage across the second semiconductor switch during a second half cycle of the AC power source;
comparing the second measured voltage to the first and second voltage thresholds; and
detecting the fault condition of the first semiconductor switch if the first measured voltage is less than the first voltage threshold and the second measured voltage is greater than the second voltage threshold.
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Accused Products
Abstract
A load control device comprises a bidirectional semiconductor switch for controlling the amount of power delivered to an electrical load, and the bidirectional semiconductor switch further comprises two field effect transistors (FETs) in anti-series electrical connection. In the event that one of the FETs fails in a shorted state, and if the load control device is using a phase control dimming technique to control the load, the load control device may provide an asymmetric waveform to the electrical load. In order to determine whether this asymmetric waveform is present, a microprocessor of the load control device use voltage thresholds and/or offsets to monitor the voltage across the FETs. Thus, the microprocessor is operable to detect a fault condition of the load control device wherein the fault condition may comprise an asymmetry condition, or more particularly, a failure condition of one of the FETs.
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Citations
32 Claims
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1. A method of detecting a fault condition of a first semiconductor switch in a load control device operable to be electrically coupled between an alternating-current (AC) power source and a load for control of the load to an on state or an off state, the first semiconductor switch coupled in anti-series connection with a second semiconductor switch, the method comprising the steps of:
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measuring a first voltage across the first semiconductor switch during a first half cycle of the AC power source; comparing the first measured voltage to a first voltage threshold and a second voltage threshold greater than the first voltage threshold; measuring a second voltage across the second semiconductor switch during a second half cycle of the AC power source; comparing the second measured voltage to the first and second voltage thresholds; and detecting the fault condition of the first semiconductor switch if the first measured voltage is less than the first voltage threshold and the second measured voltage is greater than the second voltage threshold. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of detecting an asymmetry condition in a bidirectional semiconductor switch of a load control device, the load control device operable to be electrically coupled between an alternating-current (AC) power source and a load, the bidirectional semiconductor switch comprising first and second semiconductor switches coupled in anti-series connection, the method comprising the steps of:
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measuring a first voltage across the first semiconductor switch during a first half cycle of the AC power source; measuring a second voltage across the second semiconductor switch during a second half cycle of the AC power source; and detecting the asymmetry condition in the bidirectional semiconductor switch if a difference between the first and second measured voltages is greater than a predetermined offset threshold. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A method of detecting a fault condition in a load control device operable to be electrically coupled between an alternating current (AC) power source and a load, the method comprising the steps of:
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rendering a first semiconductor switch non-conductive for a first predetermined period of time during a first line cycle of the AC power source; measuring a first voltage across the first semiconductor switch during the first line cycle; comparing the first measured voltage to a first predetermined voltage threshold; if the first measured voltage is less than the first predetermined voltage threshold, rendering the first semiconductor switch non-conductive for a second period time, greater than the first period of time, during a second line cycle of the AC power source; measuring a second voltage across the first semiconductor switch during the second line cycle; comparing the second measured voltage to the first predetermined voltage threshold; and detecting the fault condition of the first semiconductor switch if the second measured voltage is less than the first predetermined voltage threshold. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31, 32)
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Specification