System and method for limiting through-lamp ground fault currents in non-isolated electronic ballasts
First Claim
1. A ground fault sensor for a non-isolated electronic ballast having a dc power supply coupled to an inverter and a resonant tank circuit coupled to the inverter through a dc blocking capacitor, comprising:
- a filter circuit having an input terminal in communication with a ballast output terminal that is connected to the resonant tank circuit, the filter circuit operable to attenuate high frequency ac voltage components of a voltage signal at the input terminal to generate a filtered voltage signal; and
a voltage sensor in communication with the filter circuit and operable to provide a control signal in response to the filtered voltage signal;
wherein the control signal is indicative of a ground fault.
7 Assignments
0 Petitions
Accused Products
Abstract
An electronic ballast having a through-lamp ground fault sensor that may also function as an end-of-lamp-life sensor is disclosed. The electronic ballast has an inverter that receives power from a dc power supply, and delivers a high-frequency output voltage to a resonant tank circuit through a dc blocking capacitor. The ground fault sensor includes a filter circuit connected to a voltage sensor circuit. An input terminal of the filter circuit is connected to the resonant tank so as to be in communication with a voltage signal that exists between a ballast output terminal and a dc power supply output terminal. The filter provides a filtered voltage signal by attenuating high frequency ac voltage components of the voltage signal, and passing low frequency ac voltage components, such as a 60 Hz signal, and possibly also passing a dc voltage component. A through-lamp ground fault will generate a voltage signal at the power line frequency. A lamp that has reached the end of its useful life will generate a low frequency ac voltage component that is caused by flickering, as well as a dc voltage component caused by rectification. The voltage sensor provides a control signal in response to the filtered voltage signal that may be used by an inverter control circuit to control the output of the inverter. In response to the control signal, the inverter control circuit either shuts down the inverter or increases the frequency of the inverter in order to reduce the output current of the inverter.
39 Citations
12 Claims
-
1. A ground fault sensor for a non-isolated electronic ballast having a dc power supply coupled to an inverter and a resonant tank circuit coupled to the inverter through a dc blocking capacitor, comprising:
-
a filter circuit having an input terminal in communication with a ballast output terminal that is connected to the resonant tank circuit, the filter circuit operable to attenuate high frequency ac voltage components of a voltage signal at the input terminal to generate a filtered voltage signal; and
a voltage sensor in communication with the filter circuit and operable to provide a control signal in response to the filtered voltage signal;
wherein the control signal is indicative of a ground fault. - View Dependent Claims (2, 3, 4)
-
-
5. A method of sensing a ground fault in a non-isolated electronic ballast having a power supply, an inverter, and a resonant tank circuit, comprising the steps of:
-
attenuating high frequency ac voltage components of a voltage signal at an input terminal of a filter circuit in communication with a ballast output terminal to obtain a filtered voltage signal; and
generating a control signal in response to the filtered voltage signal using a voltage sensor;
wherein the control signal is indicative of a ground fault. - View Dependent Claims (6, 7, 8)
rectifying the filtered voltage signal using a charge pump; and
integrating the rectified filtered voltage signal to obtain the control signal.
-
-
7. The method of claim 5, wherein generating a control signal in response to the filtered voltage signal, comprises the steps of:
-
rectifying the filtered voltage signal using a full wave rectifier; and
integrating the rectified filtered voltage signal to obtain the control signal.
-
-
8. The method of claim 6, further comprising the step of:
inhibiting the control signal until the power supply has stabilized.
-
9. An end-of-lamp-life sensor for an electronic ballast having a dc power supply coupled to an inverter and a resonant tank circuit coupled to the inverter through a dc blocking capacitor, comprising:
-
a filter circuit having an input terminal in communication with a ballast output terminal that is connected to the resonant tank circuit, the filter circuit operable to attenuate high frequency ac voltage components of a voltage signal at the input terminal to generate a filtered voltage signal; and
a voltage sensor in communication with the filter circuit and operable to provide a control signal in response to the filtered voltage signal;
wherein the control signal is indicative that a lamp connected to the ballast has reached the end of its useful life. - View Dependent Claims (10, 11, 12)
-
Specification