Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Reexamination Certificate
2000-07-31
2001-09-18
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
C315S224000, C315SDIG004, C315SDIG005
Reexamination Certificate
active
06291946
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a circuit for interrupted feedback loop operation.
2. Problem to be Solved
Feedback loops are commonly used in electronic or electromechanical systems to regulate some parameter of interest. For example, a feedback loop can be used to regulate lamp current or power in a ballast for a fluorescent lamp. In many instances, it is necessary to interrupt the operation of a feedback loop. For example, the feedback loop used to regulate the lamp current or power in the ballast is interrupted in order to dim the lamp by modulating the time that the lamp is on and off. Pulse-width-modulation (“PWM”) is typically used to achieve such modulation. Thus, when the lamp is on, the feedback loop is regulating lamp current or power in the ballast, but when the lamp is off, the feedback loop operation is interrupted.
One problem resulting from interruption of feedback loop operation is that the state variables in the feedback loop often decay during the interruption time and deviate from their steady state operating points. This decay is typically due to the RC (resistor capacitor) networks that normally function as filters in the feedback loop. When loop operation resumes, there is a transient associated with returning to steady state operation. This transient is generally worsened by the deviated state variables. For example, in one particular commercially available lighting system with dimming capability, the state variable is the lamp power and the decay occurs during PWM dimming. As a result of the decay, the switching frequency is initially relatively low because the feedback loop operates as though the lamp power is too low. This low switching frequency can saturate the resonant inductor thereby leading to excessive currents in the circuit and increased likelihood of visible flicker in the display.
One attempt at solving this problem is to clamp the state variable, during circuit interruption, to a value near its operating value. When operation resumes, the state variables are nearly correct and the transient is reduced in amplitude and/or duration. However, variations in circuit component values and variations in operating conditions can lead to different, and non-ideal, clamping values. As the operating conditions (such as input voltage) vary, the operating point of the state variable changes. Therefore, the fixed clamp value is only perfect for a single operating point and less than ideal for all other conditions.
It is therefore an object of the present invention to provide a feedback loop interruption circuit that solves the problem inherent in the prior art circuit discussed above.
Other objects and advantages of the present invention will be apparent to one of ordinary skill in the art in light of the ensuing description of the present invention.
SUMMARY OF THE INVENTION
In one aspect, the present invention is directed to a system for substantially eliminating transients upon the resumption of feedback loop steady state operation after feedback loop interruption. The system generally comprises a first circuit for applying a state variable to a load, a second circuit for (i) controlling the first circuit, (ii) monitoring the state variable applied to the load, and (iii) controlling the first circuit to regulate the state variable applied to the load in accordance with a desired state variable, and a third circuit for storing the applied state variable. The first and second circuits and the load define a feedback loop. The second circuit further includes an input for receiving a control signal that has a first state that causes the second circuit to enable the first circuit to apply the state variable to the load, and a second state that causes the second circuit to inhibit the first circuit from applying the state variable to the load thereby interrupting the feedback loop. The third circuit stores the applied state variable and prevents decay of the stored state variable during interruption of the feedback loop. The feedback loop resumes operation and returns to a steady state operation in accordance with the stored state variable when the control signal returns to the first state thereby substantially preventing the occurrence of transients from being introduced into the system.
In a related aspect, the present invention is directed to a system for substantially eliminating transients upon the resumption of feedback loop steady state operation after feedback loop interruption wherein the system generally comprises a first circuit for applying power to a load, a second circuit for (i) controlling the first circuit, (ii) monitoring the power applied to the load, and (iii) controlling the first circuit to regulate the power to the load in accordance with a predetermined amount of power, and a third circuit for storing a signal representative of the power applied to the load. The first and second circuits and the load define a feedback loop. The second circuit further includes an input for receiving a control signal that has a first state that causes the second circuit to enable the first circuit to apply the power to the load, and a second state that causes the second circuit to inhibit the first circuit from applying the power to the load thereby interrupting the feedback loop. The third circuit, which stores a signal representative of the power applied to the load, prevents decay of the stored signal during feedback loop interruption. The feedback loop resumes operation and returns to a steady state operation in accordance with the stored signal when the control signal returns to the first state thereby substantially preventing the occurrence of transients from being introduced into the system.
In yet another aspect, the present invention is directed to a ballast for powering a load having a lamp, comprising a power circuit for applying power to a lamp, a control circuit for (i) controlling the power circuit, (ii) monitoring the power applied to the lamp, and (iii) controlling the power circuit to regulate the power to the lamp in accordance with a predetermined amount of power, and a storage circuit for storing a signal representative of the power applied to the load. The control and power circuits and the lamp define a feedback loop. The control circuit further includes an input for receiving a control signal that has a first state that causes the control circuit to enable the power circuit to apply the power to the lamp, and a second state that causes the control circuit to inhibit the power circuit from applying the power to the lamp thereby interrupting the feedback loop. The ballast further comprises a dimming circuit for dimming the lamp. The dimming circuit comprises circuitry for generating the control signal wherein the first state of the control signal effects illumination of the lamp and the second state interrupts the feedback loop and prevents illumination of the lamp. The storage circuit, which stores a signal representative of the power applied to the load, prevents decay of the stored signal during feedback loop interruption so as to enable the feedback loop to resume operation and return to a steady state operation in accordance with the stored signal when the control signal returns to the first state. In one embodiment, the storage circuit comprises a control device and a storage device. The control device is responsive to the control signal such that when the control signal has the second state and the feedback loop is interrupted, the control device prevents decay of the signal stored in the storage device.
In another aspect, the present invention is directed to a method of operating a ballast for powering a lamp, comprising the steps of applying power to the lamp, storing a signal representative of the power applied to the lamp, monitoring the power applied to the lamp, regulating the power applied to the lamp in accordance with a predetermined power, the applying, monitoring and regulating steps defining a feedback loop operation of the ballast, interrupting the
Philips Electronics North America Corporation
Vu David
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