Zener diode power dissipation limiting circuit
First Claim
1. A circuit for protecting against an overvoltage condition, comprising:
- a. a resonant circuit;
b. a load coupled to the resonant circuit;
c. a first Zener diode coupled to a node of the resonant circuit for limiting a voltage at the node when the first Zener diode breaks down; and
d. means for controlling power delivery to the resonant circuit, the means for controlling including means for reducing power delivery to the circuit to a predetermined power level when the voltage at the node exceeds a predetermined voltage level wherein the predetermined power level results in a voltage level at the node that causes the first Zener diode to continue to break down and further including means for stopping power delivery to the resonant circuit a predetermined amount of time after the voltage at the node exceeds the predetermined voltage level.
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0 Petitions
Accused Products
Abstract
A circuit that utilizes a Zener diode to protect elements of a circuit from an over-voltage condition. When a fault occurs, causing an over-voltage condition, the voltage applied to the elements of the circuit is limited by the Zener diode. In addition, the circuit senses the over-voltage condition. Upon sensing the over-voltage condition, the circuit gradually reduces the power applied to that portion of the circuit to a minimum level. If the over-voltage condition persists for a predetermined amount of time, power is shut down to that portion of the circuit until the circuit is re-started. Because the amount of time that an over-voltage condition may occur is limited, the Zener diode may have a lower power rating than would otherwise be required. This is because the power dissipation capabilities of a Zener diode conducting current under a reverse bias are greater when the reverse bias is of a short duration than when the reverse bias is of a long duration. For example, the inventor has identified a Zener diode that is represented to have an ability to withstand 500 milli-watts under steady state conditions, but that can withstand for a limited duration a peak surge of many times the steady state power rating. In the preferred embodiment, the circuit limits voltage in a resonant circuit utilizing two Zener diodes coupled in series.
124 Citations
23 Claims
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1. A circuit for protecting against an overvoltage condition, comprising:
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a. a resonant circuit; b. a load coupled to the resonant circuit; c. a first Zener diode coupled to a node of the resonant circuit for limiting a voltage at the node when the first Zener diode breaks down; and d. means for controlling power delivery to the resonant circuit, the means for controlling including means for reducing power delivery to the circuit to a predetermined power level when the voltage at the node exceeds a predetermined voltage level wherein the predetermined power level results in a voltage level at the node that causes the first Zener diode to continue to break down and further including means for stopping power delivery to the resonant circuit a predetermined amount of time after the voltage at the node exceeds the predetermined voltage level. - View Dependent Claims (2, 3, 4)
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5. A circuit for protecting a circuit element against damage caused by an overvoltage condition at a node, comprising:
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a. means for delivering power to the circuit; b. means for reducing an amount of power delivery to the circuit to a predetermined power level after a voltage at the node exceeds a predetermined voltage level; and c. means for stopping delivery of power to the circuit when the voltage at the node exceeds the predetermined voltage level for a predetermined amount of time. - View Dependent Claims (6, 7, 8, 9)
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10. A circuit for protecting against an overvoltage condition, comprising:
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a. means for delivering power to the circuit; b. a Zener diode coupled to a node of the circuit; and c. means for reducing power delivery to the circuit to a predetermined power level when the Zener diode breaks down wherein the predetermined power level results in a voltage level at the node that causes the Zener diode to continue to break down. - View Dependent Claims (11, 12, 13, 14, 15)
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16. A circuit for protecting against an overvoltage condition, comprising:
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a. means for delivering power to the circuit; b. a Zener diode coupled to a node of the circuit; and c. means for stopping power delivered to the circuit a predetermined amount of time after the Zener diode breaks down. - View Dependent Claims (17, 18, 19, 20, 21)
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22. A circuit for providing power to a fluorescent lamp and for preventing damage to a circuit element caused by an overvoltage condition at a circuit node, the circuit comprising:
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a. a power source; b. a resonant circuit coupled to the power source wherein the resonant circuit comprises the circuit node; c. a fluorescent lamp coupled to receive power from the resonant circuit wherein the fluorescent lamp requires a minimum voltage level for a minimum period of time to ignite; d. means for sensing a voltage representative of the voltage at the circuit node coupled to the circuit node; e. a controller circuit for controlling an amount of power delivered to the resonant circuit from the power source wherein the controller is unable to directly control a voltage at the circuit node and wherein the controller circuit comprises; i. means for reducing the amount of power delivered to the resonant circuit when the voltage at the circuit node exceeds a predetermined voltage level wherein the predetermined voltage level is higher than the minimum level required to cause the fluorescent lamp to ignite; ii. means for ceasing power delivery to the resonant circuit when the voltage at the circuit node exceeds the predetermined voltage level for a predetermined amount of time wherein the predetermined amount of time is longer than the minimum amount of time required for the fluorescent lamp to ignite; f. a first Zener diode having a first anode and a first cathode wherein the first cathode is coupled to the circuit node; and g. a second Zener diode having a second anode and a second cathode wherein the second anode is coupled to the first anode and the second cathode is coupled to the ground node. - View Dependent Claims (23)
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Specification