Overvoltage protection circuit
First Claim
1. An overvoltage protection circuit comprising:
- switch means having a control electrode for receiving a control signal voltage and first and second output electrodes, said switch means being turned on and thereby permitting current conduction between said output electrodes in response to the control signal voltage at said control electrode exceeding a predetermined threshold voltage with respect to said first output electrode;
a terminal having a variable voltage signal provided thereat wherein said terminal is coupled to said second output electrode of said switch means;
a resistor coupled between said terminal and said control electrode of said switch means; and
a constant current source connected to said control electrode and providing a known current;
wherein for voltages at said terminal above a predetermined maximum voltage said resistor provides current to said control electrode in accordance with the magnitude of the voltage at said terminal which current will exceed the known current provided by said constant current source by a predetermined amount, and said switch means will, in response thereto, be turned on and permit current conduction between its output electrodes thereby tending to limit the magnitude of the voltage at said terminal and said second output electrode of said switch means.
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Accused Products
Abstract
Overvoltage protection circuit (10) has a power transistor (11) that drives an inductive load (19). A resistor (16) is connected between an output electrode (14) of the transistor and a control electrode (12) of the transistor, and a constant current source (18) is also connected to the control electrode. The resistor and constant current source determine an effective zener voltage to limit the maximum voltage which can exist at the transistor output electrode (14), and this is accomplished without the use of a zener diode while utilizing a minimum number of components. This effective zener diode voltage can be readily adjusted by adjusting either the magnitude of the resistor (16) or the constant current source (18).
16 Citations
28 Claims
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1. An overvoltage protection circuit comprising:
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switch means having a control electrode for receiving a control signal voltage and first and second output electrodes, said switch means being turned on and thereby permitting current conduction between said output electrodes in response to the control signal voltage at said control electrode exceeding a predetermined threshold voltage with respect to said first output electrode; a terminal having a variable voltage signal provided thereat wherein said terminal is coupled to said second output electrode of said switch means; a resistor coupled between said terminal and said control electrode of said switch means; and a constant current source connected to said control electrode and providing a known current; wherein for voltages at said terminal above a predetermined maximum voltage said resistor provides current to said control electrode in accordance with the magnitude of the voltage at said terminal which current will exceed the known current provided by said constant current source by a predetermined amount, and said switch means will, in response thereto, be turned on and permit current conduction between its output electrodes thereby tending to limit the magnitude of the voltage at said terminal and said second output electrode of said switch means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. An overvoltage protection circuit comprising:
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transistor switch means having a control electrode for receiving a control signal voltage and first and second output electrodes, said switch means being turned on and thereby permitting current conduction between said output electrodes in response to the control signal voltage at said control electrode exceeding a predetermined threshold voltage with respect to said first output electrode; a terminal having a variable voltage signal provided thereat wherein said terminal is coupled to said second output electrode of said switch means; a resistor coupled between said terminal and said control electrode of said switch means; and a constant current source connected to said control electrode and providing a known current; wherein for voltages at said terminal above a predetermined maximum voltage said resistor provides current to said control electrode in accordance with the magnitude of the voltage at said terminal which current will exceed the known current provided by said constant current source by a predetermined amount, and said switch means will, in response thereto, be turned on and permit current conduction between its output electrodes thereby tending to limit the magnitude of the voltage at said terminal and said second output electrode of said switch means; wherein said terminal is DC coupled to said second output electrode of said switch means, wherein an inductive load is connected as a load between a source of DC power supply voltage and said terminal, and wherein said overvoltage protection circuit includes control circuit means for providing an external switch control signal to said control electrode, in addition to any signals provided by said resistor and said constant current source, to control conduction of said switch means in accordance with said external switch control signal. - View Dependent Claims (20)
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21. An overvoltage protection system comprising;
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a plurality of output stages each providing electrical excitation to a different load associated with each stage, a plurality of overvoltage protection circuits each associated with one of said plurality of output stages, each of said protection circuits being independently adjustable to provide each stage with an adjustable maximum voltage that can be provided in each stage, said protection circuits being adjusted such that each of said stages provides electrical excitation to its associated load in a substantially identical manner in accordance with a predetermined criteria. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28)
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Specification