Led driver current amplifier
First Claim
1. A circuit for powering a device based on a command signal, comprising:
- a voltage measurement device adapted to provide a device voltage measured across the device;
a current amplifier receiving the command signal and connected to the device, said current amplifier capable of linearly regulating current flowing through the device; and
a power supply having a supply voltage signal connected to the device, said supply voltage signal being regulated by said power supply based on said voltage measurement device,wherein said voltage measurement device is coupled to said current amplifier and said power supply and power dissipation in said current amplifier is minimized by varying said supply voltage signal based on said voltage measurement device, andwherein said voltage measurement device further comprises a voltage biasing circuit receiving said device voltage and providing a biased voltage signal to a control input of said power supply, said biased voltage signal set by said voltage biasing circuit such that said supply voltage signal produced by said power supply is regulated to approximately equal said device voltage plus a predetermined bias voltage.
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Accused Products
Abstract
A circuit powering an electrical device based on a commanded current signal is provided. The circuit includes a linear current amplifier which sets a desired current flow. The circuit also dynamically controls a supply voltage in order to minimize power dissipation of the linear current amplifier. The circuit may also include a voltage drop measurement amplifier, a voltage shaping amplifier, and a switching power supply. The circuit is useful for controlling electrical devices requiring precise current control and minimal power dissipation, for example, driving light-emitting diodes (LEDs) that provide illumination inside the passenger compartment of a vehicle for an imaging occupant detection system.
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Citations
13 Claims
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1. A circuit for powering a device based on a command signal, comprising:
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a voltage measurement device adapted to provide a device voltage measured across the device; a current amplifier receiving the command signal and connected to the device, said current amplifier capable of linearly regulating current flowing through the device; and a power supply having a supply voltage signal connected to the device, said supply voltage signal being regulated by said power supply based on said voltage measurement device, wherein said voltage measurement device is coupled to said current amplifier and said power supply and power dissipation in said current amplifier is minimized by varying said supply voltage signal based on said voltage measurement device, and wherein said voltage measurement device further comprises a voltage biasing circuit receiving said device voltage and providing a biased voltage signal to a control input of said power supply, said biased voltage signal set by said voltage biasing circuit such that said supply voltage signal produced by said power supply is regulated to approximately equal said device voltage plus a predetermined bias voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A circuit, comprising:
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an LED; a voltage regulator providing a supply voltage signal to said LED; and a current amplifier connected to said LED and capable of linearly regulating current flowing through said LED, wherein said current amplifier includes a transistor coupled to said LED, wherein said voltage regulator is adapted to adjust said supply voltage for a given current flow so that said supply voltage signal enables said transistor to operate linearly while allowing for power dissipation of said transistor to be minimized, and wherein said supply voltage is approximately equal to the voltage across said LED plus a predetermined bias voltage. - View Dependent Claims (9)
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10. An illumination control for an imaging system, comprising:
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an illumination source; a controller providing a command signal based on a desired illumination level; an illumination control circuit having a current amplifier receiving said command signal and coupled to said illumination source, said current amplifier linearly controlling current flowing through said illumination source based on said command signal; a power supply providing a supply voltage to said illumination source; and a voltage biasing circuit for setting a predetermined bias voltage and a voltage measuring circuit capable of measuring the voltage across said illumination source, said voltage measuring circuit coupled to said illumination source and said voltage biasing circuit coupled to said voltage measuring circuit and at least one of said power supply and said current amplifier, said supply voltage being regulated to approximately the sum of said predetermined bias voltage and the voltage measured by said voltage measuring circuit. - View Dependent Claims (11, 12)
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13. A method of controlling an LED, comprising the steps of:
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determining an illumination level; determining the current flow through the LED necessary to provide the illumination level; limiting the current flow through the LED to the determined level; determining a bias voltage; determining the voltage across the LED at the determined current flow; and providing to the LED approximately the sum of the bias voltage and the voltage across the LED.
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Specification