Instrument panel illumination dimming control

• US 4,029,991 A
• Filed: 04/14/1976
• Issued: 06/14/1977
• Est. Priority Date: 04/14/1976
• Status: Expired due to Term

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Schultz, Frederick K.
• Primary Examiner(s): La Roche, Eugene R.
• Application Number:
  US05/676,730
• Time in Patent Office: 426 Days
• Field of Search: 315/77, 315/82, 315/129, 315/130, 315/133, 315/135, 315/208, 315/291, 315/297, 315/307, 315/DIG. 4, 307/10 LS, 340/381
• US Class Current: 315/135
• CPC Class Codes: H05B 45/395 Linear regulators
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

The brightness of an LED display on an automobile instrument panel is independent of the battery voltage but does depend on the position of the instrument panel illumination dimmer potentiometer. The voltage applied to the LED is limited to a maximum by a zener diode control circuit and that voltage is reduced by a voltage detector circuit which senses the difference between the battery voltage and the dimmer potentiometer output voltage to reduce the LED voltage in proportion to that difference. The voltage detector circuit is disabled when vehicle parking lamps are turned off to insure maximum LED brightness in daytime driving.

Claims

1. In an automotive instrument panel illumination circuit for a vehicle having a power supply subject to voltage fluctuations and a manually positioned dimmer control potentiometer connected to the power supply and providing a variable dimmer voltage for instrument panel illumination, a circuit for providing a variable supply voltage to light emitting diodes on the instrument panel comprising;

control means having an input terminal for controllably delivering a supply voltage from the power supply to the light emitting diodes according to a control voltage applied to the terminal input,

voltage regulator means for providing a maximum control voltage to the input terminal of the control means to establish a maximum supply voltage to the light emitting diodes which is sufficient to provide full light intensity,

means connected to the power supply and the dimmer control potentiometer including a differential voltage detector sensitive to the voltage difference between the power supply voltage and the dimmer voltage for reducing the control voltage at the input terminal of the control means to effect dimming of the light emitting diodes according to the detected voltage difference,

whereby the light emitting diode intensity is dependent on the dimmer potentiometer position and substantially independent of power supply voltage fluctuations.

2. In an automotive instrument panel illumination circuit for a vehicle having a power supply subject to voltage fluctuations and a manually positioned dimmer control potentiometer connected to the power supply and providing a variable dimmer voltage for instrument panel illumination, a circuit for providing a variable supply voltage to light emitting diodes on the instrument panel comprising;

an emitter follower transistor device connected to controllably deliver a supply voltage from the power supply to the light emitting diodes,

a zener diode connected to provide a regulated maximum voltage to the base of the transistor device to establish a maximum supply voltage to the light emitting diodes which is sufficient to provide full light intensity,

means connected to the power supply and the dimmer control potentiometer including a differential voltage detector sensitive to the voltage difference between the power supply voltage and the dimmer voltage for reducing the voltage at the base of the transistor device to effect dimming of the light emitting diodes according to the detected voltage difference,

whereby the light emitting diode intensity is dependent on the dimmer potentiometer position and substantially independent of power supply voltage fluctuations.

3. In an automotive illumination circuit for a vehicle having a power supply subject to voltage fluctuations, a manually positioned dimmer control potentiometer connected to the power supply and providing a variable dimmer voltage for instrument panel illumination, and a vehicle parking light circuit powered by the said power supply, a circuit for providing a variable supply voltage to light emitting diodes on the instrument panel comprising;

control means having an input terminal for controllably delivering a supply voltage from the power supply to the light emitting diodes according to control voltage applied to the terminal input,

voltage regulator means for providing a maximum control voltage to the input terminal of the control means to establish a maximum supply voltage to the light emitting diodes which is sufficient to provide full light intensity,

voltage reducing means connected to the parking light circuit and the dimmer control potentiometer and operable only when the power supply voltage is applied to the parking light circuit, including a differential voltage detector sensitive to the voltage difference between the power supply voltage and the dimmer voltage for reducing the voltage at the input terminal of the control means to effect dimming of the light emitting diodes according to the detected voltage difference;

whereby the light emitting diode intensity is dependent on the dimmer potentiometer position and substantially independent of power supply voltage fluctuations.