Temperature compensated led constant current source
OwnerTimothy W. Brooksinventor
Life of this patent
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Abstract
A device and method for providing a temperature compensated LED constant current source. A positive temperature coefficient (PTC) resistor is utilized to reduce the current being supplied through a driver circuit to an LED lighting element under varying environmental conditions. The PTC resistor prevents the LED elements from overheating due to excessive ambient temperature, improper thermal design or excessive voltage. A voltage regulator may be included to linearize the temperature vs. resistance characteristics of the PTC resistor.
Claims28
An electrical circuit for driving at least one light emitting diode, comprising:
- a transistor connected in the current path of the light emitting diode, said transistor comprising a control terminal and at least one load terminal;
- and
- a PTC resistor connected between a supply voltage source and the control terminal of the transistor;
- wherein the at least one load terminal of the transistor is connected in the current path of the light emitting diode;
- and
- wherein the PTC resistor restricts the current supplied to the control terminal of the transistor as the temperature of the PTC resistor increases;
- and
- wherein the transistor restricts the current in the current path of the light emitting diode as the current supplied to the control terminal of the transistor decreases.
An electrical circuit for driving at least one light emitting diode, comprising:
- a transistor connected in the current path of the light emitting diode, said transistor comprising a control terminal and at least one load terminal;
- a PTC resistor connected between a supply voltage source and the control terminal of the transistor;
- and
- a regulator connected to the control terminal of the transistor;
- and
- a load resistor connected in the current path of the light emitting diode and the at least one transistor load terminal;
- wherein the at least one load terminal of the transistor is connected in the current path of the light emitting diode;
- wherein the PTC resistor restricts the current supplied to the control terminal of the transistor as the temperature of the PTC resistor increases;
- wherein the transistor restricts the current in the current path of the light emitting diode as the current supplied to the control terminal of the transistor decreases;
- wherein a reference terminal of the regulator is further connected across the load resistor;
- and
- wherein the regulator is configured to compensate for the non-linear characteristics of the PTC resistor by increasing or decreasing the current supplied to the control terminal of the transistor below a specified temperature.
A method for driving at least one light emitting diode, comprising the steps of:
- varying the current being supplied to a control terminal of a transistor in the current path of the light emitting diode;
- wherein the current is varied due to the varying resistance of a PTC resistor connected between a voltage source and the control terminal.
An electrical circuit for driving at least one light emitting diode, comprising:
- a linear control component connected in the current path of the light emitting diode, said linear control component comprising a control terminal and at least one load terminal;
- and
- a temperature dependent resistor connected to the control terminal of the linear control component;
- wherein the at least one load terminal of the linear control component is connected in the current path of the light emitting diode;
- and
- wherein the temperature dependent resistor restricts a signal supplied to the control terminal of the linear control component as the temperature of the temperature dependent resistor increases;
- and
- wherein the linear control component restricts the current in the current path of the light emitting diode as the signal supplied to the control terminal of the linear control component decreases.
Dependencies are inferred from the claim text.