CONSTANT POWER LED CIRCUIT
A constant power drive for light emitting diodes, such that there is automatic compensation for variation in forward voltage of the LED, both in a single unit with temperature, and also due to unit-to-unit variations.
1 - 10 . (canceled)
11 . An LED driver circuit comprising:
an inductor in series with at least one LED;
a switching transistor connected to the inductor;
a current sensor configured to provide a signal proportional to a current in the inductor;
a diode configured to block current from an input power source and admit current from the inductor; and
a switch-control circuit configured to receive the signal from the current sensor and provide an output signal to the switching transistor to control the relative amount of time the switching transistor is in an on configuration and an off configuration, wherein the output signal is based on the signal from the current sensor.
12 . The LED driver circuit of claim 11 , wherein the current sensor is a resistor.
13 . The LED driver circuit of claim 11 , wherein the current sensor is a transformer.
14 . The LED driver circuit of claim 11 , wherein the current sensor is an amplifier.
15 . The LED driver circuit of claim 11 , wherein the switch-control circuit is a low pass filter.
16 . The LED driver circuit of claim 11 , wherein the input power source is AC-line power that is power-factor corrected.
17 . The LED driver circuit of claim 11 , the output signal of the switch-control circuit is proportional to the duty cycle of the switching transistor.
18 . The LED driver circuit of claim 11 , wherein the output signal of the switch-control circuit is proportional to the forward voltage of the at least one LED.
19 . The LED driver circuit of claim 11 , wherein the output signal of the switch-control circuit is proportional to the power of an LED.
20 . The LED driver circuit of claim 11 , wherein the output signal of the switch-control circuit is proportional to the duty cycle of the power supply.
21 . The LED driver circuit of claim 11 , wherein
the time constant of the switch-control circuit is approximately 3 to 10 times longer than a complete switching period of the transistor switch.
22 . The LED driver circuit of claim 11 , wherein the switching transistor is connected between the diode and the current sensor.
23 . A constant power LED drive circuit comprising:
an inductor in series with at least one LED;
a reverse biased diode in parallel with the inductor in series with the at least one LED;
a current sensor configured to provide a signal proportional to at least one LED current;
a transistor switch serially connected between the current sensor and the reverse biased diode;
a feedback circuit configured to receive the signal from the current sensor and provide a conditioned signal proportional to the power of the at least one LED; and
a switch-control circuit configured to receive the conditioned signal from the feedback circuit, wherein the switch-control circuit is configured to control the relative amount of time the transistor switch is in an on configuration and an off configuration.
24 . The LED driver circuit of claim 23 , wherein the current sensor is a resistor.
25 . The LED driver circuit of claim 23 , wherein the current sensor is a transformer.
26 . The LED driver circuit of claim 23 , wherein the current sensor is an amplifier.
27 . The LED driver circuit of claim 23 , wherein the feedback circuit is a low pass filter.
28 . The LED driver circuit of claim 23 , wherein the input power source is AC-line power that is power-factor corrected.
29 . The LED driver circuit of claim 23 , the output signal of the switch-control circuit is proportional to the duty cycle of the transistor switch.
30 . The LED driver circuit of claim 29 , wherein the output signal of the switch-control circuit is proportional to the forward voltage of the at least one LED.