Constant-current controller with square-wave input current shaping
A constant-current controller with square wave input current shaping for driving a series of light emitting diodes (LEDs) is provided. The controller may include a sample and hold circuit that samples a current sense voltage, a first multiplier circuit that multiplies an output of the sample and hold circuit, an error detector circuit that compares an output of the multiplier circuit with a reference voltage, an error amplifier that amplifies an output of the error detector circuit, a second multiplier circuit that multiplies an output of the error amplifier by a coefficient, and an output circuit that outputs a pulse-width modulated control signal based on an output of the second multiplier circuit. The coefficient may vary depending on whether the constant-current LED driver controller is used with a boost converter or a buck-boost converter.
1. A constant-current LED driver controller comprising:
a sample and hold circuit that samples a current sense voltage;
a first multiplier circuit that multiplies an output of the sample and hold circuit;
an error detector circuit that compares an output of the multiplier circuit with a reference voltage;
an error amplifier that amplifies an output of the error detector circuit; and
an output circuit that outputs a pulse-width modulated control signal based on an output of the error amplifier circuit.
2. The constant-current LED driver controller of claim 1 , further comprising:
a second multiplier circuit that multiplies an output of the error multiplier by a topology-dependent coefficient;
wherein the output circuit outputs the pulse-width modulated control signal based on an output of the second multiplier circuit.
3. The constant-current LED driver controller of claim 2 , further comprising:
an integrator circuit that outputs a ramp signal based on the current sense voltage; and
a comparator that receives the output of the second multiplier circuit and the ramp signal, and generates a reset signal that is input to the output circuit.
4. The constant-current LED driver controller of claim 2 , wherein the topology-dependent coefficient varies depending on whether the constant-current LED driver controller is used with a boost converter or a buck-boost converter.
5. The constant-current LED driver controller of claim 4 , wherein the topology-dependent coefficient is equal to the pulse-width modulated control signal if the constant-current LED driver controller is used with a boost converter.
6. The constant-current LED driver controller of claim 4 , wherein the topology-dependent coefficient is equal to one if the constant-current LED driver controller is used with a buck-boost converter.
7. The constant-current LED driver controller of claim 1 , wherein the sample and hold circuit samples the current sense voltage at a mid-point of an interval of the pulse-width modulated control signal.
8. The constant-current LED driver controller of claim 1 , wherein the first multiplier circuit multiplies the output of the sample and hold circuit by the difference between one and a duty ratio of the pulse-width modulated control signal.
9. The constant-current LED driver controller of claim 1 , wherein the error detector circuit compares the output of the first multiplier circuit with a reference voltage.
10. The constant-current LED driver controller of claim 1 , further comprising a topology detector circuit that generates the topology-dependent coefficient, the topology detector circuit comprising:
a comparator that compares the current sense voltage a threshold voltage, and generates an output based on the comparison;
a first logic gate that receives the output of the comparator and the pulse-width modulated control signal as inputs; and
a second logic gate that receives an output of the first logic gate and the pulse-width modulated control signal as inputs, and generates the coefficient as an output.
11. The constant-current LED driver controller of claim 2 , further comprising a third multiplier that multiplies a reference voltage and a dimming coefficient to generate a product that is input to the error detector circuit.
12. The constant-current LED driver controller of claim 11 , wherein the error detector circuit compares the product generated by the third multiplier and the output of the first multiplier.
13. The constant-current LED driver controller of claim 10 , wherein the dimming coefficient is a function of a phase-cut dimming angle of a voltage source.
14. A boost-type switching power converter comprising:
a rectified voltage source;
an inductor coupled to the rectified voltage source;
a rectifier diode coupled to the inductor;
a smoothing capacitor coupled to the rectifier diode;
one or more light emitting diodes (LEDs) connected in parallel with the smoothing capacitor;
a controlled power switch coupled to the rectifier diode and in parallel with the smoothing capacitor;
a current sense resistor coupled to the controlled power switch; and
an LED driver controller coupled to the controlled power switch and the current sense resistor;
wherein the LED driver controller outputs a pulse-width modulated control signal to the controlled power switch;
wherein the current sense resistor develops a current sense voltage representing a current in the inductor;
wherein an average magnitude of the current in the inductor equals an input current provided by the rectified voltage source; and
wherein the LED driver controller comprises
a sample and hold circuit that samples a current sense voltage;
a first multiplier circuit that multiplies an output of the sample and hold circuit;
an error detector circuit that compares an output of the multiplier circuit with a reference voltage;
an error amplifier that amplifies an output of the error detector circuit; and
an output circuit that outputs the pulse-width modulated control signal based on an output of the error amplifier.
15. The boost-type switching power converter of claim 14 , wherein the LED driver controller further comprises:
a second multiplier circuit that multiplies an output of the error amplifier by a topology-dependent coefficient;
wherein the output circuit outputs the pulse-width modulated control signal based on an output of the second multiplier circuit.
16. The boost-type switching power converter of claim 15 , wherein the LED driver controller further comprises:
an integrator circuit that outputs a ramp signal based on the current sense voltage; and
a comparator that receives the output of the second multiplier circuit and the ramp signal, and generates a reset signal that is input to the output circuit.
17. The boost-type switching power converter of claim 15 , wherein the topology-dependent coefficient is equal to a duty ratio of the pulse-width modulated control signal.
18. A buck-boost-type switching power converter comprising:
a rectified voltage source;
an inductor coupled to the rectified voltage source;
a rectifier diode coupled to the inductor;
a smoothing capacitor coupled to the rectifier diode and the inductor;
one or more light emitting diodes (LEDs) connected in parallel with the smoothing capacitor;
a controlled power switch coupled to the rectifier diode and the inductor;
a current sense resistor coupled to the controlled power switch; and
an LED driver controller coupled to the controlled power switch and the current sense resistor;
wherein the LED driver controller outputs a pulse-width modulated control signal to the controlled power switch;
wherein the current sense resistor develops a current sense voltage representing at least a portion of a current in the inductor;
wherein an average magnitude of the current in the inductor equals an input current provided by the rectified voltage source; and
wherein the LED driver controller comprises:
a sample and hold circuit that samples a current sense voltage;
a first multiplier circuit that multiplies an output of the sample and hold circuit;
an error detector circuit that compares an output of the multiplier circuit with a reference voltage;
an error amplifier that amplifies an output of the error detector circuit; and
an output circuit that outputs a pulse-width modulated control signal based on an output of the error amplifier.
19. The buck-boost-type switching power converter of claim 18 , wherein the LED driver controller further comprises:
a second multiplier circuit that multiplies an output of the error amplifier by a topology-dependent coefficient;
wherein the output circuit outputs the pulse-width modulated control signal based on an output of the second multiplier circuit.
20. The buck-boost-type switching power converter of claim 19 wherein the LED driver controller further comprises:
an integrator circuit that outputs a ramp signal based on the current sense voltage; and
a comparator that receives the output of the second multiplier circuit and the ramp signal, and generates a reset signal that is input to the output circuit.
21. The buck-boost-type switching power converter of claim 20 , wherein the topology-dependent coefficient is equal to one.