Dimming LED circuit augmenting DC/DC controller integrated circuit
Embodiments include systems, methods, and apparatuses for providing a dimming function in a single stage AC input light emitting diode (LED) driver with a controller that contains an on-chip error amplifier and an on-chip fixed reference voltage source coupled to a first input of the error amplifier. The controller controls a duty cycle of a switching transistor to cause a feedback voltage, applied to a first package input terminal, to match the reference voltage. To achieve a dimming function, a voltage across a current sense resistor in series with the LEDs is applied to a first input of a high gain differential amplifier, and a variable dimming control voltage is applied to a second input of the differential amplifier. The output of the differential amplifier is coupled to the first package input terminal. The differential amplifier input signals will be matched at the target LED current level.
1. A light-emitting diode (LED) driver comprising:
a first circuit configured to receive a voltage from one or more LEDs and a user-controlled variable dimming voltage and provide a first output voltage;
a second circuit electrically coupled to the first circuit, the second circuit configured to receive a fixed reference voltage and the first output voltage and provide a second output voltage based thereon;
a driver circuit coupled to the second circuit and comprising a switch, the driver circuit configured to provide a driving current for the one or more LEDs having a magnitude based on a pulse width modulation (PWM) signal supplied to a control terminal of the switch, a duty cycle of the PWM signal set to control a magnitude of the driving current based on the second output voltage such that the voltage from the one or more LEDs matches the variable dimming voltage;
a rectifier disposed at an input of the LED driver and configured to convert an input alternating current (AC) mains voltage supplied thereto to a rectified voltage; and
a bypass diode having:
an input configured to receive the rectified voltage, and
an output coupled to the one or more LEDs and to an output capacitor coupled to ground,
the bypass diode being forward biased when a voltage of the output capacitor is less than the rectified voltage, the output capacitor being charged when the bypass diode is forward biased, the bypass diode being reverse biased when the output capacitor reaches a regulated voltage.
2. The LED driver of claim 1 , wherein the first output voltage has a magnitude based on a difference between the voltage from the one or more LEDs and the variable dimming voltage.
3. The LED driver of claim 1 , further comprising an input configured for electrical connection to a device that provides the dimming voltage.
4. The LED driver of claim 1 , wherein the second output voltage is based on a difference between the first output voltage and the fixed reference voltage.
5. The LED driver of claim 1 , wherein the magnitude of the driving current is based on the second output voltage.
6. The LED driver of claim 1 , wherein the first circuit is electrically coupled to a sense resistor to sense the voltage from the one or more LEDs.
7. The LED driver of claim 1 , wherein the magnitude of the driving current controls a brightness of the one or more LEDs.
8. The LED driver of claim 1 , further comprising:
a transformer having an input configured to receive the rectified voltage; and
a main diode connected in series with the transformer, the main diode having:
an input coupled to an output of the transformer, and with the switch, and
an output coupled to the one or more LEDs,
the transformer and main diode connected in parallel with the bypass diode.
9. The LED driver of claim 1 , further comprising a circuit element having an input configured to receive the rectified voltage and an output coupled with the switch, the circuit element connected in parallel with the bypass diode and selected from a set of circuit elements that include a transformer and an inductor.
10. The LED driver of claim 1 , wherein the second circuit is contained in an integrated circuit.
11. A light-emitting diode (LED) lighting system comprising:
a boost converter configured to be electrically coupled to one or more light emitting diodes (LEDs), the boost converter configured to:
receive an input voltage and a voltage from the one or more LEDs and a user-controlled variable dimming voltage,
generate a first output voltage based on a difference between the voltage from the one or more LEDs and the variable dimming voltage,
receive the first output voltage and a reference voltage and provide a second output voltage based on a difference between the first output voltage and the fixed reference voltage, and
provide a driving current to the one or more LEDs using a driver circuit such that the voltage from the one or more LEDs matches the variable dimming voltage, the driver circuit electrically coupled to the controller to receive the second output voltage and provide the driving current based thereon; and
a rectifier disposed at an input of the driver circuit and configured to convert an input alternating current (AC) mains voltage supplied thereto to a rectified voltage as the input voltage,
the boost converter further comprising:
an output capacitor coupled to ground, and
a bypass diode, the bypass diode having:
an input configured to receive the rectified voltage, and
an output configured to be coupled to the one or more LEDs and to the output capacitor,
the bypass diode being forward biased when a voltage of the output capacitor is less than the rectified voltage, the output capacitor being charged when the bypass diode is forward biased, the bypass diode being reverse biased when the output capacitor reaches a regulated voltage.
12. The system of claim 11 , wherein the driving current controls a brightness of the one or more LEDs.
13. The system of claim 11 , wherein the one or more LEDs comprise multi junction LEDs connected in series.
14. The system of claim 11 , further comprising the one or more LEDs.
15. The system of claim 11 , further comprising an input terminal configured for electrical connection to a device that provides the variable dimming voltage.