Driver for LED retrofit with PWM correction unit, LED retrofit and vehicle headlight
A light-emitting diode (LED) driver is described herein. The LED driver includes input terminals that receive power from a pulse width modulation (PWM) power supply operating at a duty cycle less than 100%. The LED driver also includes a current source that receives the power from the input terminals and provides a controlled current with an adjustable target value for at least one LED. The LED driver also includes a PWM correction unit that adjusts the adjustable target value of the controlled current based on the duty cycle of the PWM to provide a constant light output of the LED retrofit lamp independent of the duty cycle of the PWM.
1. A light-emitting diode (LED) driver comprising:
a plurality of input terminals configured to receive power from a pulse width modulation (PWM) power supply operating at a duty cycle less than 100%;
a current source configured to receive the power from the input terminal and provide a controlled current with an adjustable target value for at least one LED; and
a PWM correction unit comprising a variable resistor configured to adjust the adjustable target value of the controlled current by setting a resistance of the variable resistor based on the duty cycle of the PWM to provide a constant light output of the LED retrofit lamp independent of the duty cycle of the PWM.
2. The LED driver according to claim 1 , wherein:
the current source comprises a current-sense resistor, and
the variable resistor is electrically coupled in parallel with the current-sense resistor.
3. The LED driver according to claim 1 , wherein:
the current source comprises a current-sense resistor, and
the variable resistor is electrically coupled in series with the current-sense resistor.
4. The LED driver according to claim 1 , wherein the PWM is 85% or less.
5. A light-emitting diode (LED) retrofit lamp comprising:
an LED lamp body comprising a plurality of LEDs and a socket, the socket having at least one terminal for receiving power from a pulse width modulation (PWM) power supply operating at a duty cycle less than 100%; and
a driver comprising:
a plurality of input terminals configured to receive the power via the at least one terminal in the socket,
a current source configured to receive the power from the input terminals and provide a controlled current with an adjustable target value for the plurality of LEDs, and
a PWM correction unit comprising a variable resistor configured to adjust the adjustable target value of the controlled current by setting a resistance of the variable resistor based on the duty cycle of the PWM to provide a constant light output of the LED retrofit lamp independent of the duty cycle of the PWM.
6. The LED retrofit lamp according to claim 5 , wherein the driver is at least partially located within the socket of the LED lamp body.
7. The LED retrofit lamp according to claim 5 , wherein the driver is mounted in an LED driver body separate from the LED lamp body.
8. The LED retrofit lamp according to claim 5 , wherein the PWM correction unit comprises a variable resistor, and the PWM correction unit is configured to set a resistance of the variable resistor based on the duty cycle of the PWM.
9. The LED retrofit lamp according to claim 5 , wherein:
the current source comprises a current-sense resistor, and
the variable resistor is electrically coupled in parallel with the current-sense resistor.
10. The LED retrofit lamp according to claim 5 , wherein:
the current source comprises a current-sense resistor, and
the variable resistor is electrically coupled in series with the current-sense resistor.
11. The LED retrofit lamp according to claim 5 , wherein the PWM is 85% or less.
12. An automotive lighting system for an automobile that supplies power to headlamps using a pulse width modulation (PWM) power supply operating at a duty cycle less than 100%, the system comprising:
a lamp fixture; and
an LED retrofit lamp secured to the lamp fixture, the LED retrofit lamp comprising:
an LED lamp body comprising a plurality of LEDs and a socket, the socket having at least one terminal for receiving power from a pulse width modulation (PWM) power supply operating at a duty cycle less than 100%; and
a driver comprising:
a plurality of input terminals configured to receive the power via the at least one terminal in the socket,
a current source configured to receive the power from the input terminals and provide a controlled current with an adjustable target value for the plurality of LEDs, and
a PWM correction unit comprising a variable resistor configured to adjust the adjustable target value of the controlled current by setting a resistance of the variable resistor based on the duty cycle of the PWM to provide a constant light output of the LED retrofit lamp independent of the duty cycle of the PWM.
13. The system of claim 12 , wherein the driver is at least partially located within the socket of the LED lamp body.
14. The system of claim 12 , wherein the driver is mounted in an LED driver body separate from the LED lamp body.
15. The system of claim 12 , wherein the PWM correction unit comprises a variable resistor, and the PWM correction unit is configured to set a resistance of the variable resistor based on the duty cycle of the PWM.
16. The system of claim 12 , wherein:
the current source comprises a current-sense resistor, and
the variable resistor is electrically coupled in parallel with the current-sense resistor.
17. The system of claim 12 , wherein:
the current source comprises a current-sense resistor, and
the variable resistor is electrically coupled in series with the current-sense resistor.
18. The system of claim 12 , wherein the PWM is 85% or less.