Retrofit LED lighting system with circuit level enhancement
A light emitting diode retrofit lamp for replacement of fluorescent lamp or tube driven by fluorescent ballast is provided. The retrofit lamp consists of an enhanced circuit that overcomes the compatibility issues with the fluorescent ballasts. The circuit of the retrofit lamp comprises a deflickerizer circuit that prevents the flicker in the lamp when the lamp operates in the frequency range of 0.1 Hz to 60 Hz. The deflickerizer circuit further provides a method to align frequency with the ballast frequency and maintains phase to avoid low frequency interference.
1. A retrofit LED lamp adapted to work on a ballast comprising:
a plurality of input pins at the end of the retrofit lamp for connection to a first and a second lamp connection terminal of a ballast;
a bridge rectifier connected to the first and second lamp terminal connection of the ballast, wherein the bridge rectifier converts the alternating current supplied by the AC ballast to the direct current required for an LED array;
an LED array connected to the output terminal of the bridge rectifier by a reactive coupling;
a deflickerizer circuit connected to the LED array to prevent the appearance of flicker in the retrofit LED lamp when the alternating current frequency is in the range of 0.5 Hz to 60 Hz, wherein the deflickerizer circuit comprises a low dropout regulator, a plurality of op amplifiers, a plurality of resistors and capacitors, a FET.
2. The retrofit LED lamp of claim 1 wherein the bridge rectified is made of schottky diodes.
3. The retrofit LED lamp of claim 1 wherein the deflickerizer circuit shorts the light-emitting diode array.
4. The retrofit LED lamp of claim 1 wherein the deflickerizer circuit measures the current being delivered to the LED array.
5. The retrofit LED lamp of claim 1 wherein the FET in the deflickerizer circuit is a MOSFET.
6. The retrofit LED lamp of claim 1 wherein the FET of the deflickerizer circuit shorts out the LED array with a PWM signal on measuring the current.
7. The retrofit LED lamp of claim 6 wherein the PWM signal is in the range of 100 Hz to 10 kHz.
8. The retrofit LED lamp of claim 1 wherein deflickerizer circuit adjusts the duty cycle of PWM circuit in real time in response to change in ballast current.
9. The retrofit LED lamp of claim 1 wherein the reactive coupling comprise a TRIAC driven by a SIDAC, a current limiting resistor, a capacitor placed in parallel to the TRIAC, such that the gate terminal of the TRIAC is connected to a Zener diode that receives input from the second terminal connection of the ballast.
10. The retrofit LED lamp of claim 9 wherein for low frequency ballast, the SIDAC triggers at a threshold frequency which causes the TRIAC to be open circuit for approximately 25% of the half cycle reducing current flow in the ANSI reference ballast with its 60 Hz sinusoidal waveform @ 220V rms.
11. The retrofit LED lamp of claim 9 wherein for high frequency ballast, the Zener diode voltage is set to a level that the 220V rms ANSI ballast will not achieve (i.e. >315V) such that the TRIAC remains an open circuit and the conducting current can be controlled with the parallel capacitor.
12. The retrofit LED lamp of claim 1 wherein the deflickerizer circuit maintains the phase while aligning frequency to avoid low frequency interference.
13. The retrofit LED lamp of claim 1 wherein the deflickerizer circuit completes an edge detection to measure the frequency of coming waveform for each cycle of the ballast.
14. The retrofit LED lamp of claim 1 wherein the deflickerizer circuit calculates a required PWM duty cycle as a function of external diming signal, temperature diming and deflickerizing dimming for each cycle of the ballast.
15. The retrofit LED lamp of claim 1 wherein the deflickerizer circuit asserts the FET voltage for the required period in order to create the designed output level for each cycle of the ballast.