Line voltage dimmable constant current LED driver
A programmable LED constant current driver circuit for driving LEDs at constant current and dimming the LEDs using standard, off-the-shelf dimmers is provided. The current driver circuit of the present disclosure includes a temperature compensation feature which controls the on time for the LEDs based on a measured temperature of the current driver and associated circuits. In another embodiment, the current driver circuit is designed to receive a 24 VAC input and drive one or more LEDs in a transformer-based system dimming system.
1. A current driver circuit for at least one light emitting diode (LED) comprising:
an input section adapted to receive a truncated power waveform generated by a variable dimmer circuit, the truncated power waveform having a positive pulse portion and a negative pulse portion, a duty cycle of which is proportional to a desired dimming level;
a rectifier section for rectifying the input truncated power waveform to a plurality of positive pulses;
a current switching regulator adapted to provide a constant current to the at least one LED; and
a controller coupled to the rectifier section and adapted to determine a level of each of the plurality of positive pulses, wherein if the level is below a first predetermined threshold, the current switching regulator is turned off by the controller and, if the level is a above a second predetermined threshold, the current switching regulator is turned on by the controller so as to pulse modulate the constant current to the at least one LED to maintain the desired dimming level of the at least one LED.
2. The current driver circuit as in claim 1 , further comprising a time delay module adapted to delay the turning on of the current switching regulator for a predetermined period of time after the current switching regulator has been turned off.
3. The current driver circuit as in claim 2 , further comprising a temperature sensor adapted to measure a temperature of the current driver circuit, wherein the predetermined period of time for delay is based on the measured temperature.
4. The current driver circuit as in claim 3 , wherein the current switching regulator provides the constant current via a pulse width modulated (PWM) signal.
5. The current driver circuit as in claim 4 , wherein an on time of the PWM signal is based on the measured temperature.
6. The current driver circuit as in claim 4 , wherein an on time of the PWM signal is decreased when the measured temperature is above a predetermined temperature threshold.
7. The current driver circuit as in claim 3 , wherein the rectifier section is a diode bridge.