Protection from short cathode condition in LED driver and method therefor
View Patent ↗A Light Emitting Diode (LED) driver for preventing shorting has an LED driver circuit. A protection circuit is coupled to the LED driver to detect a fault condition by monitoring a cathode of an LED string of the LED driver, an LED current sense voltage of the LED driver, an LED current feedback error voltage of the LED driver circuit, and a state of a dimming switch of the LED driver.
1. A Light Emitting Diode (LED) driver for preventing shorting comprising:
an LED driver circuit; and
a protection circuit coupled to the LED driver to detect a fault condition by monitoring an LED current sense voltage of the LED driver, an LED current feedback error voltage of the LED driver circuit, and a state of a dimming switch of the LED driver.
2. A Light Emitting Diode (LED) driver for preventing shorting in accordance with claim 1 wherein the protection circuit comprises:
a logic block for sending a signal to deactivate the LED driver circuit when a fault condition is detected;
a current sense comparator having an output coupled to the logic block and inputs coupled to a current sense resistor of the LED driver and to a current sense reference voltage;
a current feedback error comparator having an output coupled to the logic block and inputs coupled to the current sense resistor and a current feedback error reference voltage; and
a dimming switch signal coupled to the dimming switch of the LED driver and to a second input of the logic block for controlling operation of the dimming switch.
3. A Light Emitting Diode (LED) driver for preventing shorting in accordance with claim 1 wherein the LED driver circuit comprises:
an LED driver stage coupled to an output of the protection circuit, the LED driver stage receiving an input voltage from a voltage source;
wherein the LED string coupled to the LED driver stage, the switch is coupled to the LED string, and the current sense resistor is coupled to the dimming switch.
4. A Light Emitting Diode (LED) driver for preventing shorting in accordance with claim 3 wherein the LED driver circuit further comprises an error amplifier coupled to the current sense resistor.
5. A Light Emitting Diode (LED) driver for preventing shorting comprising:
an LED driver circuit; and
a protection circuit coupled to the LED driver to detect a fault condition by monitoring a cathode of an LED string of the LED driver, an LED current sense voltage of the LED driver, an LED current feedback error voltage of the LED driver circuit, and a state of a dimming switch of the LED driver.
6. A Light Emitting Diode (LED) driver for preventing shorting in accordance with claim 5 wherein the protection circuit comprises:
a logic block for sending a signal to deactivate the LED driver circuit when the fault condition is detected;
a first comparator having a first comparator output coupled to a first input of the logic block and first comparator inputs coupled to a first reference voltage and to the cathode of an LED string;
a second comparator having a second comparator output coupled to a second input of the logic block and second comparator inputs coupled to a second reference voltage and to the LED current sense voltage; and
a third comparator having a third comparator output coupled to a third input of the logic block and third comparator inputs coupled to a third reference voltage and the LED current feedback error voltage.
7. A Light Emitting Diode (LED) driver for preventing shorting in accordance with claim 6 wherein the protection circuit further comprises: a fourth input of the logic block coupled to an external pulsed dimming signal.
8. A Light Emitting Diode (LED) driver for preventing shorting in accordance with claim 5 wherein the LED driver circuit comprises:
an LED driver stage coupled to an output of the protection circuit, the LED driver stage receiving an input voltage from a voltage source;
the LED string coupled to the LED driver stage;
the dimming switch coupled to the LED string; and
a current sense resistor coupled to the dimming switch.
9. A Light Emitting Diode (LED) driver for preventing shorting in accordance with claim 8 wherein the LED driver circuit further comprises an error amplifier coupled to the current sense resistor.
10. A Light Emitting Diode (LED) driver for preventing shorting in accordance with claim 8 wherein the LED driver circuit further comprises an error amplifier coupled to the current sense resistor, the error amplifier compares the current feedback signal to a reference voltage.
11. A Light Emitting Diode (LED) driver for preventing shorting in accordance with claim 5 wherein the LED string comprises a plurality of series-connected LED strings.
12. A Light Emitting Diode (LED) driver for preventing shorting in accordance with claim 11 further comprising an anti-parallel diode coupled to each of the plurality of series-connected LED strings.
13. A Light Emitting Diode (LED) driver for preventing shorting in accordance with claim 5 wherein the LED string comprises a plurality of individual LEDs connected in series.
14. A Light Emitting Diode (LED) driver for preventing shorting in accordance with claim 13 further comprising a Zener diode coupled to each of the plurality of series-connected LEDs.