LED lighting apparatus

An LED lighting apparatus can be configured to supply a number of LEDs connected in series with a requisite voltage and power even if an amount of forward voltage of the LEDs connected in series is larger than a supply voltage of a battery. The LED lighting apparatus can include a boosting circuit and an inverted boosting circuit. LEDs can be connected between outputs of the boosting circuit and the inverted boosting circuit. The LED lighting apparatus can also include a current detection circuit configured to detect an LED current, and can include a dual PWM control IC configured to control the boosting circuit and the inverted boosting circuit in accordance with the LED current detected by the current detection circuit so as to keep the LED current substantially constant. The LED lighting apparatus can include a shutdown circuit to stop supplying a power supply when a load that includes the LEDs is in a circuit that is either opened or shorted.

This application claims the priority benefit under 35 U.S.C. §119 of Japanese Patent Application No. 2006-144408 filed on May 24, 2006 and Japanese Patent Application No. 2006-144411 filed on May 24, 2006, both of which are hereby incorporated in their entireties by reference.

BACKGROUND

The presently disclosed subject matter relates to a LED lighting apparatus for lighting LEDs. More specifically, the subject matter relates to a LED lighting apparatus in which an amount of forward voltage for LEDs connected in series is larger than a supply voltage of a battery. The LED lighting apparatus can be used whenever a number of LEDs are used, such as in a vehicular lamp (e.g., tail-lights, stop lights, signal lights, headlights, etc.).

2. Description of the Related Art

FIG. 2shows a conventional LED lighting apparatus90in which a plurality of LEDs80are connected in series and lit by use of a battery supply voltage that is lower than an amount of forward voltage of the LEDs80. The conventional LED lighting apparatus90includes: a control circuit91; a boosting circuit92controlled by the control circuit91; an inverted boosting circuit93configured by using a charge pump circuit, and operated by the control circuit91; wherein the LEDs80are connected between an output of the boosting circuit92and an output of the inverted boosting circuit93through a constant current circuit96, if necessary. The conventional LED lighting apparatus90can light a requisite number of LEDs when a predetermined output voltage is supplied between the output of the boosting circuit92and the output of the inverted boosting circuit93.

The control circuit91can control the predetermined output voltage by feeding back a voltage divided between resistors94and95so as not to raise the output voltage higher than the predetermined output voltage. The LEDs80can be connected in series to the constant current circuit96as shown inFIG. 2, and can be controlled to light with stable brightness characteristics as described in further detail, for example, in Japanese Patent Application Laid Open JP2005-136157 and its English translation, which are hereby incorporated in their entirety by reference.

In the conventional LED lighting apparatus90described above, because the inverted boosting circuit93is configured by using a charge pump circuit to allow the configuration to be simple, it is difficult to adapt the circuit to high power LEDs such as those used in vehicular lamps (e.g., signal lights, front lights, taillights, stop lights, etc.) When the conventional LED lighting apparatus is used for lighting high power LEDs in a vehicular lamp, for example, use of the constant current circuit96can result in some problems like runaway temperature increases (i.e., chip fever), large architecture of the chip, etc., which may result when the current in the device flows from several mil amperes to several amperes in a FET96aand a resistor96blocated therein.

Thus, when high power LEDs that are used as a vehicular lamp such as stop lights are lit by the conventional configurative lighting apparatus, a plurality of middle-sized lighting apparatuses can be used for lighting the plurality of LEDs connected in either series or in parallel. In that case, because all of the LEDs are lit by the plurality of middle-sized lighting apparatuses, the conventional configurative lighting apparatuses can result in some problems such as complicated wiring and maintenance, increased cost, etc.

The disclosed subject matter has been devised to consider the above and other problems and characteristics. Thus, an embodiment of the disclosed subject matter can include a LED lighting apparatus for supplying LEDs connected in series with a requisite voltage and power even if the amount of forward voltage of LEDs connected in series is larger than a supply voltage of a battery. The various problems described above are thus addressed and possibly reduced or changed while also addressing and possibly reducing other associated problems.

SUMMARY OF THE DISCLOSED SUBJECT MATTER

The presently disclosed subject matter has been devised in view of the above described characteristics and problems, etc. An aspect of the disclosed subject matter includes a device that has a fail safe function.

According to another aspect of the disclosed subject matter, a LED lighting apparatus can include: a boosting circuit configured to supply power/electricity to an anode of a first LED of LEDs connected in series; a current detection circuit configured to detect a LED current of the LEDs connected in series, the current detection circuit connected between the boosting circuit and the anode of the first LED; an inverted boosting circuit configured to supply power to a cathode of the last LED of the LEDs connected in series; and a dual PWM (pulse-width-modulation) control IC (integrated circuit) with two output terminals and two feedback terminals, one output terminal thereof connected to an input of the boosting circuit and the corresponding feedback terminal thereof connected to an output of the current detection circuit, the other output terminal thereof connected to an input of the inverted boosting circuit and the other corresponding feedback terminal thereof connected to the cathode of the last LED of the LEDs connected in series via resistors if necessary. The dual PWM control IC controls the boosting circuit and the inverted boosting circuit in accordance with the LED current detected by the current detection circuit, so as to keep the LED current substantially constant.

Another aspect of the above described exemplary LED lighting apparatus can include providing a LED lighting apparatus for supplying LEDs connected in series with a requisite voltage and power even if the amount of forward voltage of the LEDs connected in series is larger than a supply voltage of the battery connected thereto. Furthermore, it is also possible to manufacture the apparatus such that it is small in size and incurs a reduced cost.

Another of the aspects of the disclosed subject matter includes a LED lighting apparatus that can include: a shutdown circuit configured to supply the LED lighting apparatus with a power supply or to stop supplying the power supply, as the case may be, wherein the shut down circuit stops supplying the power supply when the current detection circuit detects an over load current in the LED current. The LED lighting apparatus can also include: a voltage detection circuit configured to detect a load voltage, divided detection resistors thereof connecting between the anode of the first LED of the LEDs connected in series and a ground or the cathode of the last LED of the LEDs in series. The voltage detection circuit can be configured to output a signal to the shut down circuit to stop supplying the LED lighting apparatus with power when the voltage detection circuit detects an open circuit at the load that includes the LEDs.

In the immediately above described LED lighting apparatus, the disclosed subject matter can include a fail safe function in order to prevent the LED lighting apparatus from consuming useless power and for preventing damage thereof by a load failure that involves the LEDs, or the like.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the disclosed subject matter will now be described in detail with reference toFIGS. 1a-1b.

An LED lighting apparatus1shown inFIG. 1acan include a dual PWM control IC2(for example, TL1451A made by Texas Instruments, Inc.); a boosting circuit3configured to supply an anode of a first LED of the LEDs8that are connected in series with positive polarity electricity; a current detection circuit4configured to detect a LED current of the LEDs8connected in series, the current detection circuit4connecting between the boosting circuit3and an anode of the first LED; and an inverted boosting circuit6configured to supply a cathode of the last LED of the LEDs8with negative polarity electricity. Thus, the LED lighting apparatus1provides a simple configuration and enables control of lighting for all LEDs connected in series when the amount of forward voltage of the LEDs is larger than a supply voltage of a battery associated therewith, such as when connected to a vehicle battery.

A specific description of the dual PWM control IC2will now be given. The dual PWM control IC2can include; dual output circuits with common-emitter transistors; two control circuits for controlling the dual output circuits, respectively; two feedback inputs for receiving feeding back; two error amplifiers to allow feedback thereto; and two dead-time control comparators. The two dead-time control comparators can be configured to have no offset unless externally altered, and can provide 0% to 100% dead time, respectively. Thus, the dual PWM control IC2can stably control the dual output circuits for the PWM outputs, respectively.

The boosting circuit3can include: an induction coil3a; a FET3bcontrolled by one output terminal2aof the dual PWM control IC2; a diode3c; and a capacitor3d. An operational principle of the boosting circuit3can be the same as a conventional boosting circuit92(a conventional DC-DC converter) as shown inFIG. 2.

A feedback terminal2ccorresponding to the output terminal2aof the dual PWM control IC2can be connected to an output of the current detection circuit4that detects the LED current by measuring a voltage between both ends of a current detection resistor4a. Thus, an output of the boosting circuit3can be controlled so as to keep the LED current substantially constant.

The inverted boosting circuit6can include: a FET6acontrolled by the other output terminal2bof the dual PWM control IC2; an induction coil6b; a diode6c; and a capacitor6d.

An operational principle of the inverted boosting circuit6will now be described. When the FET6ais on, because FET current flows to a ground through the induction coil6bfor the diode6cconnected in inverted bias, the induction coil6bcan be charged with an electric energy. When the FET6ais next in an off state, because a corresponding inverted electricity to the electric energy is generated in the induction coil6bin order to keep charging the electric energy, the capacitor6dcan be charged with the inverted electricity through the diode6c. In that case, a positive electrode becomes a ground and a negative electrode becomes an anode of the diode6cin accordance with the direction of charging the electric energy into the capacitor6d. Because the FET6acan alternate the above on and off states by the other output terminal2bof the dual PWM control IC2, the inverted boosting circuit6can be considered an inverted DC-DC converter against a power supply9to allow output of a negative DC voltage from the anode of the diode6c.

When the anode of the first LED of the LEDs8that are connected in series is connected to the positive output of the boosting circuit3through the current detection resistor4a, and the cathode of the last LED of the LEDs8is connected to the negative output of the inverted boosting circuit6that is biased with a minus potential, the LEDs8connected in series can be connected between a high voltage having a voltage that is approximately double the voltage of the DC-DC converter output of the boosting circuit3. The LED current can be constant by controlling at least one output voltage of the boosting circuit3and the inverted boosting circuit6by using the dual PWM control IC2.

A fail safe function will be now described as another aspect of the disclosed subject matter. The current detection circuit4can detect a breakdown such as a short circuit of a load that includes the LEDs8by detecting a current that is larger than a predetermined current. In that case, a shut down circuit7can stop supplying the LED lighting apparatus via the power supply9by turning off a FET7athrough the use of an output of the current detection circuit4. Thus, the current detection circuit4can include a fail safe function in order to prevent the LED lighting apparatus from consuming useless power and in order to prevent various other breakdowns due to over current in the circuit.

The current detection circuit4can also detect a load failure by detecting a current that is smaller than a predetermined current. However, it is difficult for the current detection circuit4to detect a very small current such as when an open circuit of a load occurs, because an open circuit of a load may be suddenly generated. In that case, at least one output voltage of the boosting circuit3and the inverted boosting circuit6may suddenly increase in order to suddenly cause the LED current to decrease. A voltage detection circuit5can easily detect the open circuit of a load by measuring a voltage between divided resistors5aand5b. These resistors5aand5bare connected between the anode of the first LED and a ground as shown inFIG. 1a. However, theses resistors5aand5bcan be connected between the anode of the first LED and the cathode of the last LED by arranging the resistors accordingly. The voltage detection circuit5can also control the shutdown circuit7by using an output signal thereof. For example, when the voltage detection circuit5detects an open circuit of a load that includes the LEDs8, the voltage detection circuit5can control the shut down circuit7so as not to suddenly increase the outputs of the boosting circuit3and the inverted boosting circuit6.

Thus, when the current detection circuit4outputs a signal corresponding to a short circuit of the load that includes LEDs8, or when the voltage detection circuit5outputs a signal corresponding to an open circuit of the load including the LEDs8, the power supply9to the LED lighting apparatus can be stopped by the FET7ain the shutdown circuit7.

As described above, the above exemplary embodiment can detect a short circuit of a load by one current detection circuit and also can detect an open circuit of a load by one voltage detection circuit, because the LEDs can be connected in series. In the conventional lighting apparatus, both the number of current detection circuits and voltage detection circuits are limited by the number of LEDs. Furthermore, because circuits in the above exemplary embodiment can be divided between those that connect positive voltage to a ground and those that connect a ground to the negative voltage, the absolute maximum rating for the FET3b,3a, diode3c,6c, capacitor3d,6dand other electronic components, etc., used in the above exemplary embodiment can be the same as that of conventional lighting apparatus.

As shown inFIG. 1b, another embodiment of a LED lighting apparatus1can include a control circuit29in place of the dual PWM control IC2, the current detection circuit4and the voltage detection circuit5ofFIG. 1a. A boosting circuit20can be configured to supply positive current to an anode of a first of the LEDs28connected in series. An inverted boosting circuit30can be configured to supply a negative current to a cathode of the last of the LEDs28. The LED lighting apparatus1ofFIG. 1balso has a simple configuration and enables control of lighting for all LEDs connected in series when the amount of forward voltage of the LEDs is larger than a supply voltage of a battery associated therewith, such as a vehicle battery.

The inverted boosting circuit30can include two FETs32and33that are connected in series with a diode34and connected in parallel with an induction coil31and separately in parallel with a capacitor35.

The boosting circuit20can include a FET22connected in parallel with a diode23and a capacitor24and in series with an induction coil21.

Two resistors25and26can be connected in parallel with the LEDs28while separately connected to terminals of the control circuit29. In addition, a resistor41can be placed between sets of the LEDs28with connections to separate terminals of the control circuit29, both before and after the resistor41.

In operation, the embodiment ofFIG. 1bcan be configured to act substantially similar to the embodiment ofFIG. 1a.

While there has been described what are at present considered to be exemplary embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover such modifications as fall within the true spirit and scope of the invention. All conventional art references described above are herein incorporated in their entirety by reference.