News Column

Researchers Submit Patent Application, "Led Lighting Apparatus", for Approval

August 6, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Sakai, Keisuke (Matsudo-shi, JP); Takahashi, Rintaro (Tokorozawa-shi, JP); Akiyama, Takashi (Sayama-shi, JP), filed on July 12, 2012, was made available online on July 24, 2014.

The patent's assignee is Citizen Electronics Co., Ltd.

News editors obtained the following quote from the background information supplied by the inventors: "A lighting apparatus (hereinafter called an LED lighting apparatus) is known which is connected to an AC commercial power supply and used for lighting an LED (also called a light-emitting diode). Such LED lighting apparatus commonly operates by rectifying the power supplied from the AC commercial power supply. In particular, a pulsating or near-pulsating voltage may be applied across an LED array constructed by connecting a large number of LEDs in series without requiring the use of large capacitors.

"If a pulsating voltage is directed applied to the LED array, the light emission period becomes short; to address this, it is known to provide a circuit for adjusting the number of series-connected LED stages by detecting the current flowing through the LED array (for example, refer to patent document 1).

"FIG. 7 is a diagram showing an LED lighting apparatus illustrated in FIG. 26 in patent document 1. For convenience, FIG. 7 includes numbers, currents, etc. where necessary.

"The LED lighting apparatus shown in FIG. 7 includes an AC commercial power supply 712, a bridge rectifier circuit 705 constructed from four diodes, a first LED group and a second LED group arranged in parallel, a third LED group connected in series to the first and second LED groups, resistors R1, R2, and R3, an n-type MOS transistor (FET) Q1, and an NPN transistor Q2.

"The resistors R2 and R3 and the transistors Q1 and Q2 together constitute a bypass circuit 717. A current output terminal A of the bridge rectifier circuit 705 is connected to the parallel-connected first and second LED groups. The cathode side of the parallel-connected first and second LED groups is connected to the bypass circuit 717 as well as to the anode side of the third LED group. A current I3 passing through the bypass circuit 717 and a current I4 passing through the third LED group flow into the current sensing resistor R3 and the base of the transistor Q2 contained in the bypass circuit 717.

"FIG. 8 is a diagram showing a voltage versus current relationship for the LED lighting apparatus of FIG. 7. FIG. 8(a) shows an example of a voltage waveform for one pulsating cycle that appears at the terminal A with respect to the terminal B of the bridge rectifier circuit 705, and FIG. 8(b) is an example of a current waveform for one pulsating cycle that flows in the bridge rectifier circuit 705. The current waveform shown in FIG. 8(b) is approximately equal to the sum of the currents I3 and I4.

"The currents I3 and I4 are both equal to 0 A during a period t1 when the voltage at the terminal A is lower than the threshold voltage of the parallel-connected first and second LED groups. When the voltage at the terminal A subsequently rises and exceeds the threshold voltage of the parallel-connected first and second LED groups, the current increases rapidly for a short period t2. When the voltage at the terminal A further rises, there appears a period t3 during which the sum of the currents I3 and I4 is constant. In the first half of the period t3, only the current I3 flows through the bypass circuit 717, and in the second half of the period t3, the current I4 flows not only through the bypass circuit 717 but also through the third LED group. At this time, the currents I3 and I4 are regulated so that the base-emitter voltage of the transistor Q2 is maintained at 0.6 V.

"Next, when the voltage at the terminal A rises, entering a period t4 which contains the peak of the voltage waveform, the transistor Q2 is saturated, and the bypass circuit 717 is cut off, so that the current I3 no longer flows. In the period t4, the overall current varies substantially linearly with the voltage of the terminal A, since the current I4 is only limited by the current-limiting resistor R3. The period during which the voltage of the terminal A falls is the reverse of the period during which the voltage rises.

"The LED lighting apparatus of FIG. 7 has the advantage that, since the period t1 during which all the LEDs are turned off is short, not only does flicker decrease, but power factor and distortion factor both improve and harmonic noise also decreases.

"In the prior art, it is also known to provide an LED lighting apparatus that includes a dimmer circuit between the AC commercial power supply and the bridge rectifier circuit (for example, refer to patent document 2). In the LED lighting apparatus disclosed in patent document 2, a pulsating voltage output from the bridge rectifier circuit is smoothed using a large-capacitance capacitor, and the thus smoothed voltage is used for lighting an LED."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "FIG. 9 is a diagram showing an example in which a dimmer 901 is inserted between the AC commercial power supply and the bridge rectifier circuit 705 in the LED lighting apparatus shown in FIG. 7.

"The dimmer 901 shown in FIG. 9 is a leading-edge type dimmer, which varies the intensity of LED light by controlling the phase of the voltage waveform being output from the AC commercial power supply 712. For example, the dimmer 901 operates as if the voltage is present only in the second half portion by truncating the first half portion of the pulsating voltage shown in FIG. 8(a), and varies the intensity of LED light by adjusting the length of the period during which the voltage is present.

"FIG. 10 is a diagram showing a voltage versus current relationship for the LED lighting apparatus of FIG. 9. FIG. 10(a) shows an example of a voltage waveform for one pulsating cycle that appears at the terminal A with respect to the terminal B of the bridge rectifier circuit 705 for an ideal load, and FIG. 10(b) is an example of a voltage waveform for one pulsating cycle that the bridge rectifier circuit 705 outputs in the circuit shown in FIG. 9.

"In the voltage waveform of FIG. 10(a), the first half portion of the pulsating voltage shown in FIG. 8(a) is truncated by the action of the dimmer 901. As shown in FIG. 10(b), a gradually increasing voltage appears at the output of the bridge rectifier circuit 705 during the first half period when no voltage should be present. In the second half period, a plurality of sharp peaks appear on the voltage being output at the terminal A of the bridge rectifier circuit 705, as shown in FIG. 10(b). Here, if the current flowing through the parallel-connected first and second LED groups is increased up to a certain point, the peaks appearing as shown in FIG. 10(b) can be made to disappear, but the abnormal voltage in the first half period does not disappear.

"The reason that a faulty operation such as shown in FIG. 10(b) occurs is believed to be that there is a need to flow a certain amount of current in order to properly operate the dimmer 901. In actuality, however, in the period during which the voltage waveform of FIG. 10(a) is substantially held to zero, the current minimum necessary for proper operation does not flow to the dimmer 901.

"A faulty operation such as shown in FIG. 10(b) can occur not only when the LED lighting apparatus shown in FIG. 7 is connected to the dimmer 901, but also when the LED lighting apparatus which is a lighter load than an incandescent lamp or halogen lamp is connected to any dimmer other than the above dimmer. If the load is increased by forming a current path in parallel with the light load LED apparatus, the above faulty operation may be able to be resolved. However, increasing the load in such a manner would defeat the purpose of low power consumption of the LED lighting apparatus.

"By contrast, the LED lighting apparatus disclosed in patent document 2 is provided with a load circuit 7 for holding a minimum current necessary for the proper operation of the dimmer circuit 2. However, the LED lighting apparatus disclosed in patent document 2 is further provided with a smoothing circuit 4 which includes a capacitor, and the voltage output from the rectifier circuit 3 is first smoothed and then supplied to a lighting circuit 5 for lighting the load 6 such as an LED.

"As a result, in the LED lighting apparatus disclosed in patent document 2, the load 6 such as an LED is DC driven. To adjust the intensity of LED light in DC driving, the lighting circuit 5 detects the phase with which the dimmer circuit 2 supplies power and, in accordance with the thus detected phase, controls the DC voltage to be supplied to the load 6 such as an LED. Such lighting control requires not only complicated control circuitry but also a stable DC voltage supply. This therefore requires the provision of a large-capacitance capacitor in the smoothing circuit 4, and such a large-capacitance capacitor becomes an obstacle to reducing the circuit size. Furthermore, if an electrolytic capacitor, for example, is used as the large-capacitance capacitor, there arise problems such as reduced lifetime due to the effects of the heat generated by the LED, reducing the lifetime of the LED lighting apparatus itself or requiring frequent maintenance.

"Accordingly, it is an object of the present invention to provide an LED lighting apparatus that uses an LED as a light source, and that can operate properly even when operated using an output of a dimmer and can yet reduce power consumption.

"It is another object of the present invention to provide an LED lighting apparatus that can be implemented with simple circuitry without using a smoothing circuit and that does not cause malfunction of a dimmer.

"An LED lighting apparatus includes a rectifier circuit, a light-emitting circuit connected to the rectifier circuit and containing a single or a plurality of LEDs in which current begins to flow when an output voltage of the rectifier circuit exceeds a threshold voltage, and a bypass circuit having a bypass path for making the current flow to the rectifier circuit without passing through the light-emitting circuit, and a detecting unit for detecting the current flowing through the light-emitting circuit, and wherein when the current detected by the detecting unit exceeds a predetermined value, the bypass circuit shuts off the current flowing through the bypass path.

"Preferably, in the LED lighting apparatus, the bypass circuit maintains the sum of the current flowing through the bypass circuit and the current flowing through the light-emitting circuit constant.

"Preferably, in the LED lighting apparatus, the bypass circuit includes a current detecting resistor and a depletion-type FET placed in the bypass path, wherein the depletion-type FET controls opening and closing of the bypass path by detecting the current flowing through the light-emitting circuit by the current detecting resistor.

"Preferably, in the LED lighting apparatus, the bypass circuit includes a current detecting resistor and an enhancement-type FET placed in the bypass path, a bipolar transistor for controlling the enhancement-type FET, and a pull-up resistor, wherein the bipolar transistor detects the current flowing through the light-emitting circuit by the current detecting resistor, and controls opening and closing of the bypass path by using the enhancement-type FET.

"Preferably, the LED lighting apparatus further includes a second bypass circuit connected to the light-emitting circuit, a second light-emitting circuit connected to the second bypass circuit and containing a single or a plurality of LEDs in which current begins to flow when the output voltage of the rectifier circuit exceeds a threshold voltage, and a current limiting circuit for limiting the current flowing into the second light-emitting circuit.

"Preferably, the LED lighting apparatus further comprises a filter circuit connected in parallel with the bypass circuit and constructed from a series connection of a resistor and a capacitor.

"Preferably, in the LED lighting apparatus, the filter circuit is placed after the bypass circuit but before the light-emitting circuit.

"An LED lighting apparatus includes a rectifier circuit, a light-emitting circuit containing a single or a plurality of LEDs, the light-emitting circuit having a first power supply terminal and a second power supply terminal, and a bypass circuit having a third power supply terminal, a fourth power supply terminal, and a current detecting terminal, wherein the first power supply terminal and the third power supply terminal are connected to one end of the rectifier circuit, the second power supply terminal is connected to the current detecting terminal, and the fourth power supply terminal is connected to the other end of the rectifier circuit, and wherein when the voltage developed between the one end and the other end of the rectifier circuit is low, current flows through the third power supply terminal, and when the current flowing through the current detecting terminal exceeds a predetermined value, the current flowing through the third power supply terminal no longer flows, while when the voltage at the one end of the rectifier circuit exceeds the threshold voltage of the single LED or the threshold voltage of an LED array of the plurality of LEDs connected in series, the current flows through the single LED or the LED array into the current detecting terminal.

"A dimmer receives a voltage from an AC commercial power supply, and modifies the voltage waveform in such a manner that the voltage is present only in a specific period and no voltage is present in the remaining period. However, even in the no-voltage period, the voltage is not completely zero but a slight amount of voltage is present. Therefore, in the LED lighting apparatus, current is allowed to flow through the bypass circuit in the no-voltage period in order to stabilize the operation of the dimmer. In the no-voltage period, no current flows to the light-emitting circuit because there is a threshold voltage for the operation of the LEDs. Even when current begins to flow into the light-emitting circuit immediately after the output of the dimmer transitions to the voltage period, the stable operation of the dimmer is maintained. When the output of the dimmer transitions to the voltage period, and the current flowing through the light-emitting circuit exceeds a predetermined value, the bypass circuit is cut off, and the current thus flows only through the light-emitting circuit. Therefore, the LED lighting apparatus of the invention can operate properly even when operated using the output of the dimmer and can yet reduce power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 is a schematic block diagram of an LED lighting apparatus 100.

"FIG. 2 is a circuit diagram of the LED lighting apparatus 100 shown in FIG. 1.

"FIG. 3(a) is a diagram depicting the voltage measured at terminal A with respect to terminal B in the LED lighting apparatus 100 shown in FIG. 1.

"FIG. 3(b) is a diagram depicting the waveform of current I flowing through terminal A in response to the voltage of FIG. 3(a).

"FIG. 4 is a circuit diagram of an alternative LED lighting apparatus 400.

"FIG. 5(a) is a diagram depicting the voltage measured at terminal A with respect to terminal B in the LED lighting apparatus 400 shown in FIG. 4.

"FIG. 5(b) is a diagram depicting the waveform of current I flowing through terminal A in response to the voltage of FIG. 5(a).

"FIG. 6 is a circuit diagram of a further alternative LED lighting apparatus 500.

"FIG. 7 is a diagram showing an LED lighting apparatus illustrated in FIG. 26 in patent document 1.

"FIG. 8(a) is a diagram showing an example of a voltage waveform for one pulsating cycle that appears at terminal A with respect to terminal B of a bridge rectifier circuit 705 in the LED lighting apparatus shown in FIG. 7.

"FIG. 8(b) is an example of a current waveform for one pulsating cycle that flows in the bridge rectifier circuit 705 in the LED lighting apparatus shown in FIG. 7.

"FIG. 9 is a diagram showing an example in which a dimmer 901 is inserted between an AC commercial power supply and the bridge rectifier circuit 705 in the LED lighting apparatus shown in FIG. 7.

"FIG. 10(a) is a diagram showing an example of a voltage waveform for one pulsating cycle that appears at terminal A with respect to terminal B of the bridge rectifier circuit 705 for an ideal load.

"FIG. 10(b) is an example of a voltage waveform for one pulsating cycle that the bridge rectifier circuit 705 outputs in the LED lighting apparatus shown in FIG. 9."

For additional information on this patent application, see: Sakai, Keisuke; Takahashi, Rintaro; Akiyama, Takashi. Led Lighting Apparatus. Filed July 12, 2012 and posted July 24, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4137&p=83&f=G&l=50&d=PG01&S1=20140717.PD.&OS=PD/20140717&RS=PD/20140717

Keywords for this news article include: Citizen Electronics Co. Ltd..

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Source: Electronics Newsweekly


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