DC power source unit and LED lamp system

A DC power source unit 37 is provided which boosts source voltage from a power source portion 36. A lighting circuit 38 is provided which supplies DC voltage to loads, the DC voltage being obtained by stepping down output current of the DC power source circuit 37. A control circuit 39 is provided which controls the lighting circuit 38 in accordance with at least either voltage or current of LEDs 25 and controls the DC power source unit 37 so that a ratio of output voltage to voltage of the LEDs 25 becomes a preset fixed ratio.

INCORPORATION BY REFERENCE

The present invention claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2010-188971 filed on Aug. 26, 2010. The content of the application is incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a DC power source unit having a load control circuit for supplying DC voltage to loads, the DC voltage being obtained by stepping down output voltage of a DC power source circuit, and to an LED lamp system including the DC power source unit.

BACKGROUND OF THE INVENTION

Lamp devices housing DC power source circuits and lighting circuits for lighting LEDs by DC power output from the DC power source circuits may be used in place of, for example, a straight-tube type or self-ballasted fluorescent lamp. The LEDs of the lamp device may each low power consumption and a long life. The lamp device detects voltage or current of the connected LEDs, performs feedback control on the lighting circuit and thus stably controls lighting of the LEDs. In this case, the DC power source circuit makes output voltage fixed or variable regardless of the voltage of the LEDs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A DC power source unit of an embodiment includes: a DC power source circuit for boosting source voltage; a load control circuit for supplying DC voltage to loads, the DC voltage being obtained by stepping down output voltage of the DC power source circuit; and a control circuit for controlling the load control circuit in accordance with at least either voltage or current of the loads and controlling the DC power source circuit so that a ratio of the output voltage to the voltage of the loads becomes a preset fixed ratio.

The embodiment will be described below with reference toFIGS. 1 and 2.

InFIG. 2, the reference numeral11denotes an LED lamp system, and the LED lamp system11corresponds to, for example, a single straight-tube type fluorescent lamp and includes: a long fixture body12as a system body; a pair of sockets13as light source attaching units disposed opposite each other at both ends of the fixture body12; a (straight-tube type) LED lamp14as a straight-tube type light source, a lamp, connected between the pair of sockets13; and a DC power source unit15which is arranged in the fixture body12and is a dedicated power source as a lighting device for supplying power to and lighting the LED lamp14.

The LED lamp system11of the embodiment is, for example, a renewal system that uses the fixture body12of an existing lighting fixture using a straight-tube type fluorescent lamp as it is and uses the LED lamp14and the DC power source unit15. Alternatively, in the case where the LED lamp system11using the LED lamp14and the DC power source unit15is newly installed, it is installed as the LED lamp system11reusing the fixture body12and the sockets13dedicated to the LED lamp system11of an existing lighting fixture structure using a straight-tube type fluorescent lamp, and using the LED lamp14and the DC power source unit15.

The sockets13are attached to both ends of a main body portion of the fixture body12. Terminals are built in one of the sockets13, the DC power source unit15is connected to the terminals, and the other socket13is properly used, for example, used only for holding the LED lamp14or used for ensuring an earth connection of the LED lamp14.

The LED lamp14includes, for example, a cylindrical straight-tube type tube body21having transmittance, a light emitting module (not shown) housed in the tube body21and connection portions23which are attachment portions provided at both ends of the tube body21.

The tube body21is made of glass or resin having transmittance and diffuseness, and formed in a long cylindrical shape having substantially the same tube length, tube diameter and appearance as those of a straight-tube type fluorescent lamp. The connection portions23are provided at both ends of the tube body21.

The light emitting module includes: a slender substrate (not shown) arranged along a tube axial direction of the tube body21and LEDs25as loads mounted on the substrate along a longitudinal direction of the substrate. Light may be emitted mainly from a predetermined direction of the tube body21by making the substrate of the light emitting module flat and mounting the LEDs25on one face of the flat substrate. Alternatively, light may be emitted from the whole circumference of the tube body21by forming the substrate in a polygonal cylindrical shape and mounting the LEDs25on the periphery of the polygonal cylindrical-shaped substrate. In the LED25, an LED chip emitting blue light is sealed with transparent resin containing fluorescent matter which is excited by blue light to emit yellow light, and white light is emitted from a surface of the transparent resin. Moreover, inFIG. 1, although the plurality of LEDs25are connected in series to each other, for example, only one LED25may be used.

The connection portion23shown inFIG. 2is connected to the socket13, for example, formed of insulative synthetic resin in the same shape as that of a cap of a straight-tube type fluorescent lamp, and attached and fixed to the end of the tube body21. A pair of lamp pins (not shown) as power receiving portions similar to lamp pins of the straight-tube type fluorescent lamp is projected on an end face of the connection portion23. Moreover, the connection portion23is not limited to being constituted by the pair of lamp pins, and may be constituted by a single lamp pin or the like. Any constitution is applicable to the connection portion23as long as it can realize electric connection or support of the connection portion23with respect to the socket13. Additionally, the connection portion23may be electrically and physically connected to the socket13via, for example, an adaptor.

The LED lamp14has substantially the same outer diameter and total luminous flux as those of, for example, an existing straight-tube type fluorescent lamp.

The DC power source unit15has: a power source portion36connected to a commercial AC power source e; a DC power source circuit37as a step-up chopper circuit which is connected to the power source portion36and outputs DC voltage; a lighting circuit38as a load control circuit which is a step-down chopper circuit electrically connected to the DC power source circuit37; and a control circuit39for controlling the DC power source circuit37and the lighting circuit38.

The power source portion36includes a noise filter circuit41and a rectifying and smoothing circuit42connected to the noise filter circuit41.

The noise filter circuit41is a line filter constituted by a capacitor C1, a common mode choke coil L1and a capacitor C2. The noise filter circuit41prevents high frequency noise, which is generated from the DC power source circuit37, the lighting circuit38and the like, from being output to the commercial AC power source e side.

The rectifying and smoothing circuit42includes a full-wave rectifying element REC such as a bridge diode connected to an output side of the noise filter circuit41and a smoothing capacitor C3for smoothing output power from the full-wave rectifying element REC.

The full-wave rectifying element REC is, for example, a bridge circuit constituted by four diodes D1to D4as rectifying elements.

The DC power source circuit37is a step-up chopper circuit, power factor correction circuit, for converting output voltage of the power source portion36to a desired voltage, converts AC power having an AC sine wave or AC rectangular wave to DC power and supplies the DC power to the lamp pins of the LED lamp14through the socket13. Moreover, for example, the DC power source circuit37may be connected to an output side of an AC power source such as a fluorescent lamp lighting device for outputting AC power from a commercial AC power source.

In the DC power source circuit37, a series circuit of a chopper choke L2, which is a boosting transformer, and a reverse blocking diode D5is electrically connected between an output side of the rectifying and smoothing circuit42and the lighting circuit38, a MOSFET Q1, which is a chopping switching element as a (first) switching element, is electrically connected in parallel to a connection point of the chopper choke L2and an anode of the diode D5, and a series circuit of electrolytic capacitors C4and C5, which are smoothing capacitors, is electrically connected to a cathode side, which is an output side, of the diode D5.

A primary winding of the chopper choke L2is electrically connected between an output side of the full-wave rectifying element REC and the anode of the diode D5, and one end side of a secondary winding (not shown) thereof is electrically connected to a ground potential.

A drain terminal of the MOSFET Q1is electrically connected to the connection point of the chopper choke L2and the anode of the diode D5, a source terminal, which is an output side, thereof is electrically connected to the ground potential and a gate terminal, which is a control terminal, thereof is electrically connected to the control circuit39.

The lighting circuit38includes: a series circuit of a MOSFET Q2, which is a lighting switching element as a (second) switching element, and a diode D6, the series circuit being electrically connected between both ends of the DC power source circuit37; an inductor L3electrically connected to a connection point of the MOSFET Q2and the diode D6; and a smoothing capacitor C6electrically connected to the inductor L3and smoothing output current, and is, for example, a step-down chopper circuit, diode rectification type step-down DC-DC converter, which steps down an output voltage of 141V to 415V of the DC power source circuit37to 45V to 100V and outputs a predetermined constant current. The MOSFET Q2, the diode D6and the DC power source circuit37constitute a step-up/down type DC power source portion, and the inductor L3and the smoothing capacitor C6constitute a main circuit for lighting the LEDs25.

A gate terminal, which is a control terminal, of the MOSFET Q2is electrically connected to a switching control unit (high side driver)45which is a drive element, and the MOSFET Q2is turned on/off at high speed by a signal from the switching control unit45. The switching control unit45is electrically connected to the control circuit39.

An anode of the diode D6is grounded, and a cathode thereof is electrically connected to the MOSFET Q2. That is, the diode D6, the inductor L3, the smoothing capacitor C6and the LEDs25form a closed circuit when the MOSFET Q2is turned off.

The control circuit39is, for example, a microcomputer, can detect input voltage Vin of the DC power source circuit37, output voltage Vout of the DC power source circuit37and voltage V (and current I) of the LEDs25, performs feedback control on the lighting circuit38based on the voltage V (and/or the current I) and controls the DC power source circuit37based on the voltage V. Specifically, the control circuit39controls a switching frequency of the MOSFET Q2of the lighting circuit38by the switching control unit45in accordance with the voltage V of the LEDs25, and controls a switching frequency of the MOSFET Q1of the DC power source circuit37so that a ratio of the output voltage Vout of the DC power source circuit37to the voltage V becomes a preset fixed ratio.

Moreover, the voltage V of the LEDs25in the embodiment represents voltage of the LEDs25as one connected in series to each other. In other words, the voltage V of the LEDs25is equivalent to DC voltage output from the lighting circuit38. Accordingly, in the case of using only one LED25, the voltage V is voltage of the one LED25.

Next, operation of the LED lamp system11of the embodiment will be described.

When the LED lamp system11is started up, the control circuit39starts up to make the MOSFET Q1of the DC power source circuit37perform switching operation at a predetermined switching frequency, noise is removed by the noise filter circuit41, voltage that is output from the power source portion36and rectified and smoothed by the rectifying and smoothing circuit42is boosted by the DC power source circuit37, and the output voltage Vout that is DC voltage smoothed by the electrolytic capacitors C4and C5is output so as to be input to the lighting circuit38. At the same time, the power factor is improved in the DC power source circuit37. Moreover, in the DC power source circuit37, as the input voltage Vin is higher (lower), the output voltage Vout is higher (lower) (the output voltage Vout continuously becomes higher (lower)). Alternatively, when the input voltage Vin is higher (lower) than a predetermined upper limit threshold (a plurality of upper limit thresholds different from each other may be set), the output voltage Vout becomes higher (lower) (the output voltage Vout becomes higher (lower) step by step).

Then, in the lighting circuit38, the switching control unit45is driven by a frequency signal generated by the control circuit39, and thus the MOSFET Q2is turned on/off at a predetermined switching frequency and DC voltage (output voltage Vout) smoothed by the smoothing capacitor C6and input is converted to stepped down DC voltage (voltage V). The DC voltage V is supplied to light the LEDs25.

In the control circuit39, a frequency signal to be supplied to the switching control unit45is generated based on the detected voltage V (and/or current I) of the LEDs25, and thus the feedback control is performed so that output current of the lighting circuit38becomes fixed. Accordingly, the LEDs25are stably lit by constant current.

Additionally, in the control circuit39, the switching frequency of the MOSFET Q1of the DC power source circuit37is controlled so that a ratio of the output voltage Vout of the DC power source circuit37to the detected voltage V of the LEDs25becomes a preset fixed ratio. For example, when the voltage V of the LEDs25is relatively low (high), the control circuit39relatively lowers (raises) the switching frequency of the MOSFET Q1of the DC power source circuit37, and relatively decreases (increases) the output voltage Vout of the DC power source circuit37.

The lighting circuit38is thus controlled in accordance with at least either the voltage V or current I of the LEDs25, and the DC power source circuit37is controlled so that the ratio of the output voltage Vout to the voltage V of the LEDs25becomes the preset fixed ratio. Thus, the output voltage Vout of the DC power source circuit37can be continuously changed in accordance with change of the voltage V, an input/output voltage difference (difference between the output voltage Vout and the voltage V) of the lighting circuit38is suppressed while lighting of the LEDs25is stably controlled, and circuit efficiency of the lighting circuit38can be improved.

Since the DC power source unit15which improves the circuit efficiency of the lighting circuit38while stably controlling lighting of the LEDs25is provided, reliability of the LED lamp system11can be improved.

Moreover, in the above embodiment, the control circuit39may control the switching frequency of the MOSFET Q1of the DC power source circuit37so that the output voltage Vout of the DC power source circuit37is increased/decreased in accordance with a difference between the voltage V of the LEDs25and a predetermined threshold Vth. That is, the control circuit39may change, step by step, the output voltage Vout of the DC power source circuit37in accordance with the voltage V, for example, lowers (raises) the switching frequency of the MOSFET Q1of the DC power source circuit37and decreases (increases) the output voltage Vout of the DC power source circuit37when the voltage V is lower (not lower) than the predetermined threshold Vth. Here, a plurality of predetermined thresholds Vth different from each other may be set. In this case, the input/output voltage difference (difference between the output voltage Vout and the voltage V) of the lighting circuit38is suppressed while lighting of the LEDs25is stably controlled, the circuit efficiency of the lighting circuit38can be improved, and the DC power source circuit37can be further easily controlled by the control circuit39.

The control circuit39, in accordance with, for example, a dimming signal transmitted from a dimming control circuit (not shown), may vary constant current output from the lighting circuit38.

In place of the straight-tube type LED lamp14, an annular type, self-ballasted or the like LED lamp can be used.

A multi-light type lighting fixture may be used which uses a plurality of pairs of sockets13. Additionally, not only a ceiling direct mounting type lighting fixture but also an embedding type lighting fixture can be used.

Power may be supplied to the LED lamp14from both the pair of sockets13or one of the pair of sockets13. When power is supplied from one of the sockets13, the other socket13may be used only for supporting an end of the LED lamp14. Alternatively, it is allowed that, for example, a dimming signal is transmitted from the other socket13to the LED lamp14and the LEDs25are dimmed by a dimming circuit built in the LED lamp14. Additionally, without use of the sockets13, power may be supplied from a non-contact power supplying portion arranged at the fixture body12side to a non-contact power receiving portion arranged at the LED lamp14side in a non-contact form by a dielectric coupling method or the like. Further, the sockets13may be used only for supporting the LED lamp14and another power supplying method may be used for the LED lamp14.

Additionally, a load is not limited to the LED25, and other options are available as long as the load is driven by DC voltage.