Led lighting device and led illuminating device

A LED lighting device and a LED lighting system

The present invention relates to a LED lighting device and a LED lighting system.

In patent documents 1, the pressure of direct-current electric power produced by rectifying commercial alternating current electric power is lowered by a DC-DC converter circuit, and a LED lighting device which turns on LED is indicated.

<p><patcit num="1"><text>JP, 2008-130438, A</text></patcit></p>

<p num="0004">By the way, in art indicated by patent documents 1, since a DC-DC converter lowers the pressure using a transformer, efficiency will fall by conversion loss in a transformer. When there is little number of LED made to turn on especially, it becomes impossible to disregard conversion loss in a transformer as compared with electric power consumed by LED.</p><p num="0005">It is possible to make efficiency high by on the other hand using a back converter which uses a choke coil instead of a transformer. However, in order to operate efficiently in a back converter, it is desirable for a duty ratio of a switching element to be 10% or more. For this reason, direct-current electric power produced by rectifying commercial alternating current electric power (100V or 200V), for example, When turning on LED (about [For example, single LED 3] V) of the small number, a duty ratio of a switching element of a back converter will be less than 10%, and there is a problem that lighting efficiency falls.</p><p num="0006">Then, an object of the present invention is to provide a LED lighting device and a LED lighting system whose efficiency is high even when there is little number to turn on.</p>

<p num="0007">In a LED lighting device with which the present invention turns on LED in order to solve the above-mentioned subject, Series connection is carried out to the 1st back converter which lowers the pressure of input voltage to the 1st voltage, and the 1st back converter, The 2nd back converter which lowers the pressure of the 1st voltage outputted from the 1st back converter to the 2nd voltage lower than it, and supplies it to the LED, Voltage or current supplied to the LED is detected from the 2nd back converter, and it has a control means which controls switching operation of both sides of the 1st back converter and the 2nd back converter based on a detection result. According to such composition, even when there is little number to turn on, a LED lighting device with high efficiency can be provided.</p><p num="0008">In addition to the above-mentioned invention, the control means supplies the control signal with same duty ratio to the 1st back converter and the 2nd back converter, respectively, and other inventions control these switching operations. According to such composition, electric power supplied to LED is easily controllable.</p><p num="0009">The control signal with which other inventions are supplied to the 1st back converter and the 2nd back converter from the control means, respectively in addition to the above-mentioned invention is set up so that a duty ratio and a phase may become equal. Since the same control signal can be supplied to the 1st and 2nd back converter according to such composition, composition of a control means can be simplified.</p><p num="0010">It adds to the above-mentioned invention and other inventions are the 1st back converters, While a high side switch is constituted by switching element, a low side switch is constituted by diode element, and as for the 2nd back converter, both sides of a high side switch and a low side switch are constituted by switching element. According to such composition, when output current uses both sides of a high side switch of the large 2nd back converter, and a low side switch as a switching element, an electric power loss can be controlled effectively.</p><p num="0011">As for other inventions, in addition to the above-mentioned invention, a choke coil of the 2nd back converter is provided with secondary winding, and the 1st back converter is switched by voltage excited by secondary winding of the 1st converter. By using voltage excited by secondary winding insulated from primary winding, circuitry can be made easy.</p><p num="0012">Other inventions are while the 1st back converter has a field effect transistor as a switching element in addition to the above-mentioned invention, When the field effect transistor will be in a state of OFF, it has a switching element for electric discharge which discharges an electric charge which changed into a state of ON and was accumulated in input capacitance of a gate terminal. According to such composition, it becomes possible to set up switching frequency highly by discharging quickly an electric charge accumulated in input capacitance of a field effect transistor.</p><p num="0013">The present invention is a LED lighting system which has the LED lighting device mentioned above. According to such composition, even when there is little number to turn on, a LED lighting system with high efficiency can be provided.</p>

<p num="0014">According to the present invention, even when there is little number to turn on, it becomes possible to provide a LED lighting device and a LED lighting system with high efficiency.</p>

<figref num="1">It is a circuit diagram showing an example of composition of a LED lighting device concerning a 1st embodiment of the present invention.</figref><figref num="2">It is a figure for explaining operation of an embodiment shown in Drawing 1.</figref><figref num="3">It is a circuit diagram showing an example of composition of a LED lighting device concerning a 2nd embodiment of the present invention.</figref><figref num="4">It is a figure showing an example of composition of a control part shown in Drawing 3.</figref><figref num="5">It is a figure showing an input waveform of the 1st step and the 2nd step of back converter of a 2nd embodiment shown in Drawing 3.</figref><figref num="6">It is a figure showing input voltage of the 1st step of back converter of a 2nd embodiment and a relation of an input which are shown in Drawing 3.</figref><figref num="7">It is a figure showing the harmonics distorted characteristic of an input of the 1st step of back converter of a 2nd embodiment shown in Drawing 3.</figref><figref num="8">It is a circuit diagram showing an example of composition of a LED lighting device concerning a 3rd embodiment of the present invention.</figref><figref num="9">It is the example of composition which excepted a bipolar transistor from a device shown in Drawing 8.</figref><figref num="10">It is a figure showing change of gate voltage of a field effect transistor shown in Drawings 8 and 9.</figref><figref num="11">It is a circuit diagram showing an example of composition of a LED lighting device concerning a 4th embodiment of the present invention.</figref>

Next, an embodiment of the present invention is described.

(A) Explanation of composition of a 1st embodiment Drawing 1 is a figure showing an example of composition of a LED lighting device concerning a 1st embodiment of the present invention. As shown in this Drawing 1, LED lighting device 1 is, Input terminals 10 and 11, diode bridge 12, capacitor elements 13, 17, and 22, switching elements 14 and 18, diode elements 15 and 19, coil elements 16 and 20, resistive element 21, LED (Light*Emitting*Diode) (Light emitting diode) It has 23 and control part 30. Switching element 14, diode element 15, coil element 16, and capacitor element 17 constitute the 1st back converter, and switching element 18, diode element 19, coil element 20, and capacitor element 22 constitute the 2nd back converter. In the 1st back converter, switching element 14 corresponds to a high side switch, and diode element 15 corresponds to a low side switch. In the 2nd back converter, switching element 18 corresponds to a high side switch, and diode element 19 corresponds to a low side switch.

Here, commercial alternating current electric power (for example, exchange electric power of 100V) is inputted into input terminals 10 and 11. Diode bridge 12 is constituted by four diode elements, carries out all the wave rectification, and outputs exchange electric power inputted from input terminals 10 and 11. As for capacitor element 13, capacity is constituted by a film capacitor or a ceramic condenser several/100 to about several/10-micro F etc., for example. Capacitor element 13 functions as a bypass capacitor for attenuating harmonics generated by switching operation of switching element 14.

Switching element 14 is constituted by a bipolar transistor or field effect transistor, will be in a state of ON or OFF according to a control signal supplied from control part 30, and will flow through or intercept current inputted, for example. It will be a freewheel diode, when switching element 14 is ON, diode element 15 will be in an opposite direction bias state, will be in an interception state, when switching element 14 is OFF, will be in a forward bias state and will be in switch-on.

It is a choke coil, coil element 16 accumulates flowing current as magnetic energy, when switching element 14 is ON, and when switching element 14 is OFF, it releases accumulated magnetic energy as electric energy. capacitor element 17 -- several 10- it is constituted by electrolytic condenser etc. which have the capacity of hundreds of micro F, and current outputted from coil element 16 is smoothed and outputted.

Like switching element 14, switching element 18 is constituted by a bipolar transistor or field effect transistor, will be in a state of ON or OFF according to a control signal supplied from control part 30, and will flow through or intercept current inputted, for example. It will be a freewheel diode, when switching element 18 is ON, diode element 19 will be in an opposite direction bias state, will be in an interception state, when switching element 18 is OFF, will be in a forward bias state and will be in switch-on.

It is a choke coil, coil element 20 accumulates flowing current as magnetic energy, when switching element 18 is ON, and when switching element 18 is OFF, it releases accumulated magnetic energy as electric energy. Resistive element 21 is a resistive element for detecting current which flows into LED23, for example, has a number - tens of m ohm of resistance. Capacitor element 22 is constituted by electrolytic condenser etc. which have the capacity of a number - 10 micro F of numbers, for example, and smooths and outputs current outputted from coil element 20 via resistive element 21.

LED23 is a light emitting diode whose forward direction voltage which emits white light is about 3-5V for example.

Control part 30 (it corresponds to a "control means" in a claim) supplies the same control signal as switching element 14 and switching element 18 based on voltage which arises to both ends of resistive element 21, and controls these. In detail, control part 30 adjusts a duty ratio of switching element 14 and switching element 18, and it controls it so that voltage which arises in resistive element 21 turns into predetermined voltage, so that fixed current flows into LED23.

(B) Explanation of operation of a 1st embodiment All the wave rectification of the exchange electric power (for example, 100V) inputted from input terminals 10 and 11 is carried out by diode bridge 12, and wave quantity is outputted as pulsating flow voltage which is about 140v.

Switching element 14 will be in a state of ON or OFF according to a control signal supplied from control part 30. Drawing 2 (A) is a figure showing an example of a control signal supplied to switching element 14 from control part 30. As shown in this figure, a control signal is a signal which will be in a state of a high or a low with a fixed cycle, for example. If switching element 14 will be in a state of ON if a control signal will be in a high state, and a control signal will be in a low state, switching element 14 shall be in a state of OFF. In an example of Drawing 2 (A), a ratio with a cycle of a period when a control signal serves as a high, and a control signal is about 1:6.6 (a duty ratio is about 15%). repetition cycle tau of a control signal -- about 1 - several 10 -- it may be about microsec.

If switching element 14 will be in a state of ON, current which flows into coil element 16 will increase gradually. Drawing 2 (B) is a figure showing current which flows into coil element 16. If a control signal will be in a high state as shown in Drawing 2 (A), switching element 14 will be in a state of ON, and current which flows into coil element 16 as shown in Drawing 2 (B) will increase gradually. At this time, since diode element 15 serves as opposite direction bias, diode element 15 will be in an interception state. And if a control signal will be in a low state from a high as shown in Drawing 2 (A), switching element 14 will be in a state of OFF. As a result, since electromotive force arises for coil element 16, diode element 15 will serve as forward bias, it will be in switch-on, and current leads to capacitor element 17 from coil element 16. Since such current decreases according to magnetic energy accumulated in coil element 16, as shown in Drawing 2 (B), current decreases gradually. Current outputted from coil element 16 is accumulated in capacitor element 17 as an electric charge. capacitor element 17 -- several 10- since it is constituted by electrolytic condenser etc. which have the capacity of hundreds of micro F, in both ends of capacitor element 17, direct-current voltage with few voltage variations appears.

The same control signal (refer to Drawing 2 (A)) as switching element 14 is supplied to switching element 18. If a control signal will be in a high state, switching element 18 will be in a state of ON, and as shown in Drawing 2 (B), current which flows coil element 20 will increase from capacitor element 17 gradually. Since diode element 19 serves as opposite direction bias at this time, it will be in an interception state. Since electromotive force will arise for coil element 20 if a control signal will be in a low state from a high and switching element 18 will be in a state of OFF, diode element 19 will serve as forward bias, it will be in switch-on, and current leads to capacitor element 22 via resistive element 21 from coil element 20. Since such current decreases according to magnetic energy accumulated in coil element 20, as shown in Drawing 2 (B), current decreases gradually.

Capacitor element 22 accumulates current outputted from coil element 20 via resistive element 21 as an electric charge, smooths it, and outputs it as direct-current voltage. LED23 is turned on with direct-current voltage outputted from capacitor element 22.

Control part 30 has detected terminal voltage of resistive element 21, and when terminal voltage decreases, it makes a duty ratio of a control signal increase here (when current which flows into resistive element 21 decreases). As a result, since ON time of both sides of switching elements 14 and 18 increases, terminal voltage of both sides of capacitor element 17 and capacitor element 22 rises, and current which flows into LED23 increases. On the other hand, when terminal voltage increases, a duty ratio of a control signal is decreased (when current which flows into resistive element 21 increases). As a result, since ON time of both sides of switching elements 14 and 18 decreases, terminal voltage of both sides of capacitor element 17 and capacitor element 22 descends, and current which flows into LED23 decreases. It is controlled so that current which leads to LED23 becomes fixed by the above control.

it mentioned above -- as -- as capacitor element 17 -- several 10- since an electrolytic condenser which has the capacity of hundreds of micro F is used, terminal voltage of this capacitor element 17 serves as approximately regulated. As for a control signal supplied to switching element 18 from control part 30 as its voltage of capacitor element 17 which is input voltage is constant since control part 30 controls so that output current of the 2nd back converter becomes fixed, a duty ratio serves as approximately regulated. Such a control signal is supplied also to switching element 14, and since current proportional to input voltage will flow from input terminals 10 and 11 if switching element 14 is turned on and off by duty ratio approximately regulated, current becomes approximately sine wave-like. Thereby, high 力率 can be obtained.

Both duty ratios of switching elements 14 and 18 are since it is about 15%, output voltage of diode bridge 12 -- about -- if 140V, output voltage of the 1st back converter will be about (≒140x0.15) 22V -- output voltage of the 2nd back converter -- about 3.2 -- it becomes about V (≒140x0.15x0.15).

As explained above, while carrying out series connection of the two back converters in a 1st embodiment, Resistive element 21 which detects current is provided in an output side of the 2nd back converter, and control part 30 controlled switching elements 14 and 18 of two back converters based on this detection value. Thus, even if it is when there is little number of LED which connects two back converters by carrying out series connection, it becomes possible to make it possible to set up a duty ratio of each back converter somewhat highly, and to make efficiency high as a result. When turning on LED23 of 3.2V with a commercial alternating current power supply of 100V, more specifically, a duty ratio of each back converter can be made about 15%. When turning on LED32 of 3.2V with a commercial alternating current power supply of 200V, a duty ratio of each back converter can be made about 11%. For this reason, since a duty ratio can be made 10% or more, efficiency can be prevented from falling.

In a 1st embodiment, since two back converters were controlled by one control part 30 with the same control signal, circuit composition of control part 30 can be simplified.

(C) Explanation of composition of a 2nd embodiment Drawing 3 is a figure showing an example of composition of a 2nd embodiment. In this figure, since the same numerals are given to Drawing 1 and a corresponding portion, that explanation is omitted. With LED lighting device 1A shown in Drawing 3, switching element 14 is constituted by field effect transistor 14a, resistive elements 14b-14d, and field effect transistor 14e as compared with Drawing 1. Switching element 18 and diode element 19 are constituted by field effect transistors 18a and 18b. Control part 30 is replaced by control part 40.

Here, field effect transistor 14a is constituted by P channel type MOS-FET (Metal*Oxide*Semiconductor*Field*Effect*Transistor), for example, The Dorain terminal is connected to an end of resistive element 14b, a gate terminal is connected to an end of resistive element 14c, and a sauce terminal is connected to a cathode terminal of diode element 15. Field effect transistor 14e is constituted by N channel type MOS-FET, for example, The Dorain terminal is connected to an end of resistive element 14d, a gate terminal is connected to a sauce terminal of field effect transistor 18a, and the Dorain terminal of field effect transistor 18b, and a sauce terminal is connected to an anode terminal of diode element 15.

Field effect transistor 18a is constituted by N channel type MOS-FET, for example, the Dorain terminal is connected to an end of coil element 16, a gate terminal is connected to control part 40, and a sauce terminal is connected to the Dorain terminal of field effect transistor 18b. Field effect transistor 18b is similarly constituted by N channel type MOS-FET, The Dorain terminal is connected to a sauce terminal of field effect transistor 18a, a gate terminal is connected to control part 40, and a sauce terminal is connected to an anode terminal of diode element 15.

Control part 40 controls field effect transistors 18a and 18b according to voltage which appears in resistive element 21. Drawing 4 is a figure showing a detailed example of composition of control part 40. As a dashed line surrounds and shows to this Drawing 4, control part 40 has differential amplifier 41, PWM (Pulse*Width*Modulation) control part 42, and FET driver 43. Here, differential amplifier 41 amplifies and outputs voltage which appears in resistive element 21. PWM controller 42 performs PWM control based on an output of differential amplifier 41. PWM controller 42 outputs in detail a pulse signal which has a duty ratio according to output voltage of differential amplifier 41. For example, when an output of differential amplifier 41 is large, a pulse signal with a small duty ratio is outputted, and when an output of differential amplifier 41 is small, a pulse signal with a large duty ratio is outputted.

FET driver 43 controls field effect transistors 18a and 18b based on a pulse signal outputted from PWM controller 42. When a control signal outputted from PWM controller 42 is a high, specifically, FET driver 43 changes field effect transistor 18b into a state of OFF while changing field effect transistor 18a into a state of ON. When a control signal outputted from PWM controller 42 is a low, while changing field effect transistor 18a into a state of OFF, field effect transistor 18b is changed into a state of ON. That is, field effect transistor 18a performs control of ON and OFF like switching element 18 shown in Drawing 1. Field effect transistor 18b is controlled to be set to ON when field effect transistor 18a is OFF, while controlling to become OFF, when field effect transistor 18a is ON. In order to prevent excessive current from field effect transistors 18a and 18b being in a state of ON simultaneously, and flowing into these field effect transistors, it may be made to provide a circuit which inserts the dead time.

(D) Explanation of operation of a 2nd embodiment Below, operation of a 2nd embodiment is explained. First, operation of field effect transistors 18a and 18b is explained. Control part 40 adjusts a duty ratio of field effect transistor 18a according to voltage which appears in both ends of resistive element 21. When voltage which appears in both ends of resistive element 21 is specifically low, a duty ratio of a control signal outputted from FET driver 43 becomes large (when there is little current which flows into LED23), and on the other hand, when voltage is low, a duty ratio becomes small (when there is much current which flows into LED23). Commercial alternating current voltage inputted into input terminals 10 and 11 is 100V, and when terminal voltage of LED23 is 3.2V, as shown in Drawing 2 (A), an average duty ratio will be about 15%. On the other hand, to field effect transistor 18b, a control signal of negative phase is supplied in field effect transistor 18a. As a result, when field effect transistor 18a is set to ON, it changes field effect transistor 18b into a state of OFF, and when it changes into a state of OFF, it is controlled by state of ON. Since field effect transistor 18b will be in an OFF state if field effect transistor 18a will be in an ON state, current supplied from capacitor element 17 is supplied to coil element 20 via field effect transistor 18a. And if it changes field effect transistor 18a into an OFF state and changes field effect transistor 18b into an ON state, magnetic energy accumulated in coil element 20 will be accumulated in capacitor element 22 as an electric charge via resistive element 21 and field effect transistor 18b.

moreover -- since the Dorain terminal of field effect transistor 18a will be in a high state if it changes field effect transistor 18a into an ON state and changes field effect transistor 18b into an OFF stateA gate of field effect transistor 14e will be in a high state, and field effect transistor 14e will be in a state of ON. As a result, since current flows via resistive elements 14b-14d and a gate terminal of field effect transistor 14a will be in a high state, field effect transistor 14a will be in a state of ON. When field effect transistor 14a will be in a state of ON, current leads from the capacitor element 13 side to coil element 16. Since the Dorain terminal of field effect transistor 18b will be in a low state if it continues, it changes field effect transistor 18a into an OFF state and it changes field effect transistor 18b into an ON state, A gate of field effect transistor 14e will be in a low state, and field effect transistor 14e will be in a state of OFF. As a result, since a gate terminal of field effect transistor 14a will be in a low state, field effect transistor 14a will be in a state of OFF. If field effect transistor 14a will be in a state of OFF, magnetic energy currently stored in coil element 16 will be accumulated in capacitor element 13 as an electric charge via diode element 15.

Therefore, field effect transistor 18a and field effect transistor 14a repeat a state of ON or OFF to the same timing according to control of control part 40. Thereby, fixed current flows into LED23.

Drawing 5 is a figure showing terminal voltage of capacitor elements 13 and 17 shown in Drawing 3, a horizontal axis shows time (mS) and a vertical axis shows voltage (V). A thick line of Drawing 5 shows terminal voltage of capacitor element 13, and a small-gage wire shows terminal voltage of capacitor element 17. Terminal voltage of capacitor element 13 has the same approximately sine wave shape as a voltage waveform of commercial power. Terminal voltage of capacitor element 17 is fixed voltage although there are some Rippl ingredients.

Drawing 6 is a figure showing voltage impressed to input terminals 10 and 11, and current which flows into these input terminals 10 and 11, a small-gage wire shows voltage and a thick line shows current. from this Drawing 6, current which flows from input terminals 10 and 11 has approximately sine wave shape -- voltage -- abbreviated -- the about the same -- it has a phase. In a 2nd embodiment, high 力率 can be obtained so that clearly from this Drawing 6. A 1st embodiment of such the 力率 characteristic shown in Drawing 1 mentioned above is also the same.

Drawing 7 is a figure showing a distorted ingredient of current which flows from input terminals 10 and 11. A horizontal axis of Drawing 7 shows frequency and a vertical axis shows current. As shown in this figure, as for current which flows into a 2nd embodiment, 50 Hz which is a basic ingredient is main, and the other harmonics ingredient has decreased. It has become clear that a rate of this distorted ingredient corresponds enough more than [of class C of JIS C 61000-3-2] 25W.

As explained above, in a 2nd embodiment, it makes it possible to set up a duty ratio of each back converter somewhat highly like a case of a 1st embodiment, and can prevent efficiency from falling. When LED of 3.2V is specifically turned on with a commercial alternating current power supply of 100V, When a duty ratio of each back converter can be made about 15% and it turns on LED of 3.2V with a commercial alternating current power supply which is 200V, a duty ratio of each back converter can be made about 11%. For this reason, since a duty ratio can be made 10% or more, even if it is a case where LED of the small number is turned on, high conversion efficiency can be acquired.

In a 2nd embodiment, since two back converters were controlled by one control part 40 with the same control signal, circuit composition can be simplified. In a 2nd embodiment, it replaces with diode element 19 and used field effect transistor 18b. Since the voltage drop in a state of ON is small as compared with diode element 19, field effect transistor 18b can further reduce a loss of electric power. Especially, the 2nd back converter is one with large (for example, it is about several A) current which flows as compared with the 1st back converter, and it can decrease effectively an electric power loss by diode element 19.

In a 2nd embodiment, while improving 力率, it becomes possible to reduce harmonics.

(E) Explanation of composition of a 3rd embodiment Drawing 8 is a figure showing an example of composition of a 3rd embodiment of the present invention. Since the same numerals are given to Drawing 3 and a corresponding portion in Drawing 8, the explanation is omitted. In LED lighting device 1B shown in Drawing 8, coil element 20 is replaced by coil element 60 which has secondary winding as compared with Drawing 3, While field effect transistor 14a is replaced by field effect transistor 50, resistive elements 51, 53, and 55, bipolar transistor 52 (it corresponds to "a switching element for electric discharge" in a claim), and diode element 54 are added. The other composition is the same as that of a case of Drawing 3.

Here, coil element 60 outputs voltage which lowered the pressure of voltage which arises in primary winding from secondary winding while functioning as a choke coil like coil element 20. A turn ratio of primary winding and secondary winding can be made about into 2:1, for example. If voltage is impressed to primary winding, voltage will appear in secondary winding and it will be impressed by both ends of resistive element 55. Since diode element 54 serves as forward bias and will be in a state of ON if voltage is impressed from secondary winding, a gate terminal of field effect transistor 50 is added, a sauce terminal is subtracted, and it will be in a state of ON. Since it will be in an opposite direction bias state between base emitters of bipolar transistor 52 at this time, bipolar transistor 52 serves as OFF. When voltage has not appeared in secondary winding on the other hand, By an electric charge accumulated in capacity ("gate capacity" is called hereafter) of a gate terminal of field effect transistor 50, since between base emitters of bipolar transistor 52 will be in a forward bias state, bipolar transistor 52 will be in a state (short circuit state) of ON. As a result, an electric charge accumulated in gate capacity of field effect transistor 50 is discharged via an emitter collector of bipolar transistor 52.

Here, as shown in Drawing 9, since an electric charge accumulated in gate capacity is discharged via resistive element 53 in the case of LED lighting device 1C which does not provide bipolar transistor 52, electric discharge takes time only to a part according to RC damping time constant. Drawing 10 is a figure showing a temporal response of gate voltage accompanying electric discharge of an electric charge accumulated in gate capacity in a circuit of Drawings 8 and 9, a solid line shows change of gate voltage of a circuit of Drawing 8, and a dashed line shows change of gate voltage of a circuit of Drawing 9. As shown in this Drawing 10, since gate voltage is decreasing rapidly as compared with a circuit of Drawing 9, it turns out that an electric charge accumulated in gate capacity is discharged rapidly in a circuit of Drawing 8. Thus, switching operation on high frequency is attained by making an electric charge accumulated in gate capacity discharge rapidly. Even if it is a case where about 100 kHz is a maximum, specifically, according to the circuit of Drawing 8, operation by about 500 kHz is attained in a circuit of Drawing 9, for example. Of course, it cannot be overemphasized that it can operate on frequency less than this or beyond this depending on a setup of a circuit constant.

Although the 1st back converter was used as a high side type with which field effect transistor 50 is arranged at the plus side in an embodiment shown in Drawing 8, as shown in Drawing 11, it is also possible to consider it as a low side type with which field effect transistor 50 is arranged at the ground side. With LED lighting device 1D shown in Drawing 11, field effect transistor 50 is moved between an anode of diode element 15, and a ground from between an end of capacitor element 13, and cathodes of diode element 15 in detail as compared with Drawing 8. Resistive elements 51, 53, and 55, bipolar transistor 52, and diode element 54 are also moved with field effect transistor 50. Coil element 16 is moved between a cathode of diode element 15, an anode of between one ends of capacitor element 17 to diode element 15, and the other end of capacitor element 17. While the other end of capacitor element 13 is grounded, sauce of field effect transistor 50 is grounded. Composition of those other than these is the same as that of a case of Drawing 8.

According to an embodiment shown in Drawing 11, if field effect transistor 50 will be in a state of ON, current which flowed out of an end of capacitor element 13 will flow into a ground via capacitor element 17, coil element 16, and field effect transistor 50. If field effect transistor 50 will be in a state of OFF, magnetic energy accumulated in coil element 16 will be released via diode element 15, and will be accumulated in capacitor element 17 as an electric charge. Other operations are the same as that of a case of Drawing 8. Such low side type composition as well as a high side type can perform switching operation at high speed.

Since it was made to perform switching control of the 1st back converter based on voltage which provides coil element 60 which has secondary winding, and appears in secondary winding according to a 3rd embodiment of the present invention as explained above, Any low side [which is shown in a high side type or Drawing 11 showing in Drawing 8] type circuit can consist of easily using secondary winding insulated from primary winding.

In a 3rd embodiment, bipolar transistor 52 is provided in the gate side of field effect transistor 50, and since it was made to discharge an electric charge accumulated in gate capacity, it becomes possible to perform switching operation at high speed.

(F) Explanation of a modification embodiment An above embodiment is an example and it cannot be overemphasized that it is not what is limited only to only when the present invention mentions above. For example, although it was made to turn on one LED23, it is made to, turn on a plurality of LED by which multiple connection was carried out for example, or may be made to turn on a plurality of LED by which series connection was carried out in each above embodiment.

Although two back converters by which series connection was carried out were switched by a control signal of 1, it may be made to switch these with a separate control signal in each above embodiment. A duty ratio is the same and, specifically, it is also possible to use a control signal with which phases differ. According to such composition, noise figure is improvable by shifting timing of switching. As a method of generating such a signal, it can branch to two and one side can acquire a control signal generated from a circuit of 1 by being delayed by a delay circuit, for example. It is good also as composition which does not make a duty ratio the same by two back converters for example, from which a duty ratio of each back converter differs. In that case, it can have composition with which timing which timing set to ON synchronizes for example, or is come by off synchronizes with, or these do not synchronize. It is realizable by using two different reference voltage in a PWM control circuit as a method of generating a signal with which duty ratios differ, for example.

Although current which flows into LED23 was detected based on voltage which arises in resistive element 21, for example, voltage impressed to LED23 is detected, and it may be made to control the 1st and 2nd back converter by each above embodiment based on detected voltage.

In above embodiments [2nd and 3rd], although only the 2nd back converter was used as a detected [synchronously] type, it is good also considering both sides of the 1st and 2nd back converter as a detected [synchronously] type. As the reason for using only the 2nd back converter as a detected [synchronously] type, It is because the 1st back converter can disregard a loss by a diode element to the ability of the 2nd back converter not to disregard a loss by forward direction voltage of diode element 19 since output voltage is small since output voltage is large as mentioned above. Although it will be lost 15.6% (= 0.5/3.2) of in detail if forward direction voltage of diode element 19 uses 0.5V by 3.2V in output voltage (when it is a Schottky diode) when not using the 2nd back converter as a detected [synchronously] type, When not using the 1st back converter as a detected [synchronously] type, since output voltage is about 21v, a loss will be 2.4% (=0.5/12V). On the other hand, if ON voltage in voltage effect transistor 18b sets to 0.1V when using the 2nd back converter as a detected [synchronously] type, 15.6% of loss mentioned above can be made 3.1% (0.1/3.2).

It is also possible to incorporate with LED23 LED lighting devices 1, 1A-1D shown in each above embodiment in a case, and to constitute as a LED lighting system. As a case, an electric bulb type case can be used or it can include in a case which has cylindrical fluorescent light shape, for example. Of course, it may have shape other than this.

1, 1A-1D LED lighting device 10 and 11 Input terminal 12 Diode Bridge 13, 17, and 22 Capacitor element 14 and 18 Switching element 14a, 14e, 18a, 18b, and 50 Field effect transistor 15 and 19 Diode element 16 and 20 Coil element 14b, 14c, 14d, and 21 Resistive element 23 LED 30 and 40 Control part (control means) 41 Differential Amplifier 42 PWM Controller 43 FET Amplifier 51, 53, and 55 Resistive element 52 Bipolar Transistor (Switching Element for Electric Discharge) 54 Diode Element