Patent Publication Number: US-9888538-B2

Title: Driving current generation circuit, LED power supply module and LED lamp

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/540,806, filed Jul. 3, 2012, which claims the benefit of priority from Japanese Patent Applications No. 2011-148366, filed on Jul. 4, 2011, and 2011-251290, filed on Nov. 17, 2011, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a driving current generation circuit for generating driving current of light emitting diodes (LEDs) and an LED power supply module and an LED lamp including the same. 
     BACKGROUND 
     In recent years, as substitutes for conventional incandescent lamps and fluorescent lamps, LED lamps (in the form of incandescent bulb, fluorescent bulb, ceiling light and the like) have been widely used because of their high durability and low power consumption characteristics. 
     In connection with the above types of lamps, some techniques for providing DC power supplies and LED lamps using the DC power supplies are disclosed in the related art. 
     However, the above techniques have several problems to be overcome to realize compactness and slimness of LED lamps, in particular, compactness and slimness of power supply modules configured to supply an electric power to LEDs. 
     SUMMARY 
     The present disclosure provides some embodiments of a driving current generation circuit that can be used in implementing an LED lamp, and an LED power supply module and an LED lamp of a compact and slim size. 
     According to a first aspect of the present disclosure, there is provided a driving current generation circuit including: a semiconductor device configured to operate with a variable voltage as a reference voltage; a driving current generator configured to generate, based on an instruction received from the semiconductor device, a driving current for driving an LED; and a dimming voltage converter configured to generate a second dimming voltage set based on the variable voltage from a first dimming voltage set based on a ground voltage, wherein the semiconductor device performs a driving control of the driving current generator based on the second dimming voltage. 
     In some embodiments, the dimming voltage converter includes: a voltage/current converter configured to convert the first dimming voltage into a dimming current; and a current/voltage converter configured to convert the dimming current into the second dimming voltage. 
     In some embodiments, the voltage/current converter includes a current mirror configured to mirror a current flowing at an input side of the current mirror to generate a dimming current at an output side of the current mirror based on a difference between a constant voltage and the first dimming voltage. 
     In some embodiments the current/voltage converter includes a resistor connected between an application terminal of the second dimming voltage and an application terminal of the variable voltage to flow the dimming current flowing therethrough. 
     In some embodiments, the dimming voltage converter is further configured to generate the second dimming voltage such that the second dimming voltage remains on or above a threshold voltage as long as the first dimming voltage is set to be within an LED dimming voltage range, and the threshold voltage is a voltage below which the driving current is not variably controlled based on the second dimming voltage by the semiconductor device. 
     In some embodiments, the dimming voltage converter is further configured to generate the second dimming voltage such that the second dimming voltage becomes zero when the first dimming voltage is set to an LED off voltage. 
     In some embodiments, the driving current generator includes: a transistor having a drain connected to an application terminal of an input voltage, a source connected to an application terminal of a driving current detecting voltage, and a gate connected to an application terminal of a gate voltage; a driving current detecting resistor having a first terminal connected to the source of the transistor and a second terminal connected to an application terminal of the variable voltage; an inductor having a first terminal connected to the application terminal of the variable voltage and a second terminal connected to an anode of the LED; a capacitor having a first terminal connected to the anode of the LED and a second terminal connected to a cathode of the LED; and a diode having a cathode connected to the source of the transistor and an anode connected to the cathode of the LED, wherein the semiconductor device provides, when generating the gate voltage such that the driving current detecting voltage matches a reference detecting voltage, an offset of the driving current detecting voltage or the reference detecting voltage from the second dimming voltage. 
     In some embodiments, the input voltage is a driving voltage of the semiconductor device. 
     According to a second aspect of the present disclosure, there is provided an LED power supply module mounted on a printed circuit board, the LED power supply module including: a filter configured to remove noises and surges superposed on an AC input voltage; an AC/DC converter configured to convert the AC input voltage into a first DC voltage; a power factor correction circuit configured to perform a power factor correction and boosts the first DC voltage to generate a second DC voltage; a DC/DC converter configured to drop the second DC voltage to generate a third DC voltage; and the driving current generation circuit of the first aspect of the present disclosure, wherein the driving current generation circuit receives the third DC voltage as the input voltage. 
     In some embodiments, the DC/DC converter includes a transformer. 
     In some embodiments, the transformer has wiring terminals winding pins extending horizontally with respect to the printed circuit board. 
     In some embodiments, the transformer has terminal pins extending vertically with respect to the printed circuit board. 
     In some embodiments, the wiring terminal winding pins and the terminal pins are formed integratedly into L-shape conductive members. 
     In some embodiments, the wiring terminal winding pins project from side surfaces of a base of the transformer, and wiring terminals are wound around the wiring terminal winding pins through grooves formed at the side surface of the base. 
     In some embodiments, the wiring terminals start to be wound around the wiring terminal winding pins from the outermost wiring terminal winding pins. 
     According to a third aspect of the present disclosure, there is provided an LED lamp including: LED modules; and the LED power supply module of the second aspect of the present disclosure, wherein the LED power supply module supplies an electric power to the LED modules. 
     In some embodiments, the LED lamp further includes: a control power supply module configured to output the first dimming voltage to the LED power supply module; and a remote controller signal receiving module configured to receive a remote controller signal from a remote controller and transmit the received remote controller signal to the control power supply module, wherein the control power supply module is configured to output the first dimming voltage according to the remote controller signal. 
     In some embodiments, the LED lamp further includes a cover configured to accommodate therein the LED modules, the LED power supply module, the control power supply module and the remote controller signal receiving module. 
     In some embodiments, the LED modules are arranged according to a shape of the cover. 
     In some embodiments, the cover is a circular member, and the LED power supply module, the control power supply module and the remote controller signal receiving module are arranged at a more inner side of the cover than the LED modules are. 
     In some embodiments, the LED modules are classified into a plurality of groups based on luminescence colors of the LED modules, and the LED power supply module includes LED power supply sub-modules configured to supply electric powers to the plurality of the groups, the groups and the LED-power supply sub-modules being in one-to-one correspondence. 
     In some embodiments, the control power supply module includes: a microcomputer configured to control reception of the remote controller signal and generation of the first dimming voltage; a microcomputer power supply configured to convert the AC input voltage into a DC voltage and supplies the converted DC voltage to the microcomputer; and an output capacitor connected to an output terminal of the microcomputer power supply. 
     In some embodiments, the LED lamp further includes a relay switch configured to connect or disconnect between an application terminal of the AC input voltage and the LED power supply module, and when turning off the LED, the microcomputer decreases the second dimming voltage to a lower limit of an LED dimming voltage range, variably controls the first dimming voltage such that the second dimming voltage becomes zero, and switches off the relay switch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing an example configuration of an LED lamp. 
         FIG. 2  is a view showing an example outward appearance of the LED lamp. 
         FIG. 3  is a circuit diagram of a first example configuration of a driving current generation circuit. 
         FIG. 4  is a circuit diagram of a second example configuration of the driving current generation circuit. 
         FIG. 5  is a circuit diagram of a third example configuration of the driving current generation circuit. 
         FIG. 6A  is a view showing a correlation between a dimming voltage and a driving current. 
         FIG. 6B  is a view showing a correlation between the dimming voltage and another dimming voltage. 
         FIG. 7  is a block diagram showing a modification example of the LED lamp. 
         FIG. 8  is a front view of a first example configuration of a transformer. 
         FIG. 9  is a top view of a second example configuration of a transformer. 
         FIG. 10  is a front view of the second example configuration of the transformer. 
         FIG. 11  is a side view of the second example configuration of the transformer. 
         FIG. 12  is a bottom view of the second example configuration of the transformer. 
         FIG. 13  is a bottom sectional view of the second example configuration of the transformer. 
         FIG. 14  is a front sectional view of the second example configuration of the transformer. 
         FIG. 15  is a connection wiring diagram of the second example configuration of the transformer. 
     
    
    
     DETAILED DESCRIPTION 
     &lt;LED Lamp&gt; 
       FIG. 1  is a block diagram showing an example configuration of an LED lamp  1 . In this configuration, the LED lamp  1  includes an LED module  10  and an LED power supply module  20 . 
     The LED module  10  is a light source of the LED lamp  1  to emit light of daylight color (having a color temperature of about 5000 K) or electric bulb color (having a color temperature of about 3000 K) and includes a plurality of LED elements connected in series or in parallel. 
     The LED power supply module  20  converts an AC input voltage Vin, e.g., 80 V to 264 V, from a commercial AC power source  30  into a DC output voltage Vout, e.g., 60 V to 90 V, and supplies the DC output voltage Vout to the LED module  10 . The LED power supply module  20  includes a filter  21 , an AC/DC converter  22 , a power factor correction (PFC) circuit  23 , a DC/DC converter  24 , a driving current generation circuit  25 , an input connector  26  and an output connector  27 , all of which are mounted on a printed wiring board. 
     The filter  21  serves to remove noises or surges superposed on the AC input voltage Vin. 
     The AC/DC converter  22  converts the AC input voltage Vin input through the filter  21  into a DC voltage V 1 , e.g., 113 V to 363 V. 
     The PFC circuit  23  performs a power factor correction and boosts the DC voltage V 1  to generate a DC voltage V 2 , e.g., 400 V. 
     The DC/DC converter  24  drops the DC voltage V 2  to generate a DC voltage V 3 , e.g., 110 V to 120 V. 
     The driving current generation circuit  25  receives the DC voltage V 3  and performs a feedback control of a driving current ILED flowing through the LED module  10  such that the driving current ILED matches a predetermined target value. A circuit configuration of the driving current generation circuit  25  will be described in detail later. 
     The input connector  26  supplies the AC input voltage Vin from the commercial AC power source  30  to the filter  21 . 
     The output connector  27  supplies the DC output voltage Vout, e.g., 60 V to 90 V, from the driving current generation circuit  25  to the LED module  10 . 
       FIG. 2  shows an example outward appearance of the LED lamp  1 . The LED lamp  1  shown in  FIG. 2  is used as a ceiling light source and includes an LED module  10 , an LED power supply module  20 , a control power supply module  40 , a remote controller signal receiving module  50  and a cover  60 . 
     The LED module  10  includes daylight color LED modules  10 W and electric bulb color LED modules  10 Y. With this configuration including the LED modules  10 W and  10 Y having different luminescence colors, the overall light-tone control of the LED lamp  1  can be performed by performing a dimming control on each of the LED modules  10 W and  10 Y. Although it is shown in  FIG. 2  that the LED modules  10 W and the LED modules  10 Y are alternately arranged along a single line according to the circular shape of the cover  60 , the arrangement of the LED modules  10 W and  10 Y is not limited thereto. 
     The LED power supply module  20  includes an LED power supply module  20 W configured to supply an electric power to the LED modules  10 W and an LED power supply module  20 Y configured to supply an electric power to the LED modules  10 Y. Each of the LED power supply modules  20 W and  20 Y has the same configuration as shown in  FIG. 1 . 
     The control power supply module  40  outputs, based on a remote controller signal to be described below, dimming voltages VdW and VdY, e.g., 0 V to 5 V, to the LED power supply modules  20 W and  20 Y, respectively. 
     The remote controller signal receiving module  50  receives the remote controller signal, e.g., an infrared signal or a radio signal, from a remote controller (not shown) and transmits the remote controller signal to the control power supply module  40 . 
     The cover  60  is a circular member accommodating therein the LED modules  10 W and  10 Y, the LED power supply modules  20 W and  20 Y, the control power supply module  40  and the remote controller signal receiving module  50 . In the cover  60 , the LED power supply modules  20 W and  20 Y, the control power supply module  40  and the remote controller signal receiving module  50  are arranged at a more inner side than where the LED modules  10 W and  10 Y are arranged. 
     &lt;Driving Current Generation Circuit&gt; 
       FIG. 3  is a circuit diagram showing a first example configuration of the driving current generation circuit  25 . The driving current generation circuit  25  of the first example configuration includes a semiconductor device A, an N channel metal oxide semiconductor (MOS) field effect transistor N 11 , an npn bipolar transistor Q 11 , resistors R 11  to R 13 , capacitors C 11  and C 12 , diodes D 11  to D 13 , a zener diode ZD and a transformer TR. 
     The application terminal of the DC voltage V 3  is connected to a positive electrode terminal of the output connector  27 , i.e., the anode of the LED module  10 . A first terminal of the resistor R 12  is connected to the application terminal of the DC voltage V 3 . A second terminal of the resistor R 12  is connected to the base of the transistor Q 11  and the cathode of the zener diode ZD. The anode of the zener diode ZD is connected to a ground terminal. A first terminal of the resistor R 13  is connected to the application terminal of the DC voltage V 3 . A second terminal of the resistor R 13  is connected to the collector of the transistor Q 11 . The emitter of the transistor Q 11  is connected to a VIN terminal (a power input terminal) of the semiconductor device A. The cathode of the diode D 12  is connected to the VIN terminal of the semiconductor device A. The anode of the diode D 12  is connected to the ground terminal. 
     A first terminal of the capacitor C 11  is connected to the positive electrode terminal of the output connector  27 , i.e., the anode of the LED module  10 . A second terminal of the capacitor C 11  is connected to a negative electrode terminal of the output connector  27 , i.e., the cathode of the LED module  10 . A first terminal of a primary winding L 11  of the transformer TR is connected to the negative electrode terminal of the output connector  27 . A second terminal of the primary winding L 11  is connected to the anode of the diode D 11  and the drain of the transistor N 11 . The cathode of the diode D 11  is connected to the positive electrode terminal of the output connector  27 . A first terminal of a secondary winding L 12  of the transformer TR is connected to the anode of the diode D 13 . A second terminal of the secondary winding L 12  is connected to the ground terminal. The cathode of the diode D 13  is connected to the VIN terminal of the semiconductor device A. The capacitor C 12  is connected between the cathode of the diode D 13  and the ground terminal. 
     The source of the transistor N 11  is connected to the ground terminal via the resistor R 11  and also connected to a CS terminal (a driving current detecting terminal) of the semiconductor device A. The gate of the transistor N 11  is connected to a GD terminal (a gate driving terminal) of the semiconductor device A. A GND terminal (a ground terminal) of the semiconductor device A is connected to a negative electrode terminal (a ground terminal) of a dimming connector  28 . An LD terminal (a linear dimming terminal) of the semiconductor device A is connected to a positive electrode terminal (an application terminal of a dimming voltage Vd) of the dimming connector  28 . 
     The transistor N 11  is a switching element configured to switch on/off an electric current path from the cathode of the LED module  10  to the ground terminal. The semiconductor device A performs a turning-on/off control of the transistor N 11  such that a current flowing into the ground terminal via the transistor N 11  and the resistor R 11 , i.e., the driving current ILED of the LED module  10 , matches a predetermined value. 
     In more detail, the semiconductor device A performs a turning-on/off control of the transistor N 11  (a generation control of a gate voltage Vg) such that a driving current detecting voltage Vm applied to the CS terminal matches a reference detecting voltage. At this time, the semiconductor device A provides an offset of the driving current detecting voltage Vm or the reference detecting voltage from the dimming voltage Vd applied to the LD terminal. This configuration facilitates a linear dimming control of the LED lamp  1  based on the dimming voltage Vd. 
     When the transistor N 11  is turned on, the driving current ILED flows from the application terminal of the DC voltage V 3  to the ground terminal via the LED module  10 , the primary winding L 11  of the transformer TR, the transistor N 11  and the resistor R 11 . On the other hand, when the transistor N 11  is turned off, the driving current ILED flows in a loop of the primary winding L 11  of the transformer TR, the diode D 11  and the LED module  10 . 
     The transistor Q 11 , the resistors R 12  and R 13  and the zener diode ZD together serve as a simple regulator (an emitter follower) which receives, when the semiconductor device A is turned on, a charging current of the capacitor C 12  from the application terminal of the DC voltage V 3  and generates a power source voltage V 4  of the semiconductor device A. The transformer TR supplies an electric power to the semiconductor device A by using the driving current ILED flowing through the LED module  10 . Accordingly, after the semiconductor device A is turned on, the capacitor C 12  is charged along the current path from the secondary winding L 12  of the transformer TR via the diode D 13  and thus the electric power is continuously supplied to the semiconductor device A. The winding ratio of the transformer TR may be properly set in consideration of the power source voltage V 4  required to operate the semiconductor device A. 
     In the driving current generation circuit  25  of the first example configuration, the semiconductor device A operates with the ground voltage applied to the GND terminal, i.e., 0 V, as a reference voltage. Accordingly, a device withstanding voltage of the semiconductor device A is required to be designed in consideration of an inter-terminal voltage applied between the VIN terminal and the GND terminal. If the DC voltage V 3 , e.g., 110 V to 120 V, is applied to the VIN terminal, the semiconductor device A should have a high withstand voltage, which may result in a large size of the semiconductor device A. However, since the driving current generation circuit  25  of the first example configuration is provided with a discrete power supply circuit (formed with the transistor Q 11 , the resistors R 12  and R 13 , the diode D 12 , the zener diode ZD and the transformer TR) configured to generate the power source voltage V 4 , which is sufficiently lower than the DC voltage V 3 , e.g., about 5 V, the semiconductor device A can have a low withstanding voltage. Accordingly, in the first configuration, the size of the semiconductor device A may be reduced. 
       FIG. 4  is a circuit diagram showing a second example configuration of the driving current generation circuit  25 . The driving current generation circuit  25  of the second example configuration includes a semiconductor device X, an N channel MOS field effect transistor N 21 , a resistor R 21 , an inductor L 21 , a capacitor C 21  and diodes D 21  and D 22 . 
     The drain of the transistor N 21  is connected to an application terminal of the DC voltage V 3 . The source of the transistor N 21  is connected to a first terminal of the resistor R 21 . The gate of the transistor N 21  is connected to a GD terminal (a gate driving terminal) of the semiconductor device X. The first terminal of the resistor R 21  is connected to a CS terminal (a driving current detecting terminal) of the semiconductor device X. A second terminal of the resistor R 21  is connected to a GND terminal (a ground terminal) of the semiconductor device X. A first terminal of the inductor L 21  is connected to the GND terminal of the semiconductor device X. A second terminal of the inductor L 21  is connected to a positive electrode terminal of the output connector  27 , i.e., the anode of the LED module  10 . A first terminal of the capacitor C 21  is connected to the positive electrode terminal of the output connector  27 . A second terminal of the capacitor C 21  is connected to a negative electrode terminal of the output connector  27 . i.e., the cathode of the LED module  10 . The cathode of the diode D 21  is connected to the source of the transistor N 21 . The anode of the diode D 21  is connected to the negative electrode terminal of the output connector  27 . The cathode of the diode D 22  is connected to a VIN terminal (a power source input terminal) of the semiconductor device X. The anode of the diode D 22  is connected to the application terminal of the DC voltage V 3 . The negative electrode terminal of the output connector  27  is connected to the ground terminal. An LD terminal (a linear dimming terminal) of the semiconductor device X is connected to a positive electrode terminal (an application terminal of a dimming voltage Vd 1 ) of a dimming connector  28 . A negative electrode terminal of the dimming connector  28  is connected to the ground terminal. 
     In the second example configuration, the transistor N 21 , the resistor R 21 , the inductor L 21 , the capacitor C 21  and the diode D 21  together serve as a driving current generator Y configured to generate the driving current ILED of the LED module  10  based on an instruction from the semiconductor device X. 
     The transistor N 21  is a switching element configured to switch on/off a current path from the application terminal of the DC voltage V 3  to the anode of the LED module  10 . The semiconductor device X performs a turning-on/off control of the transistor N 21  such that a current flowing through the resistor R 21 , i.e., the driving current ILED of the LED module  10 , matches a predetermined value. 
     In more detail, the semiconductor device X performs a turning-on/off control of the transistor N 21  (a generation control of a gate voltage Vg) such that a driving current detecting voltage Vm applied to the CS terminal matches a reference detecting voltage. 
     When the transistor N 21  is turned on, the driving current ILED flows from the application terminal of the DC voltage V 3  to the ground terminal via the transistor N 21 , the resistor R 21 , the inductor L 21  and the LED module  10 . On the other hand, when the transistor N 21  is turned off, the driving current ILED flows in a loop of the diode D 21 , the resistor R 21 , the inductor L 21  and the LED module  10 . 
     In the driving current generation circuit  25  of the second example configuration, a variable voltage Va, instead of the ground voltage, i.e., 0 V, is applied to the GND terminal of the semiconductor device X. The variable voltage Va is a voltage appearing on a connection node of the resistor R 21  and the inductor L 21  and varied with respect to the ground voltage, i.e., 0 V, depending on a switching operation of the transistor N 21 . 
     If the semiconductor device X operates with the variable voltage Va as a reference voltage, unlike the semiconductor device A, as shown in  FIG. 3 , which operates with the ground voltage, i.e., 0 V, as a reference voltage, an inter-terminal voltage applied between the VIN terminal and the GND terminal is not significantly increased even though the DC voltage V 3  is applied to the VIN terminal, and thus the semiconductor device X does not need to have a high withstanding voltage. Accordingly, the driving current generation circuit  35  of the second example configuration may not include the discrete power supply circuit (formed with the transistor Q 11 , the resistors R 12  and R 13 , the diode D 12 , the zener diode ZD and the transformer TR) shown in  FIG. 3 , thereby reducing the size of the driving current generation circuit  25  and making the LED power supply module  20  more compact. 
       FIG. 5  is a circuit diagram showing a third example configuration of the driving current generation circuit  25 . The driving current generation circuit  25  of the third example configuration is the same as that of the second example configuration except that the third example further includes a dimming voltage converter Z. In  FIG. 5 , the same elements of the third example configuration as those of the second configuration are denoted by the same reference numerals shown in  FIG. 4 , and therefore, an explanation of which will not be repeated. The following description is focused on characteristics of the third example configuration. 
     The dimming voltage converter Z is a circuit block configured to use a first dimming voltage Vd 1  set based on the ground voltage, i.e., 0 V, to generate a second dimming voltage Vd 2  set based on of the variable voltage Va. Further, the dimming voltage converter Z includes current mirrors CM 1  to CM 3  and a resistor R 22 . 
     The current mirror CM 1  mirrors a current I 1  flowing at its input side to generate a current I 2  at its output side. The current mirror CM 2  mirrors the current I 2  flowing at its input side to generate a current I 3  at its output side. The current mirror CM 3  mirrors the current I 3  flowing at its input side to generate a dimming current Id at its output side. If mirror ratios of the current mirrors CM 1  to CM 3  are all 1, a relationship of I 1 =I 2 =I 3 =Id is established. Here, the current I 1  (=Id) varies depending on a difference between a constant voltage VREG, e.g., 5.6 V, applied to the current mirror CM 1  and the first dimming voltage Vd 1 , e.g., 0 V to 5 V. In more detail, the current I 1  is increased with a decrease of the first dimming voltage Vd 1 , whereas the current I 1  is decreased with an increase of the first dimming voltage Vd 1 . That is, the current mirrors CM 1  to CM 3  together serve as a voltage/current converter to convert the first dimming voltage Vd 1  into the dimming current Id. 
     The resistor R 22  is connected between the LD terminal of the semiconductor device X (an application terminal of the second dimming voltage Vd 2 ) and the GND terminal (an application terminal of the variable voltage Va) to flow the dimming current Id therethrough. As a result, the second dimming voltage Vd 2  set, which varies depending on the dimming current Id, is applied to the LD terminal of the semiconductor device X. That is, the resistor R 22  serves as a current/voltage converter to convert the dimming current Id into the second dimming voltage Vd 2 . 
     When the gate voltage Vg is generated to match the driving current detecting voltage Vm with a reference detecting voltage, the semiconductor device X provides an offset of the driving current detecting voltage Vm or the reference detecting voltage from the second dimming voltage Vds applied to the LD terminal. The second dimming voltage Vd 2  is a voltage set based on the variable voltage Va while reflecting the first dimming voltage Vd 1 . Accordingly, in the semiconductor device X, the linear dimming control of the LED lamp  1  may be performed based on the second dimming voltage Vd 2 , and further, the first dimming voltage Vd 1 . 
       FIG. 6A  shows a correlation between the second dimming voltage Vd 2  and the driving current ILED and  FIG. 6B  shows a correlation between the first dimming voltage Vd 1  and the second dimming voltage Vd 2 . As shown in  FIG. 6A , in a region where the second dimming voltage Vd 2  is higher than a threshold voltage Vx, the driving current ILED is controlled to vary linearly with respect to the second dimming voltage Vd 2 . In a region where the second dimming voltage Vd 2  is lower than the threshold voltage Vx and higher than a threshold voltage Vy (Vy&lt;Vx), the driving current ILED is controlled to vary nonlinearly with respect to the second dimming voltage Vd 2 . 
     On the other hand, in a region where the second dimming voltage Vd 2  is lower than the threshold voltage Vy, the driving current ILED cannot be variably controlled based on the second dimming voltage Vd 2  by the semiconductor device X, and as the driving current ILED, a minute current (about a few mA) which does not depend on the second dimming voltage Vd 2  flows continuously. Under this condition, a flash effect in which the LED module  10  emits light with an unintended brightness due to charges remaining in an output capacitor (electrolytic capacitor) of the DC/DC conversion circuit  24  may occur. 
     Here, the dimming voltage converter Z is designed such that the second dimming voltage Vd 2  does not fall below the threshold voltage Vy as long as the first dimming voltage Vd 1  is set to be within an LED dimming voltage range, i.e., 0≦Vd 1 ≦Va (see, white double-headed arrows in  FIGS. 6A and 6B ). That is, a lower limit Vz of the LED dimming voltage range set for the second dimming voltage Vd 2  (see, the double-headed arrow in  FIG. 6A ) is set to be higher than the threshold voltage Vy. This setting can prevent the LED module  10  from undergoing the flash effect and can be realized by adjusting a current value of the current Id or a resistance of the resistor R 22 . 
     In addition, the dimming voltage converter Z is designed such that the second dimming voltage Vd 2  becomes zero when the first dimming voltage Vd 1  is set to an LED off voltage Vb (Vb&gt;Va) (see, black arrows in  FIGS. 6A and 6B ). This setting can facilitate not only the dimming control but also the turning-off control of the LED module  10  by using the first dimming voltage Vd 1 . 
     However, if the second dimming voltage Vd 2  is set to zero under the condition where the output capacitor of the DC/DC conversion circuit  24  is not sufficiently discharged, the LED module  10  may undergo the flash effect, as explained above. Further, since the minute current (about 1 mA) continues to flow as the driving current ILED even when the second dimming voltage Vd 2  is set to zero, the LED module  10  cannot be completely turned off by only using the first dimming voltage Vd 1 . 
     A configuration to overcome the above problem will be described in detail below with reference to  FIG. 7 .  FIG. 7  is a block diagram showing a modification example of the LED lamp  1 . The LED lamp  1  of this configuration further includes a relay switch  70  configured to electrically connect/disconnect between the commercial AC power source  30  (the application terminal of the AC input voltage Vin) and the LED power supply module  20 , in addition to the LED module  10 , the LED power supply module  20 , the control power supply module  40  and the remote controller signal receiving module  50  which have been described in the above. 
     In the LED lamp  1  of this configuration, the control power supply module  40  includes a microcomputer  41 , a microcomputer power supply  42  and an output capacitor  43 . The microcomputer  41  controls a reception of a remote controller signal in the remote controller signal receiving module  50  and a generation of the first dimming voltage Vd 1  supplied to the LED power supply module  20 . The microcomputer power supply  42  converts the AC input voltage Vin into a DC voltage and supplies the DC voltage to the microcomputer  41 . The output capacitor  43  is connected to an output terminal of the microcomputer power supply  42  to stabilize the DC voltage supplied to the microcomputer  41 . 
     In the control power supply module  40  as configured above, when the LED module  10  is turned off according to the remote controller signal, the microcomputer  41  decreases the second dimming voltage Vd 2  to the lower limit Vz of the LED dimming voltage range, variably controls the first dimming voltage Vd 1  such that the second dimming voltage Vd 2  becomes zero, and switches off the relay switch  70  by using a switch control signal SW. 
     With this configuration, since the driving current ILED can flow to discharge the output capacitor of the DC/DC converter  24  while decreasing the second dimming voltage Vd 2  to the lower limit Vz for the LED dimming voltage range, the LED module  10  can be prevented from undergoing the flash effect when it is turned off. Further, since the relay switch  70  is finally switched off to cut off the supply of an electric power to the LED power supply module  20 , the driving current ILED can be set to zero to completely turn off the LED module  10 . 
     Further, in cutting off the commercial AC power source  30 , if the microcomputer  41  is shut down earlier than the LED power supply module  20 , the first dimming voltage Vd 1  may become indefinite, which may cause the LED module  10  to undergo the flash effect. To avoid this, it is important to maintain the supply of an electric power to the microcomputer  41  by providing the output capacitor  43  with a sufficiently high capacitance so that the microcomputer  41  cannot be shut down earlier than the LED power supply module  20 . 
     &lt;DC/DC Converter&gt; 
     The DC/DC converter  24  shown in  FIG. 1  includes a transformer as a voltage transforming means. For the purpose of realizing slimness of the DC/DC converter  24  (further, slimness of the LED power supply module  20 ), it is important to form the transformer as thin as possible (less than 18 mm in height). 
       FIG. 8  is a front view of a first example configuration of a transformer  100  (a conventional general-purpose high output transformer). The transformer  100  includes terminal pins  101  and wiring terminal winding pins  102 , all of which vertically extend from a printed circuit board PCB. The wiring terminal winding pins  102  need to have a specific length sufficient to wind winding terminals. Accordingly, the height of the transformer  100  (including the length of the wiring terminal winding pins  102 ) from the printed circuit board is about 25 mm. Therefore, the slimness of the LED power supply module  20  cannot be realized by using the transformer  100  as a voltage transforming means of the DC/DC converter  24 . 
     In addition to the above-mentioned general-purpose high output transformer, a general-purpose thin transformer (12 mm in height) has been conventionally put in practical use. However, the general-purpose thin transformer can hardly pass a heat dissipation test because of its small effective sectional area. Accordingly, a transformer used as a voltage transforming means of the DC/DC converter  24  is expected to have a low height while maintaining the same effective sectional area to that of the conventional general-purpose high output transformer. 
       FIGS. 9 to 15  are a top view, a front view, a side view, a bottom view, a bottom sectional view, a front sectional view and a connection wiring diagram of a second example configuration of a transformer  200 , respectively. As shown in these figures, the transformer  200  includes a gapless core  201 A, a gap core  201 B, a case  202 A, a base  202 B, a spacer  202 C, terminal pins  203 A, wiring terminal winding pins  203 B, a primary winding  204 , a secondary winding  205 , insulating tapes  206 , a core tape  207 , surface tapes  208  and adhesives  209 . 
     The gapless core  201 A and the gap core  201 B are configured to form a magnetic core of the transformer  200 . An example of the gapless core  201 A and the gap core  201 B may include a ferrite core. 
     The case  202 A, the base  202 B and the spacer  202 C are configured to form a bobbin of the transformer  200 . These are made of, for example, phenol resin and formed integratedly in  FIGS. 10 and 14 . The case  202 A is configured to accommodate therein the primary winding  204  and the secondary winding  205 . The case  202 A is disposed on the same plane as the gapless core  201 A and a gap is provided between the gap core  201 B and the case  202 A in  FIG. 13 . The base  202 B is configured to hold the terminal pins  203 A and the wiring terminal winding pins  203 B. The spacer  202 C is configured to project from the bottom surface of the base  202 B toward the printed circuit board PCB. This configuration of the spacer  202 C can alleviate damage to the root of the terminal pins  203 A when the transformer  200  is mounted on the printed circuit board PCB. 
     The terminal pins  203 A are configured to make an electrical connection between the transformer  200  and the printed circuit board PCB. The terminal pins  203 A project from the bottom surface of the base  202 B in a direction extending vertically with respect to the printed circuit board PCB in  FIGS. 10, 11, 12 and 13 . The terminal pins  203 A may be formed with, for example, copper plating pins. 
     The wiring terminal winding pins  203 B are configured to wind therearound and solder thereto wiring terminals WT of the primary and the second winding  204  and  205 . The wiring terminal winding pins  203 B project from the side surface of the base  202 B in a direction extending horizontally with respect to the printed circuit board PCB in  FIGS. 9, 10, 11, 12 and 14 . The wiring terminal winding pins  203 B may be formed with, for example, copper plating pins, like the terminal pins  203 A. This transformer  200  of the second example configuration can reduce its height to about 13 mm while maintaining the same effective sectional area to that of the transformer  100  of the first example configuration. 
     The wiring terminals WT are led outside the base  203 B through grooves SL formed at the side surface of the base  203 B and starts to be wound around the wiring terminal winding pins  203 B from the outermost wiring terminal winding pins  203 B, i.e., in a direction shown in  FIG. 12 . This configuration reduces a load applied to the primary and the secondary winding  204  and  205  during soldering. In some embodiments, the number of winding of the wiring terminals WT is more than one. 
     The terminal pins  203 A and the wiring terminal winding pins  203 B may be formed integratedly into L-shape conductive members, as shown in  FIG. 14 . Alternatively, the terminal pins  203 A and the wiring terminal winding pins  203 B may be separately prepared and electrically connected with each other by conductive members. 
     In the figures, seven terminal pins  203 A and seven wiring terminal winding pins  203 B are equi-spacedly disposed on each side surface of the base  202 B, as shown as circled numerals  1  to  14  in the figures. Here, the pin No.  5  is cut. 
     The primary and the secondary winding  204  and  205  are configured to form coils NP 1 , NP 2 , ND, NS 1  and NS 2  of the transformer  200  in  FIG. 15 . The primary and the secondary winding  204  and  205  may be made of, for example, a polyurethane copper line. The primary winding  204  corresponds to the coils NP 1 , NP 2  and ND and the secondary winding  205  corresponds to the coils NS 1  and NS 2 . In some embodiments, the primary and the secondary winding  204  and  205  are formed in such a manner as windings thereof do not go below the bottom surface of the base  202 B in  FIG. 14 . 
     The insulating tapes  206  are inter-coil/inter-layer insulating members. An example of the insulating tapes  206  may include polyester films in  FIG. 14 . 
     The core tape  207  is configured to fasten the gapless core  201 A and the gap core  201 B together from outside of the gapless core  201 A and the gap core  201 B in  FIGS. 10, 11 and 14 . An example of the core tape  207  may include a polyester film. In some embodiments, the fastening by the core tape  207  is performed twice. 
     The surface tapes  208  are configured to coat the primary and the secondary winding  204  and  205  in  FIG. 14 . An example of the surface tapes  208  may include polyester films or polyester non-woven fabrics. 
     The adhesives  209  are configured to fix contact surfaces of the gapless core  201 A and the gap core  201 B and coils (more precisely, the surface tapes  208 ) together at four sites in  FIGS. 9, 10 and 12 . 
     &lt;Other Modification Examples&gt; 
     Although it has been illustrated in the above embodiments that the spirit of the present disclosure is applied to the LED lamp used as a ceiling light source, the present disclosure is not limited thereto but may have wide applications as a technique to realize compactness and slimness of LED lamps (further, compactness and slimness of power supply modules). 
     The LED lamps according to the above embodiments of the present disclosure can be used as, for example, a ceiling light source and so on. 
     According to some embodiments of the present disclosure, it is possible to provide a driving current generation circuit capable of contributing to compactness and slimness of an LED lamp and an LED power supply module and an LED lamp including the same. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the novel methods and apparatuses described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.