LED driver, lighting equipment and light fixture

When supplying an LED light source with a first output voltage that is equal to or higher than a threshold voltage, an LED driver causes a DC power supply to output a first DC voltage and causes a switching regulator to supply the LED light source with the first output voltage. When supplying the LED light source with a second output voltage that is below the threshold voltage, the LED driver causes the DC power supply to output a second DC voltage lower than the first DC voltage and causes the dropper regulator to supply the LED light source with the second output voltage.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit and priority of Japanese Patent Application No. 2015-041688, filed on Mar. 3, 2015, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates generally to LED drivers, lighting equipment and light fixtures and, more particularly, to an LED (Light-Emitting Diode) driver configured to drive (light) an LED light source, lighting equipment including an LED light source as an illumination light source and the LED driver, and a light fixture having the lighting equipment.

BACKGROUND ART

A solid light source lighting device as a prior art is exemplified in JP Pub. No. 2012-221899 (hereinafter referred to as “Document 1”). The solid light source lighting device described in Document 1 includes a buck chopper circuit, and is configured to dim, namely adjust a light output of a solid light source (e.g., an LED (Light-Emitting Diode) light source) by controlling the buck chopper circuit so that an output current to the solid light source is increased and decreased.

With the solid light source lighting device described in Document 1, a load current (an electric current flowing through the solid light source) is increased and decreased by lengthening and shortening (increasing and decreasing) an ON time (an ON duty ratio) of a switching device (a semiconductor device such as a transistor) forming the buck chopper circuit. A dimming method as stated above is called a DC dimming method in general. With the DC dimming method, there is a limit (a lower limit) in an ON period (an ON width) of a drive signal supplied from a drive circuit for driving the switching device to a control terminal (a gate terminal) of the switching device, thereby making it difficult to perform deep dimming.

As another dimming method, there is also a dimming method with a dropper regulator (hereinafter referred to as a “linear dimming method”). In comparison with a switching regulator, the dropper regulator has an advantage of low ripple and low noise, but has disadvantages of low conversion efficiency and the like. With the linear dimming method, a load current is increased and decreased by changing ON resistance of a field effect transistor, for example. The linear dimming method accordingly has an advantage of making it possible to perform deeper dimming than dimming by the DC dimming method.

Therefore, in a solid light source lighting device (an LED driver) that employs the DC dimming method, the DC dimming method is switched to the linear dimming method in order to perform deep dimming.

However, in the case of the linear dimming method, loss increases according to an increase in a difference between input and output voltages of the LED driver, thereby decreasing the conversion efficiency.

SUMMARY

The disclosure has been achieved in view of the above circumstances, and an object thereof is to enlarge an adjustment range of a drive current for driving an LED light source while reducing loss.

An LED driver according to an aspect is configured to light an LED light source. The LED driver includes a DC power supply, a switching regulator, a dropper regulator and a controller. The DC power supply is configured to selectively output (either) a first DC voltage or a second DC voltage lower than the first DC voltage. The switching regulator is configured to reduce the first DC voltage to supply the LED light source with a first output voltage that is equal to or higher than a threshold voltage. The dropper regulator is configured to reduce the second DC voltage to supply the LED light source with a second output voltage that is below the threshold voltage. The controller is configured to, when supplying the LED light source with the first output voltage, cause the DC power supply to output the first DC voltage and cause the switching regulator to supply the LED light source with the first output voltage. The controller is further configured to, when supplying the LED light source with the second output voltage, cause the DC power supply to output the second DC voltage and cause the dropper regulator to supply the LED light source with the second output voltage.

Lighting equipment according to an aspect includes the LED driver, and the LED light source as an illumination light source. The LED light source includes a plurality of LEDs.

A light fixture according to an aspect includes the lighting equipment, and a fixture body that supports at least the LED light source.

The LED driver, the lighting equipment and the light fixture can enlarge an adjustment range of a drive current for driving the LED light source while reducing loss.

DETAILED DESCRIPTION

An LED (Light-Emitting Diode) driver and lighting equipment, in accordance with an embodiment will be explained with reference toFIGS. 1 to 4.

The LED driver200according to the embodiment is configured to light an LED light source5. In an example ofFIG. 1, the LED driver200includes a DC (Direct Current) power supply1, a switching regulator2, a dropper regulator3and a controller4.

As shown inFIG. 1, the lighting equipment100according to the embodiment includes the LED driver200and the LED light source5. The LED light source5is formed of a series circuit of a plurality of (three in the example ofFIG. 1) LEDs50. The number of LEDs50constituting the LED light source5is not limited to three, but may be two or less or four or more. The LED light source5may be also formed of a parallel circuit of LED arrays each of which includes a plurality of (e.g., twenty) LEDs in series. The LED light source5is electrically connected between output terminals of the LED driver200(between both ends of a second smoothing capacitor C3to be described later).

In the embodiment, the DC power supply1is configured to selectively output (either) a first DC voltage Vdc1or a second DC voltage Vdc2lower than the first DC voltage Vdc1.

In the example ofFIG. 1, the DC power supply1preferably includes a rectifier10configured to rectify an AC (Alternating Current) voltage Vs to produce a pulsating voltage, a converter circuit11configured to convert the pulsating voltage into (either) the first DC voltage Vdc1or the second DC voltage Vdc2, and a first control circuit12configured to control the converter circuit11. The DC power supply1further includes a photo-coupler13and a shunt regulator14.

In the embodiment, the converter circuit11includes a first inductor111A and a first switching device110that are electrically connected in series with each other and configured to be supplied with a DC voltage, and a first smoothing capacitor C1configured to be charged by at least an ON-OFF switching operation of the first switching device110. In an example, the converter circuit11is a flyback converter. In another example, the converter circuit11is a boost converter configured to be supplied with a DC voltage from a DC power supply such as a battery. In still another example, the converter circuit11further includes a switching device constituting a half bridge circuit along with the first switching device110, and the first smoothing capacitor C1is configured to be charged by an ON-OFF switching operation of the first switching device110and the switching device constituting the half bridge circuit.

In the example ofFIG. 1, the converter circuit11includes the first switching device110, a transformer111, a diode D1and the first smoothing capacitor C1. Preferably the first switching device110is an N-channel enhancement MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Thus, in the example ofFIG. 1, the converter circuit11is formed of a known conventional flyback converter.

The transformer111has a primary winding111A as the first inductor, and a secondary winding111B. The transformer111is an additive polarity transformer, and the primary winding111A has a first end111a, and a second end111bas a dot end, while the secondary winding111B has a first end111cas a dot end, and a second end111d. Polarity of the second end111bis the same as polarity of the first end111c. The first end111aof the first inductor111A is electrically connected with the positive output terminal (a high potential-side terminal)101of the rectifier10. The second end111bof the first inductor111A is electrically connected with a first terminal (a drain terminal) of the first switching device110. The first end111cof the secondary winding111B is electrically connected with an anode terminal of the diode D1. The second end111dof the secondary winding111B is electrically connected with a negative terminal (a low potential-side terminal) of the first smoothing capacitor C1. A positive terminal (a high potential-side terminal) of the first smoothing capacitor C1is electrically connected with a cathode terminal of the diode D1. A second terminal (a source terminal) of the first switching device110is electrically connected with a side of the negative output terminal (a low potential-side output terminal)102of the rectifier10. A control terminal (a gate terminal) of the first switching device110is electrically connected with an output terminal12C of the first control circuit12.

In the embodiment, the DC power supply1further includes a voltage sensor R2and the first control circuit12. The voltage sensor R2is electrically connected in parallel with the first smoothing capacitor C1and configured to detect a voltage across the first smoothing capacitor C1as an output voltage of the DC power supply1to obtain a first detection value VR2. The first control circuit12is configured to turn off the first switching device110based on the first detection value VR2.

In an example, the DC power supply1further includes an output voltage monitor120that is configured to supply the first control circuit12with, as the first detection value VR2, an error value corresponding to a difference between the first detection value VR2and a reference value. In this example, the first control circuit12may be configured to operate at a peak current mode or a voltage mode. It is desirable that the output voltage monitor circuit120include the photo-coupler13in the case where the converter circuit11of the DC power supply1includes the transformer111.

In an example of the peak current mode, as shown inFIGS. 1 and 2A, the DC power supply1further includes a first current sensor R3that is configured to detect an electric current flowing through the first switching device110to obtain a current detection value VR3. A first control circuit12includes an oscillator121, a comparator122, a main control circuit (MCC)123and the like. The oscillator121is configured to generate an oscillation signal. The comparator122is configured to compare the current detection value VR3with a target value (a target voltage) obtained by making a slope (ramp) correction to the first detection value VR2(the error value). The main control circuit123includes, e.g., a logic circuit(s) and is configured to turn on the first switching device110in accordance with the oscillation signal from the oscillator121, and then turn off the first switching device110when the comparator122detects the current detection value VR3reaching the target value.

In an example of the voltage mode, as shown inFIGS. 1 and 2B, a first control circuit12includes an oscillator121, a main control circuit123and the like. The oscillator121is configured to generate an oscillation signal (e.g., a triangular wave signal). The main control circuit123is configured to turn on and off the first switching device110based on the first detection value VR2(e.g., the error value obtained from the first detection value VR2) and the oscillation signal. In an example ofFIG. 2B, the main control circuit123includes a comparator122and a NOT circuit (an inverter)124. The comparator122is configured to receive the error value via the NOT circuit124and compare the error value with the oscillation signal to turn on and off the first switching device110based on the compared result. Specifically, the comparator122is configured to turn on the first switching device110in accordance with the oscillation signal and then turn off the first switching device110when the phototransistor131is turned on, namely when the error value is equal to or larger than the abovementioned reference value. In another example, the DC power supply1may further include a first current sensor R3(seeFIG. 2A) that is configured to detect an electric current flowing through the first switching device110to obtain a current detection value VR3. In this example, the main control circuit123is configured to turn on the first switching device110when the current detection value VR3is equal to or less than a threshold for turning on the first switching device110. Thus, the first control circuit12in the embodiment is configured to turn off the first switching device110based on the first detection value VR2after turning on the first switching device110.

In the example ofFIG. 1, the voltage sensor (a detection resistor) R2is electrically connected in series with a resistor (an impedance device) R1, and a series circuit of the resistors R1and R2forms a voltage divider circuit that is electrically connected in parallel with the first smoothing capacitor C1. Specifically, a first end of the resistor R1is electrically connected with the cathode terminal of the diode D1, and a junction of a second end of the resistor R1and a first end of the resistor R2is electrically connected with a reference terminal140of the shunt regulator14. A second end of the resistor R2is grounded. On the other hand, a detection resistor (the first current sensor) R3is electrically connected between a second terminal (a source terminal) of the first switching device110and the negative output terminal (the low potential-side output terminal)102of the rectifier10.

In the example ofFIG. 1, a diode D2, a capacitor C2, resistors R4and R5, the shunt regulator14and the photo-coupler13constitute the output voltage monitor circuit120. An anode terminal of the diode D2is electrically connected with the first end111cof the secondary winding111B. A cathode terminal of the diode D2is electrically connected with the second end111dof the secondary winding111B via the capacitor C2. The second end111dis grounded. The cathode terminal of the diode D2is also electrically connected with a first end of the resistor R4. A second end of the resistor R4is electrically connected with a first end of the resistor R5. A second end of the resistor R5is electrically connected with a cathode terminal141of the shunt regulator14. An anode terminal142of the shunt regulator14is grounded. The reference terminal140of the shunt regulator14is electrically connected with a junction of the resistors R1and R2constituting the voltage divider circuit.

The shunt regulator14has a reference voltage (e.g., 2.5 [V]) corresponding to the abovementioned reference value, and is configured to obtain, as an error value, a difference between the first detection value VR2received at the reference terminal140and the reference value. The error value is supplied to the first control circuit12via the photo-coupler13. For example, the shunt regulator14is configured to increase an electric current from the cathode terminal141to the anode terminal142when a feedback voltage (the first detection value) VR2is above the reference voltage, and decrease the electric current from the cathode terminal141to the anode terminal142when the feedback voltage VR2is below the reference voltage. The feedback voltage VR2is a voltage obtained by dividing an output voltage of the converter circuit11(a voltage across the first smoothing capacitor C1) by the divider circuit (R1and R2). The feedback voltage VR2is given by equation Vdc1×r2/(r1+r2), where Vdc1represents an output voltage of the converter circuit11when the switch device41to be described later is turned off, r1represents a resistance value of the resistor R1and r2represents a resistance value of the resistor R2.

The photo-coupler13is formed of a photodiode130and a phototransistor131. An anode terminal of the photodiode130is electrically connected with a junction of the resistors R4and R5, and a cathode terminal of the photodiode130is electrically connected with the cathode terminal141of the shunt regulator14in a state in which the photodiode130is electrically connected in parallel with the resistor R5. A collector terminal of the phototransistor131is electrically connected with a sense terminal12A of the first control circuit12. An emitter terminal of the phototransistor131is electrically connected with the negative output terminal102of the rectifier10.

When the feedback voltage VR2is above the reference voltage, a collector-emitter voltage of the phototransistor131decreases because an electric current flowing through the shunt regulator14increases and a light amount of the photodiode130increases. On the other hand, when the feedback voltage VR2is below the reference voltage, a collector-emitter voltage of the phototransistor131increases because the electric current flowing through the shunt regulator14decreases and the light amount of the photodiode130decreases.

The first control circuit12is configured to detect, from a voltage VR3across the detection resistor R3, an electric current (an excitation current) flowing through the first switching device110. As shown in an example ofFIG. 2A, the comparator122of the first control circuit12is configured to compare the target voltage obtained from a voltage received at the (first) sense terminal12A (a collector-emitter voltage of the phototransistor131) and a voltage VR3across the detection resistor R3received at a (second) sense terminal12B. The DC power supply1includes a control power supply circuit (not shown) configured to produce an operation power of the first control circuit12. Preferably the control power supply circuit is configured to produce a control power supply voltage (e.g., 3.3 to 5 [V]) from the pulsating voltage obtained from the rectifier10. The first control circuit12may be formed of a commercially available integrated circuit for controlling the flyback converter, for example.

A basic operation of the DC power supply1in the case where the switch device41is in an OFF state is now explained briefly.

The first control circuit12turns on the first switching device110by supplying the control terminal of the first switching device110with a drive signal (an ON control signal), which is a High level signal and a signal for turning on the first switching device110, on a rising edge of a rectangular pulse signal with a constant frequency (period) from the oscillator121. When the first switching device110is turned on, an electric current (an excitation current) flows through the primary winding111A of the transformer111and electromotive force having high potential at the first end111ais generated in the primary winding111A. On the other hand, electromotive force having high potential at the second end111dis induced in the secondary winding111B of the transformer111. The electromotive force induced in the secondary winding111B cannot however draw an electric current through the secondary winding111B because the diode D1is reverse biased. Therefore, electric energy by the excitation current flowing during an ON period of the first switching device110is stored as magnetic energy in the transformer111. During the ON period of the first switching device110, the diode D2is also reverse biased, and accordingly charge of the charged capacitor C2is discharged into the shunt regulator14via the resistors R4and R5.

When a voltage VR3across the detection resistor R3equals the target voltage obtained from an input voltage to the sense terminal12A (the collector-emitter voltage of the phototransistor131), the first control circuit12turns off the first switching device110by supplying the control terminal of the first switching device110with a drive signal (an OFF control signal) for turning off the first switching device110. When the first switching device110is turned off, electromotive force having high potential at the first end111cis generated in the secondary winding111B of the transformer111, whereby the diode D1is biased to conduct. As a result, the magnetic energy stored in the transformer111is discharged as electric energy into the first smoothing capacitor C1via the diode D1and is smoothed with the first smoothing capacitor C1, whereby a DC voltage (an output voltage Vdc1) develops across the first smoothing capacitor C1. The DC voltage is applied to the switching regulator2. At this time, the diode D2is also biased to conduct, whereby the capacitor C2is charged.

The first control circuit12then turns on the first switching device110again by supplying the control terminal of the first switching device110with the ON control signal on a rising edge of the rectangular pulse signal from the oscillator121. Thus, the first control circuit12turns on the first switching device110on each rising edge of the signal from the oscillator121(each oscillation period) and turns off the first switching device110based on the detection values by the resistor R2and R3so that the output voltage Vdc1agrees on a rated value (e.g., a rated voltage of 100 [V]), whereby ON periods of the first switching device110(pulse widths of the drive signal) are adjusted. That is, the DC power supply1is configured so that the first control circuit12performs PWM (Pulse Width Modulation) control of the first switching device110. The DC power supply1can accordingly convert (step up or step down) an input voltage Vs from an AC power supply8(e.g., an AC voltage in an effective voltage range between 100 [V] and 240 [V]) into a desired output voltage (e.g., 100 [V]).

In an example, in the case where the switch device41is in an OFF state, a target value of the output voltage of the converter circuit11is set to 100 [V], the reference voltage of the shunt regulator14is set to 2.5 [V], the resistance value r1of the resistor R1is set to 390 [kΩ], and the resistance value r2of the resistor R2is set to 10 [kΩ]. In this example, the first control circuit12performs the PWM control of the first switching device110so that the feedback voltage VR2agrees on the reference voltage of the shunt regulator14, whereby the output voltage of the DC power supply1is stabilized at 100 [V].

In the embodiment, the switching regulator2is configured to reduce the first DC voltage Vdc1to supply the LED light source5with a first output voltage V1that is equal to or higher than a threshold voltage Vth. Preferably, the switching regulator2includes a series circuit, which is electrically connected in parallel with the first smoothing capacitor C1, of a second smoothing capacitor C3, a second inductor L1and a second switching device20.

The dropper regulator3is configured to reduce the second DC voltage Vdc2to supply the LED light source5with a second output voltage V2that is below the threshold voltage Vth. Preferably, the dropper regulator3includes an active device30that has variable ON resistance and is electrically connected in parallel with at least the second switching device20of the series circuit (C3, L1and20) of the switching regulator2.

The LED driver200further includes a sensor circuit23. The sensor circuit23is configured to detect an electric current flowing through the second switching device20to obtain a second detection value VR6and also detect an electric current flowing through the active device30to obtain a third detection value VR8. In an example, the sensor circuit23includes a second current sensor R6and a third current sensor R8. The second current sensor R6is electrically connected between the second switching device20and the negative terminal of the first smoothing capacitor C1, and configured to detect an electric current flowing through the second switching device20to obtain a second detection value VR6. The third current sensor R8is electrically connected between the active device30and the negative terminal of the first smoothing capacitor C1, and configured to detect an electric current flowing through the active device30to obtain a third detection value VR8. In another example, the sensor circuit23includes a single current sensor that is electrically connected between the negative terminal of the first smoothing capacitor C1and both the second switching device20and the active device30and configured to detect an electric current flowing through the second switching device20or the active device30to a second or third detection value, respectively.

In the example ofFIG. 1, the sensor circuit23includes a resistor (the second current sensor) R6and a resistor (the third current sensor) R8. The switching regulator2includes the second switching device20, a diode D3, the second smoothing capacitor C3and the second inductor L1. A cathode terminal of the diode D3is electrically connected with the positive terminal of the first smoothing capacitor C1. The second switching device20is formed of an N-channel enhancement MOSFET. A first terminal (a drain terminal) of the second switching device20is electrically connected with an anode terminal of the diode D3and a first end of the second inductor L1, and a second terminal (a source terminal) of the second switching device20is connected to the ground (the negative terminal of the first smoothing capacitor C1) via the resistor R6. A second end of the second inductor L1is electrically connected with the negative terminal of the second smoothing capacitor C3. The LED light source5is electrically connected in parallel with the second smoothing capacitor C3. The switching regulator2is a known conventional buck chopper circuit, and is configured so that the second switching device20reduces the output voltage Vdc1of the DC power supply1in accordance with a PWM control signal from a controller4to supply the LED light source5with a DC voltage V1corresponding to the PWM control signal.

The dropper regulator3includes a transistor (the active device)30and a resistor R7. The transistor30is formed of an N-channel enhancement MOSFET. A first terminal (a drain terminal) of the transistor30is electrically connected with the first end of the second inductor L1(the drain terminal of the second switching device20) via the resistor R7. A second terminal (a source terminal) of the transistor30is connected to the ground via the resistor R8. An output voltage Vdc2of the DC power supply1is applied across a series circuit of the second smoothing capacitor C3, the second inductor L1, the two resistors R7and R8and ON resistance of the transistor30. That is, the dropper regulator3is configured to adjust a voltage across the second smoothing capacitor C3(an output voltage V2of the LED driver200) by varying the ON resistance of the transistor30. The ON resistance of the transistor30varies according to a gate voltage applied to the gate terminal of the transistor30from a second control circuit40of the controller4as described below.

In the embodiment, the controller4is configured to, when supplying the LED light source5with the first output voltage V1, cause the DC power supply1to output the first DC voltage Vdc1and cause the switching regulator2to supply the LED light source5with the first output voltage V1. The controller4is also configured to, when supplying the LED light source5with the second output voltage V2, cause the DC power supply1to output the second DC voltage Vdc2and cause the dropper regulator3to supply the LED light source5with the second output voltage V2. Preferably the controller4is configured to control the converter circuit11so that a voltage to be output from the converter circuit11is switched to (either) the first DC voltage Vdc1or the second DC voltage Vdc2.

More preferably the controller4includes a series circuit of an impedance device R9and a switch device41, and the series circuit (R9and41) is electrically connected in parallel with an impedance device R1. The impedance device R1is electrically connected in series with the voltage sensor R2while a series circuit of the impedance device R1and the voltage sensor R2is electrically connected in parallel with the first smoothing capacitor C1. The controller4is configured to turn off the switch device41when supplying the LED light source5with the first output voltage V1, and turn on the switch device41when supplying the LED light source5with the second output voltage V2.

In the embodiment, the controller4is configured to, when the switch device41is turned off, to control an ON-OFF switching operation of the second switching device20so that the second detection value VR6corresponds to an electric current value of a light output represented by a dimming signal for setting the light output of the LED light source5. The controller4is also configured to, when the switch device41is turned on, to adjust the ON resistance of the active device30so that the third detection value VR8corresponds to an electric current value of a light output represented by the dimming signal.

In an example, as shown inFIG. 3, the controller4includes the second control circuit40that includes an oscillator401, an error amplifier402, a resistor403and a main control circuit400. The oscillator401is configured to generate an oscillation signal. A non-inverting input terminal of the error amplifier402is electrically connected with a junction of the active device30and the sensor circuit23(the third current sensor R8). An inverting input terminal of the error amplifier402is electrically connected with the main control circuit400. An output terminal of the error amplifier402is electrically connected with the control terminal of the active device30via the resistor403. The main control circuit400is also electrically connected with an output terminal of the oscillator401, the control terminal of the second switching device20, the control terminal of the active device30, a junction of the second switching device20and the sensor circuit23(the second current sensor R6), and a control terminal of the switch device41. The main control circuit400is configured to, when turning off the switch device41, turn on the second switching device20in accordance with an oscillation signal from the oscillator401and then turn off the second switching device20when the second detection value VR6reaches a threshold (an electric current value) corresponding to a light output obtained from a dimming signal for adjusting a light output of the LED light source5form an external device (e.g., a dimmer), while turning off the active device30. The main control circuit400is also configured to, when turning on the switch device41, supply the inverting input terminal of the error amplifier402with a voltage corresponding to a threshold (an electric current value) obtained from the dimming signal, while turning off the second switching device20. The error amplifier402is configured to supply the control terminal of the active device30with a control signal obtained from a difference between the electric current value obtained from the dimming signal and the third detection value VR8.

In the example ofFIG. 1, the controller4includes the second control circuit40, the switch device41and a resistor R9. The switch device41is formed of a PNP bipolar transistor. A first terminal (a collector terminal) of the switch device41is electrically connected with the cathode terminal of the diode D1and the first end of the resistor R1via the resistor9, and a second terminal (an emitter terminal) of the switch device41is electrically connected with the reference terminal140of the shunt regulator14and the junction of the voltage divider circuit (R1and R2). That is, the controller4is configured to change a division ratio of the voltage divider circuit by connecting the resistor R9in parallel with the resistor R1while the switch device41is in an ON state.

The second control circuit40is configured to control an output level of the switching regulator40, an output level of the dropper regulator3, and a change of the division ratio of the voltage divider circuit (R1and R2). The second control circuit40may be a processor (a micro controller), or integrated circuit(s) configured to perform respective controls as described herein.

The control of the output level by the second control circuit40with respect to the switching regulator2will be explained.

The second control circuit40turns off the switch device41and also turns off the active device30so that no electric current substantially flows from the first terminal to the second terminal of the active device30. In this state, the second control circuit40turns on the second switching device20in accordance with the oscillation signal from the oscillator401. While the second switching device20is turned on, an output voltage Vdc1of the DC power supply1is applied across a series circuit of the second smoothing capacitor C3, the second inductor L1, the second switching device20and the resistor R6, and an electric current flows through the series circuit. That is, the electric current flows from the positive terminal to the negative terminal of the first smoothing capacitor C1via the series circuit. After turning on the second switching device20, the second control circuit40turns off the second switching device20when a voltage VR6across the resistor R6reaches a threshold corresponding to the light output obtained from the dimming signal. When the second switching device20is turned off, energy (magnetic energy) stored in the second inductor L1is discharged, whereby an electric current flows through the closed circuit of the second inductor L1, the diode D3, the second smoothing capacitor C3and the second inductor L1. Thus, a DC voltage (a reduced DC voltage) lower than the output voltage Vdc1of the DC power supply1is generated across the second smoothing capacitor C3, and the DC voltage (an output voltage V1of the switching regulator2) is applied across the LED light source5. That is, according to the dimming signal, the second control circuit40varies the threshold that is compared with the voltage VR6across the resistor R6, thereby performing PWM control of the second switching device20to increase and decrease the output voltage. It is desirable that the dimming signal be a signal for instructing a dimming level by magnitude of a DC voltage. The dimming level corresponding to the light output (a dimming light output) obtained from the dimming signal is represented by a ratio of the DC voltage obtained from the dimming signal to a rated voltage of the LED light source5(forward voltage of LED50×Number of LEDs50) corresponding to the light amount of 100%, as a ratio of the dimming light output to the light amount of 100%.

The control of the output level by the second control circuit40with respect to the dropper regulator3will be explained.

The second control circuit40turns on the switch device41and also turns off the second switching device20. In this state, the second control circuit40controls a gate voltage of the transistor30in accordance with a dimming signal, thereby controlling (adjusting) ON resistance of the transistor30to adjust a voltage across the second smoothing capacitor C3to a voltage corresponding to an light output obtained from the dimming signal. When the second control circuit40increases the gate voltage of the transistor30, the ON resistance of the transistor30decreases and therefore an electric current flowing through the transistor30and the resistor R7(R8as well) increases and a voltage across a series circuit of the transistor30and the resistors R7and R8increases. Since a constant voltage Vdc2of the DC power supply1is applied across a series circuit of the second smoothing capacitor C3, the second inductor L1, the resistor R7, the transistor30and the resistor R8, a voltage across the second smoothing capacitor C3decreases. Similarly, the voltage across the second smoothing capacitor C3increases when the second control circuit40decreases the gate voltage of the transistor30.

The control of the change of the division ratio by the second control circuit40will be explained.

The second control circuit40is configured to apply an ON voltage to the base terminal of the switch device41when applying a gate voltage to the gate terminal of the transistor30. That is, when activating the dropper regulator3, the second control circuit40deactivates the switching regulator2and turns on the switch device41. When activating the switching regulator2, the second control circuit40deactivates the dropper regulator3and turns off the switch device41.

When the switch device41is turned on, the resistor R9is electrically connected in parallel with the resistor R1. At this time, the feedback voltage VR2can be obtained by equation Vdc2×r2/(rx+r2), where Vdc2represents an output of the DC power supply1when the switch device41is turned on and rx represents a resistance value of a parallel circuit of the resistors R1and R9. The resistance value rx can be obtained by 1/rx=(1/r1)+(1/r9), where r9represents a resistance value of the resistor R9. In the case where the resistance value r1of the resistor R1is set to 390 [kΩ], the resistance value r2of the resistor R2is set to 10 [kΩ] and the resistance value r9of the resistor R9is set to 560 [kΩ], the first control circuit12performs PWM control of the first switching device110, whereby the output voltage Vdc2of the DC power supply1is stabilized at 60 [V].

An operation of the lighting equipment100as an representative example of an operation of the LED driver200in the embodiment will be explained in detail with reference toFIGS. 1 and 4. In the example below, a rated voltage of the LED light source is 70 [V], and a minimum voltage thereof is 50 [V].

When a dimming level instructed by the dimming signal is in a range that is α % (e.g., α=20) or more and 100% or less, the second control circuit40activates the switching regulator2with the switch device41turned off and with the dropper regulator3deactivated. For example, the second control circuit40shortens an ON period of the second switching device20as the dimming level decreases, thereby decreasing an output voltage V1of the LED driver200(a voltage across the second smoothing capacitor C3). As a result, a light amount of the LED light source5(a drive current of LEDs50) is decreased. Since the switch device41is turned off, the output voltage of the DC power supply1is kept at 100 [V] (seeFIG. 4).

When a dimming level instructed by the dimming signal is below α %, the second control circuit40activates the dropper regulator3with the switch device41turned on and with the switching regulator2deactivated. For example, the second control circuit40increases the ON resistance of the transistor30as the dimming level is smaller than α %, thereby decreasing an output voltage V2of the LED driver200(a voltage across the second smoothing capacitor C3). As a result, the light amount of the LED light source5(a drive current of LEDs50) is further decreased. Since the switch device41is turned on, the output voltage of the DC power supply1is changed at 60 [V] (seeFIG. 4).

If the output voltage of the DC power supply1is kept at 100 [V] when the second control circuit40activates the dropper regulator3, circuit loss increases (efficiency decreases) because a maximum voltage of 50 [V] (=100−50) may be applied to the resistor R7.

In the LED driver200and the lighting equipment100in the embodiment, while activating the dropper regulator3, the second control circuit40changes the output voltage of the DC power supply1to 60 [V]. Therefore, the voltage applied to the resistor R7is 10 [V] (=60− 50) at maximum and the loss can be reduced (the efficiency can be improved). Thus, the LED driver200and the lighting equipment100in the embodiment can enlarge an adjustment range (a dimming range) of a drive current for driving the LED light source5(LEDs50) while reducing the loss. Output voltage values of the DC power supply1(100 [V] and 60 [V], the resistance value r1and the like are one example, and the embodiment is not limited the exemplified values.

As stated above, the LED driver200according to the embodiment is configured to light the LED light source5(LEDs50). The LED driver200includes the DC power supply1, the switching regulator2, the dropper regulator3and the controller4. The DC power supply1is configured to selectively output (either) a first DC voltage Vdc1(e.g., the output voltage Vdc1=100 [V]) or a second DC voltage Vdc2lower than the first DC voltage Vdc1(e.g., the output voltage Vdc2=60 [V]. The switching regulator2is configured to reduce the first DC voltage Vdc1to supply the LED light source5with a first output voltage V1that is equal to or higher than a threshold voltage Vth corresponding to the dimming level of α %, for example. The dropper regulator3is configured to reduce the second DC voltage Vdc2to supply the LED light source5with a second output voltage V2that is below the threshold voltage Vth. The controller4is configured to, when supplying the LED light source5with the first output voltage V1, cause the DC power supply1to output the first DC voltage Vdc1and cause the switching regulator2to supply the LED light source5with the first output voltage V1. The controller4is also configured to, when supplying the LED light source5with the second output voltage V2, cause the DC power supply1to output the second DC voltage Vdc2and cause the dropper regulator3to supply the LED light source5with the second output voltage V2.

The lighting equipment100according to the embodiment includes the LED driver200and the LED light source5as an illumination light source. The LED light source5includes a plurality of LEDs50that are driven by the LED driver200.

Since the LED driver200and the lighting equipment100, according to the embodiment are configured as stated above, it is possible to enlarge an adjustment range (a dimming range) of a drive current for driving the LED light source5while reducing the loss.

In the LED driver200and the lighting equipment100, according to the embodiment, preferably the DC power supply1includes the rectifier10configured to rectify an AC voltage Vs to produce a pulsating voltage, and the converter circuit11configured to convert the pulsating voltage into (either) the first DC voltage Vdc1or the second DC voltage Vdc2. Preferably, the controller4is configured to control the converter circuit11so that a voltage to be output from the converter circuit11is switched to (either) the first DC voltage Vdc1or the second DC voltage Vdc2.

The LED driver200and the lighting equipment100, according to the embodiment are configured as stated above, whereby it is possible to provide a simple circuit capable of enlarging an adjustment range (a dimming range) of a drive current for driving the LED light source5while reducing the loss.

Light fixtures according to an embodiment are explained with reference toFIGS. 5A and 5B.

A light fixture6shown inFIG. 5Ais a downlight configured to be recessed in a ceiling finishing member S, and formed of a fixture body60in which an LED light source5is built, and an LED driver200configured to be installed on a rear side (an upper side) of the ceiling finishing member S.

In an example ofFIG. 5A, the fixture body60is formed of a metal member shaped like a hollow cylinder by aluminum die-casting or the like so that it has a top base and an bottom opening. The LED light source5is attached on an inner bottom of the fixture body60. The bottom opening of the fixture body60is closed by a cover61shaped like a disc. Preferably, the cover61is made from an optically transparent material such as glass or polycarbonate.

The LED driver200is housed in a metal case shaped like a rectangular case. The LED driver200is also electrically connected with the LED light source5in the fixture body60via power cables62and connectors63.

A light fixture7shown inFIG. 5Bis a downlight configured to be recessed in a ceiling finishing member S, and formed of an LED light source5, an LED driver200and a fixture body70. The LED light source5and the LED driver200are housed in the fixture body70.

In an example ofFIG. 5B, the fixture body70is formed of a metal member shaped like a hollow cylinder by aluminum die-casting or the like so that it has a top base and an bottom opening. An inner space of the fixture body70is divided into upper and lower spaces by a partition board71shaped like a disc. The bottom opening of the fixture body70is closed by a disc shaped cover72that is made from an optically transparent material such as glass or polycarbonate.

The LED light source5is housed in the lower space on a lower side of the partition board71. The LED driver200is housed in the upper space on an upper side of the partition board71. The LED driver200is electrically connected with the LED light source5via a power cable73.

As stated above, the light fixtures6and7according to the embodiment includes the respective lighting equipment100(the LED drivers200and the LED light sources5), and the respective fixture bodies60and70each of which supports at least its own LED light source5.

Since the light fixtures6and7according to the embodiment are configured as stated above, it is possible to enlarge an adjustment range of a drive current for driving each of the LED light sources5while reducing loss. Each of the light fixtures6and7in the embodiment is a downlight, but may be a light fixture except for the downlight.

An LED driver200according to an aspect includes a DC power supply1, a switching regulator2, a dropper regulator3and a controller4. The DC power supply1is configured to controllably provide at an output a first DC voltage Vdc1or a second DC voltage Vdc2lower than the first DC voltage Vdc1. The switching regulator2is operatively coupled to the output of the DC power supply1and configured to controllably reduce the first DC voltage Vdc1to a first output voltage V1to be supplied to an LED light source5. The first output voltage V1is equal to or higher than a threshold voltage Vth. The dropper regulator3is operatively coupled to the output of the DC power supply1and configured to controllably reduce the second DC voltage Vdc2to a second output voltage V2to be supplied to the LED light source5. The second output voltage V2is below the threshold voltage Vth. The controller4is responsive to a dimming signal and operatively coupled to the DC power supply1. The controller4is configured to, in response to a value of the dimming signal being greater than or equal to a value corresponding to the threshold voltage Vth, cause the DC power supply1to provide at the DC power supply output the first DC voltage Vdc1, and cause the switching regulator2to controllably reduce the first DC voltage Vdc1to the first output voltage V1in accordance with the value of the dimming signal. The controller4is further configured to, in response to the value of the dimming signal being less than the value corresponding to the threshold voltage Vth, cause the DC power supply1to provide at the DC power supply output the second DC voltage Vdc2, and cause the dropper regulator3to controllably reduce the second DC voltage Vdc2to the second output voltage V2in accordance with the value of the dimming signal.