# Patent

## Title
LED driving circuit and method using single inductor

## Abstract

The present disclosure relates to an LED driving circuit and method using a single inductor. A constant current controller controls a power stage circuit to provide a constant output signal, and thus to provide a constant current signal for an LED load. A dimming controller regulates luminance of the LED load. A constant voltage generating circuit receives the current signal at an output terminal of the power stage circuit and a reserve supply voltage for providing a supply voltage for the dimming controller. Compared with the prior art, the present disclosure does not need an independent power supply chip, and reduces components such as inductors and rectifying transistors. Thus, a peripheral circuit is simplified, and an overall size of the system is reduced.

## Background
CLAIM OF PRIORITY
This application claims priority to Chinese Application No. 201410439867.7, filed Sep. 1, 2014 (published as CN 104202874 A), which is hereby incorporated by reference.
BACKGROUND OF THE DISCLOSURE
Field of the Disclosure
The present disclosure relates to the field of power electronics, and more particularly, to an LED driving circuit and method using a single inductor.
Description of the Related Art
LED lamps are widely used in the fields of lighting and decoration, as ideal products because they are energy-efficient and environment-friendly. Some specific driving circuits must be developed to achieve constant current control due to characteristics of the LED lamps. A driving circuit typically is an integrated chip 1, as shown in FIG. 1. The chip 1 is a constant current control chip for receiving a DC bus voltage and providing a constant current signal Vout1 through a BUCK converter including switches QM1, QR1 and an inductor L1. The constant current Vout1 is used for driving the LED lamps. When the LED light source includes a plurality of LED strings, a dimming controller (for example, MCU in FIG. 1) is used for regulating color temperature and brightness by dimming the plurality of LED strings. As shown in FIG. 1, a conventional dimming controller needs an additional power supply chip. Typically, the dimming controller has a relatively low supply voltage, for example, 3.3V or 5V. So a voltage obtained from the DC bus voltage cannot be directly used as the supply voltage for the dimming controller as it is usually larger than the supply voltage of the dimming controller. Thus, a voltage converter, such as a chip 2, is necessary for receiving the DC bus voltage, and generating a constant voltage signal Vout through a BUCK converter including switches QM2, QR2 and an inductor L2. The constant voltage signal Vout2 is used for dimming controller MCU.
As shown in FIG. 1, the conventional LED driving circuit has complex peripheral components, including at least two power transistors and at least two inductors. The number of chips is 2, which increases a product cost and introduces a complex control scheme.
BRIEF DESCRIPTION OF THE DISCLOSURE
In view of this, the present disclosure provides an LED driving circuit and method using a single inductor, which, on one hand, achieve constant current control of an LED load, and on the other hand, generate a reserve supply voltage by a constant voltage generating circuit for supplying energy to a dimming controller or to a USB port. The reserve supply voltage is obtained by charging a capacitor of the constant voltage generating circuit with a current signal at an output terminal of a power stage circuit, without an additional chip. A single chip will provide constant current control and brightness adjustment of the LED load.
In one embodiment, there is provided an LED driving circuit using a single inductor, comprising:
a power stage circuit configured to receive a DC bus voltage and output a constant signal for driving an LED load;
a constant current controller configured to receive a feedback signal representing an LED load current, and control operations of a power transistor and a rectifying transistor in the power stage circuit in accordance with the feedback signal to maintain an output current of the power stage circuit to be constant;
a constant voltage generating circuit configured to be connected in parallel between an output terminal of the power stage circuit and ground, receive the output current at the output terminal of the power stage circuit, and generate a constant signal by charging a capacitor in the constant voltage generating circuit, wherein the constant voltage is configured as a reserve supply voltage of the LED driving circuit.
Preferably, the LED driving circuit further comprises a dimming controller.
said dimming controller is configured to receive a dimming signal, and control an average value of the LED load current to have a luminance corresponding to the dimming signal,
wherein the reserve supply voltage is used for providing a supply voltage to the dimming controller.
Preferably, the LED driver further comprises a USB port.
the reserve supply voltage is used for supplying power energy to the USB port.
Preferably, the constant voltage generating circuit comprises a first switch, a capacitor and a voltage controller, and
the first switch and the capacitor are connected in series with each other between the output terminal of the power stage circuit and the ground;
the constant voltage is a voltage signal across the capacitor; and
the voltage controller is configured to receive the voltage signal across the capacitor and a reference voltage signal, and output a first switching control signal, wherein the first switching control signal controls a switching state of the first switch.
Preferably, the constant voltage generating circuit further comprises a first diode configured to be connected between the output terminal of the power stage circuit and the first switch for preventing flowing back of energy from the capacitor to the output terminal of the power stage circuit.
Further, the voltage controller comprises a voltage sampling circuit, a comparator and a driver, and
the voltage sampling circuit is configured to receive the voltage signal across the capacitor, and generate a feedback signal;
the comparator is configured to receive the feedback signal and the reference voltage signal, and generate a comparison signal by comparison; and
the driver is configured to receive the comparison signal and generate the first switching control signal.
Preferably, the reference voltage signal has different values when the reserve supply voltage is supplied to different circuits.
Preferably, the LED load is one or more LED strings.
Preferably, the first diode, the first switch, the voltage controller and the constant current controller of the constant voltage generating circuit are integrated into a single chip.
In another embodiment, there is provided a driving method using a single inductor, for an LED driver comprising a power stage circuit, comprising:
receiving a DC bus voltage and outputting a constant signal for driving an LED load;
receiving a feedback signal representing an LED load current, and controlling operations of a power transistor and a rectifying transistor in the power stage circuit in accordance with the feedback signal to maintain an output current of the power stage circuit to be constant; and
receiving a current signal at the output terminal of the power stage circuit, and generating a constant signal by charging a capacitor with the current signal, wherein the constant voltage is configured as a reserve supply voltage of the LED driving circuit.
In the LED driving circuit and method using a single inductor according to the above embodiments, a constant current controller controls a power stage circuit to provide a constant output signal, and thus to provide a constant current signal for an LED load, a dimming controller regulates luminance of the LED load, and a constant voltage generating circuit receives the current signal at an output terminal of the power stage circuit and a reserve supply voltage for providing a supply voltage for the dimming controller. Compared with the prior art, the present disclosure does not need an independent power supply chip, and reduces components such as inductors and rectifying transistors. Thus, a peripheral circuit is simplified, and a product cost is reduced.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of an LED driving circuit according to the prior art;
FIG. 2 is a schematic diagram of an LED driving circuit using a single inductor according to an embodiment of the present disclosure; and
FIG. 3 is a detailed circuit diagram of an LED driving circuit using a single inductor according to an embodiment of the present disclosure.



DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE
Reference will now be made in detail to particular embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. While the disclosure will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the disclosure to these embodiments. On the contrary, the disclosure is intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the disclosure as defined by the appended claims. Furthermore, in the following detailed description of the present disclosure, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be readily apparent to one skilled in the art that the present disclosure may be practiced without these specific details.
Referring to FIG. 2, a schematic diagram of an LED driving circuit using a single inductor according to the present disclosure is shown. As shown in FIG. 2, an LED driving circuit includes a power stage circuit. In this embodiment, the power stage circuit includes a power transistor QM, a rectifying transistor QR, and a first inductor L1, together as a BUCK converter. Here, the rectifying transistor is also a power transistor, as an example. The power stage circuit receives a DC bus voltage VBUS, and provides a constant signal for driving the LED load. Here, the constant signal means a constant current signal, as those in the following paragraphs. The LED driving circuit further includes a constant current controller 101 configured to receive a feedback signal IFB representing an LED current, and control switching states of a power transistor QM and a rectifying transistor QR in the power stage circuit in accordance with the feedback signal QFB to maintain an output current of the power stage circuit to be constant.
Further, the LED driving circuit also includes a constant voltage generating circuit 102, as shown in FIG. 2. The constant voltage generating circuit is connected between an output terminal of the power stage circuit and ground. Specifically, the constant voltage generating circuit 102 includes a first switch Qs, a capacitor C2 and a voltage controller 102-1. The first switch Qs and the capacitor C2 are connected in parallel between the output terminal of the power stage circuit and ground. A voltage Vout2 across the capacitor is used as a reserve supply voltage. The voltage controller 102-1 receives the voltage signal Vout2 across the capacitor and a reference voltage signal Vref1, and provides a first switching control signal VC1. The first switching control signal VC1 controls a switching state of the first switch Qs. Moreover, an output voltage Vout1 of the power stage circuit in FIG. 2 is used as a driving voltage of the LED load.
Specifically, referring to FIG. 3, an example of the LED driving circuit is shown. The voltage controller 102-1 includes a voltage sampling circuit consisting of resistors R1 and R2, a comparator, and a driver 102-2. Here, the comparator is a hysteresis comparator. The voltage sampling circuit receives the voltage signal Vout2 across the capacitor, and generates a feedback signal Vfb after voltage division. The comparator receives the feedback signal Vfb and the reference voltage signal Vref1 and generates a comparison signal after comparison. The driver receives the comparison signal, and generates a first switching control signal VC1. It will be understood be one skilled person that the voltage sampling circuit may also be configured to directly receive the voltage signal across the capacitor as a feedback signal Vfb.
Moreover, referring to FIG. 2 and FIG. 3, the constant voltage generating circuit 102 according to the present disclosure further includes a first diode D1. The first diode D1 is connected between the output terminal of the power stage circuit and the first switch Qs. The first diode is used for preventing flowing back of energy from the capacitor C2 to the output terminal of the power stage circuit.
In this embodiment, the LED driving circuit further comprises a dimming controller MCU. The dimming controller MCU receives a dimming signal and controls an average value of the LED load current to have a luminance corresponding to the dimming signal. The reserve supply voltage is used for providing a supply voltage to the dimming controller MCU. It will be understood by one skilled person that the LED load may be one or more LED strings. In this embodiment, the LED load may be one LED string. The power transistor Q1 is connected in parallel with the LED strings. The dimming controller MCU is connected to the constant current controller 101. The constant current controller outputs a dimming signal, such as VQ1 as shown in FIG. 2, to control a switching state of the power transistor Q1 for controlling the average value (or luminance) of current through the LED string.
In an alternative embodiment, the LED load may be two LED strings. The power transistors Q1 and Q2 are connected in parallel with the two LED strings, respectively. The dimming controller MCU is connected to the constant current controller 101. The constant current controller outputs dimming signals, such as VQ1 and VQ2, to control switching states of the power transistors Q1 and Q2 for controlling the average values (or luminance) of currents through the two LED strings.
It will be understood by one skilled person that in a case that the LED driving circuit does not need dimming function, the reserve supply voltage may be used for other purposes. For example, the reserve supply voltage is used for supplying energy to a USB port. Accordingly, the reference voltage signal Vref1 may have a value which is different when the reserve supply voltage is supplied to different circuits.
The LED driving circuit according to the present embodiment has been described in connection with the above circuit diagram. In a case that the dimming controller MCU needs an expected supply voltage having a predetermined value, such as 3.3V or 5V, the reference voltage signal Vref1 should be set to a value corresponding to a divided voltage of the predetermined value by a voltage division network. In a case that the feedback signal Vfb indicates that the reserve supply voltage Vout2 is less than the predetermined value, the first power transistor Qs is turned on, and the capacitor C2 is charged by a current signal at the output terminal of the power stage circuit. In a case that the feedback signal Vfb indicates that the reserve supply voltage Vout2 is larger than the predetermined value, the first switch Qs is turned off, and the capacitor C2 is not charged by the current signal. The reserve supply voltage Vout2 is regulated to the predetermined value as required by the above operations. Additionally, it should be noted that the capacitor C2 is charged by the current signal when the power transistor Q1 is turned off, and the capacitor C2 is not charged by the current signal when the power transistor Q1 is turned on. In a case that the LED load includes two LED strings, the capacitor C2 is charged by the current signal when either of the power transistors Q1 and Q2 is turned off, and the capacitor C2 is not charged by the current signal when both of the power transistors Q1 and Q2 are turned on.
As mentioned above, the present disclosure does not need an additional chip for converting a DC bus voltage to a supply voltage. Electric energy is obtained by charging a capacitor at a load side. The power stage circuit needs only one inductor. The number of the chips is reduced because an additional power converter is omitted.
The above embodiments are described with a BUCK circuit as an example. However, the present disclosure is not limited to these embodiments. The present disclosure can be applied in any suitable power stage circuit, such as a BUCK-BOOST circuit.
Moreover, it should be noted that in the present disclosure, the first diode D1, the first power transistor Qs, and the voltage controller 102-1 of the constant voltage generating circuit, and the constant current controller 101 can be integrated into one chip, such as the chip shown in FIG. 2 or 3. Moreover, the power transistor QM, the rectifying transistor QR of the power stage circuit may also be integrated into this control chip. In a case that the LED driving circuit also includes a dimming controller MCU, the dimming controller MCU may also be integrated into the control chip.
In another embodiment, there is provided a driving method using a single inductor, for an LED driver comprising a power stage circuit, comprising:
S1: receiving a DC bus voltage and outputting a constant signal for driving an LED load;
S2: receiving a feedback signal representing an LED load current, and controlling operations of a power transistor and a rectifying transistor in the power stage circuit in accordance with the feedback signal to maintain an output signal of the power stage circuit to be constant; and
S3: receiving a current signal at the output terminal of the power stage circuit, and generating a supply voltage signal by charging a capacitor with the current signal, wherein the supply voltage signal is configured as a reserve supply voltage of the LED driving circuit. The capacitor is connected in parallel between the output terminal of the power stage circuit and ground.
Further, the LED driving circuit includes a dimming controller, the reserve supply voltage is used for providing a supply voltage to the dimming controller.
Further, the LED driving circuit includes a USB port, and the reserve supply voltage is used for supplying energy to the USB port.
It will be understood that other topologies of the power stage circuit can also be used in the present disclosure in light of the above embodiments. Details are not repeated here. The invention is intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the invention as defined by the appended claims.
To sum up, the LED driving circuit and method using a single inductor according to the present disclosure do not need an additional chip for converting a DC bus voltage to a supply voltage. Electric energy is obtained by charging a capacitor at a load side. The power stage circuit needs only one inductor. The number of the chips is reduced because an additional power converter is omitted.
The LED driving circuit and method using a single inductor according to the present disclosure have been described in detail for the preferable embodiments. It is apparent for one skilled person that other technique or configuration or circuits or electronic devices, if being equivalents, can also be used in these embodiments.
Although various embodiments of the present invention are described above, these embodiments neither present all details, nor imply that the present invention is limited to these embodiments. Obviously, many modifications and changes may be made in light of the teaching of the above embodiments. These embodiments are presented and some details are described herein only for explaining the principle of the invention and its actual use, so that one skilled person can practice the present invention and introduce some modifications in light of the invention. The invention is intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the invention as defined by the appended claims.

## Claims

1. An LED driving circuit using a single inductor, comprising:
a power stage circuit configured to
receive a DC bus voltage and
output a constant signal for driving an LED load;

a constant current controller configured to
receive a feedback signal representing an LED load current, and
control operations of a power transistor and a rectifying transistor in said power stage circuit in accordance with said feedback signal to maintain an output current of said power stage circuit to be constant; and

a constant voltage generating circuit configured to
be connected in parallel with said LED load between an output terminal of said power stage circuit and ground,
receive a current signal at said output terminal of said power stage circuit, and
generate a constant voltage signal by charging a capacitor in said constant voltage generating circuit with said current signal,
wherein said constant voltage signal is configured as a reserve supply voltage of said LED driving circuit.

2. The driving circuit according to claim 1, further comprises
a dimming controller, and said dimming controller is configured to
receive a dimming signal, and
control an average value of said LED load current to have a luminance corresponding to said dimming signal,
wherein said reserve supply voltage is used for providing a supply voltage to said dimming controller.

3. The driving circuit according to claim 1, wherein said constant voltage generating circuit comprises
a first switch,
a capacitor and
a voltage controller, and
said first switch and said capacitor are connected in series with each other between said output terminal of said power stage circuit and said ground;
said constant voltage is a voltage signal across said capacitor; and
said voltage controller is configured to
receive said voltage signal across said capacitor and a reference voltage signal, and output a first switching control signal,
wherein said first switching control signal controls a switching state of said first switch.

4. The driving circuit according to claim 3, wherein said constant voltage generating circuit further comprises a first diode configured to
be connected between said output terminal of said power stage circuit and
said first switch for preventing flowing back of energy from said capacitor to said output terminal of said power stage circuit.

5. The driving circuit according to claim 4, wherein said first diode, said first switch, said voltage controller and said constant current controller of said constant voltage generating circuit are integrated into a single chip.

6. The driving circuit according to claim 3, wherein said voltage controller comprises
a voltage sampling circuit,
a comparator and
a driver, and
said voltage sampling circuit is configured to
receive said voltage signal across said capacitor, and
generate a feedback signal;

said comparator is configured to
receive said feedback signal and said reference voltage signal, and
generate a comparison signal by comparison; and

said driver is configured to
receive said comparison signal and
generate said first switching control signal.

7. The driving circuit according to claim 3, wherein said reference voltage signal has a predetermined value when said reserve supply voltage is supplied to an external circuit.

8. The driving circuit according to claim 1, wherein said LED load is one or more LED strings.

9. An LED driving method using a single inductor, for an LED driver comprising a power stage circuit for driving an LED load, and a constant voltage generating circuit being connected in parallel with said LED load between an output terminal of said power stage circuit and ground, comprising:
receiving a DC bus voltage and
outputting a constant signal for driving said LED load;
receiving a feedback signal representing an LED load current, and
controlling operations of a power transistor and
a rectifying transistor in said power stage circuit in accordance with said feedback signal to maintain an output current of said power stage circuit to be constant; and
receiving a current signal at said output terminal of said power stage circuit, and
generating a constant voltage signal by charging a capacitor with said current signal,
wherein said constant voltage signal is configured as a reserve supply voltage of said LED driving circuit.