KR101625069B1

KR101625069B1 - Led driving cirtuit

Info

Publication number: KR101625069B1
Application number: KR1020130155704A
Authority: KR
Inventors: 홍성수; 이용철; 정광순; 박준우
Original assignee: 국민대학교산학협력단
Priority date: 2013-12-13
Filing date: 2013-12-13
Publication date: 2016-05-27
Also published as: KR20150069382A

Abstract

The present invention relates to an LED driver circuit for reducing bulk and price by applying a squek converter and improving power efficiency.
An LED driving circuit according to the present invention includes: a primary side circuit formed on a primary side of a transformer; And at least one secondary circuit formed on a secondary side of the transformer; And the energy remaining in the energy stored in the primary circuit and transferred to the secondary circuit is returned to the input of the primary circuit.

Description

LED DRIVING CIRTUIT [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED driving circuit, and more particularly, to an LED driving circuit for reducing volume and cost and improving power efficiency by applying a divide converter.

Generally, a battery power supply for a headlight of a car controls a LED current by using a buck converter or a boost converter for each output stage to drive an LED (Lignt Emitting Diode).

In the power supply device for supplying the voltage to the LED driving system, if only one output is provided to one converter, the current accuracy is excellent and the variation range of the output voltage can be reduced, thereby ensuring the efficiency and safety of the product. 1, it is necessary to construct a separate converter for each output stage, so that the price rises and the number of parts increases, thereby increasing the volume of the product.

Therefore, in recent years, a method of obtaining multiple outputs using a single converter has been widely used. In a multiple output system using one converter, there is a cross-regulation method that controls only the main output and a secondary side post regulation (SSPR) method in which a secondary-side control circuit is added while controlling the main output. In the case of the cross-regulation method, in which only the main output stage is controlled and the remaining output stage is controlled by the trunnation of the transformer, the price is lowered but the precise control of the secondary output stage is not possible.

On the other hand, the SSPR method, which controls the main output stage while the other uses the secondary control circuit, has fast dynamic characteristics, thus reducing the variation range of the output voltage, ensuring the reliability of the product, and being applicable to various fields .

However, in the SSPR system, the switching control signal of the negative output terminal must be synchronized with the switching control signal of the main output terminal, which complicates the control circuit. In order to satisfy the electromagnetic interference (EMI) regulation, LC filter is used. Therefore, inductors and capacitors must be further inserted into the input terminals, and if the size of the LC filter is increased according to the power supply apparatus, the volume of the input terminals increases, thereby increasing the volume of the entire power supply circuit.

Korean Patent No. 0729835

Accordingly, it is an object of the present invention to provide an LED driving circuit for transmitting energy to a secondary side of a transformer and returning energy of a remaining primary side to an input terminal.

It is another object of the present invention to provide an LED driving circuit having a simplified structure by fixing a duty ratio of a primary side switch of a transformer and using a switch controlled by the SSPR method on the secondary side.

In addition, the present invention can realize a LED driver circuit by applying a divide converter, thereby eliminating a buck converter or a boost converter used in a secondary side in a conventional LED driver circuit, thereby reducing the volume and cost and improving the efficiency of power conversion There is a further purpose in providing an LED driver circuit.

In the LED driving circuit according to the present invention,

A primary side circuit formed on the primary side of the transformer; And at least one secondary circuit formed on a secondary side of the transformer; Wherein the primary circuit includes a first inductor (L1) connected to the input power supply (Vin), and a third inductor (L1) connected to the second inductor And a first capacitor C1 are connected in series and a link capacitor Clink is connected between the input power supply Vin and the first inductor L1 and between the first inductor L1 and the first capacitor C1, The first switch M1 is connected in parallel to the input power supply Vin and the first diode D1 is connected in parallel to the series connection of the first inductor L1 and the first capacitor C1 The energy stored in the first inductor L1 and the internal magnetizing inductor Lm of the transformer 300 is returned to the input power supply Vin through the first diode D1, A second switch Ms connected in parallel to the second switch Ms for switching the current of the secondary side, The first switch Ml performs a turn-on / turn-off operation with a fixed duty ratio, and the second switch Ms is turned on / off with a fixed duty ratio. A second diode Ds connected in series to the second switch Ms in order of decreasing output voltage of the output terminal when the output terminal of the secondary circuit is more than two, And when the first switch M1 of the primary circuit and the second switch Ms of the secondary circuit are turned on, the first inductor L1 and the second inductor L2 are turned on, When energy is stored in the inductor Lm and thereafter the first switch Ml is turned off, the energy stored in the first inductor L1 and the second inductor Lm is transferred to the secondary circuit, The energy stored in the inductor L1 and the second inductor Lm is transferred to the secondary circuit The energy stored in the first inductor L1 and the second inductor Lm is returned to the input terminal through the first diode D1 of the primary circuit when the second switch Ms is turned off.

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In the present invention, the second switch Ms is controlled by a SSPR (Secondary Side Post Regulator) method according to the load of the secondary circuit.

In the present invention, the primary circuit 100 and the secondary circuit 200 are implemented as a divide converter.

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According to the present invention, the buck converter or the boost converter applied to the conventional LED driving circuit can be eliminated, thereby reducing the volume and cost, and improving the power conversion efficiency of the power supply device.

According to the present invention, when applied to an LED driving circuit for a headlight of an automobile, since the wiring length between the battery power source and the input link capacitor becomes long, the leakage inductance on the line increases, There is no need to additionally insert an LC filter for EMI reduction.

FIG. 1 is a circuit diagram of an LED driving circuit of a multi-output type in which individual converters are applied to respective output stages according to the related art.
2 is a circuit diagram of an LED driving circuit to which a divide converter according to an embodiment of the present invention is applied.
3 is a current waveform diagram of a main device according to the embodiment of FIG.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

2 is an LED driving circuit diagram according to an embodiment of the present invention.

2, the LED driving circuit of the present invention includes a primary side circuit 100 and a secondary side circuit 200 which are insulated from each other with a transformer 300 as a center. In the present embodiment, the primary side circuit 100 and the secondary side circuit 200 are implemented by, for example, a sepic converter. The primary side circuit 100 includes a first inductor L1 and a first capacitor C1 connected in series to an input power supply Vin and a link capacitor Clink between the input power supply Vin and the first inductor L1. And a first switch M1 between the first inductor L1 and the first capacitor C1 are connected in parallel to the input power supply Vin. And a first diode D1 for returning the energy accumulated in the first inductor L1 and the internal magnetization inductor Lm of the transformer 300 to the input power supply Vin side.

In this embodiment, the LED driving circuit may include at least one secondary circuit 200. [ That is, one LED may be driven or two or more LEDs may be driven. Therefore, when a multi-channel LED driver circuit is implemented, the secondary circuit 200 is implemented corresponding to the number of LEDs. The secondary side circuit 200 is connected in parallel to the second switch Ms and the second switch Ms which are generated on the secondary side of the transformer 300 and switch the current flowing through the second diode Ds, And a second capacitor (Co) for smoothing the voltage by the second capacitor (Co). An LED is connected to the second capacitor (Co), and the LED is driven by the accumulated energy. In this case, in the case of a multi-channel LED driver circuit, a plurality of identical circuits are connected in parallel to drive each LED.

In the LED driving circuit constructed as described above, the first switch M1 of the primary side circuit 100 operates at a fixed duty ratio and the second switch Ms of the secondary side circuit 200 operates at a fixed duty ratio And is controlled by the SSPR (Secondary Side Post Regulator) method. By fixing the duty ratio of the first switch M1, the power supplied to the LED is provided through the duty ratio adjustment of the second switch Ms of the secondary circuit 200. [ As described above, in the present invention, the duty ratio of the first switch M1 is fixed in the primary circuit 100 of the transformer 300 by applying a divide converter to the LED driving circuit, so that it is advantageous .

In the present invention, energy is stored in the first inductor L1 and the magnetizing inductor Lm while the primary side circuit M1 is turned on, and energy required from at least one load side (LED) 300 to the secondary side circuit 200. [ The energy remaining in the energy stored in the first inductor L1 and the magnetizing inductor Lm is transferred to the input terminal through the first diode D1 of the primary side circuit 100. [ Here, the energy required for the load side is such that when the first switch Ml is turned off while the second switch Ms is turned on, the first inductor L1 and the magnetizing inductor Lm of the primary circuit 100 are turned off, The second switch Ms is turned off and the energy transfer is stopped. At this time, the energy that is transferred from the first inductor L1 and the magnetizing inductor Lm to the secondary circuit 200 is returned to the input terminal through the first diode D1.

In this case, when the LED driving circuit of the present invention is applied to, for example, a headlight of an automobile, since the wiring length between the battery power supply Vin and the link capacitor becomes long, the parasitic inductance on the line increases, It appears as an LC filter. Therefore, when the energy stored in the first and second inductors L1 and Lm is returned to the input terminal through the first diode D1 in the primary side circuit 100, the returning square wave current flows to the link capacitor Clink, There is an advantage that an additional LC filter for reducing EMI (ElectroMagnetic Interference) is not required.

In the figure, a multi-channel LED driver circuit in which a plurality of LEDs are connected is illustrated, but one LED may be connected as described above. In the case of a multi-channel LED driver circuit, a plurality of secondary circuits 200 are connected in parallel. Since the operation principle is the same, duplicate description is omitted. At this time, the driving of the LEDs can be realized by adjusting the duty ratio of the second switch Ms of each secondary circuit 200 corresponding to the size of the load. Even in the case of such a multi-channel LED driver circuit, the second switches Ms are turned on in order of the output voltages of the LEDs in the respective secondary side circuits 200 so that the corresponding second diodes Ds are sequentially turned on And drives each LED. At this time, the remainder excluding the energy required for each LED is returned to the input terminal through the first diode (D1) of the primary side circuit (100).

3 is a current waveform diagram of a main device according to the embodiment of FIG.

3, when the first switch M1 is turned on during the period t0 to t1 and the second switch Ms is turned on during the period t0 to t2 in the LED driving circuit using the present invention, The current I1 in the first switch M1 increases while the first switch M1 is turned on. When the first switch M1 is turned off, energy stored in the first switch M1 is consumed. The current Im of the magnetizing inductor Lm of the transformer 300 also has the same waveform as I1. This is because energy is continuously increased while energy is accumulated while the first switch Ml is turned on as in the case of the first inductor L1 and the first switch Ml is turned off, It consumes energy and decreases. At this time, the current Is in the secondary circuit 200 of the transformer 300 occurs instantaneously when the first switch Ml is turned off (time t1) and the energy is transferred to the secondary side, and the first inductor L1, And the energy stored in the magnetization inductor Lm is gradually reduced while being transferred to the load side. This is of course done while the second switch Ms is turned on and becomes zero when the second switch Ms is turned off (t2).

Particularly, in the present invention, when the energy stored in the first inductor L1 and the magnetizing inductor Lm is supplied to the input terminal through the first diode D1, When the 2 switch Ms is turned off, the energy transfer to the secondary circuit 200 is stopped so that the current Is in the secondary circuit 200 becomes zero and the remaining energy is supplied to the first diode D1 The current Id at the first diode D1 is generated at the time t2 when the second switch Ms is turned off. This current Id becomes zero at a time t3 when the first and second switches Ml and Ms are turned on.

As described above, these waveforms can be divided into three modes over a period from t0 to t3. Thereafter, three modes are repeated. Hereinafter, the operation of the LED driving circuit in each mode will be described in more detail.

The first mode t0 to t1 starts when the first switch M1 of the primary side circuit 100 and the second switch Ms of the secondary side circuit 200 for SSPR control are turned on. The first switch M1 operates at a fixed duty ratio and energy is accumulated in the first inductor L1 and the magnetizing inductor Lm while the first switch M1 is turned on.

The second mode (t1 to t2) starts with the first switch (M1) of the primary side circuit (100) being turned off. The energy stored in the first inductor Ll and the energy stored in the magnetizing inductor Lm in the second mode are transmitted to the secondary circuit 200. [ 2, in the case of a multi-channel LED driver circuit, the second diode Ds is turned on by the second switch Ms in the order in which the output voltages of the secondary circuits 200 are low, (LED) of the light emitting diode (LED). The first inductor L1 is operated as a boost converter and the second inductor Lm is operated as a buck-boost converter according to the turn-on / turn-off of the first switch M1. do. Therefore, the dot direction of the transformer 300 should be the same as in FIG.

The third mode (t2 to t3) is started when the second switch Ms is turned off. In the third mode, the energy stored in the first inductor L1 and the magnetizing inductor Lm, excluding the energy required at the lower end of the secondary circuit 200, is supplied to the first diode D1 of the primary circuit 100 ). &Lt; / RTI >

Although the present invention has been described in detail with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the details of the illustrated embodiments. Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope of the appended claims, The genius will be so self-evident. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

100: primary side circuit 200: secondary side circuit
300: Transformer

Claims

A primary side circuit (100) formed on the primary side of the transformer (300); And
One or more secondary circuits (200) formed on the secondary side of the transformer (300); Lt; / RTI >
The energy remaining in the energy stored in the primary circuit 100 and transferred to the secondary circuit 200 is returned to the input terminal of the primary circuit 100,
The primary circuit 100 includes a first inductor L1 and a first capacitor C1 connected in series to an input power supply Vin and a second inductor L1 connected between the input power supply Vin and the first inductor L1. A first switch M1 is connected in parallel between the first inductor L1 and the first capacitor C1 and the first switch M1 is connected in parallel to the input power supply Vin, The first diode D1 is connected in parallel to the series connection of the first capacitor C1 and the first capacitor D1 and the energy stored in the first inductor L1 and the internal magnetization inductor Lm of the transformer 300 is supplied to the first diode D1 D1 to the input power supply Vin side,
The secondary circuit 200 includes a second switch Ms for switching the current of the secondary side of the transformer 300 and a second switch Ms connected in parallel to the second switch Ms for smoothing the voltage by the current The first switch Ml may be turned on / off with a fixed duty ratio and the duty ratio of the second switch Ms may be adjusted to control the duty ratio of the second switch Ms. Supplying energy to the secondary circuit,
The second diode Ds connected in series to the second switch Ms is turned on in order of the output voltage of the output terminal in the order of the output terminals of the secondary circuit 200, Is supplied,
When the first switch M1 of the primary side circuit 100 and the second switch Ms of the secondary side circuit 200 are turned on, energy is accumulated in the first inductor L1 and the second inductor Lm When the first switch M1 is turned off, the energy stored in the first inductor L1 and the second inductor Lm is transmitted to the secondary circuit 200,
When the energy stored in the first inductor L1 and the second inductor Lm is transferred to the secondary circuit 200 and the second switch Ms is turned off, And the energy stored in the second inductor (Lm) is returned to the input terminal through the first diode (D1) of the primary circuit (100).

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The method according to claim 1,
And the second switch Ms is controlled by a SSPR (Secondary Side Post Regulator) method according to the load of the secondary circuit 200. [

The method according to claim 1,
The primary side circuit (100) and the secondary side circuit (200) are implemented as a divide converter.

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