WO2015050354A1

WO2015050354A1 - Ac led driver circuit having current sources having cascode structure

Info

Publication number: WO2015050354A1
Application number: PCT/KR2014/009158
Authority: WO
Inventors: 신소봉
Original assignee: 메를로랩 주식회사
Priority date: 2013-10-02
Filing date: 2014-09-30
Publication date: 2015-04-09
Also published as: KR101549491B1; KR20150039513A

Abstract

The present invention relates to an AC LED driver circuit which has current sources having a cascode structure, i.e., switching circuit units having a cascode structure, the AC LED driver circuit, which has current sources having a cascode structure, allowing all switching circuit units to operate always under the same conditions, regardless of the characteristics, current value of each channel, external temperature, and the like of clamp elements, by constantly maintaining the headroom voltage value of each switching circuit unit. The AC LED driver circuit according to the present invention comprises: an LED lighting unit comprising a first LED, which is located at the shortest distance from the point of connection with a power supply unit, to an n^th LED, which is located at the longest distance from the power supply unit; multiple switching circuit units which are respectively connected to the output terminal of one or more LEDs forming the LED lighting unit so as to form current supply channels for the corresponding LEDs; and a voltage headroom control unit connected to the connection lines between the switching circuit units and the corresponding LEDs of the LED lighting unit. The voltage headroom control unit comprises: multiple clamp elements which are respectively installed on the connection lines between the switching circuit units and the corresponding LEDs of the LED lighting unit and biased in a common gate or common base mode; and a bias control unit which is connected to the connection lines between the clamp elements and the switching circuit units and receives as an input the node value of each clamp element and controls the bias values of the gates or bases of the clamp elements on the basis of the inputted node values.

Description

AC LED drive circuit with current source of cascode structure

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED driving circuit. In particular, in an alternating LED driving circuit having a current source of a cascode structure, that is, a switching circuit portion of a cascode structure, the headroom voltage value of each switching circuit portion is kept constant and clamped. The present invention relates to an AC LED driving circuit having a current source of a cascode structure that allows all switching circuit units to be driven under the same conditions regardless of device characteristics, channel current values, external temperatures, and the like.

AC LED driving circuit proposed to drive LED under AC power has advantages of simple manufacturing process, low defect rate and long life compared with Switched mode power supply (SMPS) method.

The basic principle of such an AC LED driving circuit is to sequentially control a current source.

Referring to FIG. 1, FIG. 1 is a view showing a conventional AC LED driving circuit according to the related art. As shown in FIG. 1, the performance of the current source represented by ILED1 to ILEDn determines the control performance of the entire circuit. In other words, the control performance of the AC LED drive circuit depends on the performance of the current sources, and thus the performance improvement of these current sources is directly connected to the improvement of the control performance of the AC LED drive circuit.

For reference, factors that determine the basic performance of a general current source include the accuracy of the current value, the impedance at both ends, the time for normal operation after the start of operation, the temperature and voltage, and the degree of maintaining the same value under various external conditions. There are various structures to satisfy these factors, and one of the widely used methods is the cascode structure.

FIG. 2 shows a basic cascode structure. Referring to this, the cascode structure basically includes a current source 10 for setting a current, a clamp cell 20 biased in a common gate (or common base) manner, and a clamp cell. It consists of a power source 30 connected to the gate (or base) of the (20). Here, when the clamp cell 20 is configured as a high voltage transistor, the breakdown voltage required for the AC LED driving circuit can be realized, and the AC LED driving circuit can be configured using the clamp cell 20.

3 is a diagram illustrating an example of an AC LED driving circuit using a cascode structure.

Referring to this, a current source of each channel is configured using M1 to M4, SA1 to SA4, and Rs, and UHV1 to UHV4 serve as clamps for each channel. The gate of the FET that constitutes the clamp receives a voltage from VCC2 to form a bias.

However, the AC LED driving circuit of the above configuration can cause the following problems.

That is, since VCC2 is fixed, the voltage of the nodes ranging from N1 to N4 is entirely determined by the threshold voltages of the current values I1 to I4 and UHV1 to UHV4 flowing through UHV1 to UHV4.

Accordingly, when the difference between the values of I1 to I4 is large, the voltage value deviation of the N1 to N4 nodes may occur, and the voltage value deviation of the N1 to N4 nodes may also occur with respect to the external temperature change. In addition, the deviation of the voltage value of the N1 ~ N4 node may occur due to the process deviation of the clamp high voltage transistor of UVH1 ~ UVH4, and when the UVH1 ~ UVH4 is implemented as an external transistor, the threshold voltage and the temperature and current characteristics of the N1 ~ N4 The voltage value deviation of the node may occur.

These problems can directly affect the performance uniformity, reliability, and lifespan of AC LED driving circuits and their products.

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above problems, and has a constant headroom voltage value of each switching circuit part in an AC LED driving circuit having a current source of a cascode structure, that is, a switching circuit part of the cascode structure. It is an object of the present invention to provide an AC LED driving circuit having a current source having a cascode structure so that all switching circuits can be driven under the same conditions regardless of the characteristics of the clamp element, the current value for each channel, the external temperature, and the like.

In order to achieve the above object, the AC LED driving circuit having the current source of the cascode structure according to the present invention includes the first LED located at the longest distance from the power supply, starting with the first LED located at the shortest distance from the connection point with the power supply. a plurality of switching circuits, each of which is connected to an LED lighting unit including an LED, an output terminal of one or more LEDs forming the LED lighting unit, and forms a current supply channel for the corresponding LED, the switching circuits and the LED lighting unit And a voltage headroom control unit connected to a connection line between corresponding LEDs to maintain a constant headroom voltage value of the switching circuit units.

The voltage headroom control unit may include a plurality of clamp elements separately installed in connection lines between the switching circuit units and corresponding LEDs of the LED lighting unit and biased in a common gate or common base manner, and the clamp elements and the switching circuit units. And a bias adjuster connected to the connection line between the clamp devices to adjust the bias value of the gate or the base of the clamp device based on the node value received from the node value for each clamp device.

The bias adjuster may maintain a voltage value of a plurality of nodes of each clamp element at a preset voltage or a similar voltage value of ± 5 to 10% of an error range with respect to the preset voltage.

The preset voltage of the bias adjustment unit may be an input voltage to the bias adjustment unit.

The bias adjustment unit may control a headroom voltage value of the switching circuit units based on the operation confirmation signal to which the operation confirmation signals of the switching circuit units are separately input.

In addition, the bias adjustment unit may be individually matched with the clamp elements to input a node value of the corresponding clamp element, and a plurality of first OP amplifiers for inputting a common threshold voltage of voltage values for switching operations of the switching circuit units. And connected in parallel on the node value input line of the clamp element for the first OP amplifier in a state of individually matching with the first OP amplifiers and controlled on / off according to an output value of the corresponding first OP amplifier. And a second OP amplifier connected in parallel with the plurality of switches and the output terminals of the switches, and at which a preset voltage for the bias adjustment unit is input. Here, the bias adjusting unit controls the on / off operation of the switches based on the node value of the clamp elements according to the output value of the first OP amplifier, the output value of the first OP amplifier is input separately. It may further include a switch controller.

In addition, the LED lighting unit in the form of a plurality of LEDs to form individual LED lights, two or more LEDs are formed in groups of one or more LED lights are connected, LED lights formed of one LED and two or more LEDs The LED circuit is formed in any one of the form that is connected is characterized in that the switching circuit is connected to the output terminal of the final LED of each LED light.

The power supply unit may include an AC power source and a rectifier circuit of the AC power source.

In addition, the AC LED driving circuit having a current source of the cascode structure according to the present invention further comprises a switching check unit for sensing whether the switching circuit unit is connected to the switching circuit unit individually, the bias adjustment unit sensing the switching confirmation unit The headroom voltage value of the switching circuit units is controlled based on the signal. Here, the switching confirmation unit may be a configuration of a current sensing unit installed at an input terminal or an output terminal of the switching circuit unit to sense an input current or an output current of the switching circuit unit.

According to the present invention, in the AC LED drive circuit having the current source of the cascode structure, that is, the switching circuit portion of the cascode structure, the headroom voltage value of each switching circuit portion is kept constant so that the characteristics of the clamp element and the channel Regardless of the current value, external temperature, etc., all the switching circuits can always operate under the same conditions.

1 is a view showing a conventional general AC LED driving circuit

2 shows a basic cascode structure

3 is a diagram illustrating an example of an AC LED driving circuit using a cascode structure;

4 is a conceptual view illustrating an AC LED driving circuit having a current source having a cascode structure according to an embodiment of the present invention.

5 is a view illustrating a main part of an AC LED driving circuit having a current source having a cascode structure according to an embodiment of the present invention;

6 is a view illustrating a main part of an AC LED driving circuit having a current source having a cascode structure according to another embodiment of the present invention;

7 is a view illustrating a main part of an AC LED driving circuit having a current source having a cascode structure according to still another embodiment of the present invention;

Hereinafter, an AC LED driving circuit having a current source having a cascode structure according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

4 is a diagram conceptually illustrating an AC LED driving circuit having a current source having a cascode structure according to an embodiment of the present invention.

As shown, the AC LED drive circuit (100: abbreviated as "AC LED drive circuit") having a current source of the cascode structure according to an embodiment of the present invention is a power supply 110, LED lighting unit 120 And a plurality of switching circuit units 130 and a voltage headroom control unit 140.

The power supply unit 110 supplies power to the AC LED driving circuit. In this embodiment, the power supply unit 110 includes an AC power source and a rectifier circuit of the AC power source, but the present invention is limited thereto. It doesn't happen.

The LED lighting unit 120 includes a third LED 120-3 positioned at the longest distance from the power supply 110, starting with the first LED 120-1 positioned at the shortest distance from the connection point with the power supply 110. It is composed. In addition, the LED lighting unit 120 forms a plurality of LEDs to form individual LED lights, two or more LEDs are formed in groups of one or more LED lights are connected, LED lights formed of a single LED and two or more The LED lighting formed of the LED is formed in any one of the form that is connected to the switching circuit unit 130 may be connected to the output terminal of the final LED of each LED lighting.

In the present embodiment, a plurality of LEDs form individual LED lights, and thus the switching circuit unit 130 is connected to an output terminal of each LED.

The switching circuit 130 is individually connected to the output terminals of one or more LEDs forming the LED lighting unit 120 to form a current supply channel for the corresponding LED. In the present embodiment, a detailed illustration and description of the switching circuit unit 130 has been omitted. As an example of such a switching circuit unit 130, a form including a field effect transistor (MOS FET) and an OP amplifier comparator may be used. Here, the field effect transistor may have a form in which a drain is connected to the LED output terminal of the LED lighting unit 120, a source is connected to the ground resistance, and a gate is connected to the OP amplifier comparator.

The voltage headroom control unit 140 is connected to a connection line between the switching circuit units 130 and the corresponding LED of the LED lighting unit 120 to maintain a constant headroom voltage value of the switching circuit units 130. do.

The headroom control unit 140 may include a plurality of clamp elements 141 and a bias adjustment unit 142.

The plurality of clamp elements 141 are separately installed in the connection line between the switching circuit units 130 and the corresponding LEDs of the LED lighting unit 120 and are biased in a common gate or common base manner.

The bias adjuster 142 is connected to a connection line between the clamp elements 141 and the switching circuit unit 130 to receive a node value for each clamp element 141, and then clamp the element 141 based on the input node value. Adjust the bias value of the gate or base. Here, the bias adjustment unit 142 may be to maintain the voltage value of the node (node) for each of the plurality of clamp elements 141 to a preset voltage or a pseudo voltage value of ± 5 ~ 10% of the error range with respect to the preset voltage. have. In addition, the preset voltage of the bias adjuster 142 may be an input voltage to the bias adjuster 142.

An example of such a bias adjustment unit 142 will be described with reference to FIG. 5.

As shown, the bias adjustment unit 142 may include a plurality of first OP amplifier 142a, a plurality of switches 142b, a second OP amplifier 142c. In addition, the bias adjuster 142 may further include a switch controller 142d.

The plurality of first OP amplifiers 142a are individually matched with the clamp elements 141 so that a node value of the corresponding clamp element 141 is input and at the same time a common voltage value for switching operations of the switching circuit units 130 is provided. Threshold voltages are input separately.

The plurality of switches 142b are connected in parallel with each other on the input line of the node value of the clamp element 141 for the first OP amplifier 142a in a state of individually matching the first OP amplifiers 142a. On / off control is performed according to the output value of the amplifier 142a.

The second OP amplifier 142c is connected in parallel with the output terminals of the switches 142b and at the same time a preset voltage for the bias adjustment unit 142 is input.

The switch controller 142d may switch the switch 142b based on a node value of the clamp elements 141 according to an output value of the first OP amplifier 142a inputted separately. Control their on / off behavior. For example, the switch control unit 142d controls to connect only SW1 when V _N1 > V _CHth , V _N2 <V _CHth , V _N3 <V _CHth , and V _N1 > V _CHth , V _N2 > V _CHth , V _N3 In case of <V _CHth , only SW2 is controlled. In case of V _N1 > V _CHth , V _N2 > V _CHth , V _N3 > V _CHth , only SW3 is controlled. Thus, through this suitable logical combination of the switch control unit 142d, it is possible to set the operating conditions of the switch 142b necessary for the headroom voltage control.

4 again, when the Vref1 value is set to the minimum value or the value slightly higher than the minimum value of the N1 to N3 node voltages required for the operation of the switching circuit units 130 through the illustrated AC LED driving circuit 100, the clamp element ( Irrespective of the characteristics of the current, the channel-specific current value, the external temperature, and the like, the voltage values of the nodes N1 to N3 converge to the Vref1 value or its value during operation, so that the switching circuits 130 can be always driven under the same conditions. do.

Next, other embodiments of the AC LED driving circuit according to the present invention will be described with reference to FIGS. 6 and 7.

First, an AC LED driving circuit according to another embodiment of the present invention will be described with reference to FIG. 6. Prior to the description, this embodiment is compared with the AC LED driving circuit 100 according to FIGS. 4 and 5. 242, there is a difference, and the bias adjustment unit 242 will be described mainly, and the same parts as the AC LED driving circuit 100 according to FIGS. 4 and 5 will not be described in detail, and the same reference numerals will be used. Reveal

As shown, the AC LED driving circuit 200 is individually input to the operation confirmation signal of the switching circuit unit 130 to the bias adjustment unit 242, switching based on the operation confirmation signal that the bias adjustment unit 242 is so input The headroom voltage values of the circuit units 130 are controlled.

That is, the AC LED driving circuit 200 may need an appropriate time for headroom control because each switching circuit unit 130 has an exclusive operation time point. For example, when the first switching circuit unit 130 (current source 1) operates, the headroom voltage control should be performed using only the voltage of the node N1, and the second switching circuit unit 130 (current source 2) is operated. Is used only when the voltage of node N2 is used, and when the third switching circuit unit 130 (current source 3) is operating, only the voltage of node N3 is used to control the headroom voltage. You may need to.

At this time, by detecting the change in the voltage value of any particular part in each circuit constituting the switching circuit unit 130 to determine whether the operation of the switching circuit unit 130, bar of the specific part for each switching circuit unit 130 The bias adjustment unit 242 may select among the voltage values of the nodes N1 to N3 using the voltage values S1 to S3 to control the headroom voltage.

Next, an AC LED driving circuit according to still another embodiment of the present invention will be described with reference to FIG. 7. Prior to the description, this embodiment is switched in comparison with the AC LED driving circuit 100 according to FIGS. 4 and 5. At the same time, there is a difference in the configuration and operation of the bias adjustment unit 342 according to the switching confirmation unit 350 at the same time, further comprising a check unit 350 and the bias adjustment unit 342 The same parts as those of the AC LED driving circuit 100 according to FIGS. 4 and 5 will be omitted, and the same reference numerals will be omitted.

As shown, the switching check unit 350 is individually connected to the switching circuit units 130 to detect whether the corresponding switching circuit unit 130 operates. Here, the switching check unit 350 may be configured to be installed at an input terminal or an output terminal of the switching circuit unit 130 to configure a current sensing unit for detecting an input current or an output current of the switching circuit unit 130. In the following description, the switching checking unit 350 will be described as an example of the current sensing unit.

The bias adjuster 342 controls headroom voltage values of the switching circuit units 130 based on the detection signal of the current detector 350.

By the above configuration, similar to the AC LED driving circuit 200 shown in FIG. 6, the switching circuit unit through the current sensing unit 350 connected in series to the switching circuit unit 130 in a method of determining whether the switching circuit unit 130 is operated. Signals S21 to S23 indicating whether a current flowing through the 130 is generated are input to the bias adjustment unit 342, and the bias adjustment unit 342 receives nodes N1 to N3 according to the input signal of the current detection unit 350. Control the headroom voltage by selecting an appropriate value from the voltage values.

As can be seen through the embodiments of FIGS. 4 to 7 described above, the AC LED drive circuit having the current source of the cascode structure according to the present invention, each switching in the AC LED drive circuit having a switching circuit portion of the cascode structure The headroom voltage value of the circuit part is kept constant so that all switching circuit parts are always driven under the same conditions regardless of the characteristics of the clamp element, the current value for each channel, the external temperature, and the like.

What has been described above is only one embodiment for implementing an AC LED driving circuit having a current source of a cascode structure according to the present invention, the present invention is not limited to the above embodiment, it is claimed in the claims below As will be apparent to those skilled in the art to which the present invention pertains without departing from the gist of the present invention, the technical spirit of the present invention will be described to the extent that various modifications can be made.

The present invention can be widely used in the LED drive circuit.

Claims

An LED lighting unit including an n-th LED unit located at a longest distance from the power supply unit, including a first LED unit located at a shortest distance from a connection point with a power supply unit;

A plurality of switching circuit units individually connected to output terminals of one or more LEDs forming the LED lighting unit to form a current supply channel for the corresponding LEDs;

A current source having a cascode structure connected to a connection line between the switching circuit units and the corresponding LEDs of the LED lighting unit and including a voltage headroom control unit for maintaining a constant headroom voltage value of the switching circuit units. AC LED drive circuit.
The method of claim 1, wherein the voltage headroom control unit

A plurality of clamp elements installed in connection lines between the switching circuit parts and the corresponding LEDs of the LED lighting part and biased in a common gate or common base manner;

A bias adjuster connected to a connection line between the clamp elements and the switching circuit part to receive a node value for each clamp element and adjust a bias value of a gate or a base of the clamp element based on an input node value AC LED drive circuit having a current source of the cascode structure comprising a.
The method of claim 2,

The bias adjusting unit maintains a voltage value of a plurality of nodes of each clamp element at a preset voltage or a pseudo voltage value of ± 5 to 10% of an error range with respect to the preset voltage. AC LED drive circuit having a current source.
The method of claim 3, wherein

And the preset voltage of the bias adjuster is an input voltage to the bias adjuster.
The method of claim 2,

The bias adjuster has a current source having a cascode structure, wherein the bias control unit controls a headroom voltage value of the switching circuit units based on the operation confirmation signal inputted separately. AC LED drive circuit.
The method of claim 2,

It is further connected to the switching circuit unit further comprises a switching confirmation unit for detecting whether the operation of the switching circuit unit,

And the bias adjuster controls a headroom voltage value of the switching circuit units based on a detection signal of the switching confirming unit.
The method of claim 6,

The switching confirmation unit is an AC LED drive circuit having a current source of the cascode structure, characterized in that the configuration of the current sensing unit for detecting the input current or the output current of the switching circuit unit is provided at the input terminal or the output terminal.
The method of claim 2, wherein the bias adjustment unit

A plurality of first OP amplifiers that are individually matched with the clamp elements to receive a node value of the corresponding clamp element and to which a common threshold voltage of a voltage value for switching operation of the switching circuit units is separately input;

A plurality of on / off controls according to output values of the first OP amplifiers connected in parallel with each other on the node value input line of the clamp element for the first OP amplifiers in a state of individually matching with the first OP amplifiers; switch;

And a second OP amplifier connected in parallel with the output terminals of the switches and to which a preset voltage for the bias adjustment unit is input.
The method of claim 8,

The bias control unit is a switch control unit for controlling the on / off operation of the switches on the basis of the node value of the lamp element according to the output value of the first OP amplifier is input to the output value of the first OP amplifier separately AC LED drive circuit having a current source of the cascode structure further comprising a.
The method of claim 1,

The LED lighting unit is a form in which a plurality of LEDs to form an individual LED light, two or more LEDs are formed in a group of one or more LED lights are connected, a LED light formed of one LED and two or more LEDs AC LED driving circuit having a current source of the cascode structure is formed in any one form of the LED lighting is connected to the switching circuit unit is connected to the output terminal of the final LED of each LED lighting.
The method of claim 1,

And the power supply unit includes an AC power source and a rectifier circuit of the AC power source.