CN201167423Y

CN201167423Y - Circuit for equalizing current

Info

Publication number: CN201167423Y
Application number: CNU200820001978XU
Authority: CN
Inventors: 张洪德; 吴家坤
Original assignee: Darfon Electronics Corp
Current assignee: Darfon Electronics Corp
Priority date: 2008-01-16
Filing date: 2008-01-16
Publication date: 2008-12-17
Anticipated expiration: 2018-01-16

Abstract

The utility model discloses a current sharing circuit. The current sharing circuit is matched with N light emitting devices which are connected in parallel, and N is a positive integer which is larger than 1. Each light emitting device comprises at least one light-emitting diode and a separate low-potential end. The current sharing circuit of the utility model comprises a constant voltage source and N first transistors. The constant voltage source is used for providing a constant voltage. Each first transistor is corresponding to one of the light emitting devices, and a first end point of each first transistor is electrically connected with the low-potential end of the corresponding light emitting device. In addition, a second end point of each first transistor is electrically connected with the constant voltage source for receiving the input of the constant voltage, and a third end point of each first transistor is electrically connected together.

Description

Flow equalizing circuit

Technical field

The utility model relates to a kind of current-sharing (current-sharing) circuit, particularly relates to a kind of flow equalizing circuit that cooperates a plurality of light-emitting devices.

Background technology

Because cold cathode fluorescent lamp (cold cathode fluorescent lamp, CCFL) have that fluorescent tube is tiny, simple in structure, surface of the light tube temperature increasing degree is little, surface of the light tube brightness height, easily be processed into different shape, long service life, color rendering is good and luminous advantage such as even.Therefore up to the present, cold cathode fluorescent lamp is widely used in the backlight of electronic equipments such as large-scale LCD, LCD TV, scanner, advertising lamp box and mobile computer.

Yet, light-emitting diode (light-emitting diode, LED) than cold cathode fluorescent lamp have more power saving, multiple advantages such as the life-span is longer, color saturation is high, reaction speed is fast, shatter-proof withstand voltage and volume are little.So, adopt light-emitting diode lamp tube as back light, be the following technology that is hopeful to substitute the traditional cold cathode fluorescent tube most.

Generally speaking, if with light-emitting diode lamp tube as back light, the backlight of above-mentioned electronic equipment also can adopt many light-emitting diode lamp tubes.Because light-emitting diode lamp tube is formed line source by point-source of light, therefore need use many light-emitting diodes.In order to make the brightness equalization of each root light-emitting diode lamp tube, certainly will make the electric current of each light-emitting diode of flowing through identical.Otherwise the brightness of whole light-emitting diode lamp tube is inhomogeneous, even influences the service quality of electronic equipment.In addition, if the light-emitting diode in arbitrary light-emitting diode lamp tube opens circuit or burns, also make the light uniformity of whole light-emitting diode lamp tube descend.

Therefore, main category of the present utility model is to provide a kind of flow equalizing circuit that cooperates a plurality of light-emitting devices, to address the above problem.

The utility model content

A category of the present utility model is to provide a kind of flow equalizing circuit.This flow equalizing circuit cooperates the light-emitting device of N parallel connection, and N is one greater than 1 positive integer.Each light-emitting device comprises at least one light-emitting diode and has each other cold end.

In according to a specific embodiment of the present utility model, this flow equalizing circuit comprises a constant voltage source and N the first transistor.This constant voltage source is in order to provide a constant voltage.Light-emitting device in the corresponding described light-emitting device of each the first transistor and be electrically connected to this cold end of this corresponding light-emitting device with itself one first end points.In addition, one second end points of each the first transistor all is electrically connected to this constant voltage source receiving the input of this constant voltage, and one the 3rd end points of each the first transistor is electrically connected.

Can be further understood by following utility model detailed description and accompanying drawing about advantage of the present utility model and spirit.

Description of drawings

Fig. 1 shows the circuit diagram according to the flow equalizing circuit of a specific embodiment of the present utility model.

Fig. 2 shows the circuit diagram that flow equalizing circuit among Fig. 1 further comprises the detection module of N series connection.

The reference numeral explanation

10: light-emitting diode 20: constant voltage source

Q ': transistor seconds

L1, L2, Ln: light-emitting device VL1, VL2, VLn: cold end

Q1, Q2, Qn: the first transistor VB1, VB2, VBn: base stage

VE1, VE2, VEn: emitter-base bandgap grading RE1, RE2, REn: resistance

D1, D2, Dn: detection module T1, T2, Tn: the 3rd transistor

Vc: control voltage

Embodiment

Please refer to Fig. 1.Fig. 1 shows the circuit diagram according to the flow equalizing circuit of a specific embodiment of the present utility model.Flow equalizing circuit can cooperate N in parallel light-emitting device L1, L2...Ln, and N is one greater than 1 positive integer.Each light-emitting device L1, L2...Ln comprise at least one light-emitting diode 10.For example, light-emitting device L1, L2...Ln can be the backlights of LCD, LCD TV, scanner, advertising lamp box, mobile computer etc.

As shown in Figure 1, each light-emitting device L1, L2...Ln can comprise a plurality of light-emitting diodes 10 and have a cold end VL1, VL2...VLn.Comprise constant voltage source 20 and N the first transistor Q1, Q2...Qn according to flow equalizing circuit of the present utility model.Constant voltage source 20 is in order to provide a constant voltage.

Light-emitting device among each the first transistor Q1, Q2...Qn corresponding N light-emitting device L1, the L2...Ln and be electrically connected to cold end VL1, the VL2...VLn of light-emitting device L1, a L2...Ln of correspondence with itself first end points.In addition, second end points of each the first transistor Q1, Q2...Qn all is electrically connected to the input of constant voltage source 20 with the reception constant voltage, and the 3rd end points of each the first transistor Q1, Q2...Qn is electrically connected.

In actual applications, each the first transistor Q1, Q2...Qn can be a pair of junction transistor (bipolar junction transistor, BJT).As shown in Figure 1, in this embodiment, this pair junction transistor is a NPN transistor.Therefore, first end points is the collection utmost point (Collector) of NPN transistor, and second end points is base stage (Base) VB1, the VB2...VBn of NPN transistor, and the 3rd end points is emitter-base bandgap grading (Emitter) VE1, the VE2...VEn of NPN transistor.

In actual applications, constant voltage source 20 can use a transistor seconds Q ' to produce constant voltage.For example, transistor seconds Q ' can be a pair of junction transistor.In this embodiment, this pair junction transistor can be a NPN transistor, but not as limit.In addition, the base stage VB1 of each the first transistor Q1, Q2...Qn, VB2...VBn can be connected to the emitter-base bandgap grading of transistor seconds Q '.

Please refer to Fig. 1.Below the effect that how to reach current-sharing according to flow equalizing circuit of the present utility model will be described.Because base stage VB1, the VB2...VBn of each the first transistor Q1, Q2...Qn are connected to the emitter-base bandgap grading of transistor seconds Q ', so the base stage VB1 of each the first transistor Q1, Q2...Qn, VB2...VBn have identical current potential.According to the characteristic of NPN transistor, when the NPN transistor conducting, has fixing voltage drop between base stage and the emitter-base bandgap grading.By this, when each the first transistor Q1, Q2...Qn conducting, emitter-base bandgap grading VE1, the VE2...VEn of each the first transistor Q1, Q2...Qn also have identical current potential.That is to say that as shown in Figure 1, the end points of resistance R E1, RE2...REn that emitter-base bandgap grading VE1, the VE2...VEn of each the first transistor Q1, Q2...Qn is connected in series has identical current potential.In addition, another end points of resistance R E1, RE2...REn is electrically connected, and therefore also has identical current potential.

Hence one can see that, and emitter-base bandgap grading VE1, the VE2...VEn electric current of each the first transistor Q1, Q2...Qn are all identical.As each light-emitting device L1, L2...Ln in normal operation the time, NPN transistor meeting conducting, and according to the characteristic of NPN transistor, the collected current of each the first transistor Q1, Q2...Qn equals emitter-base bandgap grading VE1, VE2...VEn electric current haply.Corresponding light-emitting device L1, L2...Ln because the collected current of each the first transistor Q1, Q2...Qn is flowed through, by this, according to flow equalizing circuit of the present utility model the electric current of flow through each light-emitting device L1, L2...Ln is equated haply, therefore realize the effect of current-sharing.

Please refer to Fig. 2.The flow equalizing circuit that Fig. 2 shows among Fig. 1 further comprises the detection module D1 of N series connection, the circuit diagram of D2...Dn.N detection module D1, D2...Dn are in order to detect the abnormality of each light-emitting device among N light-emitting device L1, the L2...Ln.Abnormality can refer to that the light-emitting diode 10 among any light-emitting device L1, L2...Ln opens circuit or burns.

As shown in Figure 2, each detection module D1, D2...Dn can be coupled between cold end VL1, the VL2...VLn of the collection utmost point of corresponding the first transistor Q1, Q2...Qn and corresponding light-emitting device L1, L2...Ln.In addition, each detection module D1, D2...Dn comprise one the 3rd transistor T 1, T2...Tn, and one the 4th end points of the 3rd transistor T 1, T2...Tn is electrically connected to cold end VL1, the VL2...VLn of corresponding light-emitting device L1, L2...Ln.In actual applications, the 3rd transistor T 1, T2...Tn can be a metal oxide semiconductcor field effect transistor (metal-oxide-semiconductorfield-effect transistor, MOSFET) or a pair of junction transistor.In this embodiment, the 3rd transistor T 1, T2...Tn can be nmos pass transistors, and the grid of nmos pass transistor is electrically connected to cold end VL1, the VL2...VLn of corresponding light-emitting device L1, L2...Ln.

According to the input voltage of the grid of each nmos pass transistor, N detection module D1, D2...Dn can export corresponding control voltage Vc to a protective circuit (not being shown among Fig. 2).For example, as each light-emitting device L1, L2...Ln in normal operation the time, each the first transistor Q1, Q2...Qn can conductings, and this moment, N detection module D1, D2...Dn can export the control voltage Vc of high levels to protective circuit.But when one of them light-emitting diode 10 of any light-emitting device L1, L2...Ln opened circuit or burns, N detection module D1, D2...Dn then can export the control voltage Vc of low level to protective circuit.Then, according to the demand on the practice, protective circuit can be closed the voltage source V s of supply N light-emitting device L1, L2...Ln, to avoid more multiple optical diode 10 impaired.Perhaps, protective circuit can be sent a warning signal, to inform user's light-emitting device L1, L2...Ln abnormality takes place.

Compared to prior art, can make the electric current equalization of each root light-emitting diode lamp tube of flowing through according to flow equalizing circuit of the present utility model, make the brightness of whole light-emitting diode lamp tube have consistency.In addition, also comprise a plurality of detection modules, whether abnormality takes place, further take the supplementary measures of being correlated with to detect arbitrary light-emitting diode lamp tube according to flow equalizing circuit of the present utility model.

By the above detailed description of preferred embodiments, hope can be known description feature of the present utility model and spirit more, and is not to come category of the present utility model is limited with above-mentioned disclosed preferred embodiment.On the contrary, its objective is that hope can contain in the category that is arranged in claim of the present utility model of various changes and tool equality.Therefore, the category of claim of the present utility model should be done the broadest explanation according to above-mentioned explanation, contains the arrangement of all possible change and tool equality to cause it.

Claims

1. flow equalizing circuit, this flow equalizing circuit cooperate N light-emitting device in parallel, and N is one greater than 1 positive integer, and each light-emitting device comprises at least one light-emitting diode and has other cold end respectively, it is characterized in that this flow equalizing circuit comprises:

One constant voltage source, this constant voltage source is in order to provide a constant voltage; And

N the first transistor, light-emitting device in the corresponding described light-emitting device of each the first transistor and be electrically connected to this cold end of this corresponding light-emitting device with itself one first end points;

Wherein one second end points of each the first transistor all is electrically connected to this constant voltage source to receive the input of this constant voltage, and one the 3rd end points of each the first transistor is electrically connected.

2. flow equalizing circuit as claimed in claim 1 is characterized in that, wherein each the first transistor is a pair of junction transistor.

3. flow equalizing circuit as claimed in claim 2, it is characterized in that wherein this pair junction transistor is a NPN transistor, the collection utmost point that this first end points is this NPN transistor, this second end points is the base stage of this NPN transistor, and the 3rd end points is the emitter-base bandgap grading of this NPN transistor.

4. flow equalizing circuit as claimed in claim 3 is characterized in that wherein this constant voltage source uses a transistor seconds.

5. flow equalizing circuit as claimed in claim 4 is characterized in that, wherein this transistor seconds is a pair of junction transistor.

6. flow equalizing circuit as claimed in claim 5 is characterized in that, wherein this pair junction transistor is a NPN transistor, and this second end points of each the first transistor is connected to the emitter-base bandgap grading of this NPN transistor.

7. flow equalizing circuit as claimed in claim 1 is characterized in that, further comprises:

The detection module of N series connection, each detection module is coupled between this cold end of this first end points of a first transistor and the pairing light-emitting device of this first transistor, each detection module comprises one the 3rd transistor, and the 3rd transistorized one the 4th end points is electrically connected to this cold end of this corresponding light-emitting device.

8. flow equalizing circuit as claimed in claim 7 is characterized in that, wherein the 3rd transistor is a metal oxide semiconductcor field effect transistor or a pair of junction transistor.

9. flow equalizing circuit as claimed in claim 7 is characterized in that, wherein according to the input voltage of the 4th end points, this N detection module is exported corresponding control voltage to one protective circuit.

10. flow equalizing circuit as claimed in claim 9 is characterized in that, wherein a warning signal is closed or produced to this protective circuit in order to the voltage source that will supply this N light-emitting device.

11. flow equalizing circuit as claimed in claim 7 is characterized in that, wherein this N detection module is in order to detect the abnormality of each light-emitting device in this N light-emitting device.

12. flow equalizing circuit as claimed in claim 11 is characterized in that, wherein this abnormality refers to that a light-emitting diode in this light-emitting device opens circuit or burns.