CN201533432U

CN201533432U - Mirror image current source

Info

Publication number: CN201533432U
Application number: CN2009202096094U
Authority: CN
Inventors: 何沛行
Original assignee: Shanghai Simcom Ltd
Current assignee: Shanghai Simcom Ltd
Priority date: 2009-09-11
Filing date: 2009-09-11
Publication date: 2010-07-21
Anticipated expiration: 2019-09-11

Abstract

The utility model provides a mirror image current source, which comprises a first triode, a second triode, a third triode, a first resistor, a second resistor, a third resistor and a fourth resistor, wherein an emitter electrode of the first triode, one end of the first resistor and one end of the third resistor are all connected with an output tend of a backlight integrated circuit, a collector electrode of the second triode is connected with the other end of the second resistor, a base electrode of the third triode is connected with a base band chip, an emitter electrode of the third triode and one end of the fourth resistor are grounded together, and a collector electrode of the second triode and the other end of the fourth resistor are respectively connected with a backlight lamp. The mirror image current source keeps current output by the backlight lamp balance, thereby resolving a flicker problem of backlight lamps.

Description

Mirror current source

Technical field

The utility model relates to a kind of circuit stabilizing arrangement, and is particularly related to a kind of mirror current source.

Background technology

Present most of mobile phone circuit all is with the backlight IC (integratedcircuit, integrated circuit) of step-up DC-DC (Direct Current, DC level) as backlight circuit.

The DC-DC transducer comprise boost, step-down, lifting/voltage reducing and circuit such as anti-phase.The advantage of DC-DC transducer is the efficient height, can export big electric current and quiescent current little, raising along with integrated level, many novel DC-DC transducers only need several external inductors and filtering capacitor to realize, but the output ripple of this class power-supply controller of electric is big with switch noise, cost is relative higher.Will produce new problem thus, because DC-DC output ripple and switch noise are bigger, fluctuation appears in the electric current that causes backlight to flow through, and has certain effect though add some filtered electrical in IC backlight periphery, the problem of flicker backlight still can occur.

In order to address this problem, prior art generally can connect a mirror current source earlier with the output of transducer, connects backlight again, thereby reduces the fluctuation of electric current.The schematic diagram of mirror current source please refer to Fig. 1, Fig. 1 is the circuit diagram of the mirror current source of prior art, the parameter of triode T1 and triode T2 equates and their base stage links to each other fully among the figure, the collector electrode of T1 links to each other with power Vcc with Rb by resistance R a respectively with the collector electrode of T2, the grounded emitter of T1 and T2, the base stage of T1 links to each other with collector electrode.The basic principle of standard mirror current source is the silicon type triode butt joint that two parameters are equated fully, and the electric current of definition of T 1 and T2 base stage is I _B1And I _B2, voltage is U _Be1And U _Be2, the electric current of collector electrode is I _C1And I _C2, the electric current that flows through resistance R a is I _Ref, because the base stage of two triodes is continuous, so I _B1=I _B2, U _B1=U _B2, I _C1=I _C2, and, I is arranged according to the electric current equation _Ref=I _C1+ 2I _B1, in the time of amplification factor b＞＞100, be exactly that equivalence is I _Ref=I _C1, i.e. I _C2=Ic1=I _Ref=(Vcc-U _B1)/R=Vcc/R.As can be seen from the above equation, after R determines, I _RefJust determined I _C2Also fixed thereupon, we are I _C2Regard I as _RefMirror image, but this circuit has a shortcoming, when VCC changes, I _C2=I _Ref=(Vcc-U _Be)/R=Vcc/R., I _C2Also, also cause the fluctuation of output current easily changing, even unstable, still can cause the electric current instability on the backlight, the problem of flicker backlight appears.

The utility model content

The problem that the utility model solves is to avoid occurring when the electric current instability causes backlight work on the backlight phenomenon of flicker.

The utility model provides a kind of mirror current source, be used to connect the baseband chip of mobile phone, integrated circuit backlight and backlight, described mirror current source comprises first triode, second triode, the 3rd triode, first resistance, second resistance, the 3rd resistance and the 4th resistance, the emitter of first triode wherein, one end of first resistance all links to each other with the output of described integrated circuit backlight with an end of the 3rd resistance, the other end of the collector electrode of described first triode and described first resistance, one end of second resistance and the base stage of second triode link to each other, and the base stage of described first triode connects the other end of described the 3rd resistance and the emitter of second triode; The collector electrode of the 3rd triode links to each other with the other end of described second resistance, and the base stage of described the 3rd triode links to each other with described baseband chip, and an end of the emitter of described the 3rd triode and the 4th resistance is ground connection together; The other end of the collector electrode of described second triode, described the 4th resistance links to each other with described backlight respectively.

Compared with prior art, the utlity model has following advantage: the mirror current source after the utility model utilization improves links to each other with integrated circuit backlight, make the electric current that exports backlight to keep stable, thereby backlight can keep stable operating state, has avoided the generation of scintillation.

Description of drawings

Fig. 1 is the circuit diagram of the mirror current source of prior art;

Fig. 2 is the structural representation of a kind of mirror current source of the utility model;

Fig. 3 is the use schematic diagram of a kind of mirror current source of the utility model.

Embodiment

Below in conjunction with accompanying drawing embodiment of the present utility model is described in detail.

Please refer to Fig. 2, Fig. 2 is the structural representation of a kind of mirror current source of the utility model, from the figure as can be seen, described mirror current source comprises the first triode T1, the second triode T2, the 3rd triode Q1, first resistance R 1, second resistance R 2, the 3rd resistance R 3 and the 4th resistance R 4, the emitter of the first triode T1 wherein, one end of first resistance R 1 all links to each other with an end of the 3rd resistance R 3, the other end of the collector electrode of the described first triode T1 and described first resistance R 1, one end of second resistance R 2 and the base stage of the second triode T2 link to each other, and the base stage of the described first triode T1 connects the other end of described the 3rd resistance R 3 and the emitter of the second triode T2; The collector electrode of the 3rd triode Q1 links to each other with the other end of described second resistance R 2, and an end of the emitter of described the 3rd triode Q1 and the 4th resistance R 4 is ground connection together.

Then, please refer to Fig. 3, Fig. 3 is the use schematic diagram of a kind of mirror current source of the utility model, on scheming, can see, interconnective integrated circuit backlight 11 and mirror current source, described mirror current source also connects the baseband chip 12 and the backlight 13 of mobile phone, the emitter of the first triode T1 links to each other with the output of described integrated circuit 11 backlight, the base stage of the 3rd triode Q1 links to each other with described baseband chip 12, and the other end of the collector electrode of the second triode T2, described the 4th resistance R 4 links to each other with described backlight 13 respectively.

During practical operation, the base stage of the 3rd triode Q1 directly links to each other with baseband chip 12, high level is effective, when we carry out the backlight lightening program, base stage is put height, the 3rd triode Q1 is operated in saturation condition, and the dividing potential drop of output backlight this moment can be divided to half of integrated circuit 11 input voltages backlight at the collector electrode of the first triode T1, drives the first triode T1 and second triode T2 work.When the first triode T1 and second triode T2 work, the voltage at the 3rd resistance R 3 two ends is given clamped at 0.7V, just U _Be, the 3rd resistance R 3 is 35 ohm, and the benefit of this circuit is, and no matter how the output voltage of integrated circuit 11 backlight fluctuates, and the voltage at the 3rd resistance R 3 two ends all is U _Be, in the time of amplification factor b＞＞100, the electric current I at the 3rd resistance R 3 two ends _R3=I _B+ I _e, with regard to equivalent I _R3=I _e, I just _e=I _c, I like this _e=I _c=U _Be/ R3=0.7/35=0.02 (ampere)=20 (milliampere), so the electric current that flows through of backlight 13 is exactly stable 20 milliamperes, even I backlight _eWhen output voltage had bigger fluctuation, the influence that the electric current that lamp flows through is subjected to was also very little, well solved the flicker problem.

This circuit also has an advantage simultaneously, can adjust a suitable current value, from I according to the System Performance Evaluation Corporation (SPEC) of backlight _e=0.7/R3 as long as regulate the resistance of R3, just can obtain the current value that we need as can be seen, and circuit becomes succinct convenient like this.

Though the utility model discloses as above with preferred embodiment, the utility model is not to be defined in this.Any those skilled in the art in not breaking away from spirit and scope of the present utility model, all can do various changes and modification, and therefore protection range of the present utility model should be as the criterion with claim institute restricted portion.

Claims

1. mirror current source, be used to connect the baseband chip of mobile phone, integrated circuit backlight and backlight, it is characterized in that described mirror current source comprises first triode, second triode, the 3rd triode, first resistance, second resistance, the 3rd resistance and the 4th resistance, the emitter of wherein said first triode, one end of described first resistance all links to each other with the output of described integrated circuit backlight with an end of described the 3rd resistance, the other end of the collector electrode of described first triode and described first resistance, one end of described second resistance and the base stage of described second triode link to each other, and the base stage of described first triode connects the other end of described the 3rd resistance and the emitter of described second triode; The collector electrode of described the 3rd triode links to each other with the other end of described second resistance, and the base stage of described the 3rd triode links to each other with described baseband chip, an end ground connection of the emitter of described the 3rd triode and the 4th resistance; The other end of the collector electrode of described second triode, described the 4th resistance links to each other with described backlight respectively.