Smooth Ou (isolator of Opticalcoupler) Yi Chenguang report, opto-coupler or photoelectricity coupler. It is the parts of an apparatus that transmits telegraphic signal with coming for agency solely, normally glow implement (LED) of infrared glow diode and get light implement (photosensitive semiconductor is in charge of) enclose inside same envelope. When the input end adds diode of the glow when telegraphic date to give out the light, photocurrent arises after photosensitive dynatron accepts the light, from output end is poured out of, realized changeover of ” of report of smooth — of “ report — thereby. Following graph 1-1 place show representative application circuit.

 

The main good point of smooth Ou is: Signal is one-way transmit, input end and output end realized front and laden and complete electric segregation completely, output signal does not have an influence to inputting end, reduce circuit interference, simplify circuit design, the work is steady, without contact, service life is long, transmission efficiency is tall. Opto-coupler is the new-style parts of an apparatus that 70 time development rises, use extensively already at wave of circuit of the coupling between changeover of electric insulation, n, class, drive, switch circuit, behead now implement, interval of segregation of many humorous oscillator, signal, class leaves, appearance of pulse enlarge circuit, number, remote signal is transmitted, pulse. In sheet piece in switch power source, use linear opto-coupler to be able to make circuit of smooth Ou feedback, through adjusting control carries electric current to change occupy sky comparing, achieve goal of accurate stabilized voltage.

 

 

 

Commonly used at the smooth Ou model of feedback TLP521, PC817 waits. It is with TLP521 here exemple, introduce the character of this kind of smooth Ou. Graph 2-1 place shows interior of the Ou that it is light knot composition of a picture and the graph that cite a base.

 

The former edge of TLP521 is equivalent to diode of a glow, if of former edge electric current is bigger, light intensity is stronger, the voltaic Ic of deputy edge dynatron is bigger. The ratio of Ic of electric current of deputy edge dynatron and If of electric current of former edge diode calls the electric current of smooth Ou to put big coefficient, this coefficient changes along with temperature and change, and suffer temperature the impact is bigger. The smooth Ou that makes feedback use uses change of electric current of “ former edge to will bring about ” of change of deputy edge electric current to realize feedback just about, change in environmental temperature accordingly acuteness circumstance, because the Wen Piao of enlarge coefficient is bigger, answer not to pass smooth Ou to realize feedback as far as possible. In addition, use this kind of smooth Ou to must notice to design periphery parameter, make its job is inside wider linear area, otherwise circuit is too strong to running the susceptibility of parameter, the stability that goes against circuit works.

 

Normally choice TL431 combines TLP521 to undertake feedback. At this moment, the working principle of TL431 is equivalent to an interior fiducial the voltage error amplifier that is 2.5 V (the voltage of output undertakes error enlarge is compared, combine sampling tension through smooth couple next implement feedback control arteries and veins is wide occupy sky comparing, the goal that achieves stable voltage) , be in so its 1 foot and between 3 feet, want to receive compensation network.

 

 

TL431 is production of You Dezhou instrument can control source of accurate stabilized voltage, objective is shown like graph 2-3 place. Its output voltage uses two resistor to arrive from 2.5V with respect to OK and aleatoric setting any values inside 36V limits. The typical and dynamic impedance of this parts of an apparatus is 0.2Ω , stabilized voltage diode is replaced with it in a lot of application, for example, digital volmeter, carry puts circuit, adjustable control power supply, switch power source. Graph 2-2 place is shown bring a foot to arrange for TL431 with use the figure that connect a line.

 

Common smooth Ou feedback receives a standard the 1st kind. Vo is output voltage, vd is the power supply voltage of chip. Com signal receives the error amplifier of chip to output a foot. Notice left ground is output voltage ground, the ground of right is ground of voltage of chip power supply, both between consumed Ou segregation. Graph 2-3 place shows the working principle that accepts a method to be as follows: When output voltage is elevatory, the 1 foot of TL431 (the retrorse input that is equivalent to voltage error amplifier is carried) voltage rises, 3 feet (the output foot that is equivalent to voltage error amplifier) voltage drops, the If of former edge electric current of smooth Ou TLP521 increases, the other one aspect of the matter of smooth Ou outputs voltaic Ic to increase, the voltage drop on resistor R4 increases, com brings crural voltage to drop, occupy sky comparing to reduce, output voltage is reduced; Conversely, when output voltage drop is small, adjust the procedure is similar.

 

Prep above carries the form of potential instead, a kind of characteristic — that uses carry to put puts output when carry electric current is too big (carry discharge sheds output capacity more than) when, carry put output voltage value will fall, output electric current is bigger, output voltage drops more. Accordingly, use this kind of circuit that receives a standard, must PWM (pulse width modulation) two inputs of the error amplifier of chip bring a foot to receive fixed potential to go up, and must be to be the same as prep above of Xiang Duan potential to carry potential reversely, make initiative output voltage is error amplifier tall.

 

 

Graph 2-3 place shows the working principle that accepts a method is: When output voltage is elevatory, if of former edge electric current increases, ic of output electric current increases, because Ic had exceeded the electric current of voltage error amplifier to output ability, com foot voltage drops, occupy sky comparing to reduce, output voltage is reduced; Conversely, when output voltage drops, adjust the procedure is similar.

 

The 3rd common kind receives a standard, if pursue,2-4 place is shown. With the first kind of essentially similar, different point depends on much R6 of a resistor, the action of this resistor is additional to TL431 infuse an electric current, because infuse electric current passes,avoid TL431 small and cannot work normally. If be chosen appropriately,take resistance R3 actually, resistor R6 can omit. Adjust the process basically is the same as 1 receive a law to agree.

 

The 4th common kind receives a standard, if pursue,2-4 place is shown. Should receive the law receives a standard with the 2nd kind similar, distinction depends on Com Duan Yuguang Ou received R4 of a resistor more between the 4th foot, its action and the 3rd kind of R6 in receiving a standard are consistent, its job principle receives a standard basically together 2.

 

Feedback means 1, 3 apply to any occupying to be compared for nothing (put through of time and cycle than) circumstance, and feedback means 2, 4 agree with quite in occupy sky comparing to be used than lesser circumstance. 　

 

 

The smooth Ou of switch power source basically is segregation, provide feedback signal and switch function. From high frequency transformer sub voltage provides the power source of smooth Ou in circuit of switch power source, when output voltage is in charge of voltage under stabilized voltage is to signal light Ou puts through, increase occupy sky comparing, make output voltage elevatory; Close smooth Ou to reduce conversely occupy sky comparing, make output voltage drop small. Dawn sub load overloads or switch circuit has high frequency transformer breakdown, do not have smooth Ou power source to offer, smooth Ou is controlling switch circuit to cannot rise brace up, protect switch canal not to come thereby by puncture burn down.