[introduction] when designing power source, is the issue that wants an answer above all ” whether to need voltaic segregation? ” segregation of use electric current can make circuit safer, interference rejection capability is stronger, easy implementation rises step-down changeover, reach output of easier implementation multichannel and very wide input voltage range. The develop of power source of two kinds of the commonnest segregation attacks the form is ” stimulate instead ” and ” to ” . But output to gain higher power, can use other segregation develop to be like,attack ” push-pull ” , ” half bridge ” and ” complete bridge ” .

Ask: In power source design, commonner blame segregation develop attacks what to have

When designing power source, is the issue that wants an answer above all ” whether to need voltaic segregation? ” segregation of use electric current can make circuit safer, interference rejection capability is stronger, easy implementation rises step-down changeover, reach output of easier implementation multichannel and very wide input voltage range. The develop of power source of two kinds of the commonnest segregation attacks the form is ” stimulate instead ” and ” to ” . But output to gain higher power, can use other segregation develop to be like,attack ” push-pull ” , ” half bridge ” and ” complete bridge ” . Actually, if do not need voltaic segregation, the engineer can use blame segregation power source as far as possible, because the develop of segregation attacks,the form always needs transformer or additional line, and this kind of equipment often can increase cost and volume bigger, satisfy the requirement of custom-built power source very hard normally.

Commonner blame keeps apart develop to attack

Step-down converter (Buck)

The develop of power source of switch of formula of segregation of the commonnest blame attacks the structure is step-down converter. It is inputting voltage changeover to be the output voltage under input voltage. Its structure is simple, need a two switch, inductor and two capacitor only, if pursue,1 is shown. High side switch produces pulse electricity from input end and generation opens joint to hint tension, this voltage makes a round trip between input voltage and ground concussion. Later, use LC filter produces dc to output voltage. According to signal of PWM of switch of control high end occupy sky comparing, the direct current that generates different n outputs voltage. Converter of step-down of this kind of DC-DC special province report, design also relatively simple, and yuan of parts of an apparatus of need is very few.

Graph 1.  Of step-down converter see a picture without exception (picture origin: ADI)

When designing low noise system, want advertent, step-down converter produces pulse electricity in input side, and output side has the permanent current that comes from inductor. This is step-down manostat noise is carried in the input very big and the reason with not big noise is carried in output. Step up converter (Boost) besides step-down, another kind of common develop attacks is step up. Its develop attacks the structure is comprised by cell of 5 main power, attack to differ a bit with the develop of step-down converter, if pursue,2 are shown.

Graph 2.  Of step up converter see a picture without exception (picture origin: ADI)

When choosing step up converter, need advertent data table to go up electric current of more general listed the biggest rated switch is not electric current of the biggest output. In step-down converter, electric current of the biggest switch and realizable are the biggest output electric current is direct and relevant, but with the input the electric pressure ratio between voltage and output voltage has nothing to do. In step up manostat, electric pressure ratio is the electric current of the biggest output with according to electric current of fixed the biggest switch immediate potential effect. When choosing appropriate step up manostat so, the engineer needs to understand needs output electricity not only, the input that still needs to understand a system to need and output voltage. The input of step up converter carries noise very low, because with input end connective inductance can prevent electric current,change quickly. However, output carries noise bigger, because LC filter is located in input end, we can see pulse electric current flows to exterior switch, cause output ripple. Because this and step-down develop attack to be compared, output ripple more get attention. Turn over photograph step-down – step up manostat (Inverting) the 3rd kind of common develop attacks is to turn over photograph step-down – step up converter, by composition of these 5 component. This name results from this converter uses the fact that inputting voltage and outputs its changeover voltage to lose. Besides, input voltage may is more than or little the absolute value at outputting voltage instead. For example, the 5V that inputs end or 24V may arise – 12V outputs voltage. This is feasible and need not undertake any special circuit are revised, following graphs are shown 3 times.

Graph 3.  Turn over photograph step-down – of step up converter see a picture without exception (picture origin: ADI)

In turn over photograph step-down – step up develop attacks in, inductance reachs the ground from switch node join. The input end of converter and output end see pulse electric current, exporting electricity is discontinuous, make turn over photograph step-down / the output voltage of step up converter often noise is bigger, it is so in low noise application, can be compensated through increasing additional input and output filter wave.

Turn over photograph step-down – step up develop attacks to there is a profit in power source design, it is any step-down manostat all applicable this develop attacks. Be like the ADP2441 of ADI or ADP2442, turn over photograph step-down to be step-down manostat changeover – step up develop attacks structure, inductance and output capacitance to answer with attacking with step-down develop the means of structural likeness joins, if pursue,4 are shown.

Graph 4. ADP2441/ADP2442 comes true turn over photograph step-down – step up develop attacks structure (picture origin: ADI)

Professional develop attacks structure

Besides above 3 kinds of common blame develop of switch-disconnector power source attacks besides, be like,still more develop attack SEPIC, Zeta, ? Uk and 4 switch step-down – step up. Compare above develop of power source of 3 kinds of switch attacks and, these develop attack the structure needs additional place many a little bit have power source package, can raise product cost, power changes efficiency to also can be reduced. Generally speaking, add in circuit additional yuan parts of an apparatus can increase loss. A few the mainest functions that list these 4 different develop attack simply below. SEPIC sheet carries primary inductance converter (the voltage changeover that SEPIC) allows to output voltage to be more than or is less than input voltage, output voltage by advocate accuse switch (dynatron or MOS canal) take sky comparing control. IC can use manostat of step up of step up manostat at designing circuit of SEPIC power source. Want advertent, this kind of develop attacks to need to add much extraer element in circuit (inductance and capacitance) , if the graph shows.ZetaZeta converter and SEPIC converter 7 times similar, simplify like what LT8471 Zeta and SEPIC develop attack the principle pursues (graph 5) place is shown, need two inductance (L1A and, two two L1B) , switch (Q1 and D1) with a capacitor (CF) . Zeta converter can arise or negative output voltage, in addition, it is done not have right half plane 0 (RHPZ) problem is, simplified to adjust thereby loop. Right half plane 0 (RHPZ) is contained right half plane at 0 o’clock (RHPZ) switch DC-DC transformer happens when occupying sky comparing mutation, transient process can appear the phenomenon that lose tone, this phenomenon can bring about systematic transient function to become poor, the duration that lose tone paragraph the system is easy form make a present of of positive and negative and appear not to stabilize a phenomenon, traditional frequency domain method cannot undertake controller is designed directly, because this has control to its relatively many of difficulty of the smallest phasic system.

Professional develop attacks structure

Besides above 3 kinds of common blame develop of switch-disconnector power source attacks besides, be like,still more develop attack SEPIC, Zeta, ? Uk and 4 switch step-down – step up. Compare above develop of power source of 3 kinds of switch attacks and, these develop attack the structure needs additional place many a little bit have power source package, can raise product cost, power changes efficiency to also can be reduced. Generally speaking, add in circuit additional yuan parts of an apparatus can increase loss. A few the mainest functions that list these 4 different develop attack simply below. SEPIC sheet carries primary inductance converter (the voltage changeover that SEPIC) allows to output voltage to be more than or is less than input voltage, output voltage by advocate accuse switch (dynatron or MOS canal) take sky comparing control. IC can use manostat of step up of step up manostat at designing circuit of SEPIC power source. Want advertent, this kind of develop attacks to need to add much extraer element in circuit (inductance and capacitance) , if the graph shows.ZetaZeta converter and SEPIC converter 7 times similar, simplify like what LT8471 Zeta and SEPIC develop attack the principle pursues (graph 5) place is shown, need two inductance (L1A and, two two L1B) , switch (Q1 and D1) with a capacitor (CF) . Zeta converter can arise or negative output voltage, in addition, it is done not have right half plane 0 (RHPZ) problem is, simplified to adjust thereby loop. Right half plane 0 (RHPZ) is contained right half plane at 0 o’clock (RHPZ) switch DC-DC transformer happens when occupying sky comparing mutation, transient process can appear the phenomenon that lose tone, this phenomenon can bring about systematic transient function to become poor, the duration that lose tone paragraph the system is easy form make a present of of positive and negative and appear not to stabilize a phenomenon, traditional frequency domain method cannot undertake controller is designed directly, because this has control to its relatively many of difficulty of the smallest phasic system.

Graph 5. Zeta and SEPIC develop attack structure (picture origin: ADI)

? Uk

? Uk converter but will inputting voltage changeover to be negative output voltage. It uses two inductor, one is inputting side, one is in output side, input and the noise that output side are very accordingly low, but, support this kind of develop to attack the parts of an apparatus of converter of switch power source is not much, because adjust,annulus road need loses voltage feedback to cite a base. Be like the LT8331 of ADI, its need is being inputted and two inductor and capacitor of a coupling are used between output (C5) . Coupling or block capacitor receive energy from the input side of circuit and output what its transmit circuit side. Fall in stable state condition (namely after electrify) , this capacitor the voltage of two end is constant, be equal to VIN about, if pursue,6 are shown.

Graph 6. LT8331 comes true? Uk develop attacks structure (picture origin: ADI)

Four switch step-down – step up the converter of this kind of type becomes very popular in recent years. Four switch step-down – step up is offerred from inside inputting voltage outputting voltage, this input voltage is likely prep above or under the output voltage after adjusting. The converter of this type can offer taller power source to change efficiency and need an inductor only, so this converter can replace the design of SEPIC. Be like the LT8705 of ADI, it is a synchronous quarto closes step-down – step up controller, handle input and output side each two switch, use dovish synchro switch develop to attack structure, with efficient offer high power output for constant voltage or constant current application. If pursue,7 are shown.

Graph 7. The four switch step-down that LT8705 realizes – step up develop attacks structure (picture origin: ADI)

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