How will evaluate the power source demand of a system?

 

Answer: To an actual electric subsystem, want the serious power source requirement that analyses it. It is care input voltage not just, export voltage and electricity, consider total power comsumption even carefully, the efficiency that power source achieves, power source part answers ability to the transient state of laden change, the power source ripple of the patient limits with crucial fluctuant to power source parts of an apparatus and corresponding permission, still have medicinal powder hot issue is waited a moment. Power comsumption and efficiency are closely related, efficiency is tall, total below the situation with laden same power comsumption power comsumption is little, very advantageous to the power budget of whole system, comparative LDO and switch power source, the efficiency of switch power source wants a few taller. In the meantime, evaluating efficiency is to look not just in full load when the efficiency of power source circuit, when paying close attention to light load even efficiency level.

 

 

Answer ability as to laden transient state, to a few high-powered CPU application can have firm demand, when because become,CPU begins suddenly to run onerous errand, the starting electric current of need is very big, if power source circuit answers speed insufficient, cause instantaneous voltage to drop to pass too much low, cause CPU to move make mistake.

 

Generally speaking, real value is the power source of the requirement more nominal of the value + – 5% , can calculate accordingly so a power source ripple that allow, want obligate surplus of course.

 

Medicinal powder it is important that hot issue is compared for power supply of big to those electricity and LDO, passing computation also is to be able to be evaluated whether appropriate.

 

How to choose appropriate power source to realize circuit

 

Answer: Get the specific technology target that give according to analysing systematic demand, will choose appropriate power source to realize circuit. General to weak report part, included) of converter of LDO(linear power source, electrification of converter of step-down of capacitance of switch power source and report of switch power source allows converter. Under photograph comparing, LDO designs the easiest implementation, output ripple is small, but defect is efficiency likely not tall, calorific amount is large, the voltaic look that can provide relatively switch power source is waited a moment not quite.

 

And design of circuit of switch power source is agile, efficiency is tall, but ripple is big, implementation is more complex, debug compare loaded down with trivial details to wait a moment.

 

How to choose yuan of appropriate parts of an apparatus and parameter for circuit of switch power source

 

Answer: The engineer that had not used design of switch power source very more can produce definite awe-stricken psychology to it, worry about the interference problem of switch power source for instance, PCBlayout problem, yuan the parameter of parts of an apparatus and type option issue. Wanted to understand only actually, using power source of a switch to design still is very convenient.

 

Average package contains power supply of a switch controller of switch power source and output two parts, some controller meeting general MOSFET is compositive go in chip, such use simpler, also simplified PCB design, but the flexibility of the design decreased a few.

 

Switch control implement the feedback that basically is a closed circuit controls a system, the control circuit of the sampling circuit that so commonly can a feedback outputs voltage and feedback annulus. Because this design of this part depends on assuring accurate sampling circuit, still have will control feedback deepness, because if feedback,annulus has answered slow word, answering ability to transient state can have a lot of effects.

 

And output part design included output electric capacity, output inductance and MOSFET are waited a moment, these choice basically should satisfy the balance of a function and cost namely, for instance tall switch frequency can use small inductance to be worth (mean enclose the cost) with petty gain smally, but tall switch frequency can increase interference and the switch loss to MOSFET, thereby loss of efficiency. Using the result that low switch frequency brings is contrary.

 

Choose also be special key to outputting the Rds_on parameter of the ESR of capacitance and MOSFET, small ESR can reduce output ripple, but capacitance cost can raise, good capacitance will be expensive. Ability of drive of controller of switch power source also wants to notice, overmuch MOSFET is cannot by good drive.

 

Generally speaking, the supplier of controller of switch power source can offer what specific computational formula offers an engineer to draw lessons from with use plan.

 

How to debug circuit of switch power source

 

Answer: A few experience can share everybody

 

The output output of circuit of 1) power source is worth high-power resistor to receive through low block board inside, debug first in what power source circuit can not accomplish first below the circumstance of solder resistor so, at the back of escape the influence of circuit.

 

2) generally speaking switch control implement it is closed circuit system, it is OK to if output exasperate circumstance,exceeded closed circuit pilot limits, switch power source can work abnormal, so this kind of circumstance checks feedback and sampling circuit seriously with respect to need. The output electric capacity that if used big ESR,is worth especially, can produce a lot of power source ripple, this also can affect the work of switch power source.

 

The discussion of ground connection technology

 

Why does ① want ground contact?

 

Answer: Of ground connection technology introducing is to prevent the equipment such as electric power or electron to meet with at first be struck by lightning and adopted protection step, the electric current of be struck by lightning that the purpose is a thunder generation introduces the earth through lightning rod, rise to protect the action of the building thereby.

 

In the meantime, ground connection also is a kind of of tutelar body safety significant step, the photograph string that causes when some kind of reason (if electrical wiring insulation is undesirable, circuit ageing) touch with equipment crust when touching, the crust of equipment can have dangerous tension generation, the fault current that generates from this can shed classics PE line to the earth, rise to protect action thereby.

 

As the development of electronic communication and other number domain, consider to prevent thunder and safety to already cannot satisfy a requirement far only in ground connection system. It is for instance in communication system, between a large number of equipment of signal interrelate the referenced ground that asks each equipment wants to ’ of ground of a fiducial ‘ serves as signal.

 

And as electronic equipment complication, signal frequency is taller and taller, accordingly, in ground connection design, compatible problem must give the electromagnetism such as the each other faze between signal special attention, otherwise, ground connection is undeserved the reliability that runs with respect to system of can serious effect and stability. Recently, the signal circumfluence of high speed signal also introduced the idea of “ ground ” in the technology.

 

The discussion of ground connection technology

 

The definition of ② ground connection

 

Answer: In concept of contemporary ground connection, to circuit engineer, the reference point ’; that the meaning of this term is ‘ circuitry voltage normally to systematic stylist, it often machine ark or frame; are right for electric engineer, it is green safety ground wire or the meaning that receive the earth. A more current definition is “ ground connection it is the ” of low impedance passageway that electric current returns its source. Noting a demand is ” of ” low impedance and “ access ” .

 

The discussion of ground connection technology

 

The ground connection sign with common ③

 

Answer: PE, PGND, FG- protects the land or housing;BGND or DC-RETURN- flow continuously – 48V(24V) power source (batteries) ;LGND- of ground of imitate of;AGND- of ground of number of;DGND- of ground of circumfluence;GND- job prevents Lei Bao to protect the land

 

The discussion of ground connection technology

 

④ receives local form suitably

 

Answer: Ground connection has a variety of kind, sheet nods ground connection, many bits of ground connection and the ground connection of mixture type. And only place ground contact is divided again nod ground connection and shunt-wound sheet to nod ground connection for series connection sheet. Generally speaking, only place ground contact is used at simple circuit, ground connection is divisional between different function module, and low frequency (F<1MHz) electron circuitry. Should design high frequency (be about to use much spot ground contact when F>10MHz) circuit multilayer perhaps board () of complete ground level layer.

 

The discussion of ground connection technology

 

⑤ signal circumfluence and cross intersected introduction

 

Answer1: To an electron signal, the electric regurgitate that it needs to search impedance of a lowest sheds the route of the ground, if why handle this signal circumfluence,become exceedingly crucial so.

 

The first, can know according to formula, radiation strength becomes direct ratio with loop area, the way that circumfluence of that is to say needs is longer, formation ring is bigger, it external radiant interference is bigger also, so, PCB cloth board when should reduce power source loop and signal loop area as far as possible.

 

The 2nd, to signal of a high speed, offer the signal circumfluence that has had to be able to assure its signal quality, because the characteristic impedance of the transmission line on PCB is commonly,this is with layer (or power source layer) come for reference calculative, if there is successive ground level near high speed line, the impedance of this such lines can keep successive, if have paragraph of line around did not have ground reference, such impedance can produce change, discontinuous impedance can affect the integrality of signal thereby. So, wiring when should distribute high speed line to the layer that approachs ground level, 9 ground wire perhaps walk on the side of high speed line, remove screen and nearby to provide the function of circumfluence.

 

The 3rd, power source is not crossed to break up as far as possible when why saying wiring, because signal spanned,this also is after layer of different power source, its circumfluence way is met very long, be disturbed easily. Of course, not be to ask strictly to cannot span power source is broken up, the signal to low speed is possible, because the interference of generation is compared,signal need not grant to care. Be about to be checked seriously to high speed signal, do not span as far as possible, can pass those who adjust power source part to take a line. (This is to be aimed at multilayer board many power source supply a circumstance to say)

 

To general parts of an apparatus, nearby ground connection is best, used those who have whole ground level is multilayer board after the design, very easy to the ground connection of common signal, basic principle is those who assure a line is successional, had reduced aperture amount; to approach ground level or power source is planar, etc.

 

The discussion of ground connection technology

 

Why does ⑥ want to part imitate ground and digital ground, how to part?

 

Answer: Imitate signal and digital signal want circumfluence to reach the ground, because rate of digital signal change is rapid, the noise that causes on digital ground thereby is met very big, and imitate signal is need a clean ground reference works. If imitate ground is mixed digital ground lump, noise can affect imitate signal.

 

Generally speaking, imitate ground and digital ground want apart processing, be together repeatedly through taking a line finely next, only perhaps place is received together. Total thought is to cut off as far as possible the noise change on digital ground arrives on imitate ground. Of course this also is not very firm requirement imitate ground and digital ground must part, if the digital ground near imitate part or very clean word can close together.

 

The discussion of ground connection technology

 

The signal on ⑦ veneer how ground connection?

 

Answer: To general parts of an apparatus, nearby ground connection is best, used those who have whole ground level is multilayer board after the design, very easy to the ground connection of common signal, basic principle is those who assure a line is successional, had reduced aperture amount; to approach ground level or power source is planar, etc.

 

The discussion of ground connection technology

 

The interface parts of an apparatus of ⑧ veneer how ground connection?

 

Answer: Some veneer can have external the input outputs interface, string together buccal connector for instance, connector of net mouth RJ45 is waited a moment, if be designed badly to also can affect regular job to their ground connection, for example net mouth interrelates have pile up by accident, lose a bag to wait, and can be become external electromagnetism violates a source, board the noise inside is sent outwards.

Can break up an interface ground that becomes independent together alone generally speaking, use fine connection taking a line with the join of signal ground, can string together the resistor that small perhaps block is worth on 0 ohm. Walk along a line finely to be able to be used cut off the noise on signal ground comes up to interface ground too. Same, the filter wave of ground of butt joint mouth and interface power source also wants serious consideration.

 

The discussion of ground connection technology

 

The screen layer of the cable that ⑨ takes screen layer how ground connection?

 

Answer: is not signal ground on the interface land that the screen layer of screen cable wants to receive veneer go up, because have on signal ground,this is all sorts of noise, if screen layer received signal ground to go up, noise voltage is met drive in all layer of screen of edge of modular electric current is disturbed outwards, the biggest noise that the cable with so bad design is electromagnetism interference commonly outputs a source. Of course premise is interface ground also wants exceedingly clean.