[introduction]In ACDC power source, inputting voltage is the 85V-265V communication high pressure that comes from electrified wire netting commonly, and output voltage is the dc low pressure such as 3.3V, 5V, 12V, because this needs switch power supply,will realize step-down. Switch power source has Buck, Boost and Buck-Boost3 big classical develop attacks, among them Buck and Buck-Boost all can realize step-down function. Synergy world brightness it is a world the subsidiary below be good at banner, have rich industry experience and professional technical actual strength, power source of world brightness company and FAE of ministry of facilities of new energy resources combine oneself experience, how should develop choose to attack in applying in the light of the auxiliary power source of small home appliance circuit and relevant product, spread out detailed introduction.

In ACDC power source, inputting voltage is the 85V-265V communication high pressure that comes from electrified wire netting commonly, and output voltage is the dc low pressure such as 3.3V, 5V, 12V, because this needs switch power supply,will realize step-down. Switch power source has Buck, Boost and Buck-Boost3 big classical develop attacks, among them Buck and Buck-Boost all can realize step-down function. Synergy world brightness it is a world the subsidiary below be good at banner, have rich industry experience and professional technical actual strength, power source of world brightness company and FAE of ministry of facilities of new energy resources combine oneself experience, how should develop choose to attack in applying in the light of the auxiliary power source of small home appliance circuit and relevant product, spread out detailed introduction.

One, Buck circuit

Buck circuit is circuit of a step-down, vi=Vls+Vo. Because of Vi>Vo, reason has step-down effect.

(1) switch canal S guides a phase

When switch closes, d of diode of follow on current ends, because input voltage Vi and store can inductance Ls puts through, because this is inputted – output pressing is poor (Vi-Vo) add on Ls, the electric current that makes go up through Ls increases linearly. In this phase, divide to laden power supply outside, still one part electric energy stores in inductance Ls and capacitance Cr.

(2) switch canal S passes level

When switch disconnects, ls and Vi disconnect, but mutation cannot happen in the instant as a result of inductance electric current, the electricity that because this is on inductance Ls,with respect to generation retrorse electromotive force carries with maintaining is changeless. Right now D of diode of follow on current guides, store the return that there is what D forms with respect to the course in the electric energy in inductance Ls is right laden power supply. (advocate if capacitance C is right laden power supply, this phase charges to capacitance all the time, maintaining voltage is stable)

2, Buck-Boost circuit

The input voltage of Buck-Boost circuit and the polarity that output voltage are contrary.

(1) switch canal S guides a phase

When switch closes, input voltage is returned directly through inductance L, go up in inductance Ls store can, right now capacitance Cr discharges, give laden power supply.

(2) switch canal S ends level

When switch disconnects, retrorse electromotive force arises on inductance Ls, make diode D from end become guide. Inductance gives laden power supply and charge to outputting capacitance, maintain output tension is constant.

Pass above contrast, can be informed: The input voltage of Buck-Boost circuit and the polarity that output voltage are contrary. Accordingly, buck and Buck-Boost are both the polarity that the biggest distinction depends on input and output voltage: Buck is same polarity develop attacks, namely output and the polarity that input voltage are identical, both in all; And Buck-Boost is to turn over polarity develop to attack, namely output and the polarity that input voltage are contrary, output end provides negative pressure (opposite input voltage) .

In small home appliance the power module in applying setting controls a share, the engineer is commonly used be in charge of to two-way brilliant brake (the communication switch such as TRIAC) (AC Switch) . And drive of use negative pressure communicates switch, can realize higher circuit reliability and compatibility. In using the system that communicates switch, often the Buck-Boost that first choice can output negative pressure; And in the system that does not need negative pressure drive, can choose Buck develop to attack:

? The input of Buck and output are carried in all, more benefit is extended at systematic multistage.

? The utilization rate of inductance electric current of Buck is higher than Buck-Boost. Flow in inductance report (when IL) is identical, buck can export bigger electricity (IO) .

3, the product is recommended

After knowing how to choose develop to attack, how should select a product again? World brightness FAE is recommended come from Shanghai brilliant Feng Mingyuan (BPS) BP852X series is high-powered chip of drive of switch power source, supportive Buck and Buck-Boost develop attack, have extremely brief periphery circuit, applicable assists power source design at the small home appliance of low cost, be like: Small home appliance assists drive of power source, electric machinery to assist intelligence of power source, IoT/ to live in / the many domains such as intelligent illume. This series product has numerous outstanding character, include:

Diode of compositive Vcc capacitance, follow on current and feedback diode

MOSFET of compositive 650V high pressure

Compositive high pressure is started and self-confessed report circuit

Low bide one’s time power comsumption 50mW@230Vac

Exceedingly good trends answers speed, output voltage ripple is small

Reduce frequency noise fall a modulation technology

Improve the frequency modulation technology of EMI function

Next, world brightness FAE will is with the BP85226D of this series exemple, spread out specific introducing.

Graph: Enclose with norms

Graph: Performance data expresses report

Graph: BP85226D uses principle figure

Graph: Product objective

Graph: BOM watch

4, PCB Layout and proposal

1.IC-GND can rise to come loose hot action, can copper comes loose hot. But IC-GND is voltage moves a point, satisfying medicinal powder area of hot copper of conditional lower berth should as far as possible small; Need to be far from input communication end at the same time, in order to avoid problem of EMI of generation of look sex coupling.

2. outputs inductance to may generate electromagnetism interference, while the proposal is far from chip FB foot, also be far from an input to carry in order to avoid EMI problem. Move a dot to be far from communication to input end for chip and voltage, the proposal electroanalysises the input capacitance is placed between chip and communication input end.

3.DRAIN receives input dc bus bar, for voltage static drop, can spread copper to come loose hot. The distance taking a line of proposal DRAIN and FB, IC-GND is more than 2mm.

4. reduces area of power annulus road to EMI is disturbed and raise systematic dependability in order to avoid as far as possible. It is with Buck exemple, the proposal is contractible input capacitance, inside the excitation loop that electric capacity of buy MOSFET, inductance, output forms, and the inductance, follow on current that outputs composition of diode of capacitance, follow on current answers road surface to accumulate.

Of loop of 5. proposal power go the line is broad and short, in order to raise systematic dependability, for instance bus walks along line, GND to what output capacitance to walk along a line to wait to what GND cites a base.

Area of 6. feedback loop also should be reduced with length taking a line, in order to raise dependability.

7. if as a result of objective element (for example PCB board appearance) bring about Layout to cannot be satisfied adequately the 5th, when 6 proposals, the position that cite a base can be stood by to place 100nF(104) to stick a capacitance between VOUT and GND, raise systematic dependability thereby.

Graph: Inductance chooses a proposal

Graph: Laden regulation

Graph: The weaveform that start

Graph: Output voltage ripple

Graph: Trends is answered

Graph: Conduct EMI

Graph: Surge

Graph: Group pulse checks

Graph: ESD checks *

True actual measurement tries next reaching below condition of lab of eventuate of * above test, real product inspects applied environment and batch difference, the likelihood exists different, feng Mingyuan withholds brilliant to explain advantageous position finally.

Graph: Type selecting of BP852X series product is expressed

Summary

The BP852X series chip of brilliant Feng Mingyuan is had extremely brief periphery circuit and superhigh are compositive degree, can reduce the cost that uses program and stock up difficulty greatly; Rich protection conduces to reinforce systematic stability; In addition, this product still holds an outstanding trends concurrently to answer, bide one’s time power comsumption and output are adjusted wait for function, because this suits the auxiliary power source with Yu Xiaojia report very much. Synergy world brightness can provide whole set product and relevant technical support.

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