Over het moeilijke probleem van schakelende voeding gesproken, PCB cloth plate problems is not very difficult, but if want to cloth up a refined PCB must be one of the difficulties in switching power supply (PCB design is not good, may cause no matter how to debug parameter debugging cloth out of the situation, so not scaremongering) when reason was the PCB board consideration or a lot of, such as: Elektrische prestaties, procesroute, veiligheidseisen, EMC-impact, etc.; Among the factors to be considered, electrical is the most basic, but EMC is the most difficult to understand, and the bottleneck of many projects lies in EMC. Het volgende uit 22 richtingen om de printplaat en EMC te delen.

1, mature circuit can be leisurely PCB design EMI circuit

De impact van het bovenstaande circuit op EMC is denkbaar, de ingangsfilters zijn hier; Lightning-proof pressure sensitivity; Weerstand R102 om schokstroom te voorkomen (met relais om verlies te verminderen); Key error mode X capacitance and Y capacitance with inductor filtering; There are fuses affecting the safety board; Elk van deze apparaten is van vitaal belang en de functie en actie van elk apparaat moet zorgvuldig worden beoordeeld. The EMC severity level should be considered when designing the circuit, such as the number of filters to be set, the number and location of the y-capacitor quantity. The choice of pressure-sensitive size and quantity is closely related to our requirements for EMC. Welcome to discuss the seemingly simple EMI circuit that actually contains profound truths for each component.

2. Circuit en EMC: (de meest bekende flyback-hoofdtopologie, kijk welke belangrijke delen van het circuit het EMC-mechanisme bevatten)

The circled parts in the circuit in the figure above are very important for EMC (note that the green part is not), such as radiation. It is known that electromagnetic field radiation is spatial, but the basic principle is the change of magnetic flux, which involves the effective cross-sectional area of magnetic field, namely the corresponding loop in the circuit. The electric current can produce a magnetic field, which is stable and cannot be converted into an electric field. But a changing electric current produces a changing magnetic field, and a changing magnetic field can produce an electric field (in fact, this is the famous Maxwell equation and I’m using plain language), and a changing electric field can also produce a magnetic field. So make sure you pay attention to the places where there are on/off states, that’s one of the sources of the EMC, and this is one of the sources of the EMC. For example, the dotted line loop in the circuit is the opening and closing loop of the switch tube. Not only the switching speed can be adjusted during the design of the circuit, but also the area of the wiring loop of the layout board has an important influence on EMC! The other two loops are absorption loops and rectifying loops, first understand in advance, and then talk!

3. Associatie tussen PCB-ontwerp en EMC

1.PCB loop has a very important influence on EMC, such as flyback main power loop. If it is too large, the radiation will be poor.

2. Filter wiring effect, filter is used to filter out interference, but if PCB wiring is not good, filter may lose the effect it should have.

3. The structure part, the radiator design grounding is not good will affect the grounding of the shielded version;

4. Als het gevoelige onderdeel zich te dicht bij de interferentiebron bevindt, zoals het EMI-circuit en de schakelbuis, leidt dit onvermijdelijk tot een slechte EMC en is een duidelijk isolatiegebied vereist.

5. Wiring of RC absorption loop.

6.Y capacitor grounding and wiring, and the position of Y capacitor is also critical!

I’m going to talk about this, and I’m going to talk about it more, but I’m going to give you a lead.

Hier is een snel voorbeeld:

As shown in the dotted box in the figure above, the X capacitor pin wiring has been indented. You can learn how to make the capacitor pin wiring external (using the squeeze current wiring). Op deze manier kan het filtereffect van de X-condensator de beste staat bereiken.

4. Preparation for PCB design :(if you are fully prepared, the design can be steady step by step to avoid design overturning and starting again)

There are roughly the following aspects, are their own design process to consider, all the content has nothing to do with other tutorials, are just their own experience summary.

1. Appearance structure size, including positioning hole, air channel flow direction, input and output socket, need to match with the customer system, also need to communicate with the customer assembly problems, height limit and so on.

2. Safety certification, products do what kind of certification, where do the basic insulation creepage distance to leave enough, where do strengthen the insulation to leave enough distance or slot.

3. Packaging design: there is no special period, such as preparation for customized packaging.

4. Selectie van procesroute: selectie van dubbel paneel met één paneel of meerlagig bord, volgens het schematische diagram en de bordgrootte, kosten en andere uitgebreide evaluatie.

5. Other special requirements of customers.

The structure and process will be relatively more flexible, safety regulations or relatively fixed part, what certification to do, what safety standards, of course, there are some safety regulations are common in many standards, but there are also some special products such as medical treatment will be more stringent.

For the new entry engineer friends are not dazzled;

Next list some general products general, the following is summarized for IEC60065 specific cloth requirements, for safety needs to keep in mind, encounter specific products will be targeted processing:

1. De afstand van het ingangszekeringkussen is groter dan 3.0 mm, zoals vereist door de veiligheidsvoorschriften, en de werkelijke plaat is 3.5 mm (simpelweg gezegd, de kruipafstand van de zekering is 3.5 mm ervoor en 3.0 mm erna).

2. Before and after the rectifier bridge, the safety requirements are 2.0MM, and the plate layout is 2.5MM.

3. After rectification, safety regulations generally do not require, but the distance between high and low voltage is left according to the actual voltage, and 400V high voltage is left above 2.0mm.

4. De veiligheidsvoorschriften voor de eerste trap vereisen 6.4 mm (elektrische opening) en de kruipafstand moet 7.6 mm zijn. (Merk op dat dit gerelateerd is aan de werkelijke ingangsspanning, moet u de tabel raadplegen voor specifieke berekening, de gegevens die alleen ter referentie worden verstrekt, afhankelijk van de werkelijke situatie)

5. Cold ground and hot ground are clearly marked for the first stage; L, N-markering, INPUT AC INPUT-markering, zekeringwaarschuwingsmarkering enzovoort moeten duidelijk worden gemarkeerd;

It is reiterated that the actual safety distance is related to the actual input voltage and the working environment, so it is necessary to refer to the table for specific calculation. The data provided is for reference only and shall prevail in the actual situation.

5. Consider other factors for PCB design safety

1. Understand what certification their products do and what product categories they belong to. For example, medical treatment, communication, electricity, TV and so on are different, but there are also many similarities.

2. Begrijp in veiligheidsvoorschriften de isolatiekenmerken van de nabije plaats met printplaat, welke plaats basisisolatie is, welke plaats versterkte isolatie is, verschillende standaard isolatieafstanden zijn niet hetzelfde. Het is het beste om de normen te controleren en elektrische afstand en kruipafstand te berekenen.

3. Focus on the safety devices of the product, such as the relationship between the magnetism of the transformer and the original side;

4. Radiator and surrounding distance problem, radiator insulation is not the same as the ground is not the same, the ground is cold, hot insulation is the same cloth.

5. Special attention should be paid to the distance of insurance, requiring the strictest place. The distance between front and rear of the fuse is consistent.

6. Relatie tussen Y-capaciteit en lekstroom en contactstroom.

En zo verder, het zal in detail uitleggen hoe de afstand te verlaten, hoe aan veiligheidseisen te voldoen.

6, PCB design of power supply layout

1. Meet eerst de grootte van PCB en het aantal componenten, om een ​​goede dichtheid te bereiken, of een dichte, schaarse zal lelijk zijn.

2. Modularize the circuit, take the core devices as the center, and place the key devices first.

3. Het apparaat is verticaal of horizontaal anti-positionering, de ene is mooi, de andere is een handige plug-in bediening, speciale omstandigheden kunnen kantelen.

4. Take cabling into consideration and arrange the layout in the most reasonable position for subsequent cabling.

5. Reduce the loop area as much as possible during the layout. The four loops will be explained in detail later.

Do the above points, of course, flexible use, more reasonable layout will be born soon.

The following is the first virgin PCB I drew, many years ago, it was very hard to finish, there may be a small problem in the middle, but the general layout is worth learning:

In this figure, the power density is still relatively high. The control part of LLC, the auxiliary source part and the BUCK circuit driver (high-power multi-channel output) part are on the small board, which is not taken out. Let’s take a look at the layout characteristics of the main power:

1. In- en uitgangsklemmen zijn vast en kunnen niet worden verplaatst. Het bord is rechthoekig.

Hier is de indeling van onder naar boven, van links naar rechts, en is de warmteafvoer afhankelijk van de schaal.

2.EMI-circuit is nog steeds een duidelijke stroomrichting, wat erg belangrijk is, anders is het niet mooi en slecht voor EMC.

3. The position of large capacitor should consider PFC loop and LLC main power loop as far as possible;

4. The current of the side side is relatively large. In order to run the current and dissipate the heat of the rectifier tube, this layout is adopted. De bovenste laag van hoog vermogen wordt over het algemeen negatief en de onderste laag wordt positief.

Each board has its own characteristics, of course, also has its own difficulties, how to reasonably solve the key, we can understand the layout of reasonable selection of meaning?

7. Waardering van PCB-voorbeelden

I think it is a good place to do it. Of course, there will always be defects, which can also be pointed out. It is not easy for a single panel to be so compact, so you can use this board to learn and discuss! Behind will also be for this board to explain learning, we first enjoy.

8. Understanding of the four loops of PCB design :(the basic requirement of PCB layout is the small area of the four loops)

In addition, the absorption loop (RCD absorption, RC absorption of MOS tube and RC absorption of rectifier tube) is also very important, which is also the loop that generates high frequency radiation. If you have any questions about the above figure, you are welcome to discuss them. We are not afraid of any questions.

9. PCB-ontwerphotspot (drijvend potentiaalpunt) en aardingsdraad:

Zaken die aandacht behoeven:

1. Pay special attention to hot spots (high-frequency switching points), which are high-frequency radiation points. Cable layout has a great impact on EMC.

2. De lus gevormd door hotspots is klein en de bedrading is kort en de bedrading is niet zo dik mogelijk, maar zolang de stroom voldoende is.

3. The ground cable must be grounded at a single point. Main power ground and signal ground separate, sampling ground go separately.

4. The ground of the radiator needs to be connected to the main power ground.