"Opening
This is a courseware made before. All the pictures are drawn with Sch. If you don't draw well, please forgive me and understand the meaning. Maybe some netizens will think, how come back and forth is always talking about volt second balance?
Because it is important, and it can verify the wrong use of many magnetic components.
fundamental law
Drive transformer
Note the figure below. In order not to overpressure MOS tube, clamp circuit should be added appropriately.
Note that it is a clamp circuit to protect MOS tube from overvoltage, rather than a reset circuit often referred to as.
The reason why it is not drawn on the diagram is to say that without those circuits such as RCD, the transformer can still sense a voltage to reset itself. Of course, it should be noted here that if you reset yourself, you can only return to the remanence point. That is, H returns to 0, but B does not return to 0.
half-bridge
In the figure below, it is estimated that someone has been beaten
This usage should be very common. Uc384x and the like are used more for double transistor forward excitation.
push-pull
Push pull, unable to string into the DC isolation capacitor, naturally prone to magnetic bias.
The volt second balance law can be used to check whether the circuit and parameters are reasonable
Flyback
Flyback, mostly like to use 600V tubes, so we should pay attention to the selection of voltage and duty cycle in the design of transformer. From the volt second equilibrium law, we can know whether the pressure resistance of pipes is enough in theory. Of course, theoretically enough, in fact, we still need to add margin and RCD clamping circuit. It is emphasized here again that this is used by the clamp circuit to protect the tube, not called the reset circuit.
Hysteresis loop
In brief, it can only be used in the first quadrant, assuming that the core saturation B of PC40 is 0.39.
When designing, whether inductance or transformer, Δ B can only be between 0 and 0.39.
And pay attention to the problem of residual magnetism of the magnetic core (when h returns to 0, the remaining b).
Here's a supplement. Although some special topologies can run in quadrants 1 ~ 3, the positive and negative running time are not necessarily symmetrical. Such a topology is selected during calculation Δ B cannot reach 0.8 (plus or minus 0.4).
supplement
They are magnetic components used in some special occasions. Because special magnetic materials are used, a reset circuit may be added. For example, the magnetic material used for magnetic amplification is characterized by large remanence, that is, the so-called rectangular ratio is high. If such a magnetic material is not added with a reset circuit, even if it is "open circuit", it will still be in a state of near saturation“ Of course, it should be noted here that if you reset yourself, you can only return to the remanence point. "However, adding breath can make the remanence less. With gas magnetism, the hysteresis loop becomes" flat "and the remanence is much smaller. It is estimated that this is why many people say that "forward excitation plus point air gap can prevent saturation". In fact, if remanence is considered in the design, there is no problem without air gap., Read the full text, the original title: Graphic explanation, the "volt second balance" of various topologies!
The source of the article: [micro signal: dianyuankaifa, WeChat official account: vernacular communication] welcome to add attention! Please indicate the source of the article“
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