In the design of single ended flyback switching power supply, the maximum duty cycle is D, the operating frequency is f, the turn ratio n is set, or is it first assumed that one is used?

There are many of these documents online, but it seems a lot later found inside some parameters, such as D or F have always been known as design parameters, such as Dmax=045, why choose this value, instead of 0.35, 0.25. Another design is to assume a flyback voltage Vor directly first. Can these parameters be designed as known parameters? The more detailed the answer, the better to have information

The main switch power tube, rectifier conduction and cut-off time control: high frequency, duty ratio, left switches open and close the conversion time is short; if the device cannot stop completely in this short period of time, there will be not reliable off, the equivalent of this device will instantly short-circuit. Theoretically, the maximum duty ratio of the single ended circuit is 50%, and the closer the limit is, the greater the output power of the circuit. Therefore, in the premise of meeting the requirements of the device, the bigger the duty cycle, the better.

In fact, the general power supply chip have some fixed frequency is to allow users to set up their own frequency, a frequency size that you used to other components to choose from, like the allowable operating frequency of MnZn ferrite materials from tens to hundreds of K K, your rectifier switch tube conduction losses, diode the reverse recovery time, the higher the frequency of the general magnetic element of your volume is small, of course, the cost is also lower

Because of cost considerations, the maximum duty ratio is set to 40% to 45%, while the turn ratio has direct effect on the size of the selected primary switches and secondary rectifier, so the power supply is a system, an experienced power engineers are in a different turn ratio and duty ratio between choice, and to obtain the best parameters.

The working frequency must be a known condition. Can you design the converter without even working frequency? About the duty ratio of D, in the current feeding mode so as not to exceed 50%, need to add slope compensation, otherwise it will affect the stability of the whole system, why not 0.35,0.25; because the maximum duty ratio of D directly affects the transformer turns ratio, duty ratio is smaller then the secondary turns to the corresponding the increase of,

The most important is the frequency will involve the system transfer function and compensation feedback loop, on the problem of stability of the closed-loop system transfer function and I also have very good understanding so that we can't explain to you more, I feel each have their own power engineers used a frequency, such as long as a good improvement the working frequency to do other products need to calculate things less much.