Switching power supply, also known as switching power supply, switching converter, is a high-frequency power conversion device, is a kind of power supply. The switching transistors used in the switching power supply of civil fusion are mostly switched between the fully open mode and the fully closed mode, both of which have the characteristics of low dissipation. The switching between the two modes will have higher dissipation, but the time is very short, so the switching power supply of civil fusion can save energy and produce less waste heat. The high conversion efficiency of the switching power supply is one of its advantages, and the switching power supply has high working frequency. It can also use small size and light weight transformer, and the switching power supply will be light. Civil fusion switching power supply products are widely used in industrial automation control, military equipment, scientific research equipment, LED lighting and other fields.
Flyback transformer is the core of flyback switching power supply. It determines a series of important parameters of flyback converter, such as duty cycle D, maximum peak current, etc. The flyback transformer is designed to make the flyback switching power supply work at a reasonable working point. In this way, the heating and wear of the equipment can be minimized. The same chip, the same core, if the transformer design is not reasonable, the performance of the whole switching power supply will be greatly reduced, such as the loss will increase, the maximum output power will also decrease. Let’s share the design skills of flyback switching power supply transformer in the following small class. If you are difficult to choose switching power supply, the following well-known switching power supply is an excellent choice.
1、 Select primary induced voltage vor
The value is set by yourself, which determines the duty cycle of the power supply. When the switch is on, the primary side is equivalent to an inductor. When the voltage is applied at both ends of the inductor, the current value does not change suddenly, but increases linearly. When the switch is turned off, the primary inductor discharges and the inductor current decreases.
2、 Determining the parameters of primary current waveform
The side current waveform has three parameters: average current, root mean square current and peak current. Because the output power divided by the efficiency is the input power, and then the input power divided by the input voltage is the input current, which is the average current. Therefore, corresponding to the same power, that is, when the input current is the same, its effective value is related to these parameters. Proper adjustment of parameters can minimize the effective value, heating, loss and optimize the design.
3、 Selection of transformer core
It’s based on experience. If you can’t choose one, you can estimate one and calculate it. If it doesn’t work, you can replace it with a big one or a small one. However, there are some data on how to select the magnetic core according to the power formula or area line diagram, you might as well refer to it. A lot of people usually come from experience.
4、 Determine the parameters of feedback winding
The feedback voltage is flyback voltage, the voltage is taken from the output stage, and the feedback voltage is stable. The power supply voltage of top is 5.7 ~ 9V. After 7 turns, the voltage is about 6V, which is normal. Remember that the feedback voltage is flyback and its turn ratio corresponds to the amplitude side. As for the wire, because the current flowing through it is very small, so it can be wound with the wire around the original side, without strict requirements.
5、 Calculation of primary side turns of transformer
When calculating the number of primary side turns, the amplitude B of a magnetic core should be selected, that is, the variation range of magnetic induction intensity of the magnetic core. Because of the change of magnetic induction intensity after the square wave voltage is added, it has the effect of voltage transformation. NP = vs * ton / SJ * B these parameters are primary side turns, minimum input voltage, on time, core cross-sectional area and core amplitude. In general, b values range from 0.1 to 0.2. The smaller the value is, the smaller the iron loss is. But the corresponding transformer will be larger. This formula is derived from Faraday’s law of electromagnetic induction. This law says that in the core, when the magnetic flux changes, an induced voltage will be generated. Induced voltage = flux change / time t, then multiplied by turn ratio. The above formula can be deduced by transforming the change of magnetic flux into the change of magnetic induction intensity multiplied by its area. In short, NP = 90 * 4.7 μ S / 32mm2 * 0.15 = = 88.15, take the integer of 88 turns.
Calculate the number of turns, and then determine the wire diameter. Generally speaking, the higher the current, the easier the conductor is to be heated, and the thicker the conductor is required. The required wire diameter is determined by the effective value of current rather than the average value. The effective value has been calculated above, so we choose this line. I can use 0.25 wire. Using 0.25 conductor, its area is 0.049 square millimeter, current is 0.2A, current density is 4.08. The current density is generally 4-10a / mm2. It’s important to remember that. In addition, due to the trend effect of high-frequency current, if the current is large, it is better to use two or more strands in parallel, so the effect is better.
The above is the small class today to share, about flyback switching power supply transformer design coup. After sharing in Minrong small class, everyone should have a certain in-depth understanding.
Editor in charge ajx