Design of switching power supply based on inverter power supply

In common sense, power supply is a conversion device that can provide suitable voltage, current, waveform and frequency for our electronic appliances ! For example, DC power supply can be understood as a power supply with zero frequency and linear waveform. AC power supply can be understood as a power supply with alternating voltage (positive and negative are converted between two electrodes), frequency and waveform! Regardless of the power supply, we can use differential integral mathematics to solve its value at any point in time, and there is a unique solution! For example, square wave is composed of sine waves of infinite magnitude, so square wave can be decomposed into odd harmonics and ox harmonics! We usually take the value of 3rd harmonic to meet the requirements! The fundamental wave accounts for the largest part of power.

　　Since the transformer used in our current power supply is basically a high-frequency magnetic core, the field effect tube becomes the main power device! Everyone knows that the field tube works in a switching state, so when it is used as a power tube, the power supply outputs a pulse square wave. Therefore, the power supply with the field tube as the power has a large amount of harmonics and fundamental waves! For the power supply with the field tube as a switching power tube, it is also necessary to understand that 90% of the loss produced by the field tube is produced during the opening and closing time, because there is a large instantaneous resistance during the opening and closing time! Therefore, to solve the problem of switching power supply, the main work is actually how to reduce the opening and closing losses. For harmonics, we can solve it through filters! Another point we need to understand is that the field tube is very sensitive to instantaneous voltage changes, so the power supply that supplies it must have a stable voltage! The last thing to understand is that its gate resistance is very large, and a little voltage can turn it on, and basically no current is required. So the field tube is a voltage control element.

　　Through the above, we understand that to use the field management well:

　　1. The power supply voltage should be stable.

　　2. Control the opening and closing losses.

　　3. Appropriately reduce the gate resistance to prevent misconduction.

　　4. There must be a low-pass discharge circuit and a fast charging circuit, because the field tube has capacitance on the gate, and its capacitance must be charged and discharged quickly! Therefore, a totem pole circuit must be used.

　　We want to design a good power supply program:

　　First: Determine your power supply power and input voltage. Select the switch current of the switch tube according to the power supply power, the transformer size, and the input voltage to determine the withstand voltage of the switch tube and the number of transformer input turns.

　　Second: Regardless of the voltage and power, the field tube used must have a low-pass discharge and fast charging circuit.

　　Third: The transformer must have an absorption circuit to absorb harmonics.

　　Fourth: The internal resistance of the field tube gate should be lowered by connecting a resistor to ground.

　　Fifth: Choose the appropriate switching frequency to ensure the minimum static loss and the highest field-effect transistor conversion efficiency.

　　Sixth: When the input voltage exceeds 75V, consider using the resonant circuit as a negative auxiliary circuit.

　　Seventh: When the power is too large, consider including the PFC circuit in the design.

　　Eighth: The driving signal must be stable! And it must be above 5V.

　　Whether it is a switching power supply or an inverter power supply, high-frequency design has become the main technical means and mainstream! For many people who have never designed a power supply or have not yet reached the project development capability of power supply design, when they think of design, they will think of various calculation modes! This idea is right, but the practice is wrong! Real power supply masters never calculate too much. Even if there are 1,000 components, they will not start to calculate too much! But the power supply that comes out is super effective. Why? Because of experience! Calculation is only for teachers in school! In fact, in a mass-produced factory, the boss can't wait for you to calculate! Because his delivery is limited in time! If the time limit is exceeded, you have to pay! So for friends who have never designed a power supply or are designing a power supply for the first time, don't always think about how to calculate the parameters of a power supply. The most important thing is experience.

　　A power supply designed by an expert! Enough of logic! That is, to determine the solution according to the power supply parameter requirements (which circuit to use is simple and stable, low cost, not demanding in terms of process, easy to maintain in the future, easy to purchase materials, etc.), not how to calculate it! On the power supply website, my post is an advertisement, half theory! Many netizens also come to ask me every day how to calculate this parameter and how to determine it! I say it again! There is no need to calculate when making a power supply! Enough of the mode! That is, the power supply structure! The transformer does not need to be calculated, and the field tube does not need to be calculated! Frequency is about experience! Enough of the various protections to talk about your commonly used circuit modes!

　　How does a real power engineer work?

　　1: Take over the power supply design requirements! Evaluate the cost and determine the feasibility plan.

　　2. Based on the customer's quotation! Given the approximate component cost and production cost, a feasible circuit is developed.

　　3: Conceive a schematic diagram! Determine the selected power tube, transformer, and the most stable, simple, and convenient principle solution.

　　4: Design PCB according to the schematic diagram, sample requirements or shell requirements given by the customer.

　　Five: According to the schematic diagram, assemble appropriate components and adjust the electrical parameters to make the machine work normally under the minimum requirements.

　　Six: Load test! The power reaches 80%! Check the output waveform, voltage requirements, electromagnetic performance, power tube temperature, voltage stability, and conversion efficiency. In this process, the appropriate parameters of the electronic components are adjusted.

　　Seven: Strengthen testing! That is, overload, short circuit, low voltage, overvoltage, high temperature, shockproof and other tests.

　　8. Determine the accurate parameters of the schematic diagram based on the sample, determine the orientation map and material map, send them to the production department, warehouse manager, and merchandiser, and produce the sample in small batches.

　　9. After the sample is rigorously tested and all performances are OK, the salesperson will send it to the customer for evaluation. If it is OK, it can be mass-produced.

　　10: In future production, we will track and improve the project and deliver it to customers in the shortest time and with the best quality.

　　From the above 10 points! I have not mentioned how the parameters of engineers are obtained! In fact, all the parameters of engineers come from experience and debugging. When we design power supplies, 95% of the calculations of parameters are unnecessary! For example, for an inverter of 1000W, two 55s can be used, because each can reach 500, or four 40s can be used, because each 40 can reach 350W. Transformers, why do you need to calculate! But you need experience. Of course, you can also refer to the finished product to determine! We also need to test the number of coils. Circuit parameters, for electronic components, there are several: resistors, capacitors, diodes, triodes , inductors, thermistors, varistors, field tubes, transformers, insurance, integrated circuits, etc.! The combination of various components is our basic circuit: amplification, filtering, isolation, signal source, voltage regulation, comparison, current amplification, voltage amplification and other resident circuits. Of course, you have to add some independent circuits that you think of!

　　Therefore, we can regard the power board as a unified body, and then use our common circuits to assemble it as needed. In this way, we can get a good product. For new products, we should use the circuits that we are familiar with and confident about! Otherwise, the designed products will have many problems in production!

　　Many expert engineers often design PCBs before they come up with the principle! Because even if the principle is figured out, it still needs to be changed according to the PCB! PCB is the essence of the substance! However, for this type of product, even the most senior engineers have to design similar products frequently to achieve it.