In the opening remarks, the most important factor in the design of the power supply is the current, which determines the difficulty of the power supply design. Then the current of the power supply has only begun to increase in recent years? Didn't there be a high current power supply design in the early years? The answer is of course no! So what is the difference between the high current of the power supply design and the previous years?
My summary is: one is high voltage and large current, one is low voltage and large current.
Difficulties in designing high voltage and high current power suppliesTime has returned 10 or 20 years ago. That era was not a power supply design without large currents, but most of the high-current boards were power boards or backplanes. Ordinary function boards or board-type boards, because the IO voltage of the chip operation is mostly 3.3V, 5V, the current is usually not too large, mostly below 10A, the common is a few amps. On the power board or backplane, the current is large, and the voltage is relatively high, 12V, 36V, 48V or more. So I summed up the design challenge for high voltage and high current.
In response to high pressure, we should pay attention to safety regulations and pay attention to various safety distances, including air gaps and creepage distances. Concerned about safety-related design requirements such as flame retardant and insulation. This is another big category. I won't go into details here. If you are concerned, you can look for relevant information. Yibo Technology also has relevant experts responsible for the design of safety regulations.
This type of [size=1em]PCB design will also have a large current, tens of amps or hundreds of amps. But this board has another feature, that is, there is basically no functional circuit, that is, your CPU, DDR particles, large-scale FPGA, etc., these circuits will not be implemented on the power board. The power board is the power board, which is the component that realizes the power function. The large inductor, capacitor, resistor, diode... A word summary, that is, the components are very large.
This type of design addresses the design challenges of high currents and the solution is simple and rude. Try to be as thick as possible, as wide as possible of the copper foil, if it is not enough, then thick copper, 2oz can not be 4oz, then no longer 6oz, 10oz, or even 12oz. A thick copper plate that we have shown at each seminar is a 12oz copper foil thickness design. A small piece of board, it is very heavy, our craft expert Dong Ge's introduction is: home travel, self-defense necessary ^-^
The traditional design rules deal with the high current of such power boards, and it is also a simple and rude design. Therefore, the current-carrying answers in everyone's minds are often very conservative, such as 1 amp current, about 40 mils line width; and a 10-12 mil via can only carry 0.5 amps of current, I even heard someone say The 12 mil via carries 0.2 amps of current. I was thinking, if your design is 20 amps of current, how many holes do you need to make?
So we came to another challenge in power supply design...
Difficulties in designing low-voltage and high-current power suppliesIn fact, high pressure and low pressure are not the main dividing points of these two types of problems. The main difference I really want to say is that the traditional functional circuits, that is, the CPU, DSP, and large-scale FPGA we design, often have dozens of amps of current, and the current of the IO power supply is getting larger and larger. The trend of power supply design is shown below:
At this time, it is impossible to use thick copper plates because of the large current, because after all, there are a lot of signal lines on the board, and the line width is only a few mils. The area of ​​the copper skin is sometimes limited to "layer" resources and a large number of dense vias, and the limited copper area is difficult to increase indefinitely.
With the design shown below, dense vias, limited board area and number of layers, how do we deal with the challenges of high current design? How do we calculate the necessary current-carrying channels (including copper width and number of vias)?
Low voltage will also bring other design difficulties. As mentioned in the previous article, the larger the current, the larger the corresponding ΔI is. The larger the ΔV is, the larger the induced ΔV is. The lower the voltage, the smaller the design margin, and the more difficult the design.
As shown in the figure below, the DC and AC problems together constitute a problem with the power supply design.
A power supply, to meet the design margin of 5%, must be considered together with AC and DC.
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