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Power management

Power management refers to how to effectively distribute power to different components of the system. Power management is essential for mobile devices that rely on battery power. By reducing energy consumption when components are idle, an excellent power management system can extend battery life by two or three times. Power management technology is also called power control technology. It belongs to the category of power electronics technology. It is an edge cross technology integrating power conversion, modern electronics, network formation, automatic control and other disciplines. It has been widely used in industry, energy, transportation, information, aviation, national defense, education, culture and many other fields.


The continuous increase in global energy-saving demand, the continuous advancement of digital technology, the increasing number of split power supply structures and the requirement that electronic equipment must comply with mandatory energy efficiency regulations, together with the development trend of miniaturization and multi-function of portable devices are the driving force for the development of power management technology. 


Q1: How to evaluate the power requirements of a system

Answer: For an actual electronic system, it is necessary to carefully analyze its power requirements. Not only care about the input voltage, output voltage and current, but also carefully consider the total power consumption, the efficiency of the power supply, the transient response capability of the power supply part to load changes, the tolerance range of key components to power fluctuations, and the corresponding allowable power ripple, heat dissipation issues, etc. Power consumption and efficiency are closely related. With higher efficiency, the total power consumption is less when the load power consumption is the same, which is very beneficial to reduce the power budget of the entire system (compared to LDO and switching power supply, the efficiency of switching power supply is higher). It is worth noting that evaluating efficiency is not only based on the efficiency of the power circuit at full load, but also on the efficiency level at light load.

As for the load transient response capability, there are strict requirements for some high-performance CPU applications, because when the CPU suddenly starts to run heavy tasks, the required startup current is very large. If the response speed of the power supply circuit is not enough, it will cause transient voltage drops too much, causing CPU operation errors.

Generally, the actual value of the required power supply is mostly ±5% of the nominal value, so the allowable power supply ripple can be calculated based on this, of course, a margin must be reserved.

The heat dissipation problem is more important for those high-current power supplies and LDOs, and it can be evaluated whether it is appropriate through calculations.

Q2: How to choose a suitable power supply to realize the circuit

Answer: According to the specific technical indicators obtained by analyzing the system requirements, a suitable power supply can be selected to realize the circuit. The general weak current part includes LDO (linear power converter), switching power supply capacitor step-down converter and switching power supply inductor capacitor converter. In contrast, the LDO design is the easiest to implement, and the output ripple is small, but the disadvantages are that the efficiency may not be high, the heat generation is large, and the current that can be provided is not large compared to the switching power supply, and so on. The switching power supply circuit is designed to be flexible and efficient, but it has shortcomings such as large ripple, complex implementation, and cumbersome debugging.

Q3: How to choose suitable components and parameters for the switching power supply circuit

Answer: Many engineers who have not used switching power supply design will have a certain degree of fear about it, such as worrying about the interference of switching power supply, PCB layout problems, and component parameters and type selection issues. In fact, as long as you understand, it is very convenient to use a switching power supply design.

A switching power supply generally contains two parts: a switching power supply controller and an output. Some controllers integrate MOSFETs into the chip, which makes it easier to use and simplifies the PCB design, but the design flexibility is reduced.

The switch controller is basically a closed-loop feedback control system, generally there will be a sampling circuit for feedback of the output voltage and a control circuit for the feedback loop. Therefore, the design of this part is to ensure accurate sampling circuit and control the feedback depth, because if the feedback loop response is too slow, it will have a lot of influence on the transient response capability.

The output part design includes output capacitance, output inductor, MOSFET, etc. The selection of these components basically needs to meet a performance and cost balance: high switching frequency can use small inductance values (meaning small packaging and cheap cost), but the higher switching frequency will increase interference and increase the switching loss of the MOSFET, which will reduce the efficiency; the result of the low switching frequency is just the opposite.

The selection of the ESR of the output capacitor and the Rds_on parameter of the MOSFET is also very critical: choosing a small ESR can reduce the output ripple, but the cost of the capacitor will increase (a good capacitor is expensive). The driving ability of the switching power supply controller also needs attention: too many MOSFETs cannot be driven well. 

Generally, suppliers of switching power supply controllers will provide specific calculation formulas and usage plans for engineers to learn from.

Q4: How to debug the switching power supply circuit

Answer: Shenzhen PCBA manufacturer - SysPCB have some experience can be shared with everyone: 

1: The input and output of the power supply circuit are connected to the board through low-resistance and high-power resistors, so that the power supply circuit can be debugged before the power supply circuit is completed without welding resistance to avoid the influence of the following circuits.

2: Generally, the switching controller is a closed-loop system. If the output deterioration exceeds the controllable range of the closed-loop, the switching power supply will work abnormally. In this case, you need to carefully check the feedback and sampling circuit. It is particularly important to note that if an output capacitor with a large ESR value is used, a lot of power supply ripple will be generated, which will also affect the operation of the switching power supply.

Digital power management application

Many traditional general-purpose motors used in kitchen and garage appliances, power tools, and other small appliances generally cannot accurately control speed. These motors basically only have two states, on and off, which is indeed sufficient for some applications. But in other occasions, the electric motor that uses the digital power management system for precise variable speed control has many huge advantages, including:

-Lower power consumption
-Higher security
-Longer tool life
-Easier to use
-More advanced operation control.
-Minimize the risk of electrical surge when an electrical appliance is turned on, leading to circuit disconnection