How to choose between linear voltage regulator and switching regulator?
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How to choose between linear voltage regulator and switching regulator?

Posted Date: 2024-01-16

With the rapid development of electronic technology, electronic equipment is increasingly closely related to people's work and life, and electronic equipment is inseparable from reliable power supply. Our common power supply products are basically divided into two categories: linear power supply and switching power supply. What are the characteristics of these two types of power supplies? In addition, what type of power supply should engineers choose when designing a power supply solution? You can easily get the answer by reading below.

Power supply type

First, let’s understand what a linear power supply is and what a switching power supply is. The literal meaning can be understood as: a power supply system made using a linear regulator is a linear power supply, and a power supply made using a switching regulator is a switching power supply. Next we introduce linear regulators and switching regulators.

linear regulator

Linear regulator is what we often call LDO. Its transmission device works in the linear region. To put it bluntly, it is a resistor voltage divider. It can only be used for step-down conversion. The output current is almost equal to the input current. When the input-output voltage difference is large, The system conversion efficiency is low.

switching regulator

The switching regulator uses the power tube to continuously turn on and off, and cooperates with energy storage components (inductors, capacitors) to realize energy transmission and conversion, and realize voltage conversion. Depending on how the devices in the system circuit are connected, conversions such as DC boost, step-down, negative voltage, step-up and step-down can be achieved. Under ideal conditions, there will be no energy loss in the inductor and capacitor, so the system conversion efficiency is relatively high.

Selection basis

How to correctly select the power supply type according to the program requirements is still difficult; let's briefly explain it through two examples.

Example 1. The program requirements are 12V input and 5V/2A output.

As mentioned earlier, when the input-output voltage difference is relatively large, the conversion efficiency of a linear power supply is relatively low due to its working characteristics; using a linear power supply, its maximum conversion efficiency is 5/12*100% = 41.67%, and the entire loss of the system is (12-5) V*2A=14W; when using a switching power supply, the conversion efficiency is at least 90%. The input power of the system is 10W/0.9=11.1W, and the power loss is 11.1-10=1.1W. Outputting the same power, the loss difference between the two is more than 12 times. If a linear power supply is used, a very large auxiliary heat dissipation device is required. Obviously, switching power supply is the most suitable choice for this solution.

Case 2. The program requirements are 4.5V input and 3.3V/0.1A output.

This solution has low input and output voltage difference and low output power. When using a linear power supply, its conversion efficiency is 3.3/4.5*100%=73.3%, and the entire system loss is (4.5-3.3) V*0.1A=0.12W; use The efficiency of the switching power supply will be above 85%, and the loss will be around 0.06W. The loss of 0.12W is acceptable. Considering the high cost and complexity of the switching power supply system, linear power supply is the most suitable choice for this solution.

Summarize

When selecting a power supply type, performance is the first criterion. After the performance meets the requirements, cost requirements will be considered. The following summarizes the advantages and disadvantages of linear power supplies and switching power supplies.

Advantages of linear power supply: pure output voltage, small ripple, low noise, and simple use; Disadvantage: it can only achieve step-down output, and when the input-output voltage difference is large, the conversion efficiency is low.

switching power supply

Advantages: high efficiency, small size, high power density, and can realize a variety of power conversion; Disadvantages: due to the electromagnetic conversion of power tube switches and energy storage devices, the output voltage ripple and noise are relatively large, and electromagnetic disturbance is generated at the same time, system cost Relatively high.

Both have their own advantages and disadvantages. In low voltage difference and low power situations, linear power supply can be preferred; in large voltage difference and high power situations, switching power supply is more suitable. For some input and output voltage differences are relatively large, and the power supply output voltage ripple In sensitive situations, you can consider using a switching power supply to appropriately reduce the input voltage, and then use an LDO to provide pure voltage to the subsequent stage.


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