Many people first pay attention to the difference of efficiency and power consumption between switching power supply and LDO power supply. In this article, we will talk about their efficiency. The so-called efficiency is actually the power ratio transmitted to the output, which is equal to (transmitted power / input power) * 100%. First of all, we can see their differences intuitively through the ideal simulation model.

We compare ti’s tps5430 (DC-DC) and lm2941 (LDO) from 15V to 5V. Their typical power link structures and simulation results are as follows

Tps5430 (DC-DC) (5v-3a output)

The simulation results are as follows

The input and output currents are as follows:

The input and output voltages are as follows:

When the power is v * I, the input current amplitude is 3a, the duty cycle is 1 / 3, and the output current is 3a, so the input power consumption is close to the output power consumption, and the efficiency is almost 100%.

Lm2941 (LDO) (5v-300ma output)

The simulation results are as follows

The input and output currents are as follows:

The input and output voltages are as follows:

so Because the input and output currents of LDO are the same, 300mA (in fact, a small part of quiescent current flows to the ground), and the input-output voltage ratio is 3, the efficiency of LDO is only 33%.

LDO voltage efficiency will be so low, where is the waste of power? As you mentioned in your reply, the main problem is that the internal resistance of the series regulator is consumed. What impact will it have on the chip? The biggest impact is heating, which is why the input and output voltage difference of LDO should not be too large, and the output current should not be too large, otherwise the heat output caused by the reduction of efficiency is very serious. Therefore, some LDO packages need to increase the area of heat sink, which also leads to the larger volume of LDO or the need for larger heat dissipation plane in PCB, as shown below:

It seems that the efficiency of LDO power supply is difficult to improve under the condition of high voltage difference and high current output. So, what about switching power supply? We intuitively know that the efficiency will be relatively high. From the simulation, the efficiency of the switching power supply is almost full. In fact, is there any loss in the efficiency of the switching power supply? Where is the main loss?

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