Create a power supply with your own printed circuit board! (5)

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Design Analog Power SupplyAnalog Devices

In the previous article, we concluded that the cause of the sudden drop in efficiency is "thermal shutdown."
This time, we will delve deeper into why there is a difference in efficiency between the two boards.

Investigating the cause of efficiency differences between white and black boards

Last time, we found that the efficiency of the white board dropped sharply around 1.5A, and that the cause was thermal shutdown. So why did the thermal shutdown occur only on the white board? Why are black boards more efficient than white boards?

Looking at the efficiency graph, the black board is generally 1-2% more efficient.

The only difference between the white and black boards is the board pattern, so it is easy to imagine that this is having an effect, but did the board pattern reduce efficiency and cause the IC temperature to rise? Or did the efficiency decrease because the IC temperature was high?

This is a chicken and egg question, but it's an important one! What experiments can we do to separate them?

Experimental procedure

With the help of my seniors, I decided to carry out the following experiment.

1. Operate the black and white boards under the same conditions and measure their temperatures with a thermal camera.
2. If a temperature difference is confirmed, the environmental temperature of the black board is increased in a thermostatic chamber by that temperature difference.
3. Compare the efficiency of the black board with increasing environmental temperature.

If this procedure produced any difference in efficiency, we believed we could conclude that the IC temperature was the main cause of the efficiency loss.

experiment

First, we measured the temperature of both boards with a thermal camera.

When measured with a thermal camera, the temperature difference between the black board and the white board was 23°C. Therefore, we raised the temperature of the black board by 23°C and measured the efficiency again.

Ambient temperature	VIN[V]	VOUT[V]	IOUT[A]	efficiency
24.4℃	36.0	5.1	1.0	81.1%
47.4℃	36.0	5.1	1.0	80.5%
5℃	36.0	5.1	1.0	81.6%
-10℃	36.0	5.1	1.0	82.0%

Black board Efficiency changes due to temperature change

We were able to confirm the efficiency difference due to the temperature of the black board, but even if the temperature was raised by 23°C, the efficiency only decreased by 0.6%. Furthermore, we also measured the efficiency when cooled to -10°C, but the difference from 47.4°C was only 1.5%. Even if the black board was placed under the same temperature conditions as the white board, the efficiency did not decrease as much as the white board. What we can say from these results is that the IC temperature has only a small effect on efficiency.

From these results, I concluded that the difference in efficiency between the black and white boards was mostly due to losses caused by differences in the board patterns, although temperature does have some effect on efficiency. As expected, there is a clear difference in performance between the white board on which I drew the pattern without any prior knowledge, and the black board on which I corrected the pattern following the advice of my seniors!

At the end

Through this series of tests, I was reminded of the significant impact that board patterns have on efficiency. I learned that in board design, it is extremely important not to simply place components, but to consider the current flow when designing the pattern.

In addition, I felt that the process of identifying the cause and logically solving the problem was also very important as we proceeded with the experiment. When we faced a problem, we carefully checked each factor and identified the cause through trial and error, which I think was a valuable experience.

This concludes our blog on PCB creation! Thank you for reading to the end!