Controllers on Single-sided Boards

384x-based Controllers on Single-sided Boards 

Let us take the popular 384x family for the purpose of illustrating some key routing principles in AC-DC power supplies. 

The feedback signal. This usually comes from the opto-coupler. We do try to keep it away from noisy traces and components, but in reality, it is not that prone to noise pickup as many tend to instinctively believe. 

Many years ago in Singapore, we were in the process of designing a new Flyback for a major computer manufacturer (known for its alternative operating systems). The metal box for the power supply, including all mounting locations, vents, holes, and so on, was predetermined. Somehow we had to fit within the constraints. 

We did it somehow, almost strangulating ourselves in the process. Now when I look back at this incident, I wonder why we didn t place a ceramic decoupling capacitor close to the switch, as shown in the lower half of the hgure. The bulk capacitor could have successfully managed to provide the low-frequency current components, whereas the high-frequency capacitor could have really decreased the effechve loop area in which the high-frequency components were circulating. 

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