Checking through holes is also important!

After checking the circuit diagram, I noticed that the output capacitor's capacitance was smaller than the manufacturer's recommended value.

Circuit A is 100% working fine.
If the operation becomes unstable in circuit B, which is the same circuit, it is highly likely that the device is the cause.

(I wonder if the device is really the cause...?)

As you can see by looking at the actual device, circuit B oscillates as the load fluctuation increases.

So let's check the actual machine. . .

that? Where is the output capacitor of circuit B placed?

Since there was no mounting place on the same side as the power supply IC, it is placed on the back side.

So that's it. .
Is this the only through hole?

Yes, I wanted to increase the mounting density as much as possible, so I made it one.
Is there anything wrong?

(Is this the cause?)

Layout drawings are time consuming, so I took pictures instead. Appearance does not appear to be a problem.

Cause of unstable output voltage

• The output capacitor capacity is different from the manufacturer's recommended value.
• Having only one through hole

Even if the circuit is exactly the same, if the output capacitance is smaller than the manufacturer's recommended value, problems are likely to occur during mass production. We recommend using a capacitor with the capacity recommended by the manufacturer.

In addition, the output capacitor of circuit B, which operated unstablely, was connected via a through hole, so the inductance of the through hole canceled out the capacitance of the output capacitor, resulting in malfunction.

The point of this time

・The output capacitor capacity should be the value recommended by the manufacturer, and it should be mounted on the same side as the power supply IC.
・If the output capacitor is mounted on a different side from the power supply IC, make multiple through holes.