It is necessary to remove the ground wire clamp to test the ripple noise, mainly because the ground wire clamp of the oscilloscope will absorb various high-frequency noises, which cannot truly reflect the output ripple noise of the voltage waterproof led power supply and affect the measurement results. Picture 2 and picture 3 below respectively show the huge difference between using the ground clamp and removing the ground clamp for the same product.
2.The influence of PCB layout on design
Good and bad PCB layout is a key factor affecting ripple noise in design. The poor PCB layout is shown in picture 4. The ground of the transformer output is directly connected to the ground plane on the back through the via hole, and the ground plane is connected to the output pin of the power supply. With this layout, the measured led driver power supply spike reaches 1.5V VP-P under a load of 5V/2A.
picture 5 shows a better PCB layout. After adjusting the position of the transformer, the output ground of the transformer is passed through two capacitors, and then back to the ground plane and connected to the output pin. It is measured that under the same 5V/2A output load, the noise has been reduced to 60mV VP-P, the difference is significant
3.Effect of output filter capacitor
The capacitance and ESR of the output filter capacitor also have a direct impact on the ripple noise output by the module. Test the ripple noise according to the product shown in picture 6.
Without external capacitors, the ripple noise of the test output, as shown in picture 7, is about 100mV. Under the same input and load conditions, 226 MLCC is added to the output of the power supply, and the ripple noise of the measured power supply output is reduced to less than 40mV.
