rom our KAIC lab, William demonstrates how four different capacitor types affect the ripple voltage on a boost or buck regulator. Each technology of capacitors is compared using the KAIC-RCE-001 board, which uses the same output capacitance bank at the output of a switching regulator. However, the ESR and ESL differences of each technology cause a different output ripple voltage. The capacitor types used in this video are listed below:
- Polymer Aluminum
- KAIC Lab files
Ripple voltage is the product of ripple current leaving the inductor and flowing into the bypass capacitor.
The video had a minor mistake in this section and I hope this didn’t confuse everyone too much! Please use this as a proper reference for ripple current and ripple voltage.
For all the ripple voltage measurements we used the following:
1 GHz Oscilloscope (A 100 MHz Oscilloscope can work too, but more is always better in order to capture the complete ripple voltage)
DC Power Supply
DC Electronic Load
Active Power rail probe with a SMA connection. I highly recommend an active probe as to not load down the circuit with the impedance and the SMA was used to reduce the inductance from the probe. If you do use a passive probe, please measure directly off the output of the capacitor with the shortest ground lead possible.
Passive probe to measure the switching frequency from the output of the switching mode power supply.
The following table lists the results from the different experiments that I conducted, as well as the performance and price differences between the technologies.
All these prices were obtained from one of our main distributors. Ceramic capacitors end up being the most expensive due to the ceramic capacitor shortage, the cheapest capacitor being the A765 series, Aluminum Polymer. As I stated in the video, the ceramic alternatives may work for you depending on your performance needs.
This is just part one of a three-part series that will explore the basics of measuring, testing, and debugging the output noise from a switching mode power supply. The next video will be on measuring and debugging high frequency noise on your output voltage, so stay tuned!