L-1 PSU measurements

L-1 PSUs ripple & noise measurements.

I used QuantAsylum https://quantasylum.com QA401 Analyzer and QA471 Amplifier.

Method is described here https://quantasylum.com/blogs/news/characterizing-noise-part-3

Measurements were made with 20 Ohm load at each rail of each busboard, and with no load.

Connection schematic:

I measured L-1 "New" Ultra Power System PSU, TPS7A47 based, and "Old" Power System PSU, LD1084 based.

I considered 30dB input gain from the amplifier into analyser settings:

Plot 1. PSU power off. Plot shows analyzer noisefloor:

NEW PSU

Plots with no load show about 6 uV RMS ripple & noise. When TPS7A47 has 4 uV RMS https://www.ti.com/product/TPS7A47 Good result!

Plot 2. New PSU, +12V rail, no load.

Plot 3. New PSU, -12V rail, no load.

Plots with 20 Ohm load at each rail of each busboard show under 10 uV RMS ripple & noise.

Plot 4. New PSU, +12V rail, 20 Ohm load.

Plot 5. New PSU, -12V rail, 20 Ohm load.

OLD PSU

Plots with no load show more than 30 uV RMS ripple & noise. About 15 dB higher noisefloor than New PSU.

Plot 6. Old PSU, +12V rail, no load.

Plot 7. Old PSU, -12V rail, no load.

Plots with 20 Ohm load at each rail of each busboard show at +12V about 90 uV RMS, at -12V 34 uV ripple & noise. About 20 dB and 15 dB higher than New PSU.

There in New PSU each busboard has own PSU. Here in Old PSU both busboards supply from the same PSU. So, total load will be 2 || 20 Ohm = 10 Ohm load.

Plot 8. Old PSU, +12V rail, 2 || 20 Ohm = 10 Ohm load.

Plot 9. Old PSU, -12V rail, 2 || 20 Ohm = 10 Ohm load.