Power supply drift battle: Keysight B2962A vs. MPJA 9623PS - Page 1
Forum section: electronics / testgear

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 17, 2020, 05:34:41 am
content: On the left: Keysight B2962A 6.5 Digit Low Noise Power Source designed by AgilentOn the right: Generic MPJA 9623PS Analog triple power supply designed by unknown company10 V output is recorded with a gain of 1000 and a bandwidth of 1 Hz for 200 seconds relative to a stable 10 V source (using AlphaLab LNA10 amplifier and SRS DC205 source)And the winner is: MPJA 9623PS with less than 100 uV pp noise, while B2962A just meets its specs of 150 uVpp noise.I'll have a more in-depth review of B2962A, this is just a teaser.

author: Zucca
author_rank: Unknown
timestamp: August 17, 2020, 06:53:29 am
content: mmmm...

author: exe
author_rank: Unknown
timestamp: August 17, 2020, 09:30:51 pm
content: Is Keysight a switching-mode power supply? (probably with linear post-reg).

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 17, 2020, 10:15:48 pm
content: Yes, its a switching mode supply, the RMS noise is exactly 3 mVrms 10-20 MHz, as the specs say. They make a big deal of additional low-pass filters that one can purchase (for $1k-2$k !) to filter out the switching noise. But of course it doesn't reduce the low-frequency flicker noise.

author: TimNJ
author_rank: Super Contributor
timestamp: August 18, 2020, 01:11:36 am
content: That's interesting, though at first glance, I thought you were just showing the output ripple.But then noticed the time-base. (Although, it says T: 24.00s..is this just the zoom?) The signal on the scope is the error voltage relative to the Stanford DC205, right?It's interesting how quickly the error voltage can change on the Keysight, while the linear supply seems much more reluctant to change quickly. Keysight almost has a periodic nature to it. I wonder what reference/error amplifier the Keysight uses and if it's in a sub-optimal location (thermally related?).

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 18, 2020, 08:13:28 am
content: First plots have 10sec/div scale and DC coupling with 10 V subtraction. Later plot has 2 usec/div scale and AC coupling.B2962 has an LM399 reference, so the flicker noise must be from something else. It could be interference between multiple unsynchronized switching power supplies.

author: Zucca
author_rank: Unknown
timestamp: August 20, 2020, 07:14:20 am
content: Are you using Coax cables from PSU to the scope?

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 20, 2020, 07:38:05 am
content: Yep, even got a nice double-shielded cable. One can also switch the B2962 from grounded to floating and add 50 Ohm load, which changes the shape of the switching ringing a bit.

author: Zucca
author_rank: Unknown
timestamp: August 20, 2020, 07:41:33 am
content: Interesting. Next step is a shielded box or try to be in a quiet EMI place....

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 24, 2020, 05:19:59 am
content: Here is a comparison of voltage spikes on MPJA 9623PS (similar to HY3003D), Rigol DP832 and Keysight B2962. All are taken with 5V output connected by a coaxial cable and loaded at the scope with 50 Ohm terminator. For MPJA supply similar spikes appear with the supply shut off, so that's a measure of interference (it helps to shut down my laptop while taking this data). For Rigol supply the spikes appear at some point as it starts up and are similar with the output is on or off, so it must be some clock. On B2962 the spikes also appear and change shape as it goes through the start-up sequence.MPJA 9623DP832B2962