DC-DC converters: seeking the cleanest possible output

Thread Starter

Zurn

Joined Mar 4, 2019
79
Hi everyone,

I'm wondering if anyone on here can recommend a quality DC-DC converter for me. I'm currently using this one to convert an input ranging from 12-16V (via four lithium batteries) to 24V. My output can actually be anywhere between 18-36V. Output current is in the milliamps range.

The DC-DC converter is being used to give the appropriate power to an array of underwater microphones (hydrophones), so I need the signal to be as clean as possible. The one listed above is pretty good (especially after adding the appropriate filters - namely a 3.3 uF over the output, followed by a low pass RC filter to block anything above 15kHz), but there's still a bit of line noise/harmonics that end up in the acoustic data which isn't present from a bench power supply.

I imagine getting an output from a *battery pack-charge controller-dc/dc converter* network that's as clean as a simple bench power supply is a tall order. But if anyone can recommend anything that comes close, I'd love to know.
 

crutschow

Joined Mar 14, 2008
25,271
Switching current spikes can get into the ground which are difficult to suppress.
If you can isolate the battery and converter ground from the load ground, then a common-mode filter at the converter output may help.
I had to do that for a converter I built along with an LC filter at the converter output, where I needed to reduce the noise down to the tens of microvolt region.

What is the noise level at the converter output?
 

ElectricSpidey

Joined Dec 2, 2017
1,197
I normally don't ask this kind of question, so please forgive me.

Is there a good reason you can't use more batteries to get into the range you need?
 

ci139

Joined Jul 11, 2016
1,684
the shunting linear regulator was the "old" method to get such output (you provide a bit over the required output current and shunt off from it what the load is not consuming)
if you only need few mA output that is easy to achieve . . . the efficiency however is quite low for such
 

Thread Starter

Zurn

Joined Mar 4, 2019
79
If you can isolate the battery and converter ground from the load ground, then a common-mode filter at the converter output may help.
Unfortunately the load sends a signal into a microcontroller that's powered by the battery, so the grounds need to be tied otherwise there's a lot of noise in the audio recordings.

What is the noise level at the converter output?
Without any filtering, the noise is in the range of 50 mVpp. It mostly shows up in my acoustic data in realm of 12kHz, with harmonics in the 24kHz, 36kHz, 48kHz, etc. A single 100uF cap over the output gets it as low as 10 mVpp, but still too much of that harmonic nonsense in the data.

Is there a good reason you can't use more batteries to get into the range you need?
Yep, that reason is: weight!
 

crutschow

Joined Mar 14, 2008
25,271
Unfortunately the load sends a signal into a microcontroller that's powered by the battery, so the grounds need to be tied otherwise there's a lot of noise in the audio recordings.
Okay, then you might try common-mode chokes at both the input and output (with the supply ground isolated by the choke) and possible an LC filter after that.
 
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