Empathy List Archives

MS

Mark Sims

Wed, Aug 31, 2016 7:01 PM

You have to be careful choosing a linear regulator to clean up a switching supply. Many just wind up passing the noise through. Pay attention to the noise, PSRR and CMRR vs frequency specs, etc

Take a look at the "voltage regulation" section of that home built VNA page for an example:
http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html

You have to be careful choosing a linear regulator to clean up a switching supply. Many just wind up passing the noise through. Pay attention to the noise, PSRR and CMRR vs frequency specs, etc Take a look at the "voltage regulation" section of that home built VNA page for an example: http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html

CS

Charles Steinmetz

Wed, Aug 31, 2016 7:16 PM

Mark wrote:

You have to be careful choosing a linear regulator to clean up a switching supply. Many just wind up passing the noise through. Pay attention to the noise, PSRR and CMRR vs frequency specs, etc

Precisely the reason to avoid switchers entirely and use linear-only
voltage regulators to power noise-sensitive circuits. As I mentioned
before, I had to use two stages of well-designed linear regulation to
make any switching supply acceptable (at a time-nuts level) for use with
a Tbolt.

Best regards,

Charles

Mark wrote: > You have to be careful choosing a linear regulator to clean up a switching supply. Many just wind up passing the noise through. Pay attention to the noise, PSRR and CMRR vs frequency specs, etc Precisely the reason to avoid switchers entirely and use linear-only voltage regulators to power noise-sensitive circuits. As I mentioned before, I had to use two stages of well-designed linear regulation to make any switching supply acceptable (at a time-nuts level) for use with a Tbolt. Best regards, Charles

J

jimlux

Wed, Aug 31, 2016 7:36 PM

On 8/31/16 12:01 PM, Mark Sims wrote:

You have to be careful choosing a linear regulator to clean up a switching supply. Many just wind up passing the noise through. Pay attention to the noise, PSRR and CMRR vs frequency specs, etc

Indeed..
a lot of monolithic regulators have a remarkably low cutoff frequency.

On the other hand, the LT3042 has 80 dB PSRR up to a few MHz. 55dB at
10 MHz.

Take a look at the "voltage regulation" section of that home built VNA page for an example:
http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

On 8/31/16 12:01 PM, Mark Sims wrote: > You have to be careful choosing a linear regulator to clean up a switching supply. Many just wind up passing the noise through. Pay attention to the noise, PSRR and CMRR vs frequency specs, etc > Indeed.. a lot of monolithic regulators have a remarkably low cutoff frequency. On the other hand, the LT3042 has 80 dB PSRR up to a few MHz. 55dB at 10 MHz. > Take a look at the "voltage regulation" section of that home built VNA page for an example: > http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. >

EC

Edesio Costa e Silva

Wed, Aug 31, 2016 8:07 PM

Have a look at Linear Application Note 101 by Jim Williams: Minimizing
Switching Regulator Residue in Linear Regulator Outputs
http://cds.linear.com/docs/en/application-note/an101f.pdf

Edésio

On Wed, Aug 31, 2016 at 07:01:44PM +0000, Mark Sims wrote:

You have to be careful choosing a linear regulator to clean up a switching supply. Many just wind up passing the noise through. Pay attention to the noise, PSRR and CMRR vs frequency specs, etc

Take a look at the "voltage regulation" section of that home built VNA page for an example:
http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html

Have a look at Linear Application Note 101 by Jim Williams: Minimizing Switching Regulator Residue in Linear Regulator Outputs <http://cds.linear.com/docs/en/application-note/an101f.pdf> Edésio On Wed, Aug 31, 2016 at 07:01:44PM +0000, Mark Sims wrote: > You have to be careful choosing a linear regulator to clean up a switching supply. Many just wind up passing the noise through. Pay attention to the noise, PSRR and CMRR vs frequency specs, etc > > Take a look at the "voltage regulation" section of that home built VNA page for an example: > http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html

CC

Chris Caudle

Wed, Aug 31, 2016 8:46 PM

On Wed, August 31, 2016 2:16 pm, Charles Steinmetz wrote:

I had to use two stages of well-designed linear regulation to
make any switching supply acceptable (at a time-nuts level) for use with
a Tbolt.

Did you try any passive filters between the switchers and linear regulators?

--
Chris Caudle

On Wed, August 31, 2016 2:16 pm, Charles Steinmetz wrote: > I had to use two stages of well-designed linear regulation to > make any switching supply acceptable (at a time-nuts level) for use with > a Tbolt. Did you try any passive filters between the switchers and linear regulators? -- Chris Caudle

CS

Charles Steinmetz

Wed, Aug 31, 2016 9:38 PM

Chris wrote:

Did you try any passive filters between the switchers and linear regulators?

Yes, I always use passive filters on the outputs of switching
regulators. As others have posted, it's not just a matter of the
conducted noise on the supply rail -- switching noise propogates on the
ground bus, and it is also radiated and coupled into downstream stages,
including downstream power supply buses. That is, it can very easily
bypass whatever filtering you put in the direct conduction path.

Best regards.

Charles

Chris wrote: > Did you try any passive filters between the switchers and linear regulators? Yes, I *always* use passive filters on the outputs of switching regulators. As others have posted, it's not just a matter of the conducted noise on the supply rail -- switching noise propogates on the ground bus, and it is also radiated and coupled into downstream stages, including downstream power supply buses. That is, it can very easily bypass whatever filtering you put in the direct conduction path. Best regards. Charles

time-nuts@lists.febo.com

Anybody want a Thunderbolt power supply?