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darcyrandall2004 Post subject: Isolation with a switch mode regulator
Posted: Wed Aug 08, 2007 8:11 am Colonel Joined:
Tue Feb 27, 2007 6:16 am Posts: 46 Hello. It is true
that the switch mode regulator produces alot of RF noise due to the
switching action Does the switching action of the regulator
isolate its output from noise on the supply input? If at no time the
output is directly connected to the input, then surely this is the case.
My latest transmitter project is suffering from noise creaping
in through the supply. I thought perhaps I could remove the noise creeping
in by use of a switch mode regulator and then deal with the switch mode
regs noise. What do you think? Cheers Darcy Randall,
Perth Western Australia Top IR Post subject:
Posted: Fri Aug 10, 2007 5:56 pm Site Admin Joined:
Mon Jun 27, 2005 2:02 pm Posts: 373 Location: Germany Hello,
I think that this is a bad idea to provide the direct power
supply to almost any RF circuit from a SMPS. The best practice
is to use an SMPS followed by an LDO. By this you provide both efficiency
and long battery life and a clean, noise-free power supply to your RF
circuitry. Quote: Does the switching action of the regulator
isolate its output from noise on the supply input? As far
as I know, the answer to that is no. Top darcyrandall2004
Post subject: Posted: Tue Aug 14, 2007 1:18 am Colonel
Joined: Tue Feb 27, 2007 6:16 am Posts: 46 Hello IR.
A 12V switch mode reg supplies a number of linear regulators that
supply my RF circuits. I will replace the Linear regs with LDO's
and hopefullly this will solve my problems. Cheers, you information
has been of great value. Darcy Randall, Perth, Western Australia
Top IR Post subject: Posted: Tue Aug 14, 2007 2:28
am Site Admin Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373 Location: Germany You are welcome. If:
Quote: A 12V switch mode reg supplies a number of linear regulators
that supply my RF circuits. Then I think you should add some
more decoupling capacitors and/or beads to the supply rails and also
check the PCB layout. Top darcyrandall2004 Post
subject: Posted: Tue Aug 14, 2007 6:44 am Colonel
Joined: Tue Feb 27, 2007 6:16 am Posts: 46 Hello IR.
Do LDO's typically have superior noise performance compared to the
standard typical linear voltage regulators? Top IR
Post subject: Posted: Tue Aug 14, 2007 10:27 am Site Admin
Joined: Mon Jun 27, 2005 2:02 pm Posts: 373 Location:
Germany From my experience they do have better noise performance.
There are also many LDO's available (e.g. from Micrel: www.micrel.com)
that have a dedicated pin used for extendedl noise suppression by connecting
an external capacitor. Please check Micrel's website for more
information. Good luck!! If you need more help, please let me
know. Posted 11/12/2012
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