On 2016-09-01 05:35, Charles Steinmetz wrote:
Bruce wrote:
Low noise regulators for the +12V and +5V outputs would also be useful.
Very true. By focusing on the -12v supply, I did not intend to
suggest that low noise is unimportant on the +12v and +5v supplies.
The suggestion to use LT3042s is a good one, but note that it has an
output current rating of 200mA. The Tbolt needs ~250mA at +5v, and
~700mA at +12v [at startup -- but only ~150mA steady-state, depending
on ambient temperature]. LT3042s can be used in parallel, so two of
them for the +5v supply and four of them for the +12v supply would be
required. That isn't so bad for the +5v supply, but seems excessive
for the +12v supply (particularly when three of the four are needed
only during warmup from cold).
The LT3088 and LT3080 will deliver 800mA and 1.1A, respectively, with
low noise (but not as low as the LT3042). One of those might be a
better choice for the +12v supply. Similarly, the LT3085 can deliver
500mA, so one of those could be used for the +5v supply.
Finally: Linear Technology -- Where is our negative-voltage complement
to the LT3042?
Best regards,
Charles
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I guess that you could say that I like soldering and the following
suggestions might not appeal to everyone but it would give you a very
clean supply for your Thunderbolts.
Since I tend to ignore the the bottom line cost and do things more
complicated than necessary, you might not agree with my suggestions. On
the other hand, my designs generally work well.
In the power supply of the GPSDO that I am building right now, I have
used DC/DC converters for all voltages, but I set the output voltage
slightly over the wanted voltage. I start off with +15V input from a
AC/DC supply (purchased).
For +5V, I have used a TPS62160 (TI) with the output voltage set to +5.6V.
Then low dropout (LDO) regulators are used to get to +5V. The LDO
filters out most the switching noise. The TPS62160 delivers up to 1A and
can be fitted with all surrounding components in about 16x10mm.
In my case, I use lower currents at several points of load and use a
TPS7A4901 at each of these. The active GPS antenna LNA is one of the
consumers. It works well.
For a Thunderbolt, I guess that the TPS7A4501 could be used as the post
switch regulator.
To generate +12V, I have used TPS54332 which can deliver up to 3A. In my
case, the +12V doesn't need to be filtered, but if needed a +12V LDO
(the TPS7A4501 can used here too) is used as a follower, starting with a
switch output voltage at maybe +12.6V.
For a negative supply, I have used a LT3462A to invert the voltage. This
could be used to get -12.6V output regulated by a TPS7A3001 down to -12V.
The good thing with this approach is that it generates very little
excess heat and the output voltages could have noise levels in the order
of maybe 50uV or less.
I will try to get my act together and create a web site where I can
publish a bit about my over-complicated GPSDO design.
My problem is that I prefer soldering and programing and I am not the
best web designer.
Once it is up, I will publish a link on the list.
BR/
Joakim
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