[time-nuts] Anybody want a Thunderbolt power supply

Joakim Langlet joakim.langlet at seaview.se
Thu Sep 1 03:44:26 EDT 2016

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.


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