[time-nuts] newbie question Thunderbolt supply

EWKehren at aol.com EWKehren at aol.com
Sun Aug 26 12:29:25 EDT 2012


Having played with most combinations I could think of including the 1764  
there is a lot to be said about the stability of the 7812 and mounting every  
thing on one plate since power dissipation of the OCXO decreases with 
increase  in ambient temperature and current fluctuation is minimal since input 
from the  switcher is very stable and 78 tabs are bolted to the aluminum 
plate. I am  staying with 5 V regulator fed by 7812. 
Using battery backup changes every thing and I use a switcher for the 5V  
followed by a LDO and a separate switcher for the 12 V again followed by a  
LDO.
Bert Kehren
 
 
In a message dated 8/26/2012 8:09:03 A.M. Eastern Daylight Time,  
lists at rtty.us writes:

Hi

The only real disadvantage of a 7812 / 340-12 is it's  relatively high drop 
out voltage compared to a 1764 (or similar). Stability of  any of them will 
be impacted more by thermal issues than anything else. The  colder you can 
keep the 12V regulator, the more stable it will be. The +12 is  by far the 
most sensitive supply line on the TBolt.

Bob

On Aug  26, 2012, at 6:46 AM, EWKehren at aol.com wrote:

> Having played with  several solutions I found the best is a 12 V 1 A  
> switcher with  the output voltage increased to 15 V, check the capacitors 
and if   
> necessary replace with 25 V. I laid out a PC board that has a TC7662A  
> inverter  followed by a 79L12.  Also on the board is a 7812  followed by 
a 7805.  
> Putting them in series gives me good  thermal distribution. In my opinion 
every 
> thing else is an overkill.  
> Working with very low noise PLL's I have found that getting rid of  
switcher 
> noise is much easier than 60 Hz.
> There are other pin  compatible alternatives to the TC7662A, even a 555 
will 
> work, just  more components.
> Bert Kehren 
> 
> 
> In a message  dated 8/25/2012 8:10:07 P.M. Eastern Daylight Time,  
>  lists at rtty.us writes:
> 
> Hi
> 
> The easy way to do  a TBolt supply is to start with  something between 15 
> and 18  volts.  Regulate down to 12 and 5 with linear  regulators. 7805's 
 are 
> fine for the +5. Something like a LT1764 might be  better  for the +12. 
The 
> -12 supply is very low current and does not  matter  much. People have 
had good 
> luck with voltage inversion  chips off the +15 and  then something like a 
> 79L12.
>  
> Bob
> 
> On Aug 25, 2012, at 6:41 PM,  Edgardo  Molina <xe1xus at amsat.org> wrote:
> 
>> Dear  Chris,
>> 
>> Good afternoon. I am in the process of  mounting my TBolt to a 2U 19"  
> rack enclosure and was looking  for a decent power supply. I found the 
Cisco 
> unit and I am ordering a  couple of them just in case. It would really be 
nice  
> if I could  have access to the diagram of the upgrade you did on yours to 
 
>  recreate the same performance from the Cisco unit. Please do not feel   
> compromised if it is difficult to share. I didn't mean to be rude and  if 
my  note 
> causes you any discomfort please kindly disregard  it. I jumped into the  
> thread because of experiencing the same  doubts as the originator of it.  
>> 
>> Redondo Beach?  I love visiting there whenever visiting my  brother who 
> lives in  Rancho Palos Verdes. I would invite you lunch anytime  just for 
the  
> pleasure of meeting you in person.
>> 
>>  Thank  you.
>> 
>> Regards,
>> 
>>  
>> 
>> 
>> 
>> Edgardo Molina
>>  Dirección IPTEL
>> 
>> www.iptel.net.mx
>>  
>> T : 55 55 55202444
>> M : 04455   20501854
>> 
>> Piensa en Bits SA de CV
>>  
>> 
>> 
>> Información anexa:
>>  
>> 
>> 
>> 
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>> 
>> 
>> 
>>  
>> 
>> On Aug 25, 2012, at  3:26 PM, Chris Albertson  
<albertson.chris at gmail.com> 
> wrote:
>> 
>>>  On Sat, Aug 25, 2012 at 1:06 PM, Jerry <jsternmd at att.net>   wrote:
>>> 
>>>> I am using a Cisco supply 3  voltage supply  for the T-bolt.  Is there 
>  any
>>>> performance loss if the  +12vdc rail and the  -12vdc rail are off by a 
> few %
>>>> in opposite   directions, e,g  +11.7 vdc and -12.3vdc ?
>>>>  
>>>> The true nuts here on the time nuts list will tell you  that  the 
noise 
> from
>>> a switching power supply is  bad and that you need a  regulated linear 
> power
>>>  supply.   But for most practical  purposes the Cisco supply is  a good 
> one.
>>> Being only slightly nuts   myself.  I use the Cisco   supply but I 
built a
>>>  small power adaptor board with matching connectors and some "pi"   
> filters
>>> made with RF choke and capacitors.  I  realy don't  thing the filters 
are
>>> needed but I wanted a  connectorized  installation and a small choke 
was 
>  as
>>> easy to solder in as a  length of  wire.
>>> 
>>> -- 
>>> 
>>>  Chris  Albertson
>>> Redondo Beach,  California
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