[time-nuts] newbie question Thunderbolt supply

Bob Camp lists at rtty.us
Sun Aug 26 08:07:55 EDT 2012


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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