Hi One gotcha on your proposed circuit:
The -12 supply is used for the RS-232 and the DAC that controls the OCXO. I suspect you can indeed mess things up with negative supply when the supply gets within some magic range of the DAC output. What that range is - no idea. Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Ed Palmer Sent: Monday, April 26, 2010 5:25 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Thunderbolt Power Supply Question Hi Robert, Robert Atkinson wrote: > Hi Ed,The better quality "industral" power supplies normally have a regulator for each rail. Some specifications will put a minimum load requirement on the primary supply though. You're right that better quality power supplies have regulation on all outputs. I don't think I'm comfortable using any other kind on a Thunderbolt. I was just surprised to see some 'close enough' power supplies in use. > I've been looking at a simple supply for my TBolt. I wanted to avoid switchers or multiple transformers and think I have a solution. I propose a 15V 30VA toroidal transformer (if dual secondary windings, connect in parallel) . This feeds a full wave bridge and capacitive input filter followed by a 12V linear regulator (your choice, I was looking at a LM317T). It also feeds a half wave rectifier and capacitive input filter followed by a 5V linear regulator. For the -12V there is a capacitively coupled voltage doubler feeding another regulator. I've attached a sketch of the circuit I used to simulate this arrangement. R1, R3 and R5 represent the 12, 5 and -5V loads for the simulation. I think this gives a good repeatable solution using standard parts. I've plenty of odd > multi-winding transformers that I could have used, but that would not have helped others. I hope to get it built this weekend. I was thinking of something similar, but I've never been a fan of half-wave rectification. I was thinking of running the +5 supply off the output of the +12 supply. Total current for +5 and +12 is less than 1 amp at startup and less than 0.5 amp normally. Power dissipation in the 5V regulator will only be about 2 watts. For the -12 supply, you could just use a max232 and pull off the -V from the capacitor. After all, it's just going to be used for RS-232. Ed > > Robert G8RPI. > --- On Mon, 26/4/10, Ed Palmer <[email protected]> wrote: > > From: Ed Palmer <[email protected]> > Subject: [time-nuts] Thunderbolt Power Supply Question > To: "Time Nuts Mailing List" <[email protected]> > Date: Monday, 26 April, 2010, 9:02 > > Many low cost triple output power supplies are designed to power digital circuits (e.g. +5V) with maybe some RS-232 or analog circuitry (+- 12V). Since the only 'important' voltage is +5, that's the only voltage that's regulated. The others are designed to be within maybe 5% up to the rated load. I see various power supplies on fleabay that are sold for use with the Thunderbolt that seem to fit this model. > > In the Thunderbolt the +12 runs the oscillator. Won't an unregulated, but relatively steady, +12 supply degrade the performance of the oscillator or does the Tbolt have a built-in regulator to deal with this? > > Ed > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
