[time-nuts] Thunderbolt Power Supply Question

Robert Atkinson robert8rpi at yahoo.co.uk
Mon Apr 26 15:06:36 EDT 2010

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. 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. 
Robert G8RPI.
--- On Mon, 26/4/10, Ed Palmer <ed_palmer at sasktel.net> wrote:

From: Ed Palmer <ed_palmer at sasktel.net>
Subject: [time-nuts] Thunderbolt Power Supply Question
To: "Time Nuts Mailing List" <time-nuts at febo.com>
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?


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