[time-nuts] Need help with transformer core

Bob Camp kb8tq at n1k.org
Mon Sep 1 19:41:26 EDT 2014


Keep in mind that the supply in question is likely running in the vicinity of an atomic clock. Things like stray magnetic field are pretty important if that’s the case …. It’s also quite possible that the original supply had some “supply dies not the tube” features built into it. 


On Sep 1, 2014, at 6:54 PM, Chris <syseng.greenfield at btconnect.com> wrote:

>> Thanks for the inputs everyone,
>> One of the direct replies got me the data I needed!
>> Alex, I'd like to by it that way, but A 24VDC input 3700VDC output at 4ma
>> does not seem to be available!
>> Cheers,
>> Corby
> Hi Corby,
> The way I would approach the problem would be not ask where to get a given pot core, but how do I generate 3700v @ 4mA, starting from scratch. I would limit the secondary winding count and use a voltage multiplier, Cockroft-Walton style to bring the volts up to the required level. 22w is not an insignificant power level, so I would use a switch mode regulator chip, driving a pair of small power mosfets, with a switching frequency 100KHz or higher to keep the magnetics, winding turns count and the multiplier (Use polypropylene) caps small. Lower voltage at the secondary also makes it easier in terms of rectifier diode selection. All the info is in the chip manufacturers application notes. and suggest Unitrode as a starting point. Have done a few of these in the past and they are pretty strightforward. Even the magnetics are covered by the core manufacturers data books. A pair of small E cores sounds sounds about right and will have matching moulded bobbin options with tags. Pot cores are a pita in comparison and awkward to wind / terminate using foil, which you really need when a primary winding may only have 4 to 8 turns, yet be carrying amps.
> The other point is that I would never use any switcher, however good it's claimed to be, to drive sensitive analog electronics. While many of the cheap switcher modules are fine with stable line and load, the transient response ids often dreadful and they take some time (milliseconds) to recover with step function change at either. Such instability can damage driven electronics as well. While it's common to use a switcher for initial conversion, that would always be followed by monolithic linear regulators, which typically have output noise levels of mV. For example, say you have an input voltage of 18-32v and a required output of 12v at 1A, an initial switch mode regulator to convert to 15v, then even a 7812 or similar to lose the final 3 volts...
> Regards,
> Chris
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