My Thunderbolt has a turn-on transient of as much as 750 mA on the +12V supply due to the OCXO oven. Be careful not to design to the steady-state current.
David At 06:48 AM 4/21/2008, you wrote: >David C. Partridge wrote: > > I'm in the process of buying a Thunderbolt, and will need to > provide it with > > some volts. > > > > I sat down over the weekend to design a linear supply for it. Initially > > things looked OK using a 12-0-12 transformer, and a few IC voltage > > regulators, but then I did some worst case design and dissipation analysis, > > and found that I needed to use a 15-0-15 transformer to allow for a -10% > > mains variation, and add pass transistors and lots of heat sinking to all > > the regulators to allow for a +10% mains variation. > > > > Add to that transformer regulation issues (over-size transformer), the time > > to design the PCB and the cost of getting it made, and things started to > > look expensive :-(. > > > > I can probably source a linear supply on eBay, but these are typically > > pretty large and heavy. For example: eBay item number 330201077319 > > > > So is it reasonable to use an SMPS, and add additional filtering to the > > output? Typically these talk in terms on 150mV ripple & noise which I need > > to reduce by a factor of ten or better. > > > > If you have been there, done that, I'd be interested to hear what you did. > > > > Thanks > > Dave Partridge > > >David > >You may be able to find an OEM open frame linear supply with foldback >current limiting that is suitable. >Most of these (Condor, Calex, etc) tend to use 723 regulators with >2N3055 series pass elements. > >Alternatively since you only need 25mA @ +12V, 25mA @ -12V and 300mA >@+5V (if I'm reading the right datasheet) you can use a much lower >voltage output transformer suited to the 5V regulator and use a pair of >voltage doublers or triplers to feed your 12V regulators. >A 7.5- 0 - 7.5V transformer should suffice (if you use low dropout >linear regulators), and the total linear regulator dissipation should >only be a few watts in normal operation. > > >Bruce > >_______________________________________________ >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.
