[time-nuts] Anybody want a Thunderbolt power supply

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Sep 1 00:07:32 EDT 2016

Just split  the 1uF coupling cap into 2x 2u2 in series in the Cuk dc-dc converter add a 1:1 transformer (should be small at 2MHz) between the pair of 2u2 caps to produce a floating output and use an LT3042 as a post regulator.With a mains transformer input supply a separate isolated winding for the -12V allows an LT3042 to be used for the negative regulator.
I have a quad LT3042 PCB that I must get around to assembling.One potential issue with the LT3042 is the relatively high noise at low frequencies when the capacititve bypassing of the resistor that sets the output voltage is ineffective.


    On Thursday, 1 September 2016 3:37 PM, Charles Steinmetz <csteinmetz at yandex.com> wrote:

 Bruce wrote:

> Low noise regulators for the +12V and +5V outputs would also be useful.

Very true.  By focusing on the -12v supply, I did not intend to suggest 
that low noise is unimportant on the +12v and +5v supplies.

The suggestion to use LT3042s is a good one, but note that it has an 
output current rating of 200mA.  The Tbolt needs ~250mA at +5v, and 
~700mA at +12v [at startup -- but only ~150mA steady-state, depending on 
ambient temperature].  LT3042s can be used in parallel, so two of them 
for the +5v supply and four of them for the +12v supply would be 
required.  That isn't so bad for the +5v supply, but seems excessive for 
the +12v supply (particularly when three of the four are needed only 
during warmup from cold).

The LT3088 and LT3080 will deliver 800mA and 1.1A, respectively, with 
low noise (but not as low as the LT3042).  One of those might be a 
better choice for the +12v supply.  Similarly, the LT3085 can deliver 
500mA, so one of those could be used for the +5v supply.

Finally: Linear Technology -- Where is our negative-voltage complement 
to the LT3042?

Best regards,


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