John Larkin a écrit :
On Fri, 30 Mar 2007 19:10:36 +0200, Fred Bartoli
r_AndThisToo wrote:

John Larkin a écrit :

What do you do with your 24V?

It powers some little logic-level shifters, which I posted about a
couple of weeks ago. They take a 3.3 volt FPGA output and shift it up
about 0.8 volts to drive some 5-volt CMOS logic. Without the shift,
the cmos gadgets have asymmetric prop delays and high static power
dissipation. Current required is only about 50 uA per shifter.


Ahmm, remember. So the bit of extra noise probably matters not.

Referencing C68 and C73 to GND will couple less 12V noise to the 24V
output. OK there's the filter and zener, but it's easy and you're not
doing kVs.

But we get a free extra 12 volts out of the C-W this way, which we
need for decent zener regulation. If we grounded the low side, we'd
need another multiplier section.


Nope. You don't ground the diodes, just the capacitors. Then you obtain
the same output voltage. C68 and C73 are not flying.

Some switchers will freak without that R99 thing.


Sure. Those with CM feedback and those with switch current limit.


--
Thanks,
Fred.