Re: Slow strart circuit for PS.

I would appreciate it if you would check my work on this circuit I am
considering.  I pulled it from a post by Paul Taylor.  It uses a
resistor, a zener and the coil of a 24V SPST-NO relay in series across
the output rails of the PSU.  The relay when closed shorts out a
current limiting resistor on the primary.

The PSU is for a Gain-Clone type amp with working voltage of 
+-34V.  That 68V across the rails under load,
and 73V no-load.

I have found a 24V relay with the following specs:

1440R, 16.7mA, 19.2V Pickup, 1.2V Dropout, 36V max.

19.2V / 1440R = 0.0133A (pickup current).

A 28V zener seems to be about right.

So, 68 - ( 24 + 28 ) = 16.  
16V for the resistor to drop.

16 / 0.0167 = 958.  Call it 960 Ohms.

So, pick up rail voltage will be:

( 960 * 0.0133 ) + 28 + ( 1440 * 0.0133) = 59.9

Call it +-30V.  88% of working voltage.

Now, for max dissipation:

73 - 28 = 45 and 45 \ ( 1440 + 960 ) = 0.019A no-load

0.019 * 1440 = 27.34V drop across the coil, good!

0.019^2 * 960 = 0.35W  1 Watt resistor should do, aye?

And 5W for the zener just to be safe.