[time-nuts] Re: HP z3816a DC power supply DIP switches

[Lux, Jim]

On 3/2/22 6:00 AM, paul swed wrote:
> As Ed stated Switchers feeding switchers can be problematic. What I found I
> had to do was put a relay in series with a slight time delay. This allows
> the primary switcher to come up and then gets slammed into the secondary
> SPS. Could be a fet/transistor switch. So linear is preferable.
> Regards
> Paul


Sequencing is important - You can also use the "shutdown" input on the 
cascaded switcher with an RC time delay (maybe), or an explicit timer 
(555 or counter or 8 pin FPGA programmed appropriately or...)

The challenge comes when your first stage switcher needs a minimum load 
to work properly - Shutting off the secondary switcher removes the load. 
A resistor might work, if you're not total power consumption constrained.

But yes, since switchers are "constant power" devices, they draw a lot 
of current when the input is low voltage, so you can get into a 
motorboating problem with the first one in the chain's overcurrent 
protection (or just regulation).