Transient testing rig for 3720W power supply with DCDC modules.

Hi,
We wish to do Transient testing of our 3720W power supply.
No_load to Full_load to No_load…..

Please could you advise if there is a quicker/cheaper way to do this than the attached? We need the three load switchs to switch at the very same instant.

The power supply uses Vicor DCDC modules.

you should be able to move the output side of the opto-isolators directly to the gate drive control instead of putting in the extra switch step.
one of the wall warts powering the switches could also power the debounce
you could drive the opto-isolators in series rather than parallel
debounce can be accomplished by a 74121 non-retriggering one shot whose output goes to a toggle flip flop

a simple latching 3PST relay with some reasonable isolation between the sections would do also
NO position for ON, energized for off

your circuit does not have the ability to turn one or two load bank(s) off while the others on
do you need/want that capability?

what is the tolerance on "the very same instant"?
what is the isolation between GND_A, GND_B and GND_C etc?

Very little isolation needed..they are all basically kind of grounded to the same node.....volt drops due to heavy current flows permitting.

yes we only need to switch all three at once

debounce can be accomplished by a 74121 non-retriggering one shot whose output goes to a toggle flip flop

Click to expand...

Thanks, yes i'd prefer if it was non-retriggerable...but they are not as easy to source.
Would you agree that in fact, it can actually be a re-triggerable one?...it just means the "One-shot" pulse will be a bit longer?

eg
https://www.ti.com/lit/ds/symlink/sn54ahct123a.pdf

It seems over-elaborate for what is basically a bank
of resistor-to-ground shunts.

There's an outfit selling "load slammer" products
for this role. I made my own about a decade ago.
Not as large (only needed 20A and 5V) but you
can make a larger version in the same style. The
basics are attached, modify to suit.

The MOSFET driver scheme looks pretty crappy.
You say you want them all at the same time but
time domain performance looks like it will be
poor and variable. Rather than giving yourself
the added problem of driving a high side load
switch to connect the static loads, why not
switched shunt loads?

Thanks, though they wish to do it with a high side fet, more on this later.

Do you agree that the switched FETs must have gate_source resistors for ESD and Damping reasons?...
Our contractor wants to use an LTC7000 to switch on the high side NFETs. However, we think this is unwise, because the LTC7000 can only supply 15uA to the high side FET drive….so this means that Gate_source resistors of 10k cannot be used with the fets, as the LTC7000-1 wouldn’t be able to supply them. The load bank fets are on improvised bits of stripboard and there will be wiring inductance, and as such, we believe we need gate_source resistors to damp ringing of the gate_source voltage. Also, without gate_source resistors, the FETs will be liable to EMC damage as they are handled.
We are working in an office, as we do not have a lab….and the office carpet is not ESD safe.

LTC7000-1
https://www.analog.com/media/en/technical-documentation/data-sheets/ltc7000-7000-1.pdf