10 Jun
2010
10 Jun
'10
6:23 p.m.
Philip Pemberton wrote:
"Dummy load / PSU tester" is right on the
top of my "stuff to build" list :)
I just have to figure out how to do the "constant power" regulation. I
want to go with opamps for the regulation (faster response time to V/I
transients) and a D/A to set the current/voltage/power 'setpoint'.
Constant-voltage is easy (drain enough current to bring V_in down to the
setpoint).
Constant-current is just as easy (drain a fixed current).
Constant power involves a bit of maths (a multiply and some division if
you're doing PID control or some lesser variant thereof). A
microcontroller-based implementation would work, but respond slowly to
load transients (which is hardly ideal).
Might be more complexity and designing than you wish for the task, but
JOOI, one way of doing constant-power regulation is with an
analog-multiplier IC.
I've seen this done (on the supply side) in a HV lab power supply,
using an MC1494 4-quadrant multiplier. I can supply the reverse-engineered
schematic if of interest.
The MC1494 is 70/80's-era chip, I don't know what's current these days.