On Sun, 25 Mar 2001 13:41:12 -0500 "Alex Von Yonkers"
<avy@qwestonline.com> writes:
>
>
Hi Alex,
>> I've been there with both SCR's & FET's -- at the 2 KW level.
>Nice .... Howabout 4-5KW?
Not personally but, a friend of mine made an 8KW thing for a Solid
State Tesla Coil late in the last millennium -- that was back when one
had to parallel four IRF450's per leg of a bridge driver to handle that
kind of power.
>Any suggestions? I want one that I can turn of the oscilator, and
>control the freq...
All of the parts I suggest below can either free run or be driven from
an external reference.
>As far coaxial pulse transformers... this is out of my realm....
especially
>at these power levels :(
The transformer is actually the easiest part. The secondary will be
just a couple pieces of copper pipe. The primary will only be 7 or 8
turns looped through the pipe. Add a few ferrite cores to the outside
and viola! A coaxial transformer. See Power Conversion & Intelligent
Motion magazine, June 1998, p.40 for some details and impressive photos.
>Have you considered the stress on the PFC circuitry when the PowerStage
>starts to conduct again?
The PFC output capacitor won't mind.
> It has to have enough stored energy not to shutdown everything :)
Yep, 2000 uF per KW (in a 380V PFC) is a good rule of thumb for this
cap. So, you'll need a 10000uF 450V or so capacitor -- probably more
easily obtainable as five 2000uF parts.
>I was thinking just kill the oscillator... but then it thakes time to
start
>it up
The oscillator can be free-running. The controller chips can be
turned on & off at any time.
>This is the MAIN problem Marv with turning off any part of the PS... On
time
>during CW, VOX and Break IN. You do not want to clip the first silable
>during VOX, or first character in CW mode . The on time MUST be at least
>twice as fast as these conditions.
No problem.
You can shut down the output (phase controlled converter) section of
the power supply in receive -- while leaving the PFC running in a
discontinuous mode. As long as the final output filter allows compliance
-- Use a 5 KHz filter (w/ a 100KHz switching freq.) and the supply will
come up in a millisecond. The plate, er... drain, supply will be up
before the antenna relay can switch, so there would be no noticeable
delay.
>Sure, let me have them :)
For the PFC section -- See an application note from Advanced Power
Technology (APT), APT9901, if I recall correctly viewable on their
website which includes a number of the "fine points". This is a 3KW
unit -- you would need to double up on the choke core for your
requirements and increase the output cap. size. I think they use a
Unitrode controller but, others are available from MicroLinear
(ML4812/ML4821) and Linear Tech.
Some kind of soft start circuit (relay, SCR's, or big thermistor) is
a must to keep the large PFC capacitor, mentioned above, from popping the
mains breakers at initial turn on at this power level. This kind of
thing is almost never shown in the trade magazines! And that is likely
where the start-up delay comes from that you have noticed with the
commercial supplies.
For the ZVS stage -- There are some very advanced driver IC's (with
helpful Ap-notes) made by MicroLinear (ML4818), LinearTech and Unitrode,
now Texas Instruments (UCC3895) . There are plenty of robust power
FET's available from IXYS, APT, International Rectifier (IR) to name a
few.
At your power level even the output rectifiers deserve a close look.
100A will burn 200W in a normal bridge. It may be worth considering
schottkys or hooking up a few more FET's as a synchronous rectifier. Of
course, if you are primarily running SSB, rather than RTTY or some other
high duty cycle mode, then this would only be a peak loss figure.
73,
Marv WC6W
*
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