Hi Larry,
yes, it does seem there is some nice interest in SMPS for HV . Below are
a few of my observations.
73,
Paul (KG7HF)
------------------------------
Message: 5
Date: Wed, 20 May 2009 14:45:37 -0700
From: Larry < larry @w7iuv.com>
Subject: [Amps] HV switch-mode power supply
Cc: amps@contesting.com
Message-ID: <4A147A01.5050100@w7iuv.com>
Content-Type: text/plain; charset =ISO-8859-1; format=flowed
The circuit in the article uses a huge line filter cap which makes step
start seem necessary. What is the actual maximum 120 ripple permissible
for a supply like this? How much smaller can you make the filter cap and
still be OK?
>> I'm not sure, I actually used about twice the cap than the article, it's
>> what I had available, I think though that you could easily get by with less
>> cap on the primary side.
I would like to be able to start/stop the supply with the
PTT switch for reasons which I won't go into here. I don't mind a large
inrush current if I can make the design handle it.
>> This feature is provided in W9QQ's article. He is leaving the oscillator
>> free running but controlling the primary side DC voltage to the H-Bridge
>> through the addition of a fifth fet as a switch. It also allows the pwm to
>> stabilize before applying primary power to the h-bridge.
The core material is typo'd in the article schematic and I can't make it
out. Any body know what the actual material was?
>> It was somewhat unclear, but I used FT-193-J from Amidon , big cost there!
The transformer design seems weird. I've built VHF amps like that but
see no reason to make the supply transformer that complicated. Is there
some valid reason to do so?
>> I too was not happy with the transformer, but have reproduced it in the
>> hopes of making something different later.
Seems like a large diameter toroid with conventional windings would do just
fine and be easier to construct.
The "H-bridge" seems to be the choice these days. Is that for
efficiency? My "classic" supplies just used a push-pull arrangement with
a center tapped primary. Seems simpler, but surely there must be a
reason why the larger supplies don't seem to use push-pull although all
the smaller ones sure do.
>> I think it has to do with efficiency and power handling capability. The
>> dissipation is distributed since only two parts are on at the same time.
Seems like it would be a good idea to make smaller " stackable " supplies.
Say something like 700 VDC at 2.0 amps max, then stack them in series to
get what you need, 1400V, 2100V, 2800V, 3500V. Like that.
>> In effect, this is what I did with my transformer. I wound extra wires and
>> can place them in series or parallel to change output voltage as needed.
>> It is also possible to change the input voltage as my primary is center
>> tapped, I think this would allow the input voltage to be halved and placed
>> in parallel.
I see no reason for feedback for voltage regulation. My old T-supplies
were very stiff and the supply in the article claims 50 volts drop from
ZSAC to full load. Arguments for or against? Simpler is always better as
far as I'm concerned.
>> Agreed. I only mention it because it might make the input and output caps
>> smaller.
Is there a good reference for design of this type of switcher someplace.
Preferably on-line. I have all sorts of design aids for tiny little
computer type supplies but nothing here for BIG stuff.
>> I've researched this quite a bit, there isn't much out there, at least at a
>> level I can understand. I spent some time posting my work on my web page,
>> I'll have it done in the next few days for anyone to look at.
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