Message: 4
Date: Tue, 10 Aug 2004 09:33:49 +0200
From: Angel Vilaseca <avilaseca@bluewin.ch>
Subject: [Amps] zero-voltage triac power supply
To: AMPS@contesting.com
Message-ID: <41187A5D.862A8E89@bluewin.ch>
Content-Type: text/plain; charset=us-ascii
Hi,
I just read in a book dated a few years ago about an interesting device,
but could not find it in my parts catalogs.
I wonder if someone has tried it.
It is an optically-controlled triac, called a "zero voltage triac" and
it switches off *and* on only when mains voltage goes through zero.
All classical triacs switch off when mains voltage goes thru zero, and
they switch on somewhere during the positive or negative alternance.
This of course creates large current transients, a lot of RF and also
you cannot use it to drive an HV transformer because the high-current
fast switching would create huge HV spikes.
However, I suspect that since a zero-voltage triac always waits until
mains goes thru zero before switching on or off, it could be used to
build a very well regulated HV supply. It could be wired into the
primary of the HV transformer. Since this kind of triac is optically
coupled, a simple comparator could be used in the secondary HV circuit
to check if the HV is above or below a defined level. This information
could safely be fed back through the optical link to the primary. The
isolation is several KV. If HV is too low, the triac lets several mains
full alternances through the primary. If it is too high, it stays
switched off until some more energy is needed into the circuit.
It is of course possible to use the zero-voltage triac to control a
large, classical one for multi-Kilowatt levels. The big one will then
also behave like a "zero voltage" triac.
The book I read said that the whole "zero-voltage optically coupled
triac" is packaged in an 8-pin DIL and is also very inexpensive. It did
not give any part number.
Has anyone already tried this?
Vy 73 de
Angel Vilaseca HB9SLV
There was an article published in QST July 1987 A Line-Side Regulator for
High-Voltage Power Supplies by Greg McIntire AA5C where a optically coupled
triac was used to control a conventional triac in the primary of the HV
transformer. The optical triac is a MCP3022 or H11J1.
I have just finished construction of the regulator but have not yet
installed it in my power supply for a 4CX1500A.
The author said that he experienced throbbing of the power supply at line
rate when using a zero crossing triac. He changed to a nonzero crossing
optical triac and eliminated the throbbing. Although he expected he might
encounter RFI in this mode, none was noted.
73
David C. Hallam KC2JD
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