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- Path: sparky!uunet!olivea!decwrl!sdd.hp.com!hpscdc!hplextra!hpcc05!hpscit!rkarlqu
- From: rkarlqu@hpscit.sc.hp.com (Rick Karlquist)
- Newsgroups: sci.electronics
- Subject: Re: Why are high frequency transformers small?
- Message-ID: <55550020@hpscit.sc.hp.com>
- Date: 12 Aug 92 16:27:56 GMT
- References: <1992Aug8.132315.29009@doug.cae.wisc.edu>
- Organization: Hewlett-Packard, Santa Clara, CA
- Lines: 40
-
- In sci.electronics, bender@oobleck (Duke of Canterbury) writes:
-
- > rkarlqu@hpscit.sc.hp.com (Rick Karlquist) writes:
- > : In sci.electronics, kevin@clsi.COM (Kevin Cameron) writes:
- > :
- > :
- > : > There are two basic parts to a transformer:
- > :
- > : > 1: the windings
- > :
- > : > 2: the core
- > :
- > : > the actual "transforming" is achieved by coupling between the windings
-
- > Why does an autotransformer, and it's variable cousin, the Variac, work?
-
- > mike
-
- An autotransformer is nothing but a conventional transformer with
- a connection between the primary and secondary. Coupling between
- the windings above the tap and the windings below the tap is just
- as important as coupling between primary and secondary of a conventional
- transformer. RF autotransformers tend to work poorly because of
- poor coupling between the turns of the coil, especially with an
- air core.* Adding a magnetic core does not increase the absolute
- mutual inductance, but it increases the magnetizing inductance so that
- the leakage inductance is a smaller percentage of the magnetizing
- inductance. (I.E. it increases the % coupling).
-
- Variacs are a special case because at high voltage settings, the thing
- is mainly just a shunt inductor across the line with only a minor
- amount of transformer action. At low voltage settings, where it really
- does need to act as a transformer, a lot less power needs to be
- transferred, so it doesn't need to be very efficient.
-
- *See H. Wheeler, Proc. IRE, 1959.
-
-
- Rick Karlquist
- rkarlqu@scd.hp.com
-