Re: Half-Bridge questions . . .

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Sharpe by way of Terry Fritz <teslalist-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>

Dan

Sorry, would have responded earlier, was on vacation.
Suggest you visit the Fairchild Semiconductor website and check out this AN.

  www.fairchildsemi-dot-com/an/AN/AN-9012.pdf

It specifically covers line operated (220VAC rms input) half bridge induction
heaters as used for 1kW rice cookers/steamers.  Even though the resonant
frequency is kinda of low, equations are given allowing design of circuit with
a given primary inductance to be resonant at any given frequency, up to say
150-200Khz.  The circuit as described is cheap, low cost.  Need a good
description of the resonant commutation capacitors (shunt C) shown around
IGBT's, and proper equations to size.  IMO, if a low cost 1/2 bridge up to
perhaps 1kW is desired, this AN is an excellent engineering starting point.
Another point is if you want high power with a half bridge, you should use
as high voltage as practical, but not exceeding 50% of AM ratings of devices.
220VAC input through a bridge would require at least 600V devices, with
doubling or level shift, 1kV devices would be recommended.

At the APEC conference is Miami
earlier this year, there was quite a bit of discussion of this topology for
high power converters, and protection schema in case you lose load on the
circuit (read load discontinuity due to streamer effects).  Best results
appeared to be high speed high power fast recovery diodes shunting the
1/2 bridge capacitors.

Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA

Tesla list wrote:

 > Original poster: "Mccauley, Daniel H by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
 >
 > Just some half-bridge topology questions . . . as this new design i'm
 > working on doesn't require the full-bridge topology.
 >
 > When utilizing a DC source to run a half-bridge (2 FET) the outputs would
 > the output connections typically be:
 >
 > 1.  One connection between two FETs
 >
 > 2.  The second connection centered between the DC+ and DC- rail of the
 > h-bridge with series DC blocking capacitors
 > on both side of this connection.
 >
 > I've seen it dones many different ways, and wanted to see which worked best
 > for SSTC work.
 >
 > Thanks
 >
 > Dan