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Registered Member #29
Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500
I think where the cbfull's confusion lies is that the Royer circuit actually puts twice the voltage stress on the driving transistors that the half-bridge does. (By tranformer action, the Royer "off" transistor most withstand at least 2 * Vdd, while for the H-B it must be able to stand up to Vdd).
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Again there is a bit of confusion because "Royer" is used as an umbrella term for at least two kinds of circuit.
The ferroresonant version with square wave output causes the transistors to see 2*Vdd, plus any spikes due to stored energy in the transformer's leakage inductance.
The "Mazzilli" version we use, with DC link choke and resonating capacitor (more or less the same circuit as in cold cathode lamp drivers, for all you case m0dders out there) subjects the transistors to Pi*Vdd as Sulaiman said: but with no spikes.
Registered Member #187
Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140
WaveRider wrote ...
I think where the cbfull's confusion lies is that the Royer circuit actually puts twice the voltage stress on the driving transistors that the half-bridge does. (By tranformer action, the Royer "off" transistor most withstand at least 2 * Vdd, while for the H-B it must be able to stand up to Vdd).
That's it! Thanks for pointing that out. I clearly had the facts misconstrued, I should have realized that the voltage stresses on the transistors (bipolar or field effect) are "half" what they are in the push-pull, which is what I was trying to get at. My confusion came from looking at a schematic for a bridge, and thinking that just because there are two transistors in the path from rail to rail, that the E-C (or S-D) would behave the same as though they were in series.
I have posted a basic setup below, and if you picture Q1 (upper left) and Q4 (lower right) as being one path (switches are off for example), it may appear that the two switches are seriesed, and the breakdown voltages will add, or double. The important thing that I missed was that their is an inductive load between them.
So to conclude my incredibly sloppy point, the royer (or "push-pull" setup) puts twice the voltage stress on the switches, because of the the inductive kickback from the dual primary.
Sorry for the fuss guys! I'm glad the end result has educated me.
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Half bridge or Royer ciruit?
