Alex1M6 wrote ...

When driving a transformer using a half bridge setup like this



Is the voltage that the primary coil "see's" only half of the input voltage? As when driving a flyback transformer I have to use a very low number of primary turns (4-6) in order to get a decent output voltage, compared to just using a single MOSFET setup where even as many as 10 primary turns will give a good output voltage.

Is my assumption of the input voltage getting halved in a half-bridge correct?

Thanks.

Dr. Isotop wrote ...

Yes. The peak to peak voltage swing across the primary is only your bus voltage instead of twice that like in a fullbridge.
Just halve your primary turns and you're good to go, at least for making sparks.

Turkey9 wrote ...

The primary will see +supply/2 and -supply/2. So +18 and -18 for a total peak to peak voltage of.... 36!

Alex1M6 wrote ...


So what would cause the arcs to be smaller compared to a single MOSFET driver?

Patrick wrote ...

your not really realising whats important... for ultra-high-power circuits (above 2-3kVA) you almost exclusively use a half or full bridge, as it solves some magnetic issues like saturation, and gets you away from reluctance and remenance with single switch drivers. (and you get rid of air gaps to, since energy is usually a bad thing.)

the real advantage of Half/full bridge is that you have a single primary, thus saving you window area for secondaries and air cooling. for example with a CTPP you have two primaries, thus much less secondary volume available and your cooling is not as good.

Arcing and sparking powers and distances are merely incidental to the above factors.

Stated differently, your moving the loses and complexity out of the transformer, and into the silicon. thus both (the transformer and switches) can be more highly optimized, separately for each task (power switching and power conversion). Greater efficiency and power are gained at the cost of more numerous, complicated components, and lay-out.