Re: Capacitors

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

Hi Alex,

The capacitor in series with the primary coil has 2 purposes.
Firstly, it blocks any DC bias.  This trick is used for driving
transformers with a core material.  Since we are using air cores, the
DC bias wont saturate the air or anything, so this use is sorta
negligable.  The other nice thing is that in the event of the H-bridge
staying in 1 state indefinately, the capacitors will prevent the
virtual short circuit of just the primary inductance with DC across
it.

The capacitor across the power supply rails is to soak up any voltage
spikes that are caused from the mosfets NOT switching when the current
is crossing zero.  This capacitor must be mounted physically close to
the mosfets if it is to do much good.  This cap also helps filter RF
noise that might get back into the mains.

I dont know what resistors you are talking about, could you link to a
schematic that includes them?

Steve

On 4/29/05, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: "Alexander Turkin" <alex_3@xxxxxxx>
>
> Hello
>
>   In the H-bridge in SSTC there are two groups of capacitors: one is
> connected in series with primary coil and the other is connected to the
> mains. The question is: what are they for?
>   In some circuits there are resistors connected to the mains in the
> H-bridge also. Are they really needed?
>
> Thanks
> Alex
>
>