Re: Terry's DRSSTC - Frequency/Pulse Width Controller

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Bob (R.A.) Jones" <a1accounting@xxxxxxxxxxxxx>


Hi Terry,

Subject: Re: Terry's DRSSTC - Frequency/Pulse Width Controller


> Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi All,
>
> I didn't get very far today on the Frequency/Pulse Width Controller.  I
got
> too wrapped up in the protection stuff.
>
> Here is the IGBT over temperature circuit:
>
> http://drsstc.com/Design/OverTemp.gif
>

To reduce EMI sensitivity  it's good design practice  to add a low pass
filtering to signal where its connected to the board. At say a time constant
of  1/20 or even 1/100 of the coil frequency.
You can also add  a second one to the last active element of the signal
path. You don't want more bandwidth than you need.
If you want to get real fancy add a rate of change term i.e. a bit of phase
lead to compensate for the thermal lag.  That should give a better
indication of the actually die temperature during transient conditions. This
will make it more sensitive to noise so you will also need the low pass
filter.

You should do the same on the current sensor to reduce false triggering
during switching transients. More tricky but say three or more times the
coil frequency.

You should also consider trying to make the inputs differential.  That looks
like it would only need a few more resistors. The signal reference points
should return to a stare point on the circuit board.

Bob