RE: Grounding of negative lead on SSTCs

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

Original poster: Marco.Denicolai-at-tellabs-dot-com 

Dan and Malcolm,

Stupid question of mine, sorry :)

A quick review of the stuff I have been dealing with in the last 5 years
revealed:
- SMPS input stages with rectified AC mains: can't ground those because
are "hot"
- laboratory power supplies (kind of): as you were describing, must be
left floating to provide flexibility of use
- stuff that is transformer-isolated from AC mains but grounded
elsewhere at some utility point
- devices with 2-wire mains supply (HDSL modems) that have nowhere to be
grounded to (no PE connection).

I realize now that grounding the DC negative have really never been an
option for me :)
But this discussion led me to find a circuit part in Thor's new "Timer"
card that was left floating between two optoisolators. That is, the HV
measurement input is optoisolated, commands the Timer board that, in
turn, drives through optoisolators the H-bridge boards. Got to ground
the DC-negative of the Timer board and see if I get less problems in
there.

Yes, still working on programmable burst sizes, already seen shorter
streamers produced by shorter bursts...

Best Regards

 > -----Original Message-----
 > From: tesla-at-pupman-dot-com [mailto:tesla-at-pupman-dot-com]
 > Sent: 22. syyskuuta 2003 20:54
 > To: tesla-at-pupman-dot-com
 > Subject: RE: Grounding of negative lead on SSTCs
 >
 >
 > Original poster: "Mccauley, Daniel H" <daniel.h.mccauley-at-lmco-dot-com>
 >
 >
 > Connecting the DC negative to ground is not only done for
 > safety, but to
 > reference the controlc circuitry to ground.
 >
 > The reason power supplies are not ground referenced is
 > because they are
 > typically built as ISOLATED supplies which allow
 > the use to run as ISOLATED if required.  For example, if I
 > wanted to use
 > a DC power supply to bias my gate drive circuit
 > on the high side, I could use an isolated supply output to do this
 > (provided the supply has enough isolation).
 >
 > Typically, however, you want to have your negative output
 > tied to earth
 > ground as a reference.
 >
 > Dan
 >
 >
 >
 >  > Hi all,
 >  >
 >  > I noticed on Dan's 15 kW SSTC schematics that the DC negative is
 >  > directly connected to the mains ground. I am used to see that
 >  > done (and
 >  > do that) through a capacitor. I guess there is a safety issue
 >  > here but I
 >  > can't recall the reason. Usually bench DC power supplies give the
 >  > possibily to externally ground the negative to the mains
 > ground (and
 >  > chassis): it isn't readily wired.
 >  >
 >  > Can anybody recall/explain the reason why to do it in one
 > or another
 >  > way?
 >  >
 >  > Regards
 >  >
 >  >
 >  >
 >