On Fri, 25 Nov 2005 06:42:25 GMT, Ignoramus10725
wrote:



The diode that I used in the RCD is NOT fast recovery. I just do not
have a fast recovery diode. That, I think, explains spikes that I
still observe.

Look right across the cap. If you see the spikes there as well, the
diode is working OK.

On Fri, 25 Nov 2005 18:03:07 GMT, Ignoramus29530
wrote:

On Fri, 25 Nov 2005 11:34:13 -0600, Don Foreman wrote:
On Fri, 25 Nov 2005 06:42:25 GMT, Ignoramus10725
wrote:



The diode that I used in the RCD is NOT fast recovery. I just do not
have a fast recovery diode. That, I think, explains spikes that I
still observe.

Look right across the cap. If you see the spikes there as well, the
diode is working OK.

Good idea, I will do that tonight. The cap is a CDE 940C, made for
snubbing, low ESR, blah blah. But who knows.

The spikes were extremely narrow and ended abruptly, to a perfectly
flat line, that's why I suspected diode recovery time. I will try to
get some measurements of the spike duration too. It is nice that I can
set my oscilloscope to trigger on the timing signal on channel 1,
while looking at the bus voltage on channel 2. That way the trigger is
not confused by all the oscillations in the DC bus, and I can see a
clear and not shifting picture.

In any case, I need a heatsink mountable diode, since this one
dissipates quite a bit of energy. I could mount this one also, I
suppose, although it would not be easy due to threading, need for
isolating the heatsink, etc.

What do you say Don, am I on more or less the right track so far?

i
Kind of a meandering track, but yeah, you seem to be gaining on it.
Going to a proper gate drive was a big step forward. Having the
bridge short rather than open during switchover was also a good move,
since you're switching a current source.

Try to measure rise time of the pulse - the rising edge - or falling -
that will give you an idea of the frequency components - and might lead to an
RC filter could be developed.

Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder



Ignoramus29530 wrote:
On Fri, 25 Nov 2005 11:34:13 -0600, Don Foreman wrote:

On Fri, 25 Nov 2005 06:42:25 GMT, Ignoramus10725
wrote:



The diode that I used in the RCD is NOT fast recovery. I just do not
have a fast recovery diode. That, I think, explains spikes that I
still observe.

Look right across the cap. If you see the spikes there as well, the
diode is working OK.


Good idea, I will do that tonight. The cap is a CDE 940C, made for
snubbing, low ESR, blah blah. But who knows.

The spikes were extremely narrow and ended abruptly, to a perfectly
flat line, that's why I suspected diode recovery time. I will try to
get some measurements of the spike duration too. It is nice that I can
set my oscilloscope to trigger on the timing signal on channel 1,
while looking at the bus voltage on channel 2. That way the trigger is
not confused by all the oscillations in the DC bus, and I can see a
clear and not shifting picture.

In any case, I need a heatsink mountable diode, since this one
dissipates quite a bit of energy. I could mount this one also, I
suppose, although it would not be easy due to threading, need for
isolating the heatsink, etc.

What do you say Don, am I on more or less the right track so far?

i


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