3.6VDC voltage sag on switching
On Tue, 12 Jun 2007 08:12:10 -0700, John Larkin
wrote:
On Mon, 11 Jun 2007 22:31:43 -0700, "Paul Hovnanian P.E."
wrote:
John Larkin wrote:
On Mon, 11 Jun 2007 17:57:48 -0600, "starfire"
wrote:
I'm posting the associated circuit and traces here, per request from Paul
Hovnarian. Thanks for the suggestion, Paul.
Normally, I'm not a pest about spelling, but .......
C30 is not a good idea.
John
Do you think C30 is causing the sag? I think that might slow down Q2,
but the sag is caused by having to charge C31. What kind of 3.6V battery
is that?
Hint to the OP: If you can, set your scope's trigger delay to -1 units
so we can see what things looked like before they fell off the edge of
the earth.
It could add "gain" to the sag, by increasing Rds-on when the source
voltage dips. Just get rid of it, or use a s-g cap if you want to slow
down turnon.
But, looking at the dip waveform, it's awfully fast for being a
"circuit" issue. Looks more like a layout problem. I wonder if this is
on a proto board.
---
The OP reports that it occurs when there's no load on the big MOSFET
and he sends a high to the gate of the first MOSFET, so it could be
due to the gate capacitance of the first MOSFET charging up.
--
JF
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