Paul
So ... we're still stuck at solving the gate drive overlap issue. Your's seems
to be slow to turn on
and to turn off.
Think I questioned back a while ago the driver circuit board 'trace' widths.
Since you're using perf
board I wonder if there are long runs using small gauge wires for the +V and
ground connections. If
you look at my driver board, the top (component side) is a complete copper
ground plane ... which
makes for a very low impedance ground. Screws through the four mounting holes
makes an excellent
connection between the board ground plane and the amplifier chassis. Perhaps
you can come close to
replicating this with pieces of copper flashing on the bottom of your perf
board. The IR2110 is
charging and discharging a realtively high gate capacitance ... so if the
IR2110 connections to the
+ and - 'rails' and ground aren't reasonably stout the charging and discharging
process could be
slowed ... maybe enough to cause the problem. For the record, I used #20 for
the twisted pairs ...
but the ground connection also exists through the chassis.
Jay W1VD
----- Original Message -----
From: "N1BUG" <[email protected]>
To: <[email protected]>
Sent: Friday, April 13, 2018 1:09 PM
Subject: Re: LF: W1VD amp help - finally some progress!
Today I verified board connections again, including power to the
driver IC (tnx Luis). With the scope I checked +5v and +12v power at
IC pins while operating to be sure it is clean. All looked OK.
I replaced the timing capacitors with recommended ones (tnx Jay). No
change.
I replaced resistors in the timing circuit with closely matched ones
of a different type or at least different manufacturer. No change.
I added bypass capacitors at all +5v and +12v pins on the ICs. No
change.
I replaced the 10 ohm resistor / diode on each gate lead with 20 ohm
/ diode. Finally some change! First peak of the ringing is down from
62V to 45V. This is with 12.5V drain supply. Current consumption and
power output are down about 5% but efficiency remains the same as
before.
Looking very carefully at my scope patterns and the one Jay provided
a few days ago, I still believe my gate voltage drops much more
slowly than his. I don't know why. If my gate voltage would decay as
fast as Jay's, I think the FETs would not cross conduct.
I don't know what to do next. Is there any way I can speed up the
gate turn off? Can it be the 1N4148 diodes? Mine are of unknown age
from a large batch I got quite some years ago.
Paul
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