Rik
Thanks for the reply. This particular build is current mode (choke off
center tap)... so I guess I'm dealing with voltage spikes. I didn't
notice voltage spikes while monitoring the envelopes when sending dits
from the exciter, but may not have had the scope adjusted to best
visualize them.
The driver outputs are AC coupled to the FETs using a 0.22u coupling
cap, shunt schottky (SB560), series 10 ohm, and shunt 4.7k. Should the
same behavior with extended ON time be present?
On 2/24/19 7:38 AM, Rik Strobbe wrote:
Hello Eric,
I had a similar problem:
at "key up" one of the driver outputs will remain low and the other high. As a
result the gate of one of the power MOSFETs is kept high for a time much longer that half
a period. During that time this MOSFET is in ON-state (conducting) and thus drawing
excessive current.
I solved the problem by adding monostable multivibrators that disable the
MOSFET driver when one of the driver outputs stays high longer than 3
microseconds.
Assuming that you refer to the W1VD "500W RF-deck"
(http://www.w1vd.com/137-500-500WTX.pdf): it is actually a voltage mode design (thus
having current spikes).
A current mode class D amp has a choke between the supply voltgae and the
output transformer center tap, limiting the current (and causing voltage
spikes).
73, Rik ON7YD - OR7T
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