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 tha
Addendum: 3 microseconds is for 472kHz, for a 136kHz PA it should be 10 microseconds. 73, Rik ON7YD - OR7T Hello Eric, I had a similar problem: at "key up" one of the driver outputs will remain low a
Why not AC couple your gates. That removes all possibility of latching 100nF in series, reverse biassed diode to ground shunted by 10k or so for DC restoration Or transformer couple Andy www.g4jnt.c
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 w
The driver and FET gates in mine are AC coupled (0.22u, SB560 schottky shunt, 10 ohm series, 4.7k shunt) and the problem still exists. Apparently same thing Paul N1BUG was having problems with. The
I will be watching this discussion closely. Mine is a W1VD kilowatt deck: http://w1vd.com/137-500-KWRev3.0.pdf It has blown FETs several times. The problem always occurs at the end of the RF envelope
Hello Paul, Eric, Andy, AC coupling with a large C will not solve the problem. At "key up" one of the driver outputs will remain high thus the gate of theFET connected to that output will remain high
For on-off keying of a switch mode PA you really should be using supply line control. Switching the drive then trying to reduce rise /fall times for keyclick elimination by controlling drive amplitu
Andy This recommendation is all well and good, but seems applicable to only CW where either the operator is manually keying or using computer controlled keying with a constant carrier input. With dig
IN that case some sort of protection needs to be incorporated - and few have come up with really properly designed and foolproof circuitry. I use the technique adopted in the hold Decca transmitters,
Try using a synchronous keying circuit, only uses a few ics and is reliable. I have used it on a modified Decca 5501 on 136 and a similar tx on 475 with no blown fets even to a short circuit, guard c
