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 <1551011916482.41235@kuleuven.be>
From: Eric NO3M <no3m@no3m.net>
Message-ID: <f58dcf9c-e461-239e-cd55-c10fd5e7c436@no3m.net>
Date: Sun, 24 Feb 2019 08:35:38 -0500
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Subject: Re: LF: Re: Class D current spikes
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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
>
>