Re: LF: W1VD amp help - more waveforms

[N1BUG <paul@n1bug.com>]

Thanks Hugh and everyone else who commented and provided tips on my
earlier post about this amplifier.

I will wait for Jay to have a chance to comment but I *think* I'm OK
on timing of the phase transitions. However, something is causing
major ringing (is that the correct term?) on the drains. I believe I
need to find the cause and do something about that but I have no
idea what to look at.

I've been building and even designing QRO amplifiers for 35 years
but I'm a vacuum tube HF/VHF/UHF guy! This FET class D/E stuff is
all new to me and I don't learn new tricks as easily as I once did. :)

Paul


On 04/09/2018 06:08 AM, dhchurch wrote:
> Hello Paul
>  
> You can also introduce a small delay for each extra
> semiconductor junction in the driver path, some inverters are quite
> good for this. Obviously the gate waveform should be steep not
> overly so.
>  
> Hugh, M0DSZ
> 
>     ----- Receiving the following content -----
>     *From:* N1BUG <mailto:paul@n1bug.com>
>     *Receiver:* rsgb_lf_group <mailto:rsgb_lf_group@blacksheep.org>
>     *Time:* 2018-04-08, 17:59:10
>     *Subject:* Re: LF: W1VD amp help - more waveforms
> 
>     > Always start out on the dummy load. Test in stages.　Test the
>     driver
>     > into the FETs with the FET drain supply off. Verify the waveforms
>     > with a dual trace scope to see that there's　a small　'dead zone'
>     > between the two phases. This prevents the possibility of　cross
>     > conduction. Once the gate waveforms are　confirmed　to be correct,
>     > turn on the FET drain supply. Once the amplifier is verified to be
>     > working properly add the doubler.
> 
>     Waveforms...
> 
>     Conditions for all below: Drive is from the HP 3325B at 2Fo, 5V
>     square wave, 2.5V DC offset fed into amp driver board. Amp output
>     through LPF into a quality dummy load (250W 50 ohm flange load
>     resistor known good through UHF).
> 
>     No drain voltage...
> 
>     Gates:
> 
>     http://www.n1bug.com/gates1.jpg
> 
>     http://www.n1bug.com/gates2.jpg
> 
> 
> 
> 
>     Now with 13V on the drains...
> 
>     Gates:
> 
>     http://www.n1bug.com/gates1-wdv13.jpg
> 
>     http://www.n1bug.com/gates2-wdv13.jpg
> 
>     Notice those have changed a bit with the addition of drain voltage.
> 
> 
>     Drains:
> 
>     http://www.n1bug.com/drains1-wdv13.jpg
> 
>     http://www.n1bug.com/drains2-wdv13.jpg
> 
>     It looks like one phase is "mostly" off before the other is fully
>     on, but I'm not sure if this is as much dead zone as I should see?
>     One is still going down while the other is starting to come up. In
>     any case the drain waveforms don't look good! Suggestions on where
>     to begin looking for the cause of this?
> 
>     Paul