Switching the damping resistor.

[Anonymous]

Reg sent me the following link to a Candy patent for an energy efficient PI.
http://www.thunting.com/geotech/pages/metdet/patents/US22053907A1.pdf
This re-ignited my interest in the part where Candy proposes switching the damping resistor out during the pulse on time. If anyone could look at this rather small patent and for now disregard all but the circuit, drawing and paragraph [0024] and only look at the part of the circuit comprising ground, 70,86,87,72,73 and 74, then you will see the bit that is of interest to me.
In paragraph [0024] he states "Note that during periods 61 and 63, many fets will conduct owing to internal diode action".
Therin lies my dilema. I have tried for some time, previous to seeing this patent, to do similar switching right at the coil and have given up due to the following.
If you draw a reverse protection diode across 87 then it would conduct at 62 and 69 in the drawings.
Has anyone any idea of a circuit that would avoid this and allow cleaner switching? This dummy would be very pleased to hear any ideas as I need to accomplish this for a novel idea I've played with for some years now. It's obvious I'm no engineer.
Thanks for your time,
Robby.

 

[Anonymous]

Hi Robby,
I haven't had time to fully digest the information yet, but thanks for posting it.
Energy saving is not something I have pursued as yet. My type of coil and output circuit do not readily lend themselves to this feature. What I have noticed over the years though, is that the more you hang on to the transmitter output and receiver input the more spurious responses you get, including higher noise levels. I like to keep it as simple and uncluttered as possible.
Eric.