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Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
cedric wrote ... in there system ,I don't understand why L2 is having a negative current flow when L1 is positive
As the switch turns on C is charged to +V, the high side gets grounded by the switch, so the low side goes to -V pulling a negative current through L2 and the diode, when L2 current swings positive from the LC oscillation the switch turns off and L1 increases the di/dt on the second half of the cycle to ensure abrubt turn off at high current.
wrote ... I also get some result with fast recovery diodes like :stth6012w and the u1560.
Fast recovery diodes are snappy, but snappy turn off is subtly different from DSRD ... the normal snap off effect is more suited to pulse sharpening than as an opening switch.
With DSRD you forward bias the diode for a period of time shorter than the transit time and then have a relatively long time during which reverse current can be build up before an extremely snappy turn off. Because of the short time scales this effect is hard to reproduce on fast diodes. The people who wrote the paper I linked actually use normal recovery diodes (1n5408, doesn't get much more normal than that for HV diodes) for their DSRD circuits.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Above are early non-cavity magnetron designs.
Top left - 'a' - is Albert Hull's original magnetron design of (I think) 1921.
The innards of the Hull design look tolerably like some of the early TV EHT rectifier diodes such as EY51 so it might only take a suitable magnet, a tuned circuit for electrons to rush backwards and forwards in, and, of course a microwave detector, to see whether such an unlikely contraption could actually be made to work.
I imagine the tuned circuit might be a tunable line made out of parallel copper pipes with a moveable shorting bar across it - the kind of the thing you see in antique VHF transmitters.
Registered Member #2941
Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143
Pinky's Brain wrote ...
cedric wrote ... in there system ,I don't understand why L2 is having a negative current flow when L1 is positive
As the switch turns on C is charged to +V, the high side gets grounded by the switch, so the low side goes to -V pulling a negative current through L2 and the diode, when L2 current swings positive from the LC oscillation the switch turns off and L1 increases the di/dt on the second half of the cycle to ensure abrubt turn off at high current.
wrote ... I also get some result with fast recovery diodes like :stth6012w and the u1560.
Fast recovery diodes are snappy, but snappy turn off is subtly different from DSRD ... the normal snap off effect is more suited to pulse sharpening than as an opening switch.
With DSRD you forward bias the diode for a period of time shorter than the transit time and then have a relatively long time during which reverse current can be build up before an extremely snappy turn off. Because of the short time scales this effect is hard to reproduce on fast diodes. The people who wrote the paper I linked actually use normal recovery diodes (1n5408, doesn't get much more normal than that for HV diodes) for their DSRD circuits.
I understand a bit better the charge trading on the capacitor c and I have seen this topology else where. for the DSRD ,my best result are with the normal recovery diode (2-3 ns rise time) the fast diode show the effect but as you say ,it might just be because they are snappy . when I made the board I use L-C circuit to feed the diode in one direction and the other ,I was just looking for srd effect, however the time scale is fairly short ,the pumping current have a period of maybe 100 ns ,it's a boost topology with a air inductor,well ,now that I know a bit more,I can look closer to the effect and the topology.
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vacuum diode
