grid driver circuit design, and the Recovery can also be improved
involving gently rising voltages
performance required from the by arranging to have small nega- (i.e., resonant charging and ramp
thyratron itself. Contact the appli- tive voltage on the anode after
cations engineering department at forward conduction has ceased.
charging) favor thyratron recov-
ery, and therefore allow higher
PerkinElmer to discuss the spe-
In many radar circuits, a few-per- pulse repetition rates. Fast ramp-
cific details of your requirement. cent negative mismatch between
a pulse-forming network and the
ing and resistive charging put
large voltages on the anode
load ensures a residual negative
anode voltage. In laser circuits,
quickly, thus making recovery
more difficult. The ideal charging
Conduction
Once the commutation interval
has ended, a typical hydrogen
thyratron will conduct with near-
ly constant voltage drop on the
order of 100 volts regardless of
the current through the tube.
classical pulse-forming networks scheme from the viewpoint of
are seldom used, so inverse
anode voltage may not be easily
thyratron recovery is command
charging, wherein voltage is
generated. Recovery then strong- applied to the thyratron only an
ly depends on the characteristics
of the anode charging circuit. In
general, charging schemes
instant before firing.
Recovery
Thyratrons open (recover) via
diffusion of ions to the tube inner
walls and electrode surfaces,
where the ions can recombine
with electrons. This process takes
from 30 to 150 microseconds,
depending on the tube type, fill
pressure, and gas (hydrogen or
deuterium). The theoretical maxi-
mum pulse repetition rate is the
inverse of the recovery time.
CURRENT LIMITING AND/OR
MATCHING RESISTOR
GRID SPIKE
SUPPRESSION CIRCUIT
GRID DRIVER
CIRCUIT
Figure 3. Grid Circuit
Recovery can be promoted by
arranging to have a small nega-
tive DC bias voltage on the con-
trol grid when forward conduc-
tion has ceased. A bias voltage of
50 to 100 volts is usually suffi-
cient.
(d)
Spark Gap
(a)
Filter
(b)
Zener
(c)
MOV
Figure 4. Typical Grid Spike Suppression Circuits
PERKINELMER [ PERKINELMER OPTOELECTRONICS ]
