c. Lch and PFN form a series resonant circuit.
Hence, the PFN charges
to nearly twice the power supply voltage.
d. When the PFN is fully charged, V1 stops conducting, thereby opening
the charge circuit and preventing the PFN from discharging through the load.
Learning Event 9:
THE DISCHARGE CYCLE
1. A positive trigger (Figure 68) from the timer causes the HYDROGEN
THYRATRON to conduct heavily. Now there is a discharge path for the PFN,
and current flows through the pulse transformer primary and V2.
2. The PFN discharge develops a negative rectangular pulse across the pulse
transformer primary.
The pulse amplitude is equal to nearly half the
voltage on the PFN at the time of discharge. The pulse width is equal to
two TDs and depends on the PFN characteristics.
3. The pulse transformer couples this high-voltage pulse to the magnetron
cathode. The magnetron oscillates for the duration of the pulse.
4. However, when the magnetron oscillates, it causes an impedance mismatch
between modulator and magnetron. Hence, a negative pulse is reflected into
the pulse transformer primary. A reverse current flows and charges the PFN.
5. Reverse-current diode V4 now conducts, draining the reverse charge off
the PFN.
This action of V4 keeps the PFN voltage constant from pulse to
pulse.
6. When the PFN completely discharges, V2 deionizes and the charge cycle
starts again.
The HYDROGEN THYRATRON is triggered at the radar pulse-
repetition frequency.
86
Previous Page
