MODEL 727

SCR Thyratron Driver Pulse Forming Network (PFN) charging power supply unit

INTRODUCTION

This chassis does much more than the SCR name implies. This design utilizes a SCR switch to discharge a Pulse Forming Network (PFN) into a pulse transformer, which in turn generates HV output pulses. Edges of the output pulses are then sharpened with a saturable inductor before being applied to the HN connector.

GENERAL DESCRIPTION

The PFN charging power supply is transformer isolated, rectified, filtered and shunt-regulated using a power MOSFET as the switching device. This power MOSFET can also be commanded to turn-off the SCR.

The PFN is a two-stage, two-terminal network simulating an open-ended transmission line. It is charged through a resistor and a blocking diode to limit charging current and decouple the charging power supply from the switching SCR. The trigger input pulse width is expanded and then simultaneously controls the charging power supply, the SCR gate and the MOSFET gate are used to cut off charging current to the SCR. A blanking signal is also generated to prevent trigger frequencies from exceeding the limit.

Due to high transient voltages generated by the thyratron; the MOV, filter and fast turn-off diodes are used to protect the SCR and other devices from over-voltage breakdown. Active signals, sampled from the output stage, are also fed back to turn the SCR on whenever the thyratron fires through.

EOLC signals are peak detected and also integrated. A fault interrupt is generated when a single pulse is equivalent to approx. 1000 Amp or multiple pulses of lesser current.

FEATURES

Output Specifications:

• Open-circuit peak pulse voltage is 4 kV and not adjustable
• Into 50 ohm load:
  • Peak pulse voltage is 2 kV
  • Pulse risetime (10-90%) is < 40 ns
  • Pulse width at half max. (FWHM) is 1.5 us
• Time delay from trigger input to half max. is < 500 ns
• Jitter referenced to trigger input is < 1 ns
• Monitor voltage divider

Input Specifications:

• Trigger pulse is 1 us/50 ohm
  Input amplitude is selectable between standard TTL and +40 V modulator trigger level
• External bias voltage (max.) is 150 Vdc
• AC power
  • Voltage is 120 Vac
  • Current is 1 Amp

End of Line Clipper Specifications:

• Inhibit output pulses for EOLC peak pulse current amplitude exceeding approx. 1,000 amps and for integrated current which is adjustable from the front panel.

Detection and LED displays for: AC power on, trigger input present, HV output present, if trigger input repetition rates are greater than 1800 Hz., if the thyratron misfires, if internal faults, EOLC signal present, if EOLC trips.

Mechanical Specifications:

All components are housed in a 5.25" high, 8" deep, 19" wide rack mount chassis, with perforated top and bottom covers for air circulation. Chassis cooling is by natural convection. The ambient temperature can vary from 0-50 degrees C.

Model 757 SCR Thyratron Driver

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2404 Comanche Road NE
Albuquerque, New Mexico 87107
Ph : 505-881-8887
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