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3231 Hi V pulse gen man TS (Page 28) Model 3231 Users Manual
The High-Voltage
Pulse Generator Warranty
323102 Rev A
New Focus, Inc. guarantees its products to be
free of defects for one year from the date of
shipment. This is in lieu of all other guarantees,
expressed or implied, and does not cover inci-
dental or consequential loss.
Contents
Warranty
Introduction
Safety Precautions
Theory
Operation
Appendix 1:
AC Operating Voltages & Fuses
Appendix 2:
Calibration
Specifications
2
3
4
5
6
17
21
26
Is a registered trademark of
New Focus, Inc.
2 Introduction
The New Focus Model 3231 is a high-voltage pulse
generator capable of driving <50 pF capacitive
loads (i.e., Pockels cells and bulk modulators)
with amplitudes as high as 300 V. Typical applica-
tions using the Model 3231 include pulse pickers,
optical choppers, and electronically variable wave-
plates. It is ideal anywhere a high-voltage, high-
speed (up to 1 MHz) pulse generator is required.
This pulse generator even includes an input for
triggering off of external pulse trains, as from a
mode-locked laser, and it provides a monitor out-
put for convenient low-voltage viewing of pulse
characteristics.
3 4
Safety
Precautions
IMPORTANT: Please read through the entire
manual before operating the Model 3231.
WARNING: Hazardous shock can result from
improper operation. To avoid personal injury, use
safety precautions appropriate for high-voltage
sources:
Do not work alone.
Do not operate with the cover removed.
Use extreme care when handling output connec-
tions. Do not connect or disconnect cables when
high voltage is present.
Be sure the ground conductor of the AC power
cord connects the instrument to a solid earth
ground.
To prevent equipment damage please observe the
following:
CAUTION: Loads connected to the Model 3231
must be able to dissipate up to 2-kW peak power
and 20-W average power for 300-V operation.
Loads with either lower peak or average power rat-
ings may be damaged or destroyed. The load New
Focus provides with this unit meets these criteria. 5
Theory
The Model 3231 supplies flat-topped pulses of posi-
tive or negative polarity. It has output protection
for short-circuit, open-circuit, over-current, and
over-temperature conditions. The pulses produced
from this pulse generator can have a peak level
that is adjustable from 20 V to 300 V. The baseline
level is fixed at ground. From the front panel, you
can adjust the pulse width from 20 ns to 1 µs. The
leading-edge transition time is <5 ns, while the
trailing-edge transition time is <20 ns. The pulses
are triggered either from an internal repetition rate
generator which is adjustable from 1 Hz to 1 MHz
or from a valid external sync signal (Sync In). The
unit automatically synchronizes the output pulses
when a valid Sync In signal is provided. In either
case, you can adjust the delay from the trigger
source from 0 to 100 ns. For convenience, a moni-
tor out signal is provided. It is a scaled down ver-
sion of the high-voltage output pulse waveform.
Use this monitor output for timing alignment and
fine adjustment of the output width.
Note: The Model 3231 is designed to operate with
a load impedance of 50 . For operation at 300 V,
the load must be rated for 2 kW peak power and
20 W average power dissipation. The failure modes
for loads with insufficient power ratings may vary.
Some loads will arc and behave as a short (either
temporarily or permanently). Others, instead, will
simply open up. 6
Operation
POWER UP
Before plugging the instrument in, be sure the
selection switch is set for the correct AC operating
voltage, and that a fuse of proper value is in place.
Refer to Appendix 1 for voltage selection instruc-
tions and fuse requirements.
Switching the Power switch to the on, or 1,
position on the front panel of the Model 3231
applies AC to the unit. All functions, displays,
inputs and outputs are functional at this point,
except for the High-Voltage Output and the
Output Monitor.
To turn on the High-Voltage Output and the
Output Monitor, press the High Voltage On/Off
pushbutton; the green LED adjacent to the High
Voltage On/Off switch will illuminate.
If AC is turned off and then re-applied, the High-
Voltage Output will remain off until enabled via
the High Voltage On/Off switch.
PROTECTION FEATURES
The Model 3231 pulse generator incorporates cir-
cuitry to prevent accidental damage to the instru-
ment due to shorts applied to the output, high-
voltage reflections, excessive current demand, and
over-temperature conditions.
Short-Circuit Protection
If a short or near-short appears at the output while
the Model 3231 is producing a pulse, the instru-
ment will respond by rapidly turning off the pulse
being generated. This protects the Model 3231 out-
put stage from damage. It takes effect if the short is Fig. 1
Front panel view of the Model 3231.
Made in U.S.A.
High-Voltage Pulse Generator
3231
Repetition Rate
Delay
Width
Power
Sync
Input
Output
Monitor
High-Voltage
Output
High Voltage
On/Off
Polarity
Volts
1-10 Hz
0.1-1 MHz
10-100
kHz
0.1-1 kHz
1-10 kHz
10-100
Hz
20-100 ns
0.1-1
µ
s
Amplitude
Trig
Sync
NEW FOCUS, Inc. Mountain View, CA, 94041
+ Caution:
Up to 300 V
7 8
present when the pulse begins (even if the short is
present before the instrument is turned on) or if
the short is applied after the pulse has started.
When the protection circuit turns the pulse off, the
active front-panel Polarity LED (see LED
Indicators p. 15) flashes to alert the user to a fault
condition. The output is disabled and held at zero
for about four seconds before the instrument tries
to put out another pulse. When it does retry, the
output level will be raised slowly. If a short-circuit
condition is not present, pulses are produced nor-
mally. If a short is still present, the output is again
disabled, the LED starts blinking and the cycle
repeats. The Model 3231 will continue to retry
every four seconds until it detects that a short-cir-
cuit condition no longer exists.
Over-Voltage Protection
The energy of a high-voltage pulse traveling down
a length of cable can be reflected back if the
impedance terminating the cable does not match
that of the cable itself (50 ). An unterminated
cable (open circuit) will produce a reflected wave
of double the pulse amplitude. For a long cable
and a wide pulse, the energy carried back in such a
reflection could potentially damage an unprotect-
ed output stage. To prevent this, the Model 3231
employs circuitry to clamp such reflections to a
safe level. This circuitry does not interrupt the
operation of the instrument, and the front-panel
LEDs are unaffected.
Over-Current Protection
When the specified duty factor maximum for a
given pulse level is exceeded (see Duty Factor 9
below), the Model 3231 will go into a current-limit
state and the output voltage will drop below the
selected value. Using a low-impedance load may
have this effect as well, even when duty-factor
maximums have not been exceeded. Additionally,
dialing in a large change in the level may
momentarily cause a current-limit condition.
While the instrument is current limiting, the active
front-panel Polarity LED will flash. When the
cause of the current-limit condition is removed,
the Model 3231 output will slowly rise until it
again produces pulses of accurate output level.
Over-Temperature Protection
When the specified maximum pulse repetition rate
for a given pulse level is exceeded (see Timing
Requirements below), overheating of the output
stage can result. To prevent this, the Model 3231
incorporates thermal protection circuitry that will
slowly lower the output level when the maximum
repetition rate is exceeded. The active front-panel
Polarity LED will flash. When the repetition rate
or output level is reduced, the Model 3231 will
return to normal operation.
TIMING REQUIREMENTS
Duty Factor
The Model 3231 instrument can operate at a maxi-
mum duty factor of 1% at 300 V. For operation at
lower peak voltages, the duty factor may be
increased. Table 1 shows typical maximum duty
factors for various voltage levels. If the duty factor
is too high, the Model 3231 over-current circuitry
will respond by decreasing the pulse amplitude and flashing the active front-panel Polarity LED
(as described in Over-Current Protection p. 8).
Repetition Rate
Independent of duty factor, the maximum pulse
rate depends on pulse amplitude, as shown in
Table 1. When the maximum pulse rate is exceed-
ed, the output level will drop and a front panel
Polarity LED will flash (as described in Over-
Temperature Protection p. 9).
Duty factor constraints may additionally limit the
repetition rate for a given pulse width. As an exam-
ple, the last column in Table 1 gives the maximum
repetition rate when a 100-ns width is used.
Pulse Spacing
A minimum pulse spacing of 200 ns is required
between the trailing edge of a pulse and the lead-
ing edge of the following pulse. If this minimum
spacing is not me