Avtech AVR-8F-B-P-ADB1A, Instructions Manual

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LOAD RESISTANCE
The minimum pulse width is 100 ns. The maximum pulse width depends on the load
resistance:
PW
MAX
= R
LOAD
× 10 uF, up to a maximum of 1 second
The maximum duty cycle depends on the set amplitude and the load resistance:
DC
MAX
= 100% × (P
MAX
/ 1000V) ÷ (V
OUT
/ R
LOAD
), up to a maximum of 50%
P
MAX
is 5 Watts. The maximum average output power (P
MAX
) is only obtainable at
maximum amplitude.
For example, if the output amplitude is 1000V, and the load resistance is 5 kΩ, then the
limits are:
PW
MAX
= 5 kΩ × 10uF = 500 ms
DC
MAX
= 100% × (5W / 1000V) ÷ (1000V / 5 kΩ ) = 2.5%
If the amplitude is reduced to 500V, the maximum pulse width would be unchanged at
500 ms, but the maximum duty cycle would double to 5%.
To allow the instrument to safely enforce these operating limits, the user should set the
expected load resistance value using the front panel “Load” menu or the “output:load”
computer command.
OUTPUT IMPEDANCE
The output impedance (the internal resistance in series with the output) is switchable
between zero and 50Ω, nominally.
The zero Ohm mode allows the pulser to act as true a voltage source, and to maximize
the voltage output. The voltage across the load resistance will be equal to the set
amplitude.
However, for some applications it may be desirable to have R
OUT
= 50Ω. For example,
this may be a convenient method of driving laser diodes in a probing station through
coaxial cables and probes. The diode DUT represents a transmission line impedance
mismatch, but the resulting reflections would be absorbed by the 50Ω “back-matching”
of the pulser. The internal 50Ω output impedance is capable of dissipating the full rated
average output power of the instrument (5 Watts).
If the output impedance is set to 50Ω, some amplitude will be lost across the internal
resistance, due to the resistor divider effect.
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