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c.
Adjust output voltage and Rj_ so that front-panel
meters indcates 60 V and 3.3 A.
d.
Because the impedance-matching resistors con¬
stitute a 2-to-1 attenuator, the noise spikes observed
on the oscilloscope should be less than 15 mV p-p
(instead of 30 mV p-p).
5-30
The circuit of Figure 5-4 can also be used for the
display of low-frequency ripple. Simply remove the four ter¬
minating resistors and the blocking capacitors and substitute a
high-gain vertical plug-in for the wide-band plug-in required
for spike measurements.
5-31
Load Transient Recovery Time.
Definition: The time "X" for output voltage recovery to
within "Y" millivolts of the nominal output voltage following
a "Z" amp step change in load current, where: "Y" is specified
as 75 mV; the nominal output voltage is defined as the dc level
halfway between the static output voltage before and after the
imposed load change; and "Z" is the specified load current
change of from 90% to 100% (or vice versa) of maximum cur¬
rent rating.
5-32
Measurement Techniques. Care must be taken in
switching the load resistance on and off. A hand-operated
switch in series with the load is not adequate since the resulting
one-shot displays are difficult to observe on most oscilloscopes
and the arc energy occurring during switching completely masks
the display with a noise burst, Transistor load switching devices
are expensive if reasonably rapid load current changes are to
be achieved.
5-33
We suggest that a mercury-wetted relay connected in
the load switching circuit shown in Figure 5-5 be used for
loading and unloading the supply. When this load switch is con¬
nected to a 60 Hz ac input, the mercury-wetted relay opens
and closes 60 times per second. The 25 k control adjusts the
duty cycle of the load current switching to reduce jitter in the
oscilloscope display. This relay may also be used with a 50 Hz
ac input.
5-34
Measurement Procedure. To check the load tran¬
sient recovery time, proceed as follows;
a.
Connect load resistor Rl (Figure 5-5) across output
of supply. Do not connect Rl2 and load switch at
this time,
b.
Turn on supply and adjust output voltage for 20 V on
front-panel meter. If unit switches to C-C LIMIT
mode, use OUTPUT ADJUST controls to increase
CC limit so that unit remains in CV mode.
c.
Adjust Rjj for approximately 2.229. (9A on front-
panel current meter). Increase CC limit as necessary
so that unit remains in CV mode.
d.
Turn off supply and connect Rl2 in parallel with Ru.
Do not connect load switch yet.
e.
Turn on supply and adjust output voltage to 20 V. In¬
crease CC limit as necessary so that unit remains in
CV mode.
f-
Set Ri 2 for approximately 20.2 0 (20 total resistance
across supply) by adjusting R[_2 until 6034A output
is 20 V and 10 A. Increase CC limit as necessary so
that unit remains in CV mode.
g.
Turn off supply and connect load switch and load
resistors as shown in Figure 5-5.
h.
Turn on supply and adjust output to 20 V and 10 A.
i.
Close line switch on repetitive load switch setup,
j.
Set oscilloscope for internal sync and lock on either
the positive or negative load transient spike.
k.
Set vertical input of oscilloscope for ac coupling so
that small dc level changes in power supply output
voltage will not cause display to shift.
l.
Adjust the vertical centering on the scope so that the
tail ends of the low-load and full-load waveforms are
symmetrically displaced about
the
horizontal
centerline of the oscilloscope. The centerline now
represents the nominal output voltage defined in the
specification.
m.
Adjust the horizontal positioning control so that the
trace starts at a major graticule division. This point
then represents time zero.
n.
Increase the sweep rate so that a single transient
spike can be examined in detail.
o.
Adjust the sync controls separately for the positive
and negative-going transients so that not only the
recovery waveshape but also as must as possible of
the rise time of the transient is displayed.
p.
Starting from the major graticule division represent¬
ing time zero, count to the right ImS and vertically
75 mV, recovery should be within these tolerances as
illustrated in Figure 5-6.
NOTES
1
THIS DRAWING SHOWS A SUGGEST
ED METHOD OF BUILDING A LOAD
SWITCH
HOWEVER. OTHER METHODS
COULD BE USEO, SUCH AS A TRAN¬
SISTOR SWITCHING NETWORK
MAXIMUM
LOAD RATINGS OF LOAD SWITCH ARE
5 AMPS, 500V, 250W (NOT 2500W).
2
USE MERCURY RELAY
CLARE TYPE
HPG 1002 OR WE TYPE 276B
5
SELECT CONTACT PROTECTION NET¬
WORK ACCORDING TO MERCURY
RELAY MANUFACTURER'S INSTRUC¬
TIONS.
4
Rl! MUST BE APPROXIMATELY 2.220
AND RL2 MUST BE 20.20 SO THAT
SUPPLY CAN BE SWITCHED BETWEEN
90% AND 100V. OF RATED CURRENT
Figure 5-5.
Load Transient Recovery Time Test Setup
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