HP BENCH Series User Manual

POWER SUPPLY
UNDER TEST
MODEL NO.
Rl
62I3A/62I4A
62I5A/62I6A
62I7A/62I6A
ion , [ow,t5%
65n, I0w,t57o
250n, I0w,±57o
DIFFERENTIAL
VOLTMETER
V G
Figure 5-5. Load Regulation, Test Setup
5-21 To test the line regulation, proceed as fol
lows:
a. Connect variable auto transformer be
tween input power source and power supply power
input.
b. Connect test setup shown in Figure 5-5.
c. Adjust variable auto transformer for 105
VAC input.
d. Set METER SELECTION switch to VOLTS
position.
e. Turn on supply and adjust VOLTAGE
controls until front panel meter indicates exactly
the maximum rated output voltage.
f. Read and record voltage indicated on dif
ferential voltmeter.
g. Adjust variable auto transformer for 125V
ac input.
h. Reading on differential voltmeter should
not vary from reading recorded in step f by more
than 4mV.
5-22 Ripple and Noise.
Definition: The residual ac voltage
which is superimposed on the dc out
put of a regulated power supply.
Ripple and noise may be specified and
measured in terms of its RMS or (pre
ferably) peak-to-peak value.
Ripple and noise measurement can be made at any
input ac line voltage combined with any dc output
voltage and load current within rating.
5-23 The amount of ripple and noise that is present
on the power supply output is measured either in
terms of the RMS or (preferably) peak-to-peak
value. The peak-to-peak measurement is particu
larly important for applications where noise spikes
could be detrimental to a sensitive load, such as
logic circuitry. The RMS measurement is not an
ideal representation of the noise, since fairly
high output noise spikes of short duration could
be present in the ripple and not appreciably in
crease the RMS value.
5-24 The technique used to measure high frequency
noise or "spikes" on the output of a power supply
is more critical than the low frequency ripple and
noise measurement technique; therefore the former
is discussed separately in Paragraph 5-32.
5-25 Ripple and Noise Measurements. Figure
5-6A shows an incorrect method of measuring p-p
ripple. Note that a continuous ground loop exists
from the third wire of the input power cord of the
supply to the third wire of the input power cord of
the oscilloscope via the grounded power supply
case, the wire between the negative output termi
nal of the power supply and the vertical input of
the scope, and the grounded scope case. Any
ground current circulating in this loop as a result
of the difference in potential Eq between the two
ground points causes an IR drop which is in series
with the scope input. This IR drop, normally
having a 60 Hz line frequency fundamental, plus
any pickup on the unshielded leads interconnect
ing the power supply and scope, appears on the
face of the CRT. The magnitude of this resulting
noise signal can easily be much greater than the
true ripple developed between the plus and minus
output terminals of the power supply, and can
completely invalidate the measurement.
5-26 The same ground current and pickup problems
can exist if an RMS voltmeter is substituted in
place of the oscilloscope in Figure 5-6. However,
the oscilloscope display, unlike the true RMS
meter reading, tells the observer immediately
whether the fundamental period of the signal dis
played is 8. 3 milliseconds (1/120 Hz) or 16. 7
milliseconds (1/60 Hz). Since the fundamental
ripple frequency present on the output of an
supply is 120 Hz (due to full-wave rectification),
an oscilloscope display showing a 120 Hz funda
mental component is indicative of a "clean"
measurement setup, while the presence of a 60 Hz
fundamental usually means that an improved setup
will result in a more accurate (and lower) value of
measured ripple.
5-27 Figure 5-6B shows a correct method of meas
uring the output ripple of a constant voltage power
supply using a single-ended scope. The ground
loop path is broken with a 3 to 2 adapter in series
with the power supply's AC line plug. Notice,
5-4

HP BENCH Series Specifications

General

Brand	HP
Model	BENCH Series
Category	Power Supply
Language	English