Table of Contents
Advertisement
UNLOADING
'TRANSIENT
1*» 8 3mS-4
LOADING
TRANSIENT
TRANSIENT
TRANSIENT
Figure 5-6.
Load Transient Recovery Waveforms
5-35
Temperature Coefficient.
Definition: The change in output voltage per°C change in
ambient temperature measured while ac line voltage, output
voltage setting, and load resistance are all held constant.
5-36
The temperature coefficient of a power supply is
measured by placing the unit in an oven and varying the
temperature over any span within the power supply's rating.
The power supply temperature must be allowed to stabilize for
a sufficient time at each measurement temperature.
5-37
The temperature coefficient given in the specification
table is the maximum temperature-dependent output voltage
change which will result over any one-degree interval. The
digital voltmeter used to measure the supply's output voltage
change should be placed outside the oven and should have a
long-term stability adequate to insure that its drift will not
affect the overall measurement accuracy.
f.
Disconnect DVM from Rjvj and reconnect DVM to
power supply sense terminals.
g.
Place power supply in temperature-controlled oven
(DVM remains outside oven). Set temperature to
30°C and allow 30 minutes warm-up.
h.
Record DVM reading.
i.
Raise Temperature to 40°C and allow 30 minutes
warm-up.
j.
Observe DVM reading. Difference in voltage reading
between steps h and j should be less than 70 mVdc.
5-39
Drift (Stability).
Definition: The change in output voltage for the first eight
hours following a 30-minute warm-up period. During the in¬
terval of measurement, input line voltage, load resistance and
ambient temperature are ail held constant.
5-40
This measurement is made by monitoring the output
of the power supply on a digital voltmeter over the stated
measurement interval. A strip chart recorder can be used to
provide a permanent record. Place a thermometer near the
supply to verify that the ambient temperature remains con¬
stant during the period of measurement. The supply should be
located away from any source of stray air current. If possible,
place the supply in an oven and hold it at a constant
temperature. Take care that the measuring instrument has an
eight-hour stability at least an order of magnitude better than
the stability specification of the power supply being tested.
Typically, a supply will drift less over the eight-hour measure¬
ment interval than during the half -hour warm-up period.
541
To check the output stability, proceed as follows:
a.
Connect load resistance and digital voltmeter (DVM)
as illustrated in Figure 5-2.
b.
Turn on supply and turn up output voltage, if unit
switches to CC LIMIT mode, use OUTPUT ADJUST
controls to increase CC limit so that unit remains in
CV mode.
c.
Adjust output voltage until DVM indicates exactly 60
V (maximum rated output voltage.)
d.
Disconnect DVM from power supply sense terminals
and connect DVM across current-monitoring resistor
(Rm>-
5 38
To check the temperature coefficient, proceed as
follows:
a.
Connect load resistance and digital voltmeter as il¬
lustrated in Figure 5-2.
b.
Turn on supply and turn up output voltage, If unit
switches to CC LIMIT mode, use OUTPUT ADJUST
controls to increase CC limit, so that unit remains in
CV mode,
c.
Adjust output voltage until DVM indicates exactly 60
V (maximum rated output voltage).
d.
Disconnect DVM from power supply sense terminals
and connect DVM across current monitoring resistor
<Rm>-
e.
Reduce resistance of Rl until DVM reads 33 mV, in
dicating that current output is exactly 3.3 A (max¬
imum rated power output). Ensure that power supply
remains in CV mode.
e.
Reduce resistance of R[ until DVM reads 33 mV, in¬
dicating that the current output is exactly 3,3 A (max
imum rated power output). Ensure that power sup¬
ply remains in CV mode,
f.
Disconnect DVM from Rj\/) and reconnect DVM to
power supply sense terminals.
g.
Allow 30 minutes warm up,and then record DVM
reading.
h.
After eight hours, DVM reading should not differ
from reading of step g by more than 21 mVdc.
5-42
Constant-Current Tests
5 43
The instruments, methods, and precautions for the
proper measurement of constant-current power supply
characterisitics are for the most part identical to those already
described
for
the
measurement
of
constant-voltage
Advertisement
Table of Contents
