Table of Contents
Advertisement
b.
The recovery time of the output voltage
is longer for load resistance changes.
c.
A large surge current causing a high pow¬
er dissipation in the load occurs when the load re¬
sistance is reduced rapidly.
3-61 REVERSE VOLTAGE LOADING
3-62 A diode (CR15) is connected across the output
terminals.
Under normal operating conditions, the
diode is reverse biased (anode connected to the
negative terminal).
If a reverse voltage is applied
to the output terminals (positive voltage applied to
the negative terminal), the diode will conduct,
shunting current across the output terminals and
limiting the voltage applied across the output ter¬
minals to the forward voltage drop of the diode.
This diode protects the series transistors and the
output electrolytic capacitors.
3-63
REVERSE CURRENT LOADING
3-64 Active loads connected to the power supply
may actually deliver a reverse current to the power
supply during a portion of its operating cycle. An
external source cannot be allowed to pump current
into the supply without loss of regulation and pos¬
sible damage to the output capacitor.
To avoid
these effects, it is necessary to preload the sup¬
ply with a dummy load resistor so that the power
supply delivers current through the entire opera¬
tion cycle of the load device.
3-65
GROSS CURRENT LIMIT/AUTOMATIC DUAL¬
RANGE SWITCHING
3-66 The power supply can be operated at a CUR¬
RENT setting above the high range VOLTAGE rating
as given below:
Model
Low Range
High Range
Voltage
Current
Voltage
Current
6104A/6114A
6105A/6115A
0-2 0V
0-50V
0-2.0A
0-0.8A
20-40V
50-100V
0-1. 0A
0-0. 4A
For instance, the 6104A can be operated with the
CURRENT control set to 1.5A and the VOLTAGE con¬
trol set to 30V.
However, as shown in Figure
3-13, if the load resistance draws output current
above the high range rating (i. e. greater than 1A
for the 6104A/6114A or 0.4A for the 6105A/6115A),
the power supply enters the gross current limit
region (the CURRENT MODE indicator comes on).
In the gross current limit region, output current is
maintained up to approximately 130% (at nominal
line voltage) of the high range rating (1.3A for the
6104A/6114A or 0. 52A for the 6105A/6115A) of the
supply while output voltage is maintained at the
VOLTAGE setting up to the maximum high range
rating.
If load resistance continues to change
and causes output current to exceed the gross cur¬
rent limit region, however, the supply is automati¬
cally switched to the low range and output voltage
is reduced to approximately 130% (again, at nomin¬
al line voltage) of the low range rating (26V for the
6104A/6114A or 65V for the 6105A/6115A).
Of
course, at this point the VOLTAGE setting of the
supply is overridden. Further load reductions cause
the supply to enter the constant current mode and
output voltage is further reduced as necessary to
supply the necessary output current depending upon
load requirements and the CURRENT setting. Notice
that when operated in the gross current limit region,
the supply's output is uncalibrated and may not
meet certain specifications (ripple, etc).
Note,
further, that if the supply is operated at low or
high line, the gross current limit region will, vary
(decrease at low line and increase at high line).
Figure 3-13.
Gross Current Limit/Dual-Range
Switching
3-10
Advertisement
Table of Contents
