Current Limit; Electronic Fuse; Concept Of The Hm7042; Introduction To The Operation - Hameg Instruments HM7042-5 Handbuch

B a s i c s o f p o w e r s u p p l i e s
In order to increase the total available current the outputs of
supplies can be paralleled. The output voltages of the supplies
involved are adjusted as accurately as possible to the same
value. In this mode it is possible that one or more supplies enter
the current limit mode. The output voltage remains in regula-
tion as long as still at least one supply is in the voltage control
mode. It is recommended but not absolutely necessary to fine
adjust the voltages such that the individual current contributions
remain nearly equal. Of course, the maximum available output
current is the sum of the individual supplies' maximum currents.
Example:
A load requires 12 V at 2.7 A. Each 32 V output of the HM7042-5
can deliver 2 A. First set both supplies to 12 V. Then connect both
black and both red safety connectors respectively in parallel.
The load is connected to one of the supplies. With the pushbutton
OUTPUT the voltage will be turned on. It is normal that one
output will current limit at 2 A while the other will contribute
the balance of 0.7 A in voltage regulation.
In case you should parallel power supplies of other
manufacturers with HAMEG supplies make sure
all are specified for this mode of operation. If one
supply of those connected in parallel should have
insufficient overload protection it may be destroy-
ed. HAMEG supplies are specified for series and
parallel operation.

Current limit

means that a maximum current can be set. This is e.g. useful in
order to protect a sensitive test circuit. In case of an inadvertent
short in the test circuit the current will be limited to the value
set which will in most cases prevent damage.
U
out
U
const
Adjustment of current
Current limit
The picture shows that the output voltage V
while the current I increases until the current limit selected will
be reached. At this moment the instrument will change from
constant voltage regulation to constant current regulation. Any
further load increase will cause the current to remain stable
while the voltage decreases ultimately to zero.
U
out

Electronic fuse

U
const
In order to provide a still better protection than current limiting
offers the HM7042-5 features an electronic fuse. As soon as
I is reached all outputs will be immediately simultaneously
max
disabled.
They may be turned on again by depressing OUPUT .
short cut at
approx. 20% of I
max
22
Subject to change without notice
I
I
max
out
remains stable,
out
Current limit
starts at 110% of I
max
I
I
max
out

Concept of the HM7042-5

In this instrument the advantages of a SMPS, especially high
efficiency, and those of a linear regulator, e.g. high quality
regulation, are combined. A high power DC/DC converter is
used as a preregulator for the following linear regulators, this
reduces the high losses typical of purely linear regulation. The
HM 7042-5 has 3 independent and isolated voltage sources. In
addition to the standard mode of operation as a triple output
supply all outputs may be series or parallel connected.
Exceeding the safety voltage level of 42 V!
If all outputs are series connected the maximum
output voltage can exceed 42 V. In such case tou-
ching of live parts may be fatal! Only qualified and
well instructed personnel is allowed to use such
installations!
In series conncetion the maximum available current is limited to
2 A. Paralleling the two 32 V outputs will yield 4 A at a maximum
of 32 V. Please note that series as well as parallel conncetion
may influence some specifications valid such as output impe-
dance, noise, regulation.
Output power of the HM7042-5
The maximum combined output power is 155.5 W. The HM7042-5
has a temperature-controlled fan the rpm of which will increase
with rising temperature. This will ensure sufficient cooling under
all normal operating conditions.
Switching the display on/off
All Hameg supplies feature a pushbutton which turns the out-
puts ON/OFF while the supply remains functioning. This allows
to preset all voltages to their respective desired values prior to
turning the outputs on by depressing OUTPUT .

Introduction to the operation

First time operation
Please observe especially the following notes:
– The line voltage indicated on the rear panel corresponds
to the available line voltage, also, the correct fuses for this
line voltage are installed. The fuses are contained in the line
voltage connector housing.
– The connection to the mains is either by plugging into a
socket with safety ground terminal or via an isolation trans-
former of protection class II.
– No visible damage to the instrument.
– No visible damage to the line cord.
– No loose parts floating around in the instrument.
Turning on the HM7042-5
After turning on all outputs will remain disabled, protecting the
loads. Prior to pressing OUPUT all output voltages should be
set to their desired values. Also, after turn-on the instrument
will be in the operating mode "Current limit".
The maximum current available can be set by CURRENT
. The mode "Electronic fuse" may be selected after turn-on,
but after each turn-off-on cycle "Current limit" will be set.