Current Limiting; Electronic Fuse; Concept Of The Hm 7042-4; Introduction To The Operation Of The Hm 7042-4 - Hameg Instruments HM 7042-4 Handbuch

Basics of power supplies
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 regulation as
long as still at least 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 HM 7042-
4 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 ALL CHANNELS
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
STOP STOP
those connected in parallel should have insufficient
overload protection it may be destroyed. 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.

Electronic fuse

In order to provide a still better protection than current limiting
offers the HM 7042-4 features an electronic fuse. As soon as I
is reached all outputs will be immediately simultaneously dis-
abled. They may be turned on again by depressing OUPUT ALL
“
CHANNELS .
22
“
the voltage will be turned on. It is
I
max
remains stable,
out
Concept of the HM7042-4
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-
4 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 touching
of live parts may be fatal! Only qualified and well
instructed personnel is allowed to use such in-
stallations!
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 impedance,
noise, regulation.
Output power of the HM 7042-4
The maximum combined output power is 155.5 W. The HM 7042-
4 has a temperature-controlled fan the rpm of which will increase
with rising temperature. This will ensure sufficient cooling under
all normal operating conditions. Below 50 degress C internal
temperature the fan remains disabled.
Switching the display on/off
All Hameg supplies feature a pushbutton which turns the outputs
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 ALL CHANNELS
Introduction to the
operation of the HM 7042-4
First time operation
Please observe especially the following notes:
I
out
– 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
transformer 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 HM 7042-4
After turning on all outputs will remain disabled, protecting the
max
loads. Prior to pressing OUPUT ALL CHANNELS
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 LIMIT
. The mode "Electronic fuse" may be selected after turn-on,
but after each turn-off-on cycle "Current limit" will be set.
“
.
“
all output
Subject to change without notice