Basics Of Power Supplies; Linear Regulators; Parallel And Series Operation - Hameg Instruments HM8040-3 Manuel

Basics of power supplies

Linear regulators

Linear regulators offer a very constant output
voltage even if the mains or the load may vary
considerably. The remaining ripple will be very
low with any good instrument, about 1 mV
less and may be neglected. Also, linear regulators
are free from EMI as generated by SMPS.
A conventional mains transformer isolates the
instrument from the mains. A recitifier provides
an unregulated dc voltage buffered by capacitors
which also serve as energy storage elements. A
transistor in series with the output is controlled
by a regulation loop which compares (a fraction
of) the output voltage with a highly stable
reference voltage. This analog loop is very fast
and will restore the output voltage quickly to its
desired value whenever the input voltage or the
load vary.

Parallel and series operation

Supplies must be specified for these operating
modes which is the case with all HAMEG
supplies. The output voltages to be combined are
normally independent of each other. The outputs
of one or more supplies can then be connected
in series or parallel.
Series operation
As you see (Fig. 2) the voltages are added. The
total voltage generated thus may exceed the 42
Danger! – High voltage Danger! – High voltage
Danger! – High voltage Danger! – High voltage Danger! – High voltage
Line
AC
voltage
Fig. 1: Linear regulator
or
rms
transformer rectifier
B1
TR1
C1
B a s i c s o f p o w e r s u p p i e s
Fig. 2: Serial operation
V safety limit. In such case touching live parts
may create danger of life! It is assumed that only
qualified and extensively instructed personnel is
allowed to operate such power supplies and their
loads. All outputs carry the same current, hence
the current limit adjustments of all supplies
should be set to the same value. If in any of the
series connected power supplies the current limit
will be reached this supply will enter the current
limiting mode, so the total output voltage will
decrease and become unregulated!
Parallel operation
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.
actuator
analog controller
OPVA
reference voltage
REF
Subject to change without notice
output
C2
DC
voltage
GND
23