
Industrial Environment
Switching Regulators, PCB & Chassis
PSC-Family
Edition 2/96 - Melcher AG
4 - 61
MELCHER
The Power Partners.
4.2
Description of Options
Option -9 Extended Temperature Range
The operational ambient temperature range is extended to
TA = –40...71
°C.
Option L Input filter
Option L is recommended to reduce superimposed inter-
ference voltages, and to prevent oscillations, if input lines
exceed approx. 5 m in total length. The fundamental wave
(approx. 120 kHz) of the reduced interference voltage be-
tween Vi+ and Gi– has, with an input line inductance of
5
H a maximum magnitude of 4 mV
rms.
The input impedance of the switching regulator at 120 kHz
is about 50 m
. The harmonics are small in comparison
with the fundamental wave. See also data: RFI.
With option L, the maximum permissible additionally super-
imposed ripple
ui of the input voltage (rectifier mode) at a
specified input frequency
f i has the following values:
Input voltage up to 80 V:
ui max = 22 Vpp at 100 Hz or Vpp = 2200 Hz/fi 1 V
Input voltage up to 40 V:
ui max = 12 Vpp at 100 Hz or Vpp = 1200 Hz/fi 1 V
However, the minimum differential voltage
Ui o min between
input and output voltages as specified in "Electrical Input
and Output Data" should be maintained.
Option P Potentiometer
Option P and the R-function cannot be supported simulta-
neously. The output voltage
Uo can be adjusted with a
screwdriver in the range from 0.92…1.08 of the nominal
output voltage
Uo nom.
Option C
Thyristor Crowbar
This option is recommended to protect the load against
power supply malfunction, but it is not designed to sink ex-
ternal currents.
A fixed-value monitoring circuit checks the output voltage
Uo. When the trigger voltage Uoc is reached, the thyristor
crowbar triggers and disables the output. It may be deacti-
vated by removal of the input voltage. In case of a switching
transistor defect, an internal fuse prevents excess current.
Note: As a central overvoltage protection device, the crow-
bar is usually connected to the external load via distributed
inductance of the lines. For this reason, the overvoltage at
the load can temporarily exceed the trigger voltage
Uoc.
Depending on the application, further decentralized over-
voltage protection elements may have to be used addition-
ally.
Table 9: Crowbar trigger levels
Characteristics
Conditions
5.1
12 V
15 V
24 V
36 V
Unit
min
max
min
max
min
max
min
max
min
max
Uo c
Trigger voltage
Ui min...Ui max
5.8
6.8
13.5
16
16.5
19
27
31
40
45.5
V
Io = 0...Io nom
ts
Delay time
TC min...TC max
1.5
s
Option U Ambient Temp. Range acc. UL Recognition
Underwriters Laboratories (UL) have approved the PSC
family as recognized components up to an ambient tem-
perature of
TA max – 25 K given by the upper temperature
limit of the standard PCB material. If the full maximum am-
bient temperature
TA max is required with UL approval, op-
tion U should be requested. It consists of an alternative
PCB material with a higher maximum temperature specifi-
cation.
The European approval boards have in contrast to UL ac-
cepted the standard PCB material to be operated up to
TA max = 71°C without any further precautions.