
PSS, PSK Extended Data Sheet
Positive Switching Regulator (Industrial)
REV. FEB 25, 2004
Page 15 of 19
Table 12: Insulation concept leading to an SELV output circuit
Conditions Front end
Switching regulator
Result
Supply
Minimum required grade
Maximum
Minimum required safety
Measures to achieve the
Safety status of
voltage
of isolation, to be provided DC output
status of the front end
specified safety status of the
the switching
by the AC-DC front end,
voltage
output circuit
regulator output
including mains supplied
from the
circuit
battery charger
front end 1
Battery
Double or Reinforced
≤60 V
SELV circuit
None
SELV circuit
supply,
>60 V
Earthed hazardous voltage Input fuse 3 and earthed 4
Earthed SELV
considered
secondary circuit 2
or non accessible case 5
circuit
as secon-
Unearthed hazardous
Input fuse 3 and unearthed,
Unearthed SELV
dary circuit
voltage secondary circuit 5
non accessible case 5
circuit
Hazardous voltage
Input fuse 3 and earthed output Earthed SELV
secondary circuit
circuit 4 and earthed 4 or non
circuit
accessible case 5
Mains
Basic
≤60 V
Earthed SELV circuit 4
None
≤250 VAC
ELV circuit
Input fuse 3 and earthed output
>60 V
Hazardous voltage
circuit 4 and earthed 4 or non
secondary circuit
user accessible case 5
Double or reinforced
≤60 V
SELV circuit
None
SELV circuit
>60 V
Double or reinforced insu-
Input fuse 3 and unearthed
Unearthed SELV
lated unearthed hazardous and non accessible case 5
circuit
voltage secondary circuit 5
1 The front end output voltage should match the specified input voltage range of the switching regulator.
2 The conductor to the Gi– terminal of the switching regulator has to be connected to earth by the installer according to the relevant
safety standard, e.g. IEC/EN 60950.
3 The installer shall provide an approved fuse (slow blow type with the lowest current rating suitable for the application, max. 12.5 A) in
a non-earthed input conductor directly at the input of the switching regulator. If Vo+ is earthed, insert the fuse in the Gi- line. For UL’s
purpose, the fuse needs to be UL-listed.
4 The earth connection has to be provided by the installer according to the relevant safety standard, e.g. IEC/EN 60950.
5 Has to be insulated from earth by double or reinforced insulation according to the relevant safety standard, based on the maximum
output voltage from the front end.
Safety of Operator Accessible Output Circuit
If the output circuit of a switching regulator is operator-ac-
cessible, it shall be an SELV circuit according to IEC/EN
60950 related safety standards.
The following table shows some possible installation con-
figurations, compliance with which causes the output cir-
cuit of the switching regulator to be an SELV circuit accord-
ing to IEC/EN 60950 up to a configured nominal output volt-
age of 30 V, or 48 V if option C is fitted.
However, it is the sole responsibility of the installer or user
to assure the compliance with the relevant and applicable
safety regulations.