KMP_78253C_D05 Page 4 of 5
78253 Series
MAX253 Compatible Converter Transformers
www.murata-ps.com/support
TYPICAL CHARACTERISTICS (VOLTAGE CURVES) continued
VOLTAGE DEVIATION
Voltage Deviation from Nominal
25°C Output (%)
Voltage Deviation from Nominal
25°C Output (%)
Temperature (°C) Temperature (°C)
Voltage Deviation from Nominal
25°C Output (%)
Voltage Deviation from Nominal
25°C Output (%)
Temperature (°C) Temperature (°C)
78253/35(M)C
110
105
100
95
90
-50
0
50
25
-25
75
100
78253/55(M)C
110
105
100
95
90
-50
0
50
25
-25
75
100
78253/35(M)VC
110
105
100
95
90
-50
0
50
25
-25
75
100
78253/55(M)VC
110
105
100
95
90
-50
0
50
25
-25
75
100
SOLDERING INFORMATION
1
Pin finish
Matte tin
Peak wave solder temperature
300˚C for 10 seconds
Peak reflow temperature
220˚C
2
TUBE OUTLINE DIMENSIONS
All specifications typical at T
A
=25°C
1 For further information, please visit www.murata-ps.com/rohs
2 For high temperature reflow parts see 78253J series.
0.023±0.005
(0.60±0.15)
0.16 (4.00)
0.22 (5.50)
0.43
(10.95)
0.51
(12.95)
0.15
(3.80)
0.62 (15.70)
Tube length: 18.3±0.08 (465±2). Tube quantity: 50.
Tube material: Antistatic coated clear pvc.
Unless otherwise stated all dimensions in inches(mm) ±0.01 (0.25).
TECHNICAL NOTES
ISOLATION VOLTAGE
‘Hi Pot Test’, ‘Flash Tested’, ‘Withstand Volt-
age’, ‘Proof Voltage’, ‘Dielectric Withstand
Voltage’ & ‘Isolation Test Voltage’ are all terms
that relate to the same thing, a test voltage,
applied for a specified time, across a compo-
nent designed to provide electrical isolation, to
verify the integrity of that isolation.
All products in this series are 100% production
tested at their stated isolation voltage.
A question commonly asked is, “What is the
continuous voltage that can be applied across
the part in normal operation?”
For a part holding no specific agency approv-
als both input and output should normally be
maintained within SELV limits i.e. less than
42.4V peak, or 60VDC. The isolation test
voltage represents a measure of immunity to
transient voltages and the part should never
be used as an element of a safety isolation
system. The part could be expected to function
correctly with several hundred volts offset
applied continuously across the isolation bar-
rier; but then the circuitry on both sides of the
barrier must be regarded as operating at an
unsafe voltage and further isolation/insulation
systems must form a barrier between these
circuits and any user-accessible circuitry ac-
cording to safety standard requirements.
REPEATED HIGH-VOLTAGE
ISOLATION TESTING
It is well known that repeated high-voltage
isolation testing of a barrier component can
actually degrade isolation capability, to a
lesser or greater degree depending on ma-
terials, construction and environment. This
series has toroidal isolation transformers,
with no additional insulation between pri-
mary and secondary windings of enameled
wire. While parts can be expected to with-
stand several times the stated test voltage,
the isolation capability does depend on the
wire insulation. Any material, including this
enamel (typically polyurethane) is suscep-
tible to eventual chemical degradation when
subject to very high applied voltages thus
implying that the number of tests should be
strictly limited. We therefore strongly advise
against repeated high voltage isolation test-
ing, but if it is absolutely required, that the
voltage be reduced by 20% from specified
test voltage.
This consideration equally applies to agency
recognized parts rated for better than
functional isolation where the wire enamel
insulation is always supplemented by a
further insulation system of physical spacing
or barriers.
