78250 Series
MAX250 Compatible Converter Transformers
CHARACTERISTICS 78250C/78250MC
Parameter
Conditions
Min.
1.0
Typ.
2.0
2.0
69
Max.
2.5
3.0
90
Units
mH
μH
Primary Inductance, LP
Leakage Inductance, LL
Interwinding Capacitance, CWW
Primary D.C. Resistance, RDC
Volt-time Product, Et
10kHz, 100mV
100kHz, 100mV
100kHz, 100mV
<0.1VDC
pF
1.0
2.0
Ω
Vμs
Pins1/2 or 2/3
50
FEATURES
ꢀRoHS compliant
CHARACTERISTICS 78250VC/78250MVC
Parameter
Conditions
Min.
1.0
Typ.
2.0
35
Max.
2.5
40
Units
mH
μH
Primary Inductance, LP
Leakage Inductance, LL
Interwinding Capacitance, CWW
Primary D.C. Resistance, RDC
Volt-time Product, Et
10kHz, 100mV
100kHz, 100mV
100kHz, 100mV
<0.1VDC
ꢀMaxim MAX250 compatible
ꢀIsolation to 4kVrms
9
12
pF
1.4
1.8
Ω
Vμs
ꢀIndustry-standard pinout
ꢀSurface mount option
ꢀUL 94 V-0 package materials
ꢀLow profile
Pins1/2 or 2/3
50
ORDER CODE DETAILS
Order Code
Package Type
6 Pin DIL
Packaging Type
Tube
Quantity
78250C / 78250VC
50
50
78250MC / 78250MVC
78250MC-R / 78250MVC-R
6 Pin SM
Tube
ꢀToroidal construction
6 Pin SM
Tape & Reel
500
ꢀFully encapsulated
ABSOLUTE MAXIMUM RATINGS
Operating free air temperature range
Storage temperature range
ꢀIndustrial temperature range
-40°C to 85°C
-50°C to 125°C
300°C
DESCRIPTION
Lead temperature 1.5mm from case for 10 seconds
Peak current, IPK
Isolation voltage 78250(M)C (flash tested for 1 second)
Isolation voltage 78250V(M)C (flash tested for 1 second)
300mA
The 78250 series of converter transformers
are specifically designed for use with Maxim
chipsets to provide isolated RS232 interfaces.
Carefully controlled turns ratios ensure consistent
performance whilst a toroidal construction
minimises EMI.
1.5kVrms
4.0kVrms
All specifications typical at TA=25°C
TECHNICAL NOTES
ISOLATION VOLTAGE
REPEATED HIGH-VOLTAGE ISOLATION TESTING
‘Hi Pot Test’, ‘Flash Tested’, ‘Withstand Voltage’, ‘Proof Volt-
It is well known that repeated high-voltage isolation
age’, ‘Dielectric Withstand Voltage’ & ‘Isolation Test Voltage’ testing of a barrier component can actually degrade
are all terms that relate to the same thing, a test voltage,
applied for a specified time, across a component designed
to provide electrical isolation, to verify the integrity of that
isolation.
isolation capability, to a lesser or greater degree
depending on materials, construction and environ-
ment. This series has toroidal isolation transformers,
with no additional insulation between primary and
secondary windings of enameled wire. While parts
can be expected to withstand several times the
stated test voltage, the isolation capability does de-
pend on the wire insulation. Any material, including
this enamel (typically polyurethane) is susceptible
to eventual chemical degradation when subject to
very high applied voltages thus implying that the
number of tests should be strictly limited. We there-
fore strongly advise against repeated high voltage
isolation testing, but if it is absolutely required, that
the voltage be reduced by 20% from specified test
voltage.
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 opera-
tion?”
For a part holding no specific agency approvals both input
and output should normally be maintained within SELV limits
i.e. less than 42.4V peak, or 60VDC. The isolation test volt-
age 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 cor-
rectly with several hundred volts offset applied continuously
across the isolation barrier; 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-acces-
sible circuitry according to safety standard requirements.
This consideration equally applies to agency recog-
nized parts rated for better than functional isolation
where the wire enamel insulation is always supple-
mented by a further insulation system of physical
spacing or barriers.
For full details go to
www.murata-ps.com/rohs
www.murata-ps.com
Technical enquiries - email: mk@murata-ps.com, tel: +44 (0)1908 615232
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