Fabricated on a 0.41 by 0.65 inch (10.4 by 16.5
mm) Single Inline Package (SIP) module, the OKI-
78SR series are non-isolated switching regulator
(SR) DC/DC power converters for embedded ap-
plications. The fi xed single output converters offer
both tight regulation and high effi ciency directly
at the power usage site and are a direct plug-in
replacement for TO-220 package 78xx series linear
regulators. Typically, no extra outside components
are required.
Two nominal output voltages are offered (3.3
and 5 VDC), each with 1.5 Amp maximum output.
Based on fi xed-frequency buck switching topology,
the high effi ciency means very low heat and little
electrical noise, requiring no external components.
The ultra wide input range is 7 to 36 Volts DC.
Protection features include input undervoltage
and short circuit protection, overcurrent and over
temperature shut down. The OKI-78SR is designed
to meet all standards approvals. RoHS-6 (no lead)
hazardous material compliance is specifi ed as
standard.
PRODUCT OVERVIEW
Connection Diagram
Figure 1. OKI-78SR
Note: Murata Power Solutions strongly recommends an external input fuse, F1.
See specifi cations.
External
DC
Power
Source
F1
CommonCommon
+Vin +Vout
Controller
Reference and
Error Amplifier
t4XJUDIJOH
t'JMUFST
t$VSSFOU4FOTF
FEATURES
■ Ultra wide 7 to 36 VDC input range
■ Fixed Outputs of 3.3 or 5 VDC up to 1.5 Amps
■ Vertical or horizontal SIP-mount, small footprint
package
■ “No heat sink” direct replacement for 3-terminal
78xx-series linear regulators
■ High effi ciency with no external components
■ Short circuit protection
■ Outstanding thermal derating performance
■ UL/EN/IEC 60950-1, 2nd Edition safety approv-
als (pending)
Typical unit
MDC_OKI-78SR-W36.A09 Page 1 of 11
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
www.murata-ps.com
www.murata-ps.com/support
For full details go to
www.murata-ps.com/rohs
　
(certifi cation is pending)
PART NUMBER STRUCTURE
➀ Dimensions are in inches (mm).
➁ All specifications are at nominal line voltage, Vout = nominal and full load, +25 ˚C., with no external capacitor,
unless otherwise noted.
FUNCTIONAL SPECIFICATIONS SUMMARY AND ORDERING GUIDE
Root Model
Output Input
Effi ciency
Package
➀
VOUT
(Volts)
IOUT
(Amps
max)
Power
(Watts)
R/N (mVp-p) Regulation (Max.)
VIN Nom.
(Volts)
Range
(Volts)
IIN,
no load
(mA)
IIN,
full load
(Amps)Max. Line Load Min. Typ.
OKI-78SR-3.3/1.5-W36-C 3.3 1.5 4.95 40 ±0.25% ±0.25% 24 7-36 5 0.48 84% 85.5% 0.41 x 0.65 x 0.3
(10.4 x 16.5 x 7.62)
OKI-78SR-5/1.5-W36-C 51.5 7.5 75 ±0.25% ±0.25% 24 7-36 5 0.69 89% 90.5% 0.41 x 0.65 x 0.3
(10.4 x 16.5 x 7.62)
Product Label
Because of the small size of these products, the product label contains a
character-reduced code to indicate the model number and manufacturing date
code. Not all items on the label are always used. Please note that the label dif-
fers from the product photograph on page 1. Here is the layout of the label:
The label contains three rows of information:
First row – Murata Power Solutions logo
Second row – Model number product code (see table)
Third row – Manufacturing date code and revision level
The manufacturing date code is four characters:
First character – Last digit of manufacturing year, example 2009
Second character – Month code (1 through 9 and O through D)
Third character – Day code (1 through 9 = 1 to 9, 10 = O and
11 through 31 = A through Z)
Fourth character – Manufacturing information
Figure 2. Label Artwork Layout
XXXXXX Product code
Mfg.
date
code
Revision levelYMDX Rev.
Model Number Product Code
OKI-78SR-3.3/1.5-W36-C I33115
OKI-78SR-5/1.5-W36-C I50115
OKI-78SR-3.3/1.5-W36H-C I33115H
OKI-78SR-5/1.5-W36H-C I50115H
Maximum Rated Output in Volts
-1.5/3.3 -CRoHS-6 Hazardous
Substance Compliance
78SR Series
78SR
Okami Non-Isolated PoL
OKI -
Maximum Rated Output
Current in Amps
Note:
Some model number combinations
may not be available.
Contact Murata Power Solutions.
H
Blank: Vertical Mount
H Suffi x: Horizontal Mount
W36
Input Voltage Range
7-36V
MDC_OKI-78SR-W36.A09 Page 2 of 11
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
www.murata-ps.com/support
Performance and Functional Specifi cations
All specifi cations are typical unless noted. See Note 1
Input
Input Voltage Range See Ordering Guide.
Recommended External Fuse 2 Amps fast blow
Reverse Polarity Protection (Note 9) None. Install an external fuse.
Isolation (note 5) Not isolated. The input and output share a
common return.
Start-Up Voltage NA
Undervoltage Shutdown (Note 12) NA
Overvoltage Shutdown None
Internal Input Filter Type Capacitive
Input Current:
Full Load Conditions See Ordering Guide
Inrush Transient 0.16 A2Sec.
Shutdown Mode (Off, UV, OT) 1 mA
Output in Short Circuit 5 mA
No Load 5 mA
Low Line (Vin=Vmin, Vout=nom) 0.8 Amps (OKI-78SR-3.3/1.5-W36)
1.16 Amps (OKI-78SR-5/1.5-W36)
Refl ected (Back) Ripple Current
(Note 2)
10 mA pk-pk (OKI-78SR-3.3/1.5-W36)
49 mA pk-pk (OKI-78SR-5/1.5-W36)
Output
Output Voltage See Ordering Guide
Output Current Range 0 to 1.5 Amps
Minimum Loading (Note 11) No minimum load
Maximum Output Power 5.15 Watts (OKI-78SR-3.3/1.5-W36)
7.8 Watts (OKI-78SR-5/1.5-W36)
Accuracy (50% load) ±4 % of Vnom
Overvoltage Protection (Note 7) None
Temperature Coeffi cient ±0.02% per °C. of Vout range
Ripple/Noise (20 MHz bandwidth) See Ordering Guide and note 11
Line/Load Regulation See Ordering Guide and note 10
Effi ciency See Ordering Guide and performance graphs
Maximum Capacitive Loading
Cap-ESR=0.001 to 0.01 Ohms 300 μF
Cap-ESR >0.01 Ohms 3300 μF
Current Limit Inception (98% of Vout
setting, after warm up) 3.5 Amps
Short Circuit Mode (Notes 6, 11)
Short Circuit Current Output 10 mA
Protection Method Hiccup autorecovery upon overload removal.
(Note 8)
Short Circuit Duration Continuous, no damage (output shorted to
ground)
Prebias Startup The converter will start up if the external output
voltage is less than Vnominal.
Dynamic Characteristics
Dynamic Load Response (50% to 100% load step, no external caps)
di/dt = 1 A/μSec 25 μSec settling time to within ±2% of fi nal value
Peak deviation 100 mV
Switching Frequency 500 KHz
Environmental
Calculated MTBF (Note 4) Ambient Temp. Hours
OKI-78SR-3.3/1.5-W36-C
Telecordia method (4a)
+25°C 78,721,000
+40°C 59,017,000
OKI-78SR-3.3/1.5-W36-C
MIL-HDBK-217N2 method (4b)
+25°C 14,587,000
+40°C 9,814,000
Operating Ambient Temperature Range
Full power, with derating [3] -40 to +85°C. see derating curves.
Storage Temperature Range -55 to +125 °C.
Relative Humidity to 85%/+85 °C.
Physical
Outline Dimensions See Mechanical Specifi cations [11]
Weight 0.07 ounces (2 grams)
Safety
Certifi ed to UL/cUL 60950-1
CSA-C22.2 No. 60950-1
IEC/EN 60950-1, 2nd Edition (pending)
Absolute Maximum Ratings
Input Voltage, Continuous or transient 36 Volts max.
Input Reverse Polarity Protection None. Install external fuse.
Output Current Current-limited. Devices can withstand sustained
short circuit without damage.
Storage Temperature -40 to +125 deg. C.
Specifi cation Notes:
(1) All specifi cations are typical unless noted. General conditions for Specifi cations are +25 deg.C ambient
temperature, Vin=nominal, Vout=nominal, full rated load. Adequate airfl ow must be supplied for extended
testing under power. See Derating curves.
All models are tested and specifi ed with no external capacitors. All models are stable and regulate within
spec under no-load conditions.
(2) Input Back Ripple Current is tested and specifi ed over a 5 Hz to 20 MHz bandwidth. Input fi ltering is Cin=2 x
100 μF, Cbus=1000 μF, Lbus=1 μH. All caps are low ESR types.
(3) Note that Maximum Power Derating curves indicate an average current at nominal input voltage. At higher
temperatures and/or lower airfl ow, the DC/DC converter will tolerate brief full current outputs if the total
RMS current over time does not exceed the Derating curve. All Derating curves are presented near sea level
altitude. Be aware of reduced power dissipation with increasing altitude.
(4a) Mean Time Before Failure is calculated using the Telcordia (Belcore) SR-332 Method 1, Case 3, ground fi xed
conditions, Tpcboard=+25 ˚C, full output load, natural air convection.
(4b) Mean Time Before Failure is calculated using the MIL-HDBK-217N2 method, ground benign, +25ºC., full
output load, natural convection.
(5) The input and output are not isolated. They share a single COMMON power and signal return.
(6) Short circuit shutdown begins when the output voltage degrades approximately 2% from the selected
setting. Output current limit and short circuit protection are non-latching. When the overcurrent fault is
removed, the converter will immediately recover.
(7) The output is not intended to sink appreciable reverse current.
(8) “Hiccup” overcurrent operation repeatedly attempts to restart the converter with a brief, full-current output.
If the overcurrent condition still exists, the restart current will be removed and then tried again. This short
current pulse prevents overheating and damaging the converter.
(9) Input Fusing: If reverse polarity is accidentally applied to the input, to ensure reverse input protection,
always connect an external input fast-blow fuse in series with the +Vin input. Use approximately twice the
full input current rating with nominal input voltage.
(10) Regulation specifi cations describe the deviation as the line input voltage or output load current is varied
from a nominal midpoint value to either extreme.
(11) Output noise may be further reduced by installing an external fi lter. Do not exceed the maximum output
capacitance. At zero output current and no external capacitor, the output may contain low frequency
components which exceed the ripple specifi cation. The output may be operated indefi nitely with no load.
(12) The input must remain above the Undervoltage Shutdown (UVLO) voltage specifi cation at all times to avoid
an unplanned turn off.
MDC_OKI-78SR-W36.A09 Page 3 of 11
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
www.murata-ps.com/support
MDC_OKI-78SR-W36.A09 Page 4 of 11
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
www.murata-ps.com/support
PERFORMANCE DATA – OKI-78SR-3.3/1.5-W36
Effi ciency vs. Line Voltage and Load Current @ +25˚C. (Vout = Vnom.)
Output Ripple and Noise (Vin=7V, Vout=nominal, Iout=1.6A, Cload=0, Ta=+25˚C.,
ScopeBW=100MHz)
Output Ripple and Noise (Vin=36V, Vout=nominal, Iout=1.6A, Cload=0, Ta=+25˚C.,
ScopeBW=100MHz)
Output Ripple and Noise (Vin=12V, Vout=nominal, Iout=1.6A, Cload=0, Ta=+25˚C.,
ScopeBW=100MHz)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
0
10
20
30
40
50
60
70
80
90
100
Load Current (Amps)
Efficiency (%)
VIN = 7V
VIN = 12V
VIN = 36V
Maximum Current Temperature Derating at sea level (Vin=7V. to 36V.)
0.00
1.00
2.00
20 25 30 35 40 45 50 55 60 65 70 75 80 85
Ambient Temperature (ºC)
Output Current (Amps)
0.33 m/s (65 LFM)
MDC_OKI-78SR-W36.A09 Page 5 of 11
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
www.murata-ps.com/support
PERFORMANCE DATA – OKI-78SR-3.3/1.5-W36
Step Load Transient Response (Vin=36V, Vout=nominal, Cload=0, Iout=0.75A to 1.5A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=12V, Vout=nominal, Cload=0, Iout=0.75A to 1.5A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=7V, Vout=nominal, Cload=0, Iout=0.75A to 1.5A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div
Step Load Transient Response (Vin=36V, Vout=nominal, Cload=0, Iout=1.5A to 0.75A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=12V, Vout=nominal, Cload=0, Iout=1.5A to 0.75A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=7V, Vout=nominal, Cload=0, Iout=1.5A to 0.75A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
MDC_OKI-78SR-W36.A09 Page 6 of 11
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
www.murata-ps.com/support
PERFORMANCE DATA – OKI-78SR-5/1.5-W36
Effi ciency vs. Line Voltage and Load Current @ +25˚C. (Vout = Vnom.)
Output Ripple and Noise (Vin=7V, Vout=nominal, Iout=1.6A, Cload=0, Ta=+25˚C.,
ScopeBW=100MHz)
Output Ripple and Noise (Vin=36V, Vout=nominal, Iout=1.6A, Cload=0, Ta=+25˚C.,
ScopeBW=100MHz)
Output Ripple and Noise (Vin=12V, Vout=nominal, Iout=1.6A, Cload=0, Ta=+25˚C.,
ScopeBW=100MHz)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
0
10
20
30
40
50
60
70
80
90
100
Load Current (Amps)
Efficiency (%)
VIN = 7V
VIN = 12V
VIN = 36V
Maximum Current Temperature Derating at sea level (Vin=7V. to 36V.)
0.00
1.00
2.00
20 25 30 35 40 45 50 55 60 65 70 75 80 85
Ambient Temperature (ºC)
Output Current (Amps)
0.33 m/s (65 LFM)
MDC_OKI-78SR-W36.A09 Page 7 of 11
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
www.murata-ps.com/support
PERFORMANCE DATA – OKI-78SR-5/1.5-W36
Step Load Transient Response (Vin=36V, Vout=nominal, Cload=0, Iout=0.75A to 1.5A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=12V, Vout=nominal, Cload=0, Iout=0.75A to 1.5A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=7V, Vout=nominal, Cload=0, Iout=0.75A to 1.5A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=36V, Vout=nominal, Cload=0, Iout=1.5A to 0.75A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=12V, Vout=nominal, Cload=0, Iout=1.5A to 0.75A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=7V, Vout=nominal, Cload=0, Iout=1.5A to 0.75A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
MECHANICAL SPECIFICATIONS, VERTICAL MOUNT
0.05 (1.3)
0.200 (5.1)
0.205
(5.2)
REF
0.100 (2.5)
0.06
(1.5)
0.30 (7.6)
0.16 (4.1)
0.13 (3.3)
REF
0.030±0.002
Pin #1
OVER 75-150 u" NICKEL
PIN FINISH: PURE MATTE TIN 100-300 u"
PIN MATERIAL: COPPER ALLOY
Pin #3
C
L
Pin #1
0.41
(10.4)
0.65
(16.5)
Pin #1
INPUT/OUTPUT CONNECTIONS
OKI-78SR
Pin Function
1 Positive Input
2 Common (Ground)
3 Positive Output
Third Angle Projection
Dimensions are in inches (mm shown for ref. only).
Components are shown for reference only.
Tolerances (unless otherwise specified):
.XX ± 0.02 (0.5)
.XXX ± 0.010 (0.25)
Angles ± 1˚
MDC_OKI-78SR-W36.A09 Page 8 of 11
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
www.murata-ps.com/support
MECHANICAL SPECIFICATIONS, HORIZONTAL MOUNT
.05 (1.3)±.01
C
L
Pin #3
Pin #1
Pin #1
OVER 75-150 u" NICKEL
PIN FINISH: PURE MATTE TIN 100-300 u"
PIN MATERIAL: COPPER ALLOY
Pin #1
.01
.02
+
-
0.17
(4.318)
.025 (0.635)
(3 PLS)
0.200 (5.1)
0.205
(5.2)
REF
0.100 (2.5)
0.06
(1.5)
0.30 (7.6)
0.16 (4.1)
REF
0.41
(10.4)
0.65
(16.5)
INPUT/OUTPUT CONNECTIONS
OKI-78SR
Pin Function
1 Positive Input
2 Common (Ground)
3 Positive Output
Third Angle Projection
Dimensions are in inches (mm shown for ref. only).
Components are shown for reference only.
Tolerances (unless otherwise specified):
.XX ± 0.02 (0.5)
.XXX ± 0.010 (0.25)
Angles ± 1˚
MDC_OKI-78SR-W36.A09 Page 9 of 11
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
www.murata-ps.com/support
Input Fusing
Certain applications and/or safety agencies may require fuses at the inputs of
power conversion components. Fuses should also be used when there is the
possibility of sustained input voltage reversal which is not current-limited. For
greatest safety, we recommend a fast blow fuse installed in the ungrounded
input supply line.
The installer must observe all relevant safety standards and regulations. For
safety agency approvals, install the converter in compliance with the end-user
safety standard.
Input Under-Voltage Shutdown and Start-Up Threshold
Under normal start-up conditions, converters will not begin to regulate properly
until the rising input voltage exceeds and remains at the Start-Up Threshold
Voltage (see Specifi cations). Once operating, converters will not turn off until
the input voltage drops below the Under-Voltage Shutdown Limit. Subsequent
restart will not occur until the input voltage rises again above the Start-Up
Threshold. This built-in hysteresis prevents any unstable on/off operation at a
single input voltage.
Users should be aware however of input sources near the Under-Voltage
Shutdown whose voltage decays as input current is consumed (such as
capacitor inputs), the converter shuts off and then restarts as the external
capacitor recharges. Such situations could oscillate. To prevent this, make
sure the operating input voltage is well above the UV Shutdown voltage AT ALL
TIMES.
Start-Up Time
Assuming that the output current is set at the rated maximum, the Vin to Vout
Start-Up Time (see Specifi cations) is the time interval between the point when
the rising input voltage crosses the Start-Up Threshold and the fully loaded
regulated output voltage enters and remains within its specifi ed regulation
band. Actual measured times will vary with input source impedance, external
input capacitance, input voltage slew rate and fi nal value of the input voltage
as it appears at the converter.
These converters include a soft start circuit to moderate the duty cycle of its
PWM controller at power up, thereby limiting the input inrush current.
Recommended Input Filtering
The user must assure that the input source has low AC impedance to provide
dynamic stability and that the input supply has little or no inductive content,
including long distributed wiring to a remote power supply. The converter will
operate with no additional external capacitance if these conditions are met.
For best performance, we recommend installing a low-ESR capacitor
immediately adjacent to the converter’s input terminals. The capacitor should
be a ceramic type such as the Murata GRM32 series or a polymer type. Initial
suggested capacitor values are 10 to 22 μF, rated at twice the expected maxi-
mum input voltage. Make sure that the input terminals do not go below the
undervoltage shutdown voltage at all times. More input bulk capacitance may
be added in parallel (either electrolytic or tantalum) if needed.
TECHNICAL NOTES
Recommended Output Filtering
The converter will achieve its rated output ripple and noise with no additional
external capacitor. However, the user may install more external output capaci-
tance to reduce the ripple even further or for improved dynamic response.
Again, use low-ESR ceramic (Murata GRM32 series) or polymer capacitors.
Initial values of 10 to 47 μF may be tried, either single or multiple capacitors in
parallel. Mount these close to the converter. Measure the output ripple under
your load conditions.
Use only as much capacitance as required to achieve your ripple and noise
objectives. Excessive capacitance can make step load recovery sluggish or
possibly introduce instability. Do not exceed the maximum rated output capaci-
tance listed in the specifi cations.
Input Ripple Current and Output Noise
All models in this converter series are tested and specifi ed for input refl ected
ripple current and output noise using designated external input/output com-
ponents, circuits and layout as shown in the fi gures below. The Cbus and Lbus
components simulate a typical DC voltage bus. Please note that the values of
Cin, Lbus and Cbus will vary according to the specifi c converter model.
C
IN
V
IN
C
BUS
L
BUS
C
IN
= 2 x 100μF, ESR < 700mΩ @ 100kHz
C
BUS
= 1000μF, ESR < 100mΩ @ 100kHz
L
BUS
= 1μH
+INPUT
-INPUT
CURRENT
PROBE
TO
OSCILLOSCOPE
+
–
+
–
Figure 2. Measuring Input Ripple Current
C1
C1 = 1μF
C2 = 10μF
LOAD 2-3 INCHES (51-76mm) FROM MODULE
C2 R
LOAD
SCOPE
+OUTPUT
-OUTPUT
Figure 3. Measuring Output Ripple and Noise (PARD)
MDC_OKI-78SR-W36.A09 Page 10 of 11
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
www.murata-ps.com/support
Minimum Output Loading Requirements
All models regulate within specifi cation and are stable under no load to full
load conditions. Operation under no load might however slightly increase
output ripple and noise.
Thermal Shutdown
To prevent many over temperature problems and damage, these converters
include thermal shutdown circuitry. If environmental conditions cause the
temperature of the DC/DC’s to rise above the Operating Temperature Range
up to the shutdown temperature, an on-board electronic temperature sensor
will power down the unit. When the temperature decreases below the turn-on
threshold, the converter will automatically restart. There is a small amount of
hysteresis to prevent rapid on/off cycling.
CAUTION: If you operate too close to the thermal limits, the converter may
shut down suddenly without warning. Be sure to thoroughly test your applica-
tion to avoid unplanned thermal shutdown.
Temperature Derating Curves
The graphs in this data sheet illustrate typical operation under a variety of
conditions. The Derating curves show the maximum continuous ambient air
temperature and decreasing maximum output current which is acceptable
under increasing forced airfl ow measured in Linear Feet per Minute (“LFM”).
Note that these are AVERAGE measurements. The converter will accept brief
increases in current or reduced airfl ow as long as the average is not exceeded.
Note that the temperatures are of the ambient airfl ow, not the converter
itself which is obviously running at higher temperature than the outside air.
Also note that “natural convection” is defi ned as very fl ow rates which are not
using fan-forced airfl ow. Depending on the application, “natural convection” is
usually about 30-65 LFM but is not equal to still air (0 LFM).
Murata Power Solutions makes Characterization measurements in a closed
cycle wind tunnel with calibrated airfl ow. We use both thermocouples and an
infrared camera system to observe thermal performance. As a practical matter,
it is quite diffi cult to insert an anemometer to precisely measure airfl ow in
most applications. Sometimes it is possible to estimate the effective airfl ow if
you thoroughly understand the enclosure geometry, entry/exit orifi ce areas and
the fan fl owrate specifi cations.
CAUTION: If you routinely or accidentally exceed these Derating guidelines,
the converter may have an unplanned Over Temperature shut down. Also, these
graphs are all collected at near Sea Level altitude. Be sure to reduce the derat-
ing for higher altitude.
Output Fusing
The converter is extensively protected against current, voltage and temperature
extremes. However your output application circuit may need additional protec-
tion. In the extremely unlikely event of output circuit failure, excessive voltage
could be applied to your circuit. Consider using an appropriate fuse in series
with the output.
Output Current Limiting
Current limiting inception is defi ned as the point at which full power falls below
the rated tolerance. See the Performance/Functional Specifi cations. Note par-
ticularly that the output current may briefl y rise above its rated value in normal
operation as long as the average output power is not exceeded. This enhances
reliability and continued operation of your application. If the output current is
too high, the converter will enter the short circuit condition.
Output Short Circuit Condition
When a converter is in current-limit mode, the output voltage will drop as the
output current demand increases. If the output voltage drops too low (approxi-
mately 98% of nominal output voltage for most models), the bias voltage may
shut down the PWM controller. Following a time-out period, the PWM will
restart, causing the output voltage to begin rising to its appropriate value. If the
short-circuit condition persists, another shutdown cycle will initiate. This rapid
on/off cycling is called “hiccup mode”. The hiccup cycling reduces the average
output current, thereby preventing excessive internal temperatures and/or
component damage.
The “hiccup” system differs from older latching short circuit systems
because you do not have to power down the converter to make it restart. The
system will automatically restore operation as soon as the short circuit condi-
tion is removed.
Soldering Guidelines
Murata Power Solutions recommends the specifi cations below when installing these converters. These specifi cations vary depending on the solder type. Exceeding these specifi ca-
tions may cause damage to the product. Be cautious when there is high atmospheric humidity. We strongly recommend a mild pre-bake (100 ºC. for 30 minutes). Your production
environment may differ therefore please thoroughly review these guidelines with your process engineers.
Reflow Solder Operations for surface-mount products (SMT)
For Sn/Ag/Cu based solders: For Sn/Pb based solders:
Preheat Temperature Less than 1 ºC. per second Preheat Temperature Less than 1 ºC. per second
Time over Liquidus 45 to 75 seconds Time over Liquidus 60 to 75 seconds
Maximum Peak Temperature 260 ºC. Maximum Peak Temperature 235 ºC.
Cooling Rate Less than 3 ºC. per second Cooling Rate Less than 3 ºC. per second
MDC_OKI-78SR-W36.A09 Page 11 of 11
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
www.murata-ps.com/support
Murata Power Solutions, Inc. makes no representation that the use of its products in the circuits described herein, or the use of other
technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained herein do not imply
the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifi cations are subject to change without
notice. © 2012 Murata Power Solutions, Inc.
Murata Power Solutions, Inc.
11 Cabot Boulevard, Mansfi eld, MA 02048-1151 U.S.A.
ISO 9001 and 14001 REGISTERED
This product is subject to the following operating requirements
and the Life and Safety Critical Application Sales Policy:
Refer to: http://www.murata-ps.com/requirements/