Crane Aerospace & Electronics Power Solutions
smHF single and dual dc/dc converters
28 Volt input – 15 Watt
• Fully qualified to Class H or K
• -55°C to +125°C operation
• 16 to 40 VDC input
• Fully Isolated
• Rad hard optocoupler feedback
• Fixed frequency, 550 kHz typical
• Transient protection 50 V/120 ms
• Inhibit function
• Sync function
• Topology – Single Ended Forward
• Indefinite short circuit protection
• Undervoltage lockout
• Up to 82% efficiency
The SMHF Series™ of 28 V DC/DC converters offers a wide
input voltage range of 16 to 40 volts and up to 15 watts of
output power. The units are capable of withstanding short term
transients up to 50 volts. The package is a hermetically sealed,
projection-welded metal case. Flanged and non-flanged models
the output load current and providing a constant current output
above the overload point.
SMHF converters offer screening options to Space Prototype (O),
Class H, or Class K. Radiation tolerant to Radiation Hardness
Assurance (RHA) levels of “-” (O) or “R”, per MIL-PRF-38534.
Interpoint model numbers use an “O” in the RHA designator posi-
tion to indicate the “-” (dash) Radiation Hardness Assurance level
of MIL-PRF-38534, which is defined as “no RHA”. See “Class H
and K, MIL-PRF-38534 Screening” tables for more information.
The SMHF converters are switching regulators that use a quasi-
square wave, single-ended forward converter design with a
constant switching frequency of 550 kHz. Isolation between input
and output circuits is provided with a transformer in the forward
path and a temperature compensated opto-coupler in the feed-
back control loop. The opto-coupler is radiation hardened and is
especially selected for space applications.
For the SMHF dual output models, cross regulation is maintained
by tightly coupled output magnetics. Up to 70% of the total output
power is available from either output, providing the opposite
output is simultaneously carrying 30% of the total output power.
Predictable current limit is accomplished by directly monitoring
The SMHF Series offers a new standard of performance for small
size and high power density. At just 0.33 inch high and a total
footprint of 1.7 in
, this low profile package offers a total power
density of up to 30 watts per cubic inch.
The SMHF converter’s feed-forward compensation system
provides excellent dynamic response and noise rejection. Audio
rejection is typically 50 dB. Typical output voltage response for
a 50% to 100% step load transient is as low as 1.3% with a 150
µS recovery time. Input ripple current is typically 35 mA p-p with
output ripple voltage typically 50 mV p-p .
SMHF converters provide an inhibit terminal that can be used
to disable internal switching, resulting in no output and very low
quiescent input current. The converter is inhibited when a logic
low (≤0.8 – output disabled) is applied to the inhibit pin. The
unit is enabled when the pin, which is internally connected to a
pull-up resistor, is left unconnected or is connected to an open-
collector gate. The open circuit output voltage associated with the
inhibit pin is 8.5 to 12 VDC. In the inhibit mode, a maximum of
4 mA must be sunk from the inhibit pin at 28 VDC input.
Crane Aerospace & Electronics
Electronics group (Interpoint Brand)
PO Box 97005 • Redmond WA 98073-9705
425.882.3100 • firstname.lastname@example.org
Page 1 of 15
Rev D - 20070404
Cleared by U.S. DoD OSR for Public Release
OSR case number 09S-0995, dated March 13, 2009.
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