MODELS
VDC OUTPUT
SINGLE
5
12
15
DUAL
±12
±15
DESCRIPTION
The MHE Series™ DC/DC converters offer the high efficiencies
associated with switching regulators, yet have full isolation and the
excellent regulation typical of linear regulators. No external compo-
nents are required for operation. MHE Series converters are built
using thick-film hybrid technology, and are sealed in metal packages
for military, aerospace, and other high-reliability applications.
Unscreened models are solder sealed and are guaranteed to pass
a gross leak test (maximum leak rate of 1 x 10
-3
atm.-cc/sec).
Environmentally screened models are hermetically sealed and are
screened as described in Section C2.
The MHE Series converters are pulse-width modulated switching
regulators operating in the forward mode, with a nominal switching
frequency of 125 to 140 kHz. Isolation is achieved through the use
of a transformer in the forward power circuit, and an optocoupler is
used in the feedback/control loop. The full load output power is
available over the full input voltage range. Short-term transients of
50 volts will not impair normal operation for 28 volt input models.
The efficiency is typically greater than 80% over the entire input
voltage range and from approximately 25% of full load to full load.
This feature makes the MHE Series converters ideal for either
battery or aircraft power applications.
An inhibit function is provided on MHE Series converters to allow
power shutdown and startup from a logic input. The unit is inhibited
when the inhibit input pin (pin 2) is connected to the input common
(pin 10). The open circuit voltage of the inhibit pin is 8 to 10 VDC for
12 V input models or 11 to 13 VDC for 28 V input models. During
inhibit, the input inhibit pin must sink approximately 1 mA. In the
inhibit mode, converter output drops to less than 1 V and the input
current is typically 8 mA.
Automatic current limiting circuitry protects the MHE Series
converters against short circuits.
MHE Series converters are rated to operate at full load up to a case
temperature of 85°C, with the output power derated linearly to zero
at 115°C. Because of the unit’s high efficiency, heat sinking require-
ments are minimized, but due consideration should be given to
removing self-generated heat when operating the device at
maximum ratings. To increase dissipation, heat conducting material
(PCB, copper sheet, heat sink, etc.) should be brought into contact
with the converter’s baseplate.
When the MHE Series converters are used in applications requiring
full power operation for extended periods of time, or in shock and
vibration environments, it is highly recommended that the flange-
mount option be used. This option provides improved thermal
transfer capabilities as well as a mechanically secure mounting
configuration.
DC/DC CONVERTERS
12 AND 28 VOLT INPUT
MHE SERIES 20
WATT
1
Size (max.): Non-flanged 2.125 x 1.125 x 0.495 (case H6) inches
(
53.98 x 28.58 x 12.57 mm)
Flanged 2.910 x 1.125 x 0.495 (case K7) inches
(73.91 x 28.58 x 12.57 mm)
See Section B8, cases H6 and K7, for dimensions.
Weight: 50 grams typical
Screening: Standard or ES. See Section C2 for screening options, see
Section A5 for ordering information.
FEATURES
• –55°C to +85°C operation
• 10 to 16 VDC input or
16 to 36 VDC input typical
• Fully isolated
• Opto-coupler feedback
• Fixed frequency 125 kHz typical
• Topology – Push-Pull Forward
• Transient protection
50 V for up to 50 ms 28 Vin models
• Inhibit function
• Indefinite short circuit protection
• Trimmable output on single models
• Up to 83% efficiency
