HUMMER SERIES
40 OR 70 WATT
28 VDC
EMI
FILTER
(IF USED)
H
OLD
U
P
M
ODULE
DC-DC
CONVERTER
LOAD
+V
IN
HUMMER
VCS
HOLD-UP
MODULE
CAPACITOR
CHARGED
+C
EXT
C
EXT1
+V
IN
INHIBIT
+V
OUT
28 VDC
RETURN
V
IN
RETURN
V
OUT
RETURN
CASE
GROUND
C
EXT
RETURN
V
IN
RETURN
POWER
FAIL
INHIBIT
1. EXTERNAL HOLDUP
CAPACITOR
F
IGURE
3: HUMMER M
ODULE
S
YSTEM
B
LOCK
D
IAGRAM
DETAILED OPERATIONAL DESCRIPTION
The detailed operation of the HUMMER module is divided into 4
operations: Initialization and Charging, Normal Operation, Low
Line Operation, and Power Fail Operation. For details, refer to the
following text, Figure 4 (HUMMER Module Block Diagram) and
Figure 5 (HUMMER Module Signal Diagram).
1. I
NITIALIZATION AND
C
HARGING
As the input voltage ramps up to 8 to 10 volts, the internal
HUMMER module circuits are biased to provide correct output
states on all flags. As the input reaches 14 VDC, the Power Fail
flag (active low) is released, the voltage control switch (VCS) is
closed, and the module begins operating in a boost mode to
charge the external capacitor to 40 volts. At this point, if the recom-
mended connection has been made between the Capacitor
Charged pin and the inhibit pin of the converter as shown in Figure
3, all of the module energy is dedicated to charging the capacitor
and the converter will be inhibited until the capacitor charge
reaches 36 V. If this connection has not been made, the energy
available to charge the capacitor will be the difference between the
current required by the converter’s load and the current capacity of
the HUMMER module.
Note: The HUMMER module is rated at a total operating power
more than its output rating in order to allow it to both deliver a
full load and to continue charging the external capacitor (the
HUM-40, for example, is rated at 40 W output and 60 W total
operating power, allowing it to deliver 40 W to a load and charge
a capacitor at 10 to 20 J/sec). However, if the input voltage
ramps up slowly into a full converter load, the total power drawn
at low voltage could send the module into current limit which
would shut the unit down.
When the input voltage reaches approximately 22 VDC, the VCS
is opened, isolating the stored charge on the external capacitor
and allowing the converter to operate directly from the input power
bus via the external system diode (unless the converter is still
inhibited by the connection between the Capacitor Charged pin
and converter’s inhibit pin) while the capacitor continues to charge.
When the charge on the external capacitor reaches approximately
35 volts (80% of a full charge), the Capacitor Charged flag will be
asserted (removing the inhibit from the converter if applicable) and
the HUMMER module will be in normal operation.
VCS
+V
IN
INPUT
CURRENT
LIMIT
+C
EXT
+
–
PWM
+
–
V
IN
RETURN
CASE
GROUND
+
–
C
EXT
RETURN
CURRENT
SENSE
POWER
FAIL
INHIBIT CAPACITOR
CHARGED
F
IGURE
4: HUMMER M
ODULE
B
LOCK
D
IAGRAM
®
4
CRANE [ Crane Aerospace & Electronics. ]
