A8436 Просмотр технического описания (PDF) - Allegro MicroSystems
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A8436 Datasheet PDF : 14 Pages
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A8436
Photoflash Capacitor Charger with IGBT Driver
Charging Cycles for a Completely Discharged Photoflash Capacitor
VBATT
C3
Figure 4A. Initial two cyles of charging
a completely discharged photoflash
capacitor. In these two cycles, off-time
(VSW low) is controlled by the internal
18 μs timer (Timer mode). Note that, in the
first cycle, IPrimary starts near 0 A, but in
the second cycle, it starts at a higher level.
This indicates that the transformer core did
not reset during the first cycle.
VSW
C2
IPrimary
C4
C1
VOUT
t
Figure 4B. During the intermediate cycles,
the output voltage, VOUT, has increased.
ISecondary goes discontinuous, leading to
the ringing of VSW . The amplitude of the
ringing is not great enough, however,
to pull VSW below 1.2 V, so the A8436
remains in Timer mode.
VBATT
C3
VSW
C2
IPrimary
C4
VOUT
C1
C3
Figure 4C. The final cycle of Timer mode
is shown, followed by a series of cycles in
C2
Fast Charging mode. VSW is able to ring
down below 1.2 V in every cycle as a result
of increased VOUT , triggering the turn-on of
the main MOSFET switch.
C4
Symbol Parameter Units/Division
C1
C1
VOUT
50 V
C2
VSW
10 V
C3
VBATT
5V
C4
IPrimary
500 mA
t
time
5 μs
Conditions Parameter
Value
VBATT
VIN
VBATT
VSW
IPrimary
VOUT
t
t
Allegro MicroSystems, Inc.
10
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
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