YB7002 Datasheet, PDF (5/8 Pages) YOBON TECHNOLOGIES,INC. – Photoflash Capacitor Charger with Automatic Refresh

Functional Block
YB7002
Photoflash Capacitor Charger with Automatic Refresh
Figure3jFunctional Block
Functional Description
YB7002 employs the peak-current-limit
scheme to control the charging of the inductor
current. Once the inductor reaches the preset
value determined by the Limit Pin, output
power NPN is shut off and the primary side
energy is delivered to the secondary side
capacitor. The discharging time is set to be
about 1us. Once the discharge cycle is
completed, the power NPN is on again. If the
secondary side output voltage has not yet
reached the designated value, the inductor
current will be charged up to the preset value
again. This charging and discharging sequence
will repeat itself until the output capacitor
voltage gets to the designated value and
triggers the on-off latch to hold off the power
NPN regardless the inductor current value.
As the power switch is off, output capacitor
starts to drop slowly due to its own leakage and
the resistor divider. When VFB voltage is below
VHYST, on-off latch turns on the power NPN
again and the charging cycle is enabled.
User is able to use resistors to set Limit Pin
value and V voltage. A 11uA current source is
coming out of the IC and going through the
limit resistor R to ground. Limit pin voltage
determines the peak inductor current. The
higher the Limit pin voltage,
the larger the peak inductor current would be.
USER MUST BE CAREFUL WITH THE
THERMAL EFFECT GENERATED
DURING THE CAPACITOR CHARGING
CYCLE. To reduce the thermal temperature,
user can lower the resistor R value to reduce the
peak inductor current.
YB7002 MRev1.0
www.yobon.com.tw
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