BP5250 / BP5250-24
(5) Overcurrent detection resisor(R1)
Overcurrent detection resistor is determined by the
following expression.
R1=VLT1/Iomax [mΩ]
VLT1 : Overcurrent offset voltage1(60∼76mV)
Iomax : Maximum overload current [A]
And, ISL current at short circuit is
ISL=VLT2/R1 [A]
VLT2 : Overcurrent detection offset voltage2(20∼36mV)
From the above-mentioned, fold-back current characteristic when the overcurrent protection is
operated is shown. Both Iomax, and ISL may be different value from the actual value because they are
detected at the peak current. Please make sure to confirm it in the actual operating.
(6) Input smoothing capacitor(C1)
Large ripple current flow into the input smoothing capacitor. The current is determined by the following
expression. For actual usage, please use the larger one than this numeric value.
Output current [Io]
Overcurrent protection characteristic
Output voltage [Vo]
Vo
I
SL Iomax
Irms=ir × Vo/3Vi +(ip-ir) × Vo/Vi [A]
Irms : Input ripple current actual-value [Arms]
ir : Ripple current [A]
ip : Peak current [A]
V : Input voltage [V]
Vo : Output voltage [V]
· Voltage of the used capacitor must be more than Vi × 2.
· Allowable ripple current of the used capacitor must be larger than the ripple current.
(7) Output smoothing capacitor(C2)
Output smoothing capacitor is determined by the impedance of smoothing capacitor from the mark value of
output ripple voltage.
Zc≤Vr/ir [Ω]
Zc : Impedance of capacitor [Ω]
Vr : Mark value of output ripple voltage[Vp-p]
ir : Ripple current [A]
· Voltage of the used capacitor must be more than Vo × 2.
· Allowable ripple current of the used capacitor must be larger than the ripple current.
(4) Flywhell diode(SD1)
· Rated current must be twice as much as the maximum overload
current(Iomax) or more.
· Rated voltage must be 1.3 times as much as the maximum input
voltage or more.
· Please use the high-speed switching schottky barrierdiode that
reverse recovery time is 50ns or less.
· If it used in high temperature, please be careful about the
temperature characteristics of IR.
Input voltage Vi [V]
Input voltage VS. DC reverse voltage
DC reverse vpltage [V]
50
40
30
20
10
0
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