MC33023(2009) データシートの表示（PDF） - ON Semiconductor
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MC33023 Datasheet PDF : 18 Pages
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MC34023, MC33023
1
2
+
Vref
8
R1
CSS
R2
IB
+
0
VC
Vin
-
Base Charge
Removal
15
In voltage mode operation, the maximum duty cycle can be clamped. By
the addition of a PNP transistor to buffer the clamp voltage, the Soft−Start
current is not affected by R1.
The new equation for Soft−Start is
Vclamp ) 0.6
t[
9.0 μA
(CSS)
In current mode operation, this circuit will limit the maximum voltage
allowed at the ramp input to end a cycle.
Figure 31. Buffered Maximum Clamp Level
14
12
To Current RS
Sense Input
The totem pole output can furnish negative base current for enhanced
transistor turn−off, with the addition of the capacitor in series with the base.
Figure 32. Bipolar Transistor Drive
VC
Vin
15
14
12
To Current RS
Sense Input
A series gate resistor may be needed to dampen high frequency parasitic
oscillation caused by the MOSFET’s input capacitance and any series
wiring inductance in the gate−source circuit. The series resistor will also
decrease the MOSFET switching speed. A Schottky diode can reduce
the driver’s power dissipation due to excessive ringing, by preventing the
output pin from being driven below ground. The Schottky diode also
prevents substrate injection when the output pin is driven below ground.
Figure 33. MOSFET Parasitic Oscillations
VC
15
14
12
The totem pole output can easily drive pulse transformers. A Schottky
diode is recommended when driving inductive loads at high frequencies.
The diode can reduce the driver’s power dissipation due to excessive
ringing, by preventing the output pin from being driven below ground.
Figure 34. Isolated MOSFET Drive
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