AN8031 データシートの表示（PDF） - Panasonic Corporation
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AN8031 Datasheet PDF : 21 Pages
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AN8031
Voltage Regulators
s Application Notes (continued)
[2] Operation descriptions (continued)
1. Normal control (continued)
2) Control outline description (Refer to figure 2 and figure 3.) (continued)
(4) Switching device current
The voltage generated in the current detection resistor which is connected to the switching device
(power MOSFET) is detected at the CS terminal. (for the above resistor, low resistance value is selected,
considering the power dissipation).
(5) Switching device turn-off
The CS terminal voltage and the multiplier output voltage are compared by the current detection
comparator. When the former value becomes larger than the latter one, the current detection comparator
sends the reset signal to the RS latch circuit to turn off the switching device.
(6) Output current supply
When the switching device is turned off, the current flowing in the transformer is cut off. The diode
is turned-on with inertia current of inductor, and supplies a current to the output of chopper circuit
(EOUT).
EIN
One shot
Lower limit Upper limit
VBTH voltage clamp voltage clamp
1 SVCC
6 VB
Power MOS
→ On
Power MOS
→ Off
Turn-on signal
2.5 V VREF
Timer
Latch circuit
10 V/8 V
Low voltage
protection 9 PVCC
Drive
8 VOUT
EOUT
SBD
Input voltage
monitor
MPI 3
2.6 V
Overvoltage detection
2 CS
Current detection
comparator
Multiplier
Error amp.
5 EI
2.5 V
2.5 V
Power MOSFET
Turn-off signal
Figure 3. Explanation of block diagram and normal operation
Current detection
resistor
(7) Transformer reset signal (VB) detection
When the excitation energy has been discharged and the inertia current of the inductor has been lost,
the transformer starts resonance with the frequency which depends on parasitic capacitance of the board
or parts and inductance of the inductor. This operation is detected at the VB terminal through sub-coil of
the transformer.
8
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