AN8032
s
Application Notes (continued)
[2] Operation descriptions (continued)
1. Normal control (continued)
2) Control outline description (Refer to figure 2 and figure 3.) (continued)
Voltage Regulators
E
IN
(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
(E
OUT
).
Power MOS
→
On
Power MOS
→
Off
V
BTH
One shot
Lower limit
voltage clamp
Upper limit
voltage clamp
9 V
CC
6 V
B
Turn-on signal
2.5 V
V
REF
10 V/8 V
Low voltage
protection
E
OUT
8 V
OUT
Power MOSFET
Timer
SBD
Latch circuit
Drive
2.6 V 5 OVP
Overvoltage detection
1 CS
Input voltage
monitor
Current detection
comparator
Turn-off signal
MPI 2
Error amp.
Multiplier
4 EI
2.5 V
GND 7
EO 3
2.5 V
Current detection
resistor
Figure 3. Explanation of block diagram and normal operation
(7) Transformer reset signal (V
B
) 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 V
B
terminal through sub-coil of
the transformer.
8
PANASONIC [ PANASONIC SEMICONDUCTOR ]
