an8038 Panasonic Corporation of North America, an8038 Datasheet - Page 14

• Manufacturer Part Number: an8038
• Description: Ac-dc Switching Power Supply Control Ic With Rcc Local Resonance Circuit For Improved Conformance With Energy Conservation Laws
• Manufacturer: Panasonic Corporation of North America

AN8038, AN8038S
14
[2] Operation descriptions (continued)
3. Local resonance operation (power MOSFET turn on delay circuit)
Application Notes (continued)
Transformer reset
is similar to earlier Panasonic ICs, in particular the AN8026, AN8027, AN8028, and AN8029.)
and C9 form a delay circuit for adjusting the power MOSFET turn on time.
through R9 and C9. The power MOSFET will be held in the off state while a high level (a level higher than the
threshold voltage, which is 0.25 V typical) is input to the TR pin.
at 1.5 V typical (sink current is 3 mA), and the lower limit voltage is clamped at about 0.15 V typical (source
current: 3 mA). (See figure 5.) The power MOSFET off-period is determined by the longer period of the follow-
ing two periods: the period until the TR pin input voltage becomes lower than the threshold voltage as the bias
winding voltage falls after the transformer discharges its energy, and the minimum off-period t
by the internal oscillator (see the description of the oscillator circuit). As a result, ringing in the bias winding does
not be regarded as a turn on signal during the minimum off-period.
0.25 V typ.
comparator
The AN8038 and AN8038S transformer reset detection functions detect a low-level input to the TR pin. (This
Local resonance operation is possible with circuits as shown in figure 4. C7 is the resonance capacitor, and R9
When the power MOSFET is off, the voltage that occurs in the drive winding is input to the TR pin (pin 1)
The TR pin also has a clamping capability for upper and lower limit voltages. The upper limit voltage is clamped
Lower limit clamp
Upper limit clamp
1.5 V typ.
0.15 V typ.
E
V
TR
Out
GND
IN
CC
clamp current
Lower limit
Figure 4
C9
clamp current
Upper limit
R9
Startup resistor
R1
E
IN
D
B
Voltage Regulators
C7
N
N
P
B
OFF(min)
N
S
stipulated
V
O