AN8037 Panasonic Semiconductor, AN8037 Datasheet - Page 18

• Manufacturer Part Number: AN8037
• Description: AC-DC switching power supply control IC with standby mode
• Manufacturer: Panasonic Semiconductor

AN8027, AN8037
18
[1] Operation descriptions (continued)
8. Bottom-on function (AN8037 only) (continued)
9. Notes on R9 and C9 value selection
Application Notes (continued)
on at a frequency of half the resonant frequency. Practically, refer to figure 12 and determine the turn-on delay
time so that the power MOSFET will be turned on at V
from the following formula.
therefore, as follows.
of the power MOSFET itself should also be considered. However, in this case the sample-to-sample variations
and temperature variations should be considered.
exceed the maximum rating for the IC, and incorrect operation (in the worst case, destruction of the device) may
occur. We recommend using a value of R9 in the range that satisfies the following conditions.
Select the constants of R9 and C9 to determine the turn-on delay time so that the power MOSFET will be turned
f
The turn-on delay time t
t
Note that since insertion of the resonance capacitor results in increased losses, using the parasitic capacitance
If an excessively low value is used for R9, the current flowing into the TR pin after power supply startup will
V
V
Adjust t
pd(ON)
SYNC
B( )
B( )
V
Rectified AC
IN
To AC
The TR lower limit clamp voltage ( 0.15 V typical)
The TR upper limit clamp voltage (1.5 V typical)
PD(ON)
2
7
1
6
L · C [s]
1
L · C
with C9 by taking the inductance and resonant capacitance of the transformer into consideration.
V
TR
Out
SBD
CC
SBD
Figure 13
[Hz]
C8
pd(ON)
R1
C: resonant capacitance
L: inductance of primary winding of transformer
R9
R9
to turn on the power MOSFET at a frequency of half the resonant frequency is,
C9
I
R7
D
R9 V
V
C7
B
P
DS
0 V. The approximate resonant frequency can be obtained
V
V
B( )
B( )
: negative peak voltage
: positive peak voltage
3 mA
0 V
0.25 V
0 V
0 V
3 mA
V
V
I
DS
TR
D
V
V
P
IN
Figure 14
Voltage Regulators
t
pd
V
TR
0.7 V typ.