an8038 Panasonic Corporation of North America, an8038 Datasheet - Page 15

• 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

Voltage Regulators
[2] Operation descriptions (continued)
3. Local resonance operation (power MOSFET turn on delay circuit) (continued)
Application Notes (continued)
Notes on C7 value selection
waveform.
mine the delay time so that the power
MOSFET is turned on at the 1/2 cycle
point in the resonant frequency wave-
form. Simply stated, select values so
that the power MOSFET turns on at the
zero voltage point in the voltage wave-
form. The resonant frequency can be
roughly determined using the follow-
ing formula.
transistor detection and output changeover is about 400 ns.
capacitance of the power MOSFET itself should also be considered. However, in this case the sample-to-
sample variations and temperature variations should be considered.
Notes on R9 and C9 value selection
inductance of the transformer used.
t
at the 1/2 cycle point in the resonant
frequency waveform is given by the
following formula.
will exceed the maximum rating for the IC, and incorrect operation (or even, 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.
PD(ON)
Figure 5 shows the local resonance
Select values of R9 and C9 to deter-
Furthermore, t
Note that since insertion of the resonance capacitor C7 results in increased losses, using the parasitic
V
V
V
Also, adjust t
Accordingly, the turn on delay time
If an excessively low value is used for R9, the current flowing into the TR pin after power supply startup
f
C
L : Inductance of the transformer
t
B( )
B( )
B( )
PD(ON)
SYNC
7
to turn on the power MOSFET
: Resonance capacitor
primary winding
The TR lower limit clamp voltage ( 0.15 V typical)
The TR upper limit clamp voltage (1.5 V typical)
N
N
B
S
2
V
PD(ON)
PD(ON)
L · C
O
1
L · C
7
should be set to be larger than t
by changing the value of C9 in consideration of the resonance capacitance and
7
(s)
(Hz)
V
R9
B( )
R9
N
N
B
P
0.25 V
V
V
Out
ID
E
DS
TR
V
V
IN
0 V
0 V
0 V
0 V
B( )
B( )
: The peak voltage when the voltage is negative
: The peak voltage when the voltage is positive
Figure 5. Local resonance waveform
TR
, since a response time t
V
V
3 mA
P
IN
t
TR
3 mA
t
PD
AN8038, AN8038S
TR
that is the time between
V
P
N
N
0.15 V typ.
1.5 V typ.
P
S
V
O
15