AN8038S Panasonic Semiconductor, AN8038S Datasheet - Page 13

• Manufacturer Part Number: AN8038S
• Description: AC-DC switching power supply control IC with RCC local resonance circuit for improved conformance with energy conservation laws
• Manufacturer: Panasonic Semiconductor

Voltage Regulators
[2] Operation descriptions (continued)
2. Oscillator circuit (continued)
Application Notes (continued)
1) On-period: t
2) Off-period: t
Notes on setting the oscillator frequency
This section describes the calculation of the on- and off-periods.
V (typical) and V
approximation. (See figure 2.)
(See figure 3.)
the voltage fed back to TR pin (pin 1) if that time is longer than the t
t
I
I
t
Here,
OFF(min)
t
t
C
V
V
V
V
I
I
I
I
E
N
N
R
However, the off-period for the local resonance circuit described later, is determined by the time for
The power MOSFET is turned on and off continuously by repeating the above operations.
OFF1
OFF2
ON
ON
OFF(min)
ON
OFF1
OFF2
TR
IN
The output on-period is the discharge period when the CF pin is between the peak value of V
The following formula can be used to calculate the on-period of the power MOSFET as a reasonable
The minimum off-period is the charging period from V
The following formula can be used to calculate the minimum off-period as a reasonable approximation.
CF
CFH
CFL
RSTB
FB
B
P
TR1
/R
C
1250 A typ. (V
55 A typ.
TR2
CF
V
I
I
V
(When I
V
(When I
C
ON
OFF
ON
TR
: On-period
: Minimum off-period
: Capacitance of the capacitor connected to the CF pin
: Upper limit voltage for the CF pin.
: Lower limit voltage for the CF pin
: Pin voltage that sets the light load detection level.
: Value that results from IC internal conversion of feedback current I
: On-period (CF pin discharge) current
: Off-period (CF pin charge) current when I
: Off-period (CF pin charge) current when I
: Flowing current at TR pin
: Primary winding voltage
: Number of turns in the bias winding
: Number of turns in the primary winding
: Resistors connected to the TR pin
CF
CFH
FB
FB
This voltage can be adjusted with an external resistor.
(V
FB
CFH
(E
I
0.7 V typ.
4 k
{V
TR
4.2 V typ.
.
IN
IFB
IFB
RSTB
V
280 A typ.
(V
NB/NP) / (R
FB
250 A)
250 A)
(I
FB
FB
) / I
IFB
V
0.7 V typ. to V
V
CFL
ON
RSTB
250 A)
} / I
to 4.2 V typ.)
TR1
OFF
R
0.7 V
TR2
RSTB
)
)
IFB
IFB
CFL
1 mA
1 mA
0.2 V (typical) to V
V
V
CFH
RSTB
OFF
time determined by C
AN8038, AN8038S
4.2 V typ.
3.5 V typ.
IFB
RSTB
.
CFH
CF
.
4.2
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