an8027 Panasonic Corporation of North America, an8027 Datasheet - Page 8

• Manufacturer Part Number: an8027
• Description: Ac-dc Switching Power Supply Control Ic With Standby Mode
• Manufacturer: Panasonic Corporation of North America

AN8027, AN8037
8
[1] Operation descriptions (continued)
Application Notes (continued)
Oscillation circuit (continued)
Setting the on-period (continued)
protection threshold voltage (i.e., 200 mV typical) when the overcurrent protection function of the IC is
operating.
The power MOSFET is turned off if the voltage at the CLM pin reaches the pulse-by-pulse overcurrent
The maximum on-period can be used for overcurrent protection.
When the input voltage is low, the maximum on-period overcurrent protection is possible.
When the input voltage is high, the CLM pulse-by-pulse overcurrent protection is possible.
T
C
V
V
I
I
E
NB
NP
V
R
ON
TR
ON
IN
CF
TR
FB
H-CF
Z
: On-period
: Value of a capacitor connected to CF pin
: Voltage internally converted from feedback signal I
: CF upper limit voltage
: On-period discharge current
: Flowing current at TR pin
: Voltage on primary winding
: Number of turns in the bias winding
: Number of turns in the primary winding
: Voltage on Zener diode connected to bias winding
: Value of a resistor connected to the TR pin
The minimum current is guaranteed
to prevent a limitless increase in T
CF pin voltage
Out pin voltage
PC
I
FB
Figure 2. On-period block diagram and control waveform
TR
FB
V
V
H-CF
CC
20 k
Current mirror
V
FB
1.5 V
1 : 5
AN8027, AN8037
4 V
0 V
0 V
T
because large E
increases I
ON
250 A
V
is shortened
FB
I
ON
typ.
TR
TR
Current mirror
Off
.
I
.
TR
IN
R
TR
I
ON
C
I
CF
ON
FB
V
Out
GND
CC
V
E
Z
E
IN
On
IN
E
I
TR
IN
(I
; large
ON
Voltage Regulators
); large
NP
NB