m51996ap Renesas Electronics Corporation., m51996ap Datasheet - Page 30

• Manufacturer Part Number: m51996ap
• Description: Switching Regulator Control
• Manufacturer: Renesas Electronics Corporation.

M51996AP/AFP
REJ03D0836-0201 Rev.2.01 Nov 14, 2007
Page 30 of 35
(2) In case of fly back system
Figure 31 Current to Lower The Frequency During The Over Current in The Fly Back System
The DC output voltage of SMPS depends on the V
winding is negative and the system is fly back. So the operation of type M51996A will stop when the V
becomes lower than “Operation-stop voltage” of M51996A when the DC output voltage of SMPS decreases
under specified value at over load condition.
However, the M51996A will non-operate and operate intermittently, as the V
the decrease of I
The fly back system has the constant output power characteristics as shown in figure 30 when the peak primary
current and the operating frequency are constant.
To avoid an increases of the output current, the frequency is lowered when the DC output voltage of SMPS starts
to drop using the SOFT terminal. V
because the voltage in proportional to the output voltage is obtained from the bias winding. In this application
example, the current flowing to R3 added to the start-up current. So please use high resistance or 100 k to 200
k for R3.
The start-up current is not affected by R3 if R3 is connected to C
CC
Figure 30 Over Current Limiting Curve on Fly Back System
current.
F/B
DC Output Current
To photo-coupler for
feed back signal
CC
M51996A
V
R2
is divided and is input to the SOFT terminal as shown in figure 31,
CC
R1
Collector
REG
CC
SOFT
voltage of type M51996A when the polarity of the third
Point that V
or third winding
voltage decreases
under "Operation-stop voltage"
R3
R4
VCC
C
CC
+
2 in the circuit shown in figure 18.
VCC
voltage
CC
voltage rises in accordance with
CC