m51996ap Renesas Electronics Corporation., m51996ap Datasheet - Page 28

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

M51996AP/AFP
REJ03D0836-0201 Rev.2.01 Nov 14, 2007
Page 28 of 35
If the curve becomes vertical because of an excess current, the output voltage is lowered and no feedback current
flows from feedback photo-coupler; the PWM comparator operates to enlarge the duty sufficiently, but the
signal from the CLM section operates to make the pulse width narrower.
Under the condition in which I2 in figure 24 does not become 0, the output voltage is proportional to the product
of the input voltage V
positive, V
known by measuring the F/B terminal voltage which becomes less than 2V
terminal and F/B terminal if the output current flows from the F/B terminal.
Figure 27 shows an application example.
Q1 is turned on when normal output voltage is controlled at a certain value. The SOFT terminal is clamped to a
high-level voltage. If the output voltage decreases and the curve starts to drop, no feed back current flows, Q1 is
turned off and the SOFT terminal responds to the smoothed output voltage.
It is recommended to use an R1 and R2 of 10 k to 30 k . An R3 of 20 to 100 k and C of 1000 pF to 8200 pF
should be used.
CC
is approximately proportional to V
Figure 25 Over Current Limiting Curve on Feed Forward System
Figure 26 Relationship Between REG Terminal and F/B Terminal
IN
(primary side voltage of the main transformer) and on duty. If the bias winding is
3 k
1 S
M51996A
Output Current
IN
. The existence of feed back current of the photo-coupler is
6 S
500
REG
F/B
BE
in the internal circuit of REG