M51996AP データシートの表示（PDF） - MITSUBISHI ELECTRIC
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M51996AP Datasheet PDF : 22 Pages
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MITSUBISHI (Dig./Ana. INTERFACE)
M51996AP/FP
REG
3K
500
1S
6S
F/B
M51996A
Fig.28 Relationship between REG terminal and
F/B terminal
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 Fig.26 does not become 0,the
output voltage is proportional to the product of the input voltage
VIN(primary side voltage of the main transformer) and on duty.If
the bias winding is positive,Vcc is approximately proportional to
VIN.The existance of feed back current of the photo-coupler is
known by measuring the F/B terminal voltage which becomes
less than 2VBE in the internal circuit of REG terminal and F/B
terminal if the output current flows from the F/B terminal.
Fig.29 shows an application example.
Q1 is turned on when normal output voltage is controlled at a
certain value.The SOFT terminal is clampedto 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 10kΩ~30kΩ.An R3
of 20 to 100kΩ and C of 1000pF to 8200pF should be used.
To change the knee point of frequency drop,use the circuit in
Fig.30.
To have a normal SOFT start function in the circuit in Fig.29,use
the circuit in Fig.31.It is recommended to use an R4 of 10kΩ.
SWITCHING REGULATOR CONTROL
BIAS WINDING OF
D2 THE MAIN TRANSFORMER
Vcc
COLLECTOR
VOUT
M51996A
SOFT
CVcc
TO OUTPUT TRANSISTOR
R3
C
F/B
R1
REG
R2
Q1 D1
PHOTO-COUPLER
FOR FEED BACK SIGNAL
Fig.29 Current to lower frequency during over current
VOUT
SOFT
VOUT
SOFT
VOUT
TO MAKE THE KNEE POINT HIGH
SOFT
TO MAKE THE KNEE POINT LOW
Fig.30 Method to control the knee point of
frequency drop
D2 BIAS WINDING OF
THE MAIN TRANSFORMER
Vcc
COLLECTOR
VOUT
CVcc
M51996A
SOFT R4
TO OUTPUT TRANSISTOR
R3
C
F/B
REG
R1
RSOFT
Q2
CSOFT
R2
Q1 D1
PHOTO-COUPLER
FOR FEED BACK SIGNAL
Fig.31 Circuit to use frequency drop during the over
current and normal soft start
( 18 / 22 )
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