M51995AP

Manufacturer Part NumberM51995AP
DescriptionSwitching regulator control
ManufacturerMITSUBISHI
M51995AP datasheet
 


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Under the condition of current limiting operation,the output
current I2 continues as shown in Fig.33.So the output voltage
depends on the product of the input primary voltage V
on-duty.
If the third winding polarity is positive ,the Vcc depends on
V
,so it is concluded that the smoothed voltage of V
IN
terminal depends on the output DC voltage of the SMPS.
So the sharp current limiting characteristics will be got,if the
V
voltage if feed back to VF terminal through low pass filter
OUT
as shown in Fig.35.
M51995A
V
OUT
R
VFFB
V
F
C
VFFB
Fig.35 Feed back loop through low pass filter from
V
to V
terminal
OUT
F
It is recommended to use 15k for R
VFFB
C
in Fig.35.
VFFB
Fig.36 shows how to control the knee point where the frequency
becomes decrease.
FROM
FROM
TO VF
TO VF
V
V
OUT
OUT
TO MAKE THE KNEE
POINT HIGH
Fig.36 How to control the knee point
(b)In case of fly back system
The DC output voltage of SMPS depends on the Vcc voltage of
type M51995A when the polarity of the third winding is negative
and the system is fly back.So the operation of type M51995A
will stop when the Vcc becomes lower than "Operation-stop
voltage" of M51995A when the DC output voltage of SMPS
decreases under specified value at over load condition.
and the
IN
OUT
Fig.37 Over current limiting curve on fly back system
However,the M51995A will non-operate and operate
intermittently,as the Vcc voltage rises in accordance with the
decrease of Icc current.
The fly back system has the constant output power
characteristics as shown in Fig.37 when the peak primary
current and the operating frequency are constant.
To control the increase of DC output current,the operating
frequency is decreased using the characteristics of VF terminal
when the over current limiting function begins to operate.
The voltage which mode by dividing the Vcc is applied to VF
terminal as shown in Fig.38,as the induced third winding voltage
depends on the DC output voltage of SMPS.
15k or less is recommended for R
,and 10,000pF for
the current flows through R
Icc
(START)
If the R
1
through R
FROM
TO VF
V
OUT
TO MAKE THE KNEE
POINT LOW
M51995A
Fig.38 Circuit diagram to make knee point low on
(c)Application circuit to keep the non-operating condition
when over load current condition will continue for
specified duration
The CT terminal voltage will begin to rise and the capacitor
connected to CT terminal will be charged-up,if the current
limiting function starts,and VF terminal voltage decreases below
V
THTIME
If the charged-up CT terminal voltage is applied to OVP terminal
through the level-shifter consisted of buffer transistor and
resistor,it makes type M51995A keep non-operating condition.
(
/ 27 )
23
M51995AP/FP
SWITCHING REGULATOR CONTROL
POINT THAT Vcc VOLTAGE
OR THIRD WINDING
VOLTAGE DECREASES
UNDER "OPERATION-STOP
VOLTAGE"
DC OUTPUT CURRENT
in Fig.38,it is noticed that
2
and R
will superpose on the
1
2
current.
is connected to Cvcc2 in Fig.27,the current flows
and R
is independent of the Icc
1
2
(START)
Vcc
COLLECTOR
R1
VF
CVcc
R2
fly back system
(~3V).
.