M51995 Mitsubishi, M51995 Datasheet - Page 23

• Manufacturer Part Number: M51995
• Description: SWITCHING REGULATOR CONTROL
• Manufacturer: Mitsubishi

It is recommended to use 15k for R
C
Fig.36 shows how to control the knee point where the frequency
becomes decrease.
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
terminal depends on the output DC voltage of the SMPS.
So the sharp current limiting characteristics will be got,if the
V
as shown in Fig.35.
(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.
IN
OUT
VFFB
Fig.35 Feed back loop through low pass filter from
FROM
V
,so it is concluded that the smoothed voltage of V
OUT
voltage if feed back to VF terminal through low pass filter
in Fig.35.
Fig.36 How to control the knee point
V
OUT
TO VF
to V
F
terminal
FROM
V
OUT
TO MAKE THE KNEE
POINT HIGH
R
C
VFFB
VFFB
TO VF
V
V
M51995A
OUT
F
VFFB
,and 10,000pF for
V
FROM
OUT
TO MAKE THE KNEE
POINT LOW
OUT
IN
TO VF
and the
(
23
/ 27 )
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
the current flows through R
Icc
If the R
through R
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
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.
(c)Application circuit to keep the non-operating condition
THTIME
when over load current condition will continue for
specified duration
(START)
Fig.38 Circuit diagram to make knee point low on
Fig.37 Over current limiting curve on fly back system
M51995A
1
(~3V).
Vcc
is connected to Cvcc2 in Fig.27,the current flows
1
current.
and R
fly back system
DC OUTPUT CURRENT
SWITCHING REGULATOR CONTROL
2
is independent of the Icc
COLLECTOR
VF
1
and R
R2
R1
M51995AP/FP
2
2
will superpose on the
in Fig.38,it is noticed that
POINT THAT Vcc VOLTAGE
OR THIRD WINDING
VOLTAGE DECREASES
UNDER "OPERATION-STOP
VOLTAGE"
CVcc
(START)
.