# M51995AP

Manufacturer Part NumberM51995AP
DescriptionSwitching regulator control
ManufacturerMITSUBISHI
M51995AP datasheet

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It is not necessary that the induced voltage is settled higher
than the operation start-up voltage Vcc
drive voltage causes high gate dissipation,on the other hand,too
low gate drive voltage does not make the MOS-FET fully on-
state or the saturation state.
RECTIFIED DC
V
IN
VOLTAGE FROM
SMOOTHING CAPACITOR
R1
Vcc
M51995A
R2
GND
Fig.25 Start-up circuit diagram when it is not
necessary to set the start and stop input voltage
(2)The start-up circuit when it is not necessary to set the
start and stop input voltage
It is recommend to use the third winding of "forward winding"
or "positive polarity" as shown in Fig.25,when the DC source
voltages at both the IC operation start and stop must be settled
at the specified values.
The input voltage(V
),at which the IC operation starts,is
IN(START)
decided by R1 and R2 utilizing the low start-up current
characteristics of type M51995AP/FP.
The input voltage(V
),at which the IC operation stops,is
IN(STOP)
decided by the ratio of third winding of transformer.
The V
and V
are given by following equations.
IN(START)
IN(STOP)
R1
~
V
R1 • I
+ (
+ 1) • Vcc
IN(START)
CCL
R2
N
1
P
+
V
~
(Vcc
V
V'
IN(STOP)
(STOP)-
F) •
2
N
B
where
I
is the operation start-up current of IC
CCL
Vcc
is the operation start-up voltage of IC
(START)
Vcc
is the operation stop voltage of IC
(STOP)
V
is the forward voltage of rectifier diode
F
V'
is the peak to peak ripple voltage of
IN(P-P)
N
B
Vcc terminal ~
V'
IN RIP(P-P)
N
P
It is required that the V
,and the high gate
When the third winding is the "fly back winding" or "reverse
(START)
polarity",the V
be settled by this system,so the auxiliary circuit is required.
PRIMARY WINDING
OF TRANSFORMER
N
P
(3)Notice to the Vcc,Vcc line and GND line
To avoid the abnormal IC operation,it is recommended to
design the Vcc is not vary abruptly and has few spike
voltage,which is induced from the stray capacity between the
winding of main transformer.
V
F
To reduce the spike voltage,the Cvcc,which is connected
THIRD WINDING OF
N
B
between Vcc and ground,must have the good high frequency
TRANSFORMER
characteristics.
To design the conductor-pattern on PC board,following cautions
must be considered as shown in Fig.26.
CVcc
(a)To separate the emitter line of type M51995A from the GND
line of the IC
(b)The locate the C
and connect directly
(c)To separate the collector line of type M51995A from the Vcc
line of the IC
(d)To connect the ground terminals of peripheral parts of ICs to
GND of type M51995A as short as possible
COLLECTOR
OUTPUT
R
CLM
Fig.26 How to design the conductor-pattern of type
(4)Power supply circuit for easy start-up
...............(9)
(START)
When IC start to operate,the voltage of the C
..........(10)
IN RIP(P-P)
decrease till the C
winding of main-transformer as the Icc of the IC increases
abruptly.In case shown in Fig.24 and 25,some "unstable start-
up" or "fall to start-up" may happen, as the charging interval of
C
is very short duration;that is the charging does occur only
VCC
the duration while the induced winding voltage is higher than
the C
VCC
to the "operation-stop voltage" of type M51995.
It is recommended to use the 10 to 47µF for C
times capacity bigger than C
(
/ 27 )
20
M51995AP/FP
SWITCHING REGULATOR CONTROL
must be higher than V
IN(START)
can be fixed,however,V
IN(START)
as near as possible to type M51995A
VCC
Vcc
M51995A
CVcc
EMITTER
GND
M51995A on PC board(schematic example)
VCC
becomes to be charged from the third
VCC
voltage,if the induced winding voltage is nearly equal
for C
in Fig.27.
VCC1
VCC2
.
IN(STOP)
can not
IN(STOP)
MAIN
TRANSFORMER
THIRD
WINDING
begins to