M51995 Mitsubishi, M51995 Datasheet - Page 20

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

(2)The start-up circuit when it is not necessary to set the
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
decided by R1 and R2 utilizing the low start-up current
characteristics of type M51995AP/FP.
The input voltage(V
decided by the ratio of third winding of transformer.
The V
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.
It is recommend to use the third winding of "forward winding"
Fig.25 Start-up circuit diagram when it is not
V
V
start and stop input voltage
where
IN(START)
IN(STOP)
I
Vcc
Vcc
V
V'
Vcc terminal ~
CCL
IN(START)
RECTIFIED DC
VOLTAGE FROM
SMOOTHING CAPACITOR
F
IN(P-P)
is the forward voltage of rectifier diode
(START)
(STOP)
M51995A
necessary to set the start and stop input voltage
is the operation start-up current of IC
~
~
(Vcc
is the peak to peak ripple voltage of
R1 • I
and V
is the operation stop voltage of IC
is the operation start-up voltage of IC
GND
Vcc
(STOP)-
IN(START)
IN(STOP)
CCL
IN(STOP)
N
N
B
P
+ (
V
V'
F) •
R1
R2
IN RIP(P-P)
),at which the IC operation stops,is
),at which the IC operation starts,is
N
N
are given by following equations.
P
B
+ 1) • Vcc
V
IN
R2
+
1
2
V'
R1
(START)
IN RIP(P-P)
(START)
CVcc
V
F
N
,and the high gate
N
P
...............(9)
B
..........(10)
PRIMARY WINDING
OF TRANSFORMER
THIRD WINDING OF
TRANSFORMER
(
20
/ 27 )
R
(4)Power supply circuit for easy start-up
When IC start to operate,the voltage of the C
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
the duration while the induced winding voltage is higher than
the C
to the "operation-stop voltage" of type M51995.
It is recommended to use the 10 to 47µF for C
times capacity bigger than C
Fig.26 How to design the conductor-pattern of type
It is required that the V
When the third winding is the "fly back winding" or "reverse
polarity",the V
be settled by this system,so the auxiliary circuit is required.
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.
To reduce the spike voltage,the Cvcc,which is connected
between Vcc and ground,must have the good high frequency
characteristics.
To design the conductor-pattern on PC board,following cautions
must be considered as shown in Fig.26.
(a)To separate the emitter line of type M51995A from the GND
(b)The locate the C
(c)To separate the collector line of type M51995A from the Vcc
(d)To connect the ground terminals of peripheral parts of ICs to
(3)Notice to the Vcc,Vcc line and GND line
OUTPUT
CLM
VCC
COLLECTOR
line of the IC
and connect directly
line of the IC
GND of type M51995A as short as possible
VCC
is very short duration;that is the charging does occur only
EMITTER
M51995A on PC board(schematic example)
voltage,if the induced winding voltage is nearly equal
IN(START)
SWITCHING REGULATOR CONTROL
M51995A
VCC
VCC
GND
Vcc
becomes to be charged from the third
IN(START)
can be fixed,however,V
as near as possible to type M51995A
VCC1
must be higher than V
for C
CVcc
M51995AP/FP
VCC2
in Fig.27.
VCC
VCC1
IN(STOP)
begins to
,and about 5
IN(STOP)
MAIN
TRANSFORMER
THIRD
WINDING
can not
.