M51995 Mitsubishi, M51995 Datasheet - Page 21

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

(1)To avoid the miss operation of OVP
terminal and GND for avoiding the miss operation by the spike
noise.
The OVP terminal is connected with the sink current source
(~150µA) in IC when OVP does not operate,for absorbing the
leak current of the photo coupler in the application.
So the resistance between the OVP terminal and GND for leak-
cut is not necessary.
If the resistance is connected,the supply current at the OVP
reset supply voltage becomes large.
As the result,the OVP reset supply voltage may become higher
than the operation stop voltage.
In that case,the OVP action is reset when the OVP is triggered
at the supply voltage a little high than the operation stop
voltage.
So it should be avoided absolutely to connect the resistance
between the OVP terminal and GND.
OVP circuit
It is recommended to connect the capacitor between OVP
M51995A
Fig.27 DC source circuit for stable start-up
Fig.28 Peripheral circuit of OVP terminal
M51995A
GND
Vcc
GND
Vcc
OVP
CVcc1
R1
CVcc2
PHOTO COUPLER
10k
MAIN
TRANSFORMER
THIRD
WINDING
(
21
/ 27 )
(2)Application circuit to make the OVP-reset time fast
The reset time may becomes problem when the discharge time
constant of C
condition,it is recommended to discharge the C
to make the Vcc low value.This makes the OVP-reset time fast.
(3)OVP setting method using the induced third winding
For the over voltage protection (OVP),the induced fly back type
third winding voltage can be utilized,as the induced third
winding voltage depends on the output voltage.Fig.30 shows
one of the example circuit diagram.
~
voltage on fly back system
FIG.30 OVP setting method using the induced
Fig.29 Example circuit diagram to make the
M51995A
FIN
SWITCHING REGULATOR CONTROL
third winding voltage on fly back system
OVP-reset-time fast
• (R1+R2) is long. Under such the circuit
GND
Vcc
THE TIME CONSTANT OF
THIS PART SHOULD BE SHORT
OVP
M51995AP/FP
470
CVcc
C
FIN
R2
R1
VCC
Cvcc
TO MAIN
TRANSFORMER
forcedly and
MAIN
TRANSFORMER
THIRD
WINDING
M51995A
Vcc
GND