M51995AP

Manufacturer Part NumberM51995AP
DescriptionSwitching regulator control
ManufacturerMITSUBISHI
M51995AP datasheet
 
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Page 21/27:

OVP circuit

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Vcc
M51995A
CVcc1
GND
Fig.27 DC source circuit for stable start-up

OVP circuit

(1)To avoid the miss operation of OVP
It is recommended to connect the capacitor between 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.
Vcc
M51995A
OVP
GND
Fig.28 Peripheral circuit of OVP terminal
R1
MAIN
TRANSFORMER
THIRD
WINDING
CVcc2
~
FIG.30 OVP setting method using the induced
(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.
10k
(3)OVP setting method using the induced third winding
voltage on fly back system
For the over voltage protection (OVP),the induced fly back type
third winding voltage can be utilized,as the induced third
PHOTO COUPLER
winding voltage depends on the output voltage.Fig.30 shows
one of the example circuit diagram.
(
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21
M51995AP/FP
SWITCHING REGULATOR CONTROL
R1
C
FIN
R2
THE TIME CONSTANT OF
THIS PART SHOULD BE SHORT
Fig.29 Example circuit diagram to make the
OVP-reset-time fast
Vcc
470
M51995A
OVP
CVcc
GND
third winding voltage on fly back system
• (R1+R2) is long. Under such the circuit
FIN
VCC
TO MAIN
TRANSFORMER
Vcc
Cvcc
M51995A
GND
MAIN
TRANSFORMER
THIRD
WINDING
forcedly and